q_id
stringlengths 6
6
| title
stringlengths 3
299
| selftext
stringlengths 0
4.44k
| category
stringclasses 12
values | subreddit
stringclasses 1
value | answers
dict | title_urls
sequencelengths 1
1
| selftext_urls
sequencelengths 1
1
|
|---|---|---|---|---|---|---|---|
6h5vf1 | How do pilots who speak different languages communicate with each other / air traffic control? | Is there an interpreter or something, or is the language barrier not really an issue? How does this work? | Engineering | explainlikeimfive | {
"a_id": [
"divredh",
"divtjsn",
"divrii5"
],
"text": [
"All pilots are required to know how to speak English, as are the people in the control tower. That way, everybody has a language they can all communicate in.",
"As others have said, English is the international language of aviation, and there are some specific phrases that pilots are required to know in order to be able to communicate in English. However, there are two important pieces of information missing: - Not all airports use English. Some smaller airports which are mostly used by private hobby pilots use the local language. Some airports use a mix of English and the local language. Each country publishes a list of all the airports within the country, with a load of information about each airport, and one piece of information that's published is which language is spoken at each airport. For example, at many smaller French airports, air traffic control only work during normal working hours, but after air traffic control is closed, the airport still remains open but all communication is in French. This information is published to pilots by the French authorities. - Even when the language is English, some pilots and controllers insist on using the local language. There was an accident in France many years ago (sorry, I don't remember the details and don't have time to find them right now) where a factor in the accident was that the French pilot was speaking French to the French air traffic controller. The air traffic controller made a mistake and cleared a British aircraft to take off when the French aircraft was still on the runway. Had the British pilot been able to understand the communication between air traffic control and the French pilot, he probably would have realised the mistake and questioned the instruction to take off, but because he didn't understand what was going on with the other aircraft, he had no way of knowing the runway was occupied, and followed the air traffic controller's incorrect instruction to take off.",
"There is a specific list of English phrases all pilots must know - called Aviation English. It is designed to cover almost any situation and even designed to minimise any issues accents can cause. Some pilots and air traffic controllers still speak their native language regularly but when required can use Aviation English."
],
"score": [
11,
10,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6h6ehv | How do cubesats deployed from the ISS get into other orbits? | I recently read that a lot of cubesats are now deployed from the ISS instead of piggy-bagging on a satellite launch. That left me wondering how they are moved out of the ISS orbit. As far as I know cubesats do not have propulsion systems on their own. Or maybe I'm wrong in assuming that they are moved into different orbits after deployment. But that would leave the ISS orbit "full" of cubesats, creating difficulties for approaching crafts/the ISS itself. | Engineering | explainlikeimfive | {
"a_id": [
"divvgl2"
],
"text": [
"They use a robotic arm with an ejector system to launch the satellites into their orbits. This would mean that the two orbits would cross at one point, but the difference in speed, the different drag, and the fact that the ISS regularly boosts its orbit, means that the danger of a collision is miniscule."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6h7a4o | Why aren't combustible power supplies and fuse boxes in buildings kept in an encased vacuum to stop a fire or ignition ? | Engineering | explainlikeimfive | {
"a_id": [
"diw0kkc",
"diw0lah"
],
"text": [
"Maintaining a vacuum is extremely difficult. Also the items you describe generally don't start by catching fire but rather melting due to electrical resistance. Being in a vacuum wouldn't stop that.",
"Power supplies and other devices aren't 100% efficient and generate heat. They need to get rid of this heat, and using convection/conduction through airflow is a very good way to do this. Put them in a vacuum and it gets incredibly difficult to keep them at the proper temperature. Also, an electrical fire doesn't need oxygen to mess things up. If there's a big short the energy that's melting and destroying things isn't coming from chemical reactions, but from the power lines themselves."
],
"score": [
10,
6
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6h90sq | If large buildings are made of concrete, shouldn't they be able to build it so a fire can't spread from one floor to another? | As has happened with the london tower block fire for example. | Engineering | explainlikeimfive | {
"a_id": [
"diwfxz0",
"diwn16i",
"diwg0ap",
"diwlc9h",
"diwozv2",
"diwr1mt",
"diwymst"
],
"text": [
"They do. The big, heavy steel doors to the stairways that close automatically are designed to keep the fires from spreading from floor to floor. That's why bldg security goes apeshit when they're propped open or the hydraulic closer is broken or disabled.",
"We simply cannot make a building 100% fireproof. Even with concrete and steel, there is plenty of flammable material inside a building. We rate materials in time, meaning how much time they can resist fire. Over time we developed norms that tell you how much time different elements should be able to resist depending on what type of building it is. There is also specification in term of sprinkler systems and evacuation. The problem is that a building is suppose to stay up for decades so a lot of building are not up to the current standard. The London Tower was built in 1974 for example. We can't either just ask everybody to follow the current standard because it would cost astonishing amount of money to do so. This would mean that some building would be simply abandoned because the owned couldn't pay for the renovation. An abandoned building would be even worst as a fire hazard. It would also not only affect big business, but also house owner. If you force everybody to follow the current standard, that mean home too. And the same thing would happen there, people without enough cash to renovate their home could lose everything. So you need to balance things out between security and economical reality.",
"It isn't practical to design a building as you describe. Electrical wires need to be run through conduit, ventilation passages need to exist, plumbing goes somewhere it can be accessed for maintenance, elevator shafts need to be open and straight. How do you design a stairway that humans can traverse but a 40-foot blast of flame can't? Add to that the fact concrete can crumble under extreme heat and you can make buildings fire-*resistant* but not completely fire-proof.",
"Easy to do if all you have is a bare concrete shell. Start putting anything into the building and adding finishes on top of that concrete, and you'll have materials that can burn. Add any ducts for heat/air, plumbing, and electrical, and you've got penetrations between the floors (in addition to elevator and stairways. So yes, you can build it that way, but it would be useless. No one wants to live in a fireproof concrete block.",
"An iron stove is fire proof. When you add fuel and ventilation everything in it burns. That is what happens with a concrete, fire proof shell of a building. It is fireproof until it's decorated and filled with furniture.",
"If you are referring to the London building then that was retrofitted with cladding made of polyethylene which is combustible. I can't explain why anyone would do this.",
"They do the best they can. A lot of new buildings have shafts that allow HVAC, Plumbing, and fire protection to pass floor to floor. The shafts are usually protected by 3hr fire rated sheet rock walls or concrete. Now speaking only on HVAC side. Whenever a duct system passes through a fire rated wall (usually 1 1/2hr) it has a fire damper or combination Fire/smoke damper. rated for 1hr or 3hr. The dampers have a UL rating of UL555 for fire damper, UL 555S for smoke dampers, UL555C for Fire/smoke dampers. No building is really fireproof, so these act to hinder fire and smoke spread and give fire and rescue time to act. Soure: HVAC fire life safety. edit: added in Concrete as a shaft wall."
],
"score": [
40,
28,
14,
12,
6,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6hg2on | Why are 4x4 vehicles (Such as the Jeep Wrangler) Limited in speed (80kph as per the owner manual) in 4WD mode, whereas a full time All-Wheel Drive vehicle doesn't have any such limit (within the limits of the engine) | Engineering | explainlikeimfive | {
"a_id": [
"diyap5v",
"diy2u67",
"diy2wiq"
],
"text": [
"Super short answer: Because it's not safe. Tires in 4x4 MUST skip if not going straight forward, and will thus lose traction which is not safe. AWD does not force tires to skip. Medium answer: At low speeds, with tires skidding, or offroad, you spin on some dirt or loose gravel or leaves or whatever, that's fine, you just chew up the turf. On pavement (high speeds generally), tires will try to force the vehicle to go in a straight line, and if steered anywhere but straight (to follow the road), the tires in 4x4 MUST slip because the ground (pavement) can't slip like gravel or dirt can. Longer answer: AWD means that the vehicle can turn all 4 wheels. This versus FWD or RWD where two wheels have power and the others are just free spinning and not connected to anything. Think of them like the front wheel on a bicycle, it spins but it never powers the bike, turning pedals only turns the back tire. A problem (not a necessary one, just, the way they're usually built) with FWD or RWD is that if one tire leaves the ground, or is slipping... ZERO power goes to the wheel that has grip. So imagine being stopped on the side of the road, one tire on the pavement, one tire on ice or mud in the ditch. You're thinking \"That's fine, one drive tire is still on pavement, I have half the grip I normally do but it'll move fine\"... NOPE. Mechanically, 100% of the power goes to the stupid tire that can't provide any traction at all, and the tire on pavement that could easily pull your car out of the ditch just sits there with its thumb up its ass while it's buddy revs away like the roadrunner. \"That's the stupidest thing I've ever heard, why not just power both wheels?\" That is because the cars HAVE to be built that way, and it's actually a neat trick that this is possible. A \"differential\" is a mechanical Y-splitter that lets the 2 power wheels spin at different speeds. This is absolutely necessary because when turning, the outside wheel has to spin farther than the inside wheel, it's a long path to go the longer way around. \"Really? The wheels being all of 4 feet apart makes a noticeable difference to the distance they have to travel? Bullshit!\" No bullshit. If the left tire has to travel a 100 foot arc on a gradual turn, and the right tire has to travel even 110 foot arc on the outside of that turn (a gradual turn)... that means if you force them both to travel 105 feet, each is skipping. The inside is losing traction and shoving it's way barkwards in little micro-lurches (covering the same ground twice, to add the extra feet) as the tire compresses and skids, and the outside is losing traction and popping forward (to skip ground, travel less distance). How much? 5 feet on the turn. 5 feet is a lot of skidding. \"So what did they use before the differential was invented? I don't believe that.\" Well, two points. One, a lot more dirt roads back then, even in town, differentials are old. And two, they only powered a single 1 wheel out of the 4. All the others spun free. So, all cars that drive 2 wheels have differentials that allow them to turn at different speeds. A necessary side effect of this is that any tire that loses traction on mud or ice is mechanically identical to turning a corner, the slipping tire is like the outside tire in a turn, it wants to spin much faster than the tire with grip, and the differential mechanically allows this. So, AWD is way better than just front or rear wheel drive for any kind of traction. All 4 tires can be spinning. And they usually add complexity so that there isn't infinite amounts of slip in the differential. But they might not. In general, with only mild amounts of slippage, AWD is amazing because it evens out all the differences in traction and can turn all 4 tires. \"So what is the difference between AWD and 4WD? All 4 tires are powered on both.\" Yes. 4WD is a simplified version of AWD where all axles are just locked and forced to turn the same speed no matter what. 3 out of 4 tires stuck in mud and you're towing a trailer? No problemo, that 1 tire with grip will still turn and drag the whole vehicle if it can. Great for offroading. It means that any time you're not going straight forward, tires have to slip. That's not a big deal at low speeds on crappy terrain, it'll just spit dirt or ice as it skids on corners. Unlike on pavement which, you can't just shove around with the tire, so the tire itself has to lose grip and lurch. At high speeds on pavement, a 4x4 would basically force only 1 tire to ever have traction at a time, the other 3 all slipping, or ignoring your attempts to turn and instantly drifting. Not safe. Even 80kph (~50mph) is pretty ludicrous. Some AWDs have different amounts of sometimes computer controlled \"slip\" in the differential. So, they can slip partially, but not fully. Which is really what you want for everything but offroading. Make sense?",
"So there's a difference between 4WD and AWD. 4WD drives all 4 wheels, all at the same time. AWD chooses which wheels to send power to depending on the need. Some systems are better than others, but a lot of them (like the Haldex system) are basically front wheel drive, and then send power to the rear wheels as it realizes the front tires are losing grip. What you're talking about is vehicles that have PART TIME 4WD. There is another difference between full time 4wd and part time. Any part time system is generally not recommended to use in \"high traction\" driving, so dry pavement or streets can cause damage to the drivetrain if you leave it in 4wd mode. AWD systems would just divert power to the front wheels, and full time 4wd systems can negotiate the speed differential between the front and rear tires. Generally, part time systems are not as complex. They will try and send equal power to the front and rear tires. However, your front wheels tend to rotate faster than the rears, and differences in tire tread or pressure can exacerbate this difference. This can cause the front tires to slip, which can lead to dangerous problems if you're at a high speed. TL;DR Don't use part time 4WD if you don't need to.",
"4WD locks the front and rear axles together mechanically. It's either on or off. AWD uses an differential to change how much each axle is used. Sometimes this differential is adjustable by the computer."
],
"score": [
52,
16,
13
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6hjqqq | What is the difference between AWD and FWD? | Engineering | explainlikeimfive | {
"a_id": [
"diyujn6",
"diyuoj9"
],
"text": [
"AWD is all wheel drive, the transmission drives all four wheels. FWD is front wheel drive, the transmission drives only the front wheels.",
"With AWD (All-Wheel-Drive), the transmission has the ability to spin some of any of your four tires. With FWD (Front-Wheel-Drive), the transmission can only spin one or both of the front wheels. With RWD (Rear-Wheel-Drive), the transmission can only spin one or both of the rear wheels. With 4WD (Four-Wheel-Drive), the transmission will always spin all four wheels. (There are some caveats and expansions on this scenario, but this is my shot at an ELI5 of 4WD.)"
],
"score": [
6,
6
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6hsqjw | Why is silicon wafer shaped in the form of a disc? Wouldn't being a square or a rectangle minimize wasted dies on the ends of the wafer? | Engineering | explainlikeimfive | {
"a_id": [
"dj0tqqq"
],
"text": [
"It's to do with the manufacturing process, when they make the silicone it's drawn in such a way that it produces a single large crystal of silicone. It's way easier to do this into a cylinder shape than a rectangle... then they simply slice it into wafers and reuse any wastage. URL_1 *The mono crystal is literally pulled from liquid silicone naturally producing it's shape as it's spun out. It's essentially the square pizza box argument in reverse, its just easier to produce this way. URL_0"
],
"score": [
6
],
"text_urls": [
[
"https://youtu.be/aWVywhzuHnQ?t=124",
"https://youtu.be/qm67wbB5GmI?t=101"
]
]
} | [
"url"
] | [
"url"
] |
|
6i4usj | how do window air conditioners (units that are not central but not mobile) keep on giving cold goodness without any kind of refill or coolant? Will it ever run out of coolness? | Engineering | explainlikeimfive | {
"a_id": [
"dj3jd3z",
"dj3jwyl",
"dj3p8di",
"dj3je60",
"dj3tur4",
"dj3j3ij",
"dj3q5to",
"dj3qn3y",
"dj3p0md",
"dj3wf5z"
],
"text": [
"I don't think you understand how air conditioners work, based off the nature of your question. Coolant doesn't supply coolness like gasoline supplies energy. Air conditioning works by compressing the coolant gas until it becomes a liquid. This compression creates heat which is radiated away into the outside air by the fan blowing outside air over the coil. The compressed liquid is then pumped \"inside\" the house into an evaporator coil. This allows the liquid refrigerant to convert back to a gas. As this phase change occurs, heat is absorbed from the surrounding air, which is usually inside air circulated over the evaporating coil. This cools down the air being passed over the coil. That cool air is then blown into the inside of the house as air conditioning. The refrigerant is then pumped into the outside portion of the air conditioner to be compressed. In essence, heat is created by compression and dissipated with outside air. When the refrigerant evaporates, it absorbs a similar amount of heat, which cools the inside air that is circulated through the house. The only thing that gets consumed is energy that drives the compressor and the fans that circulate air. Since the coolant travels in a closed loop, there is no need to refill unless there is a leak.",
"To explain like you're 5: Air conditioners work by moving heat to the outside of the room. The special conveyor belt that moves the heat is the coolant, but like a conveyor belt, it doesn't get thrown out or used up.",
"First, let's get rid of a common misconception. 'Cold' cannot be made, there is no such thing as 'cold'; there are only amounts of heat. 'Cold' is simply a state of less heat. One of the first things humans figured out was how make heat; more recently, we figured out how to move it from a place where we want less to heat to a place where we don't care about the heat level. To move heat, we exploit the properties of gas. Namely, the fact that when a gas expands, it absorbs heat. To maximize this, we compress the gas until it forms a liquid, then pass it through a tiny orifice into an area of low pressure where it can evaporate and soak up the maximum amount of heat. This happens in a closed loop, so the heated gas returns to the compressor and is re-compressed into a liquid. Strictly speaking, the compressor cannot compress the gas into a liquid, it simply increases the pressure of the gas. The gas exiting the compressor is too hot to condense (and liquids don't compress much, so liquid in the compressor would break it) - it still contains all the heat it absorbed, but now takes up much less space, so it's temperature goes way up. This is actually a good thing, because it raises the temperature of the gas to a point that is well above the outside temperature, allowing the air surrounding the condensing coil to absorb the heat carried outside, cooling the gas and allowing it to condense back into a liquid which makes it ready to evaporate again.",
"They are constantly refilled with electricity and will stop giving coolness the second they get no electricity. It's also wrong that they \"give coolness\". What they do is move heat from inside the room to outside (and actually add some additional heat in the process). Think of them like a pump - and in fact that kind of mechanism is called a \"heat pump\". The same mechanism is used by refrigerators, or in reverse by some heating systems (which move heat from the ground into your house even though the house is already warmer than the ground).",
"The coolant in an air conditioner is like a sponge. It removes heat from your house the same way you would remove water from a bucket with a sponge. The air conditioner in this analogy works like your hand squeezing the sponge. It exposes the coolant to your hot house which sucks up heat like a sponge would suck up water. It then exposes the coolant to the outside and squeezes it like you would a sponge to get the heat out. The difference between a sponge and the coolant is that the coolant is a gas so the air conditioner can't let the gas actually touch the air. When an air conditioner needs more coolant, it is because it has a leak and the coolant escaped. This happens more often in home systems because there is a long line from the outside actually unit to your inside unit and it's much easier to get a hole. The window AC units are compact and self contained so it's much less likely that they'll get a leak.",
"They have a refrigerant, it's just permanently sealed in, and not spent during operation. The only reason for an air conditioner to lose refrigerant is mechanical failure like faulty pipes or seals. It works the same for all air conditioners, whether mobile or not.",
"Phase change of compressed gas is what makes your AC cold, think spray cans getting cold when you spray them, like paint, air duster, whipped cream. Except it's a closed loop system. Gas is compressed, hot side, then sent to the expansion valve and coil, cold side, then returned to be compressed again, hot side again. No gas is lost unless there is a leak. It's the same as your home, except much smaller and compact. It still has a coil, blower, and condenser, just all in and a small package.",
"An air conditioner is basically the same thing as a fridge or freezer, except you're in it! Just like the fridge takes out the heat out of your food and pumps it out on the backside - the air conditioner takes the heat from your house and moves it outside! An air conditioner wouldn't work if it wasn't externally connected, just like you can't just open the fridge door to make it share it's good coldness - it'd pump out just heat as much on the backside (more actually) as it's cooling in the front. So how does a fridge work? URL_0",
"As a further question/clarification - why does the ac unit in your car need to be recharged? Is it not on a closed loop?",
"Already some great answers here, but I'd like to add that you don't need to refill it with coolant, but you do need to \"refill\" it with electricity. Constantly. In order to pull heat out of one space and push it into another space, an AC/refrigerator needs tons of power. Usually it gets this power from electricity that comes from an outlet in the wall. In the case of a vehicle, it gets power from an engine. In the case of an RV, maybe it gets the power from a propane tank or something. Coolant is not the fuel. But there is still a fuel requirement."
],
"score": [
567,
194,
52,
10,
8,
4,
4,
4,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[],
[],
[
"https://www.reddit.com/r/explainlikeimfive/comments/u3t0d/eli5_how_does_a_refrigerator_work/"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6i5c1h | Why some airlines no longer require window shades to be opened during take-off and landing? | I recently travelled on an Airbus A330. When preparing for take-off or landing, there was the usual "put the seat upright and put the table back up". However, there was no "lift the window shades" instruction. In fact, when I boarded the plane, all window shades were pulled down, which seemed to be an intentional choice by the cabin crew. So why didn't they require the window shades to be lifted during take-off and landing? | Engineering | explainlikeimfive | {
"a_id": [
"dj3ml8d"
],
"text": [
"It was never a legal requirement. URL_0 It could just be that they forgot to announce it, or maybe this airline changed their SOP."
],
"score": [
3
],
"text_urls": [
[
"https://aviation.stackexchange.com/questions/27181/is-there-any-country-that-requires-window-blinds-to-be-open-for-takeoff-and-land"
]
]
} | [
"url"
] | [
"url"
] |
6i724z | Why are European curbs 3-5 centimeters tall (and don't destroy tires) while American curbs are 6 inches (15 centimeters) tall and shred tire sidewalls. | Engineering | explainlikeimfive | {
"a_id": [
"dj3z40g",
"dj3zi7s",
"dj4d3z4"
],
"text": [
"American curbs are there to protect pedestrians, protect drivers from driving off the road, protect landscaping beyond the curb, to retain and direct storm water in the road. The height is just easier to use in a design phase due to it being 0.50 feet rather than 0.33. Curbs 3-5 centimeters are tripping hazards, not ADA compliant and serve little purpose from a storm water standpoint.",
"Normally, European curbs are ~12cm, they are only 3-5cm when parking on the curb is allowed/encouraged which is mostly just due to the fact that streets are narrower so you actually have to park on the curb.",
"Standard kerbs^1 here in the UK are about 15cm (I can't be bothered to go out and measure one, but it's about that size) We do have what are usually called \"dropped kerbs\" where pedestrians are expected to cross so wheelchairs / pushchairs can get up / down more easily, or where a driveway meets a road or the like. Those are about 3-5cm tall. Occasionally, there will be a longer dropped kerb where a section of pavement is dual use, such as a shared footpath / cycle path, or where a bus lane crosses a footpath or whatever. Googling \"dropped kerb\" finds lots of examples of the kind of thing I'm talking about. ^1 \"kerb\" in English, \"curb\" in USAian."
],
"score": [
101,
89,
12
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6i7n0c | Why are Diesel engines more fuel efficient than gas/petrol engines? | Engineering | explainlikeimfive | {
"a_id": [
"dj46e3l",
"dj4cgvs",
"dj4awcl",
"dj4gkbl"
],
"text": [
"A few reasons: Diesel contains more energy per mass unit than gasoline, meaning that you have to burn less fuel to get the same amount of power out of the engine. Diesel engines run with a much higher compression ratio than gasoline engines. This increases the expansion space during the ignition/combustion part of the engine cycle allowing more energy to be extracted from the fuel burn.",
"One more point to add: gas/petrol engines rely on a spark plug to ignite the fuel. This means that you must put in enough fuel to guarantee that at least a tiny bit is close enough to the plug to ignite when it sparks. This is sometimes more fuel than is required to make the power needed, especially at idle and sometimes during easy highway cruising. Diesel engines do not have spark plugs and just compress the air until it is so hot that the fuel ignites. This means that it does not need fuel in a specific location inside the combustion chamber, so you can put in only the bare minimum required to create the power needed at that moment. This saves a lot of fuel at idle and a little bit under cruising conditions.",
"At the same pressure, the diesel cycle is less efficient than the otto cycle. However as you increase the pressure differential, you increase the overall efficiency. It just so happens that diesels require higher pressures than gas engines to work.",
"They're not: diesel fuel simply has more energy (48 MJ/kg; 35.8 MJ/L) than gas/petrol (46.4 MJ/kg; 34.2 MJ/L). It's not that diesel engines are more efficient, it's that less diesel fuel is required to generate the same amount of energy."
],
"score": [
12,
9,
4,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6i80is | Why aren't war planes painted in light blue colors? | Whenever they show war planes they're usually black or gray. Wouldn't it be better if they were sky colored so they're harder to spot? This is feels like a stupid question, however it's really bothering me. | Engineering | explainlikeimfive | {
"a_id": [
"dj45um0",
"dj45b58",
"dj45qk2",
"dj4ghtb"
],
"text": [
"Some planes [like this Bf-109]( URL_0 ) were painted light blue on their underside and ground colored on the top side. But without its own illumination the plane is always going to be darker than the daylight sky behind it. And with advances in radar technology there's barely any point since you'll detect the aircraft long before you can see it with your eyes.",
"Planes are usually \"spotted\" electronically rather than visually. Some of the paint is radar absorbing making the plane stealthier.",
"Modern anti-aircraft weapons use heat or radar signatures to track. The anti-aircraft guns of yesteryear simply tried to fill the sky with as much shrapnel as possible, so super accuracy wasn't important. Planes are also simply fast moving. If you don't have radar (or were in a war before it's invention) you usually didn't have much time to DO something about planes before they were right on top of you. You'd have a hard time actually hitting the fast targets, and they like to make their mission as short as possible so you have less of a chance: drop the bombs and get outta there.",
"Colour doesn't really impact that much. A plane up against the sky is going to be fairly easy to see. \"air\" is actually quite bright thanks to all the light bouncing around through it. The aircraft block that light and so at a distance appear as dark spots. Being sky blue wouldn't matter. Up close on the other hand, well ww2 aircraft conducted dogfights at very close range. couple hundred meters. At that range camouflage isn't helping. There are a few times where cammo does work. Night fighters and bombers, counter intuitively would often have lights attached to em. Someone's covered Yehudi lights below, but sunrise and sunset also worked if you could keep the sun to your back. Recon aircraft were often painted to take advantage of this, hence why you can find images of [pastel pink spitfires]( URL_2 ) Older aircraft were instead painted to make them harder to spot *from above*. You really don't want someone in a fighter aircraft diving at you from above, that situation puts you at a disadvantage. hence why you can find the ususal green spitfiresand also brownish ones like [this]( URL_1 ) and why the seafires (spitfires modified for carriers) looked like [this]( URL_3 ). Other nations did similar things of course as did other british aircraft, but I've got a spitfire theme going and we're rolling with that. Of course many aircraft, especially modern ones, are unpainted. With modern radar and infrared tracking and etc cammo designed to fool the human eye doesn't help much. Paint weighs the aircraft down and modern militaries have largely decided to dispense with the weight except for what's needed for various markings. Also in the very modern era, paint is obviously going to get in the way of the radar absorbent materials and what not, and could end up making the aircraft easier to find. Unpainted metal of of course greyish, while a lot of radar absorbent material is usually a darkish grey or even black. (I mean I guess those coatings count as paint?) You may also have seen stuff like [this]( URL_0 ) in the movies. those are invasion stripes and are actually there to make the aircraft more distinctive. By time D-day rolled around the allies pretty much had air superiority over in Europe and they decided friendly fire was more of a concern than the German air force."
],
"score": [
26,
11,
10,
5
],
"text_urls": [
[
"http://i.imgur.com/QLhAkLg.jpg"
],
[],
[],
[
"https://c1.staticflickr.com/4/3745/14275602196_715046a7f0_b.jpg",
"https://hobbyking.com/media/catalog/product/cache/1/image/320x230/9df78eab33525d08d6e5fb8d27136e95/legacy/catalog/102371s.jpg",
"http://nowiknow.com/wp-content/uploads/8237-1.jpg",
"http://www.condor49ers.org.uk/images/seafir1.SeafireMk47.jpg"
]
]
} | [
"url"
] | [
"url"
] |
6idub0 | Why do cop cars have the small hub on the wheel instead of the entire rim or hubcab? | Engineering | explainlikeimfive | {
"a_id": [
"dj5f8zx",
"dj5g8gn",
"dj5mlit",
"dj5jwov"
],
"text": [
"Because when you're buying a fleet of police cars, leaving the hubcaps off can: * save you money on the overall cost of the cars * save you money on maintenance (replacing hubcaps) * make maintenance easier * keep all the cars looking standard and professional (no missing or cracked hubcaps)",
"Doing a bit of googling, the consensus seems to be because hubcaps fall off when you drive aggressively...and cops do that a lot. Better to have hubcaps that don't fall off so they don't need to blow money replacing them.",
"To avoid valve stem damage. This was answered on \"Car Talk\" some years ago. Police cars risk losing hubcaps during aggressive maneuvers, and there is greater risk of damaging the valve stem (thus risking a flat) with a full hubcap, thus the smaller hubcaps.",
"I think another thing to add is that to the other answers is that it is a signature look. An unmarked car might still have them while a civilian car will often have plain steel rims. It is something I usually spot before the hidden lights in the grill or rear deck. Most unmarked cars in my area do no try to hide the fact that they are police cars, only that they do away with the livery. It would make sense to keep all the wheels consistent."
],
"score": [
14,
10,
5,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6ieglr | What are these globe things actually doing? | URL_0 Also, why do they react when you touch the outside? Edit: extended the question | Engineering | explainlikeimfive | {
"a_id": [
"dj5kz97",
"dj5u3uf",
"dj5ksmi"
],
"text": [
"It's an orb filled with various inert noble gasses with an electrode in the center that sends out a constant current of very small amplitude towards the insulated glass orb, in order to create a pleasant looking effect. Originally invented by Tesla, during his experimentation with evacuated glass tubes and high frequency currents.",
"Electricity is coming from the center. The globe is filled with invisible gas that glows when electricity touches it. What happens when you touch it is that the electricity is attracted to your finger and goes towards you.",
"They are called \"plasma globes\" and are filled with various noble gasses which are caused to glow by a high voltage electrode in the center discharging to the glass insulator of the globe. At it discharges through the gas the ionization results in the glowing filaments."
],
"score": [
7,
3,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6igb69 | When a Soyuz, Dragon, or other capsule docks with the ISS, how does the ISS compensate for the transfer of energy from the "impact"? | Engineering | explainlikeimfive | {
"a_id": [
"dj601nh",
"dj5zo27"
],
"text": [
"It does not immediately correct for this. Currently only Soyuz and Progress docks with ISS, all other spaceships are currently birthing with ISS. Birthing is a process that involves no or only a tiny impact. The impact is applied when the CanadaArm2 grabs the other spacecraft. The difference is velocity is very close to zero so it is hard to even measure the force applied to the ISS. When docking there is a tiny impact but again the difference in velocity is very low so very little momentum is transfered. The much larger problem for the ISS is the tiny impacts with air molecules as it travels around the Earth in the ionosphere. ISS is placed as low as possible while still able to do its mission which means that it experience a lot of drag and even lift from its solar panels and other instruments. And the atmospheric conditions are very rough at that altitude. So the ISS gets tossed around quite a bit (relatively speaking) on a daily basis. To correct its attitude it have several gyroscopes on board. It can also use the solar panels and radiators as wings and rudders if needed. To correct the drag there is periodic reboosts. Currently they are all from the visiting Progress spacecrafts. The Space Shuttle were also capable of this and ISS is also equipped with its own thrusters if it is needed. This is one area of research they are doing in preparation for an extended ISS mission or a new space station.",
"The ISS has its own attitude and altitude maneuvering jets, so I can make corrective firings if it had to. However the relative mass of the ISS (~500,000 kg or about 462 US tons) is quite large relative to a Dragon capsule, which at max payload can be ~11 US tons. That, and the capsules use their own thrusters to slow to a near crawl before the two join, so there is very little kinetic energy imparted to the ISS."
],
"score": [
6,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6igmra | how does fuel injector inject fuel into the engine without lighting on fire? Since the engine is under combustion. | Engineering | explainlikeimfive | {
"a_id": [
"dj650hf",
"dj62r8b",
"dj62j1o"
],
"text": [
"Unless you're looking at a direct injection engine, the fuel injection doesn't happen at the place where the combustion happens (the combustion chamber). The injection happens at the intake plenum. In direct injection engines, like some Honda and Toyota gas engines, and diesel engines, the previous combusted mixture is already expelled from the combustion chamber before new fresh uncombusted air is pulled.",
"Let's assume that we are discussing a 4 (or 6 or 8 etc) cylinder 4-stroke engine. The 4-strokes correspond to 4 different stages: 1) INTAKE. This is where the fuel injector injects fuel into the cylinder. 2) COMPRESSION. The piston inside the cylinder moves up increasing the pressure of the fuel. 3) COMBUSTION. The spark plug lights the fuel on fire forcing the piston back down. 4) EXHAUST. Gasses and stuff left over from combustion leave the cylinder. The important part is that while fuel is being injected into the cylinder, that isn't the one that is in combustion. This is why we have multiple cylinders. This is also true for a 2-stroke engine where steps 1 and 2 are combined and 3 and 4 are combined.",
"I know this is an old video but I really love how this guy explains things. URL_0 as far as I know it is because it isn't constantly under combustion, it had lifters that will open up channels that would be to the exhaust chamber, lifter than closes and opens the intake valve and fills the combustion chamber with fuel and air and then a spark plug will ignite the atomized fuel air mixture"
],
"score": [
4,
4,
3
],
"text_urls": [
[],
[],
[
"https://youtu.be/nbCe68ck6qg"
]
]
} | [
"url"
] | [
"url"
] |
|
6ih9oq | why do cars always have those special car outlets? Those little circular 12volt cigarette ports, why do cars always have those instead of just switching over to regular wall outlets? | Engineering | explainlikeimfive | {
"a_id": [
"dj67t6m",
"dj68bsr",
"dj67lvv"
],
"text": [
"They are for cigarette lighters. Once upon a time, smoking in the car was common and electronic devices small enough to be powered by a car were science fiction. Cars thus had a device to light your cigarette, so drivers weren't distracted by their Zippo while driving. When electronica came along, the choices were: a) adapt to the cigarette lighter socket; or b) entice car manufacturers to add a different outlet. Making 120VAC house current inside a car is difficult, since cars run on DC, and the cost wasn't optimal. It seems that (a) got the most electronics deployed, so that's what the electronic people did. Over time, too many cigarette lighter to USB gadgets were sold, and cars started having USB ports in them because it's easy to make 5VDC from 12VDC. Some cars have AC outlets, but not anything like the majority.",
"Think of the \"plug\" as a way that two devices state their expectations. The shape of an outlet is saying \"hey I supply power in this way\". Plugs that fit that outlet shape are saying \"okay, I'm designed to work with that\". That way, it prevents you from plugging things into outlets and having potentially disastrous results! A wall outlet is shaped in a certain way that's associated with AC power of a certain voltage and amperage that is common for houses powered by your electrical grid. Cars are powered by an engine doing other stuff and a 12V battery and traditionally have only had to power low voltage, tiny electronics, so they have been designed to supply a different power profile. While cars *can* be made to have regular wall outlets (and some do) it's costly and complicated for minimal gains. They also increasingly have powered USB ports. As for why the port is the shape it is, that seems to date about to cigarette lighters. They were in basically all cars and needed power anyways, so their functionality duplicated as a power plug. Then as lighters became less common, that part was removed and now they're just power ports.",
"A couple of reasons -- backwards compatibility with items that were made to work with the accessory ports, especially back when they were still cigarette lighters. The other is because it delivers DC power. You would not put an AC outlet there, because that invites people to plug something in that should not be plugged in and wreck it and possibly the car's electrical system. If they do away with the accessory port completely, it will be replaced by USB ports or something similar."
],
"score": [
7,
5,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6ijjgs | Why aren't you supposed to put car batteries on the ground? | I have a small understanding of how batteries work through an Electric Engineering class in college but I still don't know why I shouldn't. I have heard the saying of "grounding the battery" but wouldn't the case around protect it from that? Would charging it afterwards not fix it? | Engineering | explainlikeimfive | {
"a_id": [
"dj6rkuu",
"dj6rldf",
"dj6rmm2",
"dj6rj6t"
],
"text": [
"This is an outdated concern. Back in the olden days car batteries were made of a rubber material which actually allowed some acid seepage...potentially leading to conductive connection to the concrete diminishing the batteries stored potential. Modern car batteries are not susceptible to this as they are made of plastics. Todays batteries are actually BETTER stored on the ground as the cold surface reduces self discharge.",
"Modern batteries dont have this problem. Edison cell nickle iron batteries were encased in iron instead of rubber and they would discharge into concrete. Batteries before that were made of wood with glass cells. Storing them on damp earth or concrete would cause the wood to swell and break the glass.",
"I was always told this too specifically for concrete- so usually I put down a piece of scrap wood, but... \" The short answer is that letting modern batteries sit on concrete does not harm or discharge them in any way. \" URL_0",
"Yeah, there is no issue on setting a car battery on the ground. The issue comes in turning a battery sideways or upside down. Sometimes a battery can become unsealed and leak causing battery acid to spill out. Grounding the battery has to do with the positive and negative terminals. Basically you don't want your positive terminal to come in contact with the negative terminal directly or indirectly (loose wires touching the chasis, etc.). Edit: This causes the stored electricity to discharge, which depending on how rapid the reaction, cause damage to the battery itself."
],
"score": [
8,
5,
4,
3
],
"text_urls": [
[],
[],
[
"https://www.homepower.com/articles/solar-electricity/equipment-products/ask-experts-batteries-concrete"
],
[]
]
} | [
"url"
] | [
"url"
] |
6irmgx | why is every microwave so damn noisy and the door closes so loudly? | Engineering | explainlikeimfive | {
"a_id": [
"dj8tuf5",
"dj94cxw"
],
"text": [
"Most microwaves doors are empty inside and there's no stability between the panels, so when closing the panels shake and the sound ressonates in the insides, (like dropping a empty metal can to the ground). Also there are Microwaves that have Magnetic doors to prevent that slam we all know of. Mine has one of those opening / closing systems. Some Microwaves use imperfect Magnetron tubes and metal Strirrer motor (to bounce the Microwaves evenly to the food). The Magnetron tube should not produce any noise, but depending on the condition it can produce some. The Strirrer is a eletric motor that is not insulated most of the times. The blades have to move so it's hard to insulated the sounds. That's what probably creates that humming. Also there's a Fan and /or rotator motor inside most microwaves that also make some noise",
"The mechanical answer below is correct. The marketing answer is because it is difficult to both get a product manager to really care about a product enough to make it nicer and convince the consumer to pay a premium for the product consistently enough that the product manager is kept around. Many people pay a premium for products like Apple Phones or Monster Headphones because they consistently focus on details. There are some examples in the housewares space like Mixmaster Mixers, Miele Dishwashers, and Dyson vacuum cleaners where the brand means detail and can consistently get a premium for it, but in general a microwave oven is treated like lumber - you just go to Lowe's and pick out the size you want and other than that they're pretty much treated as all the same."
],
"score": [
17,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6iwy4r | Why do multi-engine aircraft always start one engine at a time? | Engineering | explainlikeimfive | {
"a_id": [
"dj9qfvs",
"dja0byg",
"dj9uxzu"
],
"text": [
"Because there's only enough electrical power bandwidth to start one at a time. Otherwise you'd have to carry around multiple electrical starters.",
"When starting up an aircraft, there is a pretty methodical checklist you go through one-item-at-a-time. For everything. You confirm that A is good before you go to B. If isn't good, you stop and deal with it. Engines are just part of that process. You confirm that Engine 1 is good, then you go to Engine 2, etc. If you start all Engines at the same time and then have a problem, it may be more difficult to narrow the cause down. By starting them one at a time you've already reduced the amount of diagnostics you have to run to find the problem.",
"Another thing to consider. If there is a problem with it you want to notice and deal with it. Not fail to notice it because you are looking at more than one engine or be distracted by what's going on with it."
],
"score": [
12,
6,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6j0yiv | What is so important and special about the James Webb Telescope? | I've seen a lot of talk on reddit and other websites about how amazing it would be if we launched it, but I don't know why it would be so special. What makes this telescope better than other ones we have? (I'm not questioning the legitimacy of the James Webb Telescope, I'm just lacking in knowledge about it.) | Engineering | explainlikeimfive | {
"a_id": [
"djalx21"
],
"text": [
"As you might know the universe is expanding. So the more distant objects we see the higher speed they have away from us. Which means they will be more red shifted. The problem is that some of the most interesting objects to look at is so far away that they go far into the infrared spectrum. The atmosphere is transparent to visible light but not to all infrared light. And similarly with the main mirror of Hubble which is better for infrared astronomy then earth based telescopes but is still not the best for this and have a relatively small diameter compared to modern telescopes. So the JWST is designed from ground up to be an infrared telescope which can see parts of the spectrum which is not visible though the atmosphere or with Hubble. And the main mirror is much larger then Hubble so it can collect more light and get better resolution images. So JWST is able to look at objects further away then we currently can and in a better resolution. The objects further away is very important to find out the structure of the universe since the light from these objects have been moving for a very long time. A lot of these objects are from the time when the earliest galaxies were formed or even before any galaxies existed. So being able to look at how our universe looked like not long after it was formed may help us understand how it was formed. There is also a secondary objective in observing rouge planets and brown/black dwarf stars in our galaxy. These are also emitting light in the infrared spectrum and can be very hard to observe using existing telescopes. But JWST might be able to observe them much better then Hubble."
],
"score": [
10
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6j32kn | Regenerative braking | Engineering | explainlikeimfive | {
"a_id": [
"djb3kai"
],
"text": [
"An electric motor and an electric generator are (at a simplified level) the same thing. In one case, you're putting electrical power in and getting mechanical power out. In the other, you're putting mechanical power in and getting electrical power out. As a result, you can take an electric motor and use mechanical force to 'turn it backwards' to generate electricity. Which is precisely what regenerative braking does. It places a mechanical load on the wheels - which slows their rotation - and then converts that mechanical load to electrical power by feeding it into the motor/generator."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6j3fhb | why do older cars jolt a bit forward or backward after being put in PARK? | Engineering | explainlikeimfive | {
"a_id": [
"djb7ll2",
"djb7051"
],
"text": [
"Putting the trans in park just inserts a locking pin. The car jerks because it's the weight of the vehicle taking the slack out of the drive-train until the locking pin bear the weight of the vehicle. I've seen this pin break 4 times, and I live in the flat Midwest. It can happen to you. When that happens, nothing is holding the car in place. My father had a truck like this. We'd park it in one spot and find it across the parking lot when we came back to it. This is why you should always ALWAYS use the parking brake. It *IS NOT* the emergency brake - it's a mechanical brake on your back tires that is meant to bear the weight of the vehicle and keep it in place. It'll also keep your locking pin from breaking. It is utterly useless in an emergency as your front wheels do 80% of your braking, typically more. If your brakes fail and you need to stop, this will just lock up your back tires and put you into an oversteering skid. Now you have two problems.",
"In my understanding, putting the car in park locks the transmission but does nothing to the wheels directly. So when you park the car and let off the brakes, it lurches as the mechanical \"slack\" comes out of the drive train. That is, the wheels can move a bit before being stopped by the locked transmission. You can avoid this by applying the parking brake before releasing the brakes, as this locks the wheels directly."
],
"score": [
18,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6j49b4 | What's the difference between an airplane and a jet, regarding hardware and such? | Are specific parts either needs to specify as one or the other? | Engineering | explainlikeimfive | {
"a_id": [
"djbdni3",
"djbdp5u",
"djbdju3"
],
"text": [
"For an airplane to be a jet it must have a [jet engine]( URL_0 ). Not all airplanes do. For example, a prop plane: A plane where the forward motion is created by propeller engines is not a jet. An ELI5 explanation of how A jet engine works: Air is pulled into the engine by fan blades. This smooshes the air together. Fuel is sprayed into this compressed air and lit on fire. The resulting explosion forces air out the back of the engine very fast, creating forward thrust.",
"A plane is any type of fixed wing aircraft. A jet is a subset of a plane, which uses a jet engine (creates thrust by jet propulsion).",
"A jet is an aircraft that uses the force of ignited fuel-air mix for propulsion. Airplane is a general term for a flying vehicle. A simple Google search would have given you this answer...."
],
"score": [
5,
3,
3
],
"text_urls": [
[
"https://en.wikipedia.org/wiki/Jet_engine"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6j7dox | When and why did they switch from making planes covered with canvas, to making an all metal plane? | Engineering | explainlikeimfive | {
"a_id": [
"djc6ji0"
],
"text": [
"Around 1900, the Hall–Héroult process allowed for cheap production of aluminum and the development of Al-Cu alloys made all-metal airframes possible. The high-strength Duralumin alloys (Al-Cu), what we now call the 2000-series aluminum, were developed in 1909, and got improved until Alcoa came out with the 2024-T3 alloy (T3 being the heat treatment) in 1931, which we still use a lot of today. Wood worked well for the lightweight, underpowered aircraft of the day with the box-girder frame construction, and wire-truss, strut-supported wing. Where metal really shined was in the monocoque fuselage and fully cantilevered wing. In the older fabric skin planes, the fabric didn't take much of the load, so it added weight without adding strength. In the monocoque planes, the skin provides most of the stiffness. The cantilevered wing got rid of the cables and struts that provided strength to the old aircraft, but required a very strong main spar. So, as planes got bigger engines, and carried more payload, aluminum provided a lighter, stronger solution. Experimentation with all-metal aircraft started in World War I, with Junkers being one of the leading pioneers with their J1 and later F.13. However, the control surfaces on many aircraft continued to be fabric covered right into World War II."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6j7gpt | Why are bathroom scales so inaccurate, when all they have to do is measure pressure applied to within 0.001 accuracy or so? | It seems strange that the readings they give are often contradictory - I just weighed myself twice and gained 1.5kg in 20 seconds. And they differ greatly from the scales used by pharmacists and clinics. For that matter, the scales that *they* use have to be regularly calibrated, I believe every few months. What's so difficult and error-prone about measuring the weight of a person with a reasonable degree of accuracy? | Engineering | explainlikeimfive | {
"a_id": [
"djc4s3e"
],
"text": [
"Cheap bathroom scales are not going to be as accurate as doctors scales which cost 10 times as much. Even electronic ones are mechanical devices, and have to deal with friction of the moving parts. If you want accuracy, buy a beam balance. If you *really* want accuracy, you will need to get it calibrated every few months."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6j9doc | How does the ISS filter the C02 astronauts exhale back into oxygen? | Use small words. | Engineering | explainlikeimfive | {
"a_id": [
"djcjnkx"
],
"text": [
"The ISS uses a system called the \"Carbon Dioxide Removal Assembly\", which is a set of filters and other equipment that uses chemical absorption to remove CO2 from the air, then heats it and captures the trapped CO2 to be pumped out. There's a special material called \"zeolite\" that acts as a sort of sieve or filter that's crucial to the process. This means the CO2 is lost to space, and the atmosphere must be replinished. Oxygen is mostly obtained from cracking water into hydrogen (used for other purposes) and oxygen. There's discussions and ongoing work being done to create a closed loop system that can recover oxygen from the trapped CO2 instead of venting it to space, but this is not yet a reality."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6jaess | Recently a whale was found with its stomach full of plastic bags. How does a plastic bag get from my house and into the ocean? | Engineering | explainlikeimfive | {
"a_id": [
"djcrct0"
],
"text": [
"People don't just drop bags in the trash, they drop them in the street - or they put them in a public trash can that is full and wind, homeless people or animals come and leave it on the ground. Next you have rain which washes it into the storm drains which lead straight to the ocean. This of course, completely ignores the dickheads who leave them on the beaches or throw them from boats."
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6je5r7 | How is the maximum load of truss columns calculated? | Those columns with many triangles inside of them, usually used to hold large structures. How much one of those things can hold in weight? They look very thin for the amount of weight they hold. Sure there are many sizes but I am thinking there is a correlation between the number of triangles and how strong it is. | Engineering | explainlikeimfive | {
"a_id": [
"djdls1f"
],
"text": [
"The amount of load a column (whether part of a truss or not) can safely hold is principally based on the material,the geometry, and the nature of the load. The material (wood, steel, concrete, aluminum, masonry, plastic, etc) has a certain strength properties. Each material has a certain allowable stress (force per unit area) before failure (I.e. yielding, or permanent deformation). Also each material has stiffness properties, meaning the amount a material deflects with an applied load (called Young's modulus). This is important to know how something physically reacts under load, but more specifically is mainly used to establish buckling limits for a material, which is a different type of potential failure. The geometry is also important. For columns, the main variable is the cross sectional area of the component itself. Next is the length of the column. Next is the nature of the degree of restraint of the ends of the column (ends that are held rigidly are stronger to resist buckling than ends that are loosely held). Also of importance is the shape of the cross section of the column, the shape will dictate a property called the radius of gyration which will affect the amount of load a column can withstand before buckling. Also, the nature of the load is important to define. Loads can be applied in 6 different ways, axially (which is what I think you're wondering about), but also laterally in two directions (shear), and flexurally in three directions (bi-axial bending and torsion). All of these loads are combined to consider if the column is appropriate. Finally, most engineers use national design codes and standards given all the information above to establish the 'safe load'. As an aside, triangles are an important shape in structures (triangles in 2-dimensions, and tetrahedrons in 3-dimensions). These shapes efficiently transfer load by minimizing bending loads in a structure which will significantly reduce the strength of a component. Hence the more triangle in your structure the better. You had a good intuition regarding the presence of triangles."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6jf3ta | When they 'sweep for bugs' in a room what are they actually doing? What all are they able to find? | Engineering | explainlikeimfive | {
"a_id": [
"djdwq1k",
"djdrqsp"
],
"text": [
"As previous commenters noted, they are looking for anything that sends out a radio signal. In addition, many electronic devices accidentally emit a small amount of radio noise as they operate, and this can be searched for. In addition, some electronics *respond* to the presence of a strong radio signal by resonating and then emitting a signal back. That can be tried too.",
"The purpose of a bug - which is a listening device (or video) - is electronic. Which means to operate it must either be on to record, which uses/sends signals. Or it must be sending what it's receiving back to someone or some thing. Usually there are two types. Ones that send information back to someone and ones that must be retrieved to check the information on them. Think of using a metal detector on the beach. You are checking for metal that you can't see. A \"bug sweeper\" is very simply checking for electronic transmissions of some sort in the same manner. There are obviously more complicated versions of each part of my explanation but that's the basic."
],
"score": [
3,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6jhk2e | During space travel how do we navigate? North South East and West doesnt work once we are off earth.. | Engineering | explainlikeimfive | {
"a_id": [
"djeag6u",
"djeiz8u",
"djesbsi"
],
"text": [
"In direct relation to the position of two other known points such as the Earth and the Sun.",
"It should be generally a \"towards\" or \"away from\" a celestial object or something in reference to it/them.",
"There are multiple radar ground stations around the earth that can track objects in orbit around the Earth. There are also more sophisticated ground stations that can track objects further into our solar system, which are usually used by NASA to track the probes they send out. The ground stations then use an antenna to send out an electromagnetic wave to ping an object. The object, presumably a shuttle or something will send back the signal to the ground station with various amounts of data. Then people crunch the data and figure out where this object is based on multiple factors like distance, time traveled, angles, etc. I could throw out some bigger terms, but then it would be closer to a ELI10"
],
"score": [
3,
3,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6juhao | How the mathematical imaginary components to circuits (Sinusoidal current and voltage as well as impedance) are applied to the real world. | Engineering | explainlikeimfive | {
"a_id": [
"djh2jiw",
"djh3vtb"
],
"text": [
"The imaginary component shows up in the degree to which voltage lags current or vice versa. In a DC circuit, if you increase the voltage, the current also increases at the same time. However in an AC circuit, as the signal reaches peak voltage, it may not yet be at peak current. You might have to wait another 1/4 of a cycle to reach peak current, for example, at which point voltage has decreased. The imaginary component describes this difference.",
"So what you must realise is that imaginary components are just that, imaginary. They don't exist. What they do is allow you to represent a one-dimensional system using 2 dimensions. Why would you ever want to do that? Well, because it makes your maths easier. A waveform can now be described as a circle, and a phase is an angle. You do your math, then throw away the entire imaginary axis and look at the results on the real axis, and it all works out. If you are interested, you can further look at quaternions. That's a 3 dimensional complex plane, and allows you to use complex maths for actual three dimensional movements."
],
"score": [
7,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6jwn47 | How are LOGIC gates designed? | I'm struggling to understand boolean logic, Turing/Babbage, etc. I don't know if I'm misunderstanding, or what, but I'll try to explain. I've got to this part: Everything is Yes or No. Everything else is made of a series of Yes or No's, or 0's/1's. I don't understand how you make operations/logic gates with 0's and 1's. How do I make an *and* gate from 0's and 1's? In which sequence do I put these 0's and 1's to make the gates? How do I make an *add* function from 1's and 0's? Thanks | Engineering | explainlikeimfive | {
"a_id": [
"djhkmzj",
"djhkwry",
"djhkf8t"
],
"text": [
"I think your initial understanding is a little bit off. There are actual physical operations/logic gates on a chip. A transistor can act as a logic gate.",
"> I don't understand how you make operations/logic gates with 0's and 1's You don't. You make logic gates with electrical components. Specifically, transistors. Those logic gates are the base components that *operate* on 1's and 0's.",
"Typically we represent a 1 with a high voltage and 0 with a low voltage, but you can do it the other way (\"negative logic\"). [Here's]( URL_2 ) a NAND gate (Not AND) using CMOS logic (both n-channel and p-channel transistors). Keep in mind that a high voltage turns an n-channel transistor ON (conducting); a low voltage turns a p-channel transistor ON. The p-channel transistors are the ones with the circles on the gate terminal. To turn this into an AND gate, put an [Inverter]( URL_1 ) on the output. Print that out and write a 1/high by one input and 0/low by the other, then note which transistors are on and which are off and what resulting voltage you get at the output. Then change your inputs and see how it changes the output. As you can see, and [ADDER]( URL_0 ) is a bit more complicated. A and B are the binary numbers being added; Cin is the carry-in bit, C-out is the carry out. **EDIT**: I originally said that was an AND gate, but then I actually looked at the schematic and realized it was a NAND."
],
"score": [
6,
6,
4
],
"text_urls": [
[],
[],
[
"https://i.stack.imgur.com/GyIl6.png",
"http://tiij.org/issues/issues/spring97/electronics/cmos/IMG00006.GIF",
"http://www.boost.org/doc/libs/1_46_1/libs/polygon/doc/images/nands.PNG"
]
]
} | [
"url"
] | [
"url"
] |
6jxg8c | Why do most trash cans have a sort of taper like \_/ ? | Engineering | explainlikeimfive | {
"a_id": [
"djhr7g7",
"djhrqes"
],
"text": [
"Imagine blowing up the garbage bag inside with that shape until it was at max capacity. You would still be able to wiggle it free. If it tapered the opposite way, you would be unable to remove it. Even a can with perfectly square sides, if it wasn't 100% rigid, the walls would bulge and create a wedge.",
"The simplest reason is that you can [nest them together]( URL_0 ), making them take up much less space to warehouse and retail than they would otherwise."
],
"score": [
24,
11
],
"text_urls": [
[],
[
"https://www.nlm.nih.gov/hmd/preservation/images/trashcans.jpg"
]
]
} | [
"url"
] | [
"url"
] |
|
6jz1e5 | How come my car tells me when my oil is too low, but there's no gauge on my dashboard to indicate how much is in there all the time? | Engineering | explainlikeimfive | {
"a_id": [
"dji2hti",
"dji49sf"
],
"text": [
"Unlike gas, your car isn't designed to burn through oil. Putting a gauge on the dashboard that *shouldn't ever move* is just adding cost & clutter to the instrument panel. You've already got an easy way to check your oil levels - the dipstick in your engine compartment. Check it every time you buy gas if you're worried about your oil levels.",
"If there were gauges and indicators for everything that should be monitored by the driver, your car's dashboard would be more complicated than the inside of a Boeing 747. The \"check engine\" light is connected to a computer in most vehicles built from the 90s forward that illuminates the light when any one of these hundred or so problems happens. You, the driver, can then attach a device that will read out the error codes, telling you what is wrong. This requires less space -- only a handheld device and a booklet is needed, rather than a hundred pounds of gauges and equipment. Only the most critical thing that will cause *immediate* engine destruction is monitored: The coolant temperature. Everything else may destroy your car... but it'll probably take time. Your oil should be checked weekly to monthly depending on its age, and it's there in the owner's manual for this reason. Also -- heavy duty trucks and semis *do* have oil pressure gauges, because low oil is similarly instantly destructive. A regular automobile will (usually) give warnings of low oil before it dies -- squeaking, grinding, excessive heat (coolant temp), poor acceleration, stalling, difficulty starting. These are all signs that any motorist should be immediately alarmed about, and the oil should be the first thing checked. tl;dr -- Too complicated, here's a light bulb that blinks."
],
"score": [
14,
12
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6k0w67 | Why do modern airplanes like the A380 have cigarette ash trays in the toilets/bathrooms if smoking is illegal on all commercial aircraft? | I just noticed this travelling to the UK from australia. We flew on 777 s and A380's and they all had ash trays on the door inside the lavatory? I found this odd because every flight mentions that its a prosecutable offence to smoke under international law. So but why do they then have amenities on the plane to accomodate smoking? | Engineering | explainlikeimfive | {
"a_id": [
"djiesot",
"djiff6q",
"djievr5",
"djif0ex"
],
"text": [
"It's a legal requirement in the US. URL_0 > (g) Regardless of whether smoking is allowed in any other part of the airplane, lavatories must have self-contained, removable ashtrays located conspicuously on or near the entry side of each lavatory door, except that one ashtray may serve more than one lavatory door if the ashtray can be seen readily from the cabin side of each lavatory served.",
"The fact that smoking is illegal doesn't mean that nobody will break the law and smoke. If someone (illegally) smokes, they need to stub out the cigarette, and if there's no ashtray, the stub will end up in a bin and cause a fire.",
"It's an emergency thing. Some people can't go without cigarettes for longer periods of time. If you're used to smoking 20 cigarettes a day you just can't stop doing it for that 15 hour flight. In case somebody can't control himself/herself, they have an ashtray, so that they don't put it on the floor and burn the plane.",
"Smoking isn't banned internationally. Smoking was banned on US domestic flights in 1988, with most airlines around the world following suit by the end of the 1990s. But if the country or airline still allows it it's ok (I don't know of **any** airlines that do!) In the US it's a law to have ashtrays. But the reason they are still there in other places is to cater for the people who flout the rules and smoke anyway. Airlines fear smokers could panic and not dispose of their illicit cigarette properly, by dropping it in the sink or down the paper towel dispenser. Rather than risking a fire or alarming other passengers, it was judged to be better that planes have a safe disposal method in place. Hence they still have them. Edit a word or two"
],
"score": [
17,
10,
4,
4
],
"text_urls": [
[
"https://www.law.cornell.edu/cfr/text/14/25.853"
],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6k1je5 | How can the power company direct renewable electricity to my meter but nonrenewable to the apartment upstairs with no new wires? | I recently received a letter in the mail from my power company that I now have the option to go to 100% renewable energy. It touts how no one needs to come to the house, no new wires, and they just switch it over. I live in a split level home with separate meters. How does this work? | Engineering | explainlikeimfive | {
"a_id": [
"djikk20",
"djiki4t",
"djikpzi",
"djil1nc"
],
"text": [
"It doesn't. Electricity on the grid is fungible, which means that it makes no difference in the application of it what the source is. Power on the electrical grid may come from multiple sources -- coal, gas, nuclear, hydro, solar, wind, and so on. What the power company is offering you is the ability to purchase renewable energy -- which really means that *they* purchase renewable energy in amounts adequate to meet the demands of all of the people who signed up for the program.",
"It doesn't. The same electric flows out. The company just tracks how much flows out of the meter that should have renewable and buys that much from it's renewable source.",
"It doesn't split it. Basically what they are saying is for every 1KW of electricity you use they will generate 1KW using Renewables sources. In reality if you lived down the road from an oil, coal, gas, nuclear etc power station it would probably mostly come from that.",
"I'm guessing here, because I can't see the details of the offer from the power company, but you are probably buying renewable credits. The power that comes into your house doesn't change. In this case, the power company will generate their power from a mix of cheap fossil fuel and a more expensive renewable. A small group of people who agree to pay for renewable energy will make up the cost difference, so there is no overall price hike to the general population. In this situation, the power coming into your house won't be any different that the power going into your neighborhood's. However, you get a warm fuzzy that you're helping the power company move away from fossil fuel."
],
"score": [
16,
4,
3,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6k51ks | How does a flash bang grenade work? | Engineering | explainlikeimfive | {
"a_id": [
"djje3f9"
],
"text": [
"A flashbang grenade is a small explosive charge surrounded by a pyrotechnic compound and packed in a metal tube with cutouts along the sides. When the explosive detonates it isn't contained (thanks to the cutouts) so it doesn't cause the grenade to fragment. Instead it makes a very loud noise, and a concussive shockwave. Along with the shockwave comes the pyrotechnic powder (usually some mix of magnesium and aluminum). The heat of the explosion ignites the powder as it is ejected from the grenade, causing it to burn with an intense white light. The combined effects of the noise, shockwave, and flash serve to blind, deafen, and disorient anyone in the immediate vicinity of the grenade."
],
"score": [
22
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6k6b9x | Why do most light bulbs burn out when the switch is flipped on? | Engineering | explainlikeimfive | {
"a_id": [
"djjp5hi",
"djjox8h"
],
"text": [
"When a light bulb is turned on its filament is cold and so the resistance is low. So a giant rush of current runs through it. As it heats up the resistance goes up and current goes down and eventually reaches a balance. So this rush of current is the most stressful thing that happens to the filament. As the filament weakens from being heated eventually it will burn through the filament. This is most likely to happen during the cold to hot rush of high current.",
"remember how when things get hot, they get bigger? and that bending metal back and forth will cause it to break? and that the faster and further you bend it, the quicker it breaks? and that glowing hot metal is pretty weak? so when you first turn a light on, the filament, that little metal spring or wire thing inside the bulb that gets hot and glows....gets really hot *very, very* quickly...and therefore bends a bit because it got bigger because it got hot, and it got softer, because it got hot, and it did this quickly, as you can see the light nearly instantly. so after a bunch of times of getting hot very quickly and cooling down slowly, the filament snaps, just like any other metal bent back and forth a lot. there's one other thing happening here: because lightbulbs aren't perfect, there's some extra, unwanted, stuff inside...stuff like oxygen, hydrogen, and carbon that's nearly impossible to get completely rid of. when chemicals are hot, they usually react faster...and the lightbulb gets pretty hot....and those unwanted things, the oxygen, hydrogen, and carbon, react with the metal filament and cause it to get more brittle over time, thus exacerbating the whole process."
],
"score": [
11,
8
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6k8xfs | How come space rockets (Falcon-9, Ariane 5, etc...) don't have fins on them? What keeps them stable in flight? | Here is a picture of [Falcon-9]( URL_1 ) and [Ariane 5]( URL_0 ). As you can see there don't seem to be any apparent fins on either of the rockets. So how do these rockets remain so stable? | Engineering | explainlikeimfive | {
"a_id": [
"djkaw52",
"djk5m2d"
],
"text": [
"Some of these answers are not entirely correct, the rocket's center of drag pressure still has to be behind it's center of mass or no gimbal is going to keep you straight. So it's not just that you can add gimbals and remove fins. Fins serve two purposes, they steer the rocket and they stabilize it by providing some drag pressure towards the rear. A rocket must already be stable for it to fly with a gimbal, the gimbal is for course corrections. Space X's rocket is designed to have completely different centers of drag and centers of mass when it goes up and goes down, so just removing the mass of the upper stage needs to be sufficient to change it from being stable forwards to stable backwards. That small kink before the engines for example moves the center of drag much farther backwards when flying backwards, and even with gimballed engines and powerful nitrogen thrusters the Falcon 9 needs to deploy fins at the top of the rocket to properly be stable coming down. So it really does require careful aerodynamic design and mass balancing to be able to remove the fins as they don't just steer, they aerodynamically balance the rocket. Verneire style and nitrogen thrusters are also an important modern rocket steering technology. Fins weigh a decent amount so being able to get rid of them, is a huge boost to performance. The benefit of removing fins of course is less drag and weight.",
"The engine nozzles are mounted on gimbals, allowing them to twist to achieve [thrust vectoring.]( URL_0 ) All that is required is a bit of a monster of a control system."
],
"score": [
10,
7
],
"text_urls": [
[],
[
"https://spaceflightsystems.grc.nasa.gov/education/rocket/gimbaled.html"
]
]
} | [
"url"
] | [
"url"
] |
6k9l9h | How can the internet go through so many devices so incredibly fast like in real time? Ex: PS4 > Router/Modem > Server > Other People? | Engineering | explainlikeimfive | {
"a_id": [
"djkbkio"
],
"text": [
"It's worth nothing that it's a lot more complicated than that. There are *dozens* of devices between \"Modem\" and \"Server\" - and that's just the ones you can see! Same for \"Server\" and \"Other people\". ...which makes it even more extraordinary that we're getting data so fast. The bottom line here is that electrical signals travel at the speed of light, slowed down by the medium. Copper slows it down significantly, but it's still very, very fast. Fibre-optics are even *faster*. All the devices in between the long cables slow it down a bit more, but advanced computing power makes that bit faster, too. Basically, the bottleneck here is the speed at which devices can *process* the data more than anything else."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6k9mpn | Why are we encouraged to have good posture but then car and airplane seats are shaped in such a way that they do the opposite? | Seats like this are shaped in a concave way that turns my spine into pudding or is just plain uncomfortable. Its always bothered me. | Engineering | explainlikeimfive | {
"a_id": [
"djket2m"
],
"text": [
"It's important to know that \"good posture\" is a Victorian esq idea of how you should stand and sit as to look \"proper\". It has nothing to do with what your back wants or needs. Modern research tells us that humans should slouch in chairs, lean and generally sprall. Sitting in any way that you are not used to will cause pain and discomfort, simply because you're not used to it. So I imagine you have been told to sit one way all your life, then sit in a badly designed seat that doesn't have enough room at the feet and sides to allow sprall, and hey presto, back pain."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6kci64 | Why do toilets not have an overflow secondary drain as sinks do? | Engineering | explainlikeimfive | {
"a_id": [
"djkztpy",
"djl0og9",
"djl2uxf",
"djl3wyu"
],
"text": [
"There's still just one drain for a sink. The overflow is just getting water to the route it would if the drain wasn't plugged. For a toilet, if the drain is plugged the flow of water is going to be stopped (or slowed) entirely. An overflow drain would end up just as backed up.",
"Apparently, overflow-proof toilets already exist. [Sauce]( URL_0 ). As a justification, sinks and bathtubs are designed to be plugged purposefully, and the overflow drain prevents this intentional blockage from causing a mess. In contrast, a toilet is not designed to be intentionally plugged. EDIT: There's also already an overflow-sensing shutoff system. [Sores]( URL_1 )",
"This is a good question.... A secondary pipe that is ran alongside the main toilet drain or even molded onto the side of the entire pipe would solve this issue. Problem is if toilet paper were to get into the smaller overflow drain unclogging that might be a bit harder. But having a backup would be the best thing... Source? My child flooded my fucking bathroom tonight......",
"Toilets are different than sinks in that they have an integral trap in them. You can usually see how what you flush has to go up and then down the drain. Having an overflow for a toilet would bypass this trap, and nasty sewer gas would come out all the time. Sinks have a separate trap installed underneath them. The overflow uses the same piping as the main drain, but is really only meant to be used if the stopper gets left in accidentally. If you have a clog, it will still flood."
],
"score": [
116,
26,
8,
3
],
"text_urls": [
[],
[
"http://www.penguintoilets.com/",
"http://aquaone.com/wp-content/uploads/2012/01/Toilet-Guardian-Specifications-Sheet.pdf"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6kcjzq | How are modern buildings designed to be earthquake-resistant? | Engineering | explainlikeimfive | {
"a_id": [
"djl3vrk",
"djl69rt",
"djl31nl",
"djl3i7a",
"djl3yr5",
"djl8hby",
"djl3844",
"djl2zyc",
"djlbb04",
"djl6eg9",
"djl4910",
"djl35e7",
"djl5wxb",
"djlaczi",
"djl8dk6",
"djl7itf",
"djl8eol",
"djl5k0o",
"djl6ind",
"djl7qqs",
"djl5lmm",
"djl5xdr",
"djllz1x",
"djlez9v",
"djlafk6",
"djlsu0i",
"djl890c",
"djlo70d",
"djls9au"
],
"text": [
"I work for a structural steel construction company, and this is something I've only been told by word of ear, haven't seen it in person. For large skyscraper type buildings, the very top of it will be some kind of atrium with a large concrete ball hanging from the top. So as the building moves, the ball will move in the opposite direction, keeping the building in the same place. Wish I could provide more info but I'm drunk and about to smash some Denny's Edit: am I the only one being upvoted because I'm smashing dennys?",
"Hello, structural engineer here. I do seismic design on the west coast (high earthquake risk). First of all we have to pick a level of earthquake to design for. Generally the building codes specify an earthquake that has a 1 in 2500 year chance of occurring (smaller earthquakes will happen more often than this). This means that for a 50 year structure life, there is a 2% chance of the earthquake being bigger than what the structure was designed for. This doesnt necessarily mean that the structure will fail though. We generally allow for a certain amount of damage to occur in the design earthquake but for it to only occur in controlled locations (ie. no progressive collapse and ductile failure). We allow steel to yield (permanently deform) a certain amount, and reinforced concrete to crack. We do a structural analysis to see how the structure behaves in an earthquake. The most important thing is the period or frequency of vibration of the structure. You get resonance and higher forces on the building if it vibrates at a similar frequency to the earthquake shaking. For simple buildings you can do this on paper by hand; for more complicated structures you have to use a 3D computer model. After the structural analysis, the engineer will have an idea of the forces on the structure due to an earthquake. They would design selected critical parts of the structure to take that force and detail it to ensure it doesn't fail (lose all of its load carrying capacity) even if it becomes damaged. Damage to the structure helps to dissipate the earthquake energy and act as a fuse to limit the loads on other parts of the structure. Then you design the rest of the structure to make sure it is stronger than those critical areas you identified and designed earlier. This is the basic method of design, for more complicated structures such as highrises and long bridges engineers would use special techniques such as dampers (sloshing water tanks at the top of a high rise) or base isolation (special bearings at the base of the structure to allow it to partly move with the earthquake rather than withstand the force from trying to stay in place). TLDR: Engineers design and detail certain parts to be damaged but not fail or collapse. The rest of the structure has to be stronger than that. EDIT: Here is a 12 page pdf from the Structural Engineers Association of BC which does a pretty decent (better than me) job at outlining structural engineering for earthquakes in layman terms. URL_0",
"Am architect. There are multiple ways, and each building is different. With an earthquake, what you want your building to do, is to absorb as little of the energy/waves as possible, and to expel any with as little damage as possible. One way, for example, is not to have basements, less mass for the building to absorb energy. Another is to loosen up the steel connections in the structure, so that the energy won't transfer as much thought out the building. Steel, btw, is ductile, meaning that, to an extent, it's flexible and will return to its original position and strength after bending (ie expel energy). There will also be things like expansion joints where energy can be released. One weird example is when they might build a large concrete bathtub in the ground, and then build the building in that, so that the building has no real connection to the ground itself, limiting the energy absorption in the actual building. In general, you'll never make a building stronger than an earthquake, but you can try to tune it, so the energy absorption is less (avoid resonance with an expected earthquake frequency) . And then tune it so that the energy is expelled in controlled and safe places",
"You know how a house of cards has strength vertically, meaning you can stack multiple layers on top of each other but if you introduce any vibration or wind they collapse. That happens because they don't have lateral resistance or \"shear value\". If you take a cardboard box that is still flat and has not been folded into box form, you can push the corners together and it will squeeze together easy right? So now if you fold the box and flaps together and try to squeeze it there is resistance to it deforming. If you take six cards and tape them to each other forming a cube, you get the same resistance to deformation. This can be achieved with plywood \"cards\" nailed to the structure, metal frames, or metal X shaped structures within a square attaching at the corners. ELI9",
"Earthquakes, along with wind, apply a horizontal load or shear force to the building. Buildings are designed against shear force by different methods, most commonly with the use of shear walls and cross bracing, which keeps the building stiff. Another design method that has been used is to build the building like a tube structure where the building is modeled as a cantilevered structure; in this type of building, the exterior walls act as the shear walls.",
"Short answer: computers. Hi, I was part of the structural engineering team that designed the Benguela Belize compliant tower. It's underwater, but far taller than a skyscraper. You can read about it here (pretty weak article, really) [here]( URL_0 ) The principles are similar, though. Very tall structures have frequencies, and there is a structural engineering science called \"harmonics.\" Every structure has several natural frequencies, called modes. These are determined through advanced computer modeling. It's strange to think of building moving in waves, but it's what they do. Small changes to joint designs, material usage, angles, etc, can have dramatic impacts on the modes. To make a complicated thing more basic, the dampers many have mentioned can be controlled, and can affect the modes of a building. Earthquakes apply forces, the dampers counter the forces to put the building's vibrations into harmony, vs conflict, with the earthquake's forces. It's not just the dampers- the entire building is designed with these scenarios in mind. Structural engineers apply a process called LRFD (load and resistance factor design) to determine whether the building can stand up to different scenarios. If you've ever been to a beach, it is kind of like the difference between when you jump at the right time to float over the top of a wave vs when you miss time it and the wave punches you in the gut. I'm finding it difficult to find a place to cut this off....",
"Thought you might want some info om how they make old buildings earthquake resistant. I spent some time in the SF Bay Area and learned a few things about it. It's basically making the building stronger and more flexible. They call it \"retrofitting\". It varies by building but basically involves reinforcing the structure with things like beams and making it flexible. They way they do that with brick walls, for example, is coating the inside with fiberglass so the walls can move but remain intact.",
"There are a series of methods, but the main key to making a building earthquake resistant is allowing it to be able to move a little. If it can't, then when an earthquake happens, it is violently shaken and usually snaps kind of like a toothpick. A common method used is called base isolation. One of the projects that I've been working on in my construction management job uses this method. What it basically is is a series of rubber/steel pads between the tops of the basement columns and the first floor slab. They allow the building to move a little, which helps to dissipate any motion derived from an earthquake. This article helps explain it well: URL_0",
"Structural engineer checking in. I work and consult in Southern California, which is one of the most seismically relevant areas in the USA. Please do not receive any of what I'm writing in any official capacity beyond the intent of the question. The quick and dirty version is that earthquakes impose a specific type of load or stress upon a building, and that building needs to react to that load in such a manner that would allow it to displace, or bend, in a ductile manner. We have studied earthquakes for decades,and have written a building code that is pretty good at balancing the need for earthquake-resistant practices in building design and construction against the cost of designing and building such \"super\" buildings. Note that seismic design is not a finished or complete science. There is still much work to be done, mostly on the public and policy side, to improve and perfect our current system. At the end of the day, the citizens pay the city in the form of taxes for how \"safe\" their buildings are. Earthquakes primarily cause ground acceleration in the x-y plane, with a little bit in the z direction. We measure a building's response to the ground acceleration and call it \"drift.\" Obviously we want to minimize drift. Check out the UCSD shake table test for reference. So buildings end up shaken a whole bunch sideways, and a little bit up-and-down. This means that our structure needs to resist these sideways motions (since forces cause motions...a bastardization of Newtons first law). Our structure can resist loads by being 1) stiff and rigid, or 2) bendy and ductile. Traditionally, stiffness gives us strength. There is a trade off, however. High stiffness usually means low ductility and vice versa. It is difficult to design for both. Stiffness really sucks when it comes to handling accelerations. Imagine if your car did not crumple during a head-on collision. You would be turned into mashed potatoes. Since we have established that earthquakes cause ground acceleration, which will induce lateral movement in our building, we need the building to insulate the occupants from this motion without also collapsing due to the high stress. What we have come up with to solve this problem are ductile design provisions that incorporate something called a \"lateral force resisting system.\" This can be anything from a semi-rigid diaphragm, to a tuned mass damper, to hydraulic bracing, to shear walls with built-in ductility. The whole point is that we want our structure to bend without breaking. If our building is allowed to bend, then it can dissipate some of the earthquake's energy into the parts and pieces that are bending but not breaking. If we do experience a failure, it is better to see a ductile failure than a catastrophically brittle failure. Ductile elements typically fail after much bending and energy dissipation has occurred, allowing other systems that depend on the failing element to pick up the slack.",
"California Engineer here (PE): modern buildings resit earthquakes in multiple ways from shear walls, lateral bracing to stiff moment frames. The general theory is the building will move and we (as engineers) try and limit the movement by dissipating the energy of the earthquake. The dissipation is done through many ways. Some could be base isolation where we isolate the base structure from the subgrade and limit the amount of energy transfer into the building. Others include allowing some amount of \"yielding\" or damage in the beams to dissipate energy. This \"damage\" isn't damage in the sense that it will cause the building to collapse but can be acceptable yielding in the steel or concrete reinforcing. Here in the US we lean toward more \"flexible\" structures that move with the earthquake and just ensure that the building can handle the movement. In Japan, however, (and someone can correct me if I'm wrong) they have gone down the path of making their structures super stiff and allowing very little movement. Both have pros and cons and both have proved to work. One of the sad truths in our field is we only really gain great knowledge of the behavior of earthquake resistant structures after an event and studying the failures. tl/dr: we allow some damage but don't worry it won't fall...",
"[Taipei 101]( URL_0 ) is a tall building in an extremely earthquake prone region of Taiwan. They use a [tuned mass damper]( URL_1 ) which is meant to reduce the amplitude of mechanical vibrations and in turn reduce structural failure. [edit] fixed links and formatting",
"Along with being somewhat flexible, tall buildings may have a [tuned mass damper]( URL_0 ) - essentially a giant weight hanging in the center of the building that reduces vibration. Here's a video of a tuned mass damper during an earthquake: URL_1",
"Currently working in Christchurch New Zealand which was pretty much levelled in the 2011 earthquakes. City is still a demolition site due to the new requirements for buildings to be earthquake proof, so development is slow. In short, fuck loads of steel reinforcement and rubber expansion joints.",
"One thing I don't see covered here, is that buildings used to be designed so they didn't fall down and kill people. That was considered an earthquake proof building. After a big quake a badly damaged building would be demolished and rebuilt. After the Christchurch earthquake in particular, which cost $42bln when most of the CBD ended up being needing to be demolished, much more emphasis is now on designing buildings that can be repaired. One way to do this, is bits of the building are often designed to fail, absorbing energy in their destruction (like in cars), these bits are then repaired or replaced without having to demolish the building.",
"I work at a structural engineering firm in San Francisco and these are the kinds of questions I love to see. I'm ELI5 terms, modern buildings are designed to be earthquake-resistant by making sure that specific parts of the building bend without breaking in even the under the strongest earthquakes. This is possible by using materials (such as steel) that can be bent and stretched without losing much strength. When you use the right materials in the right parts of the structure, the design doesn't have to be perfect to be able to withstand an earthquake. For some ELI10 add ons, buildings aren't meant to look \"good as new\" after a major earthquake. Typical buildings are designed to prevent collapse and ensure that people are not trapped after the shaking stops. Many times a building will be properly designed and have to be torn down after a large-magnitude earthquake.",
"I work for a general contractor in California building hospitals so seismic design basically runs our lives. I would say one of the more prevelant designs is to use a system called base isolation. Imagine a building resting on these \"pucks\" in between plates. Every place where a column goes down to where the foundation would be, you have this base isolator. During a seismic event, the earth will be moving around but due to the pucks the building will be stationary since it can slide independently of the earth. There are other systems as well.y current project has viscous wall dampers which makes it unique because it is the only hospital in the country with such a seismic design.",
"Civil engineer here. If you ask how do we simulate the action of an earthquake on a building, there are many ways. The most common two would be: 1. We use a set of static loads applied laterally on each floor of the building. This is the static approach. 2. We use recording of previous earthquakes in the area to simulate a real earthquake on the building. This is the dinamic approach. If you ask how do we make buildings not collapse during earthquakes: 1. In case of low rise buildings (maximum 6-10 floors) we use the concept of plastic hinge. Basically we consider that plastic hinges appear in specific locations on the element of the structure, and that they dissipate seismic energy by converting it into heat energy. This is just like when you bend a cheap piece of plastic and it whitens. That white part would be the plastic hinge, and you would be the seismic action. Now just scale it up to the size of beams, columns, walls and you'll get the point. 2. In the case of high rise buildings damping sistems are used. Imagine that you are on a swing and you want to stop. What do you do? That is was damping sistems do to the whole building. This is way too advanced to explain it in a Reddit post with you having any Dinamics of structures background. 3. In the case of high rise buildings there is also another solution, base isolation sistems. Basically you put the building on rollers or \"springs\" and the ground can move freely bellow it. This is a though and complex question you have here. Hope this helps. ^_^",
"One of the systems is an isolation system. My office building has this. It basically sits on a sort of ball bearing and spring set up, such that the ground can move around it and it doesn't move as much. At least, that's what the building people told me. I've experienced an earthquake in it, and it was a very interesting sensation. When I felt an earthquake at home (a shortish, solid concrete apartment building) it was like I was laying on a giant washing machine. (I was sleeping at the time) When I felt it in the modern office building on the 24th floor, it felt like being on a boat.",
"if you're looking for an interesting, an very well designed example, check out the Sendai Mediateque by Toyo Ito! it survived, with only cosmetic damage, a 9.0 magnitude earthquake. here's a link to a video of it during said earthquake: URL_0 .",
"In Wellington, New Zealand, there's a museum called Te Papa and you can walk underground and see these big rubber and lead slabs that hold up the building and somehow help with earthquakes. You'll have to go there and read all the sciencey stuff if you wanna better explanation",
"If someone can ELI5 some Japanese buildings, I'd be very appreciative. When I travelled there I was told that some of the buildings were essentially absolutely safe as they were conjoined to absorb the pressure and act as a transmitter of force from one to the other and back, which seemed to make sense to a layman. In a place so prone to earthquakes, I did wonder how the bigger buildings would fare in a particularly powerful earthquake, can you ever completely do away with the risk it could collapse?",
"There are two big ways this is done: 1. Tuned Mass Dampers: Basically a big heavy lump held up near the top of the tower to absorb the energy of a swaying building. 2. Somewhat flexible mounting points in the foundation that let the earth move slightly without taking the building with it. These are often something like a big ball bearing in a shallow bowl (so when you shake the bowl the building stays in place), or rubber foundations that insulate vibrations. Exactly what you use largely depends on how tall the building is.",
"Geologist opinion checking in. I commonly use this USGS resource to find the peak ground acceleration (PGA) of an area. Whenever designing walls, ya gotta account for seismic conditions as well. URL_0 PGA is very dependent on the material density, moisture, shear strength, and grain size of the subgrade that the building is on. If the building is built on till, or bed rock, you don't have much to worry about. If it consists primarily of wet sands, peat, or fill than you have an issue! Lots of ways to improve the subgrade in this case, auger cast piles, pin piles, overexcavation then bridging with structural material.",
"Since I don't think it's really been mentioned here I'll throw in what I \"know\". Most people responding here are giving very technical explanations but not a lot of variety in examples, so I'll give mine. I recently saw a documentary on tv, probably PBS or something like that, about a guy who visited places after major earthquakes to survey the damage of the quakes as well as collect data on the buildings that survived. One of the most fascinating design elements that worked better than most other designs the guy looked at was the inclusion of wooden beams into the walls and structure of buildings in old buildings in the Nepal area. The wood provided flexibility and allowed for compression in the buildings during an earthquake. The guy collecting the data found a several hundred year old temple built in this method that survived the large quakes in the last few years with only very minor cosmetic damage but was overall largely un-effected. I do realize that many other comments talk about this use of flexibility but I didn't see many in historic context with examples.",
"LOTS OF WAYS! am future architect. One is to resist the energy. Use of diagonal braces, strengthened rebar and prestressed concrete beams often make it eaiser for the building to keep its shape in mild earthquakes. Another way is to absorb some of the energy. There are cross tension wires, which allow some of the building to flex without it pulling apart too much, there is tuned dampers, which are basically big weights of metal, water, or other materials that resist momentum, and allow the building to keep a center of gravity. Another ways is to have giant ball bearing on the foundations, the bottom of the foundation is a giant bowl, and then end of the building collumns are giant balls, and they sit together, and in an earthquake, they slide around a bit, but never come out. It allows the building to stay in one place eaiser than footings connceted right to the ground. And lastly one way is to mitigate the shockwave of an earthquake entirely. Earthquakes are energy waves, and by channeling the energy into something other than the ground or buildings, they can divert the energy AROUND the buildings or even cities. Many buildings in SAN FRAN and around there have giant steel bands in a circle AROUND the building, allowing the earthquake energy to be absorbed INTO the bands, around the building, and past it without actually shaking the building.",
"A lot of the answers are taking a professorial/research approach, which is fine for understanding how seismic loads occur and can affect a specific structure, but in real practice, we have pretty straight-forward equations used to calculate structural loads. If you had to write a dissertation every time you wanted to build a building (in addition to all the other documentation we already have to create), it would be a tad time- or cost-prohibitive. So we assume loads are much worse than they really will be and our lack of exactness buys us time and dollar savings. Specifically, there are codes for designing for seismic effects on buildings. The American Society of Civil Engineers provides [Standard 7-05]( URL_0 ), its basic building code book for the United States. Chapter 11 covers seismic, but you'll see there are also guidelines on calculating rain, flood, wind, snow, and other environmental loads. You calculate these separately based on maps that tell you the expected loads in a given geopgraphic area. Live loads (like people, moveable things) and dead loads (like immovable things and the building's self-weight) are also considered. Once you calculate all your loads, you multiply them by a safety factor (1.4 for live loads and 1.2 for dead loads, I don't know about the other ones), you add them up in their respective locations, then use the numbers to choose the size of your joists, beams, columns, foundations, etc. So, while southern California may have seismic, wind, rain (and maybe even flood loads) to calculate, you won't generally have snow loads. New York? Unlikely seismic activity but definitely wind, snow, and rain loads. This is all rather straight forward (even boring) in practice. It's just math based on empiral experience and what the industry has agreed upon over decades of compiling research and data. It gets updated once in a while. And of course there are local and state codes to take into consideration. But ASCE 7-05 is the place all structural engineers in the US start. TL;DR: Maps and math equations. Source: structural engineering degrees",
"[Architecture student]: I cannot provide a detailed answer (I know basic calculus and some physics, but I'm no engineer), but I know the general idea. There are several different way to resist the lateral loads caused by an earthquake,for example: South America uses a rigid system. This is when the building is heavily reinforced through cross/'x' bracing. The building acts as a single member that does not twist or bend, and it is isolated from the ground. So in construction the first thing done is an excavation of the area slightly larger than the footprint of the building and, depending on the height, ~36 feet deep. This is where the lowest concrete slab is poured (also supported by piers or piles) here there is a layer of dampeners (rubber pads) that the building will ultimately sit on. The building is then constructed floor by floor with cross bracing between columns, and near the top a mass dampener (heavy thing) that allows the building to move around it, or computer assisted masses that add and subtract weight from different areas of the building to counteract the horizontal movement (resonance) [See 'A']. In Asia the method differs from South America, and instead of designing a rigid structure to move as a whole, the buildings are designed through a more flexible structure that allowes more movement between the joints of the building. This give the entire building a spring like quality, and as a lateral force is imposed on to a building the structure may slightly twist as to coil or bend as to spring. This is similar to how buildings respond to wind forces. Taipei 101 is a great example of mass dampeners used to resist wind and earthquakes. In California smaller private homes use a denser spacing between studs or hurricane ties . Again I cannot speak to the formulas involved, and I hope my writing isn't terribly confusing. [A] Imagine you are on a train and the train begins to move. You can either pull yourself in the direction of the movement (similar to radio towers or cross bracing in buildings), or you can shift your weight forward to keep from falling back (buildings with mass dampeners).",
"Here’s a story my Dad used to tell me… I’d love some corroboration of this. During WW2, my Dad was in Hong Kong. In the days before the invasion, he had pulled some extra patrol duty in the city. He was partnered with a civilian constable… Dad would arrest any soldiers breaking the law, and the constable would arrest civilians. Dad’s a young guy – about 20, grew up on a farm in Saskachewan (small town prairie Canada). Hadn’t seen many vehicles, planes when he’s a kid before he left the farm. Now he’s in the place that’s like an alien planet. As he’s walking around, he’s noticing something odd. Some shortish apartment buildings (maybe 3 stories) are in small courtyards that are hard packed stone, with short stone walls on the outside. What’s odd is that they aren’t in the centre of the courtyard. His North American eye was struggling with it… the buildings were like they were randomly plunked in the courtyard. Right at the front, at the back, and none were square in the courtyard. He’s trying to figure out if he should bring it up with the constable, and how he would explain his question to someone who spoke somewhat broken English. Then they passed another one, and the building was right up against the short stone wall, and an old lady was struggling to open the front door and crawl over the wall to get into the building. This was too much. He asked the constable why the building was built that way. The constable looked blank, and then told him, ah, I understand. It’s because of earthquakes! The building was built on ball bearings. He took Dad into the courtyard, and showed him. He got on the ground and looked under the building “skirt” and you could see them (just). Massive hand carved stone carved bearings – he figured from what he could see that they were one and a half meters (yards), or more, through. The building was built on top of them. When there was an earthquake, the constable explained, the building bounced around inside the courtyard, but didn’t fall. But the building just wound up where it wound up after the shaking stopped. He was shown a few other buildings as well. Some had round ball bearings, some were on carved log shaped cylinders… they had a tendency to move forward and backwards. The constable said the bearings were very valuable, and would be saved and reused if the building was demolished – some were very old. I’ve always thought that was brilliant. Anyone out there that could confirm this for me? It’s a great story.",
"Structural engineer here and I would like to give my input as I am not happy with the top comments/answers. They do not directly answer the question and also have false statements. For example, mass tuned dampening is one method of helping a tall buildings reduce motion it is not required (e.g. Burj Khalifa does not have one). Also a statements such as buildings not absorbing energy or beams \"failing\" first are incorrect. So let me begin, In a seismic event different waves travel through the ground, P-waves, Shear Waves, L-waves. These waves cause motion in different directions, up and down, side to side, compression and tension etc. The side to side motion is the most damaging so let us focus on that. Imagine a simple \"lollipop\" structure. Single slender column supporting a ball of mass concentrated at the top (think water tower). As the ground shakes the the motion is transferred into the building. The displacement, velocity and acceleration of the mass depends on the stiffness of said structure (effective length, modulus of materials, moment of inertia). If the resonant frequency of the structure matches that of the earthquake that is very bad! You want a resonant frequency that is lower so it \"attracts\" less load. If it is very stiff it will excite just like the ground and forces will be high, F=ma. Think of a building as lollipops stacked on top of each other. Once an engineer determines the amount of force at each story of a building (stiffness matrix x displacement) then they design the seismic force resisting system (SFRS). To resist a lateral force several methods can be used depending on cost, efficiency, architectural requirements etc. Some methods include compression tension braces, moment frames and concrete shear walls. In tall buildings or seismically active regions or post disaster buildings (this is my field of experience, i design hospitals) the forces will be too high to design for. So engineers will instead allow the structure to yield and deform and absorb energy. If there is no yielding there is no energy absorption (think spring that you push and pull in the linear region, it never loses its shape). One can scale down the forces if they allow for more yeiding and energy abortion, but the cost typically goes up, need more concrete confinement, better welded or bolted connections. If the deflections for the tall building is too high then a liquid mass tuned dampener an be used. The mass always moves in the opposite direction of the building. Fun fact Tapei 101 turned theirs into a tourist attraction. The burj khalifa does not even use one ! it is not always necessary. These tall buildings use a techniques like shear walls in a triangular shape (think tripod wth legs deployed far out as possible) or non uniform cross section to \"confuse\" the wind and prevent resonance. If the ground vibrations are too high techniques such as isolation pads can be used, think marbles underneath your houses foundation. Ground shakes but building just sits on top. These are advanced methods that are not common in your average mid rise. Feel free to PM me with questions or corrections."
],
"score": [
9391,
1285,
1152,
136,
134,
27,
26,
25,
16,
14,
13,
12,
9,
8,
8,
7,
6,
5,
4,
4,
3,
3,
3,
3,
3,
3,
3,
3,
3
],
"text_urls": [
[],
[
"https://www.apeg.bc.ca/getmedia/4278c069-0374-4cc2-9e73-2b454a0f978a/SEABC-Eathquake-Fact-Sheet.pdf.aspx"
],
[],
[],
[],
[
"https://en.m.wikipedia.org/wiki/Compliant_Tower"
],
[],
[
"https://www.sciencelearn.org.nz/resources/1022-how-do-base-isolators-work"
],
[],
[],
[
"https://en.wikipedia.org/wiki/Taipei_101",
"https://en.wikipedia.org/wiki/Tuned_mass_damper"
],
[
"https://en.wikipedia.org/wiki/Tuned_mass_damper#Dampers_in_buildings_and_related_structures",
"https://www.youtube.com/watch?v=ohKqE_mwMmo"
],
[],
[],
[],
[],
[],
[],
[
"http://www.archdaily.com/120114/video-experiencing-the-japan-earthquake-from-the-sendai-mediatheque"
],
[],
[],
[],
[
"https://earthquake.usgs.gov/hazards/designmaps/"
],
[],
[],
[
"http://www.dres.ir/sazeh/DocLib9/ASCE%207-05%20Minimum%20Design%20Loads%20for%20buildings%20and%20other%20Struc.pdf"
],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6kd65b | what causes the seemingly random dimming of house lights? | Sometimes I notice that the lights in my house will dim and then return to normal after a second, what exactly is causing this? I've also noticed this in vehicle headlights, is it the same cause? | Engineering | explainlikeimfive | {
"a_id": [
"djl58ef",
"djl5hye",
"djl5fsj",
"djl5ux0"
],
"text": [
"It could possibly be minor power surges on the grid your house runs off that are small enough to get through your fusebox. But there's only really one answer. Ghosts. Definatly ghosts.",
"The brightness of your lights is related to their power consumption, and their power consumption is related to the line voltage When your lights dim it means something caused your line voltage to dip. A big motor or heater starting up can draw a lot of current and cause this to happen, starting something like an electric dryer would do On cars it usually happens when the subwoofer kicks, it takes a lot of power and briefly draws down the battery",
"It's likely that your circuit for your refrigerator isn't isolated, so when it kicks in, your total power is getting cut down by the condenser in the fridge.",
"When on and functioning correctly, light fixtures receive a constant stream of electricity at a constant voltage, usually 120 volts in the US. When they receive more than the specified amount they brighten, less and they dim. Inconsistency in the amount of electricity being delivered can be caused by any number of things. Damaged wiring, having too many things trying to pull more power than either the circuit or wire was meant to handle, etc."
],
"score": [
5,
4,
3,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6khqwr | How did old ships push off the dock? | Like back in the 1700's, how did large ships leave port? Mostly how did they push off the dock if winds were blowing inland? | Engineering | explainlikeimfive | {
"a_id": [
"djm52zf",
"djm4wvo",
"djm6jhx"
],
"text": [
"No expert, but one method is warping. An anchor is carried away by boat and dropped in the direction you want to go, and then you pull the ship to it using the ships winches. Repeat as necessary. Sometimes you just had to wait for a favourable wind.",
"They either: * didn't - they set anchor off-shore and took smaller boats in/out * used their sails - sailboats can sail against wind in the right conditions * used oars * used small boats to row them in/out - what we would call tugboats today",
"Know what happens when the winds aren't favorable or even when there is no wind or stormy? You don't sail! Schedules aren't kept. You sail when the captain says the conditions are for sailing. Ya hear? Yarr!"
],
"score": [
6,
5,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6kjhbv | what's the difference between ram air parachutes and the round ones? | What are the advantages/disadvantages of each type? | Engineering | explainlikeimfive | {
"a_id": [
"djmkdzb",
"djmmdto"
],
"text": [
"You can maneuver a ram air parachute. Ram airs are for stunts and for people who want control after the chute opens. You can traverse a lot of lateral distance if you want. Basically \"fly\" the chute. Experienced jumpers could jump at high altitude from far away and land on a pinpiont that is miles away from the point of opening. Great for covert military ops when you want to surprise whoever is on the ground. The disadvantage is that the ram air is MUCH less stable in flight. It requires constant maneuvering and effort to stay on target. They are less safe. There is a possibility that a novice could lose control of the chute. Round chutes pretty much drop straight down upon release, have little control, and travel wherever the wind decides to take you. The great advantage to a round chute is that they are very stable and much more safe for a novice jumper, such as paratroopers in WW2 that had little if any time to practice jumping. Round chutes are also great for dead-weight cargo drops and slowing decents of spacecraft or aircraft on short runways.",
"Greater chance of breaking a leg on landing w/ a round parachute due to less control of rate of descent."
],
"score": [
7,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
6knece | why are some outlets so difficult to plug things into, while others are very loose? | Engineering | explainlikeimfive | {
"a_id": [
"djndxbs",
"djnmyk8",
"djnny09"
],
"text": [
"Receptacles deliver power to plugs via spring clips. Everytime you plug something in or take it out, the springs take some wear and tear. They wear out over time and are rated for x amount of timed you can plug/unplug . Cheaper receptacles are rated for less times while more expensive receptacles are made better/have better materials and are typically rated for a higher amount. *edit hospital grade receptacles have a much high spring tension Or You might also be used tamper resistant receptacles and people have issues with the plastic guards retracting if the plug is not inserted properly.",
"I think you're asking about what are actually [\"childproof outlets\"]( URL_1 ) which are now required for many locations in residences in the US. IANAE but here's more discussion on it.... URL_0 These outlets seem like you really need to jam the plug in to get something into them, and you'll probably only find them in newer homes or recently renovated rooms. They're basically designed to close a door over each prong socket and neither will open unless you stick something into both sides at once.",
"Well, you see son, when a man loves a woman... I mean, there's like birds and bees, see? No, hold on. Let's say you've got a ground and a hot wire. Oh I give up, it's oxidation and that just gets in the way. Plus, sometimes things aren't made up to \"snuff\", cuz they're cheap."
],
"score": [
63,
6,
4
],
"text_urls": [
[],
[
"https://diy.stackexchange.com/questions/13414/are-there-locations-in-a-residence-where-a-non-tamper-resistant-receptacle-can-s",
"http://www.nfpa.org/public-education/by-topic/top-causes-of-fire/electrical/tamper-resistant-electrical-receptacles"
],
[]
]
} | [
"url"
] | [
"url"
] |
|
6knzwn | How do pool tables know which ball is the white ball? | Engineering | explainlikeimfive | {
"a_id": [
"djnglbh",
"djnj54b",
"djnmltd"
],
"text": [
"There's more than one method, but the most common are: * the white ball is *slightly* larger, and so doesn't fall down the same holes as the other balls * a magnet inside the white ball trips a switch when passing a certain point on the rails.",
"The ball is a different size from the other balls and has a magnet on the inside. [Here]( URL_0 ) is a video explaining how a pool table works",
"The cue balls are normally no longer larger for 8, 9 and 10 ball pool - \"According to WPA/BCA equipment specifications, the weight may be from 5.5 to 6 oz (156–170 g) with a diameter of 2.250 inch (57.15 mm), plus or minus 0.005 inch (0.127 mm). These are often referred to as 2 1⁄4 inch balls.\" Coin operated tables sometimes have a larger ball, but usually the cue balls have a magnetic core"
],
"score": [
131,
54,
8
],
"text_urls": [
[],
[
"https://www.youtube.com/watch?v=GhG_0ToGdO4"
],
[]
]
} | [
"url"
] | [
"url"
] |
|
6kp0hb | what is the difference between a V6 and a V8 engine with the same volume? | Besides the amount of pistons. For example, if I have a 4.0l v6 and a 4.0l v8 engine made from the same manufacturers, same materials etc. is there any difference between the two engines? Are there any advantages or disadvantages to having an engine with 8 pistons, to having an engine with 6 slightly larger pistons to give the same volume? Edit* Just to "ELI5" my question, the v6 means the engine has 6 pistons, and v8 means the engine has 8 pistons. The volume in that relation, unless I have been lied to my whole life, is the total combined volume of all the pistons when pulled all the way back. Correct me if I'm wrong but a 6 piston engine has 0.66 liters of volume in each piston (4l/6pistons), and an 8 piston engine has 0.5 liters of volume in each piston (4/8). | Engineering | explainlikeimfive | {
"a_id": [
"djnuk5u",
"djnp8js",
"djnw6xa",
"djobdpq",
"djo930r",
"djnuqqd",
"djnozqj",
"djok8mc",
"djodhmw",
"djohxr5"
],
"text": [
"Credit to u/semaph0r3: Edit: Lots of people asking for ELI5 of ELI5, so here goes: Engines, like all engineering, is an exercise in compromises. You need to balance a whole bunch of factors to get a solution that meets the result. In engines, there's a whole bunch of factors, but for most purposes, you can focus on these: 1. An engine needs to make sufficient power to move the vehicle 2. An engine needs to balance out all the vibrations inherent in the spinning and shaking that's going on. If you don't manage this, eventually the engine shakes itself apart. 3. The engine needs to fit inside the vehicle (and, for performance applications, be located in a way that maximizes the handling characteristics of the car). 4. The engine needs to consume only so much fuel. A V8 engine handles all 4 of these in a nicely balanced way: its not really good at any one of the 4, but its 'good enough' to make it one of the best overall engine layouts. It also sounds sexy as hell. ----- The cylinder configuration of an engine has effects on two major factors, the smoothness / vibration, and the 'packaging' or sizing / shape / how it fits in the car. Cylinder count has nothing to do with power, typically - that has to do with displacement, flow of the heads, shape of the combustion chamber, cylinder pressure, compression, ignition timing, and a ton of other factors. Up until 2013, F1 used 2.4L engines that were V8s, a size commonly set up as an I4 in commercial vehicles. V8s come in two major flavors; flat plane and cross plane cranks, which describe how the pistons connect to the crankshaft. Cross plane V8s (where if you look edge-on the crankshaft looks like a cross) sit at a sweet spot of packaging - its only 4 cylinders deep so it can fit under hoods easily, but can pack a large engine displacement in a nicely sized cube while being vibrationally balanced. They do limit RPMs a bit though because of the cross plane balancing adds rotational mass, so high performance / racing V8s tend to go with flat plane cranks. V6s have even better packaging, but are unbalanced vibrationally, forcing a tradeoff of longevity vs power. Most commercial solutions favor the longevity side of the equation, so most people's perception of a V6 is an uninspiring motor. It doesn't have to be, but a V6 that outputs a ton of power is also an engine about to shake itself to bits. Inline 4s have excellent packaging as well but are also terribly balanced, often requiring an extra shaft to keep the engine even remotely smooth, so power output is very weak. But because of the small size they can still rev well, so they're used where engine efficiency is more important than broad performance. Inline 6s are better than V8s and basically every other engine at power delivery and smoothness (its why BMW uses them) but packaging them is really hard because they're very long and practically require rear wheel drive. If what you care about is performance of an engine and no other considerations, you want an inline 6 or its bigger brother, a v12 (which is two I6s working together, so butter smooth). Horizontally opposed engines (Subaru, Porsche) are balanced and have near perfect behavior internally, but are a total bitch to package. Subaru's understeer is a result of having to hang the engine really far out in front of the wheels to make room for AWD. Older Porsches have a reputation as Widow Makers due to the engine hanging far out the back of the car causing oversteer. Flat plane V8s have lower rotational mass so they rev higher and generally produce more power, but lose some of the V8 engine balancing. These are used in higher performance engines (Ferrari uses this layout, as well as the new Ford GT350) but require more maintenance and tend to have shorter effective lives. V10s are used in some applications and have some benefits, but its mostly a 'I have a bigger number than you' sort of thing. So why are V8s so popular? They're the 'poor man's performance' engine: cross plane V8s sit at a great intersection of balanced engine, packaging, and RPM potential. They're not great at all 3, mind: in fact, far from. But if what you're looking for is everyman's performance, cross plane V8 will fit in anything and deliver great performance, while not costing too much. There are some misconceptions that are common: low RPM torque is one of them. The V8 configuration has nothing to do with that - it has everything to do with the tuning of the engine with respect to camshaft profile and flow. Racing configured engines focueds on high RPM performance tend to have really poor low RPM performance, and small I4 engines can have lower RPM torgue with turbos or by camming them down, but their peak will then suffer as a result and be even more boring. The desirability of V8s in car culture has to do with the accessibility of power at the V8 configuration. Because of the factors above, the most big engine cars commercially made tend to stick with the V8 configuration due to its ease of packaging. Car culture then connected power to V8, even though that isn't the cause. Additionally, cross plane V8s have a sound that is very distinct and to my ears absolutely sexy, though the purr of an I6 or flat 6 is equally sexy to me as well. ---- A lot of other questions. Yeah, the VR6 is worth a mention, so are Wankels, as well as I5s. All really cool solutions to interesting problems. A lot of those things have been addressed but one thing wasn't: what actually determines whether or not an engine performs well? Think about a bike. You have the easiest time pushing on the pedal when it is rotated out at 90 degrees, so the pedal arm is parallel to the ground. Another example of this is its hardest to do the bicep curl when your arm is parallel - > gravity has the best lever on your muscle at that point. A piston is the same: the goal is to get the peak combustion pressure on the piston as its descending right around when the crank is rotated 90 degrees. The problem is the engine spins at a range of speeds, and so it takes different amounts of time for the flame to reach the piston. A ton of factors go into this, and its all about balancing these issues to get an engine to perform the way you need for that solution: A long stroke forces the flame to travel further, meaning its easier to get it to strike the piston head correctly at low engine speeds. At high engine speeds, the piston is moving away from the flame very fast and its hard to get it to reach peak pressure at the optimal time. A short stroke, wide bore has a shorter distance to travel so the flame front impacts the piston best at high speeds - at low speeds you need to hold ignition until really late. The more metal turning, the more force it takes to turn it. Reducing the amount of mass in rotation and the total surface area in contact allows more of the energy to be used for moving the vehicle, yielding fuel economy and power gains. If done improperly or over-zealously, removing mass will reduce the lifecycle of the engine. The engine needs to 'flow' well, or allow air in and out at the right times. The cycle of a cylinder happens really fast, and in that period of time all the air for combustion needs to get in, injected, compressed, and ignited. Getting that cylinder packed with as much air as possible allows more fuel to be dumped in, giving more power. Everything that moves needs to have a counter-movement somewhere else. This is to handle those vibrations. I can go on and on. I love engines.",
"Hi there, assuming both engines are 4-cycle type, one difference is that the 8 cylinder engine will have 8 power cycles (8 power output pulses) per 2 rotations of the crank vs. 6 with the 6-cylinder engine. With all other things equal this would mean the power delivery is smoother. Luxury cars tend (especially in older days) have more cylinders to get the smoothest output possible - sometimes up to 16 cylinders! The torque curve (torque output vs. RPM) would likely be broader with the 8-cylinder engine again as it has more power pulses per rotation. So more cylinders for a given volume does have advantages, but also disadvantages - namely added complexity and cost. Adding 2 more cylinders doesn't sound like a lot, but that's more crank to spin, 2 more connecting rods and pistons, at least 2 more injectors, these days 2 more ignition coils etc. So if you are a car company you might stick with lower cylinder count to get costs down, and potentially have better reliability with the reduction in complexity.",
"The answer is the surface area to volume ratio. When you make lots of smaller cylinders versus fewer large ones, you are creating more surface area per given volume. This has the effect of more effective cylinder aspiration per capacity and rpm, which means youre spending less energy in getting air in and out, so more power heads out the crankshaft instead. Another big advantage is that smaller cylinders have higher rev limits. It is (a little bit) easier to make power by spinning faster over other methods like forced induction.",
"Think of it like a rowboat, where each person rows one after the other. One boat has 6 stronger guys rowing, and the other has 8 weaker guys. But their combined strength is equal. So if you're pulling something heavy, fewer stronger guys is better. If you are pulling something light and want to accelerate quickly, then more rowers is better.",
"For what it's worth, a 4.0L V8 will be able to rev higher than a 4.0L V6. That's because the per piston displacement is lower on the V8, in this case, 0.5L/piston, and the V6 would come in at 0.66L/piston. What this means is the V8 will have a smaller bore/smaller piston and a smaller stroke. This means less rotating mass and, with the shorter stroke, less movement of the piston. This means this specific 4.0L V8 would be able to rev higher without stressing the crankshaft and connecting rods. The balance (as others have mentioned) is an added perk. You'll see this come into play: for example, Porsche used a 4.5L V8 in the Cayenne introduced back in the early 2000s. General Motors (Pontiac) had a 3.8 L V6. Even though the Porsche is a larger motor, they were able to get the engine to redline at 6,500 RPM, whereas General Motors accomplished only 6,000 RPM out of their V6. There are some other considerations that play into that outcome, but the displacement of each cylinder is no small part of that difference.",
"The reason that engines with more cylinders, all other things being equal, traditionally make more power than engines with fewer cylinders (and a little less torque, and all at higher engine-speeds) is that engines with smaller pistons and shorter strokes (so engines of equal displacement but with more cylinders) can go faster, and so process more fuel, and so produce more power, for the same overall displacement. This is for three reasons: 1. engines with smaller cylinders have lower reciprocating mass in each cylinder, so they deal with smaller forces reversing the direction of travel of the piston / con-rod / crankshaft / valves at a given speed (in rpms) 2. engines with smaller cylinders tend to have shorter strokes, so the maximum practical velocity of a piston is reached at a higher engine speed. 3. engines with smaller cylinders can burn a fuel charge faster, since the flame inside the cylinder does not have to travel as far.",
"Bore (how wide each cylinder is) and stroke (how tall the height of the piston travel) determine the size of the cylinder. Bigger cylinders have higher volume to surface area, ideally leading to lower weight than smaller cylinders, but also taller stroke so the piston can't travel as quickly, leading to lower RPM. I think most sports cars have engines that are about square or oversquare, meaning stroke is equal to or less than the bore. Economy and mass market cars almost always are undersquare, so stroke is greater than bore.",
"Lots of terrible and incorrect bullshit in here, but maybe if I don't get buried I can clear it up: First of all, you can't really explain it like you're five. Understanding an engine completely basically takes a mechanical engineering degree. Ironically, your actual mechanic doesn't even understand your engine as much as he would imply he does. He might know fuel+spark=bang, but I assure that he doesn't even begin to understand the real thermodynamic realities of an engine. Assuming these engines are designed to be as identical as possible with no additional technology or special techniques between them, the biggest difference would likely be that the V8 would be smoother and possibly more powerful/higher revving due to better fuel/air mixing in the cylinder. Also, the V8 may have lower fuel economy at cruising engine loads due to frictional losses. Now, it's tricky to say for sure for this analogy because the change in cylinder size could be bore, stroke, or a combination, so let's assume proportionally scaled cylinders to not skew the analogy. Having smaller cylinders (but the same total volumetric displacement in total) means you can fill the cylinders with an air/fuel mixture faster, which allows for higher revving without losing the ability to successfully burn the fuel each combustion cycle. There's also other factors like the camshafts and valves being able to keep up (i.e. valve float), but we'll assume those are \"perfect\" in that regard. You may also have better low end power as well as even on the low end the ability to efficiently fill and combust in each cylinder will likely produce more power (again, super hard to generalize this much as a true 1:1 V6- > V8 comparison is almost impossible). Someone made an analogy to strong rowers vs fast rowers or something like that, but honestly that's more akin to comparing a high torque low revving motor vs a low torque high revving motor that output the same horsepower. So, why not make every engine a lower displacement V12 instead of of an inline 4 or V6? Biggest factor: cost. Second factor: reliability. Third factor: frictional drivetrain losses. The more cylinders you have, the more parts you have to make, inventory, and assemble. This naturally gets expensive and therefore the fewer cylinders you can use to get the power output you want, the better from a cost standpoint. Regarding reliability, this is a tricky topic as some will misinterpret it. In endurance racing, multi-cylinder engines are actually typically *more* reliable because using multiple smaller cylinders means each cylinder is producing less heat and can be more effectively cooled by the cooling system. It also means that if one cylinder fails in a non-catastrophic way, the car may still be able to continue driving successfully with minimal power losses compared to a car with fewer cylinders. However, in day-to-day situations, high cylinder count engines mean many more moving parts which introduces more potential points of failure, and it can also be difficult to tune (or, at least used to be back in the carburetor days). Going back to cost, get ready to open your wallet if you need the spark plugs or other service done as you are multiplying it by many times for that V12. As for frictional losses, this goes back to complexity. You have many more valves, valve springs, cam lobes, connecting rod bearings, etc. all creating frictional losses. This is why high cylinder count engines tend to have shitty mileage as during low throttle situations there is so much detracting from the power output and therefore requiring more fuel for the same amount of power. This further encourages companies to try to get the power they want from a 4 or 6 cylinder engine as it means (usually) better fuel economy at cruising power situations, which is where most drivers spend the bulk of their time. Now, all of this goes out of the window when you bring turbos or superchargers into the equation. All of the sought after 6 cylinder engines you hear about are durable variants meant for turbocharging, which effectively acts as artificial displacement when the turbo spools and introduces more air into the cylinders each combustion cycle. A large turbo V6 might act like a V12 with double the displacement when it comes to peak power output, but without the extra engine weight and frictional losses. Still, all of this said, it's so hard to truly make an apples-to-apples comparison as there would be so many nitty gritty differences between a 4L V6 and a 4L V8 to ever truly compare the two.",
"Ford had a 300 cubic inch inline 6 and a 302 cubic inch V-8 for many years. The 6 had a 4\" bore and 3.98\" stroke. The 8 had a 4\" bore and 3\" stroke. Same bore in both engines, but the 6 had a longer stroke to make up the same volume. One big difference between 6 and 8 cylinder engines of equal displacement is that the 8 has more valves. Since maximum valve size is restricted by bore size, and since the 2 engines have the same bore, the maximum valve size is the same in the 6 and 8 engines in this example. More valve area (because of more valves) = more airflow. More airflow = more power.",
"The biggest difference is cylinder size. First off: Piston= the part of the engine that moves up and down Cylinder= the tube the piston moves in. Revs= revolutions per minute. Redline= the maximum revolutions per minute. Bore= the width measured across the piston. Stroke= how far the piston moves. Power= how fast the wheels turn. Torque=how hard the car pushes. A 4l engine has 6x667cm³ cylinders as a V6, or 8x500cm³ cylinders as a V8. For an engine of roughly the same physical size and design, the V8 engine will rev harder, and have more power due to a higher redline, but less torque. The reason behind this is the engines size is defined as bore x stroke x number of cylinders. A longer stroke generates more torque, at the cost of a lower redline. A shorter stroke allows a higher redline, and gets to redline faster as the piston does not have to go as far. A smaller bore piston is lighter, and can rev faster, but must have smaller valves, which means less air. A smaller cylinder size must have either a shorter stroke, a smaller bore or both. The design choice is usually a shorter stroke, which gives a sportier engine, that revs fast and hard."
],
"score": [
8533,
275,
149,
102,
51,
31,
16,
8,
5,
4
],
"text_urls": [
[],
[],
[],
[],
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6kpyaa | What causes a motorcycle "death wobble" and what can be done to prevent it? | So I saw [this gif]( URL_0 ), and as a rider, it obviously makes me uncomfortable. So I began doing some looking on the "death wobble", but the [wikipedia article]( URL_1 ) is pretty dry and my mechanical engineering is not quite up to understanding the whole explanation. I also searched this sub, but most of the posts were about skateboards or bicycles going too fast. Ideally I'm looking for a good idea as to what I can do to avoid it, either while riding, or ensuring that I don't make any modifications that might induce it. Edit: spelling. | Engineering | explainlikeimfive | {
"a_id": [
"djny95k",
"djnxuni",
"djo55kb",
"djofyas"
],
"text": [
"Front swings out a bit. Physics says \"ok back wheel, follow that front wheel\" and follows the swing. Rider says \"no front wheel I wanted you to go THIS way\" rear wheel is like \"WTF dude making me swing the other way now?\" so now the front wheel and the rear wheel are in a pissing match with the driver who is now frantically trying to make the front wheel do what he wants. This causes a feedback loop making it worse and worse until they both decide to leave the party. Keep everything tight, and do not try to \"correct\" wobbles, you might hear the phrase \"ride them out\" and that just means let nature take its course, do not freak out and try to tell that front wheel to stop wobbling, it doesn't like that and will punish you thusly. Edit for fun: it's practically impossible for a motorcycle at that speed, or any two wheeled vehicle really, to wipe itself out without any external factors influencing it. Without a rider, that bike would have gone forever until it hit bumps or such. It naturally wants to right itself up and down (why you can get out of leans so easily) which also contributes to the rider causing wobz.",
"Look into steering stabilizers. I know they're available for sport bikes, presumably others as well.",
"Change your valve stems regularly even if they look fine. My stepdad and mom were at 65 on the interstate when the back tire suddenly deflated due to deteriorated valve stem. Bike started wobbling and ended up wrenching the front wheel fully sideways resulting in a tail over nose roll that catapulted my Mom. She was in the hospital for 7 months. My stepdad had checked the air pressure on before they rode. We couldn't tell what had happened until we went to air up the back tire to see if we could figure out what was wrong and the valve stem came apart in his hand when he went to turn it.",
"This happened to be once on a Yamaha R6 with no steering damper. Well I didn't fall like the guy in the video, but I started to get the wobbles after hitting an awkward dip in the road doing about 70mph. I think the key is not to panic. I grew up riding dirtbikes so having the bike wiggle I guess you could say wasn't all that foreign to me. Most people panic and try to hit the brake. This transfers the weight of rider and bike to the turned front wheel and it's all over. It's like hitting your front brake in a turn. I was able to roll on the throttle and pull out of it. I think this transfers the weight to the back wheel and allows the front wheel to straighten out. It's not first instinct to try and go faster when you start to wobble, so hopefully you can think of it in time."
],
"score": [
19,
3,
3,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6kq4d1 | How did Apollo astronauts/mission command know where on the moon they had landed? | Engineering | explainlikeimfive | {
"a_id": [
"djnxy13"
],
"text": [
"The landing areas were well planned and they had a navigation computer to help them. They memorized the features of the area they were supposed to land in as a visual aid. Once they landed, the radio dishes on Earth could confirm that they were in the correct location."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6kqmn7 | How did early colonial settlers navigate across the Atlantic Ocean to find the specific port they intended to go(i.e Plymouth, Jamestown)? | Sure, they may have been able to head in the general direction. But how would a second wave of settlers find a specific port? | Engineering | explainlikeimfive | {
"a_id": [
"djo25nc",
"djo3xtm"
],
"text": [
"Astrolabe and similar instruments have been around at least 1200 years. With charts and calibration calculating latitude is possible. Along with compasses, maps, wind maps, current maps, and telescopes navigation has been possible to high degree for a long time.",
"Finding the latitude (north/south) was the easier part of it. This is determined by the how high the sun gets at noon at any particular day. If you have a chart of the height of the sun on July 1 for various places, all you have to do is find that number on the chart. The determination of longitude was difficult because you had to know the exact time to know how far east/west you were. It wasn't until the 1700s that the sextant was invented and mariners could tell how far east/west the had gone. One way around that was to get on the right latitude for Jamestown and follow it. Eventually you would run into it. This adds a few days to the voyage, because you cannot take advantage of the Great Circle route, but if you don't know the longitude, it is the safest course to follow."
],
"score": [
9,
7
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
6krb87 | Why do cars allow you to keep the a/c setting on even when the heat is turned all the way up? | Engineering | explainlikeimfive | {
"a_id": [
"djo7dud"
],
"text": [
"In the fall and winter it is advisable to have your A/C on with the heat to dry out the air in the car a prevent fogging the widows and wind shield. In fact when you turn on your defogger/defroster, your A/C automatically turns on."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6kss7n | How do they get the CO2 inside the bottle/can of soda before packing? | I understand that in a bottle or can of soda, the CO2 is basically already inside the vessel in that little headroom area and opening said vessel basically forces the CO2 into the drink. My question is, how do they get the CO2 into the bottle or can before they seal the thing up? | Engineering | explainlikeimfive | {
"a_id": [
"djoioqf"
],
"text": [
"Actually, the CO2 is already IN the drink before you open it. It is dissolved in the water, and releasing the lid let's it ESCAPE. The dissolved CO2 makes carbonic acid, which gives soda that sharp taste (also why flat soda tastes flat). At the plant, they force high pressure CO2 through the mixed soda, just before bottling. They allow slightly more to dissolve than they want in the finished product, and seal it. The excess then escapes into the bottle and the pressure created from this keeps the rest in solution."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6kt256 | Why do most brands of microwave popcorn require one specific side to be placed up? | Engineering | explainlikeimfive | {
"a_id": [
"djom6ah",
"djou3d7",
"djokwlo",
"djpomhv"
],
"text": [
"There's a super thin lining of aluminium foil on one side of the popcorn bag which, when placed downwards, acts as a pan and causes the temperature to rise much faster than just through the microwaves heating up the water. It took the inventor of microwave popcorn, Jim Watkins, much research to find the exact amount of foil that would act as the accelerator without causing the microwave oven to break down. Source: My father owns a microwave popcorn company.",
"As a side-note: never place the bag on a plate (eg: if the microwave is dirty). The glass rotating disc on the bottom of the microwave does NOT conduct heat, so all the heat gets transferred to the seeds. A regular plate DOES conduct heat, so the oil in the bag will heat up your plate instead of the seeds. Your popcorn won't pop and your plate will break in half.",
"Usually bag construction. The idea is to allow the easiest possible expansion of the bag. If you put it upside down, it's feasible that one of the book folds would get stuck underneath the bag, leaving less room for the corn to expand into. That would then possibly make the rest of the bag break. Not super likely, of course, but may as well just tell people to put it the way up that causes the least amount of potential problems.",
"Thermal shielding (metal) on 1 side radiates the microwaves better, heating the oil & kernels more proficiently to help avoid unpopped kernels, in theory. It's never 100%"
],
"score": [
2343,
187,
13,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6kvoor | How do submarines make the sonar "pings"? | Follow up questions: - How loud are they? - Do they actually sound like "ping" or is that just the sound that the equipment uses to tell you it detected a ping? | Engineering | explainlikeimfive | {
"a_id": [
"djp5htn"
],
"text": [
"Extremely loud. From about 100 miles away it can be as loud as gunshots. It's so loud and irritating that sobre scientists believe that they're a cause for mass whale beachings. As far as the noise, here's a video. URL_0"
],
"score": [
7
],
"text_urls": [
[
"https://youtu.be/EAqUelpwEl8"
]
]
} | [
"url"
] | [
"url"
] |
6l1mul | Why is a water tower a tower? | Engineering | explainlikeimfive | {
"a_id": [
"djqdzgb"
],
"text": [
"Gravity assist. You pump the water mechanically once a day or whenever the tower gets low. Then, gravity moves the water downwards as needed. The result is less pumping than if every toilet flush on the third floor required a mechanical assist."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6l34g3 | How are bridges and oil rigs that are far off of the coast made when the deep water is already there? | Engineering | explainlikeimfive | {
"a_id": [
"djqq8dj",
"djr4ok1"
],
"text": [
"Oil rigs are built onshore and then towed to their final location and anchored. Bridges are generally not built over very deep water. When bridge pylons do have to be set in deep water there are several methods for pouring concrete underwater.",
"I once read a book on the Golden Gate Bridge b/c I had the same question. The book described them dropping a series of giant cylindrical rings to the floor of the San Francisco Bay. The rings interlocked with each other, getting taller and taller until they reached a height above the surface of the water. At that point they pumped out all the water inside the now-tall cylinder. Hungry workers even gathered all the fish left dry at the bottom. They then had this water-free workspace that extended down to the bay floor."
],
"score": [
18,
14
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6l3vvr | How are Cities created/made | I was talking to a friend about building new houses in the UK, and we asked ourselves how are Cities made? Is it just a collection of buildings which become a city. Or are they planned and set out. And If so, how do they get there name and layout? For example, I think Milton Keynes is the newest city in the UK. But how was it made and how did it get where it is and layed out like it did? | Engineering | explainlikeimfive | {
"a_id": [
"djqzqzp",
"djr4qis",
"djr5927"
],
"text": [
"Well, it's interesting that you ask that from the UK. Historically, most cities arose as a result of humans wanting to live in a location that provided some economic advantage. Examples include a crossroads on trading routes, port cities, and areas with some natural resource to be exploited. Many of these cities grew up organically based on function and common modes of travel at the time. With European colonialism, cities were 'founded' in the New World and elsewhere. These communities were often planned by a royal governor and laid out according to the best practice of the time. When the Spanish settled the Americas, for example, the [Law of the Indies]( URL_0 ) established rules for where cities should be built and how they should be laid out. In the same vein, various US cities were planned and built by a single visionary 'planner'. Examples include Philadelphia (William Penn), Savannah Georgia (James Oglethorpe), and Washington DC (Pierre L'Enfant). In all of these instances, the city streets were laid out, and spaces such as parks and squares where reserved for the public. The private sector, individual homeowners and commercial developers, built the buildings along the streets according to the established plan. In 1902, a man named Ebenezer Howard proposed a new concept for creating cities: the [Garden City]( URL_1 ). The basic idea was that a city should contain all the elements that you needed, housing, industry, commercial district, etc. in a compact area that was separated by a greenbelt from the next compact community. He actually built a few of these towns in the UK: Garden City of Letchworth and Welwyn Garden. After WWII, the British government adapted this idea to deal with the crowded conditions in cities and the need for more housing, and sets out to build a series of new communities based loosely on the Garden City model. [Milton Keynes]( URL_2 ) is one of those 'New Towns' built by the government. I hope that answers your question. Some cities grow up organically because there was an advantage to settling there and others are planned and executed from a single vision.",
"Planned towns often don't turn out the way people expect. So Welwyn Garden City (for example) was a deliberately planned satellite town in the 1920s. Its beautiful. Its a bit frozen in time (as I remember it from the eighties) Milton Keynes. Wow, thats one wierd place. Very zonal, very definitely a product of designers let loose. People who live there (in both of these cases) love it. visitors often don't Motherwell, and a bunch of other towns outside Glasgow were planned to re-house the slum dwellers from the gorbals. They turned into pretty bad places in some cases. New Cumbernauld, and the like have never appealed to me, but if I'd had to live in what they left behind (I saw glasgow in the 70s) I might feel differently. Linlithgow grew up around a chemicals, plastics and oil industry and was half way between Edina and Glasgow. Its a former royal palace town in fact. Formally, legally, its a city when its given a city charter. Historically, its when a cathedral is built there. In Australia, the economics behind trying to construct new city-like places hasn't always worked well. Allbury-Wadonga was sited at a border where the railway changed guage. rural cities by and large don't thrive in Australia because migration swelled the classic state capital cities which sprang up naturally on the coast. The exception is of course Canberra which like Brazilia and New Delhi is an entirely planned development. Old Canberra was socialize-by-rank and the style of housing reflected a 10 and 20 year planning cycle. New Canberra is now people who live there, second or third generation and its much less of a planned city culture, not everyone in Canberra is there either because of the federal government, or to sell guns, fireworks and porn out at Fyshwick. The other big exception is Queensland, which has a string of regional cities up the coastline. Since Queensland is a long thin(ish) big state, over 2000km long, maybe this worked better than it did in NSW, where the regionals like Wollongong and Newcastle are steel and coal towns, which died when the industry did (ok: unfair on both. Hit me) More recently, to try and limit the Gold-Coast Brisbane sprawl, we've had a clutch of semi-private city-like developments spring up. Springwood, and development close to the sunshine coast, partyly a venture-capital investment breaking new land (well.. farming land) and partly state government funded. The killer questions are always the same: where is the School, where is the Railway, where is the Hospital. So you can plan it, but \"if you build it they will come\" doesn't always work. You can grow what you've got, but thats urban sprawl. Planning is a nightmare. Legally, it has to be nominated and created. its just an overgrown town otherwise.",
"Most cities just grow naturally by themselves. If you dig down in many cities in Europe you will find remains of settlements dating back millennia. Even among younger settlements there usually isn't much design involved. Just a bunch of houses being built close to each other and slowly growing from tiny village to big city. Usually there is something there that makes the place a good place to settle, like a road leading to a ford in a river or a pass though mountains or in some case nearby natural resources. Towns would be recognized as such by rulers and given privileges based on their size which further helped them grow. Things like tax jurisdictions and free trade policies helped shape where and how cities grow. If the growth of the settlement is fast enough somebody might try to direct an order the whole thing, but a few centuries ago urban planning was not really too much of a thing. There are however planned cities where there were none before. Milton Keynes is one such city that was created by design and not accident. A number of countries have their Nations capital be a designed and planned city, like Brasilia and Canberra. In such cases committees of designers and architects and city planners designed the general layout of the city and what went where from the ground up. eventually natural growth may take over and to a degree."
],
"score": [
27,
5,
3
],
"text_urls": [
[
"https://en.wikipedia.org/wiki/Laws_of_the_Indies",
"https://en.wikipedia.org/wiki/Garden_city_movement",
"https://en.wikipedia.org/wiki/Milton_Keynes"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6l6rgj | Theoretically, why can't countries shut off their power grids in case of an impending nuclear strike to avoid them getting fried by the EMP? | Engineering | explainlikeimfive | {
"a_id": [
"djrhr3n",
"djrhoaj"
],
"text": [
"EMP doesn't quite work the way it does in video games. What it does is it sends out a pulse that will temporarily charge conductors, semi-conductors and other electronics. The reason this ruins power grids and electronics is because it shorts out a system. A system doesn't have to be turned on for it to short. Having said that, almost all modern systems have fuses to prevent this kinda short. Basically, any EMP attack will just pop a whole bunch of fuses. As an aside, lightning strikes release some of the most powerful EMPs and although they've been known to take down power grids, it's about as bad as you can get.",
"To protect against an EMP, you would need to completely shield all of your sensitive electronics from electromagnetic radiation. Simply turning off the grid doesn't do this. Even unplugging everything wouldn't keep them from getting fried if they were close enough to the blast."
],
"score": [
7,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6l9h3c | Why haven't we built huge trains? | I'm just watching a documentary on the Queen Mary, and it said that it contained the power of 24 or something steam trains and was as long as The Eiffel Tower is high, it made me wonder why (especially in North America), they hadn't built absolutely colossal trains? If we can build ships, planes, or even buildings many times bigger than the original, why did we not do so with trains? | Engineering | explainlikeimfive | {
"a_id": [
"djs3bo3"
],
"text": [
"Bigger doesn't always mean better. For trains, specifically, the advancement in technology has been in making the train stronger, not physically larger. There are three major reasons why making trains bigger is a bad thing. 1) Trains run on tracks, so making a bigger train would require replacing tracks with ones of a different size. While tracks have to be replaced eventually, there is no incentive to force the change by making a larger train. 2) Taller trains, which would be required to increase the size without increasing the width, would be less stable during turns, leading to more derailment and crashes. 3) Trains are already modular, and can be expanded near limitlessly by adding cars onto the back of the train. The only limit is the strength of the locomotive, and even that can be augmented by having extra cars for driving force. These trains can be collosal in their own rite, with the largest container train in the world being the 4.2 km long double-stack container operated by Canadian National Railway. The largest test-run train was the BHP Run on June 21, 2001 comprising 682 cars and eight 6000hp locomotives in Australia."
],
"score": [
13
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6lb9k2 | How does a computer 'know' how long a second is? | This question actually spans across computers, programming, and really all electronics alike. A lot of things are based around the concept of keeping time but how is that done exactly? | Engineering | explainlikeimfive | {
"a_id": [
"djsifg2",
"djsp90l"
],
"text": [
"Very simply, counting. A crystal or oscillator produces electrical pulses at a near perfect rhythm many of times every second. Components inside the device then count the pulses until it reaches the number of pulses that are in a second and keeps time that way. As a side note most time keeping devices use 32.768kHz because that's a nice round number in the binary world which most electronics use.",
"Many computers are actually pretty shit at keeping time, or at least, their onboard hardware clocks are. For extremely time sensitive applications, an external clock is often used. For example, one network I know of which provides emergency related services requires a huge number of devices to be synced up to time via GPS, which provides a highly accurate PPS (\"pulse-per-second\")."
],
"score": [
20,
6
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
6ldstv | How do CT scanners work? | I just don't get it. | Engineering | explainlikeimfive | {
"a_id": [
"djt3llk",
"djt2mdn"
],
"text": [
"Ok so basically it's just a shitload of x-ray shots. When you take a conventional x-ray, it passes through once and takes a photo, so to speak. So let's say you wanted to take a photo of a person, but someone else was standing in the way and they or your subject can't move. Or say you wanted to take a panoramic photo. You'd need to take multiple shots and tie them together. CT is like that. It shoots from multiple angles and stitches the image together to create a more 3-dimensional image, allowing for better details and thus better understanding of what's happening in there. The same thing could be done with a regular x-ray if they just kept rolling you around the table and hitting the button. The difference is that the CT puts them all together for you and allows you to see things more clearly and with less exposure time, because doing that with a conventional x-ray would take hours at least, depending on the target. Additionally, the X-ray shots would not differentiate relationships, while the CT program typically can. This means that your 3D image created by the CT would show dimensions, separating the organs and such, while your x-ray shots would not. Like maybe a doctor wants to look at the *front* of your lung, he would have trouble doing so with a regular x-ray because the heart's in the way. So why don't they do this every time? Well, a CT is super expensive and not always available. The exposure itself is also way more expensive. Last and most importantly, the patient is receiving an x-ray dose through his body at hundreds of times higher than a regular x-ray, and every exposure a person receives leaves something behind permanently, so if they did a CT on you every time you needed an image, you'd hit critical levels of life dose pretty fast.",
"A CT scanner is just an X-ray machine mounted on a circular track (around the subject). When activated, the X-ray machine moves around on the track, taking still images from a variety of different angles. The resulting images are processed by a computer which knows what angle each still was taken at."
],
"score": [
5,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
6lez22 | Torque in relation to a car's performance? | I've heard its something to do with rotatational force etc. but what does that actully mean. Is is the feeling of 'got some poke' when you accelerate in a decent car? | Engineering | explainlikeimfive | {
"a_id": [
"djtabep",
"djtdmma",
"djtb3s7",
"djtgv58"
],
"text": [
"ELI5: Torque: acceleration Horsepower: Top speed. For older than 5, It's a bit more complicated than that, there's a \"torque curve\" meaning how much torque you have at any given RPM. If you have torque at low RPM, you can feel the push coming off of a redlight. If you have good torque at high RPM, you can get a push once you're already moving, good for passing on a highway. If you have a \"fat torque curve\" you have good torque at both low and high RPM, a good car for driving on curvy roads.",
"The acceleration you feel is down to the torque at the wheels which is a product of the engine torque and the total gearing (gear and diff ratios, wheel size etc.). This means talking about engine torque isn't very useful in isolation as you need to know what gearing you can use which is dictated by what rev range the engine can produce torque over. In other words you could have a very low torque engine but if it revs twice as high as an engine with twice the torque, you could get the same wheel torque as you could gear it twice as low. Power is just the product of torque*revs/5252 so basically it takes the revs into account which makes it a useful figure for directly comparing vehicles as you don't need to know what the gearing is or anything else to get a feel for if it's a fast car (assuming it has \"appropriate\" gearing). Basically torque is transformed by gearing but power is an absolute figure that tells you how much work the engine can actually do. Perfect example being F1 vs Nascar, low torque/high revs/low gearing vs high torque/low revs/high gearing but both make similar power and perform similarly. You would predict that if you looked at their power:weight ratios but you wouldn't predict it from their engine torque:weight ratios. TL:DR \"got some poke\" comes from wheel torque which is not necessarily the result of a lot of *engine* torque...it could be due to very low gearing. Power figures cover off that issue...high power:weight ratio = fast car.",
"In terms of performance not much. What's import is the total power put out and where the power is on the rpm range. Breaking it down to a formula you have Power = torque x rpm. Torque being a measure of how much force each rotation of the engine exerts and power being the force output per second. When people say that an engine with high torque is better what the are generally actually talking about is an engine where the power is available across a wide band usually lower down the rpm range this is useful for towing for example as it saves the need for a large number of gear ratios to keep the engine at the required power. If you wanted to you could use a small high reving motorbike engine with all it's power concentrated in a narrow band at a high rpm. You would just need a hell of a lot of gears to keep the rotating at the optimal speed. This video explains much better than i could URL_0 At 20:56 it even answers the exact question in your post.",
"A scalar quantity is a number. For example 9.81 is a scalar quantity. A vector quantity has a direction and a magnitude, so imagine an arrow of a given direction and of a given length. Velocity is a rate of change in position, a vector quantity, and we call the magnitude \"speed\". For example, 30 mph going west. Force is a vector quantity, and we call it's magnitude \"acceleration\". Force applied to a mass over time will change it's velocity. So 30 mph going west and increasing west at 5 mph per second. Torque is force applied to an axis, so you can see how torque is important to acceleration. Work, force applied over a distance, will become important in a moment. The base unit is the joule. So applying 20 Newtons of force over 2 meters = 20 joules of energy. You can double the work by either doubling the weight and keeping the distance, or keeping the weight and doubling the distance. Power is work over time. The base unit is the Watt, and horsepower is a derived unit, so the two are convertible. In order to cross a room in half the time, you have to perform twice the work. So in order to go 200 mph, you need to apply torque (force) more frequently in the given period of time. So torque will increase your *speed*, but if you want to increase your *acceleration*, you need horsepower. You can have lots of torque, there are 14 cylinder cargo ship engines with pistons over 3' wide that produce ~8m ft/lbs of torque, and if that thing were fit to a car, it would absolutely get you to whatever speed you want to go, provided you had the appropriate gearing, but that doesn't mean it will accelerate you *quickly*. And this is why torque and horsepower are confusing, they're interrelated and explain the rate of change of different things."
],
"score": [
11,
6,
5,
4
],
"text_urls": [
[],
[],
[
"https://www.youtube.com/watch?v=UIQjyn95c-o"
],
[]
]
} | [
"url"
] | [
"url"
] |
6li9vc | why are house keys one-sided, while car keys are two-sided? | Engineering | explainlikeimfive | {
"a_id": [
"dju1jry",
"djuohbw"
],
"text": [
"Car keys are designed to be used in a situation where you can't easily see the lock. So your convenience they cut the pattern into both sides.",
"Contrary to conventional wisdom, it's not a design issue for convenience. Every time you insert a key into a lock, the teeth on the key wear down a bit. House keys have the teeth on one side, but realistically you only use a house key in a front door a few times a day, and you probably have multiple keys for spouse, kids, neighbours etc. Not only does your car key start your car, but (in older cars at least) it also opens the boot (sorry I'm English), the door, and sometimes even the glovebox. It's also a tonne more expensive and inconvenient to replace a car key than it is a house key, and you probably don't know where your spare is. Cutting the teeth into both sides reduces wear on the each side by 50% (statistically). The reality is only one side of the key is ever read by the locks."
],
"score": [
26,
11
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6liji2 | Why are there multiple stop lights along the sides of mountain tunnels? | Engineering | explainlikeimfive | {
"a_id": [
"dju4fqk"
],
"text": [
"They're to stop you when there is an incident up ahead so you don't become part of the incident."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6lite8 | Why did the Grenfell tower not fall like the WTC? | Engineering | explainlikeimfive | {
"a_id": [
"dju5hsz",
"djub99p",
"dju6lmz"
],
"text": [
"At least a couple of reasons off the top of my head: 1: It wasn't as tall as the WTC and therefore did not have as much stress weighing the whole structure down. 2: It wasn't slammed into by a fully laden airliner, destroying the structural integrity of the architectural engineering.",
"Grenfell tower was a typical British tower block, basically a big ugly slab of concrete. The core of those towers are a concrete lift shaft which is also a large portion of the strength of the building. They were not designed to be beautiful, or to be engineering achievements, they were built to be cheap easy housing for large numbers of poorer people built by semi skilled labor. The WTC on the other hand was a framed tube construction, much of the strength came from the outer walls. It was also designed to push the limits of engineering and to be a design statement of look how much bigger and better we can build than anyone else. With Grenfell and the other UK housing estates they would just build a thicker wall rather than work out precisely how thick it needs to be. With the WTC they took great pains to cut as much excess as possible.",
"A very tall building can probably survive: - A single large impact - A single moderately powerful explosion - A severe fire Grenfell tower survived the last one. A good tower might be able to survive two of them. WTC experienced all 3 when it got hit by fueled jet liners that crashed, exploded and burned. I think it's more remarkable it took that long to collapse."
],
"score": [
20,
7,
6
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6llflw | Why do highways cause more traffic? | Some time ago, I heard that highways, counterintuitively, cause more traffic than normal roads in cities. What is the reason exactly? Thx in advance | Engineering | explainlikeimfive | {
"a_id": [
"djunhea"
],
"text": [
"Highways make more people travel by car. This effect is often bigger then the size of the highway so you might inadvertently cause traffic to move slower. For example if you were to build a highway from a city to a nearby town then a lot of people will move out of the city to the town and a lot of the people living in the town would take work in the city instead of locally. And not only work but people would go to the city more often for events and other things. So by creating the highway you now have a massive increase in traffic."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6llit7 | When I turn on the lights in my room, the interference on my AM radio is greatly reduced. What's going on here? | Engineering | explainlikeimfive | {
"a_id": [
"djuxr57",
"djuv2lr",
"djuxy0d",
"djuz9da",
"djuz80k"
],
"text": [
"If you do have a dimmer switch and it allows some amount of current through in the off position (might be defective/damaged/not quite pushed all the way off) then it could be producing the interference. Most dimmer switches work by very rapidly flickering the power going to the light. Current running through a wire produces a magnetic field, an amplitude fluctuated (flicking the power on and off very quickly) magnetic field is an AM (amplitude modulation) radio signal, thus when the dimmer rhythmically interrupts the current it produces a weak AM radio signal. The reason the interference would clear up when you turn the light fully on is that the current is no longer fluctuating, the magnetic field is steady, and so it no longer interacts noticably with the radio. Credit to URL_0 for filling me in on dimmer switches. I can imagine a defective or damaged regular switch creating the same power flickering effect in the off position, never providing enough continuous current to cause the bulb to heat up enough to glow, though I'm not sure how specifically that might happen. tldr: a bad or broken dimmer switch can turn your wiring into an AM radio transmitter.",
"You have a dimmer switch in your room? I don't know the science behind it, but they are notorious for messing with radio reception.",
"It's a long shot, since we know nearly nothing about your wiring. Every conductor carrying a voltage is an antenna. So is the wiring in your house. The length of the antenna has to be adapted to the wave length (and therefore the frequency) of your signal. E.g. a 100Mhz signal has a wave length of 3 meters. ( Wavelength = speed of light / frequency ). Antenna length like 1/2 wavelength, 1/4 wavelength also work well. . My guess is that the length of a wire in your house matches to the wavelength of your am radio. The wire is a weak antenna, but it's close to your radio, so it can distort the signal enough to create interference. As soon as you turn on the light the switch closes and increases the \"length\" of the wire, increasing the length of the antenna. The interfering signal cannot be transmitted well be this \"new\" antenna - > the interference is gone",
"If the radio antenna is the electrical chord, as in some radios, you've connected the circuit and now have significantly lengthened the total wire length for your antenna.",
"\"Interference is reduced\" — do you mean the reception gets *better* with the light switch on? If so, the most likely explanation is that some wires in your ceiling or walls became connected that weren't connected before, and these act as antenna reflectors, changing the reception in the room. Or perhaps they *stop* acting as reflectors. The science of radio antennas is really quite complicated. If you mean the reception gets worse in your room, then the explanation could be the antenna reflector stuff I mentioned above, or more likely interference from a dimmer, or interference from the electronics in the light bulb if it's fluorescent or LED."
],
"score": [
111,
27,
14,
4,
4
],
"text_urls": [
[
"http://home.howstuffworks.com/dimmer-switch.htm"
],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6loeza | Why are many bathroom sink faucets so close to the back of the sink? | I often see sinks with rather large basins, but with a super small faucet. My hands always hit the back of the sink. Surely there's a good reason for this? | Engineering | explainlikeimfive | {
"a_id": [
"djvfggr",
"djvf4az"
],
"text": [
"Depends on the design, but I think it's at least partly because of how older bathrooms did their bathroom sinks. Basically the sink was a bowl, and you filled it up with water from the faucet, hot water would be a separate faucet, and you would add that in to get the right temperature. Then you wash your hands in the sink, and pull the drain to empty it. The faucets were thus small so they don't get in the way of your hands. I know in the UK, many people still have this style of sink in the bathroom, [they look like this]( URL_0 ). In the US at least, we have gone away from that style of sink, and just wash our hands under the tap. But we still use faucets that look similar, probably for aesthetics reasons (putting a large kitchen sink style faucet would look odd), and partly because we still do wash things in the sink other than our hands, it may be useful to have a small faucet. And finally, if you're hitting your hands on the sink, it's probably because they installed the wrong faucet. On many sinks, the holes for the faucet are pre-drilled, their location is meant for a faucet of a specific size (one that stretches some distance from the edge), sometimes people buy sinks with the holes set back and couple it with a faucet that is short meant for holes set forward resulting in a faucet that's too close to the edge. Sometimes the holes are not pre-drilled and the installer drills them too far back. Spout reach is a spec listed for the faucet on home depot, people forget to check it when picking parts sometimes.",
"The reason is probably cost reduction. The faucet is most likely a casting. Castings of consumer products are made in such a high volume that costs associated with design (such as fancy curves, etc.) don't impact the cost of an individual unit much. The primary cost is the material. A shorter faucet means less metal and a lower cost."
],
"score": [
11,
3
],
"text_urls": [
[
"https://qph.ec.quoracdn.net/main-qimg-7cc1769422d3e6313f595690eb32027c-c"
],
[]
]
} | [
"url"
] | [
"url"
] |
6ls6za | Electricity can't be stored, so when a light gets turned on, the power station must immediately produce some extra electricity. How is this possible? | Engineering | explainlikeimfive | {
"a_id": [
"djw84iv",
"djwdcjk",
"djw6p25",
"djw82i1",
"djwo8ok",
"djwduup",
"djwfg20"
],
"text": [
"As a unit of one, your house's power usage varies wildly and is somewhat unpredictable. As the unit of your residential city block of 20 homes, the small variations in personal schedules cancel out and power usage is more statistically stable. As the unit of your neighborhood of 10000 homes and 100 small businesses, the variations are even smaller. As a unit of your city of a million residents and businesses, the profile of consumer is pretty steady and predicable.",
"Electrical load on a power system is controlled at the generator which compensates for changing loads by adjusting speed and excitation voltage to the generator field. Since most commercial generators are so large these increases in load at such a small scale are inconsequential but if say 1 million people turned on a light at once then the electrician operating the power plant would notice and one of two things would happen either the generator(s) online would increase fuel to the generator(s) to maintain speed or excitation voltage would automatically increase to accommodate the increased load. Or the Electricians can start and parallel in another generator or connect another power plant into the grid if they are producing more power than it is using. In short you turning on a light is a carefully monitored and controlled dance run by thousands of people nation wide, Texas is the only state in the continental US that is not permanently connected to the national power grid.",
"It is possible to store power but this is expensive. When we are talking about the second to second variations in power output and input to the grid the energy is stored in the turbine blades in the power plants which works like flywheels. Similarly any three phase engine common in industrial applications connected directly to the grid will also work as a flywheel and help smooth out the power consumption. So when you switch on a light the power might come from your washing machine. This is actually a problem in the future as wind turbines and solar panels generally do not have a big flywheel directly on the grid as traditional power plants do. So we may in the future have big flywheels installed to better smooth out the demand for power. Or we might come up with a system of capacitors or batteries.",
"Somewhere on the grid, a power station really does adjust its output. Since the adjustments cannot be quite so precise as adjusting for a single light bulb, the amount of power on the grid is allowed to fluctuate slightly -- which is visible as a slight variation in voltage or frequency seen by thousands of users.",
"In a nutshell, as more load/demand is placed on the electricity network, the frequency starts to drop (say from 50Hz down to 49.9Hz). The power station generators have 'governors' which detect this and increase their output in response (its a feedback loop).",
"It's possible by allowing some variation in the voltage, if we have 230V supplying 100 light bulbs just fine, and you turn on another one, they'll all share a little bit less power, but they're ok with that. If your lamp is only glowing at 99% potential it's also only consuming 99%, so you're not paying that extra 1% either. But at the power station they'll soon notice that they are now a bit low so they crank up the power a bit so they can sell you and all the other 100 light bulb users another 1% of power. It's not just for selling they do it though, that was just for the ELI5 ;), they need to provide a somewhat stable voltage, they'd also decrease the production if the voltage went up 1% because someone switched off a lamp, they need to keep as close to the baseline as possible to be able to handle variations in any direction as well as possible. I heard (saw actually.. on Discovery Channel I think) that one of the most challenging situations like this for the power companies in UK are when a big football game ends, and all the britts go to boil their tea water, it produces a huge spike in the power consumption that is really difficult to respond to with the generators, so all power companies need to follow the game to be ready to respond and predict exactly when this peak will happen.",
"Isn't a battery literally \"Electricity Stored\"? Isn't OP begging the question by phrasing his query using \"Electricity can't be stored\" as a preface?"
],
"score": [
61,
56,
37,
13,
6,
6,
4
],
"text_urls": [
[],
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6lujmu | Why does a hard, sudden rainfall cause basement flooding more so than sustained ordinary rain? | Just had a very unusually hard rain fall in Brooklyn, maybe 10 minutes or less but rivaling intensity I've seen in Houston. Basement is flooded the worst it's ever been, but this doesn't happen (to this extent) even when it rains gently for days. So what's happening from a fluid dynamics/engineering/physics perspective here? | Engineering | explainlikeimfive | {
"a_id": [
"djwnolj"
],
"text": [
"Roofs and gutters are designed to channel water away from the building at a certain rate. The same is true for the drainage on the ground level So long as the rainfall does not exceed that rate, it can go on indefinitely. When the rain comes down faster than that, the rate it arrives exceeds the rate at which it flows away, and it winds up going somewhere you rather it didn't."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6lwm4d | Why do most running shoes have more padding in the heel than in the front? | Engineering | explainlikeimfive | {
"a_id": [
"djx4qvk",
"djx6fz7",
"djx5kgn"
],
"text": [
"Because people tend (correctly or not) to land on their heel first and then roll onto the front on their foot, so there is a lot more impact pressure on the heal.",
"So worked for a shoe store and an avid runner. Most athletic shoes try to help correct feet problems. Running shoes with lots of heel cusions are for runners who naturally run on their heels to try to force them to run midfoot (proper) same is true to over and under pronation.",
"Those shoes are more properly called \"jogging\" shoes. Jogging is a strange activity, because it's not natural. Yes, yes, there's such a thing as running slowly. But if you were in the middle of nowhere and wanted to get from point A to point B as quick as possible, you wouldn't jog at a comfy pace. You'd run as far as you could, then walk until you caught your breath, then run again, then walk again, etc. And it would be faster than jogging the whole way. You might jog a little bit, but long-distance jogging is really a much more odd activity than we realize nowadays. Jogging is hard on the feet because you're not moving fast enough to get your feet in the right place to land (if you were, you'd be running), so what you tend to do is heel-strike. Heels are made for standing, not impact (that's what toes and the ball of your foot are for). Thus, the need for extra heel cushioning."
],
"score": [
3,
3,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6lwoi4 | Where does human waste go on cruise ships? | Hey so I was wondering, what happens to the inevitable waste in a cruise ship? Do they save it all up to be disposed of onshore or do they dump it periodically into the sea? Does it depend on the liner? What is the standing capacity for waste before a removal has to be made? - I appreciate that the last one is going to be ship dependant but I am so confused an estimate would be great! | Engineering | explainlikeimfive | {
"a_id": [
"djx61mx",
"djx7gef"
],
"text": [
"There are two ways to deal with sewage: treatment and storage. Most modern ships are equipped with a sewage treatment plant. This plant can use either bacteria, chemicals, or other methods to break down the sewage and turn it into cleaner water. Depending on which regulation the ship follows, the treated black water is pumped over the side. If there is solid waste that still remains, or pumping over the side is not an option, the sewage can be kept in sewage holding tanks. These tanks are then emptied to sewage trucks/facilities when the ship is in port. In some cases, solid sewage is also allowed to be pumped over the side if certain requirements are met. On my ship, which has a max capacity of 26 people but regularly holds 16, our sewage tanks hold about 30 tonnes of sewage. We usually pump it ashore when it gets in the 20 tonne range, and we do so once every couple months or so. So, if 16 people produce about 10 tonnes of sewage a month, I imagine that a cruise ship of 1600 people would produce close to 1000 tonnes of sewage a month. That being said, Cruise ships also have top of the line sewage treatment plants that probably clean most of it up.",
"On submarines (cruise boat not ship) we blew it out into the ocean using high pressure air Woe to the sailor who \"flushed\" a toilet when the tank was pressurized. Basically you would get a face full of shit."
],
"score": [
23,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
6lzz0u | Did mechanical and analog computers use Logic Gates before transistors? If so, how were they implemented? | Also, if they didn't use Logic Gates, what did they use instead for arithmetic and such; and how was whatever they used instead implemented? Thanks | Engineering | explainlikeimfive | {
"a_id": [
"djxwqwx",
"djxvusc",
"djxvz51"
],
"text": [
"You can totally build mechanical logic gates and build basic computing elements like half-adders and more complex stuff from this. There are videos out there of people having build stuff like this from Lego and similar. [(Example)]( URL_0 ) The problem here is that these tend to be big and clunky and if you add up enough of them to be useful you will get into real mechanical troubles very fast. Electrically you can use devices such a vacuum tubes to have the same function as transistors made from semiconductors and build logic gates out of them. Early digital computers were build out of large numbers of vacuum tubes which had the unfortunate side-effects of burning out all the time, limiting the working time of computers and were also quiet big making miniaturization hard. Analogue computers (both electrical and others) were never that popular and didn't really use logic gates as they were never really based on the on/off dichotomy but instead worked by using what may thought of a sliding scale of values for inputs and outputs. Before electronic computer became common mechanical computers exited that may be said to be digital after a fashion, but they generally did not use the modern logic gate based design. There were calculators based on cog and wheel designs that you could use to automate basic arithmetic operations. Leibniz (who simultaneously with Newton invented calculus) created a working model of a mechanical calculator which function by means of cleverly arranged gears, cogs and cranks to allow someone to do basic calculations. This design with refinements lived on up until the point where electronics became good enough to build handheld calculators. The famous [Curta]( URL_1 ) calculator is an example of this type of mechanical computers that were used up until the 1970s.",
"Analog computers don't really operate that way. Digital computers are based on logical operations, and they're good at what they do. Analog computing lends itself more toward straight mathematical operations on continuous numbers that would be difficult to do by hand, and they're (in many ways) better/faster than digital computers for that task If you're asking what they used instead of logic, the essential components of analog computers were called \"op amps\" or operational amplifiers. They don't do the same thing as transistor-based logic gates, but they're the basic building blocks of analog computers in the same way that logic gates and flip flops are they building blocks of digital.",
"This highly depends on your definition of computer. It's name derives from \"compute\", meaning to calculate. Around 2700 bc the first such \"machine\" was used, the abacus. It bascially consists of marbles on a string, allowing you to add and subtract. (Multiplication, and division can be done via multiple applications of add/subtract.) A very simple example of an analog computer is actually a [slide rule] ( URL_1 ). The first thing most would say is a \"real computer\" was the Z3, which used relays and switches to act as transistors. But you can build the whole functionality of a computer mechanically, too. The best explanation I found actually comes from an [advertisment]( URL_0 ) - sorry. What you do is basically the following: You place whips on a board and the drop marbles on it. Some whips have weights, meaning they always return to their previous position. Some whips do not, meaning each time a marble drops on them, they reverse direction, essentially storing information. The input to such a computer would be the order in which you drop marbles. The output would be defined, by which marbles land in the left or the right at the bottom of the board."
],
"score": [
5,
3,
3
],
"text_urls": [
[
"https://youtu.be/5X_Ft4YR_wU",
"https://en.wikipedia.org/wiki/Curta"
],
[],
[
"https://www.youtube.com/watch?v=05-53R5fr8U",
"https://upload.wikimedia.org/wikipedia/commons/1/17/Sliderule_2005.png"
]
]
} | [
"url"
] | [
"url"
] |
6m1erq | Why do some structures (Radio towers specifically) have Red lights but, others use White Strobes? What is the difference between the two | Had to repost because the Bot Mods removed it because it did not have a flair. | Engineering | explainlikeimfive | {
"a_id": [
"djye5dd",
"djy5kll"
],
"text": [
"Tower climber here. I don't know the regulation by heart, but I'll say typically, a white strobe marks the top of the tower, while red (solid or strobe) act as side markers to show the tower's footprint. Not all towers are lit, it depends on the tower's height and it's proximity to an airport or flight path. So, a 199' tower that is not close to an airport may not be required to be lit, while a 150' tower, close to an airport will. You'll also find a lot of towers with heights such as 199 feet because they are built one foot shorter than the regulation requirement to be lit. You can voluntarily light a tower that is below the required height, but once a tower is lit, it must always remain lit and be registered on a FAA map. This is because, while the primary purpose is to be visible by aircraft so that they can avoid it, they also use the lights as landmarks for navigation. Lighting a tower these days can be very expensive because it requires a lot of maintenance, and also now requires a monitoring system to send a message when a light is out.",
"I'm guessing you know already the purpose of these lights is to make structures visible for aircraft? As long as the lights meet the FAA requirements (or the rules wherever you are) colour doesn't really matter. White strobe (usually a xenon globe) is better during the day, red (used to be incandescents, but now mainly leds) are better at night. A lot of places use both (especially towers in high traffic areas) but some settle on one or the other or various reasons. (e.g. cost, maintenance, not pissing off neighbours with a strobe light, etc) As long as they meet the visibility requirement, it doesn't matter."
],
"score": [
43,
37
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
6m6qob | Why are Fighter Jets so Loud compared to other Jet aircraft? and why does it make the specific sound of the sky being torn apart? | I was at an Airshow yesterday, and I noticed that out of all the Aircraft there, the Fighter Jets were by far the loudest, and you could always tell whether a jet in the air was a fighter or not based on the Roaring/Ripping noise they make. what causes this? what is happening to the Soundwaves to make them sound that way? | Engineering | explainlikeimfive | {
"a_id": [
"djzbhwx",
"djzi3ff",
"djzcc7w"
],
"text": [
"The noise is mainly caused by the huge difference in velocity between the exhaust of the jet engine and the surrounding air. Modern day passenger aircraft use turbofans with a high bypass ratio, which means that most of the air coming out of the back didn't go through the combustion chamber, but just through the large inlet fan. This is much more energy efficient, since you can get a lot more thrust if you move a large amount of air at low speed rather than a small amount of air at high speed. It also has the beneficial side effect of reducing the noise quite significantly. The loudest types of engines around are turbojet engines, which generate all their thrust with the exhaust of the engine. This is not particularly energy efficient, but those engines are a lot smaller than turbofans of equal thrust, and therefore more aerodynamic. There's also a middle ground, a low bypass turbofan. Those are not as bulky as the models used in passenger aircraft, but also not as efficient and quiet. Modern jet fighters usually use low bypass turbofans with the addition of an afterburner, which increases the noise even further if activated.",
"Were you in Yeovilton? Sad the Vulcan doesn’t fly any more. That’s an impressive sounding aircraft.",
"In addition to the technical reasons already given, there's also the factor of the effect noise has on passengers and people on the ground. For passengers, noise decreases comfort. For people on the ground, there would be a *lot* more opposition to airports or increases in flights if civil aeroplanes were as loud as military jets. Both of these would have a negative effect on airlines' profits."
],
"score": [
15,
4,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6m7d3s | How do neighboring countries that drive on different sides of the road connect their roads together? | Engineering | explainlikeimfive | {
"a_id": [
"djzfinj"
],
"text": [
"There are very few countries that drive on different sides of the road with land connections. Or at least with any major roads going though the boarder. The most famous example was Sweden which switched to right hand drive in the late 60s. All along the boarder with Norway there were signs reminding people to switch over to the other side of the road. And on the boarder the white lines marking the edges of the road switched over in a big X to further remind people to switch. At the time there were not enough traffic for big highways or even especially high speeds so the switch was not that hard to implement. But as traffic started to become a problem and cars started to become faster the Swedish government decided to switch to right hand drive before they built highway ramps and other major infrastructure."
],
"score": [
8
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6m91tk | How does the flame not spread backwards from a gas stove and cause an explosion in gas pipes? | Engineering | explainlikeimfive | {
"a_id": [
"djzskau",
"djzslk2"
],
"text": [
"A fire requires three things to burn: a fuel, an oxidizer (usually oxygen) and heat. There is no oxygen in the pipes that the gas is in, so the fire can't spread in that direction.",
"Fire is the combination of heat, fuel, and oxygen. Outside the pipe (like at the burner) you have all three so you get fire. In the gas pipe you don't have oxygen so you can't get fire. Those few times you hear of a gas pipe explosion something caused a breach in the pipe (like heat causing the gas to expand and burst the line or an earthquake, etc)"
],
"score": [
15,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6maq8q | Can you use the handbreak to stop a moving vehicle? | So i have my driving license for a while now , but only recently I started driving daily have less than 7k km drove in my life. And my city is like a crazy in terms of respecting the actual rules. And i've been put in a situation to need to stop the car to avoid a crash more than once/mo. ( people not respecting STOP , or right priority , people stoping the car after green light for no reason , people not using signal and changin lanes very close , or just not looking in the mirror and driving slowly over me , or near the dorms is like everyone is trying to get killed , had people jump in front of the car from the front of a stationary van at 150m from a crosswalk) But the closest situation was because of me , i was looking in the mirror to change lanes and when i turned the head back i realized the vehicle in front was slowing to stop and barely had time to stop with a creak. Can you actually use handbrake to stop a moving vehicle? Or will not help if the normal breaks cannot stop ? (Edit : both at the same time just in case you belive you cannot stop with normal breaks) Does it come with a risk of losing control (on sunny weather). Do you actually have time to use it to avoid a crash with a stationary object or unless for some reason you have it as a reflex it will be too late? Driving an automatic transmission if it matters. | Engineering | explainlikeimfive | {
"a_id": [
"dk065b3",
"dk089jp",
"dk07ucw"
],
"text": [
"The short answer is yes. The handbrake is a brake, it will stop your car. The longer answer is: it may not be a good idea, depending on how the brake works. Your normal brakes are almost certainly *antilock brakes* (ABS) which automatically control the rate of braking and pulses the braking so that your wheels don't skid on the road. If you use your hand brake, it will most likely result in you losing control of the car and skidding across the road. That's pretty dangerous, as you can avoid a crash not only by braking but by turning away from the potential crash. Losing control is rarely a good thing, especially since you may not stop any quicker since your wheels are losing traction. Hand brakes work in a couple different ways, depending on the vehicle. Some of them are separate systems that bypass your normal brakes. Some of them, though, just lock the normal brakes down. In that case, using the hand brake won't stop you any faster, it will just avoid the ABS and make the whole thing more dangerous. Either way, you *can* use your hand brake to stop in an emergency, but you probably shouldn't if at all possible.",
"The hand, parking, or emergency brake is usually, but not always, just your rear brakes actuated by a cable system instead of hydraulic fluid. This way it still works even if you lose all of your hydraulic fluid or if the master cylinder completely fails. But the brake pad or shoe the e-brake uses is usually the same one the normal system uses, so it won't add any stopping power if your normal brakes are working, and when used by itself it is much less effective because the front brakes do most of the stopping normally. You won't damage the emergency brake by using it occasionally, in fact it's recommended so the cables don't corrode in place, but there is another danger; The e-brake is designed to lock in place, possibly causing you to lose control of your car. To safely stop your vehicle with the emergency brake you have to remember to hold the button or other brake release so you can control how much braking force is applied and let up before the wheels lock up. This is also a good technique to use when starting from a stop on a steep hill with a manual transmission. Just keep the car from rolling back with the e-brake and release it as the clutch grabs. TL;DR - You *can* stop you car with it, but it won't be as good as the normal brakes and won't add anything if used at the same time. It should be used when parking on a steep hill or if your normal system fails, but you probably won't have fast enough reflexes to use it in a sudden emergency stop situation.",
"The handbrake is just a metal cable connected to the brakes, it is not nearly as strong or efficient as the regular hydraulic brake system. It usually is only connect to the two rear wheels, unlike your normal brake pedal which is connected to all four. It may not apply braking force evenly to both rear wheels, which could cause your car to lock up the wheels and skid. Even under the best of conditions it will take a long time to slow the car to a stop. Take your car out to a parking lot that is empty and try it out. So yes, it technically will stop your car, but it takes a long time to do so and should only be used if your normal system has a complete failure."
],
"score": [
10,
5,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6mbljo | Why do we twist pairs of wires together? | Engineering | explainlikeimfive | {
"a_id": [
"dk0du6o",
"dk0d65r"
],
"text": [
"If you're talking about data or phone wires, we use twisted pairs because each wire acts as an unintentional antenna, receiving radio signals from the air, and by making the two sides alternate, the radio effect cancels out.",
"By twisting two wires to gether it helps reduce electromagnetic interference or more easily said it helps prevent the signal being persuaded by neighboring wires signals"
],
"score": [
11,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6mdh2s | how old ships could see each other at night | how old ships could see each other at night? | Engineering | explainlikeimfive | {
"a_id": [
"dk0qn0q",
"dk0tt7t",
"dk0qpoz"
],
"text": [
"Like today ships were required to have lanterns with different colors around the ship to allow nearby ships to see them better. Ships also used lookouts who were not exposed to light so they are accustomed to the dark and can see objects using the stars and moon as lighting. Also a lantern would stick out quite much in a dark environment.",
"often, they couldn't. \"2 ships passing in the night\" is an idiom specifically because it was so easy to miss another ship in the vast darkness of the ocean at night. those that were interested in being seen used lanterns. depending on what time in history and where, ships would have the lights laid out in patterns or with colors so you could tell what they were or which way they were facing (and thus moving)",
"How old are we talking about? In 1838, the US required by law that you had to have some kind of light, but it didn't say what color or where. Before that, navy ships might sometimes have a lantern burning so other navy ships in the squadron knew where they were at night and allowed them to sail together. Otherwise two civilian ships might light a flare to show where they were."
],
"score": [
15,
14,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6mggrz | Why didn't old massive sailboats flip over, and why didn't their masts break being so far from CoM? | I'm guessing they had massive heavy fins at their bottoms for the first question, but idk for the second one. | Engineering | explainlikeimfive | {
"a_id": [
"dk1enig",
"dk1hhpl",
"dk1egso",
"dk1ggik"
],
"text": [
"not fins...ballast. The hull of a ship is typically loaded down with sand, stone, lead, etc to lower the waterline and stabilize the vessel. Much of the stonework you see in the streets and buildings of New Orleans was additional ship ballast quarried in europe and only shipped to the americas for the purpose of maintaining an even keel with its return voyage loaded down with the spoils of the new world. as for the masts snapping....they stood fine when they were trees covered in windcatching branches and leaves anchored to ground that did not give sway.",
"The masts did not break because they were designed to be strong enough not to break. Lots of experimentation and calculation went into knowing/predicting the strength of a mast. As it progressed over the course of centuries, the art of mastmaking actually laid the foundation for modern [beam theory]( URL_1 ). If you want to get a bit technical, it all depends on the [stress]( URL_0 ) in the wood. If the stress gets too high, the wood snaps. \"Too high\" depends on the type of wood, so shipbuilders would try to find the strongest species of tree to make their masts out of. The stress in the wood then depends on three things: it depends linearly on the applied force (double force = double stress), linearly on the distance from the deck (twice as tall = double stress), and inversely with the *cube* of the diameter (twice as thick = 1/8th the stress). So you take all these factors and try to set them in balance: wood type, mast thickness, mast height, and expected wind force. If you can only find weak woods to build your ship out of, then you can only use the thickest ones as masts, or you can only have a short mast. And even if you have a sturdy mast of good wood, you have to avoid wind speeds you didn't design for - you can't sail into a hurricane, for example, because the mast wasn't designed to survive that!",
"They did not have massive fins but they had lots of weights at the bottom of the hull to counteract the leaning caused by the wind pushing into the sails above. As for the mast breaking, wood is pretty strong and bends before it breaks, the sails further up on the mast were smaller to reduce the load and in strong wind some might need to be taken down to prevent the mast from snapping.",
"There was more of a concern of uprooting the mast than breaking it. The mast was basically a whole tree that was very straight and strong and cured over several years. It was then built into the ship. The large concern in really bad weather was the mast breaking loose and tearing out of the hull. That was the weak point."
],
"score": [
24,
6,
4,
3
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Stress_(mechanics\\)",
"https://en.wikipedia.org/wiki/Euler%E2%80%93Bernoulli_beam_theory"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6mka95 | Why do Air Mattress's have shaped tops? | Engineering | explainlikeimfive | {
"a_id": [
"dk2at8m"
],
"text": [
"The mattress' shape is held by support columns in the mattress. Those columns keep the flat part from ballooning out into a sphere. They're basically the same things you have with [pool rafts]( URL_0 ). In order to have a flat top, you would need an evenly distributed support structure that covered the entire area of the mattress. It's simply more economical to have a few dozen columns that maintain the shape of the mattress."
],
"score": [
5
],
"text_urls": [
[
"https://www.toysplash.com/media/catalog/product/cache/3/image/9df78eab33525d08d6e5fb8d27136e95/T/Y/TYSRAFT_131314_-00_Intex-18-Pocket-Pool-Raft.jpg"
]
]
} | [
"url"
] | [
"url"
] |
|
6mlrww | How do resealable aluminum cans work and why aren't they the norm? | Engineering | explainlikeimfive | {
"a_id": [
"dk2jy87",
"dk2jpf2",
"dk2k8mx",
"dk2k79t"
],
"text": [
"As /u/TorturedChaos says the cost of manufacturing is just too high. So the cost/benefit is way out of whack. An ali can fits it's intended purpose so well, you should really check out this video: URL_0 They really are a fucking cool example of modern manufacturing and the evolution of a single product over time.",
"The one I saw had a plastic tab that could be popped out to drinking the pushed back into place to close the can. Other option is those aluminum can bottles that have a twist off cap that can be screwed back into place. In both cases they are rare because of increased cost to manufacturer. Your standard aluminum can is an engineering marvel that has developed over the last 100 yrs or so. It takes the absolute minimum amount of aluminum to make the can and still be strong and durable enough transport. Every aspect of it has been engineered for a specific purpose.",
"Some energy drinks and half litter beverages has a resealable lid, that rotates over and off the hole. The reason they aren't the norm is that they are more expensive to produce, and often you don't need to reseal a 33cl can, as you will drink all of it in one sitting.",
"Because things in aluminum cans are single serve and generally consumed in one sitting. There is no need for the extra expense to make something resealable when 99% of the people will never actually need to reseal it."
],
"score": [
49,
48,
6,
4
],
"text_urls": [
[
"https://www.youtube.com/watch?v=hUhisi2FBuw"
],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6mmjys | Cars with a "sport mode" button and what exactly goes on inside them when you press it. | Got myself a 2017 Jeep Renegade recently but i had to go for the "Sport" model cause it's really the only one with a manual transmission nd i really get bored driving autos. It has this strange "sport" button, and when i press it, everything that involves the motor seems to work a lot better, but nobody could really explain that to me. | Engineering | explainlikeimfive | {
"a_id": [
"dk2nbqx"
],
"text": [
"It's highly dependent on the car, but what can happen may include: * If your car has a dynamic suspension, the shock absorbers may become more ridged, or the car may be lowered * Your power steering may be adjusted to be more responsive, or shut off (it typically shuts off at higher speeds anyway) * The engine mapping might change to produce more power * Traction control may adjust the threshold and parameters it engages to allow for more aggressive power transfer at the risk of some slip * Automatic or semi-automatic transmissions may adjust their shift points to act at much higher RPM * Certain features may be enabled, like launch control, if you have it EDIT: Your engine may \"work better\", but fuel economy goes right out the window. Your engine undergoes a shit ton of design and instrumented testing during it's development. They use these special test \"cells\" that control every possible operating parameter, and they run these engines through the gambit, essentially every possible speed, load, and environmental and atmospheric condition, at $10k/hr, to develop the \"map\", if you can imagine - essentially a gigantic table of all the operating parameters for the engine. Based on what the car's sensors are telling it, the computer will select the ideal operating parameters in the map. These maps are conservative, for fuel economy, emissions, and engine reliability. Normally, when driving, you're doing so under \"closed-loop\", where sensors provide feedback and the map selection is adjusted, as I had suggested above. Under the right conditions, such as under load or demand (such as going full throttle), the map switches to \"open-loop\", where the computer basically disregards the sensors and selects a mapping that produces power at the expense of all else. There's also a shorter term \"learning\" (used, very, very loosely) system that will make adjustments beyond the map. So if your engine develops a misfire, or a hot spot, or you used some shitty fuel, or you bolted on a turbocharger without tuning the engine for it, this system can mitigate all these things. So this is the system that changes when you go into sport mode. You're using a different part of the map and the operating parameters are adjusted differently for performance, sacrificing all else, which is why you turn it on when you're going to use it, and turn it off when you're not. Never just run in sport mode just because, as it puts unnecessary wear on the engine, running at higher RPM for no reason, and wastes fuel. As I said, this map from the factory is conservative, and meant to work under all conditions, appropriate for mass production and a world wide market. A tuner can adjust this map to gain performance, fuel economy, and emissions, by making it specific to your region. They can, it doesn't mean they will - because the manufacturer spent $10k/hr to develop their map, and any Joe in their garage and with a hand unit from Autozone can call themselves a tuner. If you were ever to do this, do your research and find a reputable tuner that actually knows what the fuck they're doing."
],
"score": [
10
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6mqy97 | How have we been able to determine so much about things we can’t see at all (like how the human body works at a molecular level or wireless technology - or even how the components of an atom work)? | Engineering | explainlikeimfive | {
"a_id": [
"dk3p2gn"
],
"text": [
"Scientists design experiments that would only work if a given theory is true. Then they try the experiments. For example you can't see a radio wave. But if you design a radio based on how you *think* radio waves work, and the radio functions correctly, you figure your idea may be right. Now keep doing a thousand other things that rely on your idea -- and if *everything* works, you feel your idea is a pretty good model of how that bit of the universe actually works."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6muex7 | Why do fan and propeller blades often have different shapes and angles of attack? Why does the number of blades vary, shouldn't there be an optimal design? | Engineering | explainlikeimfive | {
"a_id": [
"dk4dk5u",
"dk4gl5z",
"dk4nk63",
"dk4npoa",
"dk4pcl0"
],
"text": [
"There *is* an optimal design... for any given purpose and set of operating conditions. The problem is that such things as expected air pressure, the speed at which it's moving forward (in the case of a propeller), the amount of driving power available, whether or not the fan is ducted, and various others, will change the optimal design. Hence, different designs for different purposes.",
"> Why do fan and propeller blades often have different shapes and angles of attack? On all but the smallest airplanes, the angle of the propellers can be adjusted to match the speed, serving the same function as a transmission in a car. > Why does the number of blades vary, shouldn't there be an optimal design? For a given amount of power, few blades are better, but they have to be longer to get the same effect. The number of blades will be a tradeoff between space and efficiency.",
"Well, I know that on AC condensers/heat pumps, the design of the fan blades can affect system performance. Different blade pitches and counts can have adverse affects on fan motor amperage by increasing or decreasing air resistance, refrigerant liquid (head) pressure by changing air flow across the coil, and compressor amperage by thusly changing the temperature and therefore pressure inside the condenser coil. With infinitely many applications, designs and manufacturers of equipment, it's impossible for there to be a universal fit",
"More blades with low attack will have less buffeting, but more whoosh. Air flow and comfort tend to work against each other.",
"The reason the angle of attack changes along the blade is because out towards the tip they're traveling faster and would exceed the speed at which they can bite the air if left the same along the whole blade. Conversely inside the angle of attack is steeper to make up for slower speeds. This doesn't really matter on household fans but on propellers it is imperative that the whole blade efficiently bites the air."
],
"score": [
285,
17,
14,
7,
5
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6mwb6c | What is the differences between airplanes and jets | Engineering | explainlikeimfive | {
"a_id": [
"dk4tqqj"
],
"text": [
"All jets are airplanes, not all airplanes are jets. Airplane is a broad term for a heavier than air flying vehicle with fixed (none moving) wings. A jet is an airplane that utilizes jet engines."
],
"score": [
10
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6mwngk | How does an already established city just build an underground subway system? | Engineering | explainlikeimfive | {
"a_id": [
"dk4z1iv"
],
"text": [
"There's a variety of techniques, but most modern cities use deep tunnel boring now which uses specially designed machines to dig the tunnels underneath everything else. This avoids most existing infrastructure and modern escalators and elevators mitigate the issue of getting people down so deep underground. Older subways, like those in New York, are mostly cut-and-cover where they took existing roads, tore them up, built the subway tracks, and replaced the roadway above it. This was mostly done in the early 1900s most tunnels built like this are only a few feet below the streets. Nowadays cut-and-cover isn't used as much there is already a lot of existing infrastructure that needs to be moved (and identified as to what it even is) and it's politically unpopular because it's very disruptive to traffic and local businesses."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6mwyi5 | Why does the odometer not go to 0 rpm when the car is parked? | Engineering | explainlikeimfive | {
"a_id": [
"dk4z8zc"
],
"text": [
"You mean your tachometer, the one that tracks rpms... the odometer is the one that tracks distance travelled and can only go up. Unless you jack up the Ferrari and run it in reverse. The _tachometer_ doesn't reach 0 because the engine is still rotating. If it wasn't, the engine would be stopped; outside of the small super efficient gas engines in hybrid vehicles, most gas engines use more gas to start then they would if they idled for a red light, so its better to leave them running as opposed to turning them off and restarting them."
],
"score": [
9
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6n1qya | How does electrical equipment ground itself out on the ISS? Wouldn't the chassis just keep storing energy until it arced and caused a big problem? | Edit: the lead hardware engineer for the ISS, /u/kamiraa, has explained how the ISS achieves a safe voltage potential in great detail [here]( URL_0 ). Shout out to /u/kamiraa for making my week! I really didn't expect much from this question, but after reading all your responses --every last one-- I want to thank everyone for their thoughtful contributions. Even that one r/flatearth guy who asked if I've ever actually "seen" space. | Engineering | explainlikeimfive | {
"a_id": [
"dk73di4",
"dk67quo",
"dk65nza",
"dk67b47",
"dk63o1e",
"dk6azf2",
"dk673yy",
"dk6b1wd",
"dk63f7b",
"dk66sd7",
"dk62gt3",
"dk68gcr",
"dk63tqj",
"dk6j7yb",
"dk6iwfl",
"dk6dvi6",
"dk702sn"
],
"text": [
"I got this guys :) I used to be a lead hardware engineer for the ISS Electrical Power System. URL_0 If you guys have any detailed questions feel free to ask me here (suggested by a user) URL_1 This is my first Reddit post , someone forwarded this to me. Ok . . . . so quick answer we have a SPG (Single Point Ground in the whole vehicle). The ISS is an interesting vehicle, we have 8 power channels, each with their own solar panels which is on primary power (160V DC), these primary channels get stepped down further to a very fine regulated secondary power 124.5V DC. Let's explore a single power channel. The primary power is regulated by SSUs (Sequential Shunt Units), we basically turn on or off individual strings to from a single power channels solar array until we regulate very fine at 160VDC. There are 1 for each power channel on ISS (8). Downstream of this ORU (On Orbit Replacement Unit) is a DCSU (Direct Current Switching Unit) , this DCSU acts as a giant circuit breaker and an availability to cross strap channels during emergencies and maintenance. There are 1 for each power channel on ISS (8). But . . . because the ISS is constantly going through solar events and the arrays are getting shaded we have a battery backup that \"Kicks In\" to regulate the 160Volts when the solar panels can't do it alone. These BCDU (Battery Charge Discharge Units) charge when excess energy is available and discharge when needed. There are a 3 PER power channel on ISS (24 in total) and multiple batteries that are used in these banks (the number depends if we are using new li-ion or older style batteries). These BCDUs attempt to regulate at at a lower voltage than the SSU. Because everything flows through these BCDUs (they are always charging or discharging) the batteries contain the positive and negative. Downstream further is the MBSU (Main Bus Switching Unit), this is the unit that ties all the BCDUs and DDCUs together (explaining next). Downstream further is the DDCUs (DC to DC Converter Units). These units will buck or boost voltage up or down to regulate 124.5V DC. You can NEVER tie two power channels together. You would have converters fighting eachother trying to keep up with regulation. They must always be isolated. But there is a common SPG (Single Point Ground) in the center of the vehicle at the Z1 Truss. Ok so the interesting question. The vehicle can travel in different orientations depending on what the operations of the vehicle are. Because of this as the solar arrays are adding drag to the vehicle or collecting electrons you are building a voltage potential at different points of the vehicle. A concern early on became well what happens as the vehicle travels through plasma clouds . . . . if there is a large voltage potential difference between the ISS and this cloud would \"Lightning\" strike and destroy the vehicles hull. . The PCU (Plama contactor Unit) was created that is housed near the Z1 truss. These units started out in full 24/7 operation at the beginning of the space station. They take a noble gas (Xenon), inject the excess electrons , and expel them from the vehicle, which keeps the charge of the ISS under control. It was determined at a later date that this lightning event was not credible to destroy the ISS hull, but it was enough to shock an astronaut during an EVA. Because of such we turn these ORUs on during EVA operations (There are 2 per ISS). Ask questions :) This is fun !!",
"Ah, something I can answer. There are two aspects to this question: grounding of equipment with respect to the ISS, and grounding of the ISS with respect to the plasma environment in low earth orbit. All electrical equipment is chassis-grounded to the space station's metallic structure, which is then bonded to the negative side of the electrical bus at the Main Bus Switching Units, which are located on the center truss segment. These ground paths do not normally carry current, but they will private a return path in the event of a fault. That path will eventually return back to the solar arrays. With respect to the space environment, the ISS charging is measured using the Floating Potential Measurement Unit to determine the voltage between station and the plasma that surrounds it in orbit. I don't recall what normal readings are, but if it gets too high, or if they are doing an EVA for which the plasma potential is a problem (don't want to shock the crew members!), there is a device called the Plasma Contactor Unit, which emits a stream of ionized xenon gas to \"bond\" station structure to the plasma environment.",
"So the frame is surely a common \"ground\". However, it can still build up an absolute charge. It's not readily observable by most meters and won't make current flow. But it can have unexpected effects, as observed in an electrostatic voltmeter with the 2 gold-foil leaves which repel each other when touching a DC charged conductor. I suppose you could build a high voltage DC generator and end it in a negatively charged needle to shed negative charge. But will that even work in a vacuum? And is there any way to shed a positive charge? Well, I suppose you could use a DC generator to charge some sort of mass and then eject the charged mass, but that seems wasteful and creates space-junk hazards.",
"This was an interesting question. Makes me wonder what happens on resupply docking missions. Since both ships have their own chassis ground that could be many volts of potential difference. I read through the other thread and found that question asked a few times but never addressed. You could potentially be talking about 100's of volts of difference between the two \"grounds\" all being equalized at once when the 2 vessels touch.",
"\"Ground\" does not always mean earth ground. The term is often used to refer to the zero voltage reference point of any electronic system. For big things like cars and the ISS, it is tied to the metal frame.",
"You might have a misunderstanding of how electricity works. It seems like you think of batteries as a cup of electrons that you pour through a wire and other devices until it reaches the ground. That's not the case. Batteries or solar cells are pumps, not buckets. That's why circuits have to be a complete circuit; a closed loop. Batteries don't store electrons, they pump them through the circuit. The ground can't fill up with electrons because the battery continually pumps them through the circuit.",
"~~~Voltage doesn't matter so much as voltage differential. As long as the charge built up in a vehicle (like a car or a space station) is consistent through the chassis, nobody would know or care.~~~ Electric potential doesn't matter so much as voltage, which is the **difference** in electric potential. As long as the potential built up in a vehicle (like a car or a space station) is consistent throughout the chassis, nobody would know or care. When you measure the voltage of an electrical wire at 120VAC, that's gotta be measured relative to something. The second probe needs to touch something. If you want a good measurement, you'll touch it to something \"grounded\". But it doesn't matter whether it's connected to the literal ground. (The ground does need to be connected to the earth via a grounding rod in order for household power distribution systems to work, but that's because the earth is used as the return wire for completing the circuit.) In a similar way, how much air pressure is in your tires? Don't know; don't care. The only thing that matters is how much MORE pressure is in your tires than there is in the air around your tires. That's what a standard tire pressure gauge measures. If your tires are rated for 35 PSI, and you measure them at 35 PSI, that just means that they're 35 PSI higher than the air. (If you're at sea level, the air is around 15 PSI, so your tires are actually about 50 PSI. But the gauge won't show you that.) **Edit:** I changed \"that's what a pressure gauge measures\" to \"that's what a standard tire pressure gauge measures\" based on a comment by /u/CouchSoup **Note:** multiple people commented to point out that it's not a perfect analogy because, unlike pressure, voltage is only a meaningful concept when there is a reference. There is no absolute voltage like there is an absolute pressure. It's a little unintuitive for me still, so if you want to learn about the difference between voltage, electric potential, and charge, you will probably need a better teacher. :-/ **Edit:** I changed the first paragraph per suggestions by /u/mjk05d",
"Is this different than how you ground electronics in cars?",
"There is a defined 'ground' on any spacecraft. Normally you use the main structure, but it can be different. Obviously this ground will not be at 0V compared to the actual ground (which isn't chargeless anyway), but as long as everything is coupled to the same 'ground', it's fine, since voltages are potential differences anyway. Each subsystem in the spacecraft will have its own ground plane. These ground planes are in general all tied together, but not necessarily. Excess charge in one system can ruin other systems and often systems are shielded from each other in very complicated ways. This is one reason that space components are so much more expensive than standard electronics - even wires in close proximity to ground planes can cause interference that could completely ruin other systems (CCDs in particular are very sensitive to interference). The space environment is not nice to electronics (another reason they're so expensive, they need to be radiation hardened). There are all kinds of charging mechanisms, that affect the surface and interior of the spacecraft, sometimes in different ways depending even on its orientation. All this stuff means that designing spacecraft electronics is NOT EASY. ___________________________________________________________________________ [Source]( URL_0 )",
"\"Ground\" just refers to some arbitrary reference point that all of your electronics share. Usually you would use the metal frame of your vehicle, whether a car, boat, or spacecraft. Objects like cars or spacecraft can build up a net charge, but only by absorbing or losing charged particles. Normal electrical operation doesn't cause charge buildup. If too much charge buildup occurs, the object is more likely to attract particles of the opposite charge or lose particles of the built-up charge. So naturally, things tend to balance out. Most objects in space don't have very much of a charge density and are roughly neutral. In the extreme case, if you somehow got a ton of positive or negative charge in an object, it would just blow up in a Coulomb Explosion. But things would never get that far under normal circumstances. **International space station grounding manual**: URL_0",
"How do you ground an electrical system in a car that is isolated from the earth by rubber tires? By going back to the battery",
"Here's the ELI5 answer: The frame is connected to the negative terminal of the batteries and or generator. That is how you ground DC vehicles.",
"Can someone ELI5 this question to me? Literally don't have any idea what's going on",
"When working on fighter jets in the Air Force i was taught that in the early days of aviation the planes would build up a HUGE static charge on the plane (which is effectively the ground for all electronics on the airframe). The planes would effectively kill people from the [1.21 gigawatts of] electricity stored on the aircraft frame. So they installed nifty little static dischargers on the wings that shed the static charge. URL_0 We also had to attach a grounding cable as soon as the plane landed before we touched the aircraft. Not sure if static dischargers work in space, but that's how it works on airframes that stay in the atmosphere! :)",
"[I found this interesting powerpoint on Electrostatic Discharge]( URL_0 ) (ESD) on NASA's Website. I'm not going to pretend like I understand the entire document, but it looks like they use a 'Plasma Contactor Unit' which \"Essentially forces the collected electrons back into the environment in the form of charged particles.\" (page 19). My understanding is this is mainly for ESD and not the electrical systems on board. Somehow they balance the electrical charge of the frame with a 'cloud' of plasma around the spacecraft. They detect the plasma with a Floating Potential Measurement Unit (FPMU) that was developed by Utah State University’s Space Dynamics Laboratory. Other than that, they use insulating materials to prevent ESD between astronauts and the craft during spacewalks. Also Interesting to note that the ISS has a primary system voltage of 160 VDC, secondary system of 120 VDC, and the russian system is 28 VDC.",
"URL_0 I remembered my grandfather worked on this patent Not even close to an eli5 and deals with charge build up from the craft moving in space you are able to shed the charge into the surroundings as even at heights of the iss you still have some stuff around you and not a true vacumme However as long as the common ground is just that common it does not make much difference to onboard electronics as the potential remains the same",
"TL: DR Voltage is realitive. Space can be considered a ground since it cant hold charge. But we use the hull as the ground. Theres a device that creates a low impedance connection to space called a plasma connector unit. You use the frame of the ISS as a common ground. All the voltage regulators and protection circuits regulate a safe voltage potential. The Hull filters out external noise since the electric field inside an enclosed conductor is zero if theres no charge inside. Capacitance is what allows a voltage to be \"held\" or be stored. Voltage is an electric field and capacitance is the ability to store an electric field. Voltage is essentially a \"charge pressure\". So if you have a small capacitance aka the frame of the ISS, its relatively easy to increase the pressure of charge by depositing positive charge carriers into it. The problem is that you need a higher voltage to deposit these charge carries otherwise the current well flow in the other direction. On the flip side space has no capacity to hold charge. It is a dielectric so an electric field can flow in it, but electrons well not be \"stay still\" inside space. They'll flow through it like a particule. Thus space is considered a \"ground\". The hull can create a low impedance connection to space called a plasma connector unit to short its excess charge to space."
],
"score": [
6375,
3207,
2507,
204,
84,
53,
52,
37,
20,
18,
13,
7,
5,
5,
5,
3,
3
],
"text_urls": [
[
"http://imgur.com/a/SUbSU",
"https://www.reddit.com/r/IAmA/comments/6n717c/iama_ex_lead_nasa_engineer_for_the_international/"
],
[],
[],
[],
[],
[],
[],
[],
[
"https://redd.it/1p4bug"
],
[
"http://snebulos.mit.edu/projects/reference/International-Space-Station/SSP30240RD.pdf"
],
[],
[],
[],
[
"https://www.google.com/search?q=f-16+static+dischargers&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjjveTs_4bVAhVLwYMKHTYhDg0Q_AUICigB&biw=1207&bih=945"
],
[
"https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110014828.pdf"
],
[
"http://patentimages.storage.googleapis.com/pdfs/US3984730.pdf"
],
[]
]
} | [
"url"
] | [
"url"
] |
6n1yw5 | Why is it that airplane flight sticks are configured to roll left/right when you move the stick left/right instead of yaw left/right? | I'm not a pilot, but I've played flight sims (both "real" and arcade-like) since the 90's, and Kerbal Space Program for 4 years. This just occurred to me: Why is it that airplane flight sticks are configured to roll left/right when you move the stick left/right instead of yaw left/right? KSP uses the old gamer keyboard layout (WASD), and W/S are pitch up/down just like an airplane, but A/D are yaw left/right. Roll is set as Q/W. I've heard the flight stick described as "moving the nose" of the airplane. So it seems to me if you want to move the nose of the aircraft to the right, shouldn't you move the stick to the right? Instead, in a real airplane, you have to use the foot pedals which control the rudder, which is what actually makes the airplane yaw. Is it just some odd historical quirk that arose during the early days of airplanes and just kind of stuck? I know in those early days, all the controls were mechanical, with cables and pulleys and such connecting the controls to the rudder and ailerons. But these days, it's all fly-by-wire, so it shouldn't matter how the controls are set up, right? | Engineering | explainlikeimfive | {
"a_id": [
"dk68pr9"
],
"text": [
"The rudder isn't there for mainly steering the plane, but more stabilizing it, which is part of the reason it is controlled by foot pedals, as opposed to the stick. The rudder helps prevent slips and skids in flight. The plane performs best when the airflow comes in directly in front of the wings, going straight back, maximizing lift. If the airflow starts coming in at an angle, performance drops so we utilize the rudder to correct that. It is useful in manuevers however, such as crosswind take-off and landing, where you want to straighten out the plane to the runway, as opposed to letting it go with the wind that it wants to do. Some single-engine propeller planes, it is necessary for climbing due to [P-factor]( URL_0 ), where then the plane is moving against the relative wind in a climb, one side of the propeller blades will get a higher angle of attack as opposed to the opposite blade, resulting in uneven thrust, unintentional yawing and decreased performance (RIGHT RUDDER!) Now for why the stick controls the ailerons on the wings (which causes the plane to roll) for turning is because the wing itself is there for generating lift. In straight and level flight, the lift force is always vertical, away from the ground and opposing the weight of the aircraft. When the plane rolls, the direction of lift changes to an angle, away from straight up and not in line with the weight. The plane's lift now at an angle, with a horizontal and vertical aspect, giving the power needed to start a turn. The traditional plane shape, along with the vertical stabilizer (where the rudder is), will cause the plane to adjust to the new direction, but won't be perfect, which is where the rudder comes back into play! When you adjust the ailerons by holding that turn with the stick, you control the rate of roll, not the angle of roll. Once you get to the angle you want, you can straighten out the stick (mostly) to hold that angle, but still have that turn, but no longer needing to apply force. If you turned with rudder only, which you can do, but highly impractical, you would have to hold that the whole time, which would be a pain. To sum up, rudder stabilizes the plane, ailerons and wing makes it roll and turn, which is why the stick controls the ailerons and foot pedals control the rudder."
],
"score": [
6
],
"text_urls": [
[
"https://en.wikipedia.org/wiki/P-factor"
]
]
} | [
"url"
] | [
"url"
] |
6n2lht | How do the trolley poles of trams/streetcars and trolley buses cross over other overhead wires and through switches without dewiring? | Engineering | explainlikeimfive | {
"a_id": [
"dk68h09"
],
"text": [
"It's called a pantograph and it is springloaded to push up against the underside of the wires, so it is not truly \"attached\" in a way that would keep it from navigating a fork in the wires."
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6n4vyz | how come we couldn't use built up pressure to launch objects into space? | Or get them at least partially there? Like maybe we could shoot them most of the way up with pressure and then they finish with thrusters (or whatever those fire things are called)? | Engineering | explainlikeimfive | {
"a_id": [
"dk6ri52",
"dk705m8"
],
"text": [
"It's actually an idea, called the Verne Gun after Jules Verne's classic book *From the Earth to the Moon* and like you said, the initial object would be fired into near earth before propulsion or other means are used. The problem is pesky G forces. In a rocked it's a somewhat slow build up, but firing shit out of a massive cannon is going from 0 to hypersonic instantly. This would likely turn any astronaut into fine paste while the rest of the craft is torn apart by the atmosphere resistance.",
"Getting to *space* and getting to *orbit* are two completely different things. We've already built [a gun that can launch things into space]( URL_0 ), but they fall right back down. Staying in space means reaching a tangential (sideways) orbital velocity of 8000 m/s. By comparison, the muzzle velocity of that gun is only 2100 m/s, almost all of which is used to go up rather than sideways. Even railguns only reach up to about 3500 m/s. If you were to actually build a gun that could fire a projectile at 8000 m/s, it would immediately be destroyed by heat generated by friction with the atmosphere. We take advantage of this to slow spacecraft down from orbital velocity (reentry), but it doesn't destroy them because they have a heat shield and start out in the higher, thinner parts of the atmosphere and then descend into the thicker parts as they slow down. Therefore they're never subjected to enough heat to burn through the shield. But an object suddenly being accelerated to full orbital velocity in the thick lower atmosphere? Nothing can save it. Even if you assumed it to be indestructible, by the time it got to space it would have lost most of its velocity and wouldn't have achieved orbit. Of course, this is completely feasible on the moon. The velocity of a low lunar orbit is only about 1500 m/s and there's no atmosphere."
],
"score": [
18,
3
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Project_HARP"
]
]
} | [
"url"
] | [
"url"
] |
6n5wmk | Why are almost all boats white? | There are so many colors of cars and planes, just figured boats would follow in their footsteps. Edit: Thanks for the feedback! | Engineering | explainlikeimfive | {
"a_id": [
"dk70414",
"dk74rux",
"dk7aeb6",
"dk7bidt",
"dk7covd",
"dk7olbb"
],
"text": [
"Ever notice that the line on the side of the road is white while it is yellow down the middle? That is because in fog it is vital to see the edge of the road. White shows up better in fog. White boats don't hit each other as much in fog, then.",
"Most white boats are fiberglass. White fiberglass is the easiest / cheapest color to make and it doesn't fade. It also doesn't show scratches or dings as easy. Boats tend to last a lot longer than cars, so they need to look decent for a long time.",
"White is one of the easiest colours to see against the blue background of the water and sky. When you're looking through binoculars for something kilometres away, a white boat is a lot easier to spot.",
"URL_0 That article approaches it from the opposite direction, as they have a sailboat with a dark blue hull. In general, white is cheap and it reflects heat well, so most small civilian boats end up with a white deck if not a white hull. Commercial ships on the other hand tend to be other colors, including dark blue and red. So it's partly modern tradition, partly that white fiberglass is a thing and partly that a white deck doesn't get as hot in the blazing summer sun.",
"A red object absorbs every colour except red right? Well it is well-known that white is best suited during hot days as it is a mix of a few colours. Therefore white rejects those colours, those colours composed by photons, at the origin of heat. Thus, white allows the boat to reject, not get assaulted by heat, in the middle of the ocean.",
"White is a common colour for a lot of things (boats, trucks, vans, caravans & campers, buildings...) because it's cheap (because it's popular...), reflects heat so it stays cool, reflects light so resists UV damage (a major problem on the water as you're floating on a big mirror with zero shade), it's easy to see and it's neutral & inoffensive."
],
"score": [
30,
17,
14,
7,
4,
3
],
"text_urls": [
[],
[],
[],
[
"http://commutercruiser.com/dark-hull-boats-fact-fiction/"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
6n6awe | How the base of a building like the Freedom Towel can withstand all that weight without worry | Engineering | explainlikeimfive | {
"a_id": [
"dk73a4w"
],
"text": [
"Manhatten has a unique geology that allows for large skyscrapers without much hassle. The bedrock (solid hard rock) on the island is very shallow. Skyscrapers have foundations that drive many large pylons down deep into the bedrock. This distributes the weight among a large area and anchors the building."
],
"score": [
8
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6na65k | Why do most cars redline in the 6,250-6,500 RPM Range: never lower, rarely much higher? | Engineering | explainlikeimfive | {
"a_id": [
"dk7zo6l"
],
"text": [
"Valvetrain dynamics. At high RPM, cost effective springs are ineffective and the valves can float between open and closed, or they can bounce. In performance applications, it's desirable to open the valves for long and wide, which is harder to do at higher speeds. F1 engines use pneumatics to close their valves, and cams to open them. Older fashioned pushrod valvetrains have additional mass and thus inertia, which is a limiting factor on engines of this type. And the faster an engine operates, the harder it is to breathe, putting a limit on how much torque (force) can be applied to the engine. At high speeds, air is thick, sticky, and bouncy. Friction torque increases with the square of the speed and power increases with the cube of the speed, which becomes waste heat. There are limits to engine geometry and materials to mitigate the effects of friction and dissipate the heat. There are material limits. Ferrari had a 22k RPM F1 engine before the limit was set to 18k RPM in 2008. They had a 25k RPM engine in development for that year. Typically, in your car's engine, at top RPM, the piston is traveling at the same speed as an F1 engine's piston in the middle of the stroke. But here's the rub, your engine has a stroke of, say 6\", and it does that 6k times a second? The F1 piston is going that speed in 1/2\" 18k times a second. Those are MASSIVE forces of acceleration being applied to that piston in either direction. That's why they make their parts super light weight and out of titanium and crazy shit, it's also why their engines are only good for 2 races, while yours has to run for a few hundred thousand miles. Finally, is combustion speed. Gasoline is a bad example because, Ferrari, 25k RPM, that's on gasoline - highly refined gasoline, but your car can run off the same stuff, it's not magic, it's not exotic, it's just precise. But the speed at which gasoline is the ultimate limiting factor. A better example is diesel. The fastest diesel engine there can ever be, effectively, is ~ 6k RPM. If you ran it faster, you'd be dumping still burning, still hot expanding gases, out the exhaust manifold. Ships burn bunker fuel, which is thicker than asphalt tar (and has to be heated to a liquid before being injected into the engine), and those things, with piston diameters measured in feet and strokes measured in yards, top out at only a couple hundred RPM."
],
"score": [
24
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6ncdx1 | Why are the ceilings in supermarkets so high? | Engineering | explainlikeimfive | {
"a_id": [
"dk8hg0w",
"dk8go51",
"dk8mq8w"
],
"text": [
"1) To keep it from being claustrophobic. If it had short ceilings being in isles would feel like tunnels. 2) Heat management. There are dozens if not hundreds of people in the store at any given point in time. That produces a lot of body heat. It is cheaper for them to have high ceilings for that warm air to go to and be replaced by cooled air from the AC ducts that are set lower.",
"Because they're usually set up in warehouse space. This is necessary because the back room has pallets stacked very high; it's easier to find and rent an existing warehouse than to have a custom two-tier building built with more space in the back and less height in the front.",
"The buildings in which supermarkets are located are rarely purpose built to be supermarkets. Construction of commercial space is very, very generic. Concrete block walls support light gauge steel roof trusses and girders, which in turn support corrugated aluminium or steel roof panels. The tenants construct a drop ceiling at whatever height they desire, along with bulkheads and interior walls to give the desired shape. When the tenant leave, they [usually] rip out whatever they want to keep or are required to remove and then the next tenant moves in to a big empty cuboid space. Sometimes things get left behind. I once helped decommission an office/lab space and discovered a 30 year old 60 gallon air compressor resting on a wooden platform right above the ceiling of one fellow's office. In terms of grocery stores specifically (or any retail outlet), ballast lights and customers create a lot of heat. In order to keep the place comfortable, the ceilings are kept high. A high ceiling also opens the place up and makes it look more professional."
],
"score": [
36,
4,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.