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
|
|---|---|---|---|---|---|---|---|
eh1gpi | Since microscope and telescope both is zooming in, what is the difference? | Engineering | explainlikeimfive | {
"a_id": [
"fcc310a",
"fcc2zf9"
],
"text": [
"A microscope is for magnifying tiny things very near to the lens. A telescope is for magnifying things very far away from the lens. In each case, the way that light needs to bend is different.",
"Telescopes are about light amplification- making dim objects visible. Microscopes are about resolving power- making fine details visible."
],
"score": [
19,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
eh797j | How are the metal bars making up a building's framework connected and held together? | Engineering | explainlikeimfive | {
"a_id": [
"fcgoevj"
],
"text": [
"Rivets/bolts aren't usually used in modern buildings. Turns out, punching a bunch of holes in every single steel bar is bad for the building's strength. Buildings are mostly welded these days."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
eh9ko2 | what do the numbers/“codes” on car oil mean? (ex 5W-20, 10W-30) | Engineering | explainlikeimfive | {
"a_id": [
"fcgxopb",
"fch1qvg"
],
"text": [
"The first number is the thickness (viscosity) when cold, and the second is the thickness when hot. You want thin oil when you first start your engine in cold weather so it can squirt to all the places that need lubrication quickly. Then when it gets hot you want it thicker so it will stay put instead of dripping off quickly.",
"If we just take a single number like 5, they refer to for example an SAE 5 oil, the lower the number the runnier the oil However oil gets thick when cold and runnier as it heats up, so they add additives to reduce the thickness when it’s cold and increase it when it is hot. The W stands for winter so in the cold the oil will behave more like a thinner oil, while the 20 refers to how it behaves at operating temperatures, like a thicker oil Note that this doesn’t mean it gets thicker as it heats up, it still gets runnier, but less so than standard oil would"
],
"score": [
11,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
ehbaj9 | Why are ‘highway kilometres’ better than ‘city kilometres’ for your car? | I’m buying my first car used and many people list that they have driven mostly on the highway etc... I’m so confused about how highway driving impacts a car differently in comparison to city driving! Thanks in advance! | Engineering | explainlikeimfive | {
"a_id": [
"fchpr0t"
],
"text": [
"City driving involves a lot of starting and stopping with short trips. Motors tend to suffer the most wear when they are cold, and wear more when revs are constantly changing than when they are steady. In the city you're also using the brakes, steering, and transmission a whole lot more. Highway driving is long trips, on (usually) smooth roads, where it's all pretty much a straight line with only light to moderate braking. It allows your motor to warm up and just sit at the rev range where it is most efficient for most of the drive."
],
"score": [
17
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
ehc1e5 | Why Can You Bring Extremely Fire Hazardous Items as Hand Luggage On An Airplane? | You can buy litres of high proof alcohol after the security check, as well as bring your own lighter and things like big laptop lithium ion batteries as hand luggage. I’d be safe to assume that you could start a big fire. Isn’t that a problem? | Engineering | explainlikeimfive | {
"a_id": [
"fci4fwe",
"fci75ne"
],
"text": [
"Fires are a threat that aircrews are trained to deal with and lie within their response capabilities. Anti-terrorism forces worry about things that could take down an airplane (fuselage penetrating explosives) or allow a plane to be highjacked and used for terrorism. Fires are neither.",
"They have fire extinguishers and can monitor people to prevent it from happening. What they're more concerned with is unknown fires starting in the cargo hold which is why you have to put batteries in your carry on."
],
"score": [
10,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
ehh4n9 | How it is determined that people who died while texting-and-driving were actually looking at their phone at the time of (or time leading to) impact? | I always wonder how it is determined that people who died while texting-and-driving were actually looking at their phones at the time of (or time leading to) impact. I feel like it’s a pretty serious accusation to make - as it, in a way, provides a rationale for their death. I should clarify that I’m the most anti-texting and driving person you’d ever meet. | Engineering | explainlikeimfive | {
"a_id": [
"fcjdldq",
"fcjc5er",
"fcje2c3",
"fcjbvs3"
],
"text": [
"If the deploying airbag embeds the phone into the drivers cranium, then that’s a good indicator too.",
"Txt messages all have timestamps recorded on the phone and also on the telco side. You can match up the timestamps with the accident. A lot of accidents also have witnesses and it's really obvious when someone is using their phone while driving.",
"One way is to look at the text box where you type in the meassage, and see if there's an incomplete word or sentance at the end.",
"No way to know accurately. But some estimates based on witnesses that saw the driver texting. Seeing sent text messages with that time stamp, etc. In general cellphone in hand at the time of accident could be classified as driving and texting regardless of actual use."
],
"score": [
24,
11,
6,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
ehqvw9 | While most shower handles have around 360 degrees of rotation, why is the difference between ice cold vs. scolding hot water always determined by like a 1 degree turn? | Engineering | explainlikeimfive | {
"a_id": [
"fcl1g7g"
],
"text": [
"Maybe a bad mixer valve, or one that lacks fine control? Your shower/faucet pull in unheated water and water processed by your hot water heater. There's a device in the handle that translates position into a percentage of hot vs. cold water. If that valve isn't sensitive enough, it could translate not a lot of movement to a large change. I'd love for a plumber to weigh in on this."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
ehy9im | Why/how do F1 brakes get locked up? | I recently got into F1 and realized that their cars do not have ABS. Did not know how big of a thing it was until I saw clips where the front wheel(s) got completely jammed and the announcers called it "locking". Can someone tell me why exactly does this happen? And how do they take corners without this happening? | Engineering | explainlikeimfive | {
"a_id": [
"fcmb438"
],
"text": [
"> Can someone tell me why exactly does this happen? The braking force on the tires is greater than the force exerted from friction with the track surface, meaning the tires stop rotating and slide across the track instead. > And how do they take corners without this happening? They don't apply the brakes as hard, reducing the amount of force trying to slow the rotation of the tires to be less than that exerted by friction with the road surface. The tires then will continue to roll while slowing the car."
],
"score": [
11
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
ei3inm | How are massive fireworks, like the ones we see during new year countdowns, prepared or animated, and rehearsed? How do they know if things will go exactly as planned? | Engineering | explainlikeimfive | {
"a_id": [
"fcn6674",
"fcn7dzd",
"fcn9b0f",
"fcncs13",
"fcn8osm",
"fcnexgo",
"fcnalmu",
"fcnbhgv",
"fcnd323",
"fcne1ho",
"fcnc5v7"
],
"text": [
"Most of the time with large firework events they are all hooked up to a computer of sorts. That computer is then hooked up to tons of fuses all lined up in the right order.",
"The Royal Institute has a [YouTube video]( URL_0 ) from a professional fireworks technician that explains fireworks and shows pretty well. It's a long watch, so the TL;DW is that planning and rehearsal is usually done virtually on a computer and then that computer fires the fireworks using electronic detonators based on a timing script. There may also be some manually fired ones, but they still follow that pre-planned script.",
"So a lot of the answers center around computers but what about in the old school days before advanced computers? I remember watching a video of a dude with a giant torch and he knew which ones to ignite. Am I imagining things?",
"In 2012 San Diego accidentally launched all of their 4th of july fireworks in 30 seconds It was supposed to last 45 minutes [Link]( URL_0 )",
"Computer simulation. I saw a demo by an automation company a few weeks ago where they had a lottery machine made up from their products, but before it was actually built they’d made such an advanced physics model of the unit that they already knew exactly what errors they’d see with the ball placement.",
"Hey, this is my job! Here is a quick and dirty: Most shows aren't actually choreographed, so it's not too important. Someone (the sponsor) plays music in the background and we shoot for however long they hired us to (say 15 minutes). For these, we usually have an [e-match]( URL_0 ) connected to a time chain for the mortars. An ematch is a a device that is wired into one of our [field modules]( URL_2 ) (a hub where we can wire devices that is wirelessly connected to our remote control) and a time chain is a fuse that normally fires 10 mortars, each seperated by 3-4 seconds. So essentially this allows us to push a single button that fires 10 mortars over 30 seconds. We could individually match (fuse) mortars to fire each individually, but that is a lot of time and a lot of extra money. We will put specially effects (comets, mines, cakes) on individual cues to have precise control over those. For these non-choreographed shows, we plan it our before hand timewise, and then just shoot it manually and adjust as we go. Kinda seat-of-the-pants shooting. For choreographed shows [like this]( URL_3 ) the entire show requires everything to be individually matched and tied in to an assigned cue which is expensive and a lot of work (which is why most of our customers don't do this). What's really cool about these is we do have CAD (called Finale IIRC) that lets us build and play the show on our computer before we do it. When we're happy, it prints out a product sheet for us and a connection sheet that tells us where everything should go and what module and cue it should be plugged into. It also gives a CSV of timecodes and cues that we can upload into our firing system remote, so we can just hit play and it autonomously plays the show for us. Also, the firing system has an integrated music box to, so it plays the music itself while we shoot the show, that way the timing is exact. And our system interfaces with professional audio equipment, so we usually are plugged into our sponsor's audio board and are the ones playing the music and shooting the show. Things don't always go as planned, as products can be incorrectly marked or shoot faster or slower than what the box labels say. Some stuff just also blows up when it shouldn't (I have a lot of video of this) so safety is number 1 priority with us. We're required to wear certain PPE and we must have fire suppression equipment on hand. Sometimes our electronic firing system fails so we have to hand light. Here is a [video of us]( URL_1 ) training apprentices on how to handlight...which is as it sounds. Flare on a stick to make the booms go boom. This is really unsafe though, and we try with all our might not to do it, but sometimes if stuff goes wrong, we don't have options, so we still train people how to do it. This whole video is cool, because it is a big enough show that we have 4 firing locations, of which 3 are electronic and the 1 we're at is handlight. edit: Also, usually there is no rehearsal so we only get one shot to get it right. The only exception to that is indoor shows. In our jurisdiction we must fire the entire show for the Fire Marshall before we get approved and get the permit to perform it publicly indoors.",
"How did it work before computers? Stopwatches and coordination?",
"No one is explaining how they actually construct the firework and pack in the explosives in such a way that it makes a heart, star, or just a circle. How is that done? Just trial and error until someone gets it right and then everyone uses that same schematic?",
"At Disney world, the largest buyer of gunpowder behind the military, they always do a full rehearsal the night before. (This also helps alleviate crowds on the day of by giving them an opportunity to celebrate the day before.)",
"Display firework tech here. The shells are labeled from the factory with what effect they will be. We then design the show on a computer by taking into account run time, theme, shell availability, and client wishes. The show is then time coded for each shell, and if music is involved we would time that out at that point. All that info gets loaded onto separate firing boxes that are connected with long fuses to each rack of firework shells. Those boxes are then slaved to a master console that is the master timer and is were the tech will actually push the button to fire the show. Sometimes depending on what equipment we have, the master console may be an actual computer that controls music, any lighting effects, and the fireworks; other times it’s just a box with a timer, transmitter, and fire button. I had the opportunity this summer to see how Walt Disney World does their firework shows and they are very far ahead of anything I’ve used in the past.",
"In terms of what the actual firework will look like, e.g. shape/colour/flare etc. there are demonstrations for buyers. There was one near my hometown in Australia where the night was basically a long display of individual fireworks for buyers and then at the end there was a cool show using all the products"
],
"score": [
652,
158,
31,
27,
20,
10,
8,
8,
4,
4,
3
],
"text_urls": [
[],
[
"https://www.youtube.com/watch?v=B2Kms5xGgck"
],
[],
[
"https://youtu.be/ndVhgq1yHdA"
],
[],
[
"https://electricmatch.com/pyrotechnics/see/9/5/j-tek-igniter",
"https://www.youtube.com/watch?v=J8cu5POQ7BA",
"https://www.cobrafiringsystems.com/product_overview.html",
"https://www.youtube.com/watch?time_continue=658&v=s7ft8xFUmIY&feature=emb_logo"
],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
aly65h | How do fire hydrants work in the winter? How does the water not freeze in -20°C weather? | Engineering | explainlikeimfive | {
"a_id": [
"efhvgo3",
"efhvhgr",
"efhvip8",
"efi0fqc"
],
"text": [
"There are multiple designs, the ones that prevent water from freezing keep the water underground below the frost layer. Meaning the water is kept warm by the earth.",
"The water is underground, below the freeze line. That's why hydrants have that hard to turn valve. The stem is dry when the hydrant is off, and the air insulates the valve mechanism from the cold.",
"Fire hydrant valves are buried very deep, well below the frost depth. This keeps the water from freezing since it is surrounded by soil that isn't frozen. This is very similar to the old timey faucets in the back yard.",
"Dirt is an excellent insulator. Many \"cold-blooded\" animals survive the winter by burying themselves."
],
"score": [
10,
8,
5,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
am0ex9 | What stops the weight of the top floors of a skyscraper from crushing the lower floors? | Engineering | explainlikeimfive | {
"a_id": [
"efibgie",
"efibitj",
"efib7wq",
"efid9hs"
],
"text": [
"Strong enough materials, good design to make sure they can handle it and are built in a way to distribute it properly, good construction to make sure everything works as planned",
"Simply put, they are strong enough to hold themselves up. Proper structural design with proper materials will go a long way. The fact that there is so much stress on the structure is why when sky scrapers fail they tend to do so completely. They are designed to hold up the weight of the floors above them, but not the massive amount of stress those floors falling on them would generate. This is why you get things like the WTC where structural damage high up on the tower resulted in the entire tower cascading down on itself.",
"If the 'scraper was tall enough, they would. As it is, the materials are strong enough to stop that happening.",
"Agree with all of the above. Another common building method is the central concrete core, with lift wells embedded in it. The floors, also concrete, are cantilevered from the core, with support columns. And then the walls, often glass, are clipped to the edges of the walls. This is your classic glass-walled office tower. The central core gives the building its overall stiffness, since lateral wind loads are huge."
],
"score": [
5,
5,
3,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
am99cs | Why do overhead power lines need to be de-iced in cold weather? | Engineering | explainlikeimfive | {
"a_id": [
"efkaoc2",
"efkaikk",
"efkccu0"
],
"text": [
"Ice is heavy. If power lines get covered with too much ice, the weight could cause damage to either the lines or the supporting poles. A bunch of overhanging icicles on power lines is also a serious danger for pedestrians and motorists below.",
"Water drops on them and freezes, making an ever-growing coating of ice. While the wire is pretty strong, that ice can get to heavy and break it.",
"I'm just repeating what the above posts said to seem smart but ice is heavy and the weight can break the power lines."
],
"score": [
10,
6,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
am9dvt | How do you 3D print metal objects? Why is 3D printing better than traditional manufacturing methods? | I was wondering how titanium and other metals are used in 3D printing. I was watching this video of [Bugatti testing its first 3-D printed brake caliper]( URL_0 ) and was wondering how this would be manufactured. Also, what about 3D printing makes it better than traditional methods of manufacturing? Why would a company like Bugatti use 3D printing for their brake calipers as opposed to traditional methods? | Engineering | explainlikeimfive | {
"a_id": [
"efkc24c"
],
"text": [
"/u/ViskerRatio explained how metal 3D printing works already. Why they would want to is because 3D printing can produce shapes that cannot be made otherwise. For example, internal structures cannot usually be made by traditional methods, but can be made by 3D printing."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
ampaow | Why is it safer to spot weld battery cells instead of just using solder? | Engineering | explainlikeimfive | {
"a_id": [
"efnnya5"
],
"text": [
"Welding creates higher temperature but for a very brief time. The longer high temperature of soldering can damage the cell."
],
"score": [
8
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
amqmp2 | what are bomb squad suites designed to do exactly. | I assume they are flame retardant and possibly made of kevlar or other high weave material to prevent shrapnel penetrating. But i also see a bunch of buttons on the side and i assume there is a whole bunch of other cool things designed to protect people. Also how effective are they at keeping people safe? Like.... if a run of the mill pipe bomb goes off, how well would it shield the defuser. | Engineering | explainlikeimfive | {
"a_id": [
"efnukvj",
"efnvnw9",
"efnwgjm"
],
"text": [
"Designs vary, but some also include ballistic plates around the head and along the torso with internal shock absorption materials, and the controls to which you may be referring are common for communication and ventilation. Cannot offer anything about their particular ratings. Hope some of this satisfies any curiosity.",
"I think you meant \"Suits\" \"Suites\" are something else entirely.",
"They deal with shrapnel, and cushion the technician in case they get blown back by a blast. Spreading out the energy is the best protection available. It is not safe, or fun, to be in a suit when there is an explosion."
],
"score": [
11,
10,
6
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
an216h | Considering all the talk of colonising Marss, wouldn't it be easier to just make a moon base? | Engineering | explainlikeimfive | {
"a_id": [
"efq3y6e",
"efq4845",
"efq7bjd"
],
"text": [
"There are pros and cons either way, as I understand it. For instance: the moon is closer, but mars has enough gravity to be more comfortable (and healthier), enough atmosphere to make insulation a far simpler problem, and enough weather that erosion has made the dust similar enough that we can say with confidence that we know how to deal with it - unlike the regolith on the moon which is a bit nightmarish.",
"It would be easier, but for many other reasons, it's not very useful. There has been talk of how a moon base could be important for long-distance space exploration, as it has a much lower escape velocity (how much energy is required to get off the planet), but the moon is not survivable because of its low gravity, minimal atmosphere, and no surface water. Also, we already know quite a bit about the moon, but Mars has the possibility of fossil life and the possibility of terraforming (transforming the climate of a planet through artificial means).",
"Yes it would be easier. The problem with the moon is the lack of essential elements for life. The moon would be an excellent source of material for construction of structure in orbit of earth or spacecraft for interplanetary travel, but it lack element that support life. It got aluminium, silicate for electronics, magnesium, titanium, etc. It got oxygen, but lack nitrogen and water. There is probably some amount of water, but not enough for a large scale colonisation. In addition, the lack of gravity mean that we would need energy to produce rotating habitat to keep people healthy, would would cost more. The moon will most likely never go beyond a source of material for orbital construction and scientific experimentation. Mars have a bit of everything when it come to element. It's not sure how much water there is, but it's enough to keep a decent amount of people alive on long term. Of course, the gravity isn't as high as the earth, but it could be enough for people to live healthy life. Transporting element that are needed on a daily basic from earth isn't possible for colonisation, so if it's not in place, it's not an option. In my opinion, we will see an large scale industry on asteroid, before we anything permanent on Mars. The reason is that asteroid got something to sell to Earth and Mars doesn't."
],
"score": [
15,
7,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
an2l6x | Why are the switches that control outdoor lights often more "clicky" than the ones that control indoor lights, even though they're sometimes on the same switch panel? | I've noticed in many homes in the US that the light switch that controls outdoor lights required a little more force to move, but then swings into position much more rapidly, often with an audible "click" noise when it happens. Why is this? | Engineering | explainlikeimfive | {
"a_id": [
"efq7v97",
"efq9xb7"
],
"text": [
"Normally outdoor switches are a little more weather proof. Tighter tolerances to allow less water/dirt/etc to get into the switch.",
"The other replies give a good explanation for switches that are actually outside, but if you're talking about regular indoor switches that control lights outside, it's most likely because they're not used as often, so they're a bit stiffer."
],
"score": [
4,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
an2pxm | How can boats have holes in the bottom to drop things into the ocean? | I mean like boats that launch submarines or what-have-you. How do they stay afloat when there's a great big hole in the bottom? | Engineering | explainlikeimfive | {
"a_id": [
"efq8x1m",
"efq9b2f",
"efq99lz",
"efq8z7z"
],
"text": [
"They are kept afloat by other sections that *don't* have holes in them. Think of a twin-hulled catamaran: the whole middle is a giant hole, but each of the two closed hulls still floats.",
"It's called a moon pool, or alternatively, a wet porch. There are a number of different designs that all work a little differently. The easiest one to understand are basically a hole in the floor above the waterline of a drilling platform or ship with multiple hulls that lets gives you access to the water. In this case, the ship is behaving like an inner tube. The inner tube floats because it's still a 100% contained vessel (it has no holes to admit water into itself). A ship with a moon pool at the water level is much the same. The water isn't allowed to flow into the ships hull, so the ship remains buoyant as before. There are also moon pools below the water line. Imagine taking a cup, turning it upside down and then pushing it under water. You will have trapped some air inside the cup. The water wants to get in the cup, but it can't make a lot of progress because the air is taking up the space (the air does compress a little, but you can also increase the pressure to push the water back).",
"Two doors. Inner opens and whatnot is loaded. Inner closed. Chamber is flooded and outer is opened. Whatnot is expelled and then outer is closed. Chamber is pumped out and inner is opened. Repeat until out of whatnots",
"Water can’t get in when the air is trying to get out. Put a glass in a bucket open end down, you’ll have a giant air pocket in side the glass"
],
"score": [
9,
7,
4,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
an9hof | why do remote controllers work when you hit it | Especially old remotes or old school hand held consoles. Why do they start to work after applying mild violence? | Engineering | explainlikeimfive | {
"a_id": [
"efrpugh"
],
"text": [
"The remote has an infrared led light that pulses depending on what button you press. Example: Volume Up 2 quick pulses and volume down 1 long and one short pulse. Then that's picked up by an infrared receiver in your TV or whatever. That receiver only picks up infrared light. Using that the piece of equipment you are controlling reads the pulses and know what button you press. Edit: if you meant why it works using brute force than it's because when you hot it just puts a loose contact back in place, thus making a good connection with the battery."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
anbp8q | what makes car electronics last longer and be more reliable compared to most household items? | Car electronics are quite complicated, and yet they will likely last the life of the car. Even in extremely cold weather, your car’s radio, lights and everything else will usually work just fine. What makes these systems so robust? Are they insulated against harsh weather? | Engineering | explainlikeimfive | {
"a_id": [
"efs6fss"
],
"text": [
"Automotive electronics are specially-designed electronics intended for use in automobiles. Automotive electronics can be subjected to, and are therefore rated at, more extreme temperature ranges than commercial electronics. Most electrical devices are manufactured in several temperature grades with each manufacturer defining its own temperature ratings. Therefore, designers and engineers must pay close attention to the actual specifications on product datasheets. The list below is an example of temperature ratings/grades. Note that the automotive grade is second only to the military grade (in terms of extreme temperature ratings): • Commercial: 0°C to 85°C • Industrial: -40°C to 100°C • Automotive: -40°C to 125°C • Military: -55°C to 125°C"
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
anf6rh | Why do reverse gears on vehicles whine? | Engineering | explainlikeimfive | {
"a_id": [
"efsusqo"
],
"text": [
"Most transmissions have the forward gears cut in a spiral bevel pattern that makes them run smoothly and quietly, but aren't easy to mesh while turning and generate thrust along the rotation axis that must be handled with a bearing. Reverse gears usually aren't meshed until selected, which would be very difficult if they weren't straight cut. Straight cut gears can't have a continuous tooth contact, so they clatter more than helical gears. Straight cut gears have more of the gear tooth loaded at any time though, so they are stronger. If you've ever heard a race car with a whiny transmission, it's because all the gears are straight cut."
],
"score": [
9
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
angk3z | How does the new Tesla Roadster have a top speed of 400 km/h, 1000 km radius. Are those numbers realistic with current technology? | Engineering | explainlikeimfive | {
"a_id": [
"eft4vpe",
"eft8yxk"
],
"text": [
"Well, it's all in the marketing, you have a top speed and a max range. But the numbers aren't based on each other. You aren't going to get 1000km at 400km/h, there are different tests that happened to achieve those numbers. Also, as batteries wear, both of those will go down.",
"1000km is almost certainly going to be theoretical or 'claimed' max range - i.e. In a tailwind, on a slight decline, on a perfectly flat road surface, in ideal temperatures and with absolutely nobody in the car. These numbers are never realistic, even with IC engines. 400kph is slightly more realistic due to the nature of electric motor power output, but is still likely based on a best-case scenario."
],
"score": [
10,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
anjxz4 | Why do buses not have curved windshields? | Engineering | explainlikeimfive | {
"a_id": [
"eftwgnw",
"efud7fu"
],
"text": [
"Vehicles that travel a lot of miles in their lifetime will experience a lot of rock chips and cracked windshields. It is more economical to replace a flat two-piece windshield than a fancy curved one. This is why most semis, box vans, buses and utility/work vehicles and a lot of equipment will have flat windows.",
"On top of the answer already provided regarding replacement costs, it also allows for buses to have more passenger places. It also provides better visibility for the driver which help avoiding running into pedestrians."
],
"score": [
39,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
ankff6 | How do contact lenses stay perfectly centered on your eye and slide/rotate back into place after you move them aside? | Engineering | explainlikeimfive | {
"a_id": [
"efu1xeh",
"efu7u36"
],
"text": [
"Your eye isn't just a perfect sphere. The lens is actually a bump out from the surface and the contact is curved. Staying on the lens then is preferred because sliding off would require pulling away or deforming the contact.",
"The base curvature of the contact lens is similar to the curvature of the cornea, which has a different curvature than the rest of the eye, so the lens will naturally center itself on the part that is closest to its own curvature. Soft lenses usually come in only one or two base curve per brand because the lens can conform more easily. Sometimes lenses (hard or soft) do not stay very well-centered on a person's cornea and may be slightly decentered but as long as the vision is good and the lens is not too tight or too loose, it can be ok (this is why you need a doctor to evaluate the lens and why you can't just buy whatever contact lenses you want off the store shelf/internet). For toric lenses (for astigmatism), it knows what orientation it should be in to provide the right astigmatic correction due to a prism ballast at what should be the bottom of the lens, this acts as a weight to rotate the lens into the correct orientation. Some lenses use other methods of orienting, such as truncation, but I think prism ballast is the most common one for soft contacts."
],
"score": [
16,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
ano2kq | What are torque and horsepower and how are they related? | Engineering | explainlikeimfive | {
"a_id": [
"efuuuzt"
],
"text": [
"Torque is the twisting force of an engine. Horsepower is how much twisting it can do over a set amount of time. Let me give you an example. You have a stuck bolt on a car tire. It's rusted and so the normal tire iron isn't working. You can get a breaker bar, which has a longer handle, which lets you exert a lot of torque on the bolt and break it loose. But that torque comes at the cost of speed. You apply more torque to the bolt, but it turns slower and you have to move that bar farther for each revolution of the bolt. So the torque might be high, but it doesn't do much actual work over time. You're trading speed for torque. Say that your breaker bar can exert 100lbs of torque on the bolt, but you can only rotate the bolt 20 times in a minute. An air driver might only exert 80lbs of torque, but if it can rotate that same bolt 40 times in a minute, it's actually doing more work per second than you and your breaker bar, so it has more horse power even though the torque is less. Another way of thinking about it is using gears on a bicycle. If you use a lower gear, you have to turn the pedal crank more revolutions per rotation of the drive wheel. Thus you have a lot of torque, but you can't make the bike go very fast because you have to pedal so much faster than the wheel. If you switch into a higher gear, you now have less torque, but you are pedaling faster. The amount of power your legs put into the bike hasn't changed, but you changed some of that torque into speed. Thus even a low torque engine, could use gearing to multiply it's torque, but it would be slower, thus it's horsepower wouldn't really change, just it's gearing. So if Engine A has 100ft/lbs of torque and it can apply that torque at 5200 RPM, you would say it has 100 horsepower. But if engine B also has 100ft/lbs of torque, but it can apply it at 10,400 RPM, it's spinning twice as fast, and therefor it's twice the power at 200 horsepower. Say that Engine C only has 50ft/lbs of torque, but it can also spin at 10,400 RPM, it would also be 100 horsepower just like Engine A, even though it produced less torque, it could deliver it twice as fast, hence equal horsepower. Almost like A and C were the same engine, but using different gears on a bike :) Whatever the horsepower of an engine, if it can keep revving faster and faster, doubling it's RPM would double it's horsepower. Of course, spin it too fast and it would fly apart and explode. There are other considerations though that can make torque stronger or weaker at certain RPM's, and the ability to supply air and fuel to the engine can also change at different RPM's so this relationship of torque to horsepower isn't always linear. Horsepower is an arbitrary measurement that started as a way to compare steam engines to what they were replacing, horses and mules. If a horse were tied to a rope that pulled a mine car up a ramp, and it took it 1 minute to pull that weight 100 feet, that could be considered 1 horse power. Thus if a steam engine doing the same task could pull the same weight 200 feet in a minute, it was said to have 2 horsepower. This is ironic because the inventor of the steam engine also had his own measurement for power over time and it bears his name, it's called the Watt. In the US we use horsepower as a standard measurement of engine performance but elsewhere in the world the power of an engine is measured in thousands of Watts, IE kilowatts. We've come full circle hehe."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
anq7a0 | How can skyways withstand the weight of all vehicles passing through it same goes for buildings that have tons of people and stuffs in it? | Engineering | explainlikeimfive | {
"a_id": [
"efv7724",
"efv8r5q"
],
"text": [
"In buildings and any other structure there is a structural design that takes the loads of the building itself, plus the loads of the people and things on the structure. In a bridge you can see where the loads are transferred to and that is the towers in the middle and the anchorage, or abutment, on each end. What you not see is that with both the towers and the end abutments great care was taken to take these loads and then transfer them down to bedrock. What is under the tower and abutments is just as important as what you see up above the ground level. In a building it is essentially the same thing. The loads are transferred by beams to columns. The columns then move the loads down to ground level. On smaller buildings you can put the building right on the ground if it is properly prepared. In larger buildings they want to extend those loads as far down as possible to bedrock. & #x200B;",
"The floor or the pavement transfers the weight to the beams which transfers the weight to columns which transfers the weight to the earth. Each part is designed to use enough material (typically wood, steel, concrete, or some combination) so as to not bend too much, break, or be crushed by the portion of the load they are expected to bare."
],
"score": [
5,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
ant93h | How do rocket engines not crush themselves under their own thrust? | Rocket engines look relatively delicate, and seem like they are mostly thin metal and empty space to allow room for combustion and fuel/oxidizer flow, yet they put out thrust in the 100s of tons, how do they not crush themselves under their own trust? Are they actually more robust than they look, or are there other hidden physics at work? | Engineering | explainlikeimfive | {
"a_id": [
"efvtbq3",
"efvt560",
"efvu13d"
],
"text": [
"They are actually just more robust than they look. Careful engineering and design went into making them be able to withstand the forces they generate, a complex and technically difficult process called \"rocket science\".",
"They are often times made out of extremely strong and robust exotic metals like titanium alloys or [Inconel.]( URL_0 ) In short, super duper strong and well engineered.",
"On top of the other mentions of strength of alloys, they’re also designed to alleviate pressure. Materials break not so much due to the force, but the force per area. That’s why a sword will pierce, but a broom handle wouldn’t, given the same amount of force"
],
"score": [
18,
5,
3
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Inconel"
],
[]
]
} | [
"url"
] | [
"url"
] |
anuby3 | What exactly is bulletproof glass? | I was unsure of the flair so hope this makes it to the right people! Just as the question in the title asks, I am extremely curious about what bulletproof glass actually is, how it is made, what is different about it, and what makes it able to stop a bullet. | Engineering | explainlikeimfive | {
"a_id": [
"efw1fwc"
],
"text": [
"First, there's no such thing as bullet**proof** glass, only bullet resistant. The way such glass works is by absorbing the energy of the bullet and trapping it in the glass. They're usually built out of multiple layers of alternating hard glass and stretchy plastic. The bullet will transfer energy into breaking the glass and the plastic will catch the glass shards. The larger the bullet that you want to protect against, the more layers of this sandwich that you'll need."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
anvgn5 | Natural gas distribution | A recent incident in Michigan, USA, led to a request from a major utility for clients to reduce usage during the polar vortex last week. Even if their operations are compromised, doesn’t the distribution system allow for unaltered supply? What interest would the utility company have in asking for reduced usage? | Engineering | explainlikeimfive | {
"a_id": [
"efwb767"
],
"text": [
"With out knowing what the specifics of that incident, here are some possible answers. Pipelines can only carry a certain quanitity of gas, at a safe pressure. If everyone is drawing nat gas from the pipeline at the same time, the pressure will drop to unsafe levels. Maybe traditional non-electric pilot lights will go out due to insufficient flow, so when pressure resumes gas will leak out of the pilot light with no flame to consume it, creating a potential hazard. Equipment won't work properly with sufficient fuel. Spikes in demand also spike the spot market pricing, off of which your utility might buy some of their fuel. They might also buy some fuel from futures markets. So there is a potential their cost price might rapidly rise. On the flip side, the rate the consumer pays for the nat gas is regulated in many states. It creates a situation where the utility is selling nat gas to consumers at a lower price than what they bought it for, and therefore losing money."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
anymaa | How does a mixer tap (faucet) that runs straight to a boiler know whether it's pointed at hot without an electric signal? | Engineering | explainlikeimfive | {
"a_id": [
"efwzt8i"
],
"text": [
"The handle controls the mix of hot and cold. Visually, it's a T where hot comes in from the left, cold from the right, and the handle adjusts the amount of hot let in to a cold mix from the middle. The valve allowing one or the other is controlled by the handle."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
anz7of | How does net heat rate of a power plant relate to the net consumption of fuel used by that power plant? | For example, how would one estimate the yearly amount of natural gas needed to power a GE 9F 2xCC Plant when the net output is 889 MW, and the Net Heat Rate is 5,649 Btu/kWh? | Engineering | explainlikeimfive | {
"a_id": [
"efx57zf"
],
"text": [
"The heat rate of the plant is the inverse of efficiency. The higher the heat rate, the less efficient it is. To be more precise, the heat rate is a \"measure of how much energy, in the form of fuel, is required to produce a standardized unit of electrical power.\" So let's take a look at these numbers. When you say that the net output of the plant is 889MW, that's the *maximum power it can produce* after you have subtracted the power needed to run its own equipment. It might be running at 50% maximum rated output (445MW) if there is not enough demand on the electric grid. The heat rate is measured in Btu/kWh. That's British Thermal Units (a standard measure of natural gas fuel) per kilowatt-hour (a standard measure of energy produced). You generate 1kWh for every hour of energy production at 1kw. If you're running at an output of 5kw for one hour, you would produce 5 kWh during that same time period. & #x200B; To answer your question: To calculate how much natural gas fuel you need, you multiply the rated output (889,000 kw) by the heat rate (5649 Btu/kWh) by the number of hours in a year (8760 hours) 889,000 kw \\* 5649 Btu/kWh \\* 8760 hours = 43992378360000 Btu Now, usually natural gas is bought and sold in units of millions of Btus (MMBtu), so if we divide this number by 1 million... 43992378360000 / 1000000 = 43992378.36 MMBtu (or about 44 million MMBtu) *NOTE:* This calculation makes a couple of assumptions. First, that the plant is operating at 100% power continuously, year round. Second, it assumes that ALL of the fuel burned in the plant is used to make electrical power, and none of it is used for its own equipment."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
anzor9 | thread tapping | I would like someone to help me wrap my head around thread tapping. I see all the numbers associated with what the tap size needs to be, size of the previous drilled hole, etc. And it kinda gives me a headache lol. There are tons of applications I'd love to be able to start doing it, but I've no clue where to begin. | Engineering | explainlikeimfive | {
"a_id": [
"efx8lmn"
],
"text": [
"A thread is simply a helical groove cut into a hole that allows a bolt or screw with the opposite contour to be screwed into it. As you know, tapping is one way to cut that internal female thread. The main numbers that are associated with a tap are really the numbers that define the thread itself, and there are basically two standard systems, SAE and metric. SAE threads are defined in the format of 1/4 - 20, which means that the thread is a quarter inch thread with 20 threads per inch. Metric threads are defined as 5 x 0.8, which means that 5mm is the thread size and 0.8mm is the pitch, or distance between individual threads. The drill size for tapping an internal thread will always be somewhat smaller than the stated thread size, because the thread size will closely match the outside diameter, or major diameter, of the bolt or screw that will fit into the tapped hole, while the tap drill will cut the smaller inside diameter of the tapped hole, called the minor diameter. For instance, the tap drill for a 1/4 - 20 tap is a #7 drill, which is 0.201\" in diameter, not 1/4 inch After the hole is drilled, a tap is run down into the hole to cut the threads. There are different types of taps, but the most common is a tapered tap, which is made to be fed by hand into the hole and will cut the threads and will somewhat align itself, although care must be taken to get the tap in line with the hole. Proper lubrication for the material being tapped must be used, and a break chip movement needs to be done every so often to prevent the tap from becoming stuck in the hole and destroying both the tap and the workpiece. If you have any questions that I haven't answered, I'll do my best to answer them for you. I'm a machinist and have tapped hundreds of thousands of threads by hand and with machines in my time."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
ao6gup | When disconnecting a circuit (I.e. a car battery), why is it better to pull the negative side before the positive? | Engineering | explainlikeimfive | {
"a_id": [
"efykksi",
"efyw0rn",
"efz0k9n",
"efyk3ht"
],
"text": [
"Basically, if you take power off first and it touches any part of the engine / body it will complete the circuit (all parts are earthed) and it’ll spark like a mo’fucker. Take the earth off first and you remove that problem.",
"Batteries have little gremlins called electrons that always flow from the negative side to the positive side. When these gremlins travel to the places they’re supposed to, they’re well behaved. If they travel to places they shouldn’t be, they wreak havoc. Now, if you take off the positive side first and accidentally touch it to any metallic part of the car, the little gremlins will flow from the negative side to the positive side and into a place they shouldn’t be, therefore causing damage because of their penchant for bad behavior. By disconnecting the negative side, you make sure the little gremlins can’t travel out of the battery. Therefore touching the positive side to another part of the car will not harm it because there aren’t any gremlins there to cause harm.",
"The black wire (negative) is connected to every metal part of the car, so if you're taking off the red wire (positive) first, and your wrench slips and touches any metal part of the car, it will complete a circuit and throw up sparks. It can even start a fire. If you're taking off the black wire first, and you slip, nothing happens, because that side is already connected to the car. After you take the black wire off the battery, then the battery isn't connected to the car any more, so then you can take off the red wire without any sparks. For many decades now, engineers have designed circuits so the negative side is connected to the chassis, or case, or frame, or whatever (usually called the \"ground\"), just so there won't be any confusion. There are still a few really old cars (they switched around 1956) and farm tractors with positive ground, but you're not likely to ever work on one without knowing that.",
"In a car its more because you want to disconnect the chassis first. Less chance of a short if all the metal in the car isn't part of the circuit."
],
"score": [
17,
14,
12,
4
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
aoa9gn | Why are military boots laced? | Surely a velcro or a boa closing system would be better, especially if you need to be up and on the move quickly. Doing all those laces must take forever. | Engineering | explainlikeimfive | {
"a_id": [
"efzex13",
"efzdyui",
"efzjmqk",
"efzmtkt",
"efzdwqo",
"efzu238",
"efzlb9d",
"efzsz8t",
"efzt8ip",
"efzwcuk",
"efzilli",
"efztrls",
"efzdue5",
"efzu1v1",
"efzxgmu",
"efztdq5",
"eg0q9qj",
"efzyqnk",
"efzwo5r",
"eg0tn6z",
"efzstsc",
"efzzgf4",
"eg0m88t",
"eg0xq1s",
"efzszaf"
],
"text": [
"Laces are good for a few reasons. 1. Velcro wears out relatively quickly. Every time you undo some velcro it gets damaged a bit and every day it becomes a little less 'sticky.' This is no big deal on kids' sneakers but military gear has durability as a top priority. 2. You can easily carry spare laces and any man can replace the laces on his boots when needed. Properly attaching the velcro straps to the boot usually requires stitching them on which is a skill to be learned, hand-stitching onto tough leather isn't something anyone can just do properly especially if it needs to be done in less-than-ideal conditions. 3. You can easily adjust your lacing to make things tighter or looser on any specific part of the boot, which is good as feet shapes vary, calluses, blisters, and corns can appear requiring adjustments, etc. 4. Stuff sticks to velcro (dirt, sand, hair, clothing fibers, etc) and the velcro doesn't stick properly when it does. Shoelaces don't care how dirty they are. 5. Velcro straps are unlikely to stand up to as much stress/load as properly done strong shoelaces. 6. Boa closing systems are cool but may be more breakable, harder to replace quickly, and may work less well when clogged/dirty/wet. The military wants, as much as possible, stuff that will work fine even after being dragged through a muddy river for hours and can be replaced in 2 minutes by the person wearing them if need be. 7. Laces distribute pressure really well which is really important, it's not like you can say \"let's take a 15 minute break so I can rub my sore feet.\" To distribute the pressure as well using velcro you'd need at least as many straps as eyelets.",
"A lot of times simpler designs are preferred even if they seem less practical because of interchangeable parts. If a bootlace snaps, you lace up a new one. It costs next to nothing and spare laces are easy/convenient to have on hand at all times. Even when you don’t have extra laces, paracord can be used as a substitute. With Velcro and Boa mechanisms, a failure is far more catastrophic and can render the entire boot defective. This is not a good thing if the closest replacement is a 50 mile hike away. TL;DR, a broken lace is easier to fix in the field and won’t ruin a boot.",
"Military boots have long durable laces. You don't completely undo them just get them loose enough to get your feet out. After a few weeks of basic you can get back into your boots and secure them in just a few seconds.",
"Tanker boots don't have laces as they can become untied and tangle up on something. They can also burn, which is also why tanker boots are all leather with no nylon or canvas. Leather straps only.",
"With the way they are laced up and the “speed laces” they use it doesn’t take long to tighten them up and tie them off. Laces also have some benefits over things like Velcro that would be appealing to a military fighting force. Imagine trying to be covert and the loud ass sound of ripping Velcro pierces the night. No good. Also in a pinch, unlace your boots and use the laces for other things.",
"Quiet! The enemy might be near. Strap up your boots and lets get the hell out of here. FFFFFFFFFFSSSSSSSSSSHHHHHH",
"the Marine Corps answer: because you can't lace velcro left over right. the Army: because they exceeded their velcro budget by putting it on literally everything else. In all seriousness, Im actually kinda shocked the Army doesnt use velcro boots, they use velcro all over nearly every other uniform item. the Marine Corps would never adopt velcro boots because it would look tacky, and they have a hard on for having the best looking uniforms.",
"I don’t see anyone mentioning zips. The reason zips are not used is due to crush injuries. In the case of injuries zips can lock the boot together.",
"How do you quickly release a foot without exerting extra pressure on it when it has been damaged in the field? Cut the laces.",
"Here's an experiment you can do at home: Get some velcro, rub it through some dirt, rub it on some trees, drop it in water, drop shit on it, rub it in mud... then see how well it works... now, do the same thing with a shoe lace and see how well that works. That's basically the answer why. Something that will always work is better than something which will work better but only half the time.",
"It's simple and works. Not prone to breakage. Typically you would not need to do up your boots in a hurry, and if you do it doesn't take so much longer than any other fastening method. Also shoelaces are an excellent piece of survival kit. You can use them to cut a lot of materials, to start a fire, help erect a shelter, hold a splint in place or make a tourniquet. Velcro is a bad idea because it makes a lot of noise that is unmistakable.",
"When I was in, I didn't even tie them, just did a loop around the top of the boot, pulled the end under and over the loop, pulled it to the side to tighten, and tucked the ends between the boot and the tongue. I kept a knot on both ends which would help keep them in place. Never once had them undo themselves, not even doing boots and utes runs. As far as lacing them, you get *really* fast at that during boot camp. With speed laces, you can have them ready to go in seconds.",
"You’re trained to put on and take off your boots very quickly during training. There are also different ways to “tie them” without actually tying them.",
"I would also add that laces can be used for many other things than keeping your boots tight. You can’t easily remove velcro, or boa system when you need to improvise.",
"You don't take your boots off when you are in a situation where you may need to move quickly, you sleep in them.",
"Going I've other people's points here probably but there are quite a few reasons: - loud (not tactical) - get full of dirt (too much and they won't do up properly) - harder to properly clean than just dirty laces - you carry Extra laces if one snaps, you probably don't have room or the want to have replacement velcro straps on you. - laces are better at tightening and loosening your boots for different activities such as tabing. - on a more personal level, they aren't very formal and professional looking, soldiers Also wouldn't want to be that guy who rocks up to parade with his brand new velcro boots on. It would be incredibly hard to phase in as most people, new and old wouldn't want to look like a 5 year old who can't tie their shoes yet.",
"Are you serious? Do ypu wear Velcro shoes?",
"No yall missed the biggest reason. The military is cheap. Shoe laces are the cheapest option",
"We don't actually tie knots. & #x200B; Basically, it's pull boot on, yank laces, once around the top cuff, through the loop and tuck the laces in. Do it for 13 weeks, add boot bands and it's on autopilot.",
"Let’s not forget that Velcro comes off during a mission and it’s super loud. Which is why us going to Velcro pockets and patches was dumb as fuck",
"I saw a WWI documentary where someone mentioned that parallel laces make it easier to cut them so you can remove a boot quickly if injured. I thought that was interesting.",
"Your are kinda begging the question here. There are plenty of tactical boots with both zippers and laces. This allows the laces to be used for adjustment and the zipper for taking it off and putting it on rapidly.",
"In a combat environment silence is important. Velcro is noisy. Most people can tie thier shoes by 5 or 6, so it's not a time consuming process. A minute can be a very long time in properly trained hands. Shoe laces can be used for many other things.",
"* Velco is less durable. * Boots with laces don't take that long to put on if they're already laced. * If you need your boots to be tighter (for ankle support) you can achieve that with laces. Velcro can't handle the same loads. * Easy to replace laces * And last but not least, velcro makes noise. Noise discipline is important.",
"Laces are a tried and true method off making boots stick to feet, also if a soldier suffers a foot injury the laces can be cut to quickly remove the boot. From experience my army tried a laces and zipper boot, the zipper was the first thing to burst when weight was applied to the boot. Laces good, velcro bad when you are older you will understand."
],
"score": [
19798,
1593,
500,
245,
221,
155,
122,
78,
51,
29,
20,
16,
13,
9,
6,
5,
4,
4,
4,
3,
3,
3,
3,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
aoap0i | What is this debris that falls off the sides of a rocket during it's launch? | [ URL_1 ]( URL_0 ) & #x200B; You can see it in most (all?) rocket launches. | Engineering | explainlikeimfive | {
"a_id": [
"efzgl6y",
"efzh4jy"
],
"text": [
"Mostly ice. The fuel for rockets is often cryogenic, that means it's super cold. So cold that what's normally a gas, like oxygen, condenses to make a liquid. Even really well insulated rockets get cold on the outside when you put something this cold in them. If you put a cold thing in the humid air of a place like Florida, the water in the air condenses on it. You've probably seen this on the sides of a soda can. But this is much colder than a soda can, so the condensation freezes. When the rocket fires, the violent shaking detaches this ice.",
"Mostly just ice. The fuel tanks utilize liquid oxygen which requires them to be kept incredible cold. This means that the side of the fuel tanks will tend to collect a lot of condensation on the side that will later go on to freeze due to the temperature of the rocket."
],
"score": [
22,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
aobt3h | Why does sound only come through one headphone if the jack is orientated in a particular way? | Engineering | explainlikeimfive | {
"a_id": [
"efzqfel"
],
"text": [
"A headphone plug is comprised of three contacts, denoted as the Tip, Ring, and Sleeve. Tip is the left ear, Ring is the right, and the Sleeve is the common wire. If you manipulate the plug in the jack you can create a condition where one or more of these aren’t making contact. Most often, I recall, it is the Tip, so you lose the Left ear. I think."
],
"score": [
13
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
aof0bs | Why are 12V, 5V and 3.3V so special in electronics? | Is it an industry standard or is there a physics based reason for using these voltages? | Engineering | explainlikeimfive | {
"a_id": [
"eg0f5if",
"eg0e149",
"eg0heal",
"eg0fv6o",
"eg19dr8"
],
"text": [
"There's nothing special about those voltages. They were simply what worked best at the time. 12 volts is a good voltage to run a DC motor at for fans and spinning hard drives. 5 volts was the original voltage that almost every integrated circuit used. As the fabrication process shrunk they started using 3.3V because a smaller wire needs less voltage. But, they quickly realized that the process of chasing the improvements of chips wasn't going to work and computer components started including voltage regulators that would take an input voltage and convert it to whatever the chip needed instead of relying on the power supply to provide the correct voltage.",
"As chip fabrication shrinks, the breakdown voltages of the silicon get smaller and smaller. They also get more efficient because of this. 12V and 9V used to be very common, but now really 5V has taken their place - mostly because of USB. If you design your product to run on 5V, power supplies are abundant. Everyone has a 5V charger. The standard voltages exist so that you can use power rails (often 3.3V) to supply multiple chips on a single circuit board from different manufacturers, and also interconnect the logic without needing level converters. The numbers 12, 9, 5 and 3.3 are fairly arbitrary. There just needed to be an agreed standard.",
"Side note: the reason we have different voltages is because higher voltages can 'arc' further, and higher amperages mean more resistance and thus more heat. You need to put 12v wires further apart than 3.3v wires to maintain electrical separation. If a device needs 12 watts it could be built as 12 volts 1 amp, or 3 volts 4 amps. There will be less losses if it's built to be 12 volts, but the PCB tracks will need to be further apart.",
"Five volt for robustness of digital electronics. A low signal is between 0 and 0.8 volt, a high signal is between 2.0 and 5.0 volt. This huge band is to make it immune to noise Older chips are power hungry, specially when switching between a high or a low signal. That's why you place a small capacity next to a chip to provide the extra power. To make sure that all the high signal stayed high during this switching, the output can drop from 5.0 volt to 2.0 volt and all that time it is considered a high signal. Next thing, power usage: When difficult chips running on 5 volt got faster, they used more power and thus got warmer and burned out. Power is (I forgot the real formula) Voltage^2 * frequency. So if you increase the frequency by 10%, the power used is 10% more. But if you decrease the voltage by 10%, the power used decreases by the square of it. Now 3.3 volt for digital electronics: Backwards compatibility. A high signal of 3.3 volt against an 5 volt input is still considered a high voltage since it's between 2.0 and 5.0 volt. Plus you lose about 1.6 squared of the power needed. So you can increase the frequency with 300%.",
"Batteries, transistors, and chemistry, mostly. Sadly those are more ELI6 than ELI5. Many types of chemical cells (individual parts of a battery) are around 1.3-1.6 Volts. Some other chemical reactions generate about 2V like the lead acid cells used in car batteries. Still other chemical reactions generate about 3V. These individual cells are bundled into batteries. You get about 1.5V in most of the flashlight-style cells like AA, AAA, C, and D cells made from alkaline chemicals or zinc-carbon cells. You also get 1.5V in many tiny button cells. Put them together and you get many easy ways to make 3v, 6V, 9V, and 12V. Each configuration has more electrical pushing power. Car batteries that use lead acid cells are each just over 2V. They were commonly made with six cells pushing together. When fresh and new it works at about 13V. Over time it drops to 12.5, 12.2, eventually 11.9 or 11.8 reaching too low for use. Many lithium cell formulas start at around 3.7V or 3.8V when fresh, slowly dropping to about 3.0V. Electronics that are designed for 3.3V can handle the slightly higher voltage of fresh batteries and still operate on the low voltage of a nearly-drained cell. Lithium button cells have many 3V varieties. So that's the batteries. Next, the electronics. For transistors, the switching voltage in common early silicon transistors was about 0.7V. They were often used in DTL pairs, meaning a diode and a transistor, which needs two 0.7 volt drops to switch. 0.7V + 0.7V = 1.4V, which is close enough to 1.5V for most purposes. That is a convenient match for many of those chemical cell voltages. There is a bit of wiggle-room in voltage allowed. When transistors need symmetric logic gate levels, it becomes double that, the high output needs to be about 3.0V. Conveniently, that matches the chemistry of many batteries, given the wiggle-room in the chemistry. In the 1960 and 1970s TTL logic gates were popular. The logic gates needed about 5V to because of the chemistry and how they were combined, but they could handle a little extra power, perfect for four 1.2V or 1.3V cells. Many 5V electronics can handle 6V or a little extra, giving four 1.5V cells to power the device, or two 3V lithium cells. Some 5V electronics don't have the tolerance. AA and AAA alkaline cells are often a little on the high end, around 1.6V or more when fresh, but NiMH or NiCd rechargeable batteries are about 1.2V or 1.3V. This is a reason some electronics only work with rechargeable batteries, since four rechargeable batteries are almost exactly 5V, but four fresh alkaline batteries can easily reach 6.5V, too much for the parts involved."
],
"score": [
23,
6,
5,
5,
4
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
aogt0a | How come when writing with a pen it will sometimes not dispose ink properly but when you doodle on the side everything will work just fine, and then when you go back to writing it doesn’t work properly again? | Engineering | explainlikeimfive | {
"a_id": [
"eg0p694"
],
"text": [
"i found this very detailed explanation by u/drostie from a [previous thread]( URL_0 ) & nbsp; > The pen you are using is probably a \"roller-ball\" style of pen. This means that there is a big tube of ink, and at the bottom of that tube is a round slot, and sitting in that slot is a ball, which stops the ink from coming out. The ball sticks partly out of each side of the slot. > When you roll the ball across the paper, some of the ink rolls along the ball's surface, through the slot, onto the paper. Then the liquid inside of the ink (usually alcohol) evaporates while the ink soaks a little into the page. > Roller-ball pens stop working for two major reasons. First, an air bubble can form within the tube, stopping ink from flowing down to the pen; if the tube is open on one side you can sometimes fix this by taking apart the pen and blowing into the tube while trying to write. (You might also be able to simply hold it from its \"tail\" end and shake it side-to-side, the \"centrifugal\" force of rotation acting like blowing the ink.) > Second, some of the ink could dry on the tip, or the tip could write over something firm or gummy, like dirt or sand. In these cases the nasty gummy material is getting jammed into the slot, making it hard for the pen tip to rotate. This is probably what is happening to you, which is why you start scribbling somewhere else: \"get that ball rolling again, hopefully that will clear it out!\" > Well, sometimes it will and sometimes it won't. Gunk can be very stubborn. If a piece of gunk is stuck to the ball, the ball can still move ink, but it has to basically roll around the gunk. So when you scribble in circles, you may not be cutting through the gunk, or you might even be forcing it deeper into the slot. When you don't completely clean off the ball or clean out the slot, it's possible for the pen to jam up, especially if it rolls in the same direction that it did before. And it probably will: because most people, when they return from \"scribbling\" to clean out a pen, do not rotate the pen by 90 degrees so that they don't run into the same gunk that they ran into before! > There are some other contributing factors, too. (1) When you are scribbling you are more likely to put pressure on the ball in-line with the tube, pushing it upwards into the tube, which may give it more freedom to rotate in the ink. When you are writing the pen is usually at more at-an-angle. You might also press firmer when scribbling-to-clean. (2) When you originally failed to write, you probably tried to press harder and then again, even harder, before you tried to clean the pen. This had the effect of smoothing out the paper underneath the pen, which means that there is less friction that you have available to rotate the pen. > If you do not like these effects, consider using a felt-tipped pen. Sharpie makes some really nice ones (not their permanent marker brand) with no-bleed ink that are really nice to write with. & nbsp; [also, there are multiple ELI5 threads, might give you quicker replies]( URL_1 )"
],
"score": [
3
],
"text_urls": [
[
"https://np.reddit.com/r/explainlikeimfive/comments/44t5i0/eli5why_a_pen_wont_work_mid_sentence_but_will/czspu0c/",
"https://duckduckgo.com/?q=pen+write+stop+scribble+site%3Areddit.com%2Fr%2Fexplainlikeimfive%2F&t=ffab&ia=web"
]
]
} | [
"url"
] | [
"url"
] |
|
aoppfp | I saw a video of a plane propeller perfectly syncing with the camera and it looked like the blades weren't moving at all. How does that work? | Engineering | explainlikeimfive | {
"a_id": [
"eg2omhs",
"eg2oebb"
],
"text": [
"Cameras record at specific frame rate. The propeller is spinning at an RPM that is equivalent to the cameras frame rate so that every time the camera captures a frame the propeller is in the same position and the camera is essentially not fast enough to capture the propeller in a different position. Not an expert of anything please expand or correct me if I’m wrong.",
"If the rotations per minute of the prop and the refresh rate of the camera line up then it will be taking a new image of the prop each time it reaches the same position, causing it to appear still."
],
"score": [
6,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
aoqy4u | Why are shower faucets so sensitive that as you turn it the slightest bit to the left or right it could either become the perfect temperature, Satan's summer house, or the same temperature as my ex's cold, dead heart? | Engineering | explainlikeimfive | {
"a_id": [
"eg2xadx",
"eg2x3sr"
],
"text": [
"If it isn't the thermostatic type the pressure will tend to favour either the hot or cold side due to the expansion of the water as it is heated, you are basically trying to balance a thermal seesaw that always wants to fall to one side or the other.",
"This might be pressure related inside and compared between the hot & cold water supply. I think there’s a golden opportunity to create a geared style faucet whereby different knobs turn the faucet at different rates. This would solve many problems in many places irrespective of what’s going on inside the pipes themselves"
],
"score": [
3,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
aou1qk | Why do so many cars with automatic transmission have a rev count display? What is the purpose of it in non m a nual cars? | Engineering | explainlikeimfive | {
"a_id": [
"eg40n2q",
"eg3jc1q",
"eg4uh5d",
"eg3iyw7"
],
"text": [
"Quite simply it's actually a very useful metric to have. It's a measurement of how hard your engine is working, and has meaning far beyond 'time to shift'.",
"Gas mileage is why I use it. Sometimes cars won't shift up if it thinks you are going to need power, releasing the gas for a second will usually kick it into higher gear. Also, keep them rpms as low as possible for better mileage. Edit - Yep. Wrong direction. You know what I mean.",
"Honestly, tachometers have nothing to do with the type of transmission installed in the car. It's a measure of how fast the engine is turning, which (as someone else said) is useful information about the engine. The tachometer is there in the instrument panel whether the car has an automatic transmission or a manual one.",
"I’ll look at it before turning my key to confirm the car isn’t already on. I also check it when I’m sliding in snow to get an idea of whether my car is going to jump once I hit bare pavement again."
],
"score": [
5,
5,
5,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
aox2nx | how does having a clock on board a ship and using GMT help determine its longitude? | Engineering | explainlikeimfive | {
"a_id": [
"eg45fnz",
"eg474on"
],
"text": [
"You watch the sun as it gets towards noon where you are. When it gets to its highest point in the sky, that's local noon. You look at the clock at that time and that shows the what the time is at Greenwich at the same instant. That tells you how many hours ahead or behind GMT you are, and thus what fraction round the world you are by dividing the time difference by the 24 hours it takes for one revolution.",
"Latitude is easy to measure, so easy ancient seafarers used it. Polaris, the North Star, sits motionless above the North Pole. Simply measure the angle from the horizon to Polaris and that angle is your latitude north. A similar trick is used south of the equator. Longitude was tricker to figure out, as there is no fixed star east to west. Many tried over the centuries to work out some complicated system using stars and constellations like for latitude but nothing work. The sun moves east to west at about 15 degrees per hour. (360/24). If you start at an arbitrary point, say Greenwich, England, and set your clock for exactly noon at the exact moment the sun was directly overhead (solar noon), you now have a clock that is functionally a replica of the earths rotation. (Yes a real solar day is 23.9 hours but the ELI5 math is easier and 24 hour time is what they used in the 1700s to work this out.) Now after 1 hour, your clock says 1pm, and you can surmise that the solar noon, the line of longitude on earth directly below the sun has moved about 15 degrees of longitude to the east. So now if you maintain a clock on your ship that can accurately keep time with the time at that arbitrary point, GMT, you can determine how far west the sun as moved by comparing the position of the sun in the sky with what time GMT is. Jon Harrison, an Englishman, was the first to work out and invent a clock to use this system. Now I’m not sure if using time was his original idea or not; but Harrison was the first to invent what would be known as a Marine Chronometer. Basically a, for the time, hyper-accurate clock that would not be affected by the rolling of a ship. Prior pendulum based clocks would be horribly inaccurate with the swaying of a ship on the ocean. His idea was so revolutionary that the Royal Society, the premier science group in England, who had offered a large monetary prize to whomever could solve the “longitude problem” refused to believe it and did not give him the prize. They for years after it was proven to work insisted there had to be an astronomical method."
],
"score": [
12,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
ap1qxg | Thrust Vectoring | What is thrust vectoring and why is it important for aircraft like the F22/F35? | Engineering | explainlikeimfive | {
"a_id": [
"eg56a4g",
"eg56oyf",
"eg57lx5"
],
"text": [
"In most aircraft, a jet engine generates thrust in a fixed direction as air is pushed out the back of the engine. With thrust vectoring, a nozzle behind the engine can be moved to direct the airflow & mdash;and the thrust & mdash;in other directions. This can give more control and make the aircraft more manoeuvrable and, in extreme cases, it can allow for vertical takeoff by by directing the thrust straight down. In this configuration the engine is generating lift directly, without relying on the wings.",
"Nozzle thingy in back of plane points jet's propulsion in different directions for tighter turns/ greater muneuverability.",
"Something people aren't including is while the F-22 uses thrust vectoring to increase maneuverability the F-35B (the others don't have it) uses thrust vectoring in combination with a big fan in front to do short takeoffs (it can do vertical takeoffs but only with greatly reduced payload and fuel) and vertical landings."
],
"score": [
16,
6,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
ap326o | How do supermarkets not detect your stuff as stolen if you buy multiple of them? | Sorry if the title is a bit hard to understand. I know goods have anti-theft tags that get deactivated upon scanning, but sometimes when I buy a number of the same item the clerk would just scan one of them and enter the amount to get the payment (i.e. Only scanning one of the three Nutella jars,...). | Engineering | explainlikeimfive | {
"a_id": [
"eg5ertu",
"eg5eto4",
"eg5f3mx"
],
"text": [
"Most products like that don't have security tags. Honestly, the only food product I've seen with a security tag is meat.",
"The Nutella jar doesn’t have an anti-theft tag. Usually only high value items have such a thing, like razor blades and electronics. If the item has an anti-theft tag, just scanning the barcode doesn’t deactivate it, they have to deactivate it with something else. In this case they have to deactivate each item.",
"On a normal till, the cashier is the judge of the amount you have, on a self service, the bagging area is a scale and is programmed with how much stuff should weigh. If you scan one but put 3 down, it will detect excess weight. Some people steal things by weighing everything in as onions or other produce because that doesn't have a barcode. That's why the self service are staffed by one or two employees."
],
"score": [
13,
7,
6
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
ap6mh9 | On manual gearboxes in cars (stick shift) - with rare exceptions, usually in rally cars with sequential gearing - why is the gearstick connected to the gearbox via a 'H' pattern (or variation) instead of just a straight-line 1-2-3-4-5-6... etc? | Engineering | explainlikeimfive | {
"a_id": [
"eg66h05",
"eg64axy",
"eg6394s",
"eg63ung"
],
"text": [
"When you push the gear selector forward, or pull it back, you're pushing (or pulling) a pair of gears into contact with each other. But you can't push one gear through another to get to the next gear: you have to pull the selector back out, more it into another slot, and push a different gear into engagement.",
"The H shape allows the mechanical links between the shifter knob and the transmission to be relatively simple. When you move the leaver to first you select the first sliding gear assembly that pushes the gear for first into the transmission to be active, on the shift to second it's pulled out and the gear for second is pushed into place. On third you disengage both move to the center gear selector and engage the third gear On a ratchet shift transmission, the mechanism is a little more complicated and from what I've been told more prone to failure more moving parts per shift. [H shifter]( URL_0 )",
"Because if it were a straight line, it'd be extremely easy to skip gears and completely destroy your gear box",
"It’s hard to move the stick just the right amount. The H pattern requires fundamentally different movements to access each gear. Stick as far as it will go left, then forward. Let the stick return to the middle, then backwards. Stick as far as it will go right, then forwards. All of these can be done quickly and roughly without overshooting the gear you’re looking for. Sequential gearboxes are used more often on electrically-controlled transmissions these days, as traditional manuals have become less common. They’ve also been used for a long time in motorcycles. This is easier (or at least more intuitive) to use but requires a specific gearbox design to use it."
],
"score": [
16,
6,
5,
3
],
"text_urls": [
[],
[
"https://i.imgur.com/Ech07H3.gif"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
ap6vu1 | How do the engines of submerging vehicles (submarines, diving machines) work? As a lamen, are these combustion engines? Where do they get air from? | Engineering | explainlikeimfive | {
"a_id": [
"eg669hz",
"eg659yf"
],
"text": [
"There are different types of submersibles. The most common type is diesel electric. They have diesel engines that they can use when surfaced and at periscope depth by an air intake on the tower. In addition to propulsion the engine is mostly used to charge batteries. The batteries can be used when the submarine is submerged. Usually they have a limited speed and range in the submersible mode. There are a few exotic submarines that bring oxygen either as compressed or liquefied form or as hydrogen peroxide or other liquid oxidizer. The Swedish Gotland class submarine is most known for this. However the biggest submarines out there use small nuclear reactors to generate power and does not need air for their engine at all. The nuclear reactors give the same range and speed in submersed mode as in surface mode and also tend to have fuel for a lot longer then combustion based submarines as the fuel for the nuclear reactor is much more compact. However due to the size and complexity of a nuclear reactor this is usually only used in the biggest submarines.",
"Most of the time submersibles are powered by batteries as in old diesel submarines (the diesel engine recharges the batteries through drawing air in a snorkel, meaning they must surface regularly) or are powered by nuclear energy. As you suspected an air-breathing engine doesn't work underwater."
],
"score": [
10,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
apa7o3 | Why does a weight scale dive different readings based on where it is used? | ELI5: I have a weight scale in my bedroom (which is carpeted) and i was a few kilos over my target weight. A few days later the family ask for it and someone brings it down. Surprisingly i weigh myself and i drop like 4kg. I know carpet distorts the readin, but how and why? EDIT: Had some spelling mistakes first time round, doing this on the phone sorry! | Engineering | explainlikeimfive | {
"a_id": [
"eg6uhdr",
"eg7g88r"
],
"text": [
"Depending on the design but I'd say most numerical weight scale use something called strain gauge: a little piece of aluminum which distort when a force is applied on it with a tiny electrical wire attached on its surface. The distortion of the aluminum piece also distort the wire and so its section varies. It implies a variation of its electrical properties and here, its resistance. By measuring the resistance you can access to the deformation of the wire (which is the same of the aluminum piece) and by knowing the thickness of aluminum distorted one can compute the force applied (i.e. the weight). In consequence the measured weight may vary depending on the support the weight scale is put on (a soft support might \"absorb\" some of the deformation and therefore the weight might appear lighter than it really is). Hope I was clear enough",
"For an accurate reading, all the force due to your weight has to be transmitted to the floor via the feet of the scales. With a soft floor covering like carpet, the feet can dig into the floor, allowing the base of the scale to be partly supported by the carpet. The scale might not measure this force, depending on its design, making it read lower than in should."
],
"score": [
5,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
apl3f8 | How does gasoline itself make a cars engine work? | Engineering | explainlikeimfive | {
"a_id": [
"eg98ca6"
],
"text": [
"A jet sprays the dinosaur juice into a chamber in the engine where it **KERPLODES** like **BOOM BOOM BOOM**. Inside that chamber is the top of something called a piston, like a choo choo train has at the front. When the **KABOOM** goes off, it shoves that piston down real fast. The piston is connected to something called the crank shaft, when the piston fires it turns the crank shaft. But, in the engine there’s more than one **KERPLOSION** and more than one piston!! So when they keep firing, the crank shaft keeps turning!! The crank shaft is connected to the wheels which makes them spin around!!"
],
"score": [
17
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
apr4nl | why are CPUs designed to be so small compared to the overall size of a computer? | Engineering | explainlikeimfive | {
"a_id": [
"egalt8h",
"egambe7",
"egaovzk",
"egaw9er",
"egasziq",
"egb10c0",
"egapee7",
"egaznen",
"egaxero",
"egb2vpl",
"egb6w7l",
"egaxthk",
"egba938"
],
"text": [
"The CPU size is generaly limited due to data transfer speeds. If the CPU is bigger the data has to travel farther, which takes more time. Chips have been getting faster due to increased transistor density, not over all size.",
"Cost and speeds are a major factor. The defect rate in manufacturing is roughly proportional to the area of the chip (the die inside the CPU). Most defects cause the chip to fail and therefore be wasted. So large chips have larger chances of defects and therefore cause more loss during manufacturing. Speeds are another factor - the switching speed of the transistor is inversely proportional to its size - the smaller the faster. Also there are a LOT of signals moving through a CPU at any time and the system (to a rough factor) can only work as fast as the SLOWEST signals moving inside the chip. To increase speed - size (and therefore signal path lengths) have to decrease. Heat is probably also a factor but several things work for and against it. Clearly faster speed implies more heat. Shorter signal paths incur fewer losses and therefore lower heat. Smaller transistors require less charge/energy to switch. But larger chips are easier to move heat out of. So newer smaller CPUs require pretty sophisticated cooling in order to function (or they will pretty much meltdown)",
"No Joke: The speed of light. Electrons move pretty fast inside a cpu, but they can't move faster than the speed of light. If you have a CPU with clockspeed of 4 GHz this means it does its thing 4 billion times a second or about once ever 0.25 nanoseconds. How far can light travel in a quarter of a nanosecond? About 7.5 cm or 3 inch. That is as far as an electronics signal could travel (roundtrip) in the CPU in during one cycle under the best of circumstances. (Obviously the circumstances aren't the best.) You could build a CPU much bigger, but it would be slower.",
"I didn't see power here. Bigger chips need more power to push electrons around and more power to flip bits. Some of that power gets turned into heat, which accumulates, and above a certain threshold starts changing the material of the chip so that the components don't work properly. Smaller chips and transistors means less power and less heat for the same amount of work. So less cost to operate, and more work in the same footprint before you hit the thermal threshold.",
"2 main reasons honestly: Bigger chips are not cost-effective: the bigger is your die, the more likely a single flaw in manufacturing can invalidate the whole thing making it a waste, this is known as the yield, you wanna fit as many dies as possible in a single silicon wafer(as those are quite expensive) just ot be able ot profit out of them and increases the chances youll get good chips. 2:bigger chips are more complex so syncrhonization becomes an issue: evne on such small scales the speed at which your singla travels still matters, the speed of light is still the hard limit for a circuit that needs to get its singal at very precise intervals to function, the bigger the die the more difficult is to keep everything in sync, making design mroe complex.Plus the added size doesnt strictly means you get more computing power, heat might become an issue before speed does.",
"Related to this is the (mostly science-fictiony) idea of \"[computronium]( URL_0 )\" - \"a theoretical arrangement of matter that is the best possible form of computing device for that amount of matter\". A CPU is basically just a block of super small, cleverly arranged transistors. In theory, if you could make those transistors out of individual atoms you could reach a sort of platonic ideal of computational efficiency. A block of computronium the size of a present day CPU would probably be several orders of magnitude more powerful than all the CPUs in the world today. We have quite a way to go before we get there... see also [this]( URL_1 )",
"These answers are god awful. By far the biggest reason is cost. Making a larger die does give you more performance, but the cost scales super-linearly. You also have a hard manufacturing limit for a single die around 700-800mm^(2), dictated by the lithography machines. Moreover, most people simply don't need more than the consumer chips and sockets offer. If you look at servers, meanwhile, you'll see far beefier setups.",
"On top of everything else, CPUs (and other integrated circuits) are built on circular disks of silicon. The smaller the area of the square CPU or IC, the more they can fit on the circular wafer without getting corners cut off. Making CPUs much bigger would waste even more wafer space which drives up costs.",
"The smaller the transistors in the CPU the faster they can switch and the less power they need to switch. So transistors are made to be as small as possible to make the CPU as fast as possible and as efficient as possible. Even in a tiny space less than 1inch square you can fit billions of transistors. Now if you are asking why they don't just make the die bigger and fit even more transistors, it's because the failure rate in manufacturing goes up by the square of the surface area. So a CPU with the 2x as many transistors at the same size will likely have 4x as many duds, making it more than 2x expensive. Thus it's not viable economically without the CPU costs getting absurd.",
"The really mind blowing thing, is that the part of the CPU you think is the cpu is actually just a thermal conductor. The actual CPU is much much smaller and is suspended in that block.",
"The size of the computer your building has more to do with it's expandability then it does the size of the processor. Every connector you add adds size because there are wires to connect everything. The mother board has connectors for the CPU, RAM, expansion cards, and even the input/output connectors on the back. Those all need wires and special circuitry to connect them to the CPU. Now that we added all these extra components we need to provide power. There are is more wires and circuitry to handle all that. The more power you need the bigger those components need to be. With all that electricity flowing through all the components things will get warm. Now we need to cool it. Bigger fans are better because they move more are. Add all this up and you start to see why computers are so big compared to the CPU. You can build really small computers, but in doing so you compromise on expandability. The [Raspberry Pi Zero]( URL_0 ) is a full computer in every sense. There isn't much you can do to expand that computer. Even then, the Raspberry Pi Zero could be smaller if you got rid of the GPIO header and the connectors for power, video, and usb like they do for the their smaller [Compute Module]( URL_2 ). Even then, the connector along the bottom edge dictates the size of that computer. If you get ride of all expandability and distill a computer down to it's barest essentials you get the [Apple S2]( URL_1 ) system package that they use in the Apple Watch.",
"All computer components have shrunk over time. If you need proof. Look at your phone. It also contains a CPU and all the same components your larger desk computer does. CPUs and other integrated circuits (memory, gpus, etc) are all designed to be smaller and smaller with every generation of technology because it is more profitable for to manufacture. These things are mass produced on silicon wafers 100s at a time or more. The smaller they are, the more you can fit on a wafer. There are also positives and negatives to making them smaller from an engineering perspective. Smaller usually means less power is needed to run it. Less power also means less heat produced. Smaller also means that it becomes harder for the thing to work due to physics (capacitance issues between circuits will mess up your computations)... so their are actual limits to how you shrink things. The reason your CPU going into your desktop is relatively smaller than everything else is because desktop computers nowadays are designed usually for gaming and for more powerful components like memory and GPUs (memory cards) that take up a lot of space. In order to accommodate these, the mother board designers leave a lot of room for fans and cooling technology that just takes a lot more room. Gaming computers generate a lot more heat and use the CPUs a lot more. That's why the heat sinks are so big. We can also shrink heat sink technology but it is really expensive and not practical (not many people can keep spare tank of nitrogen in their house). So most people settle for bigger heat sinks and fans when they want better performance. Laptops, cell phones, tablets dont actually do all that much compared to a gaming PC so they dont need powerful CPUs, but you can still feel the heat they generate. (Source: my two degrees in computer engineering)",
"In the beginning computers were very large, taking up the space of a closet. This was because of the amount of electronics that existed. Then the micro-chip got invented. Basically it lets all the logic be printed on a really small machine. There were many advantages to this. * Smaller chips consume less electricity, as you need to pass less electrons and less things through the smaller parts to get the computation done. * Smaller chips are faster, because electricity has to travel less. True it travels at the speed of light, but computers are so fast it does make a difference (nano seconds matter for computers). * Smaller chips are easier to transport, use and handle. * Smaller chips are more versatile, you can place them inside more things. If you think the CPU is small, you are actually looking at the casing, while the chip is even smaller. So maybe the question we should ask why aren't computers as a whole smaller? Why are they so big when their parts are so small? To go on parts: why is the motherboard so big? The answer there is that computers are made of cheap interchangeable parts that are put together on the motherboard. While the CPU is one of the bigger parts (and the more expensive ones) all the other ones need to be brought together. This allows for computers to stay cheap. By using less off-the-shelf parts and putting everything together using chips we can do computers that consume less electricity and have more space. The ability to do this cheaply is what allows for laptops and smart phones. Any why not make chips bigger? It does happen. The actual chip, inside the casing, is called \"die\" (as in dice). Look at a GPU, it's kind of a tiny computer, with a motherboard in it, and the actual GPU inside it is smaller than the CPU. Except for the new Nvidia GPUs which have a huge die. CPUs actually do grow (and then shrink when they start hitting size limits, where shrinking is a better way to get faster) but it all happens inside the casing, this plastic box that hides the details."
],
"score": [
1910,
233,
132,
53,
13,
9,
8,
7,
7,
5,
3,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[
"https://en.wikipedia.org/wiki/Computronium",
"https://en.wikipedia.org/wiki/Limits_of_computation"
],
[],
[],
[],
[],
[
"https://www.raspberrypi.org/products/raspberry-pi-zero/",
"https://www.techinsights.com/uploadedImages/apple%20s3%20watch%20shots2-01(1).jpg?n=8275",
"https://www.raspberrypi.org/products/compute-module-3-plus-32gb/"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
apuarh | why do air conditioners need to pull air from the outside while fridges don’t, being that essentially what both do is bring the temperature of the air inside of a room? | Engineering | explainlikeimfive | {
"a_id": [
"egb86ar",
"egb5ypl",
"egb6jq5",
"egb6yy3"
],
"text": [
"A fridge and AC work in the same way: they cool one side and heat another. They both move heat, but actually do not move any air. That is, air is never exchanged between the outside and inside spaces. A fridge cools its internal space and heats your home. If the radiator were not insulated from the inside of the fridge it would have a net zero effect. You could think of the fridge as having its own little \"room\" inside. ACs cool your home and heat the outside air. If you ran an AC inside it would cool on one side and heat on the other meaning the room never actually gets any cooler. By sticking a hose to the outside world (or having the radiator hang outside for a window unit) it can heat the outside air, meaning you have a cooling effect on the room. I work in an electronics store and you wouldn't believe the number of people who think you can have an AC run without hooking it up to the window in some way. Retail truly has ruined my faith in humanity.",
"Air conditioners don't pull air from the outside and they work much the same way refrigerators do in that it uses refrigerant to cool down the air in the space. Since AC is trying to cool an entire house, you need a system of vents and fans to ensure adequate circulation of air through the system which is unnecessary in a small enclosed area like a fridge.",
"The only reason an HVAC system would bring in outside air is to prevent you from dying. Modern houses are very air tight, to conserve energy. Most operation of the HVAC system is recirculating, air from the return vents is processed and pumped out through vents. Some small fraction, controlled by a fresh air damper, is to bring in outside air. This positive pressure helps keep pollen out, and it gives you fresh oxygen. Other exterior vents, in bathrooms or kitchens, also push air out and the fresh air duct allows that to be replaced.",
"The part of your window unit outside your window doesn't suck in air. It's a metal grille that all the heat taken out of your house air gets put into, known as a heat sink, and it needs to be outside your house, or the heat just radiates out of the metal and back into the inside air. If you look behind your refrigerator you will find it's heat sink, a series of metal pipes that do the same thing for the fridge, radiating the heat taken out of the fridge into your house. If you open your computer you will also find a heat sink! It absorbs heat from the processing unit and then a small fan pushes the heat it radiates out a vent in your computer case."
],
"score": [
83,
24,
4,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
aq76vg | how do outside temperature readings in cars not be impacted by windchill, engine heat, or being baked by the sun? | I know it’s not linked to a satellite or radio reading as it reads the temperature from the garage and it changes fast once the car is outside. | Engineering | explainlikeimfive | {
"a_id": [
"egdutvf",
"egdvaun"
],
"text": [
"First, wind actually makes a thermometer more accurate. Windchill is something warm people feel because they want to be warm, and the wind makes the skin closer to air temperature, so we say wind chill because it makes our skin colder. But really wind makes things get closer to air temperature, and get to that temperature faster. For a thermometer, that means wind makes it approach the correct reading quicker, and it also means that nearby heat sources put less error into the thermometer. With that in mind, car manufacturers put the thermometer in the most windy spot of the car they can find. So yes, the sun bakes it and the engine heats it up, but as soon as you move the wind blows on it, and it quickly changes to the right number.",
"Well, technically the wind IS air temperature. You feel the chill because it's moving your heat (usually higher than air temperature) away from your body, not because it's colder than the ambiant temperature"
],
"score": [
36,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
aqcihk | How do things that rotate (drills, vehicle wheels etc) continue spinning indefinitely? | I'm trying to imagine the mechanism behind it, I tried googling it but what I'm asking I think is too vague for me to find, I can't understand how something can keep spinning without any cables or anything getting tangled on the inside I can't think of a better way to describe it than that | Engineering | explainlikeimfive | {
"a_id": [
"egf05yx"
],
"text": [
"Drills are usually driven by electric motors, an inner magnetic piece spins within (but separate from) a charged coil, there is nothing to tangle as the power is being transmitted via electromagnetism. Wheels spin on lubricated bearings, round or cylindrical pieces of metal coated in lubricant arranged around the circumference of the axle where the wheel hub connects. The bearings simply roll between the stationary part and the moving part to reduce friction. Place a pen between your hands and move your hands back and forth to roll it, that's the same action. There are other ways to separate spinning objects, but generally it's either electromagnetism or bearings."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
aqd12y | How does a diode work? | How does a diode allow electricity to pass in one direction, but not the other? | Engineering | explainlikeimfive | {
"a_id": [
"egf5wrn"
],
"text": [
"There are different types and constructions of diodes, but the most common type are created with silicon that is doped in two different ways to create P-type (positively doped, short one electron) and N-type (negatively doped, plus one electron) material. They are then put together with a depletion layer, which is like a dead zone that nothing can flow across. When a voltage is applied across that PN junction, current can flow only in one direction, once the forward voltage is overcome."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
aqjlwt | why cant we put dust sweeper to clean solar panels on a billion dollar machine ? | Engineering | explainlikeimfive | {
"a_id": [
"egggu0g",
"egggy8i",
"egglkak"
],
"text": [
"If you are asking about solar panels in space then there are a few issues specific to that environment * There is usually limited access to water in space vehicles , especially unmanned ones so dry cleaning is all you can hope for * Scratches caused by abrasion will reduce efficiency of the panel more than the \"cleaning\" would improve it * Space is hard on materials. That includes the brushes or whatever is used to clean/brush the panels. These would degrade in a short time. * The energy to power a \"windscreen wiper\" style automatic cleaner/brusher would be more than the savings even if the other problems were somehow solved. * Solar panels degrade in use in outer space over time for reason unrelated to dirt/dust. * The biggest issue that creates a need to clean a solar panel is bird droppings which are quite rare in space **Edit:** I forgot about planets such as Mars that have rovers etc. The natural winds can do a pretty good job of cleaning solar panels especially if they are mounted at an angle and if those winds are carrying dust (such as in a dust storm) then the dust would get replaced as quickly as it was cleaned off. Otherwise most of the deep space stuff I said still holds true for a planet based rover.",
"Well, first of all, Opportunity was never meant to last nearly as long as it did. It was supposed to do science for about three months after reaching Mars; it was never designed to operate for fifteen years. Two, the dust storm still would've taken it out. Its power died during the dust storm, not later because its solar panels were covered. Wiping it off would clean it for a little bit, but it was still too dusty to get enough power, and it would've gotten dirty again almost immediately.",
"For Opportunity and Spirit, If you really look at the history of the mars rovers, they actually considered it, they didn't install the sweepers because their analysis said it wasn't worth it, it would take 3 months for the dust to be an issue, and since their target was only 3 months survival, it would be extra weight and complexity for zero gain, maybe a net loss (gain past 3 months didn't count). Turns out they guessed wrong, it took 15 years for dust to be a problem. TL;DR: They guessed that it wasn't necessary to make it to 3 months, and thus wasn't worth installing. They were wrong, it took 15 years for it to be a problem, so it wasn't even a little bit worth it, they made the right decision."
],
"score": [
29,
15,
10
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
aqlnbr | Why do some staplers have two settings? | Engineering | explainlikeimfive | {
"a_id": [
"eggt0k8"
],
"text": [
"The setting that bends the staples outwards instead of inwards makes it easier to remove the staples afterwards, if you expect to need to do that. If you mean for it to be permanent, the “regular” inward setting makes for a stronger connection."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
aqr60t | How do functional prosthetic limbs work? | I see people that have prosthetic limbs that can actually move and grab things. How do they control it? | Engineering | explainlikeimfive | {
"a_id": [
"egi0swo",
"eghzuwm"
],
"text": [
"To expand on the previous comment a bit, people who need a prosthetic hand but still have some of the forearm still have much of the muscle involved in moving the hand. You can feel that yourself by gripping one forearm and moving that hand's fingers - they're moved by tendons running from the forearm. That means that if those tendons and muscles are at least partially intact, there's something moving when a person tries to move their nonexistant hand, so those can be used to reasonably accurately determine what they want to do. Even if the muscles (or the part of the limb that carried them) are gone, the nerves that used to trigger them are still there, though cut short, so with good enough electrode placement and some trial and error it's possible to pick up on those signals and operate the prosthetic with that information. Both of those can also be used by physically rerouting the nerve that would move the missing muscle and attaching them to another muscle (the pectoral is common), then having sensors read tiny movements or nerve signals when people try to move the missing limb and send directions to the prosthesis with that. I don't know if they've made fully functional prostheses using neural implants yet, but that's something that's been worked on in more recent years. If we know which specific spots in the brain have activity when each muscle is used, we can have a device monitor the brain itself and use that input instead.",
"Old school \"hooks\" are controlled by slight shoulder and arm movements. The new school cyborg style electro mechanical arms etc. Actually use nerve endings and tendon movement for input"
],
"score": [
6,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
aqs9t4 | Why do bottles have indents on the bottom | why do bottles of Lotions, Soaps, some drinks bottles and jars not have flat bottoms and their raised up in the middle | Engineering | explainlikeimfive | {
"a_id": [
"egi8ry7",
"egiauu9"
],
"text": [
"I haven't taken many physics classes, but I believe it relieves the stress on the bottom of the bottle when you squeeze it. This allows the bottle to be able to be squeezed easier and not have the bottom pop out. If the bottom pops out the bottle wouldn't be able to balance on a flat surface.",
"It is so that the bottle has a flat surface around the bottom of the perimeter. Less likely the bottle will tip over....."
],
"score": [
10,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
aqwv4o | How are tunnels built underwater? | Engineering | explainlikeimfive | {
"a_id": [
"egj3dlz"
],
"text": [
"Most underwater tunnels are dug out in the bedrock with a tunnel boring machine. They pressurize the tunnel during construction to keep the water out and further on dig in the bedrock so that as little water as possible will flow into the tunnel. However there have been a few tunnel designed using prefabricated concrete sections that have been lowered into a trench on the seafloor. This will reduce construction time and cost but you lose the protection of the bedrock overhead. There are also proposal for semi submersible tunnels where the prefabricated sections of tunnel will be floating close to the surface but tied down to the sea floor using anchors. This will make it possible to build undersea tunnels in very deep oceans. However you have more technology you need to rely on."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
aqz6d9 | Why are Super capacitors good replacement for batteries? | I seen this topic poping out in a lot of articles. | Engineering | explainlikeimfive | {
"a_id": [
"egjobna"
],
"text": [
"They're not good replacement for batteries in most cases. This is due to their high leakage current, in other words, their rapid self-discharge rate. They're good for storing energy over short periods of a few seconds to a few minutes at most. More than that, and the energy loss from internal leakage current tends to be significant."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
ar3yji | Why can't you get an electrical shock from the neutral | You can get a shock from the hot wire (obviously) but even if there's a load on the circuit, I was told that you won't get shocked by the neutral because it's basically the same as the ground. The purpose of the neutral is to complete the circuit, but I don't understand what happens to the electricity after it passes through the load. | Engineering | explainlikeimfive | {
"a_id": [
"egkmlrm",
"egkmx2j"
],
"text": [
"In a balanced 3 phase system, neutral should carry little to no current. Ground is actually fail safe. Ground is there in case the equipment becomes electrically charged. It will discharge to ground through the conductor, instead of you. In an unbalanced system, neutral will carry a current, and could shock you.",
"As someone who regularly wires things up while they are hot saying the word “can’t “ is a problem. Will you get lit up like you would with the hot, probably not. Will you get a little tickle, maybe. It happens more than you think due to leaky appliances and some fixtures. It’s this imperfect world that caused the building codes to split the neutral and ground at the disconnecting means and later to require arc fault in some instances. Remember voltage is the potential to do work and most neutral wires will have a few to up to 15 bolts on it. As long as your body completes the circuit it’s possible to get shocked. In other words I wouldn’t use my tongue to try it out."
],
"score": [
7,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
ar6t9b | What does the litre number represent when talking about car engines? | Etc 6l, 2l, 1.8l. I understand that the bigger the number the more powerful the engine but what is the number for? What's the engine doing with that amount of fuel? | Engineering | explainlikeimfive | {
"a_id": [
"egl5tf7"
],
"text": [
"It's not fuel capacity, it's the volume of the cylinders combined. The amount of air and fuel they can hold. So larger equals a bigger bang which means more power. In a very basic sense."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
ar6vty | how is concrete + steel so strong? What makes them a strong combo? | Engineering | explainlikeimfive | {
"a_id": [
"egl6s3x",
"eglbnoh"
],
"text": [
"Concrete has very high “compressive” strength, which basically means it can handle a heavy load pressing on it. However, it can easily snap like pieces of a Hershey’s bar. The steel inside the concrete increases the “sheer” strength of the pour, which basically prevents the snapping. Each part absorbs those dynamics of the load making the part’s job a little easier and the whole structure stronger as a whole. This synergy makes them a strong combo, but it is also that the thermal coefficient of both steel and concrete are nearly the same. This means that they will expand and contract at the same rate. If one expands or contracts faster than the other, their forces acting on each other can cause cracks, breaks, and voids.",
"This seems like a perfect opportunity for a link to Practical Engineering, which includes several examples of concrete failing under various types of load, and how the steel changes its properties. Why Concrete Needs Reinforcement URL_0"
],
"score": [
20,
6
],
"text_urls": [
[],
[
"https://www.youtube.com/watch?v=cZINeaDjisY"
]
]
} | [
"url"
] | [
"url"
] |
|
arag6h | Why do wind turbines have their generators way up high? | I've seen a lot of videos of wind turbines on fire and eventually throwing their blades. Why isn't the generator ground-based that's belt/pulley/driveshaft driven from the top? Wouldn't the added safety and salvagability of a failure make up for the lost efficiency? | Engineering | explainlikeimfive | {
"a_id": [
"eglumdu",
"egm7byz"
],
"text": [
"I am a steam turbine maintenance engineer, so while wind turbines aren't my area of expertise, merely thinking about a shaft that long makes me shudder a bit. So here are the main problems I see. 1) Expensive shaft. These shafts have to be extremely straight, else one end or the other is going to have its own significant orbit. You can see this by taking a bendy straw and bending the end slightly, then turn it, the bent end doesn't stay true to the center of the remainder of the straw. That would be a huge problem, you can't really have hardly *any* of this irregularity with the gears, or you will quickly end up destroying them, and gearsets like are used for this application are also hideously expensive. Due to the lower power output of a wind turbine's generator I have no doubt that the shaft and gear would end up costing far more than the generator. Then you also need to maintain this monstrosity. And what if you need to remove the shaft because it needs machining to be restored to roundness and straightness, while it runs the entire height of the tower? It'd be a good day for the maintenance crew. Bad day for whoever is writing the checks. 2) Supporting the shaft. I'm not sure on what the dimensions of the shaft would be to be honest, other than that it'd be very long. And you need something on the ground, and probably at intervals, to support the thing. In steam turbines a thrust bearing takes the axial (along the shaft) load, and journal bearings take the weight. You'd need quite a few more bearings, all of which would be somewhat expensive and finely machined (circular to within a thousandth of an inch or so, etc), all of which would require a supply of lubricating oil, and now that you're adding a ton of oil piping, pumps, etc to the equation it just gets messier in general. Though to be honest I don't know how much lubricating oil is already involved in a wind turbine, but based on what I've seen I'm pretty sure this would make everything a bit more complicated and annoying. At a guess modern wind turbines just just a simple submersion solution for lubrication, with the lower part of the gear sitting in oil, bringing more oil up to where it meshes with the driveshaft as it turns naturally. I'm guessing that because it's the simplest solution that works. 3) Oil and the revenge of the height. It's somewhat difficult to pump things up very far. Far from impossible, but it gets expensive in several ways. Now that you have so much more effective height where you need oil, you're going to need pumps to supply that need. And you'll need to maintain them. At this point we've added a lot of equipment to the unit, and that's generally a bad thing if said equipment doesn't pay for itself in some way. Anyway, those are what stand out to me the most. As far as a belt or pulley, I'm even less knowledgeable, but I don't think they'd cut it very well in this application, as far as material strength and longevity go.",
"To add to everything said already, one reason is that the blades need some sort of counterweight behind them to keep the center of gravity over the support tower. Might as well use the generator as the counterweight."
],
"score": [
14,
6
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
arfcn3 | How do the hundreds of satellites in Earth’s orbit not crash into each other? | Engineering | explainlikeimfive | {
"a_id": [
"egmsmby",
"egmsqhy",
"egn9w4t"
],
"text": [
"Most simply, the same reason hundreds of boats do not crash into each other in the open ocean, planning and a HUGE amount of space per object.",
"There are several reasons: Earth orbit is big, there is a lot of empty space. Satellites are small, so a direct hit is a pretty unique thing. Hitting another satellite is expensive. Not only do you lose theirs and yours, you also create a lot of rubbish which will be dangerous to others. So there is a reason not to let it happen. There is a registry which allocates orbits, so you know which orbit and slot you try to get into.",
"Space **very** *big*, satellites *very* **small**. Also, we put them where we don't think they will crash into each other."
],
"score": [
34,
7,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
argabs | How does a car shutting down automatically at a stop light/sign help with gas consumption? | Engineering | explainlikeimfive | {
"a_id": [
"egmzsf4"
],
"text": [
"The amount of fuel spent idling at an intersection, keeping the engine rotating are a slow speed with a light load, far exceeds the amount needed to restart the engine. Modern car engines start up very quickly."
],
"score": [
9
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
aritet | how do industrial potato peelers work ? | Engineering | explainlikeimfive | {
"a_id": [
"egnjupq",
"egnjus2"
],
"text": [
"Basically they are a drum with an abrasive on the inside - the potatoes are loaded in, the drum spins and the abrasive sides rub the skin off as the potatoes tumble around.",
"One such peeler I'm familiar with basically spins potatoes in a container with abrasive walls. Water flowing through the machine washes the skins away as they're removed and helps keep the potatoes moving about freely so that they all get exposed to the lining. Here's a link to a product page that explains it as well: URL_0"
],
"score": [
6,
4
],
"text_urls": [
[],
[
"https://www.nisbets.co.uk/what-is-potato-rumbler"
]
]
} | [
"url"
] | [
"url"
] |
|
arj9r2 | If the engines on a plane stopped mid-flight, to what capacity would the aircraft fly like a paper aeroplane? | Engineering | explainlikeimfive | {
"a_id": [
"egnke1h",
"egnvirs",
"egnkjyo",
"egnley3"
],
"text": [
"It won’t. All modern airliners are able to glide to a landing if all engines fail. Pretty neat!",
"Some real world examples: [US Air 1549]( URL_3 ) - bird strikes killed both engines shortly after takeoff [The Gimli Glider]( URL_0 ) - ran out of fuel at 41,000 feet. [Air Transat 236]( URL_2 ) - Glided over 60 miles after running out of fuel [And a whole list of other examples.]( URL_1 )",
"The best paper aeroplane I've ever built had a glide ratio of almost 50:1, meaning that it would travel 50 metres horizontally for every meter it fell while maintaining a constant velocity. My median paper aeroplane was closer to 5:1. A Boeing 747-200 has a glide ratio of 15:1 which is way better than half my paper aeroplanes but only half what a purpose built glider can be expected to do, and even that falls short of that one truly exceptional paper aeroplane I made.",
"Most modern airliners have a glide ratio of 1:15 to 1:20. So if they lost all their engines they might be able to glide for about 120 miles from cruise altitude. However current regulation does not require an aircraft to be within glide distance to an airport. Loosing all engines is quite rare, especially in a modern multi-engine aircraft. It have happened a handful of times. But as the pilots have a lot of altitude they can look for a suitable landing site and are able to do an emergency landing. So such an emergency is very survivable."
],
"score": [
20,
7,
7,
5
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Gimli_Glider",
"https://en.wikipedia.org/wiki/List_of_airline_flights_that_required_gliding",
"https://en.wikipedia.org/wiki/Air_Transat_Flight_236",
"https://en.wikipedia.org/wiki/US_Airways_Flight_1549"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
armrsj | What are the procedures and different types of headlights to not make them seem like high beams? | I'm talking about scenarios like [this]( URL_0 ) It's driving people insane these days with people replacing their bulbs and they become extremely reflective in our mirrors. So my question is, how do manufacturers know what angle to put these headlights on so they're safe for every car height and what are people doing wrong replacing their own headlights with ones that looks blue or really white? | Engineering | explainlikeimfive | {
"a_id": [
"egobdy9"
],
"text": [
"The blue white ones are HID headlamps. They use an electric arc to create a really intense light. THey're supposed to be used with [projector lenses]( URL_0 ) like this. Unfortunately projector lenses are pretty expensive to buy and install, and a lot of people don't realize that you need those lenses, so they install HID headlamps in [normal reflectors]( URL_2 ). The result is a massive splash of light that dazzles oncoming drivers. [Here]( URL_1 ) you can see the difference you get from a proper projector lens versus normal reflectors. THe idea is you have the headlamp height adjusted so that sharp edge of light doesn't go above road level so you get lovely bright illumination of the road surface, but oncoming drivers don't see any of that. TL;DR: People who want fancy bright headlamps are often cheap, don't do it properly, and everyone else suffers for it."
],
"score": [
3
],
"text_urls": [
[
"https://sc02.alicdn.com/kf/HTB1T4auSFXXXXc_XFXXq6xXFXXXS/AES-Auto-headlight-hid-bi-xenon-3.jpg_350x350.jpg",
"https://sportsautotech.com/wp-content/uploads/2011/09/pnp-vs-retrofit-cutoff-output1.jpg",
"https://www.bobdrake.com/images/Items/7/78-13028_lrg.jpg"
]
]
} | [
"url"
] | [
"url"
] |
arq5al | What is actually so amazing about the pyramids, and is their construction well understood? | I see so much stuff around "well the Egyptians couldn't have possibly built them with those tools therefor aliens/awesome science/ other conspiracies". Whilst the are spectacular and visually amazing, I dont understand what it so difficult about there construction outside of the raw physical labor side of things. Any insights on this would be cool, no anecdotes or opinions if possible; im looking for something objective, a journal or something. | Engineering | explainlikeimfive | {
"a_id": [
"egovjnm",
"egp22uo",
"egovpka",
"egp00rw",
"egphixm",
"egpikds"
],
"text": [
"No, you've got it right. There's nothing specifically miraculous about their construction, beyond the enormous focus of a society's resources on a single project. The architectural and logistical elements are impressive, but nothing that would have been conceptually unusual. It's just that they actually followed through. & #x200B; To some extent - we obviously have the technical ability to build perfect replicas now, but we don't, still, because of how much sheer manpower the task involves. That doesn't make it impossible, but it does make it remarkable.",
"The main thing is the pyramids are ancient... 4500 years old. Which meant they were already 2500 years old to Julius Caesar. So they were older to him than he is to us. Their construction is understood, it just took lots of manpower.",
"Nothing is outside the law of physics it is just the sheer mass of the stone used to construct the pyramids that is so exceptional. The Great Pyramid of Giza was the tallest structure till Lincoln Cathedral was constructed in 1311. The pyramids required a huge amount of manpower to construct and they were carefully aligned, but due to the properties of stone a pyramid is actually one of the few tall buildings you can construct out of stone - URL_0",
"They’re also aligned with Orion’s Belt or something apparently which is kinda impressive if true",
"These are great questions. The best I can give you is that if you were to transport a stoneage human or ancient Egyptian to the present day, they could keep up in school, use an Iphone, drive, and read schematics to build a skyscraper. In terms of mental and physical ability, we are essentially the same people. Our advantage today is that we have more advanced technology, but that is the only difference between us. When someone says \"we were too dumb!\" or \"we didn't have cranes back then!\" is insulting both our ancestors and our modern selves. The answer of how the pyramids were built is incomplete, but we have a *lot* of information. The Egyptians were the Twitter-shitters of the ancient world, they wrote down EVERYTHING, including their petty complaints and gossip about each other. The details of how the pyramids went up have been lost, but we know who the architects were and when it happened; we also have a lot of incidental information that can help us piece together what probably happened. I'll give you two documentaries that are youtube friendly. Please mind that these are NOT documentaries in the sense of established fact, they are best-guesses based on available information. One, general background info [PBS]: URL_1 Two, a plausible but unproven theory: URL_0 Both are good and make reference to research and records rather than aliens, though I stress again that both are somewhat speculative.",
"Even with trucks, cranes, and bulldozers, it takes a long time to build a structure of that size. The blocks weigh 2.5 tons each, on average; not exactly easy to lift up. Millions were used in the great pyramids. Just moving those from the quarry to the building site without machinery is extremely impressive."
],
"score": [
79,
18,
16,
5,
4,
3
],
"text_urls": [
[],
[],
[
"https://youtu.be/f5gjbC9AuEo"
],
[],
[
"https://youtu.be/d83mn1yxCHc",
"https://youtu.be/5FINqueRH58"
],
[]
]
} | [
"url"
] | [
"url"
] |
arr4zc | why are some firefighting suits silver and some nomex? Is one “better” than the other? | Engineering | explainlikeimfive | {
"a_id": [
"egp8ate",
"egp49xr"
],
"text": [
"There are three general types of firefighting 'suits'. Some fires burn very, very, very hot. Like a big pool of jet fuel on fire! Even though firefighters stand several feet away, the heat of the fire is radiating toward them like light waves, like a very hot heat lamp. Silver suits reflect this heat, allowing the firefighters to operate nozzles, hoses and fire trucks from several feet away to put the fire out. They work from a distance of many feet to put the fire out. These silver suits aren't as durable, get dirty easily, and wouldn't stand up to constant rubbing and scraping. These suits are usually only necessary while putting out a very large outside fire, like airplane fuel, oil fire, etc. Other fires are hot, but not nearly so hot. Like an enclosed room on fire. Firefighters wear suits with three layers - an outer fire resistant and abrasion resistant layer, an insulating later inside that just like a winter coat, and a vapor barrier with that kinda like a rain coat. These suits protect firefighters from hot (but not super hot!) fires, are also very durable allowing them to crawl around in rooms with many broken/sharp objects, and also protect them from the steam that is produced when their fire hoses put water on a fire. These suits can be black, yellow, tan, white or whatever color the department chooses. These suits are very warm (like a snowmobile suit!), so firefighters can get tired and dehydrated very quickly, and generally have to rotate in and out of a fire every 30 minutes or so. The third common type is just one or two layers of fire resistant fabric like Nomex or heavy cotton. This suit is worn when fighting fires outside, like a forest fire. Many times in this situation, firefighters work for many hours or even days at a time, and may be hundreds of feet away from the actual flames. These suits are \"just in case\" things go wrong or the fire gets too close (although some firefighters may be right up close to the flames for a time), and allow firefighters to work for many hours on days that can be over a hundred degrees while they are doing hard work. Some departments make these suits thicker with multiple layers, while others basically just have one thick layer of cotton. It is important to note that NONE of these are \"fireproof\". If any are exposed to direct flame for a period of time, they will all fail. And even if they don't fail, the temperature inside the suit will eventually be the same as the temperature outside the suit.",
"Nomex is to resist flash-fires — short bursts of flame. The silver-colored ones are to reflect heat away from the firefighter. They’re different applications, so they’d each have their uses."
],
"score": [
11,
8
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
as2w7y | Why is it called Alternating Current and Direct Current instead of Alternating Voltage and Direct Voltage? | Engineering | explainlikeimfive | {
"a_id": [
"egrdna3",
"egrdqko"
],
"text": [
"Both are entirely correct, as the voltage change is what drives the current change. Back in the early days of electricity, it seems more members of the public understood the notion of current.",
"First: sorry for my bad English, it's not my forst language and I may make some mistakes in naming physical terms. I think it's because the actual \"electricity\" is electron movement inside the conductors. Voltage is the difference of electrical potential at the ends of the conductor. It's like the wind goes from places where the air pressure is higher to those where it's lower. So with the voltage alternating, the electrons also change direction, which means both names could be actually correct. It's just that current is the actual \"electricity\", not the voltage."
],
"score": [
8,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
as75vq | Why do planes have doors to their left? | I've never seen a plane that has doors to its right. I'm curious why? | Engineering | explainlikeimfive | {
"a_id": [
"egsc1av",
"egs9ezl",
"egsdjpi"
],
"text": [
"Having passengers board on the left is probably a continuation of the nautical practice, where the left is the port side of the ship. In old ships, the steering paddle was on the right (starboard), because most sailors were right-handed. As a result, they had to dock on the left side.",
"The passengers board on the left. The maintenance crew comes in on the right for food deliveries and cleaning crews",
"Imagine if different planes have the door in different spots. The gates at the airport would be facing the wrong way for a lot of them so they'd have to have left side and right side gates. Then all the airplanes would have to have a little arrow on the dashboard like cars do to show what side the gas tank is on."
],
"score": [
29,
7,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
asb4mq | When you take your vehicle in to have the alignment adjusted what are they adjusting? | I am changing the steering rack on my 1998 Toyota Corolla. I know you are supposed to get an alignment job after this process, but I am particularly concerned about the jam nut placement holding my tie rods. The rack I bought fits, but isn't a refurbished part. Do they adjust that jam nut? Thanks! | Engineering | explainlikeimfive | {
"a_id": [
"egt0khr"
],
"text": [
"There are three primary adjustments: camber, caster, and toe-in. The caster angle is the angle at which the front wheels turn from side to side. You might think this was 0˚, that the wheels turn from side to side around an axis that's perpendicular to the pavement, but that's not the common practice. A little positive caster causes the wheel to tend to return to \"go straight\" when driven on a level surface. Camber is the angle that the front wheels are held at when pointed straight ahead. Negative camber means the tops of the front wheels are closer together than the bottoms. A little negative camber improves traction in high speed curves, at some cont in tire wear while driving straight. Toe-in is the adjustment that tie rods are for. If the front of the front tires are closer together than the back of the front tires, the car has positive toe-in. Positive toe-in improves straight line stability at the cost of cornering reaction (you have to turn the wheel farther for the car to start to turn). Negative toe-in (called toe-out) is sometimes used on Formula1 cars to make them corner faster, at the expense of twitchy behavior in straightaways."
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
ashpnt | How did 200 year old cities modernise to what they are today? | How did much of the old cities in the world (e.g Rome, Paris, New York, London) go from a city in the 1800s to a modern 21st Century city, incorporating much of their modern infrastructure like traffic lights, electrical/sewage lines, paved roads instead of cobble, high rise buildings etc.? | Engineering | explainlikeimfive | {
"a_id": [
"egukhii"
],
"text": [
"It did not happen instantly. A city that has kept up with the times used 200yr old tech 200 yrs ago; 100 yr old tech 100yrs ago, etc. Its best to think of cities as a living thing. Go to any major city in the world and the one thing they all have in common: construction. They are constantly upgrading their infrastructure to modernize and keep with the times."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
asxhej | Why do 110v electrical plugs in North America have one prong that is wider than the other? Its alternating current...so it doesn't matter which way the plug is inserted into the socket. Am I missing something? | Engineering | explainlikeimfive | {
"a_id": [
"egxeh7m",
"egxe8xo",
"egxej6d"
],
"text": [
"Its done for polarity. We use AC, but there is still a hot wire, and a neutral wire. If you touch the hot wire you will get a shock. Touching the neutral wire is not as dangerous. If there is no load on it, it should not shock you. The tall slot is neutral, the narrow slot is hot. For example, on a light bulb, the base of the bulb should be hot, and the threads of the bulb should be neutral. This is a bit safer as you could possibly touch the threads when it is in operation. Touching the neutral is ok. Touching the hot wire would give you a shock. It would be impossible to touch the base of the bulb in normal operation. In order to ensure this, the plug must be inserted correctly, so some devices have one plug wider than the other to make it impossible to put in backwards. Another idea. Lets say you are designing a toaster. You would have the hot go into the switch, and stop (when the switch is off, so the heating elements do not have any current. If you reverse the polarity, now the heating elements have current, and the wire inside the toaster leading to the switch doesn't. This is very dangerous if you were to stick a knife into a toaster to unjam it. (a toaster oven should have a ground, which would make plugging it in 'backwards' impossible, and provides additional safety, but this is the first example I could think of. There are lots of smaller devices without a ground, but polarity still matters for the same reasons.",
"One side is hot, the other is neutral. The neutral is bonded to ground in the electrical panel. In a 2 prong plug, the larger blade ensures the correct polarity. In a lamp socket, the shell of the socket is always neutral. The center contact is always hot. The switch disconnects the wire to the center contact. If plugged in backwards, the shell would always be hot, leading to a shock hazard. Any device with a switch on the hot wire would be energized at all times if wired backwards. The polarized plug is a means of protection on 2 wire devices.",
"One line is still \"hot\" and the other is neutral even though the power within it is alternating. Basically the hot is connected the source and the neutral is not. If the hot line is broken, there is no power in the system. If the neutral is broken the power stops but is now dangerous as it's still connected the source but looking to complete that circuit. Systems that are fused have the fuse connected to the hot first as if there is a short it kills all power to the whole device. If it was first on the other neutral pin and it shorted, then someone stuck a screwdriver inside there is potential for electrocution A simple lamp will have the switch attached to the hot side, so if you turn it off while you change the light bulb and stick your finger inside you won't be electrocuted. TLDR: one pin still has voltage while the other does not"
],
"score": [
12,
3,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
at548o | "Hop Test" that SpaceX is talking about | Engineering | explainlikeimfive | {
"a_id": [
"egypdd5"
],
"text": [
"The Hop Test they did with the Falcon was to launch a few hundred meters into the air and then land it. The first \"empty hop\", only went 2m. The last test was like 800m up and down in 1-2 minutes. They are starting to talk about Hop Tests for the BFR/BFS/Spaceship with a 500m like max altitude, based on license filings."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
atjas3 | How does a mechanical tachometer or speedometer convert revolving motion into a steady reading? | Engineering | explainlikeimfive | {
"a_id": [
"eh1gqnz"
],
"text": [
"Flexible cable geared to transmission output shaft leads to the back of the speedometer. At the end of the shaft there is a disk shaped magnet that fits inside an aluminum cup. As the magnet rotates faster it induces a field in the cup causing the cup to drag along with the magnet. The faster the magnet rotates the greater the drag force. The cup is attached to a shaft that is attached to the speedometer indicator needle which has a spring applying force towards zero. As the car speeds up the drag force gradually overcomes the spring and the needle moves up the scale."
],
"score": [
13
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
atmxsi | How do bunker busters penetrate then blow up? Instead of just blowing up on impact? | Engineering | explainlikeimfive | {
"a_id": [
"eh23oic",
"eh2bkud",
"eh293r5",
"eh2ksw6",
"eh2lyvf",
"eh2901q",
"eh2shm6",
"eh2tz19",
"eh2atnf",
"eh3oizs",
"eh2xer7"
],
"text": [
"The explosives used are not set off by impact but need ignition. The initial impact of hitting the target sets a fuse, delaying ignition so that the buster can dig in from its momentum before exploding.",
"Its all about the fuse. Pretty much every explosive in use these days in impact resistant, that's why TNT replaced dynamite and nitroglycerin, they were just awful to work with as they would explode under moderate shocks(or extremely light for nitroglycerin). This means that you can fill your bomb with explosives and it won't detonate until the detonator(tiny triggered explosion) goes off. To get through you would want to encase your bomb in a strong material like steel and potentially give it a nice hard/dense tip like tungsten carbide to punch through the outer layers of armor. You also want it to be really heavy but really narrow so it applies a lot of force over a small area creating a high pressure. There are a bunch of triggers that can be used, sometimes you want it to be timed from first impact, sometimes you want it to punch through a fixed distance of material, sometimes you want it to hold off detonation until a short distance after it has stopped going through material so its in the hollow bunker. You'd generally want to put your fuse on the back so it won't get squished by the initial impact. You can see this on the [WWII Disney Bomb]( URL_0 ) with its steel casing around its high explosive filler and a wire sticking out to the side to start the timer. The Disney Bomb was also rocket boosted so it would hit the ground with higher speeds and penetrate further.",
"So, specialized penetrator bomb bodies do not have a fuze in the front, instead they come to a solid point. They have a very fancy electronic fuze in the rear, which the pilot can actually 'talk' to, and tell exactly what to do, based on what the guys on the ground tell him. In order to get the penetration, before they drop it, they tell the fuze to 'wait' (in milliseconds), after it senses that it just hit something using its impact sensor, before it sets off the bomb.",
"Most bombs these days use the fuze fmu-139 as pictured here URL_0 on the back you’ll notice various settings depending on the mission profile you are flying. High drag settings for low level bombing and low drag for high altitude strikes. Bombs are quite stable and can be dropped from very high altitude and if the pilot hasn’t armed it will hit the ground in a relatively safe state. These fuses are usually fitted up the bum of the bomb. On the top middle of the bomb is a little wind turbine that deploys when the bomb is dropped and the fuze won’t arm unless the bomb is travelling a minimum speed. On the nose you usually have a proximity sensor or solid nose that can be fitted. I used to build bombs for a living many years ago. I’m a little rusty but if you have any specific questions I’ll try and answer them.",
"Bunker busters are designed to measure acceleration (or deceleration in this case) once initial impact occurs (impact activate the warhead). Once deceleration \"freezes\" that means the missile is either stopped or in an open room, thus triggering detonation at the optimal time of being in the cavity of an underground room.",
"There are also bunker busters that are basically a double warhead. the first is the exterior layer which will penetrate a first layer, releasing the second smaller warhead that was inside the first to reach the room beneath the surface.",
"Ahhh, my kind of thread. To the OP, I was a 2w1 weapons loader in the airforce, and know all about bombs, missiles and munitions in general. If you have any questions, feel free to ask. Also, the top post by r/kahBhume has already answered your question pretty sufficently. I could add more, but that is the gist.....Actually, I cant help myself. What happens is a few things. The bunker busters that we currently use in the USAF and most militaries in the world, use what are known as JDAMs (Joint Direct Attack Munitions). They are just dumb bombs that come with fancy equipment to make them super smart and capable, versus their standard configs. What the top poster mentions, about the fuse and delayed ignition, is partially true. I mean, they did you a ELI5 explanation, but to give more, the fuze has a delay element itself known as an INITIATOR. This initiator arms the fuse (per se) when the bomb is falling from the sky. Once the fuze is armed, it starts a timer (set by the type of fuze and mission requirements) that does exactly what the top poster mentions... Anywho, time for some fun stuff. While working in Kuwait, I had the opportunity to snap these pics of what Bunker Busters did to a \"fortified\" bunker, during Iraq War I. [ URL_0 ]( URL_0 ) What is awesome about those pics, is that the inside of the structure was fairly unharmed. The bomb hit its intended target well within its parameters, and pretty much left everything else inside unharmed. Even the structure itself is fairly well off, all things considered. And that is what makes bunker busters, aka JDAMs so fucking cool. They are very strategic weapons, that can do far more than their \"dumb bomb\" variants.",
"Time delay fuse and penetrator housing. There are myriad ways one can initiate your time delay. Typically for reasons of safety - multiple inputs must be tripped to initiate the delayed detonation sequence. Sometimes PFC fuckstick drops a god damned bomb on the load line and it would be bad if the bastard went off just because a shock sensor was tripped. Now all of the preceding assumes your penetrator can, well, penetrate. Meaning not pancake on impact. Inertia translates into depth. You gain inertia with mass and speed (which in a free fall situation is limited by height and the terminal velocity of the butt plug you want to send to mom down in her bunker). All of that means you need a penetrator housing that can A > Survive an impact which on its own, without detonation, is gonna fuck shit up B > Shield your fuze assembly and any other goodies microseconds away from vaporization, granted this stuff is in the ass of the bomb but pancaking introduces the ends of the weapons together in a rapid and uncontrolled fashion. This kills the bomb. C > Shaped in such a way so as to maximize terminal velocity while allowing satans sounding rod to dig home. This is a balancing act. The company I work for has some serious secret sauce we throw into nose assemblies that uncle sam drops on camel fortifications to the tune of 180K per assembly. Which is just the tip. The explody bits are some other fucks problem. I would love to tell you the alloys we use and all the fun shit I get to do to them so that the USA can reach out and fuck anyone under not more than 20m of reinforced concrete but ITAR regulations and my own desire to not get raped by angry GITMO detainees means I am gonna stop here. SO in summation: Buy my shit and go fuck the sun.",
"Shells/bombs designed to penetrate armor are often a two stage solution. The first stage does the \"easy\" part with simple kinetic energy then a secondary charge (usually shaped) goes off to defeat inner defenses.",
"It thinks of random things, like baseball, and star wars. Sometimes, that still won't work and it will go off early, leaving the bunker on the edge. At that point, it usually has to go in for some manual stimulation to make sure the bunker is satisfied.",
"From Wikipedia:The traditional fuze is the same as a classic armor-piercing bomb: a combination of timer and a sturdy dynamic propeller on the rear of the bomb. The fuze is armed when the bomb is released, and detonates when the propeller stops turning and the timer has expired. Modern bunker busters may use the traditional fuze, but some also include a microphone and microcontroller. The microphone listens, and the micro controller counts floors until the bomb breaks through the desired numbers of floors. ATK is working on a Hard Target Void Sensing Fuze (HTVSF) for 2000 and 5000 pound weapons to explode when they reach an open space in a deeply buried bunker.[8]"
],
"score": [
5221,
356,
128,
33,
13,
8,
8,
7,
4,
3,
3
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Disney_bomb#/media/File:Disney_Bomb_Diagram.png"
],
[],
[
"http://cjchivers.com/post/16494763207/know-your-weapons-left-the-fmu-139-bb"
],
[],
[],
[
"https://imgur.com/a/IpGiDgh"
],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
atnijp | why do american fuel pumps have one nozzle for multiple fuel selections? surely they'd all mix | URL_0 | Engineering | explainlikeimfive | {
"a_id": [
"eh27wn0",
"eh282li",
"eh28m6j",
"eh28z1p"
],
"text": [
"It'll mix, but not a lot. Getting a little bit of 87 octane in your full tank of 93 octane isn't going to make a bit of difference. & #x200B; However, there are different infrastructures, pumps, and hoses for gasoline vs diesel. & #x200B;",
"They do mix a little bit. Whatever octane was pumped previously will be filling part of the hose when you go to purchase your own fuel. So, if the person before you bought 88 octane and you buy 93 octane you are going to get maybe half a liter of 88 octane before you start getting the 93 octane you paid for. The price difference comes out to a few pennies and there is no harm to the car. The vast majority of the fuel you pump (assuming you're filling a decent fraction of your tank) will be the correct octane. There would be much more of a problem if gasoline and diesel were mixed so you'll never see a single hose for those two types of fuel.",
"Pipelines do this too. They used to seperate products in pipelines with plugs called pigs, but they realized it didn't matter and stopped.",
"Actually, what you get IS a mixture of fuels, by design. In the pump, they combine a couple different grades of fuel in varying amounts to produce the multiple grades they sell. There may be some residue of a different grade in the hose, and other posters have already addressed that issue. Diesel fuel is usually dispensed from a separate pump."
],
"score": [
9,
5,
4,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
atve2v | How do spacecrafts not melt off through launch if the temperature in the exosphere is 1700 degrees celsius? | I had an argument with a flat earther, and they told me to google the temperature in the exosphere, asking how come every launch goes so smoothly *if* temperatures are really so unbearably high and nothing could survive through them. I wasn't sure how to go about explaining this. EDIT: thank you all for replying! Honestly, the flat earther is my mom, she keeps telling me she isn't one, saying things like says "according to *their* theories", all the while claiming to question the reality of the situation since she herself can't literally go and check if the earth is round. It frustrates me to no end since she used to be such a logical, easily comprehending person. Now its all about "their theories make sense if you read them" and "i just haven't seen proof with my own eyes". I tried explaining to her along the lines of what you all said, which completely makes sense to me, but doesn't make much difference because she just says it still doesn't make sense to her. She says things like: "If you google the exosphere temperature, why would it say such a high number if it doesn't even truly affect anything?". I've tried giving examples like ships seeming to "sink" below the horizon and the sun setting in the same way, but she claims she never sees the ships sinking and the sun just orbits around the flat earth according to *THEIR* theory. She likes to say she is just sceptical and doesn't fully believe either idea. Anyhow, this was super helpful for me to understand so thank you everyone, next time she starts this bs again i'll have an informed and factually correct response. EDIT 2: grammar and cohesiveness EDIT 3: Also apparently the flat earth theory has a made up answer for everything if you look at their diagrams, with explanations for seasons, gravity, time zones, you name it. Everyone's responses have been great but theres no reasoning with someone who chooses to be sceptical about the whole system. | Engineering | explainlikeimfive | {
"a_id": [
"eh3o73e",
"eh3nzcw",
"eh401fl",
"eh3mph0",
"eh3n4w8",
"eh4ckcy",
"eh4cwjz",
"eh3oqk5",
"eh47a01",
"eh3n72p",
"eh44rdc",
"eh4ji2s",
"eh4f7o4",
"eh4cr09",
"eh46xed"
],
"text": [
"For ~~temperature~~ HEAT in the atmosphere you can look at [this chart]( URL_1 ). As you can see, generally tends to decrease, and at no point is it hotter than at ground level, except when you factor in sunlight, where ~~temperatures~~ HEAT may reach 128ºC. Even then, that's VERY far from the 1700ºC this guy mentions. This leads me to think he's talking about heat during reentry, not during ascent. How does stuff (the pieces actually made to survive it) survive reentry? There's multiple things to factor in: * You're coming at ludicrous speeds, this compresses air and heats it up (it's not due to friction, like most people believe) * That same compression can separate the heat from the ship (Depending on the general shape anyways, not all of them do this), thus you don't need to survive the full temperature, just a fraction of it. Even then, there's multiple ways to survive such temperatures: * Ablative shielding: A shield made of little particles that will fly off when hot enough, thus taking the heat away with them. * High temperature resistant materials: Carbon-Carbon and ceramics (both used on the Space Shuttle) come to mind, they have really good heat absorption capabilities. They'll absorb and store the heat and slowly dissipate it away. [This video shows the ceramic tiles in action.]( URL_0 ) * Active cooling: Used on some rocket engines and proposed for the SpaceX Starship, cool liquid circulates trough the material, absorbing the heat and carrying it away. Hope that clears it up. **Edit, adding extra stuff to complete this post:** There's temperature, and there's heat. * Temperature is a measure of how much energy individual particles have. * Heat is a measure of how much energy is contained by all the particles in a given volume. The thermosphere and exosphere are incredibly sparse (as in the opposite of dense), so even though individual particles hold a lot of energy (Temperature), there's not enough of them in a given volume to effectively transmit that energy to a body (as heat). Given this conditions, the only way those particles have of heating something up is trough radiation, and countering this is as simple as making them out of \\[heat\\] reflective materials. You can actually calculate how hot sunlight can possibly make a bulk object at a given distance from the sun, using the [Stefan–Boltzmann law]( URL_2 ). It's a simple formula and I don't think it breaks the 5 years old theme. We need to know the equilibrium temperature of a body, which is the temperature in which the body radiates heat at the same rate it gets heated up, in this case by the sun and particles in the exosphere/thermosphere. & #x200B; Equilibrium Temperature = Temperature of the sun (580ºK) \\* (radius of the sun / distance to the sun), so: T = 5800K \\* (695000km / 1.5x10^(8 km)) T= 395K 395K = 122º Celsius, or 251º Fahrenheit. Your satellite is not going to get hotter than about 250ºF. & #x200B; **Super important edit 2:** & #x200B; /u/RapidCatLauncher, /u/deja-roo and others (tagged only the two of them because they actually explained stuff) have pointed out that the definitions provided for temperature and heat are not accurate. While I do agree with that, the reason I left them uncorrected is because I do believe they explain the stuff better than the real, factually accurate definitions for those two words. I of course invite you to read their corrections in the replies below (that's why I tagged them in the first place). Lastly, /u/NogodsaMan provided the best TL;DR: > Since other explanations seem way too confusing, the temperature can get to 1700 C, but theres not a lot of particles at that temperature (thin atmosphere) and so the hot particles are barely actually transferring much energy since there’s so few of them to do so & #x200B; & #x200B;",
"What everyone else said about heat transfer in extremely rarefied atmosphere is correct, but the bigger issue is why argue with a flat earther? There's literally no facts, evidence, proof, etc. that would change his or her mind. On the other hand, I'd ask how they know the exosphere is 1,700 degrees C. I assume it's from some information they learned online or in a book that was determined and published by some sort of science-based organization (NOAA, NASA, etc.). Unless they went up to the exosphere and took some measurements themselves, they're relying on data provided by an organization that undoubtedly reports the earth is not flat. Why would they believe that information and disbelieve the information those same organizations say about the earth being a sphere?",
"if you put your hand in water thats even 105degrees, you'll be extremely uncomfortable and any higher will risk burns. & #x200B; Yet, you can hang out in a sauna at temperatures upwards of 190degrees Farenheit, even though it contains a small amount of dissolved water (humidity), the lower density of water in this situation demonstrates how it reduces the ability to transfer that heat to an object. & #x200B; As for proving air pressure drops in the exosphere, well, that can be demonstrated for yourself with as little as an elevator trip up a tall building. Obviously something more extreme starts to risk our health, you cant exactly stick your head out the window of an airplane or something, so you would have to trust the pressure instruments at that point.",
"The pressure is so low that it will cause the molecules to be extremely spaced apart. Thin air does not transmit heat very well.",
"Temperature is effectively a measurement of how fast particles are moving. Or the kinetic energy they have. Since there are so little particles in the upper atmosphere the heat will hardly transfer. Although the particles themselves move very quickly.",
"I'm just wondering why she believes the scientists and engineers who say that exosphere temps are 1700C, but doesn't believe the same scientists and engineers when we say Earth is a fuckin sphere.",
"A more ELI5 way to show the difference between temperature and heat is to look at your oven. Have you ever lined a pan with aluminum foil? You can reach into the hot oven and pinch the foil that dangles over the edge of the pan and it will only feel a bit warm. But if you touched the aluminum pan next to it, it would burn your hand instantly. They're the same material at the exact same temperature. The difference is the *quantity* of heat in each object. Temperature is just the average heat in the material; it doesn't tell you how much total heat is in it. A larger mass of aluminum like a pan carries much more total heat than a thin film of aluminum. I have no idea what the temperature in the exosphere is, but even if it's way higher than at the surface, the air is so thin up there that it would carry very little total heat.",
"Firstly , spacecraft don't launch through the exosphere. The exosphere is the outermost layer of Earth's atmosphere, and it begins hundreds up km up, depending on solar activity. By the time a spacecraft reaches that altitude, it's already in orbit, and well past launch. All human activity takes place below the exosphere. Secondly, the exosphere is so thin that for all intents and purposes, it's a vacuum. It's a better vacuum than the most perfect vacuum we can create here on the ground. Temperature is just the average measure of the kinetic energy of gas particles. So yes, the particles in the exosphere have a lot of kinetic energy, which means that they have a high temperature, but there are so few of them there's basically no energy transfer. The actually temperature of objects in this part of Earth orbit is roughly 121 degrees Celsius (250 degrees Fahrenheit) in sunlight and -157 degrees Celsius (-250 degrees Fahrenheit) not in direct sunlight. Yes, that's right. Objects in this part of space are hundreds of degrees *below 0* unless they're in direct sunlight. And finally, stop arguing with flat earthers. They'll never change their minds and have no intention of having any rational discourse. You're just banging your head against a wall. & #x200B;",
"She can easily check, she just chooses not to. She may have noticed that her favorite shows are on TV earlier in New York than San Fransisco. The reason (easily verified by watching any live outdoor programming) is that the sun sets about 3 hours earlier in NY than SF. It rises in the east, peaks at noon and sets in the west. It does this everywhere in the world (again, easily verified without leaving the living room). So the question is, how does light work so that it can't be seen from flat New York when it is directly over flat Tokyo and that \"due south\" rotates 360 degrees every 24 hours? With a bit of patience (and the need to leave the living room), she could chart where in the sky the sun, moon and one or two planets are over some period of time. If she thinks that Kepler was a fraud, she can easily check this herself but she *chooses* not to. Now here's the bit that might make it easier for you. All scientific models are just that: models. If you are framing a house or playing marbles, a flat earth is a totally useful model. If you are traveling very long distances (sailors, pilots etc.) or researching space, the flat earth is a very inconvenient model and a sphere is better. If you are modeling global ocean currents, even a sphere may not be accurate enough as you need to account for the bulge due to spin. It is not that you *can't* model the earth as flat and light as curved, it just requires the use of some awkward geometries and making otherwise simple things like calculating the position of the sun or moon, the range of a marine radio or the shortest distance from New York to Tokyo really, really hard. As long as your mom doesn't have to do any of those things then her choice of model is not an issue.",
"It's actually impossible to measure the temperature of the exosphere because everything is so spread out. Individual particles might be 1700 degrees, but the air itself is not heated uniformly as it would be when you step outside from your house because of the space between those particles. I would also argue that not every space launch \"goes so smoothly\". I would also point out that these spacecraft are designed to endure extremely high temperatures. NASA's thermal protection system for its space shuttle program protected the shuttle from re-entry temperatures of up to 1,650 degrees Celsius (and that excludes the boundary layer of air beyond the surface that could rise to 5,500 degrees Celsius.",
"Ask her to pour boiling water into two cups. One a metal or ceramic cup, and one a Styrofoam or double-walled thermos cup. Then hold one in each hand - wrapped around the container, no handles - and see how long she can hold them. The thermos is low density, low thermal transfer, the metal or ceramic is high density, high thermal transfer.",
"\"Google it!\" \"Eeerm... Okay... Sure!\" URL_0 > The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Despite the high temperature, an observer or object will experience cold temperatures in the thermosphere, because the extremely low density of gas (practically a hard vacuum) is insufficient for the molecules to conduct heat. A normal thermometer will read significantly below 0 °C (32 °F), at least at night, because the energy lost by thermal radiation would exceed the energy acquired from the atmospheric gas by direct contact. In the anacoustic zone above 160 kilometres (99 mi), the density is so low that molecular interactions are too infrequent to permit the transmission of sound. I didn't know disproving flat earther nonsense is as easy as reading Wikipedia. 🤔",
"If earth is flat where is the edge?",
"I just want to thank you for properly using the word 'affect'. As a partial answer / parallelism to help illustrate in ELI5 fashion the difference between temperature and heat: The exosphere is so 'dilluted', as in it is so thin out there, that the temperature of its particles may be high but the heat they store is low. Compare to putting your hand inside an oven at 250ºC (482ºF), which is bearable for a while and dunking your hand in boiling water (100ºC - 212ºF) which will make you scream in pain right away. This is because air in the oven is less dense, it is thinner than water. So the heat it transmits is lower, though the temperature is higher.",
"Everyone else has mentioned the answer for the exosphere. Why hasn't anyone talked about how to directly observe the earth being round? There are several ways to do this, the simplest is to go to a port or harbor and watch some ships go over the horizon. The ships appear to sink as they pass out of sight which is caused by the curvature of the earth. Alternatively, you can get a telescope/binoculars and a relatively tall building. Use the telescope to compare how far you can see from the ground to how far you can see from higher up inside the building."
],
"score": [
630,
394,
72,
27,
23,
21,
15,
14,
13,
10,
8,
8,
6,
4,
3
],
"text_urls": [
[
"https://www.youtube.com/watch?v=Pp9Yax8UNoM",
"http://acmg.seas.harvard.edu/people/faculty/djj/book/bookchap2-8.gif",
"https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law"
],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[
"https://en.wikipedia.org/wiki/Thermosphere"
],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
au1c7t | How does the pre-flight airplane check actually ensure that the plane is safe to get up in the air again, and what do the pilots check? | I'm a fearful flier and I've been doing a lot of research lately to understand all the aspects because I want to fly again. My main concern is the plane not being able to take off and sudden electronics failure. & #x200B; Having said this, I was wondering how does a simple superficial check of the outside of the plane ensure that the electronics will not fail, or that the engines will not explode mid air, or that it won't stall all of a sudden? | Engineering | explainlikeimfive | {
"a_id": [
"eh4ut48"
],
"text": [
"Electronics can fail in flight, and engines can also fail. The key thing you need to understand it that you will not die if this happens. You probably won't even know about some failures. This is because airplanes are engineered with resilience and redundancy. There is no one part on a plane that can fail and have everybody die as a result, that's the \"no single point failure\" criteria. If an electronic box fails, the pilots switch it off and use the backup box. None of the passengers ever know that the box failed, it just gets replaced as part of routine maintenance. Even the pilot is redundant, one person can fly the plane if the other dies. I've been on a plane that had an engine explode, it was called a \"compressor stall\". We had to land short of our scheduled destination and transfer to another plane. The airline was mostly concerned about parking the plane so we wouldn't see the giant burn mark on the hull. We got on another plane, and arrived 3 hours late. I've been 3 hours late many times, but this is the most interesting story. When walking around the plane, the crew is looking for three things: ice, leaks, and missing parts. Ice can form under many conditions where you might not have ice on the road. Ice is heavy and they have to get it off or the plane will fly poorly and use too much gas. This is undesirable, not just because they get in trouble with their bosses. Leaks mean something might be broken, and they want to have a mechanic look at that. Parts come off more often than you'd think, particularly little parts like probes or door handle covers. These also cause poor gas mileage, and might facilitate a more serious problem."
],
"score": [
13
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
au1umt | why dont car batteries need recharging? | Engineering | explainlikeimfive | {
"a_id": [
"eh4yuig"
],
"text": [
"The alternator uses engine power to charge it while you’re driving. So it is being recharged, but you don’t need to plug it in."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
auc255 | What makes a modern internal combustion engine built today different from the ones fifteen, or even ten years ago? | Engineering | explainlikeimfive | {
"a_id": [
"eh73gm4",
"eh73pel"
],
"text": [
"Electronics and the degree of monitoring and control are really what sets engines apart. Fuel injection that is tailored at all times to the needs of the engine allow cars to be much more powerful, much more efficient, and at the same time produce far less pollution. The general ideas of the combustion engine are not new, just refined. For instance, I have a 1976 Chevrolet pickup truck that got somewhere around 8 miles to the gallon when it was new. I have built an engine with a homebuilt fuel injection system that gets 19 miles to the gallon on low octane fuel, using a block that was cast in 1975 and heads that were produced in 1981. The differences are not mechanical, they are poorly electronic sensors and controls. The engine makes almost twice the horsepower with double the mileage.",
"The big change that have happened is the electronics. A ten year old engine would have a lot of mechanical adjustments. So if you for example wanted to change the type of fuel you used or wanted to make the engine run more optimally in a certain temperature range or pressure you had to adjust a lot of different components and maybe even change some components for different variants. However today there is a lot of electronics that does these adjustments on the fly based on different sensors. So for example if you fill up with a different fuel then you usually use then the engine control system will detect this and tune the timing and fuel ratio to better fit the new fuel. Same thing when the temperature of the intake air or engine changes or when the pressure or humidity changes. The next generation engines will likely get rid of a lot of mechanics and instead of having the computer adjust the mechanical components it would do the operations directly. We already see some of this in for example fuel injection and high performance racing engines may have computer controlled valves. This does allow for far better control of the engine by the computer and can also allow for engine types that would otherwise be impossible."
],
"score": [
8,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
auciu2 | How do you make sure a surface like an outdoor basketball court is flat with no incline? | Engineering | explainlikeimfive | {
"a_id": [
"eh76toh"
],
"text": [
"First you make the ground underneath it flat. This is done in a process called “grading.” You essentially use large levels, or tolls that help you find where it’s flat, and you scrape out a flat area of land. *Then* you pour the concrete which makes itself flat because it’s in a semi-fluid state and then you scrape the top of the semi-dry concrete to make sure it’s flat and smooth."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
aue265 | Why are rail bridges in service for so much longer than road bridges? | In Vancouver there's a 115 year old rail bridge that AFAIK has no replacement plans. Right next to it is the 80 year old Patullo bridge which will soon be replaced with a modern one carrying the same amount of lanes. The explanation given is that its "dangerously old"... yet the rail bridge beside it built before WW1 is fine? Edit: Thanks for all the responses everyone! I vaguely assumed these were the reasons why but I wanted to know specifics. | Engineering | explainlikeimfive | {
"a_id": [
"eh7jzrs"
],
"text": [
"It might seem like one bridge is just the same as another bridge, but actually rail bridges tend to be built to be much stronger than regular road bridges. This is because a normal vehicle is going to be driving on a load which can be carried by rubber tires and under the reasonable pulling power of a truck, while a rail car is sitting on steel wheels riding directly on steel rails and can be carrying enormous loads. A semi-truck has a maximum total weight of around 80,000 pounds while a loaded rail car can weigh up to 315,000 pounds, and it is expected that such fully loaded rail cars might be following directly one after another. So rail bridges tend to be built *way* stronger than regular roadway bridges, and all structures are overbuilt on top of their expected load by some percentage. If we then assume that age weakens the bridge materials by some amount then the rail bridges have a bigger absolute buffer in strength. Also I suspect the wear patterns of a rail bridge differs considerably from a road bridge in that all the load of the rail bridge is coming from the rails themselves and those can be replaced as they wear down (which isn't much considering the extremely low friction). Water can freely drain away and different from roads the structure is never salted and exposed to such corrosive effects. A road though would tend to hold water more in that it must have a reasonably unbroken road surface where water can seep into cracks, carrying salt in the winter down to corrode rebar and other supports of the structure."
],
"score": [
9
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
auekmf | How are cranes removed from skyscrapers after the building has been finished? | Engineering | explainlikeimfive | {
"a_id": [
"eh7mdez"
],
"text": [
"Great minds think alike. I've searched tha seven seas fer an answer. Yer not alone in askin', and kind strangers have explained: 1. [ELI5: How do engineers remove the cranes on skyscrapers, once the building is finished? Refer to photo. ]( URL_1 ) ^(_32 comments_) 1. [ELI5: How do they get those giant cranes down from skyscrapers when they're through building at the top? ]( URL_4 ) ^(_17 comments_) 1. [ELI5: How do workers get the last crane off the top of a skyscraper when they finish building it? ]( URL_2 ) ^(_12 comments_) 1. [ELI5: How can a construction company remove a crane from the top of a skyscraper after construction has finished? ]( URL_0 ) ^(_9 comments_) 1. [How do they remove cranes from the tops of skyscrapers? ]( URL_3 ) ^(_3 comments_)"
],
"score": [
10
],
"text_urls": [
[
"https://np.reddit.com/r/explainlikeimfive/comments/1g6nyz/eli5_how_can_a_construction_company_remove_a/",
"https://np.reddit.com/r/explainlikeimfive/comments/24yw4e/eli5_how_do_engineers_remove_the_cranes_on/",
"https://np.reddit.com/r/explainlikeimfive/comments/75xic1/eli5_how_do_workers_get_the_last_crane_off_the/",
"https://www.reddit.com/r/NoStupidQuestions/comments/a8hlo0/how_do_they_remove_cranes_from_the_tops_of/",
"https://np.reddit.com/r/explainlikeimfive/comments/387rjd/eli5_how_do_they_get_those_giant_cranes_down_from/"
]
]
} | [
"url"
] | [
"url"
] |
|
aui05r | Why is a trackless train still a train and not a bus? | Engineering | explainlikeimfive | {
"a_id": [
"eh8bzjq",
"eh8cin0",
"eh8as05"
],
"text": [
"The original usage was \" number of vehicles or pack animals moving in a line\" e.g. camel train",
"A train is a bunch of cargo vehicles in a line. A railroad is a type of train.",
"It is not the first time such a vehicle have been called a train. The most famous examples are the Australian road trains which is any truck with three or more trailers. The \"trackless trains\" that have been published in China is intended to have many of the same benefits as light railways such as higher passenger capacity thanks to its length."
],
"score": [
3,
3,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
auivzc | why do car radios and infotainment systems turn off for a few seconds when starting the engine? | Say you’re in ignition position 2, and the radio is on. You then start the engine, and your radio turns off for a second, and then turns on again. Why does this happen? | Engineering | explainlikeimfive | {
"a_id": [
"eh8ezim",
"eh8fa7i"
],
"text": [
"Battery is used to start the car, so it can’t power all electrical sources and start the engine at the same time.",
"a motor can't start itself up, it somehow needs to get in motion to keep running. this is what the handle is used for on very old cars. & #x200B; modern engines have a starter engine instead of the handle, which usually is an electric engine that rotates the combustion engine until it starts combustion in all pistons. & #x200B; this starter engine needs a lot of power to get the heavy engine going, so the battery can't power the starter engine and the radio at the same time consistently."
],
"score": [
4,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
auw4rr | Triple-Expansion Engines | Engineering | explainlikeimfive | {
"a_id": [
"ehb20hh"
],
"text": [
"This is a type of steam engine. A regular steam engine works by creating high pressure steam by heating up water and then have the steam expand in cylinders or turbines where you extract the energy. The issue is that a cylinder is not able to get all the energy from the steam but the steam will still be somewhat compressed when it leaves the cylinder. So they found out that there were enough compressed steam left over in one cylinder to drive another cylinder to get even more energy from the steam. This second cylinder would need to be bigger as the steam have now expanded to fill a bigger volume. But even the second cylinder is not able to use all the energy so they would have a third cylinder to get all the energy from the steam. Later on they would replace the third cylinder with a steam turbine as it is more efficient."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
av2mby | how do inspectors know a building or an elevator is safe? | Engineering | explainlikeimfive | {
"a_id": [
"ehcd08g",
"ehd9nbw",
"ehct1bu"
],
"text": [
"Maths. You can work out the breaking strain of cables, take off a bit for safety and that’s the maximum weight the lift can take.",
"Here's a link to [what's checked]( URL_0 ) in Washington (state) They check the condition of the governor (which kicks in if the cab starts to plummet), the wire ropes, ensures that there's an SOS switch, the condition of the safeties, makes sure there's buffer oil (whatever that is -- presumably they already know), they make sure that the governor and safeties work, and, of course, that the various tags are in place.",
"They don't know absolutely that it is safe. But they do have a long checklist of best practices (ie, the \"building code\" and other codes) that they know lead to safe construction. So they inspect the building periodically during construction to insure that the codes are being followed. If they are not, construction is halted until the violations are fixed. The engineer in charge of designing the building and drawing up the plans also follows these codes, and also has a legal responsibility if he fails to do so. Any public building also has to pass inspection by a fire inspector, who checks for working alarms, extinguishers, adequate sprinkler system, and that enough exits exist (and in the right places) to allow evacuation in case of fire."
],
"score": [
3,
3,
3
],
"text_urls": [
[],
[
"http://www.lni.wa.gov/Forms/pdf/621051af.pdf"
],
[]
]
} | [
"url"
] | [
"url"
] |
|
av2q9f | Understeer and oversteer | I'm old enough to have learned to drive 40+ years ago on a stick shift. (A 1970 Fiat 124, heaven help me.) I watch "Top Gear" and "The Grand Tour" and I'll flip through Road & Track magazine at the barber shop. But I confess: I do not really know what understeer and oversteer are, or why they matter, and why whichever one is desirable (or not) in any given circumstance. Please help. ETA: Thanks for the very helpful answers. | Engineering | explainlikeimfive | {
"a_id": [
"ehc6fvm",
"ehc6txs"
],
"text": [
"Understeer: turn wheel, car doesn’t turn enough, driver sees tree they hit. Oversteer: turn wheel, car turns too much, driver doesn’t see tree they hit. Front-wheel drove cars usually understeer as the wheels are having to pull the car and steer. Rear wheel drive cars usually oversteer as there’s more power pushing the back end around. As for why it matters, it’s for the driver to understand who to correct an oversteer. Also those two programmes love to highlight the back end careering out as Clarkson comes around the Eboladrome... looks more exciting perhaps.",
"Understeer is when the grip on the front wheels give out before the rear wheels. Oversteer is the opposite. Both conditions occur when attempting to corner over the grip available on the tires. With understeer, the front of your car refuses to turn in, so if you hit anything, it will be with the front of your car. With oversteer the rear of your car \"steps out\" and most likely you'll hit something with the rear of your car. Understeer is \"easier\" to correct for beginner drivers because the natural reaction of getting off the gas and on the brakes helps reduce the understeer. You'll typically see understeer with front wheel drive cars. Oversteer is less natural to correct, as you need to steer into the \"sliding rear\" and stay lightly on the gas. If you hit the brakes or get off the gas quickly when oversteering, you will cause the car to go into an uncontrollable spin. Race drivers prefer oversteer because they can control the car using gas and corrective steering and therefore lose less time through a corner and exit at a higher speed. Understeer forces the driver to reduce speed to control and is therefore not preferred. Oversteer and understeer characteristic is usually mostly \"built in\" to the car by design although a skilled driver should be able to induce oversteer in most cars by braking and turning in quickly (thereby pushing the weight to the front giving more front grip and causing the rear to unweight and break loose) and then rapidly but gently getting back on the gas to control the oversteer. Rally drivers can also initiate oversteer by using the handbrakes to brake the rear wheels (the J turn maneuver) which is done when they want to make a sharp corner at high speeds and slide \"around\" the corner. & #x200B;"
],
"score": [
18,
8
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
av5pw7 | Is bamboo a viable alternative to trees for paper goods; e.g. toilet paper, paper towels, etc | Engineering | explainlikeimfive | {
"a_id": [
"ehcs7mq"
],
"text": [
"While it is possible to make paper pulp from bamboo and this is being done by some paper mills in Eastern Asia, there are different types of cellulose fibers from the different types of plants. Even different types of trees produce different paper. For example newspaper and toilet paper are very different from each other and a lot of this is down to what kind of pulp have been used. Bamboo is mostly used for newspapers and other stiffer papers and would not make a very good source of material for toilet paper or paper towels."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
av8r95 | If sihpons can move water upwards with zero external power, why are pumps used almost exclusively instead? | Engineering | explainlikeimfive | {
"a_id": [
"ehdet3q",
"ehdf95f",
"ehdk7w6"
],
"text": [
"siphons don't move water up. they provide a path for 50miles high column of air to push water thru a pipe that happens to go up for a little bit, then goes down lower. siphons work on air pressure. the difference in air pressure between the inlet and the outlet of the siphon",
"Because siphons only work if the source of the water is higher than the destination. The pipe/tube in between can have portions where the water is flowing upwards (against the force of gravity), but the end of the pipe has to be lower than the source end. If you need to move water upwards and have it stay there, you have to put in energy to overcome gravity, i.e. a pump.",
"> If sihpons can move water upwards with zero external power They can't. Siphons can only work where the water ends up lower than it was, because they work on gravity. There might be sections that go upwards, but the overall result from source to destination is that the water gets lower. That has to be the case for a siphon to work."
],
"score": [
8,
8,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
avbtxu | what are Universal Testing Machines, how do they work and why are they used. | If possible please help me get a better understanding thanks in advanced. | Engineering | explainlikeimfive | {
"a_id": [
"ehe47er"
],
"text": [
"Universal test machines (UTMs) are pieces of test equipment used to test the tensile (pulling apart) and/or compressive (pushing together) strength of materials or assemblies. Imagine a big frame with two clamps, one fixed and one that can slide back and forth. Whatever you want to test (the test \"sample\") gets attached to the clamps. Then the clamps are either moved farther apart (tensile testing) or closer together (compressive testing) and the machine measures how much force it takes to do that. Knowing the tensile and/or compressive strength of materials or assemblies can be important in making sure your designs will work correctly. Say for example you want to hang a lighting fixture from your ceiling. You'd probably want to use something like chain or rope (high tensile strength) versus a rubber band (low tensile strength). Or, in the opposite direction, if you need a box to stand on because you can't reach your cabinet, you'd probably want something with high compressive strength (like wood) versus low compressive strength (like cardboard). In both of those cases you could use a UTM to test your materials (rope, chain, rubber band, wood, cardboard) ahead of time and determine if they are strong enough to perform the functional you want."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
aveb43 | What makes kevlar better against bullets than steel (or any metal)? | Engineering | explainlikeimfive | {
"a_id": [
"ehedrur",
"ehecw6z",
"ehf5vmb",
"eheckz8",
"eheyhgr"
],
"text": [
"There are two ways to stop a moving object: you either have something hard and heavy enough to stop it over a short distance, or you have something flexible with high tensile strength that \"catches\" it and slows it down over a longer distance. In the case of the hard and heavy, this is what you typically see on vehicles because, well, it's heavy. The thickness of the material is usually porportionate to it's effectiveness. The projectile will impact the side of the armor and shatter/deform because the hardness and mass of the armor is higher than that of the projectile. Obviously there is a sliding scale here, as the heavier a projectile and the faster it moves, the harder it is to slow it. This is why tank rounds are designed the way they are: very high velocity, dense (hence depleted uranium) and a small cross section (discarding sabot). The intent is to overwhelm the armor by concentrating a significant amount of energy in a small area. Kevlar, on the other hand, takes a different approach. Instead of trying to resist and stop the moving projectile at the surface, Kevlar will \"give\" and flex under the impact. But because Kevlar has such a high tensile strength, it doesn't break as it gives. It effectively acts as a kind of 'catcher's mitt' to slow the bullet to a stop. This is why even if your armor stops a bullet, it hurts like a fucker because your body is still being hit very hard, it's just dissipating that energy over a larger area. As you can imagine, however, the threshold for the effectiveness of Kevlar is much lower than that of steel or composite armor, which is why kevlar vests are usually only rated for certain kinds of handgun rounds, and only resist rifle bullet impacts with the addition of ceramic inserts and below a certain caliber/velocity.",
"Veteran/Cop here: One's not better than the other. There are trade offs for both. Kevlar is lighter and more flexible than steel or ceramic plates. The disadvantage is that kevlar will only stop some handgun rounds. Steel/Ceramic will stop rifle rounds, but it is *much* heavier. Typically the plates are carried in a kevlar carrier. So it's a tradeoff. Police typically wear kevlar vests because they're more likely to be shot by handguns. Military wear kevlar vests with ceramic plates because they're more likely to be shot by rifles. I've also got a plate carrier with steel plates in my patrol car I can put on if needed.",
"It's not the fall that kills you, it's the landing. When two objects collide, there is an energy exchange that takes place and the more you can slow that down and spread out the force over a larger area, the less damage it will cause. In the case of a bullet, it's a projectile colliding with a person and imparting it's energy in a very short period of time, to a very small area (the size of the bullet itself). So if you can spread that force out over a larger area, and slow the bullet down, you can prevent it from penetrating and killing a person. Steel is very strong, but it is rigid and hard. When shot it absorbs the impact at the site of the shot and either shatters if it's hard steel, or deforms if it's ductile. Either way the energy is concentrated at a small point, and the steel gets a hole drilled into it. Kevlar is not hard, but it has a high tensile strength, which is a measurement of the amount of force it can handle stretching or pulling on it. It doesn't shatter, it bends and stretches. The kevlar fibers are woven in overlapping layers and in different directions so that they reinforce each other and no matter what direction a bullet comes from, it will be stretching as many fibers as possible at impact. When the bullet hits, the fibers begin to deform and stretch and as they do so, they spread the force of the bullet out over a large area. when you grab a blanket in the center of the bed and lift up, the entire blanket gets pulled inwards, so the force of your lifting, is resisted by, and spread out over the entire bedsheet. A similar thing happens with the kevlar. What makes a knife more deadly than a punch? They have the exact same amount of force behind them. But the punch is spread out over the size of your hand, and a knife concentrates all of that force into the very tip of the blade. Kevlar vests turn dense, high velocity kinetic energy into diffuse, lower velocity kinetic energy. It turns a knife tip into a fist. The persons body still absorbs the energy, but it absorbs it more like a punch, than a puncture.",
"It's softer and stretches out without breaking so better at absorbing the bullet's energy.",
"& #x200B; Kevlar® is most-generally used in body armour, so it may be assumed that the question is intended to be \"Why is Kevlar® preferable to steel as an element of body armour against bullets?\" & #x200B; The answers to that are dependent on many factors. & #x200B; If the focus is on wearability, including weight and flexibility, then Kevlar® enjoys many advantages. & #x200B; If the focus is on protection, including strength, density, and mass, then steel enjoys many advantages. & #x200B;"
],
"score": [
260,
50,
6,
4,
4
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
avjlxa | Why can't rockets start like airplanes? | Engineering | explainlikeimfive | {
"a_id": [
"ehfmdhx",
"ehfmmrv",
"ehfmnjm"
],
"text": [
"Because it requires a ton of force to reach an orbit altitude (or to escape Earth's atmosphere). The rocket starts at a 90 degree angle but then tilts and angles as it climbs, it doesn't fly straight up. This trajectory uses less fuel than a horizontal launch would, and also helps ensure a smooth trajectory (flight path). Also, conventional airplane engines don't work at higher altitudes where space stations operate because there isn't enough oxygen for the engines to function.",
"Here at sea level the atmosphere is very dense. That means that there is a lot of friction between the rocket and their air. The longer you are in this dense part of the atmosphere, the more fuel you are spending on it. By going up first to a level where there is a less dense atmosphere it will be more efficient to push through. Once you are up there, you need to turn to go in orbit around the planet. To succeed in that you need a much higher speed than the speed to go up. But because there is nearly no friction there it can be done much more efficient. Source: hours of KSP :-)",
"Getting to space is a lot easier than staying in space. To get to space you only need to go straight up ~100 miles, so you’re above the atmosphere. To stay in space, you have to go above the atmosphere and then accelerate sideways to ~17,000 mph. Trying to go that fast in the atmosphere would incinerate your spacecraft, so step #1 is to get above it as quickly as possible."
],
"score": [
9,
6,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
avjnwc | How do water treatment plants turn wastewater back into drinkable tap water? | I'm especially curious to understand how water treatment plants get rid of chemicals from soaps and toiletries that go down the drain after we wash up. How do they filter out all the inedible/inorganic substances? What happens to the stuff that's filtered out afterwards? Plus, what happens to the medication we take that we end up peeing out? Is there a way to filter out pharmaceuticals? | Engineering | explainlikeimfive | {
"a_id": [
"ehfoqjg"
],
"text": [
"The wastewater goes through a few separate stages. First, they run the water through some coarse filters to remove the big things (anything from dead animals to condoms to children's toys). Next, they pump the water into huge open storage tanks that doesn't let the water move around too much. There the majority of the solids (aka shit and toilet paper) settle out to the bottom of the tank. These are removed occasionally and treated separately. From there, it depends on the plant. Some plants just discharge the water back into nature and let nature do filtering. Others do more advanced filtering that involves bacterial digestion of additional solids and other chemicals or addition of sanitizers such as bleach. And as far as medications, it's actually a bit of a problem. It's been documented that groundwater in areas have measurable levels of things like birth control hormones or antidepressants. This not only comes from drugs being excreted in urine, but also from people just dumping old bottles of pills down the crapper. & #x200B;"
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
avk3if | How are damaged airplanes transported to a repair facility? | Let's say an aircraft crashed and its tail is damaged, cabin is leaking, had an uncontained engine damage, etc. but could be repaired to be put back into service later. How are damaged airplanes transported to a repair facility if it can't safely fly? A standard twinjet can fly with one engine, however it is difficult to take off and maneuver. | Engineering | explainlikeimfive | {
"a_id": [
"ehfqfpz",
"ehfqhwh"
],
"text": [
"Former aircraft mechanic here. Depending on damage aircraft can be repaired on site. I've flown to smaller airports where we have rented hanger space and got to work. Parts and tools are shipped to you. Often a representative from the manufacturer will also arrive to help coordinate. Sometimes you will be there for a long time. If that isn't an option aircraft can be disassembled and shipped via truck to a maintenance facility. This is very difficult with large aircraft. For minor damage it comes down to airworthiness and the minimum equipment list (mel).",
"Assuming the airplane is at an airport and not somewhere in the middle of nowhere: There are a lot of spare parts which can be moved around, up to full engines. ( URL_0 ). The airport will have the space to store the plane until the spare parts are there and replace faulty parts. Once the airplane is airworthy it will most likely be flown back to the repair facility of the airliner and then fully tested and certified again before passengers are allowed back in."
],
"score": [
17,
4
],
"text_urls": [
[],
[
"https://www.qantasnewsroom.com.au/roo-tales/that-time-when-we-strapped-an-extra-engine-on-to-a-jumbo/"
]
]
} | [
"url"
] | [
"url"
] |
avk7ua | Is there a practical reason for a car's driver to be on the side rather than the middle? | Engineering | explainlikeimfive | {
"a_id": [
"ehg3hj6",
"ehfr373",
"ehfs1gs",
"ehg8bf4",
"ehghlrv",
"ehg8iey",
"ehgn95z",
"ehg859c",
"ehfrn6d"
],
"text": [
"Others have mentioned the proximity to the door. The only thing their answers don't explain is why cars with front bench seats (which are rare these days, but used to be common) don't have the driver in the middle. This is because of a couple of reasons. First, the steering column. This is a relatively straight piece of metal connecting the steering wheel to the steering rack (or in older vehicles, the steering box). This box needs to be on one side, because the engine is in the middle. The other reason is that older cars were predominantly rear wheel drive, which means the transmission sits between the driver's and passenger's feet. This means that if the driver was in the middle, log room would be minimal, and there would be no room for pedals.",
"You can fit more people in the front row. Also it makes the seat closer to the door, and makes better use of available space.",
"The main reason is so you are closer to the centre of the road, you can see the oncoming traffic easier easier. Also as other people have said, it's easier to get into a seat next to a door rather than in the middle and makes better use of space.",
"Visibility. If you've ever driven a left or right handed drive in a country that predominantly uses the other system, you'll learn real fast why the seat is where it is. It's annoying to see anything ahead of you safely when you're on the wrong side.",
"Overtaking someone is a pain if you are not seated at the same side as eveyone else. People driving a car that is build for right lane traffic ( stearing wheel on the left) in a left lane country (like driving a german car in britain) or vice versa know that problem. You can't very well edge out to check omcomming traffic. Cars with seats in the middle suffer from the same problem. To a lesser extent, but that problem exists no matter the country you drive in. Any McLaren divers here that can confirm this?",
"When you’re trying to move into the passing lane on the highway how easy is it to see around a car or truck from the passenger seat? Is it any easier in the middle?",
"Sitting on the side makes it easier to see what's going on when overtaking/merging. That's why the side the driver sits on varies depending on what side of the road though drive. Sweden hade left-hand drive cars while driving on the left. Thet decide a change would increase safety, so switched to driving on the right.",
"In St Thomas, USVI, steering wheels are on the left (like elsewhere in the US) but vehicles ride on the left side of the road (like in British lands). When we asked our taxi driver why, he waited until we were atop a curved precipice to open his door to show the steep drop unprotected by a guardrail. He claimed that drivers need to be as close to the edge of the cliff as possible to ensure the wheels remain in the road!",
"Imagine having to move all the way to the middle of your car to start it and begin driving. If you have passengers in the front with you, the space would be crowded and unsafe. You ever sit in the middle seat of a car on a trip with 2 other people? Take that and now you have to use the wheel and be able to see the mirrors as well as check behind you for danger. That's why the seat is on the side of the car. To provide space to look around as well as enter and exit the car safely and quickly."
],
"score": [
229,
87,
50,
27,
8,
6,
5,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
avkmst | what is involved in the growing of Bonsai trees that differs from regular plants? How do they make them look like scale model trees? | Engineering | explainlikeimfive | {
"a_id": [
"ehfu01z",
"ehfu1ja"
],
"text": [
"They're regular trees that have their roots smashed into a smaller area which restricts how much they can grow. They also prune them and clip them meticulously to keep them to very artistic shapes and tiny sizes. They have to be cared for with tons of attention.",
"The people who grow them meticulously groom them for years and years cutting and shaping them to stunt their growth and make them look the way they want them to. It takes a lot of skill and artistic vision. (It also looks like you're killing the tree for most of the process.)"
],
"score": [
5,
5
],
"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.