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kddid9 | I've heard "wavy" walls use fewer bricks than straight walls. How can that be possible? | I don't know anything about architecture, so I don't know if this is a really dumb question. I saw it from post that said those wavy walls were popularized in England. | Engineering | explainlikeimfive | {
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"A straight wall must be constructed double-wide ([there are some different ways to lay the bricks, but note the “English bond,” alternating stretchers and headers]( URL_0 )). Just one layer wide of brick is too thin—it would easily topple over to one side. A[wavy wall]( URL_1 ) uses alternating half-circles to keep a single line of bricks from falling to either side; it does not need to be double-wide. So even though one wall is wavy and uses more bricks length-wise, it still saves total bricks used against a straight but double thick wall.",
"Apparently you can make the wall thinner this way, without it falling over as badly. Normal brick walls are two or more bricks thick, but the serpentine walls can have just one layer, since you sort of have a third dimension built-in.",
"Try to stand up a sheet of paper on it's edge. It falls right? Well you can make it stand easily two different ways. You can lean it against another sheet, or you can fold it. Fold it back and forth and a single sheet will stand up just fine, using half the paper as the other method. Same with bricks. Edit: use a half sheet of paper split lengthwise to see the effect more clearly and to make it easier to lean against another of the same",
"Take a piece of paper, and hold it vertically by the bottom two corners. It will quickly stop standing up straight and flop over. Put it back upright, and then move your fingers closer together so the paper bends like a wavy wall. Now, it won't flop over. It will stay standing straight up. The same basic thing is happening with the wall. A narrow wall will easily topple. One way to strengthen it is to make it wider, which will use more bricks. Another way to make it stronger is to make it wavy. That will also use more bricks, but not as many as making it wider."
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kdh7o7 | Why does the M1 Abrams use a smoothbore gun? | To my knowledge, rifles are better than smoothbores at firing solid ammunition (not shotgun pellets or like, a missile), since they give extra range and accuracy. So why does this tank use a smoothbore? | Engineering | explainlikeimfive | {
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"Because of the type of rounds they’re firing. And not that those rounds are self guided or anything. The m1 Abrams is typically firing longer, thinner, projectiles. Which are more necessary to penetrate armor. The thinner a projectile, the faster it needs to spin to get the same increase in accuracy. Because of inertia reasons. But think of this, what is easier to throw accurately by giving it a spin, a nice thick football, or a dart. Relative to their size, your typical bullet is actually a lot thicker that a round the abrams is firing (like if you took a bullet, and then scaled it up to where it was just as long as the abrams round your comparing it to.) So the improvements they would get for rifling the barrel were determined to not really be worth it. Plus because rifling the barrel does then increase production costs, and possibly increase wear and tear on the barrel. Tl:Dr Becuase of physics the type of rounds an abrams typically fire don’t get the benefits of rifling to the same extent as your normal bullet, so it was deemed not worth the extra cost/maintenance.",
"a lot of modern tank guns fire things more closely resembling rockets. rockets use fins for stabilization. it would be impossible to stabilize with a rifled chamber. modern armor is effective. and solid ammunition is not effective against armor."
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kdxv02 | If I get in a cold car and want the temperature inside to be 71, so I set it for 71 or set it higher until I am uncomfortable? | Engineering | explainlikeimfive | {
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"It's \\*different\\* if you're talking about a car or a room, so let's split those up. A car will try to output air at whatever temperature you set. If you set 71F, it will try to output 71F. It's not \"closed loop\", it's not paying attention to how hot the car itself is, it's just regulating how hot the air coming out of the vent is. So if you set it to max, it will put out the hottest air it can. This will warm you up faster. So, in a car, set it to max until you're at at the temperture you want, then dial it back. Note: fancy cars that have \"auto\" modes or computer-controlled climate may do this on their own, but it won't hurt. A house only has \"on\" or \"off\". It doesn't control the output temperture, it controls how \\*long\\* the furnace runs. It will turn on and run until it gets to the set temperature. It doesn't matter if you set 70F or 100F, it'll just be \"on\" for as long as it takes. As a result, it doesn't heat faster if you set a higher temperture, so you should just set the temperature you want.",
"Well, in a house, the heater kicks on full blast and then turns off when the thermostat senses that it's acheived the desired temperature, so setting your thermostat hotter won't make it get warm quicker. As for a car, however, I'm not positive, but I believe that your temperature knob usually controls the voltage going to the heating element, therefore THEORETICALLY turning it all the way up can help get hot quicker. Maybe someone else can fact check me on that one. Edit: Spelling",
"Setting the thermostat way too high is an emotional impulse. Not even Data responded to emotions, and he had a positronic brain. Your thermostat does not.",
"Just set it to where you want it. 99% of temperature systems don’t slow down as they get close to cut off. They heat FULL POWER HEAT UP RIGHT NOW! Until the thermostat says “yeah we’re warm enough now” If you set it higher than you want it, you waste energy overshooting where you need to be. Plus you end up too hot then."
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kdzv1i | What does alternating current (AC) actually mean and how does it work? | Engineering | explainlikeimfive | {
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"If you think of electricity like water, DC is a river, endlessly flowing in one direction. AC is a wave pool - sloshing back and forth but not actually going anywhere. The current flows one way, then the other, many times per second.",
"So you have a voltage, and that voltage allows for the flow of charge through a circuit. In a DC circuit, this is all that you have, charge flows one way, and you have one voltage to describe it. AC works by repeatedly flipping that voltage, akin to swapping the terminals on a battery. The frequency of the AC circuit is a measure of how often the voltage flips."
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kemmed | What are the benefits in performance of a petrol/gasoline car compared to a diesel car and vice versa? | Engineering | explainlikeimfive | {
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"Diesel engines are *significantly* more efficient than gasoline engines, especially at \"steady state\". Due to the way diesel engines function they have a far lower operating speed, usually limited to around 5000RPM on the high side whereas gasoline engines, depending on technology, can often rev to 7000RPM or higher. Diesel engines often are turbocharged which allows for a fast onset of torque that performs through the entire useful engine speed. Gasoline engines benefit from turbocharging as well but they don't typically make max power until higher on their RPM range (engine speed). Due to the diesel combustion cycle their engines typically produce far more torque than a similarly sized gasoline engines. Back to what I said about \"steady state\"; diesel engines can perform in their upper RPM range making maximum power essentially forever. Gasoline engines cannot do this because they can't run at those operating speeds to produce maximum power for any significant amount of time. This comes back around to the efficiency. Most of the efficiency difference between the two engine types is lost to heat in a gasoline engine; they essentially cook themselves to death. Most stuff that runs constantly like industrial generators, heavy equipment hydraulic pumps, etc take advantage of this increase in efficiency at steady state.",
"In general, gasoline engines spin faster, and have shallower cylinders, so coupled with a good transmission, this speed can be translated into high speeds for the vehicle. Diesel engines typically have deeper cylinders and spin slower, and this usually translates into more torque / power, for towing heavier loads. But, it depends a lot on the design of the engine, and there are many cars that use diesel engines, and they can go as fast as gasoline cars. And there are many gasoline \"heavy load\" or towing trucks, and they can perform too. Basically, it's the job of the transmission to convert the engine's speed and power to speed or power (or both) \"at the wheels\", so there isn't a clear cut between diesel and gasoline usage."
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keold6 | how does traction control work? Like how exactly does your car know when the wheels are sliding? | Engineering | explainlikeimfive | {
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"The car’s onboard computer is continually measuring the speed of rotation of each individual wheel. When the car detects that one (or more) wheels is moving slower or faster than the other wheels (and/or slower or faster than the car expects the wheels to be turning given the overall speed of the vehicle and driver inputs such as braking and acceleration) the car will decrease or increase power until it senses the wheels are “balanced” again. The full version is obviously a lot more complicated, but that’s the ELI5 version."
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kerq9k | How does jumpstarting a motorcycle without cables work? | A friend of mine is a mechanic, and long ago he told me if my motorcycle's battery fails and I can't get another vehicle to help me with jumper cables, what I have to do is have the ignition ready, get it into 4th gear, and after giving it some momentum to suddenly release the clutch. How does this work, and why 4th gear specifically? | Engineering | explainlikeimfive | {
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"To start, the engine just needs to be spun fast enough that it can 'catch'. Releasing the clutch connects the wheels to the engine, causing the bike's momentum to spin the engine if the bike is moving. Each gear will spin the engine a different speed. Lower gears will spin it faster but with less efficient use of the bike's momentum. It sounds like your mechanic friend has decided that fourth gear is the right balance of speed and momentum-efficiency. Interestingly, this can also be done with manual transmission cars.",
"The main thing that starts an internal combustion engine is the starter motor. This is why cars/motorcycles don’t need dangerous hand cranks. Some motorcycles and dirt bikes have kick starters. The idea, is to put it into a gear that will spin the engine easily, get it moving so that gas will get sucked into the chambers then assuming the battery has enough charge to spark the spark plugs, it’ll start working. Once the engine is running, it’ll recharge the battery. (it’s easier for the battery to trigger the spark plugs vs spinning the starter motor from a stop)",
"The old bump start. & #x200B; Essentially, the hardest work your battery has to do is start your engine. It's really hard and requires a lot of energy. But if you can manually get the bike/car rolling by pushing it and get going to say 4-5 mph and then sudden engage the engine... thats enough to do 90% of the work. If the battery has any life left in it at all, it'll ignite the spark plugs and then your generator will recharge your battery while powering the engine. & #x200B; It's a good trick to know if you ever find yourself in a pickle. Starter switches on motorcycles are notoriously prone to failure."
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ket9q5 | How come steam can work for a train and go really fast but not cars? | Let's pit a steam train and a run-of-the-mill car, nothing like a sports car, like a normal car a suburban family would have like a Nissan or something. If steam power is so ineffecient, why is the train faster than the car? Wouldn't the same logic work for cars if that's the case? | Engineering | explainlikeimfive | {
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"Trains have a lot less friction to overcome compared to a car. That's why they are able to go a lot faster. They have less friction to overcome because they run on steel tracks and use steel wheels. Metal rolling on metal is very low friction. Interestingly this also means they have almost no traction so trains *really* struggle to go up even the slightest inclines that a car wouldn't even notice. & #x200B; Car users rubber on dirt/asphalt/concrete/etc. This is great for traction which helps make the car easier to control and stop but hurts efficiency.",
"steam is „slow“ compared to ICE engines, there is no getting in, and driving off within seconds. its also pretty bad at speed fluctuations. that being said, check out jay lenos garage on youtube - he has a few steam cars in his collection!",
"Modern trains don’t run on steam anymore. They use electric engines, or diesel engines like trucks. Steam trains in the old days were generally slower than modern cars. Big ships still use steam turbines though. Steam turbines have a lot of power and efficiency, but weigh a lot. When your ship already weighs so much the extra weight is hardly noticeable. You can also run them by burning almost literally anything, so they burn the really really bad and polluty oil.",
"Good answers already, but I want to add that steam power efficiency is highly dependant on size. A huge boiler will be a lot more power than two of half the size. But it will take hours to preheat and you don't want to start your huge steam car at 4AM to get to work in time. Also it's very high maintenance. Imagine having to get into the boiler in regular intervals to chisel the calcium away. (Unless you can afford fully desalinated water)",
"There were steam cars way back in the day. The problem is that the cars were huge. The boiler would be large and cast iron which would add too much weight for the use of moving 2-4 people. Also most steam engines used coal or diesel as fuel and needed water tanks. All of which would take up space and add weight.",
"The record for speed held by a steam train is the Mallard at 126MPH. An ungoverned modern standard car with tires that can handle it can achieve that. The car also won't have any wheel slip and will have an early lead down our imaginary drag strip, too. In everyday life, trains benefit from the block system. A high speed train can go 250 km/h regularly or however fast it goes be cause it's known that nobody else is on the tracks. The roads are shared."
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kf6oam | why do (almost) all car doors hinge from the front, what was wrong with the old ‘suicide’ door? | Engineering | explainlikeimfive | {
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"Primarily, the reason is airflow. A door hinged at the front will tend to find itself pushed closed by the force of onrushing air; a rear-hinged door will find itself torn open. Additionally, were someone to fall out of a rear-hinged door, the physical presence of the door might prevent them from falling all the way clear; they may end up dragged along for the ride, causing further injury.",
"You cannot see traffic heading toward you, hence “suicide doors”. If you open it at the wrong time, a car can hit and crush you."
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kfi5cy | What is the difference between a Car battery and a RV battery | ELI5 What is the difference between a Car battery and a RV battery Lets keep it simple and stick to lead acid battery for both the car and RV (house) battery | Engineering | explainlikeimfive | {
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"The short answer is that the batteries for the car are designed to deliver a very high current to start the engine. The RV batteries is designed to deliver a lower current for longer time and better survive being fully discharged. The goals result in different designs. For Lead-Acid the main difference is you have a lot of thin plate in the car battery for max current. The RV batteries have thicker plates. So a car battery would not last as long if you use it as an RV battery and an RV battery might be damaged if not be able to start an engine at all especially if it is cold. [ URL_0 ]( URL_0 )"
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kfiwa8 | Why can’t music engineers just turn down the master volume when a live show is too loud? | Yesterday I was at a concert at an arena that’s know for it’s poor acoustics, and I was at the other end of the arena and there was a lot of reverb and the sound was too loud to the point where it was painful. However, I was fairly close to the control booth and it seems unlikely that the engineers weren’t hearing it. Isn’t it as simple as to turn down the master volume in this situations? Is there more to it? Are there other implications? Ps: Don’t know if this counts as Engineering but I had to add a flair so I thought that was the most suitable. It is Sound Engineering technically | Engineering | explainlikeimfive | {
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"Being at a concert, during a global pandemic, the sound engineer knew the audience didn’t really care if they die.......so he wasn’t concerned about preserving their hearing either.",
"Louder music sounds better then quiet music. This is the basic principle behind the famous loudness war that have caused so many musical albums to be remastered multiple times in the last couple of decades. So the audio engineer have to balance the volume so that it is as loud as possible without being too negatively affected by the equipment and acoustics. Hitting this balance can be hard. Especially as people perceive the music differently, some prefer it louder and some prefer it higher quality. Part of the issue is that sound engineers and others within the music industry often experience the music very differently from most listeners, both due to their experience but also through physical changes in their hearing.",
"As lifelong Sound Engineers, their hearing has probably been damaged after years of loud venues and the volume didn’t seem as loud to them as it did to you."
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kft7qz | From an engineering standpoint, can someone explain to me what is clean coal? | It’s been politicized so much that I can’t really find any helpful information. With all these initiatives of cutting down emissions by “going green” what is “clean coal”? I’ve heard that the filtration systems in these coal plants are excellent, that they cut out most of the pollution before it gets into the air. Then again, I never heard it from an engineering perspective. What are we using today with the current technology we have? | Engineering | explainlikeimfive | {
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"It's basically a marketing term. The point is to use filtering and carbon capture systems on the power plant exhaust stacks to remove as much of the pollution from the burning coal as possible, as well as preparing the coal before sending it into the reactor in order to remove a lot of the impurities that lead to the worse emissions (e.g. SOx compounds). It's definitely *way* better than unfiltered coal emissions (particularly in terms of the toxic and carcinogenic emissions), but it'll also emit a large amount of greenhouse gases and pollution to the atmosphere. It's largely being abandoned as an idea in the US as we speak, entirely because of fracking and the resulting glut of natural gas available in the United States. Natural gas, basically by nature, will burn considerably cleaner and have virtually no serious emissions other than CO2 and a little methane, and because of the massive glut coal just can't compete in terms of costs.",
"From a truth perspective Clean coal is a marketing term. It's a good start, but coal will never be the energy solution for the world simple because it is limited, and dirty. Clean coal is a term of a collection of technologies to make coal less destructive, but coal will never be \"clean\" just less awful. Part is to wash the coal before burning, crushing it, mixing it with a liquid and letting the unwanted impurities settle out before burning. Another example of reducing the sulfur dioxide emissions by mixing in limestone that reacts with the sulfur to make synthetic gypsum, used in drywall. One might also capture the carbon dioxide emissions and sure them underground, but that's expensive to do, and not a permanent solution. There are a few more examples you can read about here URL_0 if you want. TL:DR The gist of it is clean coal is a marketing term to make you think coal is cleaner than it is. But also a collective term for some innovative solutions to at least make coal a less awful energy source, because it's very hard to just stop burning coal all together till we come up with a long term sustainable solution.",
"There is no such thing as \"clean coal\" It is a lie perpetuated to fool an intentionally ignorant segment of the body politic into believing that a politician can stave off the obsolescence of the coal industry. It cannot be described in engineering terms because the term is political propaganda. Coal, like any other fossil fuel, is a \"dirty\" fuel. Burning it produces waste. The major forms of waste are CO2 (which pollutes the atmosphere as a greenhouse gas), SO2 (which pollutes rainwater to create acid rain), and the heavy metals, such as mercury, which are either released into the atmosphere during combustion, or which leach into groundwater from stored coal ash products. The term \"clean coal\" is a euphemism for the process of capturing CO2 from burned coal and storing it somewhere, either by injecting it deep underground where it may be trapped by rock formations, or by incorporating it into plastics or other materials. The term does not address the toxic leachate from coal slag/ash piles, and it does not speak to the heavy metals released into the atmosphere. \"Clean coal\" is a hoax. People who use the term in a serious way are lying to you."
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kg1315 | Why do cities pipe hot water? | I had noticed something interesting in r/CatastrophicFailure , and there was an interesting [video]( URL_0 ) of a heat pipe bursting. Why do some cities pipe hot water to buildings and homes? Wouldn't it be more efficient to have water boilers when you need hot water instead? | Engineering | explainlikeimfive | {
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"It's normally hot water that's a byproduct of some other process. Like power generation. Running all of that hot water in pipes throughout a city is a great way to provide heat. Because you need to cool that hot water off, might as well do something useful with it. Basically nowhere is going to heat water up specifically to run it through pipes. (unless they have a lot of geothermal which most places dont have) EDIT: in case it's unclear this water is basically never actually for use by residents.",
"Some places have city wide heating. China does this in northern cities. Your radiator pipes run to a central regional boiler plant instead of every building having its own boiler. NYC also has a central steam system. Can't remember what it still powers but it's still functioning",
"It's not a big city but I lived on an island in Alaska and the town had an incinerator for most of the garbage (to avoid filling up the tiny landfill too fast.) It was at the edge of our college campus and the heat from the incinerator was piped through steam tunnels to heat the buildings on campus. The tunnels were under some of the sidewalks which kept them clear of ice in the winter. It was a pretty neat setup."
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kg1ud4 | Why are commercial planes never black? | I've seen jet planes of several colors. Almost always white but never black. Is it a heat absorption thing? | Engineering | explainlikeimfive | {
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"Heat plays a factor but the largest factor surprisingly, is weight. Dark-colored paints weigh more due to larger amounts of pigments. When you spread that over multiple layers for the size of a large aircraft, it's significant enough that there isn't really a benefit to doing it. Additionally it can be harder to spot damage on dark surfaces, which is bad. It's used by the military in some instances because it's easier to hide a plane at night if it's dark-colored.",
"There are actually many reasons for this. 1. Black paint is heavy and weight is important 2. Black absorbs heat and planes need to run at cool temperatures 3. Black isn't reflective and can be harder to spot for other planes or ATC",
"The reason is that there is no incentive to. Commercial planes certainly can be painted black, Southwest Airlines used to paint their planes to look like Shamu. Just google \"shamu livery\" and you will see lots of commercial planes painted black."
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kgdjrz | how do 'green' energy providers work? | I get flyers and see little informational tables set up everywhere for switching from my city's electric provider to various renewable energy companies. How does this work if I'm still connected to the same grid? Would I still be connected to the same power grid? | Engineering | explainlikeimfive | {
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"You will still be connected to the same grid. But instead of paying people to burn fossil fuels, you will be paying people to build up renewable energy infrastructure. Of course, another option is to just have a company come by and install a bunch of solar panels on your property and take you off grid, but that's really rare.",
"A power grid is really separated into two portions - generation and distribution Your city's power company handles distribution but is going to buy from companies that generate the power. When you switch to a green energy provider you're saying that you want your payments for generation to be directed to a green energy provider. Whether you actually used their energy or not isn't factored in anywhere At the end of a month, the power company will tell the green energy provider that it \"sold\" X kWh last month, if it generated less than it sold then its going to need to pay one of the other generating companies for what they made to cover its shortfall, but since you generally pay a bit more for the green energy provider they still make some money off this that they can use to expand their generating capacity. Its all the same grid, its more a matter of distributing funds the way you've selected rather than providing you electricity the way you have selected"
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kgdrgf | How energy efficient is it to switch off a car engine at a red light? Is it worth it? | Engineering | explainlikeimfive | {
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"If it has an auto stop/start function, it’s much more fuel efficient, which was explained and I think tested by the YouTuber “Engineering Explained” However, if your car does not have that function, it’ll wear out the starter so it’s best to just let it running. Auto stop/start cars have a different system that can handle the off/on nature"
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kgf112 | How airplanes measure their height? | Engineering | explainlikeimfive | {
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"They measure air pressure. However, the air pressure (even at a constant altitude) changes depending on the weather, so whenever you talk to an airport, thy give you an altimeter setting (QNH) --- the pressure there would be at zero altitude (sea level). You can also get that on the ground by setting your altimeter so that it shows the actual elevation of the airfield. Knowing your altitude has two slightly different purposes: you want to stay above ground (generally, planes fly very badly underground, the resistance is just terrible) and you want to stay away from other planes. To makes things simpler (to avoid changing your altimeter setting a lot when you fly somewhere far away), when you're above some altitude, you set your altimeter to a standard sea level pressure (1013.25 hPa, IIRC). The altitude above which you do that is called a _transition altitude_ and is set by the local authorities (so that you are definitely above any mountains there might be), the altitudes above that are not called altitudes, but flight levels (eg. FL100 means 10000ft as measured when yout altimeter is set to 1013.25hPa) and because everyone else around you is using flight levels too, you keep vertical separation (staying at different heights) without too much hassle. Did I forget anything?",
"A combination of multiple different instruments, not all planes have all of these instruments bit all use a combination of them to determine altitude. Radar and Lidar, functionally similar just send out a signal towards the ground and measures how long it takes to bounce back. Pressure sensors, measure the outside air pressure and estimate the altitude based on that. Radio signals from ground stations and GPS satellites, functionally the same way your phone knows where you are when you use it to navigate, it's measuring signal time from various known points and using triangulation to determine where it is in 3d space. Accelerometers, the plane is calibrated on the ground to know where it is on the ground then it measures how far it has traveled(particularly in the \"up\" direction)."
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kgh5us | How are cinder blocks/bricks a viable solution to foundations to homes and mobile homes? | Engineering | explainlikeimfive | {
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"Concrete and most masonry has great compressive strength. Foundations are below grade, so exposed to moisture. Masonry obviously doesn't rot. Foundations need compressive strength much more than tensile. Also, they are cheap and easy to work with. You don't need heavy machinery to stack blocks, just labor. A normal sized delivery truck can get to a tight jobsite to deliver blocks and mortar bags. You can get strong enough, durable enough, and precise enough for residential construction at a viable price point. Why would you think they aren't viable?"
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kgjqs6 | How do they make those glass blocks with three dimensional images laser-etched into them? How does the laser only mark a certain spot within the block? | Engineering | explainlikeimfive | {
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"They use two lasers. And where those two intersect, the energy is higher and enough to set off some chemical reaction."
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kgo8wa | How strong the wooden apartments are? Specially the ones having 4 floors or more. | Engineering | explainlikeimfive | {
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"They’re fine, shaking is caused by cheap walls and flooring, not anything structural. Wood is just as strong in most buildings as stone or brick, and a lot of wooden apartments are supplemented by cement or other materials.",
"As a soon to be licensed structural engineer, buildings are built to a specific code. These codes are determined over time to hold up to not only day to day scenarios but also overload scenarios. It’s designed correctly but may not always be built 100% to drawings. Sometimes a connection for a beam to girder might have to be adjusted. Maybe a joist (truss) isn’t connected properly. These along with general movement by a person cause the problems you’re seeing"
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kgspge | why do car doors need to be banged shut, even if slightly? Why don’t they just click shut like normal doors? | Engineering | explainlikeimfive | {
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"Car doors have sealing gaskets that prevent water running off the roof from entering the inside of the car, and to insulate them against road noise and exterior air. Those gaskets need to be compressed between the door and the frame, so you need more force to close the door."
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kguk0m | How is diamond machined? | Or the hardest materials in general. I mean, doesn't the process require one material to be harder than the one that's being machined? But if you're machining the toughest material there is, how does it work? | Engineering | explainlikeimfive | {
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"Diamond saws are used to cut diamonds. The saws use diamond dust and are consumable. They take hours to make each cut (face) because they feed very slowly.",
"No one really machines diamonds, They are hard but they break pretty easy at convenient straight lines. So we shape them by making them break along their natural planes. No one is really out there carving diamonds into things. There ARE materials harder than diamonds and ways to ablate things that aren't solid surfaces that could machine a diamond but we just don't really have tons of really giant diamonds sitting around we want to make into complex shapes. So we just use them in cut or dust form."
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kgyz9g | How has the ISS managed to stay in orbit for over 20 years and not be obliterated by random space junk moving faster than a bullet? | Engineering | explainlikeimfive | {
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"It moves out of the way of larger bits and tanks the very small ones using [Whipple shields]( URL_0 ) on the important parts. Sometimes stuff gets knocked out and replaced.",
"There's an unimaginable amount of empty space up there (imagine firing a bullet in a random direction in the middle of the Sahara desert or Antarctica. Are you really worried? Now imagine much more empty space than that) but even then it HAS been hit lots of times, but only by very small objects, which makes sense since very small objects are like 99 percent of space junk. That's why it has so many layers of shielding. They repair them sometimes. They also lost an antenna once, if I remember right. Almost (?) every satellite, including the ISS, is moving the same direction, too, and needs pretty much the same speed to STAY in orbit, so it's really unlikely to get a \"bullet\" coming retrograde (the other direction) in exactly the right place. For big rare stuff, they track it already (and lots of other satellites and earth-based stations track big stuff, too) and can nudge themselves a tiny bit out of the way (or speed up or slow down slightly) if necessary. A tiny adjustment makes a big difference.",
"In addition to what’s been said about debris tracking and shielding, the ISS orbits at a very low altitude—low enough that it experiences a trace amount of atmospheric drag. This drag causes orbiting objects to lose their orbital velocity over months or years, eventually plunging into the atmosphere and burning up. The ISS can be re-boosted by visiting spacecraft to maintain its velocity, but debris cant, and so the ISS’ orbit stays relatively free of hazards."
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kgzwry | How is it that just a few millimetres of insulation in space suits is enough to protect astronauts from the extreme heat/cold of outer space? | Engineering | explainlikeimfive | {
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"Space is a terrible thermal conductor. On earth you're either in atmosphere or water, and heat transfers much easier within those mediums. In a vacuum you dont have matter pressed up all around you for heat to conduct through.",
"True ELI5: In order for something to move from hot to cold, there has to be something for the hot to move TO. Have you ever touched a big piece of metal on a cold day and felt how cold it is compared to the air? That's because the metal has a lot of stuff in it for the heat from your hand to move to, and the air around you doesn't have as much stuff (but it still has some, just a lot less than the metal). Space, on the other hand, is very, very empty. There just isn't that much stuff for the hot to move into. So, while it may be very cold in outer space, it won't cool you down very quickly at all.",
"Terrible cold in space is mostly a myth. Yes, if you were in the shadow of an object (or very far from the sun), an object with no heating would get very cold - but it would do so very slowly. The reason is that space is a perfect insulator against all forms of heat transfer except radiation - and heat radiation is a very slow process at low temperatures. The heat generation of a human would alone be sufficient to counteract heat loss. Bigger problem is cooling - and space suit deal with this problem by having water cooling and an active heat exchanger.",
"The way a thermos flask works is that it has a layer of vacuum inside its walls. This means that heat transfers very slowly out of the flask, because heat radiates faster when it can go through matter. So when you're in space, you're surrounded by vacuum. So it's actually very hard to heat to leave, and a big issue for space travel is how to vent heat properly so as not to boil your astronauts. This also means that a human can survive in space longer than most people believe. The first thing that's going to kill you is suffocation (though the lack of pressure will injure you pretty severely). If you just bring a scuba mask and oxygen tank (assuming those work in space?) you'll be able to survive for a fair old while, though you will be hospitalised once you get rescued.",
"Few millimeters? Have you SEEN the spacesuits they wear outside in space? The current NASA one has 14 layers of heating/cooling, mylar, ventilation, etc. They also have to be strong enough to survive vacuum. But anyway, the biggest advantage is that they're completely sealed, so your body doesn't lose much heat at all. You keep generating it, and it keeps staying inside. This works so well that they also have cooling systems! Wrap yourself in a very thin layer of plastic wrap sometime and wait 20 minutes and you will see. Protip: leave an air hole!",
"The thermal conductivity is a large factor as others have said, but also what the few millimetres of insulation is made up of is very different to what we normally have in warm clothing that we buy in typical Earthling clothing. In space suits, the insulation is made up of \"Multi-Layer Insulation\" (MLI) which has many layers (often 10 or more) of insulating material (such as mylar or kapton) which are separated by spacers with a low contact area (basically a grid of the spacer material). Which separates the conducting layers which means that the heat transferred from the inside to the outside (and visa-versa) doesn't have a large surface area to conduct through between layers and therefore is much more effective than \"normal\" insulation. Source: Masters degree in Space Systems.",
"There's a few wrong answers here. A lot of people seem to be making the assumption that because space is a vacuum, heating/cooling isn't that big of an issue. This isn't true. In earth orbit, if you're in direct sunlight you can expect temperatures of around 120 degrees C, dropping to -157 degrees C in the shade. that's roughly 250F to -250F. So here's what you need to understand: Heat can be transferred a number of different ways: Conduction, Convection or Radiation. Conduction is where heat is transferred through matter: Put a spoon into a hot cup of coffee and the spoon will get hot. The heat is conducted from the coffee through the spoon. Convection is the transfer of heat through fluids (both liquids and gasses). Hot fluids will flow from warm areas to cooler areas, taking their heat with them. Turn on a heater in your room, and the warm air will flow around the room warming it up. Radiation is what we're interested in here. Radiation is electromagnetic energy and doesn't require a medium to pass through. This is why we can feel the warmth of the sun on earth despite there being over 147 million kilometers of vacuum between us and it. So, heating and cooling is a huge problem is space. In direct sunlight you're getting blasted by thermal radiation without the benefit if an atmosphere to insulate you from it. When you're in shadow, and not getting hit by that radiation, you also don't have an atmosphere to retain heat and insulate you from the cold vacuum of space. So, how does a few millimeters of insulation protect astronauts from the extreme temperature differences of space? Simple answer is...it doesn't. Basically, don't think of a spacesuit as an item of clothing, it's more like a wearable spacecraft. It's a fully pressurised, climate-controlled environment in suit form. So, in space, we don't have to deal with conductive or convective heat. We only need to worry about radiated heat from the sun, and the heat generated by the astronaut's body. A modern spacesuit has 13 layers. The outer layer (the shell) is white, reflective mylar designed to to reflect sunlight to help prevent radiated heat from the sun from getting inside. This is further backed backed up by various insulating fabric on the inner layers. This is where things get fancy. On the astronaut's back is a big backpack called the PLSS (The Primary Life Support Subsystem). While this provides breathable air and scrubs carbon dioxide from the suit environment, it also takes care of heating and cooling. Basically, the PLSS has a sort-of portable air conditioner inside it, only instead of just cooling or heating the air inside the suit, the inner most layer of the suit is called the LCVG (Liquid Cooling and Ventilation Garment)..which is is basically a full body suit laced with thin plastic tubes. Water is cooled by a heat exchanger in the PLSS and is pumped through the LCVG carrying away the astronauts body heat. EDIT : Changed miles to kilometers for the distance from Earth to the Sun.",
"The reason they don't need much insulation is because space isn't actually very \"cold.\" Imagine if I asked you \"What's the sea level in this room?\" And you told me 0. I would say \"Wow so the tide must be extremely low right now!\" You would tell me \"No the tide isn't very low, the sea isn't very low in here, the sea just isn't in here.\" It's the same with temperature - you need stuff (matter) for there to be temperature. You don't need much insulation because there really isn't matter in space for you to measure the temperature of. You brought all of it with you in the same way that if you went swimming inside a building you would only need to be prepared for about as much water as you could bring with you.",
"There are three mechanisms for heat transfer: Conduction, Convection, and Radiation. In normal human experience, conduction dominates. We're used to touching the cold thing and immediately feeling that it's cold or the hot thing and feeling that it's hot. There's not enough matter outside the space suit to conduct heat in or out of the suit, so it essentially doesn't matter. Next, we have convection. When you turn on the HVAC, it's because the air in the room is one temperature and you want it to be another. The HVAC plant does this by heating or cooling a lot of air and then moving the conditioned air into your room and the objectionable air out. Again, we're not gonna be moving any air into or out of our space suit, so that doesn't matter. All that's left is radiation, and by that, we mean infrared light, not RF/radio radiation or ionizing radiation that causes radiation poisoning. All of the light poring onto the space suit from the sun would very handily heat that side of the suit up to hundreds of degrees, save for one crucial fact, the space suit's white. The reflected color white, as we all know, is a reflection of *all* colors, that includes IR light from the sun. This helps the suit control how hot it gets while in direct sunlight. On the other hand, an astronaut working in the space station's shadow, while not getting any excess light radiation from the sun, it is always emitting its own IR radiation, which is, in fact, cooling the suit down. However, radiation is the weakest of the three forms of heat transfer, so radiating its heat away into space happens very, very slowly. It's easily offset by heaters keeping the environment inside the space suit, and the astronaut herself, warm and comfortable.",
"In addition to the vacuum of space doing a poor job at conducting heat away from your body that others have mentioned, the “temperature” of space can be misleading. Space is very empty. Temperature needs lots of air or particles to mean anything, but you still can calculate it even with only a little bit of air/few particles. In space these few particles might have been drifting for years without much affecting them, making them slow (meaning cold). They could also have been thrown really hard from a supernova (space explosion) making them really fast (really hot). So sometimes places talk about the temperature of space, but it doesn’t mean the same thing that we understand temperature to mean here at home."
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kh8ihf | Why wind turbines always have 3 blades? | Engineering | explainlikeimfive | {
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"Any number of blades is possible, but they cost money. Adding more blades increases the blade cost more than the power output. One requires a counterweight that produces no power. Two blades have no moment in one direction, so that's not as stable. Three is the lowest number with good stability.",
"Cost is certainly a factor, but for a lot of wind stations 3 is fairly optimal. 4 can work, but you need a specific situation and some design cost. Three works best on most situations, so three is sort of \"standard\". If go into the blade element theory in windmill and propeller design, you'll find that too many blades interfere with each other and too few don't provide or generate enough power. This is definitely not a one size fits all answer, for example the a400m out of Airbus has crazy looking props because of how fast it flies at altitude."
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khdf6e | why does the engine of motor verhicles emit a buzzing sound instead of continuous small booms? | Engineering | explainlikeimfive | {
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"Well, it does. Sort of. At low RPM, you can hear individual pops. [Here]( URL_0 ) is a video I found from a quick YouTube search of a super low-RPM engine. However, especially in cars and other vehicles, you will likely also hear various other moving parts. Belts, transmissions, etc. At higher RPM, your explosions blend together into a buzz. The sound that we recognize as a buzz is really just a buh-buh-buh-buh sound but really fast.",
"Most passenger automobiles idle at between 600 and 1000 rpm. That is revolutions of the crank shaft so in a 4 cylinder engine each cylinder will have a detonation within it for every revolution. This means 2400 to 4000 explosions a minute, or 40-66 per second. That speed of little booms tends to blend together into a buzzing or hum.",
"It's because most car motors are so called 4 stroke motors. Only one of these strokes contain the explosion the ignites the fuel. The other three strikes just prepare the cylinder for this. As a result, what you really have is a rapid series small booms. HOWEVER, since most motors have 4 or more cylinders, in any given point in the cycle, you have a small explosion. And when you consider how fast a car motor spins, normally between 1000 and 5000 revolutions per minute, all those many small booms come together to form the buzzing sound. Think of a bee. You don't hear individual flaps of the wings, but the constant fast beating of the wings makes a buzzing sound. This is also how speakers and most sound works."
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khhudz | How do submarines surface and resubmerge? Does air pressure come into play? | So back when I was in primery school, a teacher showed us a cool trick with a pen cap, some weights and a sealed full bottle of water, where if the cap was floating inside the bottle, with a small bubble of air trapped inside it, pressing on the sides of the bottle would make the cap rise or fall inside the water. Is this how submarines work? Do they have air chambers that are compressed to submerge etc? What actually makes air bouyant? Is it the amount of gas molecules which are lighter than the water or their density? | Engineering | explainlikeimfive | {
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"Things sink or float in water based on whether they are, as a whole, more or less dense than water. Submarines have tanks inside them that can be filled with water, or pumped out and filled with air. Water is heavier than air, so they can control the density of the whole submarine to be slightly more or less dense than water. When they are underwater, they actually want it to be exactly the same density as water, so it doesn't sink or float on its own, and they steer up and down using fins, like an airplane.",
"Submarines have air chambers that are the inside rooms, occupied by gear and people, and the air that they need to breathe. They're designed to float (their size is big enough that when you combine the weight of the metal parts + the lightness of the air-filled parts, the average density is less than water, so basically they float). To sink, they pump some water into special pressure-resistant chambers inside the submarine, so basically the submarine \"fills up with water\" becoming heavier until it sinks. To resurface, they pump this water out (basically replace it with air, becoming light enough to float). Fish do it with air; they have a \"[swim bladder]( URL_0 )\" that they fill with air, to become lighter and rise up to the surface. EDIT: > What actually makes air bouyant? Is it the amount of gas molecules which are lighter than the water or their density? Gravity pulls everything down, rocks, water, submarines, boats, air. The heavier (more dense) things like rocks \"push\" the less dense stuff out of the way so they can sink down. The \"pushing\" is what buoyancy is. Rocks make the water \"float\" on them (if you want to think in terms of liquids, water floats on lava (molten rock)), and air floats on water. Boats also float on water, and helium or hot-air balloons float on air. Because their overall density is less than whatever they float on. All because of gravity.",
"Submarines have two systems. Firstly they have buoyancy tanks, filled with water and the submarine becomes heavier and sinks. Pump the water out into the sea and replace it with air and the boat becomes lighter than water on average so it rises. But in addition they have hydroplanes. Sort of horizontal rudders at the bow and stern. As the submarine moves through the water they adjust the tilt relative to the horizontal. Tilt up and the propeller drives the boat upwards, tilt down and she dives. Point both sets the same way and the boat will rise or sink while staying horizontal. Hydroplanes have a much faster effect for surfacing and diving while moving but obviously the buoyancy has to be adjusted to maintain the desired depth or the submarine will sink or rise as it slows. In WW2 U-boats the crew weight was also used to increase the tilt for crash dives. Watch the film \"Das Boot\" and they portray a mad dash of all the spare crew into the nose of the submarine to get it pointed downwards after being surprised on the surface."
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khsz2e | Why are washers and dryers separate and not one machine? | Engineering | explainlikeimfive | {
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"There are single unit washer-dryers, mostly popular in Europe, but I have one in Canada too. It takes longer to dry, and while it’s drying you can’t simultaneously wash another load for example, so that might be the convenience consumers are looking for.",
"They do have combo machines but it makes sense to keep them separate. Washing machines need to be water tight. Dryers need to be the opposite and have good airflow through them. It's possible to make a combo unit, but it's more prone to reliability problems and more expensive.",
"Where I’m from (Poland/Europe) combi-machines are very common. I put a load in and set it for wash, then it dries that load immediately after. Maybe in America where you have larger houses in general people just get two machines but I personally don’t see a need and haven’t found my washer/dryer lacking.",
"When I first moved to America, it was the first time I became aware that these two machines were available separately!",
"Washer drum needs to hold water, and might have small, valved (complex) openings for dryer air. A dedicated dryer will have large drum vents to dry faster, no need to contain water.",
"Company named splendide makes single unit washer/dryers. I work on a lot of them in RVs. Generally speaking, the product is crap, but the customer service is awesome. They have smaller washer load sizes, longer drying times, and in my experience using them they just don't clean as well as standard separate units.",
"There do exist all in one machines but they aren’t as efficient or as good as having two separate ones. The short answer to your question is that from a design perspective it isn’t worth combining. This means that the benefits of a combined machine are outweighed by the drawbacks. For example, most people that can purchase a washer have enough room in their house for separate machines so the space savings isn’t a huge deal. Second, it’s often cheaper to buy separate ones than a combined machine. And finally, it might be overly complicated to have a single machine that can safely take in water, drain water, and use natural gas to heat clothes. So the short answer is it’s not a good idea from a practical standpoint."
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khukz0 | How does a skyscraper get the proper support? | How does a skyscraper get the proper support? How does the bottom layer hold up all the other layers/floors? How come it doesn’t just collapse? Explain Like I’m Five please | Engineering | explainlikeimfive | {
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"Well, it doesn't. Imagine a shelving unit. The bottom shelf doesn't hold the shelves above it. The backbone of the shelving unit (likely in this case the wall) bears all of the weight. Skyscrapers have huge steel and concrete pillars which support the weight of the building above. The walls themselves don't bear the weight, but these huge beams do. As for how they do this, steel and concrete are incredibly resistant to being crushed. Honestly, most materials are, but concrete and steel are especially good. Imagine trying to crush a tooth pick - I bet you'd have difficulty doing so. On top of that (heh, puns) skyscrapers are mostly hollow. There is actually relatively little weight. Sure, tons of weight, but it is still mostly just air."
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ki3prh | Why do car batteries discharge in cold weather? | Just why it happens in winter and not in summer? | Engineering | explainlikeimfive | {
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"As far as I know they don't actually discharge, it's just that they don't produce the same power as in the warm. It feels the same, but isn't lol. The reason is that the power is produced by chemical reaction, and reactions happen more slowly when it's cold. Slower reaction means slower release of energy. The result when you turn the key feels the same as if the battery has discharged.",
"It doesn't discharge. The internal chemical reactions are slower in cold weather and the battery produces less energy"
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ki6qra | Why do turn signals flicker quicker when they are broken? | Engineering | explainlikeimfive | {
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"They're designed to do that to warn you (and maybe others on the road?) that there's something wrong with your turn signals and you should get it checked. Usually it's a busted/burned out bulb. Park your car, turn on the signal on the side that's flickering quickly, and check the bulbs to find out which one is out.",
"Just like on your old thermostat at home there is a bimetal strip. When the electricity flows through the power relay it heats up and changes the shape of the metal. The same happens when it cools. That action opens and closes the circuit causing the light to blink. When there's a change in current, such as when a bulb is burnt out, the time it takes to heat the bimetal strip changes, in turn changing the speed at which the circuit is closed and opened. There could be any number of problems with the wiring of the lights causing it to blink faster, but it's usually just a burnt out light.",
"There are two components of electronics worth understanding slightly. Resistors drain energy. Capacitors store energy like a spring. When you have them connected together and let the energy of the capacitor drain through the resistor, you find that the time it takes is related to the multiplied quantities of the capacitor and resistor (C * R). So if you doubled the resistor (or capacitor) value, it would take twice as long for that energy to drain. So the circuit that controls your blinker has one circuit for the left side, and one for the right side. Each blinker has one resistor in it (the light itself). When one burns out, now your resistor value is half of what it was, and therefore it takes half the time for the circuit to do its thing. Given that the circuit causes the blinker to blink, that half-resistor value equates to double blinking speed.",
"Back in the day it was because of the old mechanical flasher cans. They used to flash on and off using a bimetallic strip. Strips of two different metals that expand at different rates as they heat are glued together. Pass an electric current through them, and they flex. This strip was used as a switch. When the lights are turned on, current would pass through the strip, it would heat up in a set period of time, and flex. This flex would break the circuit, and the light would turn off until the strip cools and flexes back to its original position, turning the light on again. When old incandescent bulbs burned out, often they failed by shorting the live to earth. The filament would burn at one end and internally short the bulb. This creates a low resistance, and a very high current to be drawn when the light should be on. The higher current causes the bimetallic strip to heat up much faster than it usually would, and so the light is on for a much shorter mount of time than usual, and resulting in a faster flash. I have no idea what clarketech magic works the new led versions though, or if or why they would flash faster other than to indicate a fault with the same symptoms as the old tech. People are used to certain symptoms and certain solutions. Your flashers flash faster when broken because thats what they have always done. How many of you remember floppy disks? So why is it the universal save symbol? God i feel old.",
"Thank goodness most of you don't work in electronics. 1) bimetal strips worked because heat from a heater would bend them making them contact. This would bypass the heater letting them cool and disconnect. With all bulbs working in parallel the lights drew more current so they would heat up the strip more causing a longer cool-down time causing it to blink slower. When you lost a bulb the heater wouldn't get as hot so the cool-down time was shorter causing a fast blink indicating you lost a lamp. 2) todays automobiles are all computer controlled. Lighting is usually controlled by the BCM. They monitor the current draw on the bulb circuits. This determines the blink rate in software. If your current draw drops, the computer makes the light blink faster just like the old bimetal strips indicating there is some kind of fault with your signal lamps. Nowadays its just a digital signal line turned on and off driving a transistor, or mosfet, or other higher current device. Not even relays any more."
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kit17y | Why does it take time for the sink faucet to get hot, but gets cold right away even when it’s already hot? | Engineering | explainlikeimfive | {
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"Faucets don't magically produce water of different temperatures on their own. They are valves that open and close pipes, the cold directly from the main source of water and the hot from a device that heats water. The device that heats water (a \"water heater\") has hot water within it that is maintained at increased temperature waiting on use. But the pipe leading from it to the faucet is full of unheated water which needs to be pushed out ahead of the hot water. This is why it takes time for the water from the faucet to get hot. The cold water source is always unheated. Opening it always gives cool water instantly."
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kj1zho | What is hydraulic head? | I'm adding mechanical pumps to a large stormwater treatment system. I'm a scientist but I'm completely new to engineering, and I cannot seem to get my mind around the concept of "hydraulic head." This means that I am utterly incapable of understanding pump curves. Can someone please explain what hydraulic head is, and why it falls as flow from a pump increases? | Engineering | explainlikeimfive | {
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"Hydraulic head is kind of like the potential energy of a fluid. This is usually measured in vertical feet/other height unit, but could also be measured with pressure. But it’s basically, if you had water somewhere high, like a pond, and then in flows 10 feet down a hill into a second pond, it’s lost 10 feet of hydraulic head, or potential energy. This is important in things like water towers that feed towns, because it is the hydraulic head of all the water stored way up on the air, basically the pressure of that water so high up, that pushed the water through the water system pipes and to your house. A pump typically adds head, because it is putting energy into the system. A turbine typically loses head, because it is taking energy out of the system (like in hydroelectric power, turning the head into electrical energy) So, if a pump is saying it can add 10 feet of hydraulic head, that means it can (ideally) pump water 10 feet up. This is obviously in an ideal system, the friction of the pipes on the water, along with bends and turns in the pipe will slow the water down and pull energy out of it, I can’t tell you exactly how much you’ll lose with each turn, though I’m sure there’s tables for it somewhere, but typically the harsher the angle, The more head you’ll lose."
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kj5o9p | Pinking shears for fabric edges | People use pinking shears on the edges of raw fabric as a way to finish the seam and prevent fraying like a straight cut would get. But I can’t get my head around how/why exactly the zig zag edge makes it less likely to fray. If anything I’d think the little triangle points would be easier to fray. | Engineering | explainlikeimfive | {
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"> If anything I’d think the little triangle points would be easier to fray. Sort of. It's slightly easier for micro-frays to start, but they can't spread. The edge of a piece of fabric looks sort of like ±±±±±±±±±±±±±±±. If something snags that upper ––––––––––––––––––– thread, there's hardly any weaving to hold it in place, so it can pull *all* the way out; then the _ _ _ _ _ _ _ _ _ _ _ thread shown is exposed, and something can snag *it* in turn, and pull it out. (ELI5's rule about explanations having to be text in the comment is dumb.) When the edge is pinked, only the very tips of the zig-zag edge are vulnerable: the threads exposed along the edge of the cuts are still woven in over-under-over-under at least a few turns; there's enough friction to hold them in place.",
"Do you know about how cutting on the bias virtually eliminates fraying? It’s cutting on the bias in opposite directions one after another so there are never straight cuts!"
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kjam6l | What is the brushing/scrubbing sound made by a lot of boom lifts etc. | I hear this quite a bit and drive them myself so I understand it is normal but I don't understand exactly what or why the noise is made. I've noticed a lot of boom lifts, scissor lifts, cherry pickers etc. tend to all make a similar noise particularly when reversing that isn't the usual beeping or warning they have but a consistant scrub scrub scrub sound. It seems consistent no matter the speed you are travelling but just curious as to what the heck it is. Thanks!! | Engineering | explainlikeimfive | {
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"It's white noise, researchers found that it stood out more to people in busy or loud environments as opposed to the beeping noise that is used on reversing lorries and buses. So ultimately it's a safety feature to alert people to the presence of the vehicle."
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kjj8yj | Why does asphalt look a bit reflective when viewed at a distance and with a certain angle? | Engineering | explainlikeimfive | {
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"This is usually due to a mirage effect, where the hot asphalt heats the air above it. Light bends slightly when passing through the hot air compared to the surrounding cool air and creates a mirror kind of effect."
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kjkbd0 | Why can a house’s frame be rained on no problem? | Houses get rained on all the time while being built but why is there no continuing mold problem after this? | Engineering | explainlikeimfive | {
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"Lumber used in home construction is almost always sealed and treated with biocidal compounds like copper that not only naturally repel/kill pests such as termites but also inhibit the growth of mold or mildew as well. Additionally, mold requires a favorable environment to grow- dark, warm and damp. This is why showers or bathrooms are often where you find it. That environment doesn't persist for a home frame under normal circumstances, even after being rained on. So mold is unlikely to thrive there."
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kjodjr | What are the mechanical differences between regular sneakers and basketball sneakers for? | How are they any different? I know they are built differently, but does it really make any difference performance wise? And what is the reasoning behind the differences? Asking because in today’s world, basketball sneakers look more like “fancy” running shoes to me then before when they were high topped and beefier. Is it all just a gimmick? | Engineering | explainlikeimfive | {
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"I can’t speak to the more specific differences but for the most part basketball shoes go up higher on your ankle so that you don’t roll your ankle, as it’s a relatively easy thing to do in basketball."
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kkgvjo | How are railways built in desert? | I wonder how they protect the rails from the sand. | Engineering | explainlikeimfive | {
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"From what I know, they lay down a heavy layer of rock and gravel to support the weight of the train and ensure the track has a good foundation.",
"With difficulty, but by raising the rails you can have the sand blow past the rails and not block them.",
"The question of how to lay a railway across an area of unstable and unfirm ground has been a problem for railway engineers since the very early days. In fact, [the very first commercial passenger railway in the world]( URL_0 ), which went from Manchester to Liverpool in England in 1830, was considered unbuildable by many engineers as it needed to cross several miles of swampy, boggy ground, known as Chat Moss, on the outskirts of Manchester. The lead engineer for the project, George Stephenson, eventually solved the problem by sinking a \"floating foundation\" of heather and tightly bound branches, and topping it with rubble and tar. Although it sounds tremendously low-tech, similar solutions are still used by railway engineers today. The technique is essentially one of building a substrate which is loosely bound at its lower reaches, allowing it to intermingle naturally with the underlying groiund material. Once that's been achieved then a hard upper surface can be added, upon which rails can be secured. TLDR: 200 years ago they worked out how to \"float\" a railway across a swamp, the same techniques (although with modern materials) are still in use today."
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kkhzx7 | In automotives, what are drivetrains, powertrains and transmissions and what do they do? | I don't know too much about automotives, so please explain as simply as possible, thank you. | Engineering | explainlikeimfive | {
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"Power train: everything that makes the car move. this includes; Engine, Transmission, Driveline, Differential, Axles, Hubs, Bearings, etc. Drivetrain: same as above minus Engine. Transmission: takes the engine speed, Generally measured in RPM(revolutions per minute) and then multiplies those revolutions through different gear ratios, I.E. a 1:2 gear ratio would mean if the engine turns 1 time, the output of the transmission is turning 2 times. ratios can be less than less than, greater than, or equal to 1:1.",
"Making an analogy with the bicycle... The powertrain is the person, the one who generates the energy. The drivetrain is all the components that transmit the power (pedal, chain, etc.) and the transmission is one of those components. The car transmission is the clutch, gearbox and differential set.",
"Drive trains turn wheels, so axels. Powertrains provide the power from the engine to drivetrains. Transmissions modify that power in different ways to provide different levels of torque. Not a mechanic just my understanding of it."
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kki383 | - How resistors used in electrical circuits? | I understand that resistors are meant to oppose the flow of current. I can't fathom how a certain value of resistance is placed at a certain position and what it achieves. Why does the current flowing through a circuit need to be opposed? What can opposing said current be used to achieve? Are there rules or laws that are applied in the arrangement? | Engineering | explainlikeimfive | {
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"The main law we use is called Ohms Law. It states V=IR, or, Voltage = Current * Resistance. Opposing the current is one way of thinking about it. The common analogy is that adding a resistor is like narrowing a water pipe to restrict flow. But the way I like to think about it is that we can place resistors to control what voltages we get in the circuit. A very common circuit is something called a [resistor divider]( URL_1 ). This is a small circuit which takes an input voltage (Vin) and reduces it to a smaller voltage (Vout). If we apply Ohm's law to this circuit we get Vin=(Z1+Z2)*I , so the current flowing through the circuit depends on the resistances. We can do some analysis (it isn't too complicated, but is beyond the scope of ELI5) and find out that Vout = VinZ2/(Z1+Z2). So you can see here that we are controlling a voltage with the resistances. Another place we need a resistor is when we're powering an LED. LEDs are interesting in that they will always cause the voltage to drop by about 1.7 volts. This means that if we plug an LED straight into a 9V battery, it will cause the wires to get very hot (and probably also damage the battery), as we need to dump the rest of the voltage somewhere (the low resistance of the wires causes a large current to flow, meaning that they will get hot). In this situation we will [put a resistor]( URL_0 ) inline with the LED. This means that the LED can drop the 1.7 volts, the resistor can drop the remaining 6.3 volts, and we don't damage the battery. This is pretty complicated stuff to start learning, so I'm happy to clarify/explain anything that isn't clear.",
"Thank you to everyone that responded. My understanding of resistors is a lot better now.",
"Resistors in DC circuits somewhat limit the amount of current that can flow. This is important for components that are sensitive to current. A very small wire can only carry a certain amount of current before it heats up too much, melts and gets destroyed because of that. Imagine a light bulb. The more current you put trough it, the brigther it shines and the hotter it gets. Until the melting point of the wire material is reached and the light bulb burns out. Resistors can therefore be used to divide a current into smaller portions of the current so one can build circuits that use components which only can handle a portion of the starting current. The most basic law involved here would be Ohm's Law: I = V / R where I is the current, V is voltage and R is Resistance. Here we can again see that with increasing resistance and constant voltage we get a decreasing current. If you want to go a bit further, have a look at Kirchhoff's circuit laws which set the rules for resistor circuits on how current and voltage split depending on the circuit's structure."
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kko7nv | Why can phones run games without active cooling or a real heatsink but leaving your desktop CPU uncooled is a terrible idea even when idling? | Engineering | explainlikeimfive | {
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"Your computer is hilariously more powerful than your phone. Your desktop might as well be considered a rocket ship compared to your mobile phone being a race car. Rocket ships can do amazing things and go incredibly fast, but they need a lot of support to turn on those huge engines. Racecars can go pretty fast and get you around things you need to do day to day and do it well, but it's never going to the moon, but it just keeps chugging on without a lot of maintenance or extra work to keep it going.",
"Your phone is never running an equivalent game, it has a few orders of magnitude less processing power A midrange desktop CPU could use around 60W when loaded up, a high end laptop might use 40W, but a phone will be around 5W. Everything for the phone is scaled down, the physics is simplified, the graphics are simplified, everything is made simpler because you don't have the power available(electrically or computationally) and the smaller screen makes it easier to hide poor graphics. For a sense of scale here, a Qualcomm Snapdragon 865+ has an Adreno 650 GPU in it which puts out around 1400 GFLOPs and this is a recent flagship phone level chip which is pretty much the best you can get in a phone right now. 1400 GFLOPs puts it neatly between an nVidia GT 1030 and a GTX 1050 at 1100 and 1700 GFLOPs, these were never flagship cards they were the two weakest cards that nVidia released around 4 years ago at this point. A top of the line phone GPU is roughly equivalent to a bottom of the line desktop GPU from 4 years before because they needed the better processes to take the power consumption down from 30-50W to 2-5W.",
"Because your phone generally isn't doing anything like the same amount of work as your computer. Take a game that you can get on phone and PC, maybe something like PUBG. Compare the graphics on the two devices, and you'll see that the PC is rendering much more detailed images, or you can see further (so is rendering a much bigger environment)."
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kkw08i | How does the stylus and vynl records work? | Engineering | explainlikeimfive | {
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"The simplest I can put it goes like this. The groove in a record is full of bumps. As the stylus (needle) passes over the bumps, it wiggles a lot. That motion is applied to a diaphragm in a manner very similar to a microphone. The assembly then converts the diaphragm’s motion to electrical impulses which is sent to the speakers to convert back into motion and sound."
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kkwg3h | Why do LED light bulbs use less energy than regular light bulbs? | Engineering | explainlikeimfive | {
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"Because they’re extremely efficient. The diode fluoresces as electricity is applied, with minimal energy being dissipated as heat. Traditional bulbs with a tungsten wire in a vacuum or gas give off heat as their primary byproduct with light being secondary. Fluorescent bulbs fall somewhere in between, generating more light than heat in the bulb itself, but then generating a bunch of heat in the ballast. Because the anode and cathode are in close proximity in a diode and are part of the actual substance used for conductance and luminescence, LEDs don’t need the ballast that the larger fluorescent tubes do, with their anode and cathode at opposite ends of the tube and an alternating current being driven to cause the fluorescence.",
"Incandescent (regular) bulbs push a lot of electricity through a wire that isn’t good at passing electricity. This causes the wire to heat up so much it glows. The light is only part of the electricity used, the heat is another big part. In LED lights, there are two types of tips inside each diode. The electricity is sent from one to the other, but the second one has fewer spots for electrons so they shoot off as light. This means that in LEDs almost all the electricity used goes to making light and is not wasted making heat. This means that for the same 8watts, you get more light from an LED than an incandescent. This also means that if you want a certain amount of light in your room, an LED will be able to do it for less electricity."
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kl1m1e | how are we able to contain something that burns at 100 million degrees C and make it not burn everything around it? | Engineering | explainlikeimfive | {
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"They hold the plasma that's at that temperature suspended away from the walls of the chamber using magnets, so nothing is really touching it. Plasma is material that's heated so high more than half the electrons separate from the atoms in it. Someone will probably have a more detailed explanation, but that the basics."
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kld3xn | How do ski lifts work? On the middle parts cars are far apart but they bunch up on the ends. How does this happen? | Engineering | explainlikeimfive | {
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"They are taken off the main cable, if not you would have to hop out at the speed you traveled wich would be a pretty wild ride.",
"Those type of ski lifts typically have a piece sticking out of the chair at the top near where it clamps to the cable with a big spring on it. When the chain gets near the top or bottom of the lift, a metal track by the cable pushes on that piece, compressing the spring and releasing the clamp. You can think of it like something compressing a binder clip to release the paper. Another mechanism then moves the chair at a slower pace while the cable continues to move quickly. As the chair exits the top or bottom lift station, the metal track ends and the spring decompresses, forcing the chair to clamp back on to the cable. Note that not all ski lifts work this way. Older or shorter ski lifts have chairs that are clamped to the cable all the time and move at the speed of the cable even when loading or unloading. These typically can't go as fast and are harder to get on and off, but back in the day that's how all ski lifts worked and it's simpler to maintain since there are fewer moving parts (and replacing working lifts is expensive)."
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klei03 | How does a geared bicycle move forward while the pedals and chain are motionless? | As in, when you stop pedaling the chain and pedals just stop while the bike is moving forward. | Engineering | explainlikeimfive | {
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"They have a [sprag clutch]( URL_0 ) or something similar which catches one way and runs smooth the other. When you stop pedaling it allows the wheels to keep spinning.",
"There is a device attached between the rear cogs and the rear axle called a freewheel. This is a circle containing mostly ball bearings. However, around the outside edge are teeth that have a 90 degree angle on one side, and a gentle slope on the other. On the inside edge are (usually three) pawls - \"paddles\" which are pressed against the teeth. When the cyclist is pedalling, the pawls lock into the 90 degree side of the teeth, meaning the inside edge of the freewheel moves along with the outside edge, transferring the movement from the chain/cogs to the wheel. If the wheel continues moving but the cogs stop, the pawls come out of their teeth and start running along the teeth, unable to lock. This causes the \"clicking\" noise when freewheeling. One of the clever parts of this design is that the freewheel usually fails by seizing up due to dirt and wateer ingress, lack of lubrication etc. When this happens, it fails in the \"drive\" position, e.g. you can pedal, but you have to continue pedalling when slowing, otherwise your chain will be thrown off. This allows you to cycle home with slightly modified behaviour, rather than being stranded with freely spinning wheels."
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klmept | Why coat steel in paint but not non corrosive metals? | We always paint steel to stop rust from forming. But it decays and has to be repainted every few years. Why not just coat the steel in brass, copper, or aluminium to stop rust? It's seems like it would last much longer than paint. They wouldnt have to reapply it like they do paint every few years. They could also coat rebar. Stopping it from rusting and cracking concrete. | Engineering | explainlikeimfive | {
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"The short answer is [we do]( URL_1 .). For example, if you've ever heard of \"galvanized steel,\" that is steel with a protective layer of zinc, which does corrode over time. You couldn't use brass or copper to coat steel because of [galvanic corrosion]( URL_0 ).",
"The question is, whether other metals would stick to steel close enough as to not letting any gaps. Sometimes this method is actually used. E.g. Audi and your wheel barrow will have zinc on top of the steel... URL_0 Rebar is generally “coated” with concrete...and you want a good contact with the concrete. The cracks are causing the rust and not the other way round ;)",
"Plenty of good stuff about galvanizing, but here's an explanation on why paint instead. Galvanizing or plating need to be done in an industrial environment since we're using either molten metals or huge amounts of electricity to cover the steel. These coatings won't last forever though--especially zinc which only protects the metal by corroding instead. After 10-15 years that metal coating needs to be replaced which means you'd have to take apart your radio tower or bridge or oil rig, send the parts back to the factory for recoating, and then effectively build the thing all over again. It ends up being cheaper in material and labor costs to just paint it at the beginning and then just repaint it every other year or so than to use other metals to protect the steel"
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klo4ju | Why do electric cars almost never have more than a single speed gearbox? | I know the commonly given explanation is that electric motors generate maximum torque from zero RPM, which eliminates the need for more than one gear. But wouldn't an electric motor mated to a CVT mean better range from smaller batteries because of less energy draw from lower motor RPM? I feel like I'm missing something here. | Engineering | explainlikeimfive | {
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"It has to do with how electric motors develop power and their efficiency map. Internal combustion engines have a relatively small operating window where they're most efficient. About 75% throttle at medium revs. They need gears to stay close to that range regardless of the vehicle speed. Likewise, they don't make much power at low revs. An engine that develops 200 horsepower at 6000 rpm would normally make something like 75 horsepower at 2000 rpm. So if you need a lot of power, you have to use different gears to keep the revs high. Electric motors aren't like that. An electric motor that makes 200 horsepower at 6,000 rpm would also make close to 200 hp at 2,000 rpm, so a lower gear wouldn't give you much of an advantage. They also have a much wider window of maximum efficiency. An electric motor doesn't really care whether you use high revs, low revs, high load or low load...it'll always be 90+% efficient.",
"> less energy draw from lower motor RPM? You have a bit of a misunderstanding there. A gearbox ruins the efficiency of electric motors. What causes an uptick in current draw through the coils (which increases resistance losses) is higher *torque* not higher *RPM*. And if you want to use a gearbox to speed rotation up from a lower RPM, you'll need to put in more... torque. To get the best efficiency out of an electric motor you simply want to remove every bit of friction loss between it and the wheel. A gearbox is a massive friction loss for no benefit.",
"Electric motors can go up to like 20,000 RPM, and it can stay at very high RPMs without getting damaged from it. This means they have a huge operating speed range. Imagine a regular car in 2nd gear (I say 2nd not 1st only because 1st is a really low gearing), but instead of being limited to 6 or 7 thousand RPM, it can easily go to 20,000. You can then go fast enough in second gear that you just wouldn’t need any more than that. Some electric cars like the Porsche Tycan and formula E racing cars have 2 gears so they don’t lose torque at higher speeds, but for most electric cars you don’t care about acceleration at 100+ mph."
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klrg8c | Why is reaming so much more accurate than drilling? Isn't it still just a different kind of drill bit? | Engineering | explainlikeimfive | {
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"Reamers cut a very small amount along the length of their flutes, generally no more than a couple thousands of an inch. Drills cut with their cutting lips and can wander quite a bit and tend to cut a hole slightly bigger than their actual diameter. I'm sure an engineer will come along and explain this more completely than me.",
"Dill bits cut at their end, they are the initial step for creating a hole or bore. They can wander because the only thing acting as a \"pilot\" (something to maintain concentricity with the hole) is their outer diameter which isn't a perfect fit. Reamers cut with their flutes at their radius so they act as a form tool cutting in their own precise shape and size. They can't really wander either because they create their own cutting pressure simply by being too big for the hole until the reaming is finished.",
"We want to do two things when making a hole: we want to remove a lot of material very quickly, and we want to make a hole with the appropriate accuracy. A \"drill bit\" does the first thing. A \"reamer\" does the second. Because the distinction is important, they get different names."
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klupbw | How long would it take for electricity and water (or general utilities) to stop being functional in an apocalyptic setting? | I have this idea for a story were the surrounding infrastructure is intact. Now barring regular maintenance, how long would it take for existing infrastructure to not function? How long could a house run on existing utilities? Thanks for the help! | Engineering | explainlikeimfive | {
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"There was a whole documentary series on the History Channel that went into detail about the idea of \"what if all of humanity suddenly disappeared?\" It's called [Life After People]( URL_0 ). The gist of it is that most stuff fails within hours or days without human supervision, such as coal power plants running out of fuel, but other places (like hydroelectric dams) can keep operating for months on end, or even longer, completely unsupervised. Almost everything fails entirely within a year however. The structures themselves, however, can last for decades, possibly even centuries, before they collapse.",
"Minutes to hours, even if the apocalypse suddenly killed all humans without breaking everything. To start with water. The water treatment plant could run for a few days on its own likely. Depends if the control system has things like backwash cycles fully automated. Either way, it's eventually going to fail. Things are going to go into alarm that need operator input, chemicals are going to run out, reservoirs are going to overfill or empty. Potable water production is going to stop within a couple days at best. The water distribution system again is somewhat automated. Depending on how well automated it is, it could run for a few days before things start to go sideways. But this is all rather irrelevant, as it hinges on electricity. Some parts of the water system might have back-up diesel generators to keep it going for a few hours, but that's not going to last long. Now onto power. The power system will probably crash and burn within hours. It's a delicate balance of matching power produced to power consumed. Generators need to change inputs to maintain speed, generators need to come online and offline, power billing rates are adjusted on the fly, power is sold to other regions over lines. This need to happen every second, 24/7. A lot of this is automated, especially on the fast and small swing end. That's why turning on your light switch doesn't crash the grid to a hault. However, the larger scale fluctuations need human input. The issues and alarms of the plant and grid need human input. Everyone dying is definitely going to cause an unexpected shift in demand. And all it takes is one error not being addressed to crash a large part of the whole thing. In 2003 50 million people in North America lost power because of one hiccup at one plant. One plant took down about 250 of them. Things are going to get pretty out of control fast with cascading issues without anyone directing the system, without anyone responding to issues, and without the demanding being predictable. Now, something immediately killing all humans but not damaging any of this semes unlikely. You more than likely are going to have downed power lines, broken transformers, ruptured water lines, out of control fires. Even if the apocalypse just kills humans, that's a lot of car crashes. That's a lot of planes falling from the sky. That's a lot of stove tops setting buildings on fire. That's a lot of factories and plants exploding. I'm leaning on the answer is within an hour most shit is well beyond repair.",
"The water needs electricity to pump it and to power the processing so as soon as the water plants lose electricity there will be no mains water. Most electricity plants are automated so will continue to function for days after, however there may be issues with shorting happening in the distribution and some plants having automated shutdowns to avoid problems, coal fired power stations will rapidly run out of fuel so will likely be the first ones to stop."
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klwnar | How does percussive maintenance actually fix anything? | Engineering | explainlikeimfive | {
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"Some of the time a problem might be a broken connection due to something breaking or coming loose. Percussive maintenance can knock the connection back together for a time.",
"I can give you a specific example. Steve Jobs didn't want any fans in one model of early Apple computer, but it put off enough heat to really justify a fan. Because of this heat, things could warp and unseat chips on the board (this was back when most chips were plugged in, not soldered). The simple solution was to pick up the computer and drop it from an inch or two height. This would reseat the chips.",
"So, I work on very expensive and sensitive pneumatic laboratory equipment. There are screw style linear stepper motors for driving out a pump, and they have little sensors on the end of the travel to detect when the motor has hit it's 'limit'. The issue is, if this sensor somehow missed the little tab that is supposed to \"see\" it, the motor seizes -- the screw gets too tight on the \"knut\" of the housing that guides it. The reason percussive maintenance works to fix it is because there are two principles on which friction works. When things aren't moving (when they are bound), the surfaces have imperfections that will nest in each other and get stuck. When things ARE moving, those imperfections kind of bump over one another and momentum keeps everything going. Hitting it is just the force needed to jostle the imperfections apart and get moving."
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klx09f | What happens if someone dies on a submarine while underway for weeks, months at a time? | Engineering | explainlikeimfive | {
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"Submarines have large freezers where they keep all the food that's necessary for their extended missions. Let's just say that if someone dies on board, there's going to be a *lot* of ice cream at the wake.",
"I witnessed a burial at sea while in the coast guard. Crew members got ash scattered on them. Funny now but not then.",
"I work on a submarine base. I can confirm, unfortunately, that when a sailor dies while underway (at sea) they bag the body, stash it in the freezer, and then get to port ASAP where they might not even stay any longer than it takes to offload the remains. Thankfully I've only ever had to be part of that once, but even that was more than enough."
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klyw6d | Square bottle vs round bottle | Looked at the label on one of those 32oz square brown hydrogen peroxide bottles and notice it says "Square bottle uses less plastic than a similarly sized round bottle". I'm assuming both bottles would hold the same volume of liquid. How would a square bottle use less material than a round bottle of the same internal volume? | Engineering | explainlikeimfive | {
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"Perhaps they are referring to packaging? You can fit more square bottles in a given size box, or use less shrink wrap if that is how they are packaged.",
"A sphere has the minimal surface area (packaging) for a volume. Next up is cylinder, then cuboid (square) having the most of the three. So the bottles use more packaging. But I guess the cartons they ship in can be smaller due to very little wasted space between bottles compared to cylinders.",
"My guess, and this is just a guess, is that a square bottle may not in fact be made out of less plastic, but uses less in terms of production, storage And shipping. Round bottles need more space in packaging and take up more room where square ones would stack and fit together easily.",
"I don't think that statement is generally true. For that particular product it might be accurate due to the construction of the bottle. Flat walls can be made thinner when the edges can hold the shape of the bottle for example, or the production process might have less waste. It is hard to answer this question with certainty without knowing what the company is referring to exactly. Purely mathematically a cylinder has less surface area then a cuboid of the same volume, though.",
"The thickness and strength of a round or cylindrical bottle needs to be consistent across the entire surface area. A square or cube / cuboid bottle will have strong edges and thinner walls since the stress points are on the edges. The difference is enough to use 'less plastic' overall."
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kmda5z | how does the sensor which measures the level of fuel of a car know pretty precisely how much fuel there is in the tank? | Engineering | explainlikeimfive | {
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"The sending unit usually uses a float connected to a potentiometer, typically printed ink design in a modern automobile. As the tank empties, the float drops and slides a moving contact along the resistor, increasing its resistance.[2] In addition, when the resistance is at a certain point, it will also turn on a \"low fuel\" light on some vehicles.[3] A thing floats in the fuel and as it lowers it slides along the electrical sensors indicating the amount of fuel.",
"If you know the volume, shape and orientation of a container then you can determine the exact amount of liquid inside of it by only having the *height* of the liquid column as information.",
"It does not it's is a rough estimate based on a single measuring point that uses a float on an arm, this arm rises and lowers with the fuel level giving you a reading on your gauge. They are not accurate."
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kmdahy | How does the start/stop feature in newer cars save fuel and not just wear out the starter? | Engineering | explainlikeimfive | {
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"They just design the starter motor to be used constantly. There are tonnes of electric motors out there that spend all day stopping and starting.",
"An average car burns about 1/200th of a gallon each minute the car idles. Restarting the engine takes 1/2000th of a gallon. So if the car engine is off for more than about 6 seconds it saves fuel. Starters are much higher quality today and last a very long time today (when was the last time you had to change a starter on one of your cars).",
"It doesn't save very much fuel because the fuel burned during idle is very small compared to the fuel burned during driving. It does have a somewhat larger impact on emissions because it is very hard to get complete combustion in the engine cylinders when there are only small amounts of fuel. This results in more leftovers like soot and unburned hydrocarbons. Emissions equipment such as filters and catalytic converters will also work less well because they will fall below optimum temperature. Manufacturers are legally obliged to meet the national emissions standards, and they need to make compromises on price, performance, etc to achieve the standards. The authorities check compliance by making the manufacturers run standard 'drive-cycles' using test engines in laboratories. If the manufacturer can achieve a small easy win like allowing the engine to be stopped during the 'idle' part of the test, then they can use this advantage to maybe add a bit of performance in another part of the drive cycle, or reduce the cost of the catalytic converter slightly. They do some tricks to save the starter from wear such as by very precisely controlling the engine to stop at the point in its rotation where it is easiest to re-start, and by giving the starter a gentle ramp-up of current, rather than simply throwing a switch and giving it full current straight away. These were just the tricks I could think of, but there's no doubt more. The result is that starters are much less likely to wear out than they used to, so they can use and abuse them that much more without troubling owners. (I don't have any data, but in my personal experience I've needed to replace 2 starters in the past, but none on more modern cars).",
"Mild hybrids like the new BMW 5 also switch off at cruising speed, and the \"starter motor\" pushes the car."
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kmjp9i | With drone technology and automation available, why are commercial planes still flown by pilots? | Not to say that we don't need pilots anymore, but that pretty much all the mechanics to fly a plane can be automated now, no? Also, with drone technology you can technically fly a plane remotely and it's two lives saved in the event of a rare disaster and it would enable the FAA to better investigate if it was caused by human error vs. technical difficulties. | Engineering | explainlikeimfive | {
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"In case of problems, having someone inside the plane able to look around in all directions quickly, not rely on a network connection that might drop, and being able to move physical switches/levers is absolutely vital. Computers are good, but they're not very good when getting inconsistent reading if a sensor breaks. Even if an airplane is fly-by-wire (the \"steering wheel\" doesn't directly move anything, it's just input to the computer) there are some physical overrides. Usually making the landing gear (wheels) drop in case they won't come down on their own involves operating some crank. So you want someone to do that. As for investigations, modern airplanes are already streaming information in realtime about their operation. With trained humans on board we also have recordings of what they say in the event of an... incident... which can help immensely, and we can feel a bit better that they're watching over things when that signal goes down because they plane is half way across the Atlantic ocean.",
"Autopilots are very good, but only at predictable things. In certain bad weather situations, with unexpected failures, in quite a few airports... the pilots have to be at the controls because the autopilot can’t handle the situation. If an airport is fogged up to the point where planes need to make fully automatic landings they also need to keep more distance, with lower airport capacity and delays as a consequence. The reason why they’re not flown remotely is because fitting it with 2 extra seats is probably a lot easier than relaying the instrument information and pilot inputs continuously. Also there can be no communication between ground and airplane over oceans."
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kmkp46 | How do ocean (or underwater) support beams for a bridge resist corrosion/erosion/rust from water? | I never understood how underwater bridges never collapse. Like they are constantly submerged under water, how do they resist rust? Like ships and other man made objects in the water always het destroyed so how do they do it with bridges? | Engineering | explainlikeimfive | {
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"With some clever science tricks a) corrosion can be directed to a sacrificial anode (basically a piece of more reactive metal that would rather corrode than the bridge metal) (Note: corrosion is still technically happening but to a different piece of metal. b) paints and cement can act as a barrier to inhibit corrosion too."
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kmsuhu | why do space rockets take off from a upright position instead of taking off of a runway like a plane, reach 40,000 ft and entering space from there. | Engineering | explainlikeimfive | {
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"A rocket has to go really fast to reach speeds fast enough to orbit, and the atmosphere is thickest close to the ground. So a rocket tries to get out of the thickest part as fast as it can to save fuel, then it turns sideways to get to orbital speeds. Basically it would waste too much fuel going through the atmosphere like a plane.",
"There are some concepts for high-altitude launches from a plane (Virgin), but the reason that most space programs don't pursue this is that it adds an extra layer of complexity on top of getting your already-complex engines to fire. With the efficient engines that have been designed recently, it's really not too wasteful to just keep the traditional vertical launch profile, especially for large rockets that any aircraft just can't lift.",
"It takes less fuel, which is the most restrictive part of rocket design. By going straight up the ticket gets above most of the atmosphere, eliminating must of the drag on the rocket. This means that girl is not spent shoving air it if the way, but in accelerating the rocket. The rockets do turn and start moving sideways fairly soon though, to build up lateral speed. the hard part about teaching orbit isn't getting the height, it's getting the sideways speed to circle the earth before it \"falls back\" to the ground.",
"It's less energy to go straight up than to go horizontally and angle up. Rockets are already massive things that are almost entirely fuel storage. It would just be adding steps and complexity that aren't as efficient as vertical launches. You'll need wings now, you'll still need a rocket system at altitude to get to escape velocity, and there would be a lot more time in the atmosphere trying to get to speed which means more heat, more drag, and more energy.",
"It takes a lot of power to get into orbital altitudes, and the best way to reach that amount of power is to just burn a ton of fuel up to get the necessary amount of momentum going in a really short amount of time.",
"Just to add to the other answers something I didn't see: doing what you're suggesting would require the rocket to have wings, and wings are essentially dead weight for the main part of the rocket's flight because it'll be in atmosphere too thin for them to help. Any extra weight you add to your rocket has a significant fuel cost, which means you have to make the fuel tanks larger and the rocket itself larger, and everything gets very expensive very quickly."
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kmxtbp | Does the city detect gas pipe damage or leaks | A while ago the gas company knocked at my door and had everyone immediately evacuated. My neighbors in our cul-de-sac were evacuated out of theirs too. They dug up our driveway to fix a gas leak or cracked line leading to our house. They left after fixing it up and checking the inside of our house. I never smelled any classic rotten egg smell and my neighbors didn't either so there was no suspicion that anything was wrong. So how was it possible that the gas company knew? | Engineering | explainlikeimfive | {
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"I was once awoken by some serious digging sounds outside my bedroom window, which faces the driveway where the gas meter is. I go outside to see a backhoe digging near my gas meter. Turns out there was a leak below ground, where the horizontal pipe coming from the street turns upwards to meet my meter. The fitting was leaking. They detected this from a vehicle driving slowly down the street. Not so much the exact source of the gas, but a detectable level of gas \\~20m from the meter. Once he got the warning in the truck, the driver stopped and got out more sensitive equipment and pinpointed my meter in a few minutes. They didn't need, or ask, for my permission. Which is a good thing, I suppose. No need to evacuate, since it was a small leak. So, at least where I live, the gas utility actively checks for gas leaks.",
"Used to be a gas leak surveyor contracted by the local energy company. If I recall right it's a federal regulation that every four years a given gas line must be inspected. How that's done probably varies but I would physically walk the lines with a sniffing gadget plopping along the ground, as well as follow the line to customers gas meters and inspect those as well for leaks, corrosion, and abnormal operating conditions. Not sure what happened in your situation though. Underground leaks aren't always too obvious smellwise and a driveway sitting above it may have made it that much harder for the smell to be noticeable."
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kn4omg | how are sparkling wine corks fitted into the bottle? | Hello, My friends and I were zooming and drinking prosecco when this question popped out, could you explain like I'm five? A | Engineering | explainlikeimfive | {
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"It's hard for the bottle to say no when the cork is shoved into it by a machine that can exert hundreds of kilos of downward force. URL_0"
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knillc | what do the electricity rating numbers on the back of a plug-in mean? | In my quest to figure out what exactly is safe to plug in to my new USB + “9A”[??] lamp, I’ve noticed that all my little phone USB power bricks have Input and Output numbers on them. For example, the one I’m currently plugged into says: Input: 100-240V - 50/60Hz 0.4A Output: 5.0Vdc, 100-2100mA What do these numbers mean? TLDR; Can you please ELI5 input and output ratings of volts, hertz, and amps on consumer electronics and how to tell if they’re safe to plug in to other things? URL_0 | Engineering | explainlikeimfive | {
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"Hertz and volts are the \"type\" of electricity and change from country to country. Some have 110 V others 220 V, some have 50 Hz, other 60 Hz. \"Input: 100-240V - 50/60Hz\" means it can be plugged in anywhere in the world (like most electronics these days). The amount of Amps. is the amount of electricity going though, like the flowrate in a faucet. More amps, more juice. Roughly, volts times amps gives you the power provided. Your power brick provides a current from 0.1 to 2.1 amps at 5 V. I doubt that the \"9 A\" in your lamp means 9 Amps, unless it is a very, very bright lamp, because 5 V * 9 A = 45 Watts and that is a very intense LED lamp.",
"> Input: 100-240V - 50/60Hz This basically means it will run on any wall outlet in the world safely. North America uses 120V 60 Hz, Europe uses 240V 50 Hz, and Japan uses 100 V 50/60 Hz. By supporting 100-240V you don't need a voltage adapter just a plug adapter to use it The 0.4 A after that means it will pull no more than 0.4A while operating. A low power outlet will still have at least 5A available so this again works in any outlet The output specs need to align with what the lamp is expecting. It will put out 5V(the standard voltage for USB devices) and can supply 100-2100 mA of current so you need something that pulls at least 0.1A but no more than 2.1A for good operation Always use a UL/CE/VDE certified USB power supply and you won't run into unsafe conditions. It might not work as expected but it won't burn up"
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knozdu | How do airports keep noise of a plane landing and taking off inside the main terminals ? | Engineering | explainlikeimfive | {
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"When you're near an airport, you have to fly in a very specific path called a circuit. Circuit altitude is normally 1000 feet above ground level, and the circuit is a big rectangle. One side of it is along the runway, and the other three sides are always out, away from the airport. So between the 1000 feet of altitude and the horizontal distance, you don't hear too much from the planes that are going around the circuit. Planes landing are usually throttled back, unless they have to fight a really outrageous crosswind, so they're relatively quiet. Planes taking off will run up to full power so yes, those are a little loud. It also helps that jet noise is most intense in a cone-shaped region directly behind the engines, and the engines are pointing parallel to the runway during takeoff/landing. That means most of the noise is \"aimed\" past the terminal building rather than at it."
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ewyvr4 | What is a thermoradiative cell and how/why does it work? | There are news stories all over talking about how they generate power both during the day and at night by radiating heat away into space, which sounds doubly wrong. What's the actual source of energy? How does it convert that energy into current using PV cells? Why does it specifically need to radiate energy to generate energy, instead of generating it directly and not having waste radiative heat? The only explanation I can find is "like a regular PV cell but backwards." But that would be an LED, and LEDs don't generate electricity. Source: URL_0 | Engineering | explainlikeimfive | {
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"I don't know, on a physical level, how this system works. Frankly, I'm too tipsy to research it. However, I can answer some of this from a thermodynamics perspective: Energy alone is not normally useful. It tends to become chaotically distributed everywhere. This is best demonstrated by heat, where the kinetic energy of atoms and molecules gets sort of distributed evenly between all of them and becomes useless. In order to use energy, we actually need to harness its transition into a more useless state. The energy in sunlight is in a very useful state - we call this \"low-entropy\". Normally it just generates heat in small amounts, which is considered \"high-entropy\" and not very useful. The energy in a gas engine is fairly useful, as it is at high temperature, but could in theory be less useful than sunlight which is at even higher temperature. Basically, the get useful energy, we put a dam between energy in a more and less useful (lower and higher entropy) state. The warmth of the Earth is high entropy (as it is relatively low temperature) and so normally quite useless unless we find something of *even lower* temperature. Luckily for us, space is even lower temperature than the Earth, and so by putting a dam between the (relatively) low-entropy energy of Earth and the higher entropy of space, we can harness useful energy."
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ex598u | step up transformers vs converters? | Why do they sell plug adapter for us to uk? And why do people have success with them? Wouldn't they also need a step up or down transformer to accompany it??? How can someone just use an adapter and have it work?? | Engineering | explainlikeimfive | {
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"text": [
"Many devices can run on both 110v 60Hz or 240v 50Hz. Just need to be carefull you don't plug a 110v only into 240v, BANG!",
"Ok first, please calm down with all the question marks. One is enough. Also, I have no idea what you mean when you say \"why do people have success with them\". Some devices work on multiple voltages. Pretty much all electronic devices like phones, laptops, and tablets can run on anything from 100-240v at both 50 or 60hz. For those, you only need an adapter for the plug to fit in the outlet. Some devices like hairdryers and whatnot have s electable voltage options. For these you also don't need a transformer, just an adapter and to make sure you've selected the right voltage. Then there are devices that are only meant to work on 1 voltage. If you have a 120v device and are traveling to a country with a 240v power supply, you'll need a converter. Otherwise the 240v flowing through your device will blow it out, melt it, and maybe start a fire. Likewise, if you have a 240v device and are traveling to a country with 120v, you'll need a converter, because the 120v supply will not power your device, or it may power it but too slowly. It's rare to need an actual transformer. For traveling, a converter will do, if you even need one at all. The only time you'd need a transformer is for an electronic device like a computer that does *not* accept dual voltages."
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exd87h | Why are a lot of gears (not only in trans mission) in cars twisted instead of being flat like for example those LEGO Technic ones? | Engineering | explainlikeimfive | {
"a_id": [
"fg7lvl6",
"fg7jfu8"
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"text": [
"Recall the sound a manual car makes when reversing? That sound is made by the straight-toothed spur gears used for reverse. Each tooth makes a slight click when it makes contact with the other gear, and all those clicks together make that gearbox whine. All the forward gears use twisted helical gears. Because the gears are at an angle, the teath slide together instead of clicking, making the gears quiet.",
"The terms you are looking for are spur vs helical gears. Helical are generally stronger and quieter."
],
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10,
7
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exg418 | My house uses hot water heat. Why can't a system run frigid water through it for cooling instead of needing a separate forced air A/C system? | Engineering | explainlikeimfive | {
"a_id": [
"fg7zy25",
"fg80f8i"
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"text": [
"You could. There are plenty of houses that use ground water for controlling the temp in the house. You might have issues with using frigid water though, especially if you live in a humid environment. The condensation might cause more harm than it's worth.",
"In Celsius, room temperature is about 20 degrees, the water can be just under boiling temperature, say 90 degrees. That's a 70 difference, pretty efficient for heating up the air. For chilled water, you can't go past freezing point, so, let's say 5 degrees, so that's only a 15 degree difference, not so efficient for cooling the air. Issue number 2: heated air rises, so you place the elements close to the floor, and the heated air will rise up into the room. Cold air descends, so for maximum efficiency you'd have to have the elements close to the ceiling, to cool the hot air up there, and let it descend down into the room. Issue 3: Air has moisture in it, and colder air will hold less moisture. Basically, as you chill the air, water will condense on the elements and drip on the floor. You'd have to have a mechanism for collecting this water so it doesn't run the floors. Basically, a chilled water system would also function as a dehumidifier."
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13,
6
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exk646 | How does electricity flow | Engineering | explainlikeimfive | {
"a_id": [
"fg8nf5y"
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"text": [
"Batteries are like a pump, wires are like a hose, the size of your battery is the size of your water tank, and electrons are your water. Batteries push electrons through wires like water through a pipe. Infact you can think of voltage as pressure, and amperage as how much water is flowing. A more complicated description is conductive materials allow electrons to pass by nearby nuclei. And a battery produces electrons through electrochemical reactions, these electrons push other electrons through the wire. Edit: Thanks u/ka36 for pointing out voltage is pressure and amperage is flow. I had them backwards."
],
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11
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|
exm1tq | Why can't cars have a pull starter cord as a back up starter? | Engineering | explainlikeimfive | {
"a_id": [
"fg995t9",
"fgaxy2f"
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"text": [
"Car engines are huge and very difficult to crank compared to pull-starters. Your lawnmower might be 5 horsepower, but even your aunt's minivan is 120 horsepower or 24 times as big as the lawnmower. The lawnmower is hard enough to start with a pull - that van is gonna be impossible.",
"The engine is so large so you would not be strong enough to pull it with a simple cord. Cars did have hand starts in the past but they where crank handles not a puller cord because you need to apply enough force. You can see [it here]( URL_1 ). The continued to exist even when electric starters were introduced because they were reliable. But as time passed and electric starter become reliable the were removed because they were almost never used and they add complexity to the car. Today when engines are not inline with the car but across the crank handle would need o to be on the side of the car or have complex gearing. I am not sure when they start to disappear in regular cars but it looks like a lot of the hand had removable handles until 1960. If you look in military WWII vehicles almost all have a crank handle. It was even the standard way to start some of them like Germain tanks. The German tanks did have a starter engine but the reliability was not great so the was for an emergency start when cranking the engine was not an option. The is [how to start a Tiger II tank]( URL_0 ) If I remember correctly the US/UK tank uses the electric start in regular usage and the crank was a backup. Except for the Sherman models with a radial aircraft engine that you need to turn it around manually to move the lubricants around. So cars did have a pull starter equivalent until the was no longer needed. If you have a car without a manual gearbox you can get it going without an electric starter or some pull system. Just get the car moving by push the car manually perhaps with a friend or tow it behind a car. If you then press down the clutch, put in gear and release the cutch the momentum of the car will force the engine to turn and you can start the car. That wok fine if it is the start engine that had died or if the battery is not strong enough to start the engine but is still not flat. I suspect flat battery would make hard if all part of the engine is computer controlled then you need to move is so the generator provides enough power for the electronics."
],
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36,
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"https://www.youtube.com/watch?v=DArvPMlxHeQ"
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exnnx5 | How do construction workers drill through mountains to make car tunnels? | Engineering | explainlikeimfive | {
"a_id": [
"fganpj0"
],
"text": [
"Deep tunnels often use tunnel boring machines. This is basically a big tube with a drill on the front that removes dirt, sends it back and supports a section of the tunnel behind it. Precast concrete sections are placed on the wall for support or shotcrete (a type of sprayed on concrete) is sprayed on the walls and this prevents them from falling in. Tunneling has actually been done for a very long time, largely for mining and water transportation. Basically just dig a horizontal hole and put supports behind you so it doesnt collapse. Tunnel shields help support the front of a tunnel but still allow digging in front of them and were invented for digging in soil thats too weak to support itself for the small section of the tunnel ahead of the supports"
],
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7
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|
exzuoj | How do the cable guided cameras, in football games, work and move? | The cameras mounted over the field and move with the players. How does the reel system work? Is it from the camera setup, or large reels around the stadium? | Engineering | explainlikeimfive | {
"a_id": [
"fgej6x4"
],
"text": [
"The wires run to motorized winches. A computer moves the camera in response to an operator joystick. The winches, with their big spool of wire, are part of the stadium."
],
"score": [
3
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eybs3d | why do pickup truck manufacturers engineer their engines' peak power so high in the rpm range? | Im in the market for a full size gasoline pickup for towing and hauling. Doing ALOT of homework, and most of the different truck brands have power bands at around 4000 rpm. (Lowest was ecoboost @3500) That seems awful high? Wouldnt you want to engineer the power band closer to 2500-3000 rpm where most tow rigs cruise at highway speeds for the sake of fuel efficiency? | Engineering | explainlikeimfive | {
"a_id": [
"fgg9oy1"
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"text": [
"Well you don't particularly care what the RPM is for peak power, it can be fixed in the transmission. Also, peak power is always going to be at a high RPM, as higher RPM means more cylinder worth of fuel/air mixture per second. You expect power to basically go up with RPM until you hit the peak RPM. Second, you don't want to tow at peak RPM, you want to tow at peak efficency at the required power. That's usually a lower RPM, and that's usually how the transmission is optimized. If you need peak power (for a hill or whatever) you downshift to get that."
],
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10
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eyeul1 | How were the NYC subways built? | ELI%: I know they were built around 1900, and that the city was not as populated, nor had as many buildings as today. I also know that train tunnels were built with dynamite to get through mountains. But Manhattan is an island. How did they create what is a massive rabbit warren under it? An elderly friend remembers the city taking down the elevated lines in WWII for metal recycling and she swears that the city had a lot more stops as well. Research keeps sending me to three articles, but none of them go into detail. Help please? | Engineering | explainlikeimfive | {
"a_id": [
"fggr1jm",
"fgguryn"
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"text": [
"The majority of the system was built using the cut and cover method. Essentially, you dig an open pit down to the depth you want to subway tunnels and stations to be, and then build a ceiling on top that's strong enough to support the weight of whatever is above it. Many lines run under streets, so they would excavate the area, build strong concrete and steel supports on top, and then pave the street right over that. Other parts were built using tunnel boring machines. A tunnel boring machine works kind of like an earthworm digging a tunnel. It's a giant cylindrical machine that cuts up whatever rock is in front of it and pushed it out the back, leaving a circular tunnel as it moves forward.",
"The Sandhogs, the miners union for NYC, has been features in many interesting [documentaries]( URL_0 ). It's a seriously dangerous profession, using explosives underground."
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3
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eyyti5 | Why Do Home Appliances All Hum at the Same Tone Frequency? | My washer, dryer, microwave, and dishwasher all hum at the same frequency (roughly the tone G). We have 2 microwaves at work - different brands, sizes, years of manufacturing - both hum at roughly G. How is that possible? | Engineering | explainlikeimfive | {
"a_id": [
"fgk4pun",
"fgk5uih"
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"text": [
"Your electrical power is alternating current - switching back and forth 60 times per second. You will hear that 60 Hz tone, as well as overtones of 60 Hz (such as 120, 180, 240 Hz). edit: typo in overtone frequencies.",
"Because the hum of the appliances isn't being caused by the appliance itself. You've probably heard about how the electricity in our houses is of a type called alternating current. Without really going into the specifics of why we use it, what this actually means is that the direction of the electricity in your home and coming through your power outlets reverses direction many of times a second, usually 50 or 60, depending on your country. We refer to as 50 or 60 hertz, hertz is abbreviated as Hz which is just a unit meaning times something occurs per second. As a result, many appliances have components in them which will also operate at this same frequency. They may produce a small sound at a certain point during every cycle of the current, think of the sound a tiny switch would make, and so all of those small sounds add up to produce a constant tone at the same frequency of the electricity running through them. Depending on your country this will either cause the device to produce a G note if the power grid is operating at 50 hertz, or an A sharp/B flat if the device is operating at 60Hz."
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21,
5
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eyzyfo | How do fire hydrants not freeze in the winter? | Engineering | explainlikeimfive | {
"a_id": [
"fgkbdzf",
"fgkbl64"
],
"text": [
"Hydrants aren't full of water. They are dry until you open the valve and water flows up from the main. Water mains are buried deep enough that they never freeze.",
"The hydrant water line is below the frost line in the ground. Nothing freezes below the frost line. When the open the line (it's a screw valve) the valves location is also below frost line. The water is pressurize and once the valve is opened up comes the water."
],
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18,
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ez7ngn | Why planes won't crash because of turbulence? | Engineering | explainlikeimfive | {
"a_id": [
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"fglk3t9",
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"text": [
"Turbulences are to planes what ocean waves are to ships. They actually can damage the vehicle, yet like at water and ships we can estimate the strongest turbulences possible and design the aircraft to withstand them. Also even if a major turbulence hits a plane, the plane itslef just shoots through it due to its high mass and velocity. Also if the plane doesn't break in half, it just tumbles and falls until it has enough forward speed to generate sufficient lift again. Edit: Typo",
"Because planes don't break apart that easily. You could say its like driving over some bumps in the road.",
"Turbulence, in aviation terms, is used to mean \"regions of air where there are strong vertical or horizontal currents\". There are a few distinct kinds of turbulence, depending on their causes, and some more dangerous than others. The first kind of turbulence, what the pilot typically warns you about, is caused by weather systems. Wherever there's a weather front (cold and hot air masses colliding) this causes significant vertical movement of air, which creates the rainclouds and also turbulence in the atmosphere. This sort of turbulence results in a bumpy ride, but nothing near strong enough to damage a plane. The second kind of turbulence, sometimes called \"blue air\" turbulence, can come from various causes, but is characterised by being invisible. Again, it's usually not strong enough to damage planes, but because it happens suddenly without warning it can be a danger to passengers and aircrew walking around the plane. The third kind of turbulence is turbulence caused by air flowing over mountains. This gives strong rising air on the upwind side, and strong sinking air on the downwind side. In addition, something called \"mountain wave\" can form behind the mountain, causing strong rising and sinking air up to three or four times as high as the mountaintop. Finally, downwind of the mountain a \"rotor\" can form, which is effectively a very turbulent roll of air. This rotor can be somewhat dangerous, mostly because it happens at low altitude, so it will mostly affect planes that are landing or taking off - the most difficult parts of a flight. The most dangerous turbulence is that caused by large thunderstorms. These storms can reach up past ten kilometers high, so you can probably guess how powerful the air currents inside will be. Aside from turbulence, such storms also contain hail, or water that can freeze onto the airplane, both of which can cause serious problems even for large airliners. This is why pilots avoid going through storms, and most airliners are equipped with weather radar to help with that. A final mention goes out to wake turbulence: the wingtip-vortices left behind by other airplanes. A big jet-liner can cause such a disturbance in the air that it can flip a smaller airplane completely upside down. Dangerous if it happens at high altitude, and probably fatal if it happens close to the ground. This is why air traffic control keeps track of especially heavy planes, and doesn't let anyone land or start directly afterward.",
"Because turbulence is just when a plane passes through air that's moving in different directions, it's not like a tornado or a hurricane. Planes aren't made of tissue paper. We build them to be strong enough to withstand even the most severe turbulence. Turbulence poses no danger to the structure of a plane, and is not capable of causing a plane to lose control to the point of crashing."
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ez7xpf | Why do airplane communications sound so bad? | From pilot microphone to passengers, to radio/plane communications, it sounds like it's a microphone from the 1950's | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It's because the signal is still transmitted by changing the amplitude of the carrier (AM). AM is subject to RFI and distortion much more than FM/PM. Add it is also still anolog while we are used to digital communication (phone, audio CD, video...",
"There are some effort being made to make ATC communication with aircraft better. The EU SESAR project has a lot of modernization ongoing for air traffic, and one of these is digitized comms via radio and via satellite. That will also introduce authentication/integrity protection, and allow for long distance atc, such as over the Atlantic where traffic is currently not handled by ATC (aircraft out of radio range). On mobile, but a bit of googling should help you out.",
"Radio communications aren't as bad as they might appear. Pilots use jargon specifically designed to be understood in poor conditions, and they get used to understanding things even when there is some interference. Also, the communications are in a pretty set format, the pilot already knows what most of the message will be, all they have to do is pick out whether they are clear to land and which runway they should use. It might all sound like a garbled mess to the layman, but it is perfectly clear to the pilot.",
"It's analog for reliability reasons. The sound quality might not be great, but you can understand what's being said. The purpose isn't to make great YouTube recordings. Digital communications are great when they are working and nothing when you're out of range or under bad conditions. Nothing isn't acceptable for safety functions. They'd much rather have low quality audio than \"no sound\".",
"the radio is likely narrow-bandwidth (300hz - ~4khz): [Voice Frequency]( URL_0 ) the microphones and associated electronics may also be optimized for those frequencies as well which would impact the sound for even in-cabin audio."
],
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ezb5jw | Since the ISS is moving so fast, does NASA need to account for doppler shift in the radio signal? How do they account for this considering the ISS uses FM? | Engineering | explainlikeimfive | {
"a_id": [
"fgm2wx7",
"fgm2ud4",
"fgm470c"
],
"text": [
"NASA (and all communications with fast moving satellites) use Dynamic Doppler Compensation, where the frequency of the broadcasts are adjusted progressively through the broadcast to ensure that the receiver maintains a solid signal on the correct frequency.",
"The ISS is moving from side to side for most links, not the inward/outward path that would maximize Doppler shift. The dishes do move, to keep pointed at the ISS. The transmitters and receivers use phase locked loops to tune the carrier signal, so the shift is mostly tracked as it shifts.",
"out of interest i did the calculations. The ISS broadcasts at 145.8MHz, and the maximum shifted frequency of the received waves on earth due to doppler shift would be 3.7kHz above the intended frequency."
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3
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ezdjca | What are relays and why are they used in every cars' systems such as headlights/fuel pumps, etc.? | I do not understand their purpose. I cannot, for the life of me, find an easy and understandable explanation online for me to grasp. Why you cannot get power directly from the battery for example? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"As in your example, headlights draw a lot of power. You don't want that power running through the switch on the dashboard, the switch would require extra heavy design, there's an increased risk of fire, etc. So instead, your dashboard switch operates a relay. A relay is a switch that is operated by a small electromagnet, or a solid state equivalent. The relay is built to handle the power requirements of the headlights; all the switches on your dashboard can be designed to a single standard low power. Or, in modern cars, the computer can operate the relays also.",
"A relay is a device that allows a switch and a small wire carrying a small amount of current to control a device needing a large amount of current. What happens is that the wire comes from the battery positive side to the switch, then back to the relay. This allows you to switch the relay on and off with a very small amount of current, requiring just that small switch and thin wire. The relay then controls a larger current, allowing it to run say the headlights or the starter motor or some other large electrical device. Those devices draw way too much current to be switched by the small switches in the cabin of the vehicle, and would require large, thick wires to run behind the dashboard if they were to power the devices directly. Instead, the small wires run to the relay, which then controls the larger electrical devices under the hood. Relays are either electromagnetic or solid state, with the former being a switch that is magnetically activated by the current through the small control switch and the larger being an electronic switch that is activated by the small current through the control switch. Their function is identical in most cases."
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ezeyfm | Why can’t airplane cabins be pressurized so ears don’t pop at all during flight? | Engineering | explainlikeimfive | {
"a_id": [
"fgmtl1x"
],
"text": [
"To sustain the higher pressure, the metal would need to be thicker. The thicker metal would weigh more. The additional weight would decrease fuel efficiency. The decreased fuel efficiency would raise operating costs. Higher operating costs would raise ticket prices. You wouldn't be willing to pay more to fly in a higher pressure plane, so no airline would buy them, so no airplane manufacturer makes them."
],
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25
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|
ezkm3t | How were the undersea cables that power the internet implemented? | Engineering | explainlikeimfive | {
"a_id": [
"fgnuwdy"
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"text": [
"A ship carries a cable and drops it to the sea floor. That's really pretty much it Like, they literally just go across the ocean unspooling thousands of kilometers worth of cables."
],
"score": [
6
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ezrv5j | Why do older cars have a kind of line pattern on the headlights and it is a little blurry while newer cars have nice and transparent headlights? | Engineering | explainlikeimfive | {
"a_id": [
"fgp3c3y"
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"text": [
"Normal driving light (not high beam and not parking lights) has to be asymmetrical, meaning the beam of light needs to light up the road differently. Towards the middle/traffic, the light has to hit the road sooner than towards the side. This is to not blind the oncoming traffic, yet provide enough light (and give you enough time) to react to pedestrians/bikes/animals that could be on the side of the road. One could now think that the lightbulb towards the middle is just pointed lower than the one to towards the outside. But that's not the case. Both bulbs are shining on both sides. Asymmetrical. On older cars, this effect was achieved by making lines and making the glass thinner and thicker different places, it creates this difference in where the light beam hits the road (if you know about the lights refraction in glass). Today, this is done in a much more technical way, thus the lines are not needed anymore (also making it much cheaper to replace a broken headlight glass)."
],
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28
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|
eztyuh | How does buffing a scratch out on a car work? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Cars are painted in 3 primary layers. From bottom to top they are: 1. **Paint Primer** - this layer is a specific blend of paint that adheres well to the bare metal of the vehicle as well as other paint. It also better protects the vehicle than regular paint alone. It doesn't color very well and is layed on pretty thick. It is usually a flat matte, gray color. 2. **Cosmetic/Colored paint** - this is the actual layer that you see. It's comes in all different shades and styles. It's actually the thinnest coat on the vehicle. 3. **Clear Coat** - this is not really paint at all, but actually more like a resin. It's applied about 2-3 times as thick as the cosmetic coat, and is see-through (hence the name 'clear coat'). After the clear coat is dry it is buffed - this smooths out any imperfections. Essentially, buffing melts the clear coat in a localized area and smooths it out, so when it cools it is more evenly distributed and gives a nice shine finish to the car. Since the clear coat is so thick, most scratches will not penetrate all the way through it (i.e. down to the cosmetic layer). You can buff the area with the scratch and it will once again melt/smooth out the clear coat in that area. If a scratch goes all the way down to the cosmetic/primer layer, however, you'll likely have to have that area 'touched up' with new paint and clear coat. Buffing alone won't do anything.",
"Buffing essentially sands the surface of the paint with progressively finer and finer grits. What starts as a hazy, scratchy mess becomes finer and finer scratches until those scratches are smaller than can be resolved by the human eye. At that point it looks smooth."
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f03rat | Why does some smartphones get slower with time? Is it a hardware or a software problem? | Engineering | explainlikeimfive | {
"a_id": [
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"fgsiztc"
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"text": [
"Both On the software side of things not only are newer programs typically more demanding, but newer operating systems are designed with newer/more powerful devices in mind. As for hardware, the only real thing that degrades over time is the battery. As they age, and go through more charging cycles, batteries tend to be able to store less charge. What's more important for performance though, is that they also can provide less current. As electronics are under more load they draw more current, and if the aging battery isn't able to keep up then that effectively puts a speed limit on the device as a whole.",
"Well, eventually the software becomes too advanced for the hardware to handle. Something static cannot keep up with the ever changing demands of dynamic software.",
"it is called \"Planned Obsolescence\". Companies deliberately make products to last a certain time, usually around 5 years, so you have to keep buying new products. This is not a conspiracy theory, this is legitimate. Apple did admit that makes their phones slower, saying that will extent their life, but it just forces people to buy new ones.",
"I read sth. about cpu degradation - transistor aging. URL_0 It looks like a system becoming slower over time is possible without changes in software and storage. Modern CPUs will degrade over time when in use."
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f05msd | How does computer security software actually work. It’s obviously terrible, how can it improve? Need an update from Hackers (1995) | Engineering | explainlikeimfive | {
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"Security is actually great. Users are the problem, they're susceptible to social engineering like phishing as well as using bad passwords and not changing them or using a password manager. Like you may hate google and Facebook but if you try and use a service without OAuth your information isn't safe. There are bugs that cause problems, but we're pretty good at eliminating their causes. End to end encryption, HTTPS everywhere, using password managers... it's tough to actually write dangerous software these days. Everyone knows the pitfalls. Every so often we get fundamentals problems. Some can be fixed, like heartbleed, which was a software bug. Others like Spectre/Meltdown were actual hardware problems you can only fix with a new CPU. They pop up, but computers are actually really good at not fucking the pooch securely outside physical access. Don't use an easy password."
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f0ags8 | Why are drones and helicopters shaped so differently? | Why are drones and helicopters shaped so differently? Is there a reason why drones have four or more horizontally placed propellors and helicopters one big one small one which a positioned perpendicular to eachother? Wouldn't it be more logical for the 'perfect' design for a flying, hovering machine to look more alike? | Engineering | explainlikeimfive | {
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"Both need rotating blades but some kind of counter-rotation to keep the body from spinning opposite the blade direction. Both also need some mechanism for heading in a specific direction. They achieve both of these 2 different ways. Drones optimized for volume manufacturability. It’s really easy to make the same simple motor + fixed rotor assembly 4 times. They choose direction by varying how much power is sent to each of the 4 rotors. The only moving parts are the motors directly driving the blades. Helicopters optimized for flight efficiency. Helicopter blades rotate, but they’re also mounted on a highly complex gimbal and usually have independent pitch to each blade. The direction the rotor assembly faces can pivot to spend energy driving the helicopter forward. Then a separate tail system fights counter rotation. This is super mechanically complex but much more fuel efficient for improved range.",
"Stability and economics. For a helicopter, a single large engine is cheaper, more efficient and leaves more room for passengers / cargo. Because having this big heavy thing at the top causes the part below to want to spin in the opposite direction, the smaller blades at the back to fight against that rotation and stop it spinning out of control. Drones, being electric, can have multiple motors and rotors from one battery withless space / weight cost. Many drones also have built-in software that does some of the flying for the operator, making it easier to fly. You can get drone size helicopters (and smaller, I've seen down to matchbox size), just for some reason drones became super popular. Possibly because they look cooler.",
"The ideal designs look alike if they serve the same purpose. In this case they do not. Helicopters are designed to carry people, which means they need to lift high loads to air and in some cases take these high loads to distances with high speed. You need to apply force to the air to push air down and the vehicle up. For that reason you need the blades as long as possible as only some portion of the blades are actually effectively pushing the air down (for causes like tip vortices). But there is a limit to that as the blades should not break with the forces they apply. When designing the propeller of a helicopter, you end up with a single long (or two depending on how you look at it) blade turning in one direction. As the propeller turns in one direction, and as the helicopter is not attached to anything after take off, the body will try to turn in the opposite direction. So as to overcome this, you need another propeller to oppose this turning. You put it at the end of the tail, so the distance to the center of rotation is large, so you do not need to apply too much force, hence this propeller is smaller. This is good as you need the vertical propeller only for stability and maneuverability, and you do not need to pay money and increase the weight of the total vehicle too much. Drones are designed for maneuverability. Their payloads are smaller, so the concern is not applying much force but being able to change direction and alignment very fast. First you put electric motors where you can change the force output very fast, then you attach four to six motors (and propellers) with some distance to each other, so you can easily balance the forces in any way you like. As you do not care about carrying high payloads you are not limited to how efficiently you apply forces to the air, so shorter propellers do. And as your propellers are symmetrical and hence balanced, you do not need a vertical propeller to balance the force trying to rotate the vehicle. As you do not need to attain high speeds with respect to the air you do not care about the fact that your body is not very streamlined and your area facing to the direction you are flying is very high during a flight in a straight line."
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f0bfrh | Why are water bottles so much thinner and flimsier than soda bottles? | Engineering | explainlikeimfive | {
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"Water is not carbonated, soda is. Carbonation adds stress to the bottle that flimsy bottles wouldn't be able to handle. On account of all the bubbles.",
"Soda bottles are under pressure because they contain dissolved CO2. That's why if you shake a bottle of soda then open it, it spews everywhere. If you shake a bottle of water and then open it, it just sits there, staring at you and being judgy.",
"Because the bottled water industry has been under pressure from environmentalists and they have been trying to reduce the amount of plastic used in their bottles in an attempt to appear more environmentally conscious. The soda industry hasn't had the same level of scrutiny and negative attention regarding their bottles. If you go back and look at bottled water from the late 90s and early 2000s, they used to use pretty thick plastic bottles similar to soda."
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f0d1fq | how are micro SD cards able to store entire TV shows, albums and movies without any kind of electricity to keep them "active"? | Engineering | explainlikeimfive | {
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"imagine it's like those little push buttons on the top of a soda cup. The ones that indicate if it's diet, or Dr. Pepper, or whatever. An SD card has millions of those little buttons. They can be pushed back and forth, showing up or down, (0 or 1). They stay in the position they are in regardless of power.",
"The way any type of flash memory works, uses what's called Non Volatile storage. A common one is called NAND flash and here's a way of visualizing how it works. To represent one cell, one 'bit' of storage, imagine there is a tank of water with a pipe leading into it, and a pipe leading out of it. Like this: Pipe in===| |=== Pipe Out | | | Tank | |_ _ _ | || Drain Imagine, normally, the tank is full. So if you pump water into the tank, it will come pretty quickly out of the other pipe, because the level is full. Let's call that a \"0\" state. Now, you want to write data into that cell, so what you do is you drain a bit of the water level off, so the tank is sitting half full. Let's call that a \"1\" state. How do you determine what state that cell is in? You pump in a set amount of water. If the tank is full, you'll get flow from the output immediately. If you don't, all that will happen is the tank will fill a little, but you'll get no output. That way you know what's what, and once it's been set, it doesn't matter if there's power to it or not, it'll remain as it was. That's not a perfect analogy, but it's roughly how the individual cells of storage work in flash memory. Instead of water, though, you have electrical charge.",
"Basically they have a process (Fowler-Nordheim Tunneling) to trap electrons in an area surrounded by insulators, so the electrons can't go anywhere. Now, if they have electrons trapped, it creates a change in the local electric field compared to if there weren't electrons trapped there. They can use the electric field to switch on and off a current flow that is external to the trapped electrons. So, because the electrons are trapped, and surrounded by insulators, you don't have to apply power, unless you want to read the memory.",
"Your regular hard drives also store everything saved on them while unpowered same as a SD card, and you also need electricity to read/write on both though the cards require less. The difference between the two is that regular hard drives save data magnetically on a spinning disk while SD cards save it electrically on millions of tiny transistors.",
"They \"cheat\" and there's static electricity in them. Microscopic amounts, but it's still there. They work similarly to how you get zapped when wearing a wool sweater. Electrons get trapped in billions of tiny \"wells\", which makes up the ones and zeros on the chip.",
"Electric charge is stored in tiny capacitors built into microscopic transistors. In quality parts the charge takes years to leak out, but flash cards are not archival storage for the long term.",
"They store bits by sandwiching them between an insulating material. Because the electrons are sandwiched in the insulator they will stay there even when you power the flash memory off. The data does leak over time but so slowly that you can store it for decades without having to refresh it.",
"Your mind is gonna be blown when you find out about CDs, DVDs, floppy disks, laser disk, BetaMax, VHS, Hard drives, ect.",
"Books don't need ink to keep the words active. Once they're written, they're always there. SD cards need energy in the form of electricity to be read, books need energy in the form of you (opening the book and reading the words) to be read.",
"Imagine you've got a table full of rechargeable AA batteries, a battery charger, and a lightbulb. If a battery is fully charged, that represents a binary 0. If the battery's not fully charged, that represents a binary 1. Initially, all of the batteries are fully charged. So if you have 8 batteries, the data is just 0-0-0-0-0-0-0-0 (8 bits, which in this case represents the decimal value zero). You can check each value (each bit) by putting its battery into the battery charger and seeing if the \"charging\" light comes on. Even if you check a week later, they're still all fully charged. Now let's say you want to write the first piece of movie data. Let's say it's the number 128; to do that, you want to encode a 1 into the first bit position (the first battery). You'd hook up a light bulb to the first battery, and let it discharge for a while. After an hour, you take the bulb off, and the battery's only half full. A week later if you check each battery with the charger, you'll see they're all still full, *except* that one you discharged. There's the bit we set! Your data is reads out as 10000000 (128), as expected. If you want to reset it back to 00000000, then you hook up the battery charger to that first battery, but *this time* actually press the start button. Once the charging light turns off, you're done! Now, imagine this scaled waaaaay down (using capacitors instead of batteries), and operating lightning fast. That's an SD card, and a marvel of technology. Technically speaking, batteries store their energy using a chemical reaction, while capacitors store the actual static electric charge, and some of that charge does leak out (since barriers holding the static electrons aren't perfect, and electrons are even able to \"tunnel\" through otherwise impermiable barriers, thanks to the bizarreness of quantum mechanics). So, over many years, SD cards *will* lose data, however they also implement some corrective algorithms to minimize it within timeframes we normally worry about. Still, an SD card likely won't hold its data for hundreds of years.",
"I really like fluid analogies for electricity because it really gives you a *feel* for how electricity flows. But it isnt a perfect analogy. If top comment didnt quite connect with you, perhaps the following will help. Imagine there are millions of super tiny switches in your sd card. You can send signals via one pathway to turn certain switches on and off. This is how data is written to the card. In order to read the data, another seperate pathway through those same switches determines which switches are on and which are off. It uses some clever properties of electronics to do this that I dont personally understand. On switches are read by the processor as \"1\" and off switches are read as \"0\". These ones and zeros are then read as a sort of code called \"binary\" that your computer then converts into real usable data using a decoder(programming language, essentially). Even when you remove the electricity to the whole thing, those switches are still in either their on or off positions. When you plug it back in, the computer only sends electricity through the \"read\" pathway so as not to disturb the positions of said switches until you decide to \"write\" something new to those same cells. This isnt quite how it works, really... I'm pretty sure... I'm far from an expert. But its a useful way to think about it.",
"Think of your SD cards as an arrangement of 1s and 0s which make up your data storage. Now imagine your house is an SD card, your light switches in your house at any given time are either in an on (1) or off (0) position. If your house loses power or electricity, the switches are set in place even if they don’t have power, and when the power is restored the on (1) and off (0) positions in their original position.",
"This is a great question with great answers! But I just cant seem to grasp how a sound or video is stored on an object.. it's crazy awesome though",
"An SD card is like a tiny book with information in it. The book/sd card does not need electricity to hold information. But yes to change and access that information.",
"Active is bad. Active changes things. For storage you want things to stay in the position you put them in, you only need power to change it to something else.",
"Much like a piece of paper can store information when a pencil is applied. The state of the object changes. It is not stored as energy, it is stored as matter.",
"Each bit of data is like a switch. It can be on or off. Just like a light switch it doesn't need to have electricity to stay in whichever state it is.",
"Basically, in an oversimplified analogy, each bit is a trap that holds a charge even when power is cut. It still needs elecricity to read/write the data, but can hold onto the electrons until needed",
"Because if charge (your data) has no where to flow it can stay where it is. In that case data is only lost if charge escapes by diffusion. You don't need to act on a charge reservoir in any way to keep it \"active\" its just there, ready to do work.",
"If you make really pure and flat sand, and make pictures in it using the kind of light that gives you sunburn, you can make boxes that trap lightning in them if you jam the lightning in hard enough. It takes very little energy to see if the lightning is still inside or not, but if you jam a lot more lightning in later you can empty the box. Usually you just put new lightning in an empty box and ignore the one you wanted to empty until you can empty a whole row of boxes at once, since you might do that accidentally (lightning spills easily when you have a lot of it being jammed into boxes). If you make a few trillion boxes you can store enough instructions to make a TV play any movie or show you want. This works because most chemical elements either really don’t like lightening and will just heat up a ton and vaporize, and other elements like lightening so much they just let it pass through without much complaint. Sand is made up of a lot of stuff that has rules about how much lightening can go in which direction and when."
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f0kn60 | please how do jet engines keep heavy rain out of their combustion chambers? Or do they not? | Engineering | explainlikeimfive | {
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"They don't. Jet engines are designed and tested to work in a heavy monsoon downpour. URL_0",
"The spinning fan blades fling a good amount of water outward so that it goes through the bypass ducts instead of the combustion chamber. Since, in modern jet engines, most of the air goes through the bypass duct instead of combustion chamber, almost no water goes into the combustion chamber, and the engine can handle any that does make it in, unless it's some sort of catastrophic, biblical amount of water."
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f0ptte | how DRM is added games, movies and music and on what language they are coded? | Engineering | explainlikeimfive | {
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"depends where what and why. usually it's coded in the same language that the game is made in. other times it comes as an extension to an SDK or as a straight library (.dll files you see in the game folder) or anything. Certain DRM systems work on tokens which only the company is able to hand out on ROM chips or whatever; other DRM systems work on obfuscating game data, relying on tokens to de-obfuscate it for it to be read and run and others rely on the previously mentioned tokens being handed out by a specified game server and others by simply relying on online only gameplay where a million different checks can be made as to the \"legitimacy\" of the copy - usually product keys being checked. DRM systems are broken by either removing the link between the DRM and the rest of the game's content or by using exploits/bruteforce breaking the DRM via its own system. depends what, where and why. And they are ALL eventually broken, believe me. The majority of the programming and cryptographic talent is not inside of the company making the DRM - it is the outside world, which the company is trying to protect its system from (and, at the same time, sell it to them). it's a fucked up system that a lot of games developers opt to just avoid implementing because it's a maintenance headache and stinks for everyone - including honest buyers.",
"DRM isn't a programming-language-specific thing, you can implement DRM in any language you please! As to how it's added, I presume you really mean to ask how it *protects* things, and that really depends on what it's protecting. For digital music, usually the music data is encrypted in some way (mangling the data so it can't be understood by the player). It can only be decrypted on authorised hardware, or if you know a certain password, because that information is used to perform the decryption (that information is part of the \"key\"). For movies on BluRay disc, there is lots of different DRM; there's DRM on the discs, but there's also DRM between the player and the TV. The discs are encrypted the same as the music and come with a key. The player can read this key, and combine it with its own key, to generate *another* key (called a title key) that can be used to decrypt the movie. If you're playing that movie on a computer, there may also be a Shared Bus Key which is used to encrypt the data read from the disc when it gets sent to the player (which can then decrypt it again) so that no programs can snoop on the video that has been extracted from the disc. And this whole sequence of keys is designed to be updateable so that if any of the keys leak (and thus let anyone decrypt the discs) they can change them and lock everything up again on any new discs they make. On top of that the discs contain a special physical irregularity which won't get copied onto another disc if you try and copy the movie; the irregularity has to be there or a player will refuse to play the disc (more accurately, it *can't* play the disc; the irregularity is part of the decryption process). But that's not all! In case the security keys are compromised, they also sometimes deliberately store *scrambled,* encrypted video on the disc, such that if you only decrypted it, you still can't see anything. Then there is special code on the disc which the BluRay player must use to descramble the decrypted, scrambled video! The way this part works is entirely up to the people who design it so it can change all the time, making it harder to crack than just decrypting the discs. BUT WAIT, THERE'S MORE. The disc may also include code which looks to ensure that all the previously mentioned protection measures are still in place; if they're found to be missing, it might stop the disc from playing. BUT WAIT, IT'S NOT OVER YET, some discs make the player secretly add watermarks (special, hidden marks that you won't see or notice while playing the movie, but which can be detected by special software) which contain identifying information about the player, such that if you did manage to crack the player and get it to play discs so you could copy the movie from it, they can identify the player or drive responsible for leaking the copy (which may lead the authorities to your door, but more likely is just going to result in that make & model of player being blacklisted from working with all new BluRay discs). And that's just the protection on the disc and player!! Then there's also HDCP to protect people trying to copy the video stream as it travels down the cable from the player to your TV. Once again, this involves encrypting everything and decrypting it on the other end. As for games and software... really there's so many different ways to do it. Some DRM just involves fingerprinting your computer (uniquely identifying your computer, like your operating system, CPU, hard drive, graphics card all have unique IDs and/or serial numbers, so they can tell it apart from others) and then checking with online services whether that unique computer is allowed to use the software. Some older techniques looked for a physical object like a CD/DVD or a special USB dongle and if they find a genuine one they will let the software run (if you've ever heard about NoCD cracks and things, you'll know this doesn't work very well! It's easy to analyse the program as it runs and find and cut out the part that performs the check by watching the program's execution in a debugger and then editing it with a hex editor). If you're interested in DRM you might like this guy's channel, he's done loads of videos on games console DRM, really interesting stuff: [ URL_0 ]( URL_0 ) Also this is a great channel, generally nothing to do with copy protection but he did cover one example at least: [ URL_1 ]( URL_1 )"
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f0qzat | What makes some weapons more accurate than others? | Engineering | explainlikeimfive | {
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"Many factors. For example, some bullets are physically larger than others, and so get pushed more by wind while in the air. Some travel slower, and thus spend more time in the air getting pushed by wind and falling because of gravity. Some weapons have shorter barrels than others; the bullet doesn't spend as much time getting pushed (and so is going slower) and getting spun (so is spinning slower and not evening out it's weigh as effectively). Some weapons have a barrel that's not as rigidly fixed to the frame as others; it shifts more when the gun is fired, changing where it's pointed. Even the bullet matters. A swaged round tend to be more consistent, and thus more accurate, than a cast round."
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f0rcjx | what prevents a camera lens to have huge aperture capabilities? | For example why can't a 25-70mm be f/1.4 instead of f/2.8? | Engineering | explainlikeimfive | {
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"The aperture isn't given as a fixed size, it's the ratio between the focal length and the diameter of the lens's pupil. To make a 25mm lens have an aperture twice as wide, you need the actual lens to be twice as wide. This makes the lens a lot bigger and more expensive.",
"There is nothing stopping someone from building a 24-70mm f1.4 in theory. In practise however, it is something of an impossible task. The main challenge is the engineering - the aperture corresponds to the effective width of the lens, so the wider the aperture (lower f numbers) the larger all of the glass elements need to be, and the larger the elements are the harder they are to make to a suitable quality for optics. The wider apertures also mean narrower depths of field, so everything needs to be more precise as any slight misalignment becomes more noticeable and alters the image, so focus systems need to be more precise, and generally every tolerance needs to be even tighter than before. What this means is that a 50mm f1.8 lens is an incredibly simple design that can be sold for < $100, a 50mm f1.4 is a step up in quality that sells for ~$300, while a 50mm f1.2 (and even wider do exist) is a lens that takes significant R & D and cost to produce and sells for thousands... Completely separately from this however, you have the issue of zoom - when you have a zoom lens, you have to design a suitable set of optics for a 24mm lens plus a set of optics for a 70mm lens, then find some way to combine the two designs so that they can share the same set of glass elements (which also work at all the in-between points of the zoom range). This added complexity means a zoom lens is a lot harder to design than a simple prime lens, so to make the designs practical and cost effective they have to put limits on things like the aperture (remembering a smaller aperture lens is easier to make). Another layer of complexity comes from whether the aperture is variable or not - the simplest designs allow the aperture to change over the zoom range, but with some additional engineering work they are able to make designs that keep the aperture constant (which photographers generally prefer) So a 24-70mm f3.5-5.6 is a cheap lens with a narrow, variable aperture, while the effort in designing and building a 24-70mm f2.8 means a four figure price tag. At the end of this, it almost certainly would be possible to build a lens like a 24-70mm f1.4, but the design would be hugely complicated and require such a high level of precision that it just isn't worth the cost to the companies to build. And that is before you consider the size and weight such a lens would be with that much glass needed..."
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f0zl90 | why do kitchen scissors have middle teeth? | Why do kitchen scissors have those metal teeth in the middle? | Engineering | explainlikeimfive | {
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"Are you talking about above where you grip? That's used to crack nuts, lobtser/crab shells or grip to open small bottles. Some kitchen scissors have many tools on it (like the end being a flathead screwdriver, or a bottle opener for pop)",
"If you are talking about the curved, metal nubs just behind the hinge they are typically intended to be used as nutcrackers. I suppose you also might be able to use them to get a grip on anything else you wanted to grip very tightly or crack, such as bones in meat."
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f109kf | How is concrete poured on a slope? Wouldn't it gradually become level? | Engineering | explainlikeimfive | {
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"Concrete can be ordered at a range of viscosities. When tbe truck rolls up they do a couple test pours to see if it meets the clients needs and away we go."
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f12x5g | How did ancient civilizations make ovens so hot that they could melt metal without the kinds on materials we have today? | EDIT: Thank you to everyone for such an insightful conversation! | Engineering | explainlikeimfive | {
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"Making a really hot fire doesn't require modern technology. That's all you're doing when you're working with metals or building kilns to fire pottery - just making a really hot fire. It's perfectly easy to make a fire that's thousands of degrees with just wood or coal. All you need is some structure to contain the heat (brick, ceramic, stone...etc), fuel, and some way to blow oxygen to get the fire really hot and keep it hot. These are all things that require no modern technology whatsoever.",
"It progressed over time Early copper was cold worked, aka not melted. Then someone figured out bellows and made a kiln that could melt copper allowing it to be cast and then worked. Once you can melt copper you can also melt tin so now you've got some bronze which is harder than copper. Iron was the hard one. Without coal you can't really liquify iron and make proper steel so ancient cultures relied on clay bloomeries which would give you a blob of iron and slag that needed to be worked to beat the slag away and give you decent iron. Early iron would have been comparable or worse than the bronze of the era and it wasn't anywhere close to even basic iron that you'd get today.",
"Clay and stone are *really* hard to melt. Copper, tin, bronze, iron, gold, and silver (common primitive metals) don't have the highest melting points compared to other metals, and some melt at rather low temperatures (relatively speaking). Take a fire in a carefully shaped furnace made of clay, blow in a significant amount of oxygen (you can make a good bellow fan with a few sticks, some thread, some bark, and more clay), and you can make a furnace that gets hot enough to melt metal. It's really not all that hard. Finding the material's actually harder, but we did that too.",
"You can make a something capable of melting iron out of clay you dig up locally and basic fuel, like coal. It’s not difficult. You just need proper airflow. Also, to work metal you don’t need to melt it. Just heat it until you can work it with a hammer and tools. That’s why it’s such old knowledge. It’s what let us get to the point we can melt materials with a much higher melting point,like tungsten."
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f14itd | How do doors automatically swing shut when they let go? | Basically the title. How do some doors automatically close when you let go of them? And how do they always swing close one way and not the other? | Engineering | explainlikeimfive | {
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"They normally have some type of spring mechanism at the top. They normally look like two or three hinges linked together while attached to a pipe.",
"Used to build, fit and maintain door closers. The 2 main commercial types are the external top mounted units that only open / close one way and are attached to a normal hinged door. The other main type is a small box mounted in the floor under the \"hinging\" side of the door (no actual hinges used in this case) These have a small pivot mounted in the top of the frame and the bottom of the door mounts on to a shaped pin coming from the box in the floor. The box in the floor is oil filled, has 2 springs and an oil damper to slow down the door movement. These floor mounted unit can be either one way opening or swing in both directions. As well as these 2 types, there's various forms of sloping hinge so the door lifts to open and then drops back down to close, simple springs fitted to one side of the door, etc"
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f19240 | When you turn the AC on, turn the speakers louder or turn on a subwoofer in a car, does fuel economy decrease in order to create more power? | Engineering | explainlikeimfive | {
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"1 hp is about 750 watts. The alternator is in the ball park of 70 % efficient. Your AC compressor will take 2 or 3 hp mechanically from the engine. Take your electric load, divide by .7 and divide by 750, this is the load your placing on the engine. A modern car engine will have a fuel consumption of .4 to .5 pounds of fuel per horsepower per hour. This is the extra fuel your burning for accessories. ETA: double checked my numbers, some new cars are getting fuel consumption down into the low .3s. Didn't think they could go that low.",
"When you turn A/C on the compressor gets power from one of the engine belts. The compressor turning puts more load on your engine therefore reducing fuel economy. The stereo and subwoofer use electricity which is generated by your alternator. The alternator like the A/C compressor runs off an engine belt as well but the alternator is always running so the only way you could potentially lose fuel economy is if the stereo/subwoofer use enough electrical current to rob power from the engine's ignition system (spark plugs). The A/C will definitely effect fuel economy, the stereo or subwoofer is debatable depending on how much electrical current is provided by the alternator."
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f1dnrm | How does aircraft grounding for Pstatic and lightning strike work? Is the charge "bleed" off to the surrounding air? | Engineering | explainlikeimfive | {
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"Yes. The charge tends to distribute itself over the outside of the aircraft skin (since electrons repel each other, they want to get as far away from each other as they can, and the outside surface lets them do that). Then it slowly bleeds off into the air starting at pointy bits. To control this discharge (since sparks would generate RF interference with the radios) there are specially designed \"pointiest parts\" of the plane called [static wicks]( URL_0 ). The electricity slowly dissipates into the air through them."
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f1gay5 | How do public water pipes not freeze in very cold weather? If house pipes freeze easily when there isn’t enough heat to keep the water in a liquid state, then why don’t pipes under the street freeze? | Engineering | explainlikeimfive | {
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"They are buried below the frost line. They are kept deep enough that the radiant heat of the earth keeps them above freezing. This is usually about 4 feet deep as a decent safety margin in the lower 48, not sure about Alaska though, I bet they go deeper.",
"Here in Alberta (Canada) the frost can reach 4' so we bury pipes (and building foundations) lower than that so they aren't exposed to freezing temperatures. Pipes are generally buried quite a bit deeper than that...up to 8' or even more."
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f1jejo | What do ISS spacesuits do? I know they provide an at atmosphere but do they have insulation? I'd guess not because there's no atmosphere to cool you down, but what about depressurization? | Engineering | explainlikeimfive | {
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"They are insulated because space is a wild set of climates. Imagine standing inside a huge deep freeze with a million watt floodlight 10 feet from you pointed at your back. So you wrap yourself up in crazy amounts of insulation to keep from freezing and boiling at the same time. But now all that body heat you generate is trapped in there with you. So you have to remove that and radiate it away. Spacesuits have chilled water lines running through then and that keeps you cool. So the spacesuits provide full climate control along with the proper amount of atmosphere.",
"Space suits perform a whole lot of things. The suit is heavily insulated. Because if it's in sunlight, the side exposed to the sun is going to get very hot, because there isn't an atmosphere to get in the way. It also has a bunch of tubes with water running through it to cool down the astronaut and take away body heat. ~~The suit is also pressurized to earth normal pressure. They used to keep it lower, but that involved the astronaut needing to do time consuming things to keep the nitrogen in their blood from killing them. So they stopped doing it for the most part.~~ Edit: was mistaken about pre-breathing. Suits are kept at a pressure lower than earth normal pressure. The astronauts need to do time consuming things to keep the nitrogen in their blood from killing them",
"Turns out. Air is really hard to keep in. And space, you don't cool off, which is kinda good, until you are sweating balls from working. As it turn out, having sweat floating everywhere on your face where you CANT WIPE WHILE WORKING is really, really, not desired. so it have a cooling part. Pressure comes from air mass both INSIDE AND OUTSIDE. If theres literally nothing outside, the only thing you need to watch out is the pressure of keeping the air in, which is alot easier than underwater, where you have the ocean crushing on you. Space also have a SHIT TON OF RADIATION, so unless you plan on having all kinds of cancer, you need protection, which is why the helmet LITERALLY HAVE A SHEET OF GOLD. It also provides exo movement, because in space where you can grab nothing, the only thing you can do is propell your self with air. It also houses radio so you can talk, and water and urine collection, because small things like human right to a non hostile working condition (somewhat) and mission success."
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Subsets and Splits