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
|
|---|---|---|---|---|---|---|---|
dqhuib | How do boilers heat water so quickly? The pilot light goes out on my boiler and I get no hot water. I put the pilot light back on and then in the space of a minute my radiators are getting warm and I'm getting hot water out of the tap. | Engineering | explainlikeimfive | {
"a_id": [
"f644qsh",
"f65nfua",
"f65tvzv",
"f664l75",
"f65l9dt",
"f66b3nb",
"f66kiqz",
"f66b617"
],
"text": [
"My Original post. Simply, insulation. Depending on your units tempature settings, it will heat up the water to.. let's say 140f. When it drops to 115 the unit turns on and warms the water back to 140... Does this dozens of times a day.... No matter if you're home or not. Also, pilot lights aren't supposed to go out. Their job is to stay on and reignite the gas heating element. Unless your unit is electric and then it just uses a spark to ignite. Mechanical Insulator by trade. ____ Edit1: I reread your post and I either didn't read it right or you may have edited it. Some water heaters are like a big pot of water and it takes a while to heat up. Some water heaters are filled with coils... Which allows the fire to warm more surface area.. hence how tankless water heaters work. ________ Edit 2: Everyone is getting way off topic. The question was how does a water heater get water warm so quickly. Not about gas leaks or pilot lights. Gas leaks rarely happen to a untampered unit. It's an urban legend that a pilot light going out will cause a house to explode. There are some good answers here by other tradesmen, in a field a lot closer to this answer than mine. We're all right here, just about different aspects of the situation.",
"I’m a hvac tech by trade and a journeyman gas fitter so I’m going to try chime in here, I’ve read replies about gas filling your home if the pilot goes out, even the oldest boilers I service do not have standing pilots, they have a thermocouple attached to them in the “pilot assembly” that, when heated will provide the tiny little solenoid in the gas valve with a tiny little bit of voltage to open the solenoid, releasing gas through the pilot tubing to the pilot assembly, where your pilot flame is. Once the flame goes out the thermocouple stops producing voltage and closes the solenoid, no flame=no gas. Most common issue is a bad or dirty thermocouple. Have a licensed gas fitter replace the assembly and adjust the pilot, you can adjust the amount of gas that will be fed to the pilot light on the gas valve. To answer your question regarding the pilot light being out and having no hot water, the pilot needs to be lit to provide the gas valve a signal that proves there is flame present for the main valve to open. It’s not your pilot light heating the water, it’s the flame that is substantially larger that comes on after. A typically pilot light is like 400 btu/h. A 40 gallon hot water tank is typically 40,000 btu/h. Hope this clears things up. Cheers",
"Sounds like you have an “on demand” boiler. The water goes through a heat exchanger to get hot. Think of the heat exchanger as an old fashioned radiator for heating a room. Water passes through the inside of the radiator and fire is passing on the outside. This is done in an efficient way so that the water enters cold on one side and leaves hot on the other. It’s a wonderful system! :)",
"Follow up question to this, I've tried to research but always hit a wall. How EFFICIENT are on demand hot water heaters? I get it heats up the water faster and less gas or whatever they are using, BUT it takes a lot of energy to heat up water ON DEMAND to the temperature you want it to be. That seems like there might be some inefficiency there, no? Anyone know?",
"Here is how you tell if your gas device(boiler/furnace/water heater/etc.) has a pilot safety system that cuts off the gas if the pilot is out. If part of lighting the pilot involves holding something down for ~30 seconds after lighting the pikot, either a button or the selector knob, then you have a pilot safety system. Holding down the button/knob actually bypasses the safety system so the pilot will stay lit long enough for the system to sense the pilot is lit. If you can just light the pilot and immediately walk away, then you don't have a safety cutoff system and should look into replacing that device.",
"The heaters are designed to extract as much heat from the gas as possible before it escapes upwards. This means the inside of the GWH (Gas Water Heater) is basically a donut. The air heats the water as it passes by. Add in the delivery of cold water is done by the dip tube. It deposits water at the bottom of the heater, and hot water is extracted at the top. This ensures the output is relatively consistent as the cold water rises and mixes up to the extraction point. Lastly is the heat output. As another post mentioned, you get 40,000BTU out of the heater assembly itself. Stoves are 3000-7000 for a single burner. So imagine a 6 burner stove all on high; that's the output not over a whole stovetop but by a ~10\" burner focused by the GWH to heating water. So a combination of delivery, design, and tons of BTU means quickly heating water.",
"It really comes down to surface area. The larger the surfaces are that are transferring heat the more heat can transfer at all at once. Your boiler is designed so that there is a lot of surface area with water on one side and fire on the other so heat can easily go from fire side to water side. If you want to do an experiment try putting the same amount of water in a sauce pan and in a frying pan set them on the stove at the same temp, you should find the frying pan boils faster because there's more surface area in contact with the water and the heating element. (Industrial boiler technician here)",
"If the pilot light wasn't out for a long time then the water is probably still hot. Water heaters are built with lots of insulation so that they don't have to constat heat water. Otherwise it's just that there's a big flame inside that you can't see. That's what heats the water, not the pilot light!"
],
"score": [
1364,
628,
79,
16,
16,
15,
5,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dqmmjr | How do tankless water heaters work? | Been looking at various home improvement projects and stuff lately. I’ve heard a ton about tankless water heaters but don’t quite understand them. Are the pipes just really hot? Wouldn’t that make them dangerous? | Engineering | explainlikeimfive | {
"a_id": [
"f67s4pe",
"f66qslv",
"f66qy8o"
],
"text": [
"Sort of. Not to insult anyone but to dumb it down basically cold water supply goes into tank. Goes through heating process and in the middle there’s a “big” burn chamber. That’s where the flame rods ignite when the unit is needed, the burn chamber gets super hot and extremely quickly heats water as it passes through. Then goes through some more tubes and comes out hot. It all happens instantaneously pretty much. They’re quiet and if you do proper annual maintenance they last 12-15 years. Maintenance is key though. Have a licensed plumber do it though. Flush the tank (as part of maintenance) once every one to two years. A proper flush takes an hour with proper solvent or vinegar. They’re more expensive to buy than a regular hwt. However in my experience they outweigh the tanks in pros vs cons.",
"The pipes are not heated up that high and are often made of material that can handle being heated all the time. But input water runs through those hot pipes and get heated up on the fly by passing through.",
"They are either gas or electric. Basically It sparks in the combustion chamber inside and heat the water at high temperatures as it passes through the chamber. It’s a smaller amount of water needed to be heated up at one time so it can do it quickly which will give you hot water literally all the time for most families."
],
"score": [
6,
3,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
dqvii7 | How are metals moulded into specific shapes for car body or for the body of a macbook ? | while observing day to day objects around me i saw lot of shapes that were made from metals like aluminium and iron but how were they made into a particular shape with various smooth dents and fluid like shapes. What fiels of engineering is needed to learn this art . | Engineering | explainlikeimfive | {
"a_id": [
"f6acg2u",
"f6acg5r"
],
"text": [
"There's a few different ways it can be done. This isn't going over any of the prep work or cleanup, just the main manufacturing Metal casting. This isn't used for any of the products that you mentioned, but it's still really common. A mold is made of the part you want to make and molten material (such as metal or plastic) is poured in and solidifies. CNC machining. This is how macbook bodies are made. This is a computer controlled machining process. you start out with a block and cutting tools come in and cut off material. Look up some videos of this, it's pretty cool. Sheet metal forming. This is how car bodies are typically made. The metal used for this is a (relatively) thin sheet. Stamps are used to cut out chunks of metal (like cookie cutters) and various tools are used to bend the sheet metal into shape (some of this can be done at the same time as stamping). From here, parts are welded together. Edit: this isn't a list of all manufacturing techniques. It's a few that highlight the specific parts and characteristics that the OP mentioned",
"Depends on the need Casings for car parts like around the transmission are made by casting molten metal into a mood made of sand. Body panels on a car are made by using a giant press to stamp them into shape. The body of a MacBook is made by taking a plate of material and cutting it with a CNC mill"
],
"score": [
9,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
dr5cmn | " Why can't we just plug 10 chargers into an electric car and charge it 10x faster? | ELI5: Why can't we put 10 different batteries into an elecric car and charge them individually so that the charging could be 10 times faster? Could be any electrical device, such as smartphones, etc. Edit: I feel like a few people didn't get the point. I know there are special "superchargers" that charge faster (while ruining the battery a bit). Think of it this way: charging one electric car takes as much time as charging 10 electric cars. So why can't we put 10 separate batteries in a car and charge them with 10 separate chargers? | Engineering | explainlikeimfive | {
"a_id": [
"f6faf7w",
"f6f37x6",
"f6f0681",
"f6f8juc",
"f6f3ikf"
],
"text": [
"For a car charger the limitation for home use the limitation is not the car but the power that a outlet can deliver or the electrical connection to the house. The car or the battery in the car is not the limiting factor. A Tesla supercharges station have 480 DC charger that can deliver 250kW That is 250000/480=520A. In the US where there are 220V to the house you would need 1136A fot the same power. A outlet for a electrical oven that would be what is relative common and use a lot of power max out at 60A or 1/19 of what is need for a Tesla supercharges I Europe where 3 phase to homes at 400V is not uncommon you would ned 250000/400/3=208 Amp per phase. For a very large home in a cold environment that is heated by electricity you might have 3 phase and 35A fuse So for residential charger it is not the car or the charger that you might need that is the liming factor but the connection to the power grid. Because 3 phase and higher voltage is common in Europe Teslas sold here have charging electrons that support the plugged in direct to the car. & #x200B; A Tesla model X with the largest battery have 100 kWh and it take 100/250=0.4 hours = 24 minutes to charge them full if it is 100% efficient. At this point it is the cooling system of the batteries that is the liming factor. So charging speed is in most case limited by the power grid and not the car and you need expensive electrical system and chargers before it is the car that is the liming factor.",
"It's totally feasible, kinda, just not that practical. It would require more complicated charging circuits for one. Batteries can either be in series, or in parallel. Batteries being in series provides more voltage, while batteries in parallel provide more max current and more capacity. A battery pack is usually wired in one way. When you charge the battery pack, which is actually a bunch of smaller batteries, you pass current through all of them at once. Your idea would require the battery to be able to change it's internal wiring so each charger passes current through a different subcomponent of the battery. Possible, yes, but it seems like it's too much of a pain from a manufacturing and a use standpoint to be worth it. It's also very possible that the circuitry already does this to a degree, but that, as other people have stated, heat has become the limiting factor.",
"Because you're relying on a chemical reaction to take place in a battery to charge a battery. The faster the battery charges the more heat it creates.",
"Heat. Transferring energy creates lots of heat. Heat can destroy batteries and other electronics.",
"An electric car's battery is made of hundreds, if not thousands of individual cells. Whether all those cells are charged in one big series string, or as ten separate batches, or a hundred separate batches does not change the effective charge rate. You're still using the same amount of energy. Let's simplify the numbers to give us a general sense of how this works. One cell can store 1 Amp-hour, or 5 watt-hours. One cell can charge at a maximum rate of 10 amps. To charge one cell at max rate, you need to push 50 watts into it, or 10 amps. Now, let's put ten cells in series. The whole string can charge at a max rate of 10A, which is the same as the single cell. However, since the voltage is much higher, the charging power is 500W. Put ten cells in parallel, charging current is now 100A. However, voltage is the same as a single cell, so power is, you guessed it, 500W. This is because power is a function of voltage and current. P = I*V. Or, W = V*A. In very broad terms, no matter how you configure a battery pack, it will always store the same amount of energy, and it will always take the same amount of time to charge at the maximum safe current. (dont @ me about these numbers) Now, as to your question, some EVs *do* use multiple battery banks. I know that at least one of the tesla models split the battery into two parallel banks. The reason for doing this is simply to knocn the voltage down. It doesn't really give you any additional energy storage or charge rate, but it makes things slightly safer by halving the voltage, and reducing the need for voltage-converting circuity that can lose power to heat."
],
"score": [
26,
14,
12,
4,
4
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
drck92 | Why does a Porsche 6 cylinder make 500hp where as a 370z nissan makes 329hp | I know some engines maybe detuned or something like that But what determines how much power an engine makes without a super/turbo charger? | Engineering | explainlikeimfive | {
"a_id": [
"f6hcftl",
"f6hcpih",
"f6hd54k"
],
"text": [
"If you're taking about the same Porsche 6 cylinder that I think you are, some of it comes down to having the best airflow money can buy, some of it comes down to having twenty percent more displacement, and some of it comes down to having a redline of over 8000 rpm due to extremely well balanced and light rotating components and valve train components, many made from titanium. Because of the way horsepower is calculated, the increase in redline makes a tremendous difference in horsepower.",
"There are many, many overlapping reasons, but my best stab at eli5 are these: 1. HP is essentially a function of the engine torque and the engine speed. So if a given engine has a higher rpm or makes maximum torque at a higher rpm, it will put out more Hp, all else equal. 500 hp normally aspirated Porsches have much higher redlines and I believe higher rpm where they make torque than the Z cars. This is due to tuning, as well as expensive engine parts that don’t fly apart at high speed and under large power loads. 2. Engine displacement. Two cars might have the same number of cylinders, but if one has bigger cylinders, more air and gas get burned and more power is generated, all else equal. 3. Tuning/engineering for applications. Cars are tuned for best performance in a given application. This is a choice. 370Zs are overwhelmingly driven on the street and not really intended to be “serious” on the track from the factory. As a result they have been engineered with a broad torque curve, high reliability without expensive parts to achieve it, lower redline, reasonable compression ratio, fuel economy, etc all being balanced for street use. The hotter Porsche engines are track ready, peakier power, higher redlines, higher compression ratios, etc- because they are intended to be competitive in a track application. They are, of course, less practical and far more expensive than a Z motor.",
"The simplest way to make more power with the same number of cylinders is to increase the displacement of the engine. That is, to make the individual cylinders hold more air which means it can burn more fuel. You can either increase the diameter of the cylinders (the bore) or increase the height of the cylinders (the stroke) or both. Increasing the stroke gives you more mechanical advantage since the connecting rods become longer, but it comes with the expense of generally making the engine not rev as high. The other simple way of making more power with the same number of cylinders is to increase how fast the engine can spin. This, generally is limited by how fast you can get air into the engine so you need more intake valves per cylinder and the cams need to have a higher amount of lift (it allows the valves to open wider) but this comes with the drawback of reduced low RPM performance. Displacement and bore/stroke being equal RPM to make more power you need to play with valve geometry to allow the engine to rev higher and draw in air more freely. I'm going to assume you already know how a 4 stroke engine works, if you don't there's literally thousands of YouTube videos that explain it better than I can. All engines will rev to a point where they make the peak amount of power then power slowly starts tapering down, this is because engineers design the engine to be driven for a certain purpose. If it's a race engine then they will make it make peak power at high RPMs where the engine will spend most of it's time, if it's a street driven engine then they will make it fuel efficient and make more power towards the mid range; most if this is done by manipulating valve geometry and the design of the heads. The valvetrain of a race engine is designed to withstand high RPMs. If you overspeed a car's engine (drop it into too low of a gear at too high of a speed and release the clutch) the biggest danger is something called valve float. This occurs when the valve springs don't shut the valves quick enough and the pistons strike the open valves damaging them. Race engines, which have to cope with much higher RPMs have stiffer valve springs. Since the valve springs are stiffer it makes it harder to turn, you increase parasitic loss from the valvetrain and increase wear and tear. That's why you don't necessarily want stiffer valve springs on a car. However, if you did for whatever reason decide to upgrade your valve springs to stiffer ones, the other problem you run into is volumetric efficiency. When engineers design an engine for a street driven car, they want an engine with a flat torque curve. That is, when you floor it at 3,000 RPMs you accelerate roughly the same as you would when you hold it at 5,000 RPMs. This makes the car driveable on normal road conditions since you don't want to constantly be shifting gears. If valve float were not an issue, volumetric efficiency becomes one. At too high of an engine speed the airflow into the cylinders gets less and less efficient. That is, when you floor it at 3,000 RPMs when the piston moves down during the intake stroke it draws in more air than it would at 7,500 RPMs. Cars rely on something called the scavenging effect to maximize the air drawn in during each stroke; when exhaust gasses leave the cylinder they leave in 3 pulses: 1. The first pulse occurs when the valve begins to open and the cylinder pressure equalizes with the pressure in the exhaust manifold 2. The majority of the gasses come out in this pulse when the piston rises to expel the gasses out the cylinders 3. This is where that extra umf comes in, scavenging. The exhaust valve stays open while the piston moves down during the intake stroke and while the intake valve is slightly open. The exhaust gasses inside the exhaust system have inertia and want to move towards the muffler, while both valves are still open the exhaust gasses scavenge some of the air inside the cylinder out that would otherwise remain trapped if the exhaust valve closed the instant the intake valve opens The amount of time both the intake valve and exhaust valve remain open is called overlap, the more overlap you have the harder it is for the engine to operate at low RPMs but the more power you make at high RPMs. This is what gives old muscle cars the distinctive rumbling sound at idle."
],
"score": [
12,
10,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
dree33 | Why does hitting the remote a couple times make the batteries work again? | Engineering | explainlikeimfive | {
"a_id": [
"f6hkz4i",
"f6hlrkh"
],
"text": [
"It doesn’t. However, often the problem is caused by the contact between the battery and the terminal. Percussive maintenance moves the battery within the battery compartment creating a better connection.",
"While in regular use, the contact between the battery terminals and remote contact points, produces non-conductive gunk which builds up over time. When you hit the remote a few times, it dislodges and your battery can conduct again."
],
"score": [
66,
9
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
drgcla | if all door locks are different and different keys open different locks, how does a universal key work? | Engineering | explainlikeimfive | {
"a_id": [
"f6ifbsg",
"f6hx5gl",
"f6hx90f",
"f6idtvg",
"f6i423s",
"f6hz21v",
"f6hx8j3"
],
"text": [
"This is a question that’s really hard to explain and understand without a visual aid Here’s a link to a gif that shows how it works URL_0 Notice how those pins have multiple spots where they can line up. A master key moves the pins into the other position where the whole thing can turn",
"The lock opens because the \"rings\" inside align. The way some locks are made is that there are two sets of rings - one unique for each key, and one same for the master key. Longer answer is, lock is a small cylinder inside large cylinder, and there are \"pins\" going between them that prevent the inner cylinder from turning. Correct key pushes them out, thus freeing inner cylinder and allowing it to rotate. To enable master key, you just add an additional cylinder, which results in pins having 3 total possible positions - \"at rest\", \"unique opened\" and \"master opened\".",
"A standard lock has pins with different lengths that correspond with the lengths of the notches/ridges on the key. When the right key is inserted, the pins are aligned and the lock can rotate freely. With a master key, the pins in the lock are segmented so that they can align with two different lengths of notches/ridges. Locks that share a master key all have the same lengths for the first segment but different lengths for the second segment.",
"Probably only for advanced 5 year olds but [this paper explains master keyed lock sytems and how to make a master key when you only have a regular key. I might be odd but I think its a riveting read.]( URL_0 )",
"Every lock in a set of locks has two sets of buttons inside them. The key presses one set of the buttons to allow you to turn the key and open the lock. One set of buttons works with the specific key for that lock. The other set works with the master key. The \"universal\" key is not universal. It works with a specific set of locks that was purpose made to be part of that same set. As an example, there might be a master key for an apartment building, or a motel. Those locks were all made to fit a specific master key. Different master keys will not work on every lock you encounter in the world, just on the specific locks from that set. In theory any way. There are probably people out there who happen to have identical keys and locks, but there's no way of knowing which locks, so that doesn't matter.",
"As a side question, what are the chances that a random key you have fits a random lock? Is there a chance my door key works on someone else’s door?",
"Instead of a single pin in each section of the barrel there are multiple pieces to each pin which makes different keys work in the same lock"
],
"score": [
37,
27,
19,
5,
5,
4,
3
],
"text_urls": [
[
"http://ichiya.com/Lock/images/fig/pinCylinderAniFull.gif"
],
[],
[],
[
"https://www.google.ie/url?sa=t&source=web&rct=j&url=https://eprint.iacr.org/2002/160.pdf&ved=2ahUKEwjTltDx3NDlAhXyunEKHfCBBtoQFjAOegQICRAB&usg=AOvVaw2Yx6L6LmfZaRNh6a5x0QR8"
],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
drj0aq | Why do electronics (laptop for example) lose battery when they’re not in use or are asleep? | Engineering | explainlikeimfive | {
"a_id": [
"f6imexw",
"f6in2h1"
],
"text": [
"They are still \"on\". In order for you to be able to wake your phone by looking at it, or boot your computer by clicking on the mouse, parts of the system are on all the time. That's been true for decades, ever since electronics stopped having a big ON/OFF toggle switch.",
"If they’re asleep they’re still powered and draining the battery slowly through electronic functions. But batteries are just chemical reactions. Lithium Ion batteries in particular continue to react even if they’re not connected to anything, releasing energy as heat and new chemicals at the anode. Nickel Metal Hydride batteries have a significantly lower depletion rate when not in use, as they need the electric current in the electrolyte to trigger the reaction at the anode in any volume. But LiIon is the most energy dense battery format we currently have, and so has been used in most electronics for over a decade. Because of the continuous reaction, it also doesn’t suffer from the memory effect and lasts through more recharges."
],
"score": [
5,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
drl5ca | How are thermal cameras made and how do they work? | Engineering | explainlikeimfive | {
"a_id": [
"f6j71b3"
],
"text": [
"Warm things emit infrared light with hotter things emitting a larger spectrum of frequencies of infrared than cooler things. The sensor of a thermal camera is sensitive to infrared light, then the signals from the sensor are mapped to the visible spectrum so that we can see them."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
drp57d | Why Do Floorboards creak? | Engineering | explainlikeimfive | {
"a_id": [
"f6k65n0",
"f6k68y2"
],
"text": [
"Real, old and rather thick floorboards were made to fit very tightly. As they get used and older, the support from underneath wears down and the floorboards themselves can move a little. Now, when you put weight on them, they want to bend downwards but are held in place by their neighbors. That's what happens right before they creak. When they do creak, it's the tight fit floorboards rubbing against each other and bending a little themselves. Additionally, floorboards are usually made of very hard wood and treated with oils. This makes them a little 'moist' and more likely to creak instead of just gliding past each other.",
"When temperature change or pressure makes the individual boards expand, contract and bend in different ways, they often rub up against each other and make noise."
],
"score": [
4,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
drscoc | How do split lentils get split? | I'm not looking for recipe suggestions - in the store you can buy lentils that are not cooked, but already cut in half (aka, split lentils). What kind of machines or processes do the food companies use to split them? | Engineering | explainlikeimfive | {
"a_id": [
"f6kt21g"
],
"text": [
"It involves a giant machine designed for doing specifically that, this [video]( URL_0 ) will help explain it better than I can."
],
"score": [
7
],
"text_urls": [
[
"https://youtu.be/BgA68WoPKqs"
]
]
} | [
"url"
] | [
"url"
] |
drvvhr | It seems to me that traffic circles move traffic through intersections a lot more efficiently than stoplights do. Why then do the overwhelming majority of intersections have lights instead of circles? | Engineering | explainlikeimfive | {
"a_id": [
"f6ldhyw",
"f6ldt63"
],
"text": [
"Traffic circles are more efficient for low levels of traffic. Once you have a high level of traffic it starts to lock up and it relys on drivers operating efficiently.",
"Traffic circles suffer from severe limitations when a lot of traffic needs to flow. People fight over lanes and such more, and every lane you add is substantially less useful than the last. The great big 8-lane roads that you can encounter in really busy areas would have absolutely no use for a roundabout. Stoplights are the way to go in this case."
],
"score": [
15,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
ds2au1 | Why does a drop in power supplied to an electrical grid cause a drop in frequency? | As the title says. I am currently doing a essay on the UK power network and I would like to know more about why this happens. | Engineering | explainlikeimfive | {
"a_id": [
"f6mlubh",
"f6mmcwl"
],
"text": [
"The AC frequency is determined by how fast the generators at the power plants are spinning. If one power plant goes offline, the load on the remaining ones goes up, and that means the generators will be harder to spin. If the remaining power plants don't take measures to drive their generators harder (such as producing more steam), the generators will slow down and the AC frequency drops. This is how you can picture it: [ URL_0 ]( URL_0 ) How much force you need to spin this magnet will depend on how much power is being drawn from the outputs.",
"The electrical grid has basically no storage: there are not (yet!) batteries big enough to store that much energy, and what's created by generators is used immediately. Generators are very heavy spinning machines full of wires and magnetic fields. If the grid's users demand more power than the generators are producing, that power's got to come from somewhere: it comes from the rotational kinetic energy of the generators. So if demand exceeds supply, the grid makes the generators slow down. Since their spin rate also sets the grid's AC frequency, the frequency drops too. Power plant operators must carefully monitor the frequency: if it drops, they know they're not producing enough electricity, so they \"step on the gas\", burning more coal or gas, or opening the hydropower dam a bit more, or whatever to bring the generators back up to speed."
],
"score": [
10,
4
],
"text_urls": [
[
"https://i.imgur.com/lIACOng.gif"
],
[]
]
} | [
"url"
] | [
"url"
] |
dseqdr | what is the difference between all wheel drive and 4 wheel drive? | Engineering | explainlikeimfive | {
"a_id": [
"f6oxldh",
"f6ow2fk"
],
"text": [
"4WD systems are typically RWD with an option to engage 4WD. But the thing is, the front and rear drive shafts are typically coupled together, which is fine for off-roading, but on grippy asphalt though, that's no good because the front and rear drive shafts would ideally want to turn at different rates on turns. The result would be slip of one of the wheels. AWD systems on the other hand are always engaged, and have a centre differential to allow for that difference in the front and rear axles. This makes them less useful for off road for the same reason - on the simplest systems, if one wheel loses grip, all the drive can get sent to that wheel so it sits in the air spinning while you're otherwise stuck. For on road grip, they do have advantages though.",
"Basically, AWD is where a vehicle is capable of using any/all wheels to drive as needed at any time and 4WD is a RWD vehicle that you have to select the front wheels to be drive wheels if conditions necessitate."
],
"score": [
36,
6
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dsqvsc | Knitting fancy patterns is hard to do with machine, but how do sock manufacturers manage the crazy weaves with multiple colours, textures, thicknesses, and even small letters for left, right, and size all in a seamless sock? | Engineering | explainlikeimfive | {
"a_id": [
"f6r6w4g"
],
"text": [
"The simple answer, complex weaving Looms, multiple 'shafts' ,and a big fat computer to do all the thinking and work-source, I am a weaver"
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
dswvnt | 5: How do pulleys magnify your strength? Seems like you're getting something for nothing. | Engineering | explainlikeimfive | {
"a_id": [
"f6s82x5",
"f6s8rw8",
"f6selva"
],
"text": [
"Definitely not something for nothing. The set ups might reduce the weight experienced by the person pulling but it’s exchanged for distance pulled. The same “work” is done. If something weighs 100 lbs and you have a setup that allows that to be halved you’d double the distance pulled. If it’s quartered, meaning the “weight” is now 25 lbs from the pulling end the distance is now quadrupled. This is not exact. This is just breaking down the basic concept.",
"It's called force reduction, for each wheel in the pulley system you cut the force required by half, however at the same time you double the distance you must move to lift the weight the same distance. So you aren't getting something for nothing, the law of the conservation of energy ensures that. However your over all load is \"lighter\" so you can go farther with the same amount of energy. Here is a quick example. A 100kg object requires 1000 Newton's to move it 1m in 1 second. By putting the object through a 4 pulley system you reduce the force neccisary to move it to 250 Newton's. However at 250newtons you must move 4 meters to achieve a 1 meter difference on the objects end. So in the end you've still expended 1000 Newton's, but you've distributed it over a longer period.",
"You're using a trick and a fulcrum. In the easiest case that's just a tree stuck into the ground. By using a piece of rope to pull your load over the tree, the weight of your load is \"leaning\" on the tree. If you build a set with more than one \"wheel\", you can use the tree (or trees, or fixing points at the top of the building) to \"carry\" or hold up the weight several times. The weight you have to pull is thus split between you and each tree/anchor. As the previous replies already said: The amount of work is not reduced. You now have to pull the rope up and down several times and the total pulling distance is increased. However, the additional supports reduce the weight of the load. Note, of course: If your weight is too heavy, you'll just rip the pulley out of the ceiling and cause damage to your pulley system. This could be more expensive than hiring a second person to help you lift."
],
"score": [
15,
6,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dsyscl | why is it better for the turbines on a jet to sit under the wing rather than over it? | Engineering | explainlikeimfive | {
"a_id": [
"f6sti12",
"f6ua6o7",
"f6twadv",
"f6u87e9",
"f6tbzrv"
],
"text": [
"It's partially just easier to have the engines be below the wing from a construction and maintenance perspective. In addition, with the engines below the wings, when the engines spool up that tends to pitch the nose of the plane *upwards*. Conversely, if you mount the engines above the wings, that'll tend to pitch the plane *downwards*. The upward pitch is more preferable so long as you don't stall the plane. Edit: I should mention that the above comment on mounting the engines relates to when you mount the engines **directly over or under the wings**. There are aircraft with engines mounted above the wings in service, but they tend to have engines mounted as far back on the aircraft as possible (typically on the tail structure), which achieves the same kind of upward pitch because of how the engines interact with the planes center of lift and center of mass.",
"I'll give two more reasons that I didn't see other commenters add: 2. For commercial airliners, passenger comfort is a big deal. Having the engines below the wing and away from the cabin mitigates the noise. 3. If the engine were to detach in flight then it's better for it to be able to fall away cleanly rather than potentially falling onto the wing or worse hitting the control surfaces at the rear.",
"Along with everyone else's answers, the wing would act like a shield against the engine noise, making it quieter in the cabin. Of course, this really only applies to low-mounted wings. Edit: spelling",
"When I did ground school we talked a lot about parasitic drag [ URL_0 ]( URL_1 ) I'm not an AeroEng but I'd think that you would not want to break the air flow over the top of the ~~where~~ wing where 80% of lift is generated. Edit: typo",
"Don't tell Honda! [ URL_2 ]( URL_2 ) [ URL_1 ]( URL_1 ) The Honda Jet is unique but there can be an aerodynamic benefit to putting the pod above the wings. The Cirrus Jet mounts the engine in a weird location as well; [ URL_0 ]( URL_0 ) The big caveat to this is that these are small engines with (relatively) low fuel flow. It would be hard to fit a GE90 on top of the wing because of how cartoonishly huge the intake is. It would have to be up and out and the structure of the wing would have to be totally redesigned. Probably the most obvious reason is that maintenance is a lot easier with the turbine closer to the ground."
],
"score": [
165,
27,
17,
13,
13
],
"text_urls": [
[],
[],
[],
[
"https://en.wikipedia.org/wiki/Parasitic\\_drag",
"https://en.wikipedia.org/wiki/Parasitic_drag"
],
[
"https://cirrusaircraft.com/aircraft/vision-jet/",
"https://www.hondajet.com/otwem",
"https://www.hondajet.com/"
]
]
} | [
"url"
] | [
"url"
] |
|
dt04j5 | Some street lights don’t change unless there is a car there, how does this happen? | Engineering | explainlikeimfive | {
"a_id": [
"f6t69s4",
"f6t61rw"
],
"text": [
"The old style of sensor is a loop of wire in the pavement. There's an electrical signal going through the wires at a consistent frequency. When a car drives over the wire loop, the iron in the car's frame has an impact on the frequency of the signal through a process called induction. When the frequency drops, it sends a pulse to the traffic light controller, and that's how the controller knows that a car is waiting. The new style of sensor is a really fancy camera on the signal arm. The camera can detect when there's a car waiting to cross.",
"There are sensors in the road. Look for a rectangluar perimeter patched with asphalt. That’s where your car should be."
],
"score": [
14,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dt7a3c | Why can't we stop spammers from spoofing phone numbers? | Engineering | explainlikeimfive | {
"a_id": [
"f6v0zmp"
],
"text": [
"There's actually something being put in place now. It's called STIR/SHAKEN. Basically, everyone who owns numbers will have a cryptographic certificate that they will use to generate a token for every outgoing call saying \"Yes, this is my number. I own it.\" That token gets passed through the telephone network and received at the destination. The token is then verified. If a call comes in without an authentication token, your phone carrier has the option of rejecting it or flagging it as \"scam likely\"."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
dtfkf2 | how could I get shocked when something is already unplugged? | I was unplugging a WaterPik I had just used and my hand was wet. The plug fell onto my wet hand and I got a pretty bad shock. If it's already unplugged how does this happen? Would I have still gotten shocked if my hand was dry? | Engineering | explainlikeimfive | {
"a_id": [
"f6w9awg",
"f6wva8u",
"f6x2e8b"
],
"text": [
"There are capacitors connected across the prongs to filter electric noise. They are tiny (1-2nF at most) so they discharge very quickly, but if you yank the cord and touch it fast enough in the right conditions (or if the device has a not super well designed filter) it might still have enough charge to give you a sting. Edit: [Schematic of an AC filter]( URL_0 ) The X and Y-capacitors are the ones that can sting you. R1 (the bleeder resistor) is responsible for discharging them. If it's too high resistance, the capacitors empty slower and you might get a shock. If it's too small, it wastes too much power when the device is plugged in.",
"There's those things called capacitors in electronics which act like short term batteries. They are used to stabilize voltage.",
"Be ultra careful if you are servicing air conditioners or furnaces. They have large, motor starting capacitors that will knock you flat."
],
"score": [
34,
3,
3
],
"text_urls": [
[
"https://www.researchgate.net/profile/Davide_Montanari/publication/228870450/figure/fig1/AS:300653697093641@1448692835610/General-purpose-AC-filter-with-X-and-Y-capacitors.png"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
dth029 | Do cars still use gas going down hills? | ELI5: This is a really stupid question, but suppose you’re in a car with all the AC off and you go down a long hill without hitting the gas. Does the car still use gas during this or is it “saving” gas? | Engineering | explainlikeimfive | {
"a_id": [
"f6wiz8b",
"f6wjah8",
"f6wls1v"
],
"text": [
"When you are coasting without touching the gas pedal, the car's computer shuts off the fuel injectors. Since the motion of the car is turning the engine over, it doesn't need to burn any fuel to keep turning . Old cars with carburetors didn't do this, because the amount of fuel they used was determined by how much air was going through the engine as it turned, there wasn't anything to cut it off completely.",
"No, they don't use gas going downhill. When the RPM goes high while the throttle is closed, the ECU will cut off the fuel supply to the engine. If your car has a fuel consumption meter you can observe that the consumption goes low during the cut-off.",
"This all depends on how old the vehicle is. Modern cars shut down the injectors when coasting and use the wasted compression of the cylinders to slow the car (engine brake)"
],
"score": [
16,
6,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
du378y | why aren’t aerosol spray cans powered by plain old compressed air? | Engineering | explainlikeimfive | {
"a_id": [
"f71hbbn"
],
"text": [
"You want the propellant gas to be in its liquid state inside the can so it takes up as little space as possible. So you want a gas that you can liquify at moderate temperatures using moderate amounts of pressure. Butane for example has a vapor pressure of a few bars at room temperature, so the can would have to hold about as much pressure as a car tire to keep the butane liquid. You can easily do that with a cheap metal can. Liquifying air is not really an option for something like deodorant because there would be very low temperatures and/or extremely high pressures involved. It'd be a pipe bomb, more or less, and since air can only be liquid at cryogenic temperatures, the container would have to kept very, very cold. Using air in its gaseous state would work, but you would either need a heavy, expensive steel container (something like a miniature scuba tank) to store enough air at high pressures, or if you wanted to keep the pressure lower for safety reasons, you'd need an extremely large container. Bottom line, using gases that are easier to liquify than air allows you to squeeze a lot of gas volume into a tiny, cheap container. Liquid butane has an expansion ratio of 1:233, so 0.1 liter of butane inside a can gives you 23.3 liters of gas coming out of the nozzle. Compressed air at 5 bar (about right for a commercial spray can) has an expansion ratio of 1:5, so you'd need 4.66 liters of volume inside the can for the propellant. So your deodorant spray would look more like a fire extinguisher."
],
"score": [
17
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
du3a61 | If a supercharger charges a Tesla in 1 hour, why can't they make smartphone chargers that charge phones in 1 minute? | Engineering | explainlikeimfive | {
"a_id": [
"f71fyr2",
"f71kkf4",
"f71p3wo",
"f71g5nq"
],
"text": [
"Loading a battery with charge too quickly can result in burning out the circuits used to charge and drain the battery. Tesla batteries are made to charge quickly for their size to be convenient, phone batteries are capable of lasting all day on a single charge with moderate use.",
"you would need a phone battery that could handle the resultant heat. tesla batteries need to withstand accidents without exploding, so the added weight and complexity to make them charge quickly is relatively minor. for the 5 oz of phone in your pocket it's more significant.",
"A Tesla's battery isn't actually one big battery. It is instead composed of many cells of lesser capacity all linked together as one. This means the issue isn't filling one huge battery in an hour but rather filling a bunch of small cells in an hour simultaneously. For your phone that means the equivalent feat would be filling its battery in an hour. And yes, that can be done.",
"Imagine eating a full course meal in a minute, not fun sounding right? Your body isn't made to consum that much that quickly. Its puts a lot of stress on the battery to charge it that quickly, can hamper charge hold-ablity. A battery is filled with cells, it takes time to fill them properly."
],
"score": [
14,
7,
7,
4
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
du6qls | Why is dead weight so much heavier. Example; if I'm carrying an awake 5 year old, he feels much lighter than if he is asleep. Why? | Engineering | explainlikeimfive | {
"a_id": [
"f72m1ys",
"f72dl71",
"f72gy5k",
"f72nzuf"
],
"text": [
"My theory about that (and I've done a lot of carries a lot in combat rescue) was that conscious people tend to move with you like a good gyroscope. They contribute to your own inertia, allowing you to move more easily than if they just went completely limp like a sand bag. And, like another poster said, they tend to hold you differently, which aids in weight distribution. Conversely, people that are actively resisting being carried will cancel your movements, making it far more difficult than a simple dead lift. Think of how dancers can magically lift another dancer high into the air. This is an extreme example of how the person being lifted is contributing their inertia to your ability to carry them. They would expend far more effort to dead lift 100lbs over their head. Professional wrestling moves can work on much the same principles. The overall amount may not be much, but it is noticeable.",
"Usually when a child is awake, you carry them differently than if they are asleep. Carrying a child if they are laying across your arms, (like if you pick them up off the couch to transfer them to the bed and you keep then in the laying position) throws off your center of balance more than if you hold them upright and close to your body. This makes it more difficult to carry the weight. They also tend to hold on to you at least a little bit which will affect the way it feels to carry them and the stress on your arms.",
"Not heavier but harder to manage and harder on muscles since the wieght is more likely to shift and has to be c9ntrolled more",
"Disbursement. When he is awake they hold their head up and probably their arms and legs. So their weight is more centered. When they're sleeping, their weight will constantly shift, and wont be centered."
],
"score": [
87,
39,
6,
5
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
ducf4q | Why do energy saver cycle on washers, dryers and dishwashers take a longer time to complete than the regular one? | Engineering | explainlikeimfive | {
"a_id": [
"f74qj7j",
"f75l4zy"
],
"text": [
"Energy saving cycles save energy by moving less and letting the laundry sit longer in the water to clean it. Most energy is used by heating the water, then it is the motor turning the drum. The least amount of energy is used for the electronic.",
"To add to what has already been said, the liquid/powder contains enzymes that require some time to reach full effect, and with lower temperature out often needs more time instead. This is also the reason why there are periods where nothing seem to happen (that, and maybe generally just letting the stuff soak a bit in the water)."
],
"score": [
9,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
duolaj | how do structures with several stories support so much weight? (For example, parking garages, apartment buildings, Empire State Building.) It seems like the structures should crumble under that much weight without support beams every few feet. | Engineering | explainlikeimfive | {
"a_id": [
"f77i0i9",
"f77gce6"
],
"text": [
"There are a few aspects to this, but one major one is this: Force is funneled into the vertical support beams, which run straight down and are immensely strong. Every floor only holds its own weight - the weight of the floor above goes into the vertical support beams which do not rest on the floor below. You can imagine it like branches on a pine tree - each branch is connected to the trunk, and not the branch below. The vertical support beams, meanwhile, are thick structural steel I-beams, and can bear a rather staggering amount of force.",
"The size of the columns gets larger or more closely spaced the further down you go. Gravity loads are relatively straightforward to design; what gets crazy is seismic design, especially on high rises."
],
"score": [
8,
6
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dusn4a | How does electricity flow in a one wire O2 sensor? | Please keep in mind I have very little knowledge of how electricity works and how atoms behave. So I want to know exactly how the PCM or ECM receives a signal from a one wire oxygen sensor in a car. I know that the sensor creates it's own power by comparing exhaust air to reference air inside an element which creates a small voltage I'm just uncertain how the ecm reads this voltage. Since the sensor is grounded to the chassis of the vehicle my mind instantly goes to "The electrons will follow the path of least resistance" and flow to ground instead of following the signal wire to be red by the ecm. I believe it's the same concept with single wire crankcase sensors as well. Please use the water analogy if possible. It helps me understand the concept better. | Engineering | explainlikeimfive | {
"a_id": [
"f77z4h7"
],
"text": [
"The electricity flows from the cars computer, thru the o2 sensor element, then to ground thru the sensor body. The amount of o2 present changes the elements resistance and thus the flow of current thru it. The ecm is essentially measuring the resistance of the sensor like a voltmeter would"
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
dut4u0 | How does a vacuum cleaner work and how is it able to suck like that? | Engineering | explainlikeimfive | {
"a_id": [
"f782ahz",
"f782eno"
],
"text": [
"The extraction fan in a vacuum cleaner reduces the pressure inside the canister. Atmospheric air, which is at an absolute pressure of about 14.7 psi, is driven by that pressure up the hose towards the evacuated canister, and carries with it all of the debris you are trying to clean up. As atmospheric pressure is near constant, you can never get more pressure differential than that, so what makes one vacuum cleaner more powerful than another is simply how much air it can move. Powerful vacuums can maintain that pressure differential even with large bore hoses.",
"A vacuum cleaner basically has a powerful fan in it that blows air out of the cleaner. Now, when there's more air on the outside, there has to be less on the inside, which is the case. We will need this again later. Air is not weightless. The more you stack, the more weight pushes down on the part that's all at the bottom. This is for example why the air is thinner on mountains where there's just less air pushing down and creating pressure. This pressure is called atmospheric pressure and at sea level 1 Bar. Now back to the vacuum cleaner. There's now air \"missing\" inside the machine, but the atmospheric pressure that exists even in your house is still trying to compress the air below it. The air below it doesn't want to be compressed and looks for places to go, which happens to be your vacuum cleaner. This flow of air, also called wind, now blows dust into the vacuum cleaner where it's collected in a bag."
],
"score": [
5,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dv4oiw | how did the first planes work | I’m talking Wright brothers and WWI planes. How did they work? How do they fly? I know that the turbines on modern planes are what move them into the sky but how did the first planes work? Like, how do propellers let you fly? | Engineering | explainlikeimfive | {
"a_id": [
"f7akx5x",
"f7al6if"
],
"text": [
"Instead of turbines they used propellers to push the air, and the propellers were turned by piston engines much like the ones in a car.",
"The first planes were more like big box kites with a fan. They fell a bit less slowly the faster they went, with the angles of the wings driving \"lift\". Modern planes have a lot more engineering but use the same physical principles"
],
"score": [
6,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
dvaqwl | How does burning coal generate electricity? | Engineering | explainlikeimfive | {
"a_id": [
"f7bhu38",
"f7bim51",
"f7bhzmr",
"f7bhspg",
"f7bi67w",
"f7c63c7"
],
"text": [
"Almost all electricity is generated by a turbine (which is a spinning thing that is attached to a magnetic coil). Coal is burned below water, which turns the water into steam. The high pressure steam is then directed into the turbine, thereby spinning it and creating electricity.",
"All thermal energy generation is basically the same process, including coal-fired, gas-fired, oil-fired, and nuclear power plants. You heat and boil water in a confined space, raising the pressure and temperature of the steam significantly. You then allow it to expand through a turbine, and some of the thermal energy is extracted as mechanical/rotational work. Attach that turbine to a generator, and the mechanical work becomes electricity.",
"You use the coal to heat a large boiler containing water. As the water heats up it turns to steam creating a huge amount of pressure. At a certain point, a valve opens releasing the steam into a large turbine (like a propeller in a pipe). Because the steam is very hot it moves very fast and pushes the turbine around. This turbine is connected to a large magnet that moves and creates electricity",
"Burning coal is a relatively efficient way to turn water into steam, which turns turbines, which generate electricity.",
"You burn coal to make stream, you run the stream through a turbine to make that spin. You attach a magnet to the shaft of the spinning turbine to get a rotating magnetic field, then you put coils of wire in a housing around the spinning magnet so the magnetic field rotates through them. A rotating magnetic field passing through a conductor _induces_ a current, and that's how you turn coal into electricity! Thank you Story Bots! < Edit: > Seriously, Story Bots has a really good episode explaining how electricity is made.",
"The exact same way burning coal makes a ship or train locomotive move: a steam engine. So to start, you load the coal into a furnace and light it on fire. Inside the furnace are tubes filled with water. As water enters the tubes, the heat from the fire causes it to rapidly flash over into steam. Depending on the design, the steam might pass through the fire multiple times so it gets really hot, or superheated, and thus has more energy. As more water is converted into steam, pressure builds. The pressurized steam then gets directed into a turbine. It's sort of like a jet engine. As steam enters the turbines, it hits a bunch of tiny blades inside that cause the turbine to rotate. Some plants will have multiple high and low pressure turbines, so they can use the same steam multiple times. As the turbine rotates, it turns a generator. Magnets inside the generator produce a current in the wire, and that's how you get electricity. Most thermal power plants work this way: coal, nuclear, oil, natural gas. All use something hot to turn water into steam, which runs a turbine."
],
"score": [
32,
16,
10,
3,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dvgt9p | Why is the zipper merge faster? | I watched this [video]( URL_0 ) on why zipper merging when driving is better than merging early. I understand the first 3 reasons they lay out for why early merging is bad: 1. Early merging opens up space for a dbag to just fly through (ironically zipper merging is asking for everybody to be that dbag, hence nobody is a dbag). 2. Early merging can create a traffic gum up well before the merge for people who would be otherwise unaffected. 3. Early merging creates more traffic accidents. What I don't understand is the 4th reason--that it is slower. In the video it says "when you force a bunch of cars to basically come to a stop in one lane, it gets everybody through the bottleneck slower." When I studied operations (only one class to be fair) in school, we were taught that the bottleneck is really the only thing that matters. Speeding things up before the bottleneck doesn't impact flow time. So why is the zipper merge faster? | Engineering | explainlikeimfive | {
"a_id": [
"f7cmdx0"
],
"text": [
"The fourth point relies on a little bit of knowledge about traffic jams. Traffic jams occur when one person slows down for some reason. We'll call him \"1\". When 1 slows down, the person behind him (2) has to slow down slightly more than 1, because 2 doesn't have psychic knowledge of exactly how slow 1 is going to go. The person behind 2 (3) now has to slow down even more than 2, for the same reason. This goes all the way back down the road until suddenly some unlucky fellow (A) has to come to a complete stop. This is a traffic jam. When A is able to move again, he does so slowly, because the person in front of him is moving slowly as well. This causes a whole bunch of starting, stopping, creeping, and stopping again, which translates to more backed up traffic far behind them. The zipper method offers a solution that keeps cars moving, which is the ultimate method of preventing traffic jams. If everyone moves at a constant, albeit slow, pace, then there is no traffic jam. The method only has the one drawback; everyone has to be on board with the zipper. If even one person tries to skip ahead and jam in, he's gonna cause a lot of issues down the line."
],
"score": [
21
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
dvrxuz | How does turning down the temperature while away from home actually save energy? | It seems to me that maintaining an internal temperature would require less energy than letting the house cool and then having to crank the furnace on high for an hour or more to raise the temperature back up to a comfortable level, assuming the external temperature is much colder than the internal temperature. Follow up question: When the external temperature is much colder than the internal temperature, are there any energy savings in keeping the internal temperature lower, say around 17 Celsius vs 21 Celsius? | Engineering | explainlikeimfive | {
"a_id": [
"f7edbir",
"f7ebiua",
"f7efy1l"
],
"text": [
"> It seems to me that maintaining an internal temperature would require less energy than letting the house cool and then having to crank the furnace on high for an hour or more to raise the temperature back up to a comfortable level, assuming the external temperature is much colder than the internal temperature. Everything I've learned about heat transfer says this isn't true. In short, heat transfers faster when the temperature difference is greater. Heaters and A/C output a constant temperature when they're on, no matter what your thermostat is set to. Think of it this way, if it's 40 F outside and your thermostat us set to 70 F, you're trying to keep the house at a constant temperature. As soon as it hits 70 F, your heat shuts off, because 70 F to 40 F is a big difference, it loses heat very quickly. As the difference in temperature falls, the rate of heat loss also lowers. In comparison if you have your thermostat set to 60 or 65 while you're away, there is still a big difference from 60-65 down to 40 but that difference is less than from 70 down to 40, which means your house loses heat more slowly because your thermostat is lower. This means the heat doesn't run as often as if you try to keep it 70 the whole time. So yes, it may seem maintaining a higher temperature would be better, but the actual energy required to raise the house (in winter) from a maintained 65 F to 70 F when you return, is less than the energy required to maintain 70 F the entire time. This is because the greater the temperature difference between inside and outside your house, the more often your units have to turn on, the more often they turn on, the more energy they use. While on, they use the same energy whether they are heating the house 1 degree or 10 degrees, the only difference is how long they run, and heating the house 10 degrees takes less time than heating the house 1 degree 10 times (due to how heat transfer works).",
"Heating the house back up is something of a fallacy. What you are doing is replacing heat lost to the outside. Think of it as a \"black box\". The only input is your power supply. The only output is heat escaping that needs to be replaced by the supplies you are paying for. The energy loss is a function of the difference between inside and outside temperature summed up over the day so you want to keep that as low as possible.",
"The energy to heat up a house a degree is constant, that is as long as the house is warmer than the freezing temperature of water. The rate that heat leaves the house trough thermal conductivity trough the wall depends on the temperature difference. The energy loss is a constant that depends on the isolation multiplied by the temperature difference. So the lower temperature difference the lower the heat flow from the house is and the temperature drops lower. Let's say that it is required 720 000J= 200Wh to raise the temperature 1 degree and the heat loss is 10W/(degree difference). The number is completely made up of simple calculations. So not correct for a real house but they show the principle. If the outdoor temperature is 0 and the indoor temperature is 20 the heat loss is 10\\*20= 200W so 200Wh per hour. That is the energy required to keep the house at that temperature per hour. For 3 hours you need 3\\*200=600Wh If you turn off the heater and simplify the calculation so the temperature only change at the end of the hour to avoid differential equation. A correct solution will show an even larger difference. The first hour you loos 200Wh. That would result in a drop in the internal temperature of 200/200=1 degree to 19 degrees. In the second hour, the temperature difference is only 19 degrees so the energy loss is 10\\*19=190Wh . The temperature will drop by 190/200=0.95 degrees to 18.05 degrees. The third hour the energy loos is 10\\*18.05=180.5Wh and temperature drop is 180.5/200=0.9025 and the temperature is 17.1475 degrees To heat up the house to 20 degrees you need to heat it 20-17.1475=2.8525 degrees and you need 2.8525\\*200=570.5Wh of energy to do that. That is lower then the 600Wh you need to keep it a lover temperature & #x200B; So that simplified calculation shows that the energy needs to keep a constant temperature is higher than to let it drop and to heat it up again. For the same reason, you save energy by lowering the temperature because the heat flow is lower. Estimation of energy-saving is (17-outdoor temp)/(21--outdoor temp) so at * 0C is 17/21= 0.81 so a reduction of 19% * \\-20 C ( 17+20)/(21+20)= 0.90 so 10 % less The most extreme case is if it is 17 degrees outdoors when you need no heating if indoor is at 17 degrees but you need heating to get to 21 so the difference is infinite. Reality is more complex than this, for example, the ground does not have the same temperature as the air, you have ventilation and heat is lost that way."
],
"score": [
28,
4,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
dw23cm | How does having two coupled locomotives, or two truck cabs chained in series, actually help to pull a heavy load? | Engineering | explainlikeimfive | {
"a_id": [
"f7g6esk"
],
"text": [
"When the vehicles are working in unison, the power being applied to the wheels from both vehicles are creating more torque allowing the 2 vehicles to pull more weight. Imagine 3 equally powered people. 2 people on one end of a tug-of-war rope and only 1 person on the other side. The 2 people will generate more torque and power than just the 1 person on the other side. As long as the resistance on the other end is persistent, then the 2 vehicles will continue to provide power and torque against that resistance. Once resistance is eliminated the power from the 2 vehicles will immediately cause those vehicles to leap forward. Which is why the more powerful vehicle should be the first in the chain. Otherwise the more powerful vehicle will accelerate into the first less powered vehicle. This is also why you have your most powerful “anchor” on the end of a tug-of-war rope."
],
"score": [
10
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
dwgu0g | Why do non-engine related problems trigger the “check engine light” in cars? | I JUST had my engine replaced two days ago. Then, the check engine light comes on. Tragic. The diagnostic code was P0073, which apparently often pertains to the Ambient Air Temperature Sensor. This makes sense considering it’s 40 degrees outside and my car says it’s 85 degrees. Point is. Why can’t they just assign these non-engine related problems to a different warning light? Why is it programmed this way? | Engineering | explainlikeimfive | {
"a_id": [
"f7j3b94",
"f7j3caz"
],
"text": [
"The check engine light has nothing to do with drivability (engine performance) and everything to do with emissions. Any time a fault occurs more than once, the light illuminates to alert you of a new code for that fault. These faults would cause your car to produce higher emissions than rated, so the light turns on to tell you so you get it fixed. EDIT: To further explain, your Ambient Air Temp sensor reads ambient air, compares it to intake air temp as part of what's used in order to make fuel delivery and spark timing calculations. These allow the most efficient use of fuel with the least amount of emissions produced. If the sensor isn't reading correctly, then preset tables are used to make those calculations which can cause higher than normal emissions. Thus resulting in the light illuminating. EDIT 2: True engine faults will illuminate other lights. Engine oil pressure, overheat conditions, charging system, for instance have their own lights to alert you of issues that are a danger to your vehicle's continued operation. A severe misfire will make the MIL/Check Engine Light light flash. If you ever see it flashing while driving, stop as soon as you safely can before it stops itself.",
"Because it all controls the operation of the engine. In your example, The air density changes with air temperature so the engine management system needs to accommodate this change by adjusting timing/fuel trim for the engine to run at optimal efficiency. Also by doing it this way, it saves on manufacturing costs by not having to design a new light, build a new light/socket, run extra wiring,and general assembly costs associated with this. Having one “Malfunction Indicator Lamp, or Check Engine Light” it saves money and time."
],
"score": [
10,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
dwjnzu | What does Amp do in a DC motor? | Hi, The title says it all. If I increase the volt, the motor will run faster. But what will increase when Amp is increased? Again, will it run when powered by a lower amperage power supply than rated? Thanks all Edit: Thank you all for explaining it. | Engineering | explainlikeimfive | {
"a_id": [
"f7joyyj"
],
"text": [
"Amp is related to torque, how hard the motor turns. However, the causality is different. You don't increase the amperage to the motor. You increase the load and the motor pulls more Amps."
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
dwskt5 | When trying to start a car with a low battery, what does "flooding the engine" mean and why is it bad? | Engineering | explainlikeimfive | {
"a_id": [
"f7l5k0a",
"f7lafhg",
"f7l5zio"
],
"text": [
"Flooding the engine means putting too much fuel into the engine. It's bad because if there's too much, you wouldn't be able to start the engine anyways. Too much fuel won't allow for proper vaporization, so it can't ignite. There's not enough air to burn the large amount of fuel. It's a headache to clear the engine of excess fuel",
"In the days of carburetors (1980's and before) cranking the engine automatically sucked fuel into the cylinders. Pumping the pedal also squirted fuel into the engine whether it was running or not. It was easy to get too much fuel and this would prevent it from firing. You could fix this by holding the pedal down all the way and cranking until it cleared, or sometimes waiting 10-20 minutes. This isn't as much of a problem as it used to be with fuel injection and computers. Generally what you do with the pedal before you start it doesn't matter.",
"The low battery is not really the cause of flooding the engine with gasoline. It is the pumping of the gas pedal that actually floods the engine. No really a problem with most modern cars but it can still happen if you keep pushing the pedal. Most cars no longer require that you push the pedal at all because they use fuel injection."
],
"score": [
15,
7,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dwtvp9 | How does a pen work? How can we write so much with what seems like not so much ink? | Engineering | explainlikeimfive | {
"a_id": [
"f7ler79"
],
"text": [
"Every line you make with your pen only uses a SUPER TINY amount of ink. The \"height\" of the ink you put on paper is about same as human hair. So the ink you have will last you a long time. As for how - depends on pen. If you're talking about ballpoint, then ink gets smeared on the ball, which rotates the \"smeared\" part towards paper, and then rubs it off on paper. Imagine taking a large tube, with a ball underneath, and putting some paint on top. As you move the tube, the ball's top side gets smeared with paint, but as the ball rotates, it stains the surface underneath it. That's ballpoint pen."
],
"score": [
11
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
dx2tcb | why do cars in the US typically have much larger engine displacement than cars in the EU? | Engineering | explainlikeimfive | {
"a_id": [
"f7n3py6",
"f7n5ver",
"f7n4gfp",
"f7n3i6p",
"f7n6p77",
"f7n55r2",
"f7n5gt7",
"f7n6jia",
"f7n56ub",
"f7n7fkr",
"f7n9eo7",
"f7n7u6w",
"f7n77dh",
"f7n8zby",
"f7n8cgh",
"f7n8k62"
],
"text": [
"Our fuel over here is almost twice the price of what it is in the U.S, for a start. [Gasoline price comparison]( URL_0 ) Add the fact our Road Tax (an almighty rip off) is based upon emissions (was once done on engine size), then it’s easy to see why our little 1.6l’s become the norm. A lot to be said for the size of our countries also. We would rarely have the need to take extremely long drives, where as the sheer scale of the U.S would likely make such road trips more likely.",
"The answer to this is a combination of a couple things. One item is that some European countries levied heavy taxes against engine displacement, which incentivized consumers to buy smaller displacement engines, which lead car makers to focus on small engines. In the United States, many automakers made large trucks which used large engines to tow/haul heavy loads. To save money, automakers tried to share some of the components of the truck engines with car engines. These engines also tied in well with the muscle car scene in the USA. You still see some of this today, especially with the big 3 American automakers. Other factors include emissions regulations, cost of fuel between Europe and the United States, and differences in how the different populations used cars. The United States stretches over a huge area of land with lots of open space between with long sections of freeway. Many European cities are very old and we're constructed long before automobiles were even remotely close to being an idea in someone's head. These small narrow streets make it hard to fit the larger cars that tend to accompany larger engines.",
"They think nothing of driving 10 hours at highway speeds. Bigger engines run at lower RPM at higher speeds. Lower RPM means less wear and better fuel efficiency over the excessive distances and higher speeds they regularly drive. In large part, most EU driving is in town in traffic where smaller engines are more efficient.",
"Because fuel is considerably cheaper in the US. Also they don’t tax based on engine displacement. Some other countries tax based on engine displacement so they try and keep it as low as possible.",
"In the U.S., you can drive at highway speeds for an hour and not have left town. In the E.U., you could drive at U.S. highway speeds for an hour and have broken the speed limit in three separate countries.",
"Mostly vehicle size. European cars are smaller, because European roads are smaller, often following city plans which predate automobiles.",
"A lot of reasons why we have *some* bigger engines. However, most cars in the US are relatively small displacement 4cyl. Even pickups like the F150 have a 2.7L engine option. My pickup is a 1.8L diesel. Sports cars and Trucks/SUVs are the only ones you're going to really see with the big engines. Most other cars usually come with a 1.5-2.0L engine. First though, the US is massive and we drive long distances all the time (I've actually got a 900 mile drive to my inlaws for Thanksgiving week, and 900 miles back). Larger engines run at lower RPMs compared to smaller engines, so our larger engines have less wear and better fuel efficiency over those long distances while small displacement engines would wear out quicker. Second, our gas is ridiculously cheap compared to Europe. The average is somewhere around $2.60 a gallon, but ranges from $2.21 in Texas to $3.99 in California. In Germany right now it is an average $5.79 per gallon (converted from Euro per liter). Third, we don't tax based on engine size.",
"Its literally just a culture thing and the way things have been done. In Europe it has always been about making small cost effective vehicles that help you get around. Distances travelled are generally much smaller. And there has always been a big focus on efficiency. In the US larger distances are travelled, there is the mentality bigger is better, bigger is more powerful, and space is not an issue.",
"To continue on the wonderful points everyone is making from highway efficiency to city efficiency to size and use of the vehicle. Let's talk about fun, as another user once put it America is so large and for the most part well laid out that we have streight roads, in essence drag strips with stoplights. What's fun on a drag strip? A powerful car with plenty of traction. Like what everyone drives around here Edit; AMERICA FUCK YEAH",
"1. Cars in the US are generally larger because the roads are larger, parking spaces are larger etc. It’s hard to fit a 8l engine into a fiat 500. 2. Fuel is much cheaper in the US. 3. Regulations on things like CO2 emissions are tougher in Europe.",
"All the misinformation in this thread just makes me think of Dennis explaining homosexuals to a gay man at a titty bar. The smaller engine actually let's the bigger piston know how much force to apply",
"because Americans arent as good at engineering as Germans or that ferarri guy so we became obsessed with \"muscle\" . i need atleast a 3.2 V tech engine and thats basically a girls car .",
"In addition, the new small engine cars with turbos and injection behave like bigger engines and are more efficient on mpg.",
"Two reasons. 1. Petrol is a lot more expensive 2. Dick size is not measured by car size 3. Public transport is better. We have three reasons.",
"Lots of reasons why. One of the largest was world war 2. Post ww2 the US had the resources to waste as they didn’t need to build and our car manufacturers were already good at building big engines because of the war. so they stuffed big engines into big cars because “why not?”. It wasn’t until the oil crisis that smaller displacement engines were a staple in the market. Also independence is important as well.",
"I think the most answers here do not really get it right. I know some US branded cars and I am from Munich (home of BMW and near to the home of Audi), a lot of my friends are in the car industry. Typical US cars tend to be big and cheap. They have simple piston engines like European car manufacturers had them in the past (20 years ago). The bigger the engine, the more power you get. Nowadays this seems to change. Our engine trend towards downsizing does not come with less power in the output. Instead engines get increasingly more expensive and complicated. They add turbo chargers, run on 3 cylinders, add hybrid style electric engines and so on. This is done purely for better fuel efficency. Best examples are the luxury end Audis and BMWs. Engines got smaller but power stayed the same. You can run on them the same speeds and get the same travel lengths. However, wear on a turbocharged engine could be higher. Tdlr; It is only about fuel efficency."
],
"score": [
523,
466,
188,
66,
29,
23,
20,
11,
10,
6,
5,
4,
3,
3,
3,
3
],
"text_urls": [
[
"https://www.statista.com/statistics/221368/gas-prices-around-the-world/"
],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dx8822 | How do ATMs count cash? | Sometimes the banknotes I put into the machine are a tad creased or not aligned, yet in most cases, it manages. | Engineering | explainlikeimfive | {
"a_id": [
"f7o6ajk"
],
"text": [
"It runs each bill through a sensor that measures the magnetic properties of the ink. These properties are compared to pre-stored values for the various notes in circulation, and if the magnetic signature matches a 5'er, that's what the machine \"sees\". That way if there is a little folding of a phone number on the bill it will still work."
],
"score": [
16
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
dxdu54 | What is a posterior wall fracture? | Tua Tagovailoa sustained a dislocated hip and posterior wall fracture. I need a medical professional's explanation as to what exactly occurred to satisfy my pea brain. | Engineering | explainlikeimfive | {
"a_id": [
"f7p7a7x",
"f7p6ue1",
"f7paalg",
"f7pmond",
"f7ttcyb"
],
"text": [
"It's probably referring to the posterior wall of the acetabulum, which is the medical term for the hip socket (comes from the Latin for \"vinegar cup\"). The hip is a ball and socket joint. The top end of the femur (thigh bone) has a ball on it which fits into the acetabulum (socket). In a dislocation, the thigh is pulled away from the pelvis so strongly that the ball comes out of the socket and can't get back in. At the same time the posterior surface - the back surface - of the socket has cracked. Sore.",
"Okay so your hip joint is a ball in a socket. The socket is the part of your hip that is called the acetabulum. During certain types of impacts the ball of the hip gets forced into the back of the socket, and fractures it. That is a posterior wall fracture.",
"You have anterior and posterior - similar with shoulder dislocation. You can tell the way the persons arm is going/where the feet are pointed",
"Posterior hip dislocations are usually accompanied by some kind of bone injury, most of the time of the posterior wall of the acetabulum. It could be a little fragment( not really important) or big enough to cause instability and need surgery. It’s a serious injury for a prospect like him. Look up Bo Jackson’s hip injury.",
"I had a complete complex acetabular fracture back in 2006. We were hit head on by a driver and my knee hit the dashboard and drove the head of my femur through the posterior acetabular wall essentially “blowing out” my hip socket. I ended up with multiple plates and 16 screws to rebuild the socket. My femur still rattles around in there and I only have about 50% range of motion. The surgical inscison took 57 staples to close. Still hurst everytime I take a step. Obviously, Tua’s hip is not as bad as mine was, But I can not see a return to 100%, as his femur just wont fit into the socket like it used to. Will be prone to further dislocations. I can only describe the pain associated here as ungodly. It hurts so badly that I did not think tjose pain levels existed.... and it was months before the pain levels went down. I was non weight bearing x4 months"
],
"score": [
34,
6,
5,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
dxhzyp | why dont all rear wheel drive cars have the engine in the rear to avoid power loss in the differential? | Engineering | explainlikeimfive | {
"a_id": [
"f7qlz6q",
"f7qjb9c",
"f7qkae3",
"f7qwf0i"
],
"text": [
"rear engine design with water cooling has a problem of routing coolant to the front mounted radiator. you'll basically have two 10ft pipes carrying coolant that needs to pumped back and forth and not leaking. front engine design also helps with safety. in a frontal impact, the engine is the heavy mass that absorbs alot of the energy, leaving the occupants with less energy to dissipate",
"Rear engines are quite dangerous for a few reasons. Foe one, that's a lot of weight *behind* the passengers which can crush them during a collision. Meanwhile, it makes it inconvenient to have the transmission near the driver as most RWDs are manuals. Lastly, a differential is necessary no matter where the engine is. No power is lost through transmission down a driveshaft.",
"You would still have a differential. The differential would be built into the transmission and would then be called a transaxle. For example, the Porsche 911 has had a rear engine and a rear transaxle for decades. The differential isn't an individual component, but it is there inside of the transmission.",
"In addition to the other answers, weight distribution is important. The heavy engine sitting over the front wheels — the ones responsible for steering, is desirable for many applications."
],
"score": [
10,
8,
7,
6
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dxnpdh | since there is a lot of space debris circling earth at the moment, how do spacecrafts maneuver through it in order to go to different planets? Will they or won't they hit these debris? What happens when they do hit it? | Engineering | explainlikeimfive | {
"a_id": [
"f7thcpv",
"f7tsfng",
"f7tjac5"
],
"text": [
"There is a lot, but not so much that we can't get through it, the so called [Kessler Limit]( URL_0 ). Many things have been hit by tiny bits, they have to be tough enough to take it. The larger pieces are tracked, and paths chosen to fly around them. Eventually we're going to have to start picking up the trash, but NASA projects to do that still seem too expensive.",
"We watch for the big ones and avoid them. The little ones tend to come from a similar source as the big ones so there's some clustering but even if you spread them all out evenly there really isn't that much debris compared to the amount of space out there. Space is big! Mindbogglingly big, yadda yadda yadda. There are about 128 million pieces of space debris with over 99% being smaller than 1 cm. For easier math lets consider 1 Billion pieces that are each 1 meter wide floating in an orbit of 400 km(about the height of the ISS). That makes 1 billion square meters of that shell unusable, but that that orbital shell is 183 trillion square meters so that generous assumption of debris takes up 0.00055% of the orbital real estate even in this conservative estimate. In reality, satellites and the debris are spread around in a thick shell over Earth so they're quite spaced out. Similar to flying through the asteroid belt, if you pick any random straight path the odds of you hitting something are very low.",
"While there is a lot of debris out there there is an awful lot more space out there, the debris is tracked by radar and visual reports so they know where things are and generally can avoid them, also the debris is concentrated in certain areas and levels. When they hit the speed normal means that they create even more debris so making the situation worse - URL_0"
],
"score": [
66,
17,
11
],
"text_urls": [
[
"https://en.wikipedia.org/wiki/Kessler_syndrome"
],
[],
[
"https://youtu.be/Km2uemAqbbM"
]
]
} | [
"url"
] | [
"url"
] |
|
dy0d9s | how a 100 watt 220v bulb will perform the same at 110v. Wouldn't it become dim in low voltage? secondly if the performance is same isn't it more economical and conserving? | Engineering | explainlikeimfive | {
"a_id": [
"f7xnuci"
],
"text": [
"A classic bulb with a glowing filament (a white hot wire) wouldn't perform the same on 110v as on 220v, so that premise isn't correct."
],
"score": [
9
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
dy4esa | How do people build tunnels through mountains or underwater? | Surely if you dig out a mountain or a hill the soil above could collapse, or with an underwater tunnel I'm not sure how you would do that? | Engineering | explainlikeimfive | {
"a_id": [
"f7y9nve"
],
"text": [
"Tunnel boring machines drill through the rock and line the hole with a concrete structure. This prevents them from caving in, or flooding with water. Most underwater tunnels are not also underground very far. They are concrete forms that are fit together under water, usually in a trench. They are sealed to each other and then the water is pumped out to make a tunnel."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
dy6zvh | what prevents a car with horrible mileage from being able to use an engine from a car that gets great mileage? | Engineering | explainlikeimfive | {
"a_id": [
"f7yvvxi"
],
"text": [
"Technically, any car can use any engine that fits under the hood. You might need some additional modifications to make it play nicely with the transmission and driveshaft, crankshaft, etc., but it's all doable. However, part of what gives certain cars their MPG rating, is more than simply the engine under the hood. It's a combination of the gear ratio, the weight of the vehicle vs the power of the engine output, the use or lack of use of energy saving techniques like regenerative braking, or computer controlled features that cut the engine at stops and restart when you hit the accelerator, etc. So taking an engine from a car that has 40 MPG, and dropping it into your 17 MPG SUV, doesn't mean you'll magically have a 40 MPG SUV. That engine is likely underpowered for the size of the vehicle, and you'd use more gas to make it go, reducing your MPG (and possibly breaking things in the vehicle along the way. Cars really are, for lack of better term, fine tuned well oiled machines."
],
"score": [
13
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
dyeyj0 | How can some watches be more accurate than others? | I don't know much about watches, but I remember reading some watches only make a few seconds mistake each day, whilst others have larger error range. Isn't there a mechanical system that keeps the thing automatic? How can that create errors? Also some watches can remain accurate for decades, if one watch maker can do it, why can't other do it? I guess I'm just confused as to why there are errors and if there are errors, why some brands have larger margin of errors. Thank you in advance for your answers. | Engineering | explainlikeimfive | {
"a_id": [
"f80qfhy",
"f80qzbf"
],
"text": [
"Quality control and tolerances. In any machining operation your parts have tolerances. A tolerance is how far out of the specified dimensions the part can be. Very exacting tolerances get rapidly more and more expensive, as they require much higher quality of both manufacturing equipment and labor, and a quality control system that is willing to throw away potentially very expensive parts for being a *tiny* bit too big or small. A mechanical watch with very tight tolerances will be very expensive to make, but it will be extremely accurate because you know to a very high degree of certainty *exactly* how all the parts interact. A watch with loose tolerance will be much cheaper to make, but won't keep time as accurately because bits and pieces are going to be a little bigger, or a little smaller, or a little heavier than they should be, and in unpredictable ways.",
"There are two primary methods of timekeeping used that I'm aware of: analog (clockwork) and digital (crystal). There are also hybrids of the two. The first is the earliest type, though there are still watchmakers who build them and people who swear by them. It relies on a series of intricate gears that are carefully ratioed to provide a fairly close analogue to seconds when active, fed by the unwinding of a spring for energy. The user has to keep the spring regularly wound (hence the old thing about \"winding your watch\"), and is only as precise as human hands can make it and the materials don't deterioriate. That said, they can be pretty damn precisely made by master Craftsmen, so don't just assume they're inferior! Crystal watches use the power of **ELECTRICITY!** A crystal within the watch is excited with energy (from a battery, maybe solar in a few one-off instances?) and forms part of what is called an oscillator, or an electronic circuit that provides a constant output signal, which is then fed to more complex computing bits to count each second and apply electronic logic to vary the display. The crystal's composition determines the timing of the output voltage, and quartz remains the most consistently used material due to price and accuracy. However, while incredibly similar, all quartz crystals are not exactly 100% literally identical, so there will be variance in using them for oscillation. I believe there are a handful of super expensive watches using some more precise material, but I don't know what kinds of crystals are used off the top of my head. There is a middle ground, I should note, of quartz clocks (even in watch form, they're clocks, e.g. clockwork, albeit far less mechanically complex). Basically, replace that spring from the analog example earlier with a battery powering a tiny electric motor as the motive power behind the \"hands\" of the device, and the oscillator as a replacement for the complex series of gears and such for timing. There's still a bit of gearing to sync the movement of the two hands, though, so it's not nearly as reduced in mechanical complexity as a full digital watch, though the digital is obviously far more electronically complex."
],
"score": [
28,
7
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
dyf6ry | How do CPUs and graphics cards get better while remaining relatively the same size? | Engineering | explainlikeimfive | {
"a_id": [
"f80saw4"
],
"text": [
"To explain like you're five- think of it like writing. When you were young, you could probably barely write your name on a Post-It note. As you got older, it became easier to write your name on it. Then as you continued to get older you could write a sentence and then a paragraph on it. That's the extremely basic idea. What's being \"written\" on it initially can be written in a shorter way. And over time, we've learned shorter and shorter ways to write it. Add to that that we can fold two post-it notes to look like it's one (that's again an easy way of describing it but it gives you an idea). Basically we can write more with the same space by doing it in shorthand. And at the same time, we can now give more memory to the same area."
],
"score": [
12
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
dyuvdk | Why not use an oxidizer on jet engines, wouldn't it provide better efficiency/power output? | Engineering | explainlikeimfive | {
"a_id": [
"f83mjlb",
"f83p80c"
],
"text": [
"Because carrying thousands of pounds of liquid oxygen would cause the craft to have to be significantly larger and use more fuel because of that. It would also make the thing more of a moving bomb. The air to fuel ratio for jet engines from what I gather is around 60:1 so it would take A LOT of oxidizer.",
"Because carrying thousands of liters of an oxidizer is worse than using the oxygen in the air which is already present and is easily usable in every conceivable way. Why would you make a plane larger and heavier (thus requiring even more fuel) just to carry something that's already all around you and you can use? It's like bringing a bathtub full of water with you to a pool. Why are you gonna lug all that water to the pool? The pool already has all the water in it."
],
"score": [
9,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dywuce | Why are broken escalators so difficult to walk up? | Engineering | explainlikeimfive | {
"a_id": [
"f83yo3w"
],
"text": [
"Their depth (front to back) and height (height to the next step) are both bigger than is standard for stairs."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
dyzufw | How do waterless urinals work? And if they work, why aren’t all new urinals waterless? | Engineering | explainlikeimfive | {
"a_id": [
"f84dro3"
],
"text": [
"Great minds think alike. Yer not alone in askin', and kind strangers have explained: 1. [ELI5: why aren't all urinals the \"waterless\" kind? ]( URL_7 ) ^(_3 comments_) 1. [ELI5: is there anything special about a waterless urinal? isn't it just basically a urinal without the flush mechanism and scented cake? why not make all urinals waterless? ]( URL_6 ) ^(_4 comments_) 1. [ELI5: How do waterless urinals work? ]( URL_5 ) ^(_4 comments_) 1. [ELI5: how a waterless urinal works. ]( URL_1 ) ^(_1 comment_) 1. [ELI5: How does a waterless urinal work? ]( URL_4 ) ^(_7 comments_) 1. [How do non flushing or no water urinals work? ]( URL_2 ) ^(_3 comments_) 1. [ELI5: Waterless urinal ]( URL_3 ) ^(_3 comments_) 1. [ELI5: Why do some urinals have standing water? ]( URL_8 ) ^(_2 comments_) 1. [ELI5: What technology is behind a \"waterfree\" urinal as opposed to a bowl with a hole in it? ]( URL_0 ) ^(_2 comments_)"
],
"score": [
15
],
"text_urls": [
[
"http://reddit.com/r/explainlikeimfive/comments/3g0wid/eli5_what_technology_is_behind_a_waterfree_urinal/",
"http://reddit.com/r/explainlikeimfive/comments/1bh3h3/eli5_how_a_waterless_urinal_works/",
"http://reddit.com/r/NoStupidQuestions/comments/cwevqs/how_do_non_flushing_or_no_water_urinals_work/",
"http://reddit.com/r/explainlikeimfive/comments/16lerb/eli5_waterless_urinal/",
"http://reddit.com/r/explainlikeimfive/comments/29djmu/eli5_how_does_a_waterless_urinal_work/",
"http://reddit.com/r/explainlikeimfive/comments/19b5d9/eli5_how_do_waterless_urinals_work/",
"http://reddit.com/r/explainlikeimfive/comments/56wpiq/eli5_is_there_anything_special_about_a_waterless/",
"http://reddit.com/r/explainlikeimfive/comments/4z6tji/eli5_why_arent_all_urinals_the_waterless_kind/",
"http://reddit.com/r/explainlikeimfive/comments/7nwxx8/eli5_why_do_some_urinals_have_standing_water/"
]
]
} | [
"url"
] | [
"url"
] |
|
dz4rck | How Do Boat Anchors Work? | How does a boat's anchor hold it in place despite being so much lighter than the boat itself? Surely the anchor doesn't always catch on something on the sea/lake bottom, otherwise it would be hard to retrieve right? Esp as it relates to large vessels like cruise ships the anchors seem so small in comparison. Is there some ratio of anchor-to-boat size that makes it all work? | Engineering | explainlikeimfive | {
"a_id": [
"f857uc4",
"f85acfc",
"f85vjrq"
],
"text": [
"I know that this answer applied to large ships (merchant ships, cruise liners, Naval vessels). The anchor does not hold the ship in it's position while anchored. Instead, the anchor serves as a weighted end to assist in paying out the chain. The anchor drops to the ocean floor and the momentum (assisted with the ship moving slightly astern) carries out additional chain. The collective weight of this chain and anchor is what holds the vessel in place. Source: US Sailor",
"> Is there some ratio of anchor-to-boat size that makes it all work? I think you're comparing the wrong things in your head. You're comparing the weight of the anchor to the weight of the boat but the anchor isn't fighting against the weight of the boat. The anchor needs only counteract the lateral force of the waves/currents/wind pushing against the boat. Also keep in mind that the boat can freely drift so that its bow is naturally pointing where the anchor is, meaning the currents are pushing against the angled bow itself and exerting a minimum of force.",
"The anchor always catches on the seabed. That is what holds the vessel in place. With a chain rode, the weight of the chain helps keep the holding force more parallel to the seabed, and thus mitigates the anchor pulling up. This is called the catenary of the rode. In higher winds, thus more surface force on the vessel, the catenary will start to straighten out. The anchor design and weight are based on keeping it in the seabed up to a designed wind force on the vessel. The vessel weight does not directly come into play here, but rather the surface forces do. An anchor is retrieved by moving the vessel over the top of it, and pulling up the rode, which typically releases it from the seabed."
],
"score": [
70,
15,
7
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
dzacte | how do electric motors generate movement from electricity? | Engineering | explainlikeimfive | {
"a_id": [
"f86a1n4",
"f86scsy",
"f871lf1",
"f86aaby"
],
"text": [
"They use magnetism. You suspend a electro magnet on a axle inside a magnetic field. It will move to a balanced position if you electrify the magnet. Now the trick is that if you switch the polarity the axle has to turn halve a spin to be in balance again. If you keep switching the polarity it keeps spinning to find balance. It's like holding a carrot infront of a donkey. The balance is the carrot and it's always just out of reach",
"Electricity and magnetism are intertwined as two sides of the same force \"coin\". Basically, if you move magnets around electrically charged particles (i.e. electrons) the electrically charged particles experience force and want to move around. If you make (\"induce\") current through wires, it creates electric fields around it that are felt by nearby magnets. So in the case of an electric motor, there is electric potential from, let's say a battery, and it creates some current. The current needs to be AC or \"alternating\" but that's not super important for the basic point. If you have a few magnets connected in a circular pattern around/near a part of this wire with current running through it, the magnets feel the electric field created by the electrically charged particles moving around. The magnets get \"pushed\" around by the electricity moving around, and you can get mechanical motion that way. If you had a gas generator, or a steam turbine, and you connected magnets to it and connected some wires in the right way, you can do this in the reverse direction: turbine spins from the steam and magnets move around and the electrons in the metal wires \"feel\" the magnetic field getting moved around and they start flowing in a current, basically.",
"You know how two magnets either snap together, or can't be pushed together no matter how hard you try? If you attach a magnet to a shaft, and surround it with magnets, that's a motor. Then, electrical current alternates thru the magnets, switching which \"end\" is closer to the shaft. It works like an endless stream of magnets shoved past the one that won't let you touch.",
"An electric motor has a coil of wire (which we call a stator,) and a metal rotor going through the middle of the stator. When you run an electrical current through wires, it creates a magnetic field. So the stator is hooked up to alternating current, which creates a magnetic field that alternates direction every time the current alternates. The magnetic field attracts the rotor to it. Since the magnetic field keeps switching direction, the rotor keeps spinning. Hook up your spinning rotor to a driveshaft, and boom, you're getting rotational power from electricity."
],
"score": [
19,
4,
3,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
dzfl9p | How is a bit measured? | So bits are just ones and zeros, and we use logic gates to perform operations with them, that much is clear. But I wonder how exactly are the bits measured. For example, how does the computer distinguish between, say, 1 and 11? The system is always on, so I'm guessing it should have something to with time, but if this is the case, then how many nano(?)seconds does it take for the electricity to constitute as a bit? | Engineering | explainlikeimfive | {
"a_id": [
"f87963v",
"f87tw1j"
],
"text": [
"If I have a 16 bit bus then I have 16 individual lines... Every line tied low (negative voltage) is a 0. Every line tied high (positive voltage) is a 1. The actual read times for each individual data line will change depending on the system. If I am operating a system at 10hz then it can read the data lines at most 10 times per second, however modern processors operate in the billions of times per second (GHz) If I were to take an 8 bit RAM chip then it would have 8 address pins (input), 8 output pins (the output data), at least 1 ground pin, 1 power in pin, and then one pin that will either be tied high or low depending on whether you want to read or write. If the input pins are tied as follows: 00000000 then the output will be the data saved at address 0 (for most ram chips I have used this defaults to FF or 11111111). So on your average chip that has no data saved all the output data lines will be high and thus will be 1's Things are different when you transmit data electronically as we send everything over a single frequency (not 64 frequencies for 64 bit data). In this case the time for each bit will also be dependant on the frequency that it is being transmitted at. At 2.4GHz (the frequency of most consumer WiFi, though there is also 5GHz) you will have a maximum of 1 bit transfered approximately every 1.5-3 nano seconds depending on configuration and how new the hardware is. Edit: something tied low won't necessarily have it be tied to a negative voltage, it could still be positive. An example are some systems will have the high be 5V and the low he 1.8V however this is being pedantic and doesn't really have an impact on the question.",
"To summarize the posts here, bits are separated by time and space. As some have noted, within a CPU, different bits will be separated by different channels. So if you wanted to represent 2 bits, you will have two channels, or pathways, each dedicated to one bit. So you don't need to compare 1, with 11, you would compare, 00, 01, 10, and 11, all of which are easily distinguished. However, multiple bits sometimes need to travel down the same channel, for example, down a cable when traversing a network. In this case the bits are separated by time. Basically bits come in pulses. The timing is dictate by set and agreed upon protocols and all computers are designed with this timing built in. So rather than 11 simply being a drawn out 1, each 1 is actually an individual pulse. So 11 would be two pulses separated by brief pauses."
],
"score": [
5,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
dzfmay | How does rubbing a blade on a strop sharpen it? | Engineering | explainlikeimfive | {
"a_id": [
"f878ozo"
],
"text": [
"It doesn't sharpen it, it strops or hones it. The difference is, sharpening removes metal, stropping just straightens up the edge. Honing polishes the edge to a fine finish. With use, the very very fine microscopic edge of the blade can get rolled over and dulled slightly that way. The strop realigns the edge, and brings the sharp edge back to the fore, as well as buffing the edge up to extreme sharpness. Hence their common use with straight razors in a barbershop."
],
"score": [
20
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
dznjhy | How are ammunition sizes chosen? | I have always wondered why ammo sizes are all over the place. 5.56mm 7.62mm .338 caliber, 30-60, 30caliber etc. Why not do something in even increments like 5mm, 6mm, 7.5mm or 30, 35, 40 etc calibers? Is this just for companies to get extra money making an odd proprietary size? What gives? | Engineering | explainlikeimfive | {
"a_id": [
"f88ubfa",
"f88wmp4",
"f88u3pa",
"f88wh2f",
"f89jye4",
"f89h57r",
"f88w9kb",
"f88y5cj",
"f89rxdj"
],
"text": [
"They're just different scales measuring the bore of your weapon (imperial vs metric). To explain; 7.62 mm *is* 30 calibre. The calibre of a weapon is the diameter of the barrel, and 30 calibre is .30 of an inch across. 0.30 of an inch is 7.62mm. The different calibers are about range and power. A bigger bullet will go further, faster and harder, but will need more powder to do so. They were standardised when inches were the normal unit. Now, we make new weapons with mm rounds, but the legacy of the old inch based rounds remains.",
"Both of the other answers are correct, but also consider that the caliber doesn't tell you a whole lot in isolation. A bullet's power comes both from how heavy the bullet is and how fast it's moving. So a 7.62 AK bullet is the same caliber as a 30-06 hunting rifle, but the 30-06 bullet is heavier and has much more gunpowder behind it, so it adds up to radically more power. Therefore, companies do a lot of tweaking the bullet size, shape, weight, against the gunpowder amount and type, which leads to lots of different bullets that look similar but are optimized for different jobs.",
"There is no such thing as a proprietary size. A company can make ammunition in any size they see fit. The is largely going to be arbitrary, based on local traditions, and equipment that is available. Consider that you want different size guns for different warfare purposes. If I have a gun that fires 5mm ammunition, it really doesn't benefit me to also get a gun that fires 5.1mm ammunition or 4.9mm ammunition (all other things being equal). If I want a larger or smaller gun, that ammunition is going to have to be some degree larger or smaller. How much smaller or larger? Well, that's hard to quantity and different ammunition and firearm makers are going to make partially arbitrary decisions in that area. Not to mention that the manufacturing of ammo predates codified ammunition sizes like calibre, so when creating such a system, you're going to base it off of the existing ammo sizes which won't necessarily fit a nice neat scheme.",
"Guns calibers were mostly standardized in the Imperial system of used when they were first developed. Even today when a [new cartridge]( URL_0 ) is designed the bullet often fits one of the standard calibers. Further there are all sorts of different ways to measure a bullet and caliber. Most measure the barrel diameter, but sometimes this is done in the grooves of the rifling, other times it's done on the lands or raised surfaces of the rifling. Further some cartridges aren't measuring the projectile diameter, at all. The famous example is the .44 magnum which is actually .429 diameter. 44 is the diameter of the case walls. There are certainly efforts to capture a standard, but most of the time, a wildcatter (independent cartridge R & D) changes a round to meet some need of theirs and other people like the result.",
"Cartridge history can actually be really fascinating to research, but I'll try to be relatively brief. Ammunition is sized based on the diameter of the bullet first. The .308 is a .308\" diameter bullet. 7.62mm = 0.300\" = 30 caliber. The large variety of calibers in the world is because guns have been around a long time, and humans are always trying to make technology better. As far as metric vs. inches/caliber... it just matters which came first. Sometimes a name (like Ackley, Remington, Nosler) is added just so the makers can gain notoriety. I'm not aware of any royalties collected.... In the case of handguns, 9mm came about before anyone really made a .35 auto (that caliber DOES exist, but is super rare) and .45 auto came about someone made an 11.5mm cartridge. In the case of rifles, 7.62x39 was developed outside the US, while .308 (the same bullet, different cartridge) was developed inside the US. Now, there ARE a few proprietary cartridges out there(like the 50 Beowulf for Alexander Arms - everyone else has to us the designation \"12.7x42\", but it's the exact same). But some cartridges are highly unique. The most common \"unique\" cartridge is known as a Wildcat. Wildcats are a cartridge that someone has modified from an existing cartridge. Some of them become popular and are used on a larger scale, or are developed commercially, but their roots are still Wildcat. Examples of this include: * 300 Blackout. A modified 5.56 cartridge to accept 30-caliber - .308 - bullets, often used in an AR15 platform for hunting, because the 5.56 is too small to legally or ethically hunt with * .22-250. Based on the Savage .250 to accept a 22-caliber - .223 - bullet, often used for long range shooting due to its high muzzle velocity * 6.8mm SPC. Based on the .30 Remington and designed by US military special forces for more lethality without having to move away from the M16 platform The most confusing aspect of cartridge sizing is probably that the designation is not JUST the size of the bullet. The size and shape of the brass can make a huge difference in the performance of the bullet after you pull the trigger. For example, a 6.5 Grendel and 6.5 Creedmoor fire the same bullet, but the Creedmoor has a much larger brass case and is capable of higher muzzle velocities which translates to longer ranges (and you can shoot heavier bullets without loss in performance or safety). The 6.5 Creedmoor is a highly popular long range target shooting cartridge right now. Similarly, a 7.62x39, 7.62x51, and 7.62x54 are all very different cartridges. The first and last are often associated with Russian firearms, while the x51 is the exact same as a .308, but the 7.62x51 sizing was introduced for international NATO compliance. Usually, in something like the 30-06 or 45-70, the first number is the caliber, and the second number has some meaning attached to it that can vary (the 30-06 was developed in 1906, the 45-70 uses 70 grains of black powder). So... Like I said.... cartridge history can be REALLY fascinating.",
"Great answers here. To add some of my own views: You're asking two different questions at once. 1) Why the different calibers (bullet diameter), and 2) why the different rounds (ammo). Bullet sizes have been discussed well. Ammunition size has been touched on but what I have seen is that each has a unique history of how they got there. For example if the round has a rimmed base or not deals with the magazine style. Rimless will fit into a tubular magazine, where rimmed is a lot more awkward, but rimmed cartridges were easier to extract from the gun. Necked rounds give a larger diameter space behind the bullet for more gunpowder. If it were straight walled, the cartridge would be too long and you might have uneven burning problems. Belted rounds are usually because the pressures are so high that you may separate the case between the walls and the base. The extra brass helps the cartridge stay together. Two rounds that I'm somewhat familiar with and love for their stories are the 45-70 and the7mm BR. 45-70 - IIRC this is an OLD west round that was made for reloading in the field. After priming the cartridge (don't ask me how they did that in the frontier, probably used a hammer and a pocket knife) they would literally fill the cartridge flush to the top with what was 70 grains of black powder. Then they would tamp the powder in by shoving the bullet in the neck. It's called a compressed load and it had a good chance of blowing up just because you were pressing the bullet in. (Most rounds have air space between the powder and the bullet) The reason I love the round is they can throw nearly 1/10 lb of lead down range so slow that you can see it travel but it'll take down whatever it hits. It's just a monster of a round (assuming you don't already own a 50 cal) 7mm Bench Rest - A 7mm round is quite quick and responsive round, on the small side in the groups that I have traveled. But what if you wanted some speed AND knock down power out of it. Well, but a heck of a cartridge behind it. The 7mm BR is made by necking DOWN a 30-06 to 7mm and adding a bit more powder. Think of the energy behind a 30-06, now put that energy behind a little 7mm lightweight bullet. Oh, and by the way, shove all of that into a pistol instead of a rifle. They shoot quick and flat (and a good flame out the end of the pistol!). My exposure to them was through IPSIC and IMSA metal silhouette shooting, where you can shoot livestock (metal cutouts) without killing any of them. Stand them back up and shoot them again. Fun stuff. Those are my opinions. Feel free to correct me as you will. It's been fun for me to learn about the history of some of these rounds.",
"* 5.56mm = .22 inches (caliber) * 7.62mm = .30 inches * 9mm = .357 inches * the list can go on... The different sizes are generally because guns were created for specific purposes (war, different kinds of hunting, different firing distances, etc.), made by different manufacturers, or made in different countries. Today, we have access to all of those things due to the global economy, so we are left with lots of different sizes.",
"Almost every caliber has a long story behind it. I recall that the American .243, .257, and .284 calibers seemed arbitrary. However these were new cases added to bullets that were made on expensive existing barrel-drilling equipment developed years before for the European market. 6mm, 6.5mm, 7mm.",
"There are several factors in ammunition development. Ballistic coefficients, trajectory, energy, weight, effective range, overall length, compatibility with a specific platform, and so many more. Typically you’ll have someone say they want a round with a list of parameters and people will go to work on finding the combination of bullet size, weight, shape, construction, case size, primer type, case volume, case design, powder type, powder charge, chamber pressure, barrel profile, and barrel twist rate that most efficiently meet those parameters. There’s a lot of physics to caliber development and sometimes the cost of designing an entirely new bullet is more cost effective."
],
"score": [
271,
43,
19,
10,
10,
9,
8,
5,
4
],
"text_urls": [
[],
[],
[],
[
"https://en.wikipedia.org/wiki/Caliber#Metric_and_US_customary"
],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
dzteld | when "tuning" an engine... What are y'all doing under there? | Engineering | explainlikeimfive | {
"a_id": [
"f8a2cp6",
"f8a7xm7",
"f8aang8"
],
"text": [
"'Tuning' in the strict sense means fiddling with the amount of fuel that's injected and the timing of the ignition. In pretty much all cars since the mid 1980s both are controlled by a little computer (ECU), so it's a matter of changing the data tables that the computer has stored. In the case of turbocharged engines the ECU also controls the amount of boost pressure, so it's often possible to increase the boost in software. In a broader sense of the word the things you do to increase the power output of an engine are centered around being able to burn more fuel. And in order to do that, you first need to increase the amount of air that the engine is flowing. Of course there are tons of different ways to do that.",
"Adjust air/fuel mixtures, idle speed, and chokes on carbureted engines, ignition timing on distributor equipped engines. More modern tuning is done via laptop and is much cleaner. Race cars are another story.",
"all cars leaving a factory are detuned from their 100% capability for both longevity as well as usability. the same car has to run \"good\" in Arizona broiling 120degrees in desert as well as at Aspen at 8000ft when it's -20below. that means giving up something at either end to make it run good always. this also means that premium cars that run on 93octane gas still need to run \"goodish\" when fueled with 87octane. tuning takes the car that runs at factory reduced capacity and takes it to run closer to its capacity in the conditions that satisfy the driver, sometimes at the cost of portability and longevity. it could mean the car is no longer capable of running that well on 87octane. or much better in Aspen, but would suck in Arizona. or better in Florida, but would suck in Aspen."
],
"score": [
13,
4,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
e00pym | how do foam soap dispensers work? | And can I refill a bottle with any old other liquid soap? 🧼 | Engineering | explainlikeimfive | {
"a_id": [
"f8b68ji"
],
"text": [
"The soap in the dispenser is actually just regular soap diluted with water. There is a mechanism in the dispenser to agitate/foam up the water and soap mixture. You can use any old liquid soap but you have to dillute it with water for it to foam up. I have done this before by mixing bulk softsoap from costco and water in an old Bath and Body Works dispenser at a ratio of 1 part soap to 3 parts water. Mix them to combine before trying to use the dispenser pump."
],
"score": [
9
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
e06pdu | Limits of a Hydraulic Press | I understand the basics of a hydraulic press - how you can use an effectively non-compressible liquid to transfer the application of a smaller force exerted over a longer distance to crush or compress something on the other side of a press. My confusion is the other details about the limits of this process. For example - if you were trying to crush something significantly less compressible than the material the hydraulic chamber itself was made of, wouldn't the fluid rather rupture the hydraulic chamber and escape rather than be forced into moving a "less compressible" object? Similarly, could ANY object be theoretically crushed if you used a strong enough piston? At some point wouldn't the water disassociate or something - are liquids TRULY non-compressible? Thanks! | Engineering | explainlikeimfive | {
"a_id": [
"f8cb6xl",
"f8c8o5t",
"f8c8i8f"
],
"text": [
"Presses are built with safety features that prevent them from operating over a specified limit. The limit is set by the materiels the press is built from - the simplest method is to use a pump that will stall out and stop moving fluid before enough pressure to damage the press is reached.",
"> if you were trying to crush something significantly less compressible than the material the hydraulic chamber itself was made of, wouldn't the fluid rather rupture the hydraulic chamber and escape rather than be forced into moving a \"less compressible\" object? Yes, although typically I think the failure mode would be the press head deforming rather than the hydraulic chamber exploding. There would be a pressure release valve that would pop before turning the hydraulic system into a bomb. > Similarly, could ANY object be theoretically crushed if you used a strong enough piston? In theory I suppose so, until you get up into exotic materials like degenerate neuron matter. > are liquids TRULY non-compressible? No substance is non-compressible. This is just a simplification given to new engineering students to remove irrelevant factors from their calculations, and many seem to have taken it to be literally true. We can prove this by imagining a truly non-compressible object which is given a tap with a hammer. Since it cannot compress this tap must be conveyed instantaneously to the other side, exceeding even the speed of light! Obviously then such a substance is physically impossible.",
"The trick with hydraulic presses is that they split the fluid across many pistons, which has a multiplying effect. So imagine one pump in one piston, but then it gets split to two pistons at the base of the hydraulic press. It goes twice as slowly now but with twice the force, and the force is distributed across the pistons. It’s sort of similar to using gears and pulleys. The really big industrial ones have many many splits like that which is why they go very slowly but have a lot of force"
],
"score": [
11,
5,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
e0qdig | How do jet engines keep planes in the air? | Engineering | explainlikeimfive | {
"a_id": [
"f8g36dh",
"f8g40gk",
"f8g36l8",
"f8g2yvo"
],
"text": [
"They don't. The wings keep the plane in the air. The engines give you speed, which makes the air move over the wing. The air passing over the wings creates lift.",
"Jet engines make speed, and speed allows the plane's wings to deflect air downward which in turn pushes the wings upward. The engines themselves are basically propellors inside of carefully-shapes tubes which are spun by a turbine engine. A turbine engine itself has a bunch of fan blades which compress air, and then burn fuel in it, before allowing it to escape at a higher speed than it entered and spin more blades.",
"They burn fuel together with air coming in the front of the engine and being compressed. That creates a larger volume of exhaust moving at high speed exiting at the rear which creates thrust, pushing the aircraft through the air. As the wings are pushed through the air, air flowing over them creates lift which keeps the aircraft in the air.",
"My understanding is that the engines push the plane fast enough for the wings to catch air in a way that causes lift"
],
"score": [
22,
8,
7,
4
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
e0si3a | How can a water or electricity company cut off or turn on services to an individual household without being physically present? | Engineering | explainlikeimfive | {
"a_id": [
"f8gqex4",
"f8gs107",
"f8gxs8p",
"f8grsjs"
],
"text": [
"water cannot be cut remotely, but the shutoff valve is normally outside the house/building. Most electric switches can be thrown remotely whether inside or outside buildings",
"As far as electricity there's a few diffrent ways. One, with smart meters they can do it remotely. I don't have any experience with those but the other two ways are: at the meter attached to the house (which most utilities have a right to access) you pull the meter and either leave it out and replace with a window, or put plastic \"socks\" on the blades of the meter and put it back in. If the meter is not accessible then you can climb the pole and either de-energize the transformer or cut the service to the house open. In the case of an underground transformer you can disconnect the particular house you wish to.",
"The junction to your house is accessible from the outside so they can do maintenance without having to rely on access. Therefore they can send a guy who goes to your backyard and shuts off your water or electricity.",
"Companies use a relay to measure how much power is used. Newer relays are smart and can talk to a network, so the companies can read how much power is being used remotely, but can also stop power being used remotely. Not sure how they’d turn off water, unless where you live they install solenoids on the water supply."
],
"score": [
12,
11,
3,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
e0t75l | How does a manual transmission operate versus an automatic transmission? | I'm someone who's only ever driven an automatic and never have someone willing to teach me manual. How do the mechanics of a manual transmission work and what are the pros and cons versus an automatic transmission? | Engineering | explainlikeimfive | {
"a_id": [
"f8h0smr"
],
"text": [
"Manual transmission: manual stick shift link to synchronizing collars that connect the input shaft to the output shaft to the wheels. Automatic transmission: Magic haha. In all seriousness you would be better to see a YouTube video on how a manual and automatic work as opposed to seeing a written explanation. A manual is pretty understandable but automatic transmission is really complex and the function is pretty amazing. As far as pros and cons: in this day and age, the automatic is pretty much all around better than a manual as far as fuel efficiency, ease of use, and availability (especially in the US, it's pretty difficult to find manuals here). Manual has a couple of upsides: 1) you have full control of the powertrain - the car does not shift gears unless you tell it to. There are remote instances in which an average driver would find this useful, but it's more fun than anything. It can useful if there is an instance in which you need quick acceleration by downshifting to a lower gear, like passing a car on a two lane road, whereas there is a delay with automatics because they have to detect oil pressure differences (I think...) 2) they are cheaper to maintain and cars with them are cheaper overall by a couple thousand dollars. 3) Really beneficial for racing since you can control the powertrain entirely. It's a complex subject, but loads of videos can help visualize how they work. I have a manual transmission Honda Accord and I love it."
],
"score": [
8
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
e0z0b4 | Why are buses so shaky and unstable? | Engineering | explainlikeimfive | {
"a_id": [
"f8k4bj0"
],
"text": [
"They are shaky, but they are very stable, in part due to the shakiness it is extremely difficult to tip over a bus due to the low centre of gravity and the long wheelbase, the shaking comes from the generally poor suspension which prevents the bus from \"bouncing over\"."
],
"score": [
11
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e122a2 | Why do cell phone screens need to be made of glass? Wouldn't a more flexible and durable plastic composite (or something) make more sense? | Engineering | explainlikeimfive | {
"a_id": [
"f8l7h6w"
],
"text": [
"Anything that's flexible and durable is going to be malleable, malleable things are inherently not hard, and things that aren't hard are easier to scratch."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e16drx | Why do most commercial airliners have those little pods on the bottom of the wing? Are they for stability or extra fuel storage? | Engineering | explainlikeimfive | {
"a_id": [
"f8n02c2"
],
"text": [
"They are Flap Track Fairings which contain the necessary gear to move the flaps on the wings. They can also be Anti-Shock bodies, which reduce wave drag at transonic speeds."
],
"score": [
10
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e1cq9b | What caused the Concorde to go under and is it likely to ever come back? | Engineering | explainlikeimfive | {
"a_id": [
"f8o911o",
"f8o91jw",
"f8ocf8v",
"f8oapte",
"f8o9h1k",
"f8o9rz1"
],
"text": [
"Noise and flight paths. Breaking the sound barrier is loud, as such the flight path had to be well outside a residential area before it could get up to speed. Basically it all just became too difficult and thus not economical.",
"Wasn't making the money it needed to. $5-10k per seat in the 80's and 90's was too much. 3 hours from NY to London? Cool. 7 hours for 1/75th of the price. Even cooler.",
"Cost was a major contributing factor but it wasn't helped by the major crash URL_0 caused by a tyre being punctured by debris on the runway. Serious questions were raised about the quality and safety of the tyres used and a lot of money was spent trying to get an alternative. Meanwhile the industry moved on and it became less desirable and viable to keep flying concord. It's a pity because it was an iconic plane.",
"Simply put, Concorde was no longer profitable when they decided to stop running it. It had also lost most of its cachet and extravagant appeal by that time (and, arguably, it wasn’t ever truly economically valuable to the airlines when compared to the rest of the fleet, and especially so without the “halo effect” of that cachet). Concorde embodied an optimism in supersonic air travel, and the expectation was that it would become much more widespread in air travel generally. There’s value in being the first mover, in a market, for a dozen reasons, one of which being that you own the market and have a huge advantage when new competitors come. But neither happened: not the widespread increase; no competition. A lot of factors went into the *why:” - Concorde was *tiny.” Cramped, with low ceilings and a narrow body. With the introduction of more wide body commercial aircraft, Concorde couldn’t keep up the luxury. - Nuisance factor. Concorde was loud, and not just for sonic booms. It was loud on takeoff, and loud inside. Concorde had TONS of opposition in almost every market it flew into. - Operating costs vs. revenue. From fuel costs to gate and runway requirements, there just wasn’t enough revenue from 100 seats to make enough money to sustain it. - The market for supersonic travel never materialized. It was expected that the aviation market would move to lots more supersonic planes, but it never happened. - Widebody planes - starting with the 747 - were just a far more attractive option for both passengers and the airlines. More comfortable, spacious, and luxurious for travelers; huge capacity meant that costs could be spread over 300+ vs. 100 for Concorde. So, in the end, Concorde was built with great expectations for the future of air travel, but it never came to pass. It eventually was too expensive to run, and its market dwindled while it was constrained to a tiny 100 seats. Had supersonic travel grown in the way it was predicted, Concorde would have birthed a half-dozen newer, better, fancier planes, and we’d look it Concorde as the visionary, intrepid beginning of a new era of travel.",
"I don't know much about it but I believe it was mostly cost. As you can imagine accelerating a passenger aircraft above the speed of sound won't be too cheap and it couldn't carry nearly as many passengers as more modern airliners... In the end I think BA could make more money with a fleet of high-capacity aircraft than one of high-speed",
"Basically cost. The need for supersonic travel decreased a lot as the internet became more accessible, giving the ability to communicate effectively and instantly across the globe. Supersonic travel cost a lot: it burned a LOT more fuel per passenger-mile travelled. An efficient two-engine jet could easily accomplish the same journey for a far lower price and take marginally longer for many trips, especially given that supersonic travel above land was discouraged since it creates a lot of noise."
],
"score": [
13,
10,
4,
4,
3,
3
],
"text_urls": [
[],
[],
[
"https://en.m.wikipedia.org/wiki/Air_France_Flight_4590"
],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
e1rtzi | How auto shutoff pumps at the gas station work | Engineering | explainlikeimfive | {
"a_id": [
"f8rewj6"
],
"text": [
"They use a diaphragm that is pressure balanced to hold a pin that keeps the flow valve open.they need constant atmospheric pressure to stay on. A small pipe called a venturi runs alongside the gas nozzle down to the outlet. When the end of the venturi pipe becomes submerged in the rising gas, it chokes off the air pressure that holds the nozzle handle open and shuts down the flow of gas. Or to put it simple, as long as the mechanism has acsess to open air the thingy stays on and when it gets blocked it loses it's balance and trips the nozzle shut off."
],
"score": [
59
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e1ssxp | How does Tesla manage to use Lithium Ion batteries to power an entire vehicle? | It even powers that new Cyber Truck. How on Earth does a Lithium Ion battery survive Tesla cars, SUVs and Trucks? I read that a transmission isn't even needed and a single gear powers it all. Somehow they got majority of weight closer to road like a Ferrari. I work IT and I constantly dispatch Dell techs to replace batteries that are Lithium Ion so am so freaking lost. I'm sure the braking aspect extends range of car as in case of Prius. But with all that charge recharge cycle, I just don't understand how the batteries survive long enough. Guess that Musk dude is really taking stuff out of this world. | Engineering | explainlikeimfive | {
"a_id": [
"f8rkov5",
"f8rm1m2",
"f8rs2h0",
"f8s5uma",
"f8sbl8n"
],
"text": [
"Each tesla has thousands of batteries, and drains from all of them equally, which basically you have thousands of times the battery life.",
"Tesla cars are basically big ass RC toy cars you can ride. Same lithium ion battery pack and motor and gearbox technology. With a lot more heavy duty components and safety measures. But it still is basically a huge ass batt pack, electric motor, gearbox, axles, wheels, tires.",
"Though I know next to nothing about batteries, I can address your transmission query. Combustion engines, no matter how they are configured, will have moving pistons. These moving parts can only move so fast before the mechanical parts will fail due to momentum. you then change your final drive gear ratio simply by shifting gears in your transmission. In doing that you bring your RPM’s down and are back into the safe/reliable rpm range. Well electric motors don’t have these moving mechanical parts. They are copper (or similar) windings that spin in a singular direction which allows them to spin at incredibly high rpms thus eliminating the need to change gear ratio’s Edit: to add to the whole “not needing a transmission”: combustion engines have a torque curve. Little torque at very low and high rpm’s but plenty of torque around 2/3 of your RPM range. Electric motors however don’t have the same torque curve. You pretty well have 100% torque at all rpm ranges, making them incredibly fast to accelerate even under heavy load",
"Combustion engines need to compress the fuel-air mix before detonating it, which means they only work effectively (i.e. high torque, high efficiency) in a rather narrow RPM range. Which is why you stall a car if you slow down too much while it is in gear (and you do not have an automatic transmission to counteract that - or disconnect the clutch). So you need multiple gear ratios to make sure your engine is in the optimum RPM range. An electric motor, on the other hand, can output peak torque from a stationary position, and if at any point the maximum torque drops from peak, it is only because you would otherwise exceed its power or RPM limits. So you can deliver torque at pretty much any gear ratio, making a multi-speed transmission pretty much unnecessary. You just need to make sure that max torque and max RPM are in spec for your desired acceleration and top speed, respectively. The ability to produce torque from a standstill is also the reason electric motors are used as starters for combustion engines. An electric motor cranks your engine shaft when you turn the key to start until the engine's own power can take over. That takes quite a bit of current, so a regular car's battery is already quite big. Now imagine running your entire car from that. You need a lot more than a standard car battery for that. A car battery is about equivalent to 10 laptop batteries - but the laptop batteries put together are both lighter and smaller. So if we just fill the entire floor of the car with laptop batteries, you end up with a healthy dose of power supply.",
"It's best to think of a Tesla as a giant RC car. So an electric RC car will run off a lithium polymer battery pack. Typically two to three cells, sometimes more for large high performance racing models. That battery is connected to an electronic speed controller (ESC), which regulates current to the motor, allowing the car to drive at variable speeds. The controller also contains a \"battery eliminator circuit\" (BEC) that provides power at the right voltage to the RC car's radio, steering servo, and any accessories from the main pack, without need for an additional separate battery. EVs operate on much the same principles, just scaled up. They'll have a lot of lithium ion cells. Usually mounted in the floor to give the car a low centre of gravity, which helps stability. These batteries will be a mix of series (multiplies the voltage) and parallel (multiplies the capacity) cells to give both the power and range a full size road car needs. To maintain the batteries, the car will employ a balanced charger, which monitors the voltage of each individual cell and charges them up to the same level. Other sensors will monitor the health of the cells. Cooling and heating systems are used to keep EV batteries at their optimal operating temperature. As for not needing a transmission, the beauty of electric motors is they apply instant full torque (turning power) right at 0 rpm, and that torque curve stays pretty flat right up to their max operating speed. Unlike a gas engine that starts with very little torque, which increases the faster it revs. This is also why EVs like the Tesla Model S do so well in a drag race against some pretty powerful petrol cars. Train locomotive engines and ships also use electric motors for the same reason. That instant torque is needed to get big loads moving."
],
"score": [
8,
5,
5,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
e1uk9e | How are weirs constructed? | I'm not talking about large infrastructure projects like dams, I'm talking about small-scale weirs that span the length of a relatively small river, like [this]( URL_0 ). Like... where does the water flow whilst the weir is being built? I've never noticed channels around where weirs are in rivers that could have been used to redirect the river temporarily. | Engineering | explainlikeimfive | {
"a_id": [
"f8rvj7f"
],
"text": [
"How do you know that there was not a small channel with a pipe that diverger the water around it when it was build and then the pipe was removed and filled in? You would not see any traces of a channel after a few years. The pipe might even remain underground and the inlet is just covered. Another option is a temporary cofferdam upstream and diverged the water in a pipe on the ground. The water flow in that river will be very low in the dry part of the year so you do not need a large pipe. Then you just remove the temporary dam with an excavator. Another option is to build it on two phases with a cofferdam the keep half the width dry and you build the wire there. Then you build a slightly higher cofferdam and keep the other side dry when water flows over parts that you already have built. There might even be a removable section/hole in the wier so you build half with a hole in it, diverge the water through it and the last thing you do is to lower the final part /plug the hole and let the water rise."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
e1uoag | Why are airline jet engines made of so many separate metal sheets on the outside? | Pretty much the title. Especially the bump on the top is made of a seemingly crazy amount of sheets with even more screws. How is that not inefficient? Here's a picture I took: URL_0 | Engineering | explainlikeimfive | {
"a_id": [
"f8ruy8i",
"f8ruqqn",
"f8rurjh",
"f8ry10p"
],
"text": [
"It’s quite simple really. Repairs. Since planes can’t pull over on the side of the atmosphere when they break down, airplanes have pre-emotive repairs and part replacement after a certain pre-determined number of flight hours. So, since it’s the engine we’re discussing, a small piece in the back may be up for replacement at a different time than, say, a turbine in the front. Because these repairs range from tiny to huge, it’s most effective if the people doing the repairs can get to that area with the least amount of trouble. Having to remove a massive cowling or cover could be a huge job, whereas a small part could be replaced in a matter of hours. Planes undergo service, maintenance and mandatory rebuilds/replacements far more often than you know. It can happen on your layover and you might not even notice. This is because they can get to that space easily and quickly.",
"Usually there’s wiring and other electrical components as well as hydraulic mechanics. Easier to remove one or two metal panels than an entire subsection.",
"It’s easier for internal repairs to remove specific panels as opposed to the whole damn thing.",
"Modern aircraft are what's called semi-monocoque structures. That is, the stresses of the aircraft are carried both by internal ribs and the skin of the aircraft, as opposed to a monocoque structure, like a car where the skin provides nearly all the structural rigidity or the reverse of that which uses fabric over airframe. The individual panels carry the majority of the stresses of the aircraft, so you can't hold them down with just 4 screws on each corner. You need entire rows of screws to keep the air pressure from ripping them straight off. The panels are made to be easily removable to get to critical components underneath them for repairs and periodic inspections."
],
"score": [
8,
4,
3,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
e1vcud | How do adjustable desk chairs go up and down? | I've seen some desk chairs that are older than time and still work perfectly. | Engineering | explainlikeimfive | {
"a_id": [
"f8ry7dr"
],
"text": [
"There's a pneumatic (gas pressurised) cylinder that pushes the seat up when the hand lever is pulled. The manufacturer sets a specific pressure in the cylinder so that when the typical weight range of a human is on the seat, the pneumatic cylinder will not be able to hold the weight and slides down. When there is nothing on the seat and the hand lever is pulled, the pressure is enough to push the seat back up."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
e2eeip | Why are the doors bigger on 2 door cars? | I mean obviously, I get that there’s more space to make them larger; but from a manufacturing point of view, surely it’s easier to only make smaller doors made for the 4 door models, and just use them on the 2 models as well? On top of that, two door’s struggle to fit into tighter parking spaces because the larger doors require more space to open, which is counter intuitive when you consider two door cars are thought of as smaller. I’d have thought smaller doors would be stronger too, since shorter cuts of metal will flex less easily, and it would give more space to better reinforce the rear, door-less part of the car. Am I overlooking something obvious here? | Engineering | explainlikeimfive | {
"a_id": [
"f8uz3wq"
],
"text": [
"If the car is 2 door but still have 2 rows of seats you need larger door else it would be almost impossible to get into the back seats. I have not idea if there is a car with a 2 and 4 door variant where the 2 door variant only has front seats and the 4 door variant has a front and back seat where you using the same doors could mase sense."
],
"score": [
16
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
e2gq7y | How are fires put out in skyscrapers? | Engineering | explainlikeimfive | {
"a_id": [
"f8vbpi2"
],
"text": [
"The biggest factor aiding fire fighting in tall skyscrapers is actually in their initial design and construction. Building the structure with good fire suppression between levels allows for any fires which break out to be contained (more so than a residential home made out of essentially seasoned firewood). Thus, in many cases the firefighters are safe to enter the building, and set up a control point a floor or two below the existing fire, where they can get water supplied from the building's own plumbing, and swap out breathing apparatuses and other gear, man power, and sort of daisy-chain the rescue operations, rather than the idea of a single fire fighter scaling 70 floors, fighting the fire, grabbing the evacuees and carrying them 70 floors back down."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e2ugca | How do the differences between 91, 95 and 98 unleaded petrol effect a car? I’m trying to understand the physical differences happening between them in a car that can use all 3. | Engineering | explainlikeimfive | {
"a_id": [
"f8xoy5a",
"f8xpcv0"
],
"text": [
"Octane in fuel changes its ability to withstand compression without detonating/preignition. Detonation at the wrong time in gasoline engines is bad*, because you’re getting combustion (and therefore, expansion force) of the fuel charge at the wrong time - when the piston and crank aren’t in the right position). This is both inefficient (you’re burning fuel that isn’t actually used for motion), and destructive. When combustion happens at the precise millisecond the piston and crank are ready, there’s no damage, because the piston is at/just past the top of its arc, and down is the path of least resistance. When combustion happens before this point - especially when the piston is moving upward - the path of least resistance is to eventually blow holes through the cylinder walls, piston head, or cylinder head. Higher octane fuels withstand higher compression in the combustion cylinders without detonating. This is useful, because higher compression means you can pack more fuel+oxygen molecules into the same volume in the cylinder without it igniting before the spark plug fires, leading to higher power output potential (and, to a certain extent, higher efficiency). Engines that specify low-octane fuels are relatively low in compression, so they are much less likely to have detonation issues. They run on higher-octane fuels without any effect, negative or positive. Engines that specify high-octane fuels have relatively high-compression, and they need a fuel with detonation resistance - the octane - to run at their most powerful and highest efficiency. When you give a high-compression engine low-octane fuel, you’ll get detonation, but the effect is compensated for using *knock sensors.* Knock sensors listen for the particular sound of detonation/preignition - knocking and pinging - sending the signal to the engine management computer, which adjusts things like fuel/air ratio and spark timing to stay one step ahead of the detonation. The trade-off is lower power and reduced performance. Basically, no compensation is needed moving up in octane vs. spec, but compensation is needed when moving down in octane vs spec. All modern vehicles have knock sensors, even those with low-compression engines, as a way of compensating for varying fuel grades and octane availability. > *Not so with diesels, where detonation from compression is actually their means of combustion.",
"Cars work by pumping a mix of petrol and air into a container, compressing it (by pushing a cylinder down on top of the mix), and then exploding the mix which shoves the cylinder back up. Higher ratings means the fuel can be under higher pressure before it explodes on its own. More pressure means more power, but if the petrol explodes before your car is ready for it, it can damage the engine. That's why you don't want to use a fuel with a lower rating than the one your car expects. Putting a higher-rated fuel in your vehicle than it's tuned for will work just fine, but if your car is tuned for 91, it won't compress the higher-rated fuels any more so you don't get any extra power- you're just throwing your money away by using the more expensive fuel."
],
"score": [
20,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
e30dhi | How it's possible for people trained in brazilian jiu jitsu to defeat much bigger and stronger but less skilled opponent in combat? | Engineering | explainlikeimfive | {
"a_id": [
"f8zemut",
"f8zj1kw"
],
"text": [
"Leverage leverage leverage, and knowledge of how other people's bodies work and what their typical reactions are like.",
"The most illuminative moment of my life in terms of floor fighting was when my high school wrestling coach specifically pulled me aside in the hall and asked me to join the wrestling team. I was dumbfounded. At 15 I was about 6\"1' but weighed about 135 lbs. I knew from experience that my reach was a huge advantage in a standing fistfight, but I said \"Why are you asking me to be on the wrestling team, you can see how skinny I am\" He then tells me that he stopped me because of how long my arms and legs are, and asks me if I know about mechanical advantage. I said that I do. \"Your levers are longer than anyone else's in your weight class, what you see as a problem is actually a huge natural advantage.\" That guy helped my self esteem so much. He took something that everyone had always made fun of me about (being a beanpole) and made it a desirable strength. More than that, though he taught me that knowledge of how to use your natural advantages to capitalize on your opponent's weakness can carry the day. Which brings me to my second point- if you are smaller than your opponent don't look at the fight as defeating them as a whole- defeat them in parts. If a guy carries a lot of weight in their arms and torso their upper body weight can assist you with disabling their legs- Genki Sudo vs Butterbean in Pride is a good example of this. Skill and knowledge can turn what your opponent thinks as a disadvantage into an overwhelming surprise."
],
"score": [
3,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
e37269 | How do old planes from ww2 and such fire their machineguns through a rotating propeller? | Engineering | explainlikeimfive | {
"a_id": [
"f91fudx"
],
"text": [
"There's actually something called a synchronization gear (or interrupter) in the engines of those planes that would basically send a firing pulse to the gun when the propeller was in the proper position. If the pilot's trigger was pulled, the firing pulse hit, and the gun was ready to fire (not ejecting a spent cartridge or loading a new round, etc) then it would fire."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e38s71 | In a car’s transmission, why is 1st gear the “strongest” especially during driving at an incline? | Engineering | explainlikeimfive | {
"a_id": [
"f91pv98",
"f91som3"
],
"text": [
"Because in a low gear, the engine, which is the thing delivering the power, can turn more times for a given distance you've moved. That means that movement has more pushing power behind it, and such is more effective at climbing hills.",
"Imagine biking up a hill. In low gear, you spin your legs a hundred times with very little resistance to move up a hill. It's more cycles for your legs, but it's ok because the resistance is so low. You can shift up as you build momentum. In high gear, you can't get your legs to move the pedals while on an incline. You'll struggle to move the pedals in even a single full cycle, and so you'll move slowly and burn energy while never building momentum. Same for your car."
],
"score": [
8,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
e3djcm | What is the downside to dams? | From my simplistic view, dams seem like the best source of renewable energy. Water flows naturally down a river, we dam it, water then spins generators and power is produced. Seems like a win-win. Obviously there is a reason we haven't damed every river, can someone explain it to me, like I'm 5? | Engineering | explainlikeimfive | {
"a_id": [
"f92ejuy",
"f92g468"
],
"text": [
"They can cause huge ecological damage by flooding the habitats of other animals when reservoirs are formed. They can also cause the downriver portion to silt up because the volume of water below the dam is lower so it doesn't wash away the silt as effectively.",
"You need the right geograpy, ideally a deep narrow valley in a rather hilly area. Without a height of water you don't generate much power. Try putting a dam across river running in fairly flat land and you need a very wide barrier to span the distance between ground rising higher than the water level you want to get. In turn, it will flood a huge area behind it to a depth of only a few tens of feet. The knock-on effects will be unacceptable. Roads, railways and other communications tend to run along that sort of area precisely because the gradients are gentle. It will also be good farmland from the silt and nutrients deposited by the river and therefore expensive to buy up simply to flood."
],
"score": [
15,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
e3jnf2 | How do the walk in cold rooms in Costco maintain the cold temperature at the barrier where they're exposed to the outside? | Engineering | explainlikeimfive | {
"a_id": [
"f93e4q2"
],
"text": [
"Air curtains/air doors. Essentially they're like one of those cool dyson hand dryers except they create a thin jet of the inside cool air and blow it downwards. The air on the outside gets _entrained_ by the downard air and delfected so it doesn't get inside. Not as efficient as an actual curtain, but in most cases keeps something like 60-80% of the outside air _outside_... which dramatically reduces the work the inside air conditioning has to do. The air curtains usually come down from above, but I've seen a few that come from the side as well."
],
"score": [
12
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e3zczs | Why can you patch tread but not sidewall or near sidewall on tires? | I get it's a safety issue, but what is different between the tread and sidewall? Does sidewall get more pressure? If so how? | Engineering | explainlikeimfive | {
"a_id": [
"f95twgw",
"f95qliz"
],
"text": [
"The sidewall is thinner than the tread so many patch methods are not reliable. In addition, sidewall holes tend to be more of a tear than a puncture, making repair almost impossible. The movement and manipulation of the tire shape while in use also affects the ability to repair the sidewall. Much like how a bandaid covers a wound on the flat length of your finger but does not work as well when the wound is at the joint where your skin moves and flexes as your finger bends: The tread mostly remains in one shape - flat on the road. The sidewalls are constantly rolling and curving to absorb the weight of the car - notice that tires appear fatter at the point where the weight of the car rests on the road. That bulge is always present so as the tire rolls around, the wall has to flex - the sidewall also flexes as it absorbs impacts to the tire from holes and bumps in the road. - the sidewall also flexes to absorb the side-to-side physical forces created while turning. (consider the 3,000 lb vehicle traveling at 50 mph while rounding a highway curve - the tire battles the inertia that wants to keep the car going forward as the driver turns the wheel - that force is applied disproportionately to the outside edges and sidewalls of the two tires on the outside of the curve). These forces exceed the force from mere inflation pressure. The flexibility of the sidewall is crucial for accommodating those forces. Next time you have a chance, look at a tire that is off the rim. You can easily push and manipulate the sidewalk, but not the tread because of the thickness and the steel component The tire plug, for example, needs the glue to adhere to the interior of the hole it passes through as well as to expand into a bulb on the inside to completely seal the hole. An interior patch may work for a sidewall hole, as will placing an inner tube inside the tire, but much more labor is involved and they are not reliable repairs for modern driving conditions.",
"Pressure would be the same throughout the inside of the tire. The sidewall is constantly flexing, or bending, as the tire rolls down the road with so much weight on it. A patch would be a weak place in the sidewall and would probably fail rather quickly. Also, this flexing causes heat, so the sidewalls get hotter, which would also weaken the patch."
],
"score": [
4,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
e41zq3 | Why do buildings say from the 16th century and before last so long and take the pressure of subsidence ? Is it because the materials back then were weaker and more flexible ? | Engineering | explainlikeimfive | {
"a_id": [
"f96hfay",
"f96cwjf"
],
"text": [
"What you have here is a case of survivorship bias, the ones that are left survived whereas many others did not. - URL_0",
"You mean like the Leaning Tower or Pisa, erected in 1173? There was much less scientific civil engineering back them. Buildings were substantially over-engineered, which also takes advantage of lower labor costs back then. The alternatives simply fell down along the way. Ruins of 16^th century buildings are also around today. The ones that are still standing were either lucky, or have been stabilized after their construction. The Egyptian buildings are in a desert where bedrock is very close to the surface, that's a wise location choice for long life expectancy buildings like the Great Pyramid."
],
"score": [
6,
4
],
"text_urls": [
[
"https://youtu.be/geOdDSs0tjY"
],
[]
]
} | [
"url"
] | [
"url"
] |
|
e4e5zj | How do automatic watches work? | Engineering | explainlikeimfive | {
"a_id": [
"f99oqes"
],
"text": [
"An automatic watch is a form of mechanical/clockwork watch - which typically use a coiled spring to power the mechanism. When the spring is wound up tightly, it wants to uncoil, and this movement is used to power the mechanism that regulates and tells the time in the watch. Traditional watches were manually wound - the user would wind up the mainspring (usually by twisting the crown of the watch) and let it run. If you forget to wind your watch up then the spring unwinds and the watch stops. An automatic watch uses the same basic mechanism, but with an extra part to wind up the spring automatically. Inside the back of the watch there is a small weighted wheel - every time the wearer moves their wrist, this weighted wheel can rotate in response (the weight always wanting to be at the bottom, or being moved about by momentum). When the wheel sounds, a small ratchet mechanism causes the spring to wind a bit tighter. So as your wear the watch, your movement is constantly moving the weighted wheel, which is constantly winding up the spring a little at a time."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e4kpb4 | How do bottling companies insert champagne corks into the bottles when they make them? | Engineering | explainlikeimfive | {
"a_id": [
"f9cfcgc",
"f9diprr",
"f9cl7gq"
],
"text": [
"When the champagne is bottled, the fermentation process hasn't completed yet and the yeast continues to make carbon dioxide. The corks can more or less be pressed in (usually by a machine) like normal wine bottling. The fermentation process continues after bottling and this produces the carbon dioxide that dissolves in the \"wine\" to make it bubbly when the bottle is uncorked. At least, this is how it worked for my home made bubbly!",
"fun fact - cork has a Poisson ration of about zero, which means that as you press down on it it does not expand sideways. Without that it would not be easy to use it to push into a bottle top, as the expansion sideways would resist your efforts",
"The cork on a champagne bottle is a cylinder before it is pressed into the bottle with a press machine. This gives it the done like head. A wire holder is then placed on top and twisted, this keeps the cork in place as to withstand gas pressure in the bottle"
],
"score": [
56,
21,
8
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
e4nhry | Does it matter, and if so why, if I put my headphones on with the with the left and right ears backward? | Engineering | explainlikeimfive | {
"a_id": [
"f9dik7z",
"f9dik5z"
],
"text": [
"Most obvious one is stereo panning. Games and sometimes music will pan things to the left or right. This is especially important in games, so that what happens in screen, eg big flash on the left, matches with the audio, explosion in your left ear. On top of that, some headphones are shaped ergonocamlly so having them on the right way is a lot more comfortable",
"Only for things using surround sound, like movies. Shouldn't really make a difference for music - the sound coming out of each headphone usually *isn't* identical, but it shouldn't make any difference to enjoyment of the song."
],
"score": [
16,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
e590om | Why can't airplane engines with inertial starter be restarted in the air from windmilling? | Engineering | explainlikeimfive | {
"a_id": [
"f9ig9s8"
],
"text": [
"For aircraft with props fixed to crankshaft (most civil, general aviation) then they can restart by windmilling. Not sure about turboprops. Helicopters have Sprague clutches so the engine doesn't slow the rotors in autorotation. So they must restart with starter motor."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e5b57f | Why do cars sound the way they do? | My basic understanding of combustion engines is that a small explosion happens..... somewhere in there, and that moves the pistons. A lot of cars make that nice smooth vroom kind of sound though, where does that come from and why is it different from the loud poppy sound of, say, a Harley motorcycle? | Engineering | explainlikeimfive | {
"a_id": [
"f9iv6uw"
],
"text": [
"A 4 cylinder gas engine has 1600 explosions per minute, or just under 27 per second at 800 rpm (an average idle). All the explosions overlap and you can't separate out the individual explosions. With a harley, the distinctive pop noise is from the exhaust valve opening, not the cylinders firing. However, sound design is a thing. engines, cars, and harleys especially are designed to sound a particular way and that isn't necessarily as quite as possible. This is in part why a commuter car sounds very different from a sports car (the sports car is designed to convey power and the commuter car is designed to isolate the driver from the road and driving). The distinctive sound a harley makes is part of the brand (they even tried to patent it). Although originally that may have just been the way the engines they uses sounded, now it is a very deliberate branding decision. The explosions in the cylinder make noise along with other components (like the exhaust valves). Various parts in the car absorb and amplify various sounds and they can be tweaked to produce a desired sound."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
e5bgdy | How does missile targeting detection works. | Engineering | explainlikeimfive | {
"a_id": [
"f9iv8xo"
],
"text": [
"In order for an early missile to find the right target, the launcher illuminated the desired target with a high energy, narrow radar beam. Inside the F-16 there is a gadget called a \"Radar warning receiver\" that listens for this sort of narrow beam. When it detects one it displays an alert, indicating the brand of radar most likely sending the signal."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e5bhvv | Why do boats have propellers at the rear, while planes have them at the front? | Could this be reversed? | Engineering | explainlikeimfive | {
"a_id": [
"f9ivs3u",
"f9iy9nr",
"f9iwa5j"
],
"text": [
"[Some planes have them at the rear]( URL_0 ). Steering is most controllable when accomplished from the rear. Powerboats steer by physically turning the propeller, so the propeller is in the back. Airplanes steer with by manipulating control surfaces on the tail, which makes it difficult for the engine to be back there as well.",
"I believe props at the front can blow air over the wings with greater velocity than ground speed, which would reduce takeoff v2 speed and allow shorter runways.",
"Yes, they can be reversed, there are pusher-propeller planes. The wright brothers first plane was a pusher. Pull propeller ships aren't a good idea, if you run aground, you hit the prop first, which means you can't get ungrounded = very bad. Water is very, very dense in comparison to air. Puller-prop planes get to spin the prop in smooth, undisturbed air. This provides more efficient operation because the air is uniform."
],
"score": [
11,
4,
4
],
"text_urls": [
[
"https://www.bing.com/th?id=OIP.WP7IBdW9pqPUfequkGmgLwHaFI&w=234&h=163&c=7&o=5&dpr=2&pid=1.7"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
e5ewzu | If wings generate lift by creating a pressure differential above and below, why do paper planes with flat wings fly? | Can't seem to find information on this. It's easy to think that singe the wing typically is tilted back some (has higher angle of attack), the air hits it and moves down, generating lift. But as I understand it, actual wings are shaped so that the distance from the front, under the wing, to the back, is shorter than the distance from the front, over the wing, to the back, creating a higher pressure on the bottom that the plane "floats" on. So why do "flat" paper plane wings seem to work? | Engineering | explainlikeimfive | {
"a_id": [
"f9jck13",
"f9jjdkv"
],
"text": [
"Paper planes don't fly, they glide. The flat wings don't provide lift. They let the plane ride on the air much like a boat on the water. If you angle the wings the right way the airflow can push the nose of the plane up giving the illusion of lift. It's still just falling with style.",
"> But as I understand it, actual wings are shaped so that the distance from the front, under the wing, to the back, is shorter than the distance from the front, over the wing This sounds like some variant of the [equal transit]( URL_0 ) fallacy, which is false. A flat wing will produce lift (just not very efficiently). Some aircraft have symmetrical airfoils whose top and bottom surfaces have the same shape."
],
"score": [
9,
9
],
"text_urls": [
[],
[
"https://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html"
]
]
} | [
"url"
] | [
"url"
] |
e5l5ci | Why does a car's recommended tire pressure depend on the car, not on the tire? | Shouldn't the tire pressure be dependent on the manufacturing of the tires, not the design of the car? | Engineering | explainlikeimfive | {
"a_id": [
"f9kck9y"
],
"text": [
"The weight of the car determines the required pressure All tires have the same sized contact patch at ideal pressure. Narrow tires have a square patch while wide tires have a very rectangular patch, but both have the same area. This constant area times the tire pressure will equal the weight of the car. A heavy car will push down more so you need more pressure for the tire to hold it's optimal shape and a light car won't push down as much so it'll ride on a smaller patch if kept at the same pressure as the heavier car You have to understand the constant contact area otherwise it does seem like it should be up to the tires rather than the car, but the tires are rated for maximum safe pressure rather than optimal performance"
],
"score": [
10
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
e5q42y | How does a chronometer work? | I recently read about English clockmaker John Harrison, who made it. However, I have not yet understand how his device works, despite referring to many online sources. Hence, this ELI5 post. | Engineering | explainlikeimfive | {
"a_id": [
"f9la1ve"
],
"text": [
"John Harrison was an amazing designer that got shafted by the British Crown because he was not of noble stock. His instruments were a whole series of devices that got better and better. To the point that he was able to meet the needs of the British navy for navigation. A chronometer is just a fancy name for an accurate time keeper. His secret was the invention of a mechanism (escapement) that would not change its tempo on the open seas. It also had to take into account temperature changes going from chilly England to toasty Bermuda. He did this by abandoning the normal pendulum and moving to a seesaw beam. This he discovered had a problem with a very specific motion a ship might have so his final clock used the now normal torsion wheel to set the tempo. Modern mechanical wristwatches now use a form of his escapement. If you see a video with a tiny bicycle like wheel first turning one way then the other, you are seeing John’s brilliance."
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
e5spg6 | How do torpedoes work? | If I fired a rocket launcher underwater it wouldn’t go very far due to, well, water. But a torpedo sails through water. How do torpedoes work, and why do they work but above ground rocket launchers underwater don’t? | Engineering | explainlikeimfive | {
"a_id": [
"f9lpz0s",
"f9lpbob",
"f9lx1ce"
],
"text": [
"Rocket launchers are designed to work in air so they use a high thrust rocket to move at extremely high speeds through the air. Torpedoes are designed to work in water which has a lot more resistance than air. They have a propeller on the back driven by a gas producing reaction in the torpedo that provides a constant thrust. They're also rounded on the end to make them more streamlined in the water(aerodynamic and hydrodynamic shapes are different due to water being thicker) There are torpedoes that are driven by a rocket engine, they generally use a creatively shaped nose to create a pocket of steam around the torpedo. This means that only the tip is pushing through the water so there is wayyy less drag which lets these torpedoes reach 300-500 kilometers per hour vs < 150 kph for standard torpedoes",
"A torpedo is actually a little propeller-driver boat, or miniature submarine if you like. It's designed to go through water just like a boat or sub would, while rockets are designed to go through air. Enginerds like me spend our time crunching the numbers to make each vehicle work where it's meant to.",
"Well, first, you absolutely can have rocket-powered torpedoes, and they in fact do exist. They just have to be designed to travel through water instead of air, but that's a fluid dynamics issue. If you're thinking that rockets need air to work, that's incorrect. A torpedo is basically just a miniature submarine with am explosive warhead attached. Most torpedoes are powered by propellers or pump-jets just like ships or submarines, but again, rocket powered torpedoes can and do exist. You just can't use a rocket designed to fly through the air."
],
"score": [
12,
6,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
e5xqg9 | what does the positions of the notch in a RAM stick signify? | I want to buy some RAM to upgrade a friends PC, but I don’t know how to check if it will fit without eyeballing it.... please help. | Engineering | explainlikeimfive | {
"a_id": [
"f9mgs7g",
"f9mhp4c"
],
"text": [
"there are different types of RAM: DDR1, DDR2, DDR3, etc... they each have the notch at different position so you don't accidentally put lets say DDR2 into DDR3 slot. And for the how to check part: look at the motherboard specs to see which version of ram it supports (most likely it will be DDR4)",
"They are mostly there so you don't try to cram your RAM stick into a slot it wasn't designed for. Every new generation they move the notch a bit so that you can't cram a new stick it into an older incompatible slot or an old stick into a new slot. The notch also serves the secondary purpose of ensuring that you put the RAM stick in the correct way. The notch is offcenter so you can't put the RAM-module in upside down. Side note: I hate the position of the notch on DDR4 sticks as it is too close to the center and I keep having to turn it around after noticing that I misjudged which way up the stick would go. DDR3 was easier to tell at a glance. At least it makes comparison easier than DDR and DDR2 were which looked just close enough to be mistaken for each other unless you read the label or tried to insert it into the wrong slot."
],
"score": [
6,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
e691a3 | What does lifting your truck/SUV do? | I don’t know car terms, excuse me. But if you lift the truck up, all the “under carriage” (axel, etc) stays at the same height so it’s not exactly like you have higher clearance...? Help. | Engineering | explainlikeimfive | {
"a_id": [
"f9okviw"
],
"text": [
"There are suspension lifts and body lifts. By lifting the suspension, you gain room for more suspension travel and larger tires/wheels. Larger tires and wheels provides more overall lift for the axles and chassis and gives more ground clearance. A body lift raises the chassis off the frame, providing room for even larger wheels/tires which will (again) give more overall clearance. A combination of the two can allow some pretty crazy ground clearance and suspension capabilities, though trouble can arise from extreme driveshaft angles and drivetrain and suspension stressors. There are ways around most of those problems, none of which are inexpensive."
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
e6iiug | How do wood-burning stoves heat an entire house? | When I have my oven on all day baking Christmas cookies, the upstairs is noticeably colder than downstairs (despite turning on the fan in our furnace to try to move the hot air around). How did old wood-burning stoves heat an entire house with no extra device to move the air? | Engineering | explainlikeimfive | {
"a_id": [
"f9qe507",
"f9qgkxd",
"f9qwf3h",
"f9s4p1y",
"f9qh1sg"
],
"text": [
"They didn't. They really only heated the room they were in. The same with any kind of stove that just makes heat in one place. I stayed with grandmother often enough to know that the bedrooms there were always really chilly in winter and the only warm rooms in the house were the living room and the kitchen.",
"I grew up in a house heated with coal burning stoves (hotter than wood)... One in the living room, one in the dining room. Can confirm the other rooms were never warm. At best the room directly above the heated room had it's chill broken a bit but not enough to be comfortable. We put heavy extra blankets on the beds in winter. Damn I miss sleeping like that under all that cozy weight. 😁",
"They didn't. The rooms near the stove were warm, sometimes too warm, and those far away were cold, but still warmer than the outside. People would use devices, like hot water bottles and trays full of embers, to keep their beds warm. Plus lots of blankets.",
"They don't much, without extra work to distribute the heat. Of all the woodstove heated houses I've stayed in, the only one that did a really good job of distributing the heat from the stove had the woodstove in the basement. Get it going nice and hot and the heat filtered up from the basement into the rest of the house, getting reasonably well distributed. Now, even a woodstove that doesn't do a great job heating the far rooms of the house will still keep them well above freezing. They just will be much colder than the directly heated rooms.",
"A wood stove have (one or more) chimneys that run through rooms and radiant heat comes from them - my grandmothers house had a wood stove with 4 chimneys - basically they would open or close a chimney flute depending on where they wanted heat directed - it was pretty neat and worked to heat up the bedrooms nicely. In modern times some wood stoves have fans that move heat through a ducting system similar to what a regular furnace uses. We have a fan for our fireplace which uses the heat from the back of the fireplace box and circulates it though open grills - it's pretty impressive how much heat comes out of these grills."
],
"score": [
7,
4,
3,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
e6l91z | How could old-fashioned telephones transport sound across the world? | Engineering | explainlikeimfive | {
"a_id": [
"f9r3m3g",
"f9r2xq0",
"f9ro969"
],
"text": [
"Undersea cables have repeaters. Amplifiers that take the incoming signal, boost it and pass it on. Both electrical and fibre optical cables use them.",
"Undersea cables & satellite. Your voice goes from your phone, down the wire to the local phone switch. From there it gets routed to another switch. And another. And another. Eventually, it hits an international gateway and from there it gets transported via undersea cable or over satellite (usually cable). Then it lands at the international gateway there. Then it goes from switch to switch to switch until it connects to your Aunt Molly's phone in the UK.",
"For much of the telephone's history, they couldn't. Copper wires have internal resistance that causes voltage to drop over long distances. In the early days, they had to operate long distance lines at high voltages. Even then, intercity calls were often too quiet to be of any use by the time they reached the other end. You could forget overseas calling. It wasn't until the early 1900's when the triode vacuum tube came out. Which could be used to amplify weak electrical signals into something usable. This finally made clear intercity calling possible. But calling the UK from the US was still a difficult prospect. The signal would degrade too much in conventional copper wires, over such a long run, that it couldn't effectively be amplified on the other end. So you needed in-line amplifiers (aka repeaters), ones built into the cable, to boost the signal along the way. Which is easier said than done. You needed very reliable vacuum tubes (since they couldn't be frequently serviced), and a way to get power to them. Technology that didn't exist at the time. The first transatlantic calls instead used radio, starting in 1927. A single 3min call cost £9 at the time, roughly equal to £555, or $730 USD, today. The first transatlantic telephone cable wasn't laid until 1956, when the above mentioned technology finally became practical. Even then, it could only handle 35 calls at a time. Which still made international calling prohibitively expensive. Analogue phone calls eat up a lot of bandwidth. It wasn't until the mid-70's when cables were laid that could handle over 1000 calls at once. At the time, it was actually cheaper to record your voice on a cassette tape and mail it, than it was to call someone overseas. Indeed, a lot of people did just that. Real practical, and affordable overseas calling only came about in the late 80's with the advent of fiber optic cables. These use beams of laser light shone through glass wires. Which can carry a lot more analogue and digital signals than copper, and which don't degrade as much over long runs. This is when the internet started becoming a practical reality."
],
"score": [
3,
3,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
e6ttdq | Why do some firearms have a magazine that is fed behind the trigger grip/back half of the gun? | Like is there a combat/mechanical advantage to these designs? | Engineering | explainlikeimfive | {
"a_id": [
"f9t3jwd",
"f9t8qlo",
"f9t3np9",
"f9tb1ha",
"f9t4mwd"
],
"text": [
"Yes, you can have a longer barrel without having a longer gun.",
"From back to front, pretty much any bolt-action or (semi)automatic gun needs to have the following: & #x200B; \\- Area where the bolt moves backward when ejecting a round and chambering a new round. \\- Area where the magazine is \\- The breech, where a cartridge is loaded so it can be fired \\- and only then, after all of that, the actual barrel. And usually the grip and trigger will be BEHIND all of that stuff, or at least behind all of it except for the area where the bolt moves backwards. & #x200B; Since rifle bullets are pretty long, that's at least three rounds length of area between where you hold the gun, and where the barrel starts. That's a lot of wasted space (and rifle rounds can't go inside the grip like most pistols). Most of the stock of many guns is wasted space. & #x200B; By putting all that stuff behind the grip, you can make a shorter gun with the same length of barrel. This makes the gun easier to handle. They are called bullpup rifles. & #x200B; The downside is that people often just don't really like bullpup rifles or find that the long mechanical linkage between the trigger and the action is clumsy and doesn't feel precise.",
"This reduces the total size of the gun, by moving the base of the barrel as far back as possible. So it's easier to carry, and easier to maneuver in close quarters.",
"Positives: * The barrel begins in front of the magazine, so you can have a shorter gun with the same barrel length (or a longer barrel with the same gun length. * The recoil force happens in the chamber, right at the start of the barrel. When you have it behind your grip, the recoil is less likely to make the aim drift a lot. Try holding a stick whick someone is pushing the front of, compared to a stick where someone is pulling the back, and you'll see the difference. This is the reason they have better hipfire stats in games. Negatives: * The mag is in an awkward position, requiring more movement to reload, making reload slower and more prone to mistakes. * They are harder to make so that they can be used left handed. Spent casings will be ejected into your face if you use it left handed. Some guns get around that in various ways. The P90 drops the ejected casings straight down. The F2000 ejects them forwards, in a somewhat complicated and error prone construction. * The trigger mechanism is a bit more complicated.",
"The bullpup design gives you a long barrel relative to the total size of the weapon. Still accurate but shorter, lighter, and easier to maneuver and transport."
],
"score": [
17,
12,
10,
10,
7
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
e6u7jg | How does Rocket Lab's propulsion cycle work? | Engineering | explainlikeimfive | {
"a_id": [
"f9tbbg1"
],
"text": [
"It’s called the Rutherford engine. Liquid rockets work by mixing fuel and oxygen. They do this by using a pump to bring in fuel and oxygen from the tanks to burn. In most liquid rocket motors, some of the fuel and oxygen is burned elsewhere to power the pump. The Rutherford engine uses an electric engine to do the pumping. It has a battery pack to provide power. This means it doesn’t have to waste fuel and oxygen to run the pump, but also means they have to carry the battery."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e70b0u | why do stoplights that are red seemingly at random turn green when no cars are on that street? | I notice it a lot on my way to work, I go to work at 2 am and it’s not uncommon for my light to turn red and the opposite to turn green when no one else is on the road | Engineering | explainlikeimfive | {
"a_id": [
"f9u9j7s",
"f9u9pzl"
],
"text": [
"Not all lights are controlled by traffic. Many are on timers. Of those on timers, some may or may not adjust the rate of changes by time of day.",
"To add to the timer argument, a lot of cities have an algorithm that are intertwined with other intersections to help the flow of traffic."
],
"score": [
8,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
e72f7b | Why does it take a professional to tune a piano but nearly any other instrument is tuned by the musician themselves? | Engineering | explainlikeimfive | {
"a_id": [
"f9us8vq"
],
"text": [
"Because it's harder to do and the owner doesnt need to do it often enough to justify learning how to do it themselves."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
e73d48 | how does a configurable nuclear weapon work? | I've read that e.g. the B61-12 can be configured to have a blast of between 1/3rd kT and 150kT - how does this work? do they open the bomb and change the interior? | Engineering | explainlikeimfive | {
"a_id": [
"f9v7389",
"f9v7ohp",
"f9v42so"
],
"text": [
"The bomb isn't in a constant state Seconds before detonation the deuterium and/or tritium gas is released which will serve as the fuel for the fusion stage. If you release all the gas you can get the 340 kT max yield. If you release no gas and muck with the timing then the fission stage fizzles and you get the 0.3 kT. If you release a bit of gas and let the fission stage go off normally get a midsized boom and you can adjust your final yield by adjusting how much gas will be released into the fusion section. It's set by a switch on the bomb before it's dropped and when it gets close to detonation it releases the desired amount of gas",
"They do so by changing the timing of events in the implosion. A lot of effort goes into maximizing the efficiency of the fission event, throwing that off reduces the yield, hence, you can use that to your advantage and dial-a-yield appropriate for your application. Fissile material, typically uranium-235 or plutonium-239, is shaped into a \"pit\" - ostensibly it's a hollow sphere, but that's only a simple model, in reality it's almost always some sort of hollow ovoid shape. Conventional explosives surround the pit and are used to compress it, driving the implosion that allows the exponential chain reaction. This gets tricky, the thickness of the explosive has to match the shape of the pit, and ultimately has to crush it down to a uniform sphere. Furthermore, the explosive is covered in detonators, all of which have to be perfectly coordinated for a uniform implosion, BUT, what you get are a number of shock waves emanating from each detonator. When two shock waves collide, the pressure is higher at that point, creating jets of higher pressure. So the conventional explosive is actually a complex geometric shape of slow burning explosives, to compensate. Once this layer of the explosive combusts to the point of a uniform shock wave, there's a second layer of fast burning explosive to provide the real kick. With all that going on, you can selectively delay the ignition of the detonators to reduce the efficiency, and lower the yield. There is a device called a tamper. This is simply a metal plate that acts as a buffer between the explosive shock wave and the pit itself. Earlier weapons held this in place with Styrofoam, others would suspend the pit with wires and there will be an air gap between the tamper and the pit. The point is to average out the pressure from the shock wave onto the tamper, which will accelerate across the air gap, and hit core with more, and more uniform force, than the shock wave itself. The choice of tamper can change the yield. The device can be built without one, or often the tamper is made of lead. The Tsar Bomba, the largest nuclear weapon ever detonated at an estimated 50 MT, was actually designed to be tested at 100 MT, but the choice of tamper was changed at the last minute, principally to assure a successful test. The original tamper was going to be made out of uranium. Then you have deuterium and tritium. These are isotopes of hydrogen that provide 2 and 3 additional neutrons, respectively. Nuclear weapons rely on neutrons to cause the nucleus of the fissile material to split. The naturally occurring decay of the fissile material is enough to detonate such a weapon, such is the nature of the significance of the implosion; you collapse the pit to such an extremely dense core that exponential growth of decay is unavoidable, in a fraction of a second. Adding hydrogen \"boosts\" this process, increasing the efficiency. It doesn't take much, literally hundreds of atoms are enough to get a significant yield. There is a hydrogen generator that is a little device which will produce hydrogen through electrical or chemical reactions, and inject it into the pit through a tiny port hole in the side, moments before detonation. You can adjust or omit the timing of this to change how much boost the pit gets. Then finally, we know the weapon designers try to inject, capture, and reflect as much energy into the core as possible. Energetic nucleus are more likely to split than those at a lower energy level, so the outside of the core is surrounded by Styrofoam filled with beryllium, which reflects neutrons. There are also other x-ray and gamma ray reflectors, and it's also believed that radiation pressure is a significant factor in causing compression. To add to all this, there are small particle accelerators, called flash tubes, that blast the core with x-rays during detonation. You can omit or delay the timing of this to reduce the yield. All these design decisions and variables effect atomic bombs. You then have thermonuclear bombs - fusion weapons. These weapons also rely on compression. That compression comes from an atomic bomb. So atom bombs are the first stage of a thermonuclear bomb. The second stage is roughly the shape of a paint can, if you believe the diagrams. The can is made out of u-238, which isn't fissile, but it doesn't have to be - this stage of the weapon doesn't rely on chain reactions. The can is filled with lithium-6 and -7, which are neutron heavy isotopes. When they fuse, under the compression of the atomic bomb and it's massive amounts of x-rays and gamma rays, all of which the compression generates fantastic amounts of heat, the excess neutrons are cast off. The energy level of these neutrons is where the \"thermo\" part of the weapon's name comes into play. Thermal neutrons are so energetic, they're moving at 17% the speed of light. They blast right through the uranium housing like it's not even there. Right through the nucleus of those atoms. Such energetic neutrons are what's required to get uranium-238 to split, releasing tremendous amounts of energy. The housing from the second stage is where most of the radiation comes from in the fallout from these weapons. But as for varying the yield of a second stage, I don't know enough about them to say. Obviously, varying the yield of the first stage is going to have an effect on the second, but I don't know more than that.",
"Nuclear bombs don't like going off, and require precise timings and such. These timings can be shifted slightly to waste more fuel. Fusion bombs also use a gas as a booster for the explosion, which can be easily moved around to vary the yield."
],
"score": [
10,
5,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.