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9n0s3u | Why does a video still needs to buffer when you rewind the video? | Engineering | explainlikeimfive | {
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"Video consumes a lot of memory. As a video is transmitted over the internet it's usually compressed to save bandwidth, but after decompression can be pretty big. As the video plays, the older parts are \"forgotten\" to clear room for upcoming parts of the video."
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9n0usg | How do housebuilders ensure new builds don't rot in the rain or snow before they're completed? | Engineering | explainlikeimfive | {
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"Wood doesn’t just rot the instant it gets wet. It can get rained on and it will dry out and be fine. In general though, they finish framing most homes pretty quick, and the very next thing they do is put the roof on and install the windows and Tyvek on the exterior. This is enough to keep everything dry while they finish doing everything else.",
"Residential construction is generally done with spruce, fir or pine wood. While these woods are generally not particularly rot-resistant, generally speaking it takes quite some time for rot to occur. Rot is essentially various micro-organisms causing bio-degradation of the wood. These microorganisms like moist, warm-ish atmosphere. While being exposed to rain makes a more pleasant environment for these organisms, once the structure is completed, that environment goes away.",
"The schedule to go from foundation to the watertight stage is quite brief. Floors, walls, and trusses are often prefabricated. Then its a matter of roofing, house wrapping (the plastic or tyvek membrane around the house), and installing windows. While the wood parts can get wet in this process, it's often a month or less. Once watertight, they let the wood dry out before finishing the walls. That's also when the plumbers and electricians are filling the walls with unseen wonders.",
"Good treated lumber can usually take this sort of abuse for a time. A build isn't likely to be going for even a solid year, let alone several, if it is wood construction. Treated lumber typically used chemicals to preserve the wood and make it last longer, and they might also choose to apply some sort of sealant to aid in weather resistance while they build.",
"I just wanna point out that a surprising amount of modern builds do suffer water and mold damage during construction. As the housing market boomed construction is in quantity and not quality. The damage doesn't show for 5-15 years anyway and good luck proving it was during construction the problem started by then and fighting in court over that. If you do things properly it isn't an issue as many others have pointed out.",
"We are building our house right now. Last Monday we had a first floor frame, by Thursday we had a full second floor and roof, by Saturday we had our roof wrapped. The house should be wrapped by this Friday. Our house is about 2400 SQ FT. So I’m less then two weeks the framing and wrapping will be finished. Some of our trusses are discolored- they were waiting there on site before the foundation was even poured. The discoloration is simply just that. There’s no rot or impact to wood itself.",
"residential construction grade materials are usually rated to be exposed to the elements for 12 months before real degradation will take place.",
"Timelines are important, but they aren't always able to ensure rotting doesn't occur. I've been in plenty of new construction where i've seen moldy floor joists, framing, OSB, etc. Hopefully once the home is complete and hvac systems are on, moisture will be down to a level that causes any rot-causing life to go dormant. We build homes out of very moisture-sensitive materials these days. There are a lot of ways moisture can penetrate a home and cause issues. We build homes with more insulation and greater air-tightness today. It used to be that homes would be able to get wet and then dry because they were more permeable and leaky. The old timber was more rot-resistant. In the winter if the home got wet, the heat from the inside would push moisture outside, and in the summer if it got wet, heat from the outside would cause moisture to migrate inwards and evaporate. Now we have drywall, OSB, plywood, fast growth low density timber and airtight insulated buildings and when moisture gets inside, it can really linger and cause damage. Moisture control is an important thing to consider in a home. But when building them, they can get wet and dry out quickly, because they're so open."
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9n3vy1 | Why are bullets bullet-shaped rather than football shaped? | I know that bullets are partially inside the shell prior to being fired. But wouldn’t having them be football shaped make them more aerodynamic, and this able to fly straighter for longer? | Engineering | explainlikeimfive | {
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"Theoretically, sure. But the thing you have to remember is the bullet is being propelled from the gun. WIthout the flat surface for pressure to build against you're gonna have a hard time with it actually leaving the barrel.",
"A football shape isn't actually a particularly great shape for stability. What's usually meant by \"aerodynamic shape\" when talking about droplet shaped objects is the reduced pressure loss drag and not their stability. Bullets from rifles and guns are usually spin stabilized. They are spun up through the rifling in the barrel resulting in a rotation around their axis when leaving the barrel. This has 2 effects. 1 rotating objects tend to resist changes to their rotational axis. Much like how a yoyo is stable when spinning. 2 any asymmetries in the bullet shape will not change the bullet path in a particular direction. The asymmetry is spun around the bullets axis and will cyclicly produce the same forces in all directions so that they cancel out and the bullet path is stable. Bullets can also be drag stabilized. So additional drag at the tail end can actually be desired to increase stability. If the bullet starts to fly sideways the tail end will get hit by the oncoming wind. This results in a force acting on the tail end of the bullet which pushes it inward and the bullet will return to its orientation along the direction of the flight path."
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9n5bfm | How can a 1 mpg improvement in fuel efficiency for a truk save more fuel than a 5 mpg improvement in a Prius? | Below is a link to the article that makes me ask. I do not understand the logic here at all. They say for the same number of vehicles, traveling the same distance the truck saves more fuel, how? This seems like a bullshit commercial for trucks. URL_0 | Engineering | explainlikeimfive | {
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"> This seems like a bullshit commercial for trucks. Let us try some mathematics. Suppose our Prius gets 50 miles per gallon and our truck gets 15 miles per gallon. We are driving both 200 miles, so how much fuel do they each burn? The Prius burns 200/50 = 4 gallons of gasoline. The truck burns 200/15 = 13.33 gallons of gasoline. Now let us suppose the Prius gets 5 mpg better and the truck 1 mpg better, then we travel the same distance. The Prius burns 200/55 = 3.64 gallons of gasoline. The truck burns 200/16 = 12.5 gallons of gasoline. How much was the reduction of gas by the change? The Prius reduced by 4-3.64 = 0.36 gallons. The truck reduced by 13.33-12.5 = 0.83 gallons. Even though fuel economy for the truck increased by only a fifth of that of the Prius it managed to reduce its fuel consumption by more than double that of the Prius.",
"1 mpg is a much larger difference for a vehicle with a low fuel efficiency. To compare, translate to a unit like gallons per 100 miles. 4 mpg to 5mpg is the difference between 25 gallons and 20 gallons for 100 miles traveled. 49 to 50mpg is a difference between 2.04 and 2 gallons to travel 100 miles.",
"Simple. 1) a truck that gets 10 mpg and gets a 1 mpg increase just saw a 10% increase. Now that truck goes from taking 10 gallons per 100 miles to taking 9.09 gallons. This means .91 gallon of gas is saved. A Prius that used to get 50 mpg and now getting that 10% increase now gets 55 mpg. To go 100 miles in now takes 1.818181 gallons instead of 2. So it saves .181818 gallons of gas. So for the same 10% increase in efficiency the one saved 7 times as much gas for the same distance driven. They also make the point of there being so many more trucks so even if they both saved the same amount of gas per vehicle the sheer number of trucks vs Prius means the money is better spent on improving truck performance."
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9n8l5t | How are bridge foundations in water made? | Engineering | explainlikeimfive | {
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"They lower a so called [Caisson]( URL_0 ) into the water, which is basically a box that reaches from the bottom all the way to the surface of the water. Then they pump out the water on the inside to get a dry place to work in.",
"Another way it's done is the body of water such as a river, is diverted or partially so. Work is then carried out as would be without water."
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9n8ovs | Do kevlar vests protect you from stab wonds? | Engineering | explainlikeimfive | {
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"Yes, and no. There are 2 types of these vests. One of them is the ballistic resistant which protects you against bullets and one is stabbing resistant which protects you from stabbing.",
"No, they are specifically for high energy impacts, not blades. But there are special anti penetration vests."
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9ncqlf | How are braces able to move teeth without loosening them or making their roots weak? | Engineering | explainlikeimfive | {
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"My orthodontist had a brochure that explained how it worked with a diagram. I can make an analogy that is almost there since I can't draw a diagram for you, then we can connect that to how teeth work. Think about a fence post in the ground, only it's crooked, not straight. Imagine you push against it to straighten it. It won't stay unless you hold it up, because now there's a gap between the post and the dirt on which it used to rest. Now imagine you fill in that gap with more dirt and pack it solid. If you let go of the post, it will stay straight. That's what braces do. They pull on your teeth and move them slightly. Your body's gum tissue grows to fill in the teeny gaps this creates. That has the effect of permanently changing the position of the tooth. Or my orthodontist was a liar, or this is an oversimplification.",
"Braces reposistion your teeth slowly and over time. I hade my braces for 2 years, before that 1 year of a retainer, and before that I had 2 teeth pulled from up as well as down to make room to reposition them Since the adjusting is done very slowly your body is abled to keep your teeth fixed during the ordeal. I guess you could maybe compare it to the \"trick\" with the iron string through a block of ice. What happens here is that the pressure of the string, weighed down with two weights on either side, causes the ice under the string (think a fraction of a mm) to melt and the string sinks through it. Once it sunk the small distance, the ice reforms above the string and the pressure melts the next fraction underneath. After anwhile the string will have cut through the ice entirely but the ice will not be cut in half! I suppose you could see your jaw doing the same. Giving in a little under pressure and letting your teeth move a fraction, while closing the fraction of the hole that is now created. After two painstaking long aganozing years your teeth have moved and your jaw still holds on to them.",
"I don't have braces, but I would imagine it's because the changes they induce are so gradual that your teeth/roots/gums have a chance to get used to the changes, and grow back in around the teeth... (?)",
"My dentist told me she could see bone loss (lower jaw) on my X-Ray and said it probably was from wearing braces.",
"Bracework does reduce the length of your roots , that's one of the reasons they do x-rays to determine if you're a good fit for braces. If your roots are already short you're better off keeping your crooked teeth rather than shelling out for straight teeth that will then fall out in a couple years time."
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9nkm6s | How do servers that provide accurate time actually work? | NTP (Network Time Protocol) servers, something we all trust, how do they actually work under the hood? Was the time just set manually and we trust that? If so, wouldn't it be a huge problem if all of them went down at once (hypothetically) and we couldn't recover anything? If not, what methods are used for ensuring that it's as accurate as possible at all times? | Engineering | explainlikeimfive | {
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"The first question is how accurate is accurate? Do you need accuracy within milliseconds? Most servers are run by institutions with an atom-clock and they're directly hooked up to it. Could you manipulate it? I'm sure you could. But what would the point of that be? There are other systems that really require an accurate time. For example any kind of positioning system such as GPS. Since those are synced as well, you can always get the accurate time from these satellites as well. But back to your question: there are thousands of time servers. I still remember times when it wasn't automatically implemented into windows and you could install atom-clock software to pull the time from any time server you like. But I mean, like I said above, theoretically it would probably be possible to change them. But it would be insanely difficult. By the way: the atom-time isn't only distributed by time-servers but also in other ways, such as long-range antennas for radio operated clocks. The distance can be a few thousand kilometers for those."
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9nnw9f | Hydraulics and their role in airplanes | From my understanding it's a liquid that is pumped round the plane to move things like the aileron. How does a liquid do that? Could someone explain the whole system from the movement of the yoke to the movement of the aileron/elevator? | Engineering | explainlikeimfive | {
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"The hydraulic system is simple in theory. Liquids, like oil or water do not compress when they are under pressure. This means you can fill a hose or metal pipeline with oil. You apply pressure on the oil at one end, and the other end will feel the same pressure. This means you can transfer pressure over long distances through a pipeline. In an airplane, the pilots controls, like the control stick or the pedals are hooked up to a device (master cylinder or pump) that converts the force or movement of the pedal / stick into oil pressure in a tiny pipeline. This little pipeline can bend and turn through all the nooks and crannies of a plane's frame and deliver that pressure wherever it needs to be. There's a device at the end of the line (slave cylinder or hydraulic motor) that converts that pressure into force and/or movement to operate a device like an engine throttle, or flaps, or brakes etc. Finally, the shape of the master and slave cylinders make a difference. They can be designed to amplify the pressure or force, either through their relative size, or by using electric or pneumatic boosters. This allows a small force from the pilots controls to be converted to a bigger force at the device, if needed.",
"Originally they had levers and wires to push and pull, connecting the pedals and yoke to the wing and tail surfaces. Then they used hydraulics, because oil (or any liquid) doesn't compress, so when you push the pedal it pushes the oil all along the pipe and the piston at the other end can push the wing surface. And nowadays they can also use electronics / motors; push the button and a motor pushes the wing surface. Hydraulics are used in brakes and power-steering in cars, in various industrial machines (bulldozers, etc.), and in airplanes and other vehicles. The advantage of hydraulics is that if you already have an engine that provides main power to the car or airplane or whatever, you can attach a hydraulic pump to the engine and \"borrow\" power from it, so you can gently touch your brake pedal, and the engine power will compress/pressurize the hydraulic oil and deliver much more power to the brakes or to the wing surfaces than your weak foot could achieve. The physics equations for how liquids behave when subjected to pressure are based on [Pascal's Law]( URL_0 ).",
"> How does a liquid do that? Most liquids are very difficult to compress very much. All the weight of the water above the water at the bottom of the ocean only compresses it by less than 5%. What this means is if you push on fluid in a container without gaps then it pushes out on the walls with the same force. Rather than trying to convey physical force through levers you can instead run a sturdy hose to a mechanism and actuate it with the pressure of the fluid, which is the basic idea behind hydraulics.",
"Really short answer: The same way it works the brakes in your car. When you push on the pedal, you're pushing a piston into a cylinder full of oil. That forces the oil to flow through a hose that forks out to the wheel assemblies, where it forces four pistons to move against levers that apply the brakes."
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9np4e0 | How does a plane become "invisible" to radar? | Engineering | explainlikeimfive | {
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"1. Coated in a radar-absorbing paint mixture. 2. Shaped in a way that bounces radar waves off in a different direction than their source, which works because most radar devices have the transmitter and receiver in the same place.",
"Radar is a series of electromagnetic waves sent out, when they hit something those waves return to the source and register. Usually aircraft don't just become invisible, but if it's a \"stealth\" aircraft, such as a F-117 Nighthawk, the angles of the aircraft are made to deflect those waves in other directions, either making the radar signiture significantly smaller or unseeable all together. EDIT: Holy crap, wasn't expecting gold! Thanks!",
"Radar basically works by shooting out radio waves at the sky. The radio waves bounce off stuff in the sky and sometimes, they bounce in such a way that they come back to the place where you shot off the original radio waves. You can do some fancy math and calculate some information (distance, velocity, direction) about the thing that the radio waves hit based on how many of the radio waves you get back and how long it took for them to bounce back. If you are an object and you'd like to not be seen by radar, you shape yourself so that you deflect radio waves off in different directions (but not back at the thing that shot the radio waves in your direction). Also, you can use special materials that absorb the energy of the radio waves so that even if they do bounce back, the radio waves do not have enough energy to be detected.",
"Simplistically, radar works sort of like a bat/dolphins detection system. It sends a pulse out, and listens for what bounces back. Large flat surfaces will bounce more back. So the aim of an 'invisible' plane design is to dilute, capture or distort the radar so it doesn't return to thr origin point and give away it's position or shape. This is also where the term 'under the radar comes from' as planes used to attempt to fly so low that the radar was scanning the air above them, they could hide behind objects that would block the radar and remain hidden for longer before detection. Hope that explains? Let me know if you'd like more :)",
"They are not invisible. Stealth tech works to minimize the radar cross section of an asset be it a plane, ship, ETC. They can still be seen by radar but the object appears smaller than a similar asset of the same size.",
"The reason you can see light things and not dark things is because they reflect the light back at you. Ordinary objects do the same with radar. If they absorb the radar rather than reflect it, we don't know it's there. Same with black holes. Light goes in, but never reflects back out. We have no idea what they look like.",
"Another way a plane can go invisible that people haven't mentioned yet is to fly really low. Many radars are line-of-sight. You need to be able to draw a straight line from the radar to the object without hitting any wall to find it. By flying really low, planes can hide behind hills, between valleys, and below where the radar is located.",
"In a secondary surveillance radar system, all one has to do is turn off/keep off the transponder and your plane will not be visible on ATC screens. Primary surveillance (like you'd imagine military radar to be) is like how everyone else is describing.",
"Think of detecting something with radar like throwing a ball at that thing. In order to know it's there, you have to catch the ball after it bounces off. If you throw a ball at something shaped in a particular way, the ball will almost never come back to you. Or it can be made out of something that just sucks the ball in, like jello. Or both."
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9nukdz | Why is it called clean energy if Nuclear Power creates Nuclear waste? | Engineering | explainlikeimfive | {
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"Nuclear power generates no emissions. There is waste, but it is contained at the plant, not released into the atmosphere like a coal-fired plant does with it's CO2 waste.",
"Nuclear plants create very little nuclear waste. A 1 GW nuclear plant will create about 20 tons of nuclear waste per year. Most nuclear plants have a capacity factor of 90% or higher so that 1 GW plant would make about 8 TWh so that's 2.5 grams of waste per MWh. It takes 120 kg of coal to generate 1 MWh of power. All of that coal turns into either exhaust gasses, soot, flyash(some of which is reprocessed), or bottom ash(all reprocessed). That means nuclear generates 1/48,000th the waste gasses and dust of coal. That's pretty clean",
"Because nuclear power doesn’t produce much CO2 if any at all, so it's “clean” as it doesn’t impact our carbon footprint and global warming, And yes nuclear waste is dangerous, but it does not contribute to pollution if properly stored (but we haven’t got around yet to doing that for the long term)",
"Besides what all these guys are saying, some nuclear plants are designed to use the nuclear waste of other nuclear plants as fuel.",
"So, um, what about CO2 generated from mining and refining fissile material? Honest question, not trolling here."
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9nvdh3 | does the infrastructure difference between downtown and the suburbs change weather patterns in the area? | Engineering | explainlikeimfive | {
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"Absolutely. Alot of urban and downtown infrastructure generates alot of heat. NYC literally has underground steam pipes pumping hot steam around. Blacktop roads also contribute to heat patterns, and of course dense urban roads cause more contributing than sparse rural roads. And not to mention the cars on those roads."
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9o37sx | what makes a phone vibrate? | Engineering | explainlikeimfive | {
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"In many cases it is just an unbalanced mass on a motor. [Just a motor with a half-circle of weight]( URL_0 ), and as the motor turns it pulls the entire mechanism around to vibrate whatever it is attached to. iPhones are a bit different with their \"taptic engine\" being basically a speaker except instead of pushing around a diaphragm to vibrate air they push a reaction mass in order to produce vibration in the phone. This allows much finer control to provide force feedback for things like touch interaction on the screen."
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9o451x | why do small planes crash so often with many mortally injured passengers? I thought even with a broken engine they can glide to the next bigger street or field? | Engineering | explainlikeimfive | {
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"Several reasons I can't think of: * Often flown by less experienced pilots * The aircraft is more likely to sit for extended times without use * Maintenance items more likely to be blown off * Checklists not followed as strictly * Often flown without copilot who might catch an error or help in an emergency That said, they're still not all that dangerous overall. The fact that they still make the news says a lot about how uncommon crashes really are.",
"In addition to the other reasons given here, I'll address your question about streets or fields: Streets are almost always a no-go. There are trees that grow over them, and power lines and bridges that cross them. Power lines are possibly the worst issue, since you wouldn't see them until it was too late. Reasonably speaking, you'd need a half-mile stretch of road where the overhanging trees are at least 50 feet away from each other all the way along, where there are no overpasses, where it's reasonably straight, and where the pilot has a good reason to believe there are no power lines. Oh, and there are no cars on the road. You do see small planes land on highways from time to time. That's about the only place you can do it. As for fields, those are usually the preferred choices, but you won't know until touchdown if there are any moguls or chuck holes that can catch a wheel and flip the plane over. That does happen a lot.\\* Other factors: commercial airliners are always multi-engine and can fly with one out. Most small planes are single-engine. If the engine cuts out on takeoff, there's really no option but to land straight ahead and there's no chance to look for a road or a field. If there's trees in your path, well then you're coming down in the trees. Even small twin-engine planes are dangerous this way, as they're typically designed to be *just barely* flyable on one engine. If your single-engine training is not up to date, then you're looking at a stall-spin accident. ---- \\*Anecdote: during my primary training, my instructor set me up with an engine-out practice over a field. As a good little student pilot I lined up beautifully into the wind (you normally land into the wind if you can). As we got close, my instructor told me: \"See how the field was plowed back and forth across our path? If we were to touch down on that, we'd flip for sure. It's much more important to land along the direction of plowing than to worry about the wind.\"",
"Big planes=pilots with many years experience. Little planes= pilots with few years experience",
"Small planes don't really crash that often. They're about as safe as motorbikes. Having said that, they do crash with fatalities from time to time. And there are two common reasons: - Flying into bad weather, with a pilot who's not qualified to fly in bad weather. - Getting too slow, especially while turning to line up with the runway, resulting in what's called a \"spin\", which can be impossible to recover from at low altitudes. In both of these events, the aircraft is likely to hit the ground whilst out of control, and that is why they end up with fatalities. In engine failures, as you said, fatalities are very rare, because the aircraft will almost always hit the ground the right way up, at low speed, while not turning, etc. Edit to add that all three of these (engine failure, spin avoidance, and a combination of both avoiding bad weather and what to do if you do get into bad weather) are covered during basic pilot training. Pilots are humans, and make mistakes, but there's nearly always an element of bad judgement involved in the kinds of accidents where people get killed.",
"Depends on the plane. Bigger planes like an A320 have a second engine so a single engine failure won't take them down, they also flight high(30k-40k feet) and have fairly high glide ratios(17 for an A320 or 737) Small planes like a Cessna 172 have just a single engine, fly relatively low (13,500 feet or less), and have a much lower glide ratio of around 9. In the event an A320 suffers a double engine failure at cruising altitude(we'll say 35k feet) it could cover a bit over 112 miles before reaching the ground. If a Cessna 172 experiences a single engine failure(far more likely) at its cruising altitude of 13,500 feet it can travel just 23 miles before reaching the ground. If you're flying over mountains or a forest, 23 miles may not be nearly far enough to get you to a suitable landing site."
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9o59tu | How does a clicking torque wrench work? | I cannot find any clear diagrams or explanations of how clicking torque wrenches work on a mechanical level. Can anyone explain (possibly with diagrams) ? | Engineering | explainlikeimfive | {
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"On mine, the handle flexes once the set value is reached. There is a spring of sorts inside which creates resistance to keep the handle straight. You adjust the amount of force needed to \"pop the spring\" and make the handle flex by lengthening/shortening the mechanism. The mechanism makes the sound when the spring piece flips or pops. I'm not sure if spring is the exact word.",
"Here's a site I found with not exactly an eli5 but seems to be clear: URL_0 the setting of the torque screw pushes the spring with more or less strength to the head of the tool. The head can swivel, and if too much torque is applied, it will \"skip\" basically causing the red cube in the picture to rotate and give way under the pressure. If you imagine pressing on this cube with more force, it will be tougher for it to skip, meaning the tool will allow more torque. If the spring applies less force, the cube will skip more easily and the tool is set for less torque."
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9o65wl | Wouldn't the best place to build a space elevator be on the North/South pole? | I thought, one of the reason that we haven't built a space elevator is due to the limitation of current building materials, not being able to withstand the speed in which the very end of elevator will be going. So why not build it on either pole? Wouldn't that be less stressful on the materials? | Engineering | explainlikeimfive | {
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"A space elevator is useful because it is held taught from the end being thrown out by the Earth's rotation. At the poles this won't happen. As such you would just essentially be building a really tall tower, which is *much* harder.",
"Placing such a project near the equator would enable the orbital momentum of a counterweight to keep the structure supported in space. Placing such a project on the poles would lose that benefit, and the entire weight of the structure plus reaction forces (not countered by deformation of the structure itself) would have to be supported by the base of the structure. So by changing that design, you largely turn an issue of a material not being able to withsrand huge tensions into a matter of surviving massive compression and a huge bending force.",
"Those would be the worst places to build space elevators. Space elevators rely on the centrifugal (yes, im gonna call it centrifugal!) force to throw them out and away from the planet."
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9o7gq8 | why do sinks have aerators | Engineering | explainlikeimfive | {
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"To conserve water so we use less, and to increase the surface area of the water you are using too hit more of the object you want to wash.",
"Aerators are used to bubble up the water so less water is used but it still covers a large enough area or has enough volume"
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9oh6d1 | How does a fuel pump and regulator work in an engine. (Mainly bike engine) | As the title says. How does it all work? I've tried to look on YouTube to see if anyone is explaining it and I can't seem to find anything. Edit: I get the general idea of it but why and how and what does it do/help do? | Engineering | explainlikeimfive | {
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"First of all, there are many types of fuel pressure regulators. Basically when close the pressure goes up and when open the pressure is released back to the fuel system. Example... Let’s say that A electric fuel pump is capable is pushing 80PSI at “X” volume.... the current “X” engine requires 45PSI to start and idle.... ——this is the tricky part—— The injectors used in this application have to be able to maintain a spray pattern in order to maintain the proper fuel ratio needed for that engine... if the fuel pressure is low the injector may drip instead of spray.... As the driver attempts to accelerate, the injector need to spray more fuel to increase the engine speed. now the fuel pressure will drop because the injectors are more “open” than in idle.... now the regulator “sees” the drop in pressure and attempts to compensate rising the fuel pressure to 45 or higher while the engine still under load; and once the load is gone adjusts back to 45PSI. Hope this help a little I just remembered, there are certain engines that do not use regulators at all but the fuel pump are fine tuned for the changes as needed."
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9ozl7d | Why does laundry sometimes get smaller when you wash them? | Engineering | explainlikeimfive | {
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"text": [
"Clothes are made out of stretched fibres. If you disturb the structure on a molecular level by adding heat, the tension in the fibres is released. This means they bunch up and shrink."
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4
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9oznzf | Why is the EPA allowing asbestos back into construction? | Engineering | explainlikeimfive | {
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"**They're not.** Not really. The regulatory changes in question are called **SNUR** - Significant New Use Rule. There are many applications for asbestos which *have never been illegal*. These applications aren't really in use currently, since it's still a liability. SNUR proposes to *make these uses illegal* unless they are approved at some later date. So, in fact, the EPA has *further restricted* asbestos usage, not allowed it. So what's the problem? Well, the seeds of SNUR started during the Obama administration, when it was intended to fully ban all asbestos uses. The regulation introduced this year is more limited. It includes a path to making uses legal. It also does not cover all uses; many products which contain asbestos fiber would not be covered, for instance, and so would remain fully legal. Additionally, there are concerns about how uses might get approval. SNUR explicitly states that existing scientific data on asbestos *will not be considered*. The body of scientific evidence linking asbestos to health issues is *huge* - some of the strongest stuff we have. Why is this happening? Well, the current administration is very far to the right. The American right-wing tends to value corporate freedoms above citizen safety.",
"The EPA no longer protects the earths environment. Unfortunately, it now helps businesses save/make money.",
"Probably because of the current US administration's deregulation push for a lot of things, which surprisingly coincidentally is good for Russia as they are the world's largest manufacturer of asbestos."
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9p5uku | Why can't a furnace and air conditioner be on at the same time? Wouldn't just one or the other start working based on the temperature? | Engineering | explainlikeimfive | {
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"It's incredibly inefficient to alternate between heating and cooling just to maintain a constant temperature, as the system would be running for much longer than if it were allowed to rest above or under the target temperature. Or to answer the above question, for air conditioning systems, the heating mode of the system uses the same equipment used for cooling, just runing to move heat in the opposite direction.",
"There are systems where you just put the control panel on \"auto\" and it activates the heating unit or the air conditioning unit based on temperature."
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9p9f9u | Why are tires filled with air instead of being solid rubber? | Wouldn't this be a solution to flat tires? | Engineering | explainlikeimfive | {
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"Pneumatic tires come with several benefits. The first is cost. The materials are more expensive than the manufacture. Weight. It is incredibly fuel inefficient to get wheels that heavy - as solid rubber tires, rotating. It's even harder to get that much weight to stop. And the steel wheel would have to be thicker, the breaks larger, or we'd have to go back to drum brakes on cars, which are themselves more expensive and dissipate heat less. All that weight puts additional strain on the drivetrain and breaking system. Traction. Since the tire is solid rubber, the face can't deflect - flatten out to increase surface area contact. This reduces traction. Wear. Such large and heavy masses, rotating at high speed, I'm not sure the tire could even hold itself together. Even if it can, what do you do once you wear off the tread? Do you put new tread on top? Do you cut new tread into the existing rubber, and wear the thing down to a nub like an eraser? Do you replace the whole wheel and recycle the materials? & #x200B; Pneumatic tires are also part of the suspension, since they act like a spring. The whole point of the suspension is to keep the rubber on the road, and make the ride comfortable. A solid rubber wheel, you would feel every rock, every crack, every \\*leaf\\*. And pneumatic tires can deflect around small surface imperfections.",
"Because driving a car with solid tires is a very shaky, unpleasant experience. Imagine rising a bicycle with no tires; it would be like that.",
"Don’t forget about the weight of a solid rubber tire. That would be a significant increase to an automobile. Rubber is pretty heavy.",
"You answer was covered pretty well (weight, suspension, expense, heat dissipation), but I thought you might appreciate this article: URL_0 Turns out - airplane tires are pumped up with more pressure than a car tire to increase its strength.",
"Some tires are solid rubber, it depends on the needs. They can carry greater loads and resist punctures. However, they are heavier, and provide less comfort (transmit more bumps). Additionally, they heat up more significantly, and flex less, which can contribute to faster degradation.",
"Why is nitrogen filled tires a better thing than air tires? Or was that just clever marketing I read at the auto shop?",
"We have solid tires we even use fluid filled tires in industrial settings where you need to use machinery to lift a lot of weight. But air is compressible, which means that they are softer riding and more comfortable to drive on."
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9pabn4 | How does engine angle in a “V” setup change the characteristics of the engine? | For example, is a V 90^o better for torque than a V 60^o ? Edit: I mean the cylinder bank angle, not the rotation of the engine itself. | Engineering | explainlikeimfive | {
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"None of the answers really do justice. There isnt any difference in the bank angle with regards to power or torque. Balancing the engine at different bank angles is different but doesn’t mean one angle is necessarily better/worse than another. The biggest reason is packaging. Fitting the engine in a specific sized engine bay will dictate things, the type of valve train changes the head size and the spacing requirements. This is why you see so many solutions in industry from inline cylinders, 30 degrees in some front engine V6’s. 60 degrees in others, 90 degrees in American style V8s and even 180 degree flat boxers. All different solutions to the packaging problem.",
"Not the power. But proper bank angle will make a balanced running engine vs unbalanced rocking engine. V8 are best at 90deg. V6 at 60degrees. Reason is that there is sideways momentum because the connecting rod is opposite of the crank counterbalance so there's a pendulum swing effect when crank is rotating.",
"The 90 degree angle is the most common and has the best balance, but the wide, heavy engine also needs an internal cam-pushrod-rocker assembly (and the low redline that comes with it) or a complex and heavy dual overhead cam system. Narrower angles do find use in some racing and specialty applications because they can be thinner and lighter, or even run on a single overhead cam. They're unbalanced though, and will rattle themselves apart over time without extra balancing mass."
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9pcrtw | How do toilet water mechanics work? | Alright, so you know how there is always a particular level of water in the standard Western toilet before you pee or take a dump in it? How, after flushing (long or small flush), does the water level stay exactly the same? What are the mechanics at the base of the pipes of the toilet that allow a perfect amount of water to leave it? Also another related question. How is the water in the toilet after a flush always clean (or clean looking)? I'm assuming that the previous piss/shit version of water does not mix (or mixes very minimally) with the new version of water. But how can that happen so efficiently? Sorry for ruining your breakfast. | Engineering | explainlikeimfive | {
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"Do you have a bendy straw? See if you can bend it into a J shape (or a U shape, really) and add water to it. You'll notice that the level of water on one side of the J (or U if you will) is always at the same height as the water on the other side of the J/U. & #x200B; That's what your toilet looks like (sort of). The level of the water in the bowl is the same level as the water if you were able to see past the hole in the bottom of the toilet bowl. It goes up, and then down. So when you add water to the bowl, it pushes the water through, just like if you add more water to the tall side of the J-shaped bendy straw, the other side of the J will have water flowing out of it. & #x200B; If the tank were too small (didn't have as much water), you would definitely have some mixing of the previous contents of the bowl. The amount of water in the flush matters for getting the old stuff up and out of the S shaped pipe that leads out of the bowl."
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9pcu14 | Why is so difficult to make a robot that walks upright like a human? | Engineering | explainlikeimfive | {
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"Not a robotics expert but consider how hard it is to balance an action figure. It’s a tall thing balanced on two very small things l. The reason you can stand is you have your brain constantly monitoring your relation to the ground and adjusting your muscles to compensate. That’s why you don’t just fall over in the wind, your body automatically adjusts. Doing this is hard for a robot. Consider just having it adjust because of an uneven surface, it can’t feel the different like we do so it it can’t adjust it’s foot so it falls over.",
"For starters, walking is a difficult problem for *humans*. Infants don’t learn the trick of standing upright and taking their first steps until close to a year; it’s usually another year before they can run semi-reliably. There’s a sixth (or seventh) sense most people aren’t taught about, akin to smell or sight or touch called *kinesthesia* or *proprioception* which we generally all possess. This is the sense of our own motion and the position of our own body. It informs us of our balance as we walk or stand, and it’s a vital component in how we accomplish either. Simply put, training or writing a robot’s software to mimic a human’s sense is extremely difficult, regardless of the task. Consider how long it took to develop even rudimentary voice recognition. Or facial recognition. Many of these problems require us to reverse-engineer how human perception works in a specific context. If we understood, or had a working theory for how human perception works *in general*, it might help solve these problems in developing autonomous machines. But if we knew how perception works, we’d have the answer to how *consciousness* works, and that’s one of the biggest current mysteries there are."
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9pgao1 | How car clutch works | Learn how to drive about 3/4 months ago, now i drive everyday to college. Still wondering how clutch works, watched some YouTube videos but still can't get it. & #x200B; EDIT: Thanks for the help guys, appreciate em | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"[Transmissions]( URL_1 ) have many gears, so they can convert the spins from the engine into faster or slower spins of the wheel. When you switch gears, you need to disengage some of the gears, and engage different gears; the gears disengage / engage by making contact with each other. So you can't have the engine put in all its power while you're trying to match gears, because the teeth of the gears will grind when they touch, if there's power being fed into the system while you're moving gears around. So that's where the [clutch]( URL_0 ) comes in. The clutch pedal disconnects the engine from the transmission box, by basically pulling it back and spacing it so it spins in air. With the engine spinning in air, you're free to try to align the gears to engage a new gear, then you let go of the clutch to apply engine power and get the wheels to move at this new gear ratio.",
"When you push the cluth pedal in, it disconects the fly wheel, or the piece that connects the engine to the transmition. Then when you change gears, and let the clutch out it engages that fly wheel to the transmition again and off you go."
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9pizh5 | How does a thermostat accurately sense the air temperature in a room when it's installed inside a small space heater that's generating heat? | Engineering | explainlikeimfive | {
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"text": [
"It measures the temperature of air coming into the heater which is at the temperature of the room in general, the heat exiting the heater generally has to go around the whole room to get back to the heater. Practically all heat transfer in a typical domestic setting is by convection, meaning the air *below* the heater is about as cold as anywhere in the room and the heat exits upwards. Some heater types use a non-trivial amount of radiative heat transfer, but providing the thermostat's heat sensor isn't in the path of this radiative heat, it's unaffected."
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9plqt7 | Why does water temperature change during a shower and how do old pipes make it worse? | Engineering | explainlikeimfive | {
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"There is only one pipe that brings (cold) water into your house, and then that pipe branches off to all the bathrooms, kitchens, hoses, etc. in your house. One of those branches also goes to your hot water heater. There is only one hot water pipe from your water heater that branches off to your kitchens, bathrooms, etc. When you're in the shower and someone flushes the toilet, they are basically stealing some of the cold water pressure that's running to your shower (because there's only one source of cold water and they are stealing part of yours). That makes it get hot."
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9pmhaf | Why is it that a 1200 watt toaster over can safely run in a house, yet a 1200 watt space heater blows fuses or trips circuit breakers? | Engineering | explainlikeimfive | {
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"As I said last time > This is a problem in your specific house. The circuit you're connecting the space heater to must already be loaded > If you run the coffee maker, toaster, and microwave at the same time you'll likely trip the kitchen breaker unless someone ran a dedicated circuit for the microwave If you plug in the space heater where you plug in the toaster oven I bet it'll run fine"
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9pp41s | Why aren't more buildings built into cliffs or subterranean holes? | Engineering | explainlikeimfive | {
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"There are a couple of problems building into the ground or cliffs. One of the main factors is that earth/stone is heavy and difficult to remove. Building such a structure would require all the same parts and steps as above the ground, but first you would need to remove the material in that area which is a big project in itself. You also need to keep the hole in which the structure is built clear which means reinforcing from collapse and keeping water out of it such as with pumps. With a cliff perhaps it filling with water is less of an issue but rocks falling on it from above or the entire cliff face breaking off and falling away is a problem. Now supposing you have such a structure built there are further detriments. One of course is emergency exits in the event of a fire; if you are underground it greatly limits the possible routes of escape or rescue. Ventilation in general can be a challenge as lack of fresh air or even toxic atmospheres from spills (ammonia from refrigerators, etc) can lead to injury or death. We haven't even touched on the aesthetic penalty of storing people in a windowless box; people resent being sent away to the basement and covet corner offices with windows on two walls, how do you think they will feel having an entire building underground? Add therapy to the costs associated with such a building plan. When all of these factors are against such an idea it is a good sign that other solutions are superior.",
"The answer is not as difficult as if might seem. Why remove the rock and then put the house in when you could just place the house on the ground? Why would you move several tons of rock, then build your skyscraper, rather than just building your skyscraper? Places with lots of cliffs are not really conductive to roads. Why make a road on a cliff when you can just make a road? In general, how does going into a cliff reduce the growth of cities? Who would want to live in a cliff, rather than, say, a house or an apartment in the city. People who want to live away from the city and use a car to get to work will live in a house, people who want to live in the city will live in an apartment in the city, and moving an entire city to a large cliffside is not as feasible as it might seem. Going deep underground is even harder. Aquifers, fault lines, cave-ins, and just the soil being unsuitable to the task are all major concerns, as well as the massive cost of the whole project. Then you have to make it livable for humans, as well as maneuvering the infrastructure to do so, and you have to supply air now."
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9pq18n | How does adding different gears make this wheel spin faster? | [The video in question]( URL_0 ) Can someone please ELI5? | Engineering | explainlikeimfive | {
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"Wow...lots of really wordy explanations here. Let's try for less... Big gears have lots of teeth. Small gears have few teeth. When the big gear rotates once, it spins the little gear multiple times, so the wheel spins faster",
"Imagine a giant gear with **12 teeth**, and you're standing at a point with a timer where you can observe each tooth passing by. If you were asked to give a rate of gear teeth passing by you, you'd probably say something along the lines of \"there are **4 teeth passing by me per second**\". You're a brilliant 5 year old and somehow learnt multiplication before the education system would teach you, and deduce that it then takes **3 seconds** for the gear to make a full turn. Now, you can picture how gears work. Their teeth have to mesh completely for it to work, which is the whole basis of gears. So if their teeth are meshed, they have to move at the same rate. Let's use the previous example of a 12 tooth gear spinning at 4 teeth/second. But instead, it's connected to a gear that has **8 teeth**. Because they're meshed, they have to connect, tooth for tooth. So in that rate, the teeth amount passing by has to be constant. So that means the 8 tooth gear is spinning at 4 teeth/second as well. But since it has less teeth, it makes a full revolution faster than the gear with more teeth. Your smart brain deduces that it makes a full rotation in **2 seconds**. Thus, it rotates faster. TLDR: If two gears are meshed, the bigger gear will spin slower, and the smaller gear will spin faster, as well as anything attached to it.",
"That's the whole point of gears with different ratios. The teeth on each gear engage 1:1, each tooth pushes a corresponding tooth on the other gear. So if one gear is small and has 5 teeth, and the other is big and has 50 teeth, then the ratio of turning will be 10:1. And the ratio of torque (how hard it is to turn each gear) will be 1:10. Gears trade speed (of turning) for torque (how hard it is to turn). And that's how they're used. If you have a crane, you have a motor that turns very fast, but maybe is not that powerful, but with some gears you can trade speed for torque/power and (very slowly) the crane can lift 1 ton. If you have a car, the engine turns somewhat slowly, but has 300 horsepower, so with some gears you trade the horsepower for speed (a horse can go 20-30 mph, race cars can go 200 mph). [Simple Machines]( URL_0 )."
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9pvgd2 | the difference between piston plane engines and car engines | As far as I understand, they work similarly, so why are plane engines more complicated to start / more expensive / require maintenance more often / etc. | Engineering | explainlikeimfive | {
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"if car engine breaks down, you putter to side of the road and call AAA. & #x200B; if your plane engine breaks down, you fall out of the sky and call FAA. & #x200B; if you maintained your car engine at same level of your plane engine, you'd be doing inspection every morning before leaving for work. oil changes every month, certified mechanic inspections every year."
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9q418n | How does pulling up the knob on a bathtub faucet make the water come out the shower head? | Engineering | explainlikeimfive | {
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"text": [
"When you lift the lever ..inside the faucet is a flap. The flap.closes making the water move up the pipe. If you have a small stream and put your hand in front of it..the water goes where there isn't a hand . Same thought"
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9q47im | In most machines and appliances, why does an engineer choose, for example, a Philips head screw for one component but a flathead or hex for another? One would think that what matters are the specs of the screw itself rather than the head. | Engineering | explainlikeimfive | {
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"Philips are designed to \"cam out\" once a certain torque is reached. Flat heads are a bit more difficult to use drills or automatic equipment on, meaning they're likely installed by hand. Flat heads are quite difficult to really torque down, forcing operators to not crank it like arm wrestling a gorilla. Hex can take more torque and may be used for applications requiring more clamping.",
"The heads all have different purposes. Phillips heads keep you from over tightening a screw as the bit will pop out. Hex and torx are both quick for a machine to use, and torx heads will let you use high torque(its kinda in the name) without stripping the screw As for why there may be different screw heads in a product, its actually more about manufacturing than design If I've got a product that has one piece held on by screws that need to be at least 1\" long or they won't hold, another held on by screws that must be less than 0.5\" or they'll hit something they shouldn't, and a third that should have a 0.75\" screw torqued down to 10 in-lbs then i have some choices. If I make them all the same head then there's a chance that someone mixes the screws and puts a 0.75\" screw in the first piece and it strips out or a 1\" screw in the second piece and damages the assembly. If I give you a 1\" Phillips, a 0.5\" T5 Torx, and a 0.75\" T8 Torx and the only screw gun at station 1 has a Phillips bit then even if you get some of screw 2 or 3 in your bucket you can screw it up because you don't have the ability to put it in the hole This is called Poke-Yoke and helps idiot proof the production line. If two pieces can be used interchangeably then they should be identical, if they shouldn't be interchanged then it should be impossible to do so.",
"One reason is to stop curious hands from getting electrocuted; weirdly shaped bits can stop you from opening a power supply if you don't know what you're doing, for example. Another reason is simply mechanical, some heads are better suited to be screwed in with more force and without stripping. This matters on an assembly line where you don't have time to go slow.",
"There is lots of advantages and disadvantages to different screw heads, but don't go too hard looking for deep reasons for literally every single choice. It's a mix of carefully considered technical choices and just practical stuff like \"the tools we already had work with this screw so our next product will use that too unless we have a really good reason to switch\". Some choices are made because a specific screw needs a specific behavior and some are made because 'our supplier said they could get us these at 50% off and they work for what we need so we did that\""
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9q4lyl | What's the use of the tail exhaust on a commercial airplane? | Engineering | explainlikeimfive | {
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"Inside the tail is a tiny engine called an Auxiliary Power Unit which provides electrical power when the main engines aren't running. The \"tail exhaust\" is just the exhaust for the APU.",
"It's the exhaust for the plane's Auxiliary Power Unit (APU). The APU is a small gas turbine that provides auxiliary electrical power to the aircraft when the main generators powered by the engines are off.",
"Larger airplanes often have a auxiliary power unit (APU) that is located in the tail. In a jetliners it is a small gas turbin that is in principle a small jet engine. It is a small engine to provide energy when the large engine is operating like when the airplane is on the ground. It provide electrical power, air for engine starting, and air-conditioning. Airplane have batteries but the the small for emergency in the air or to start the system. The cant be used so operate a airplane for a long time on the ground w. So you have power connected from a external source, the main engines or a APU. You can't start the large jet engine with battery power but you can start the small APU. With the high pressure air from the APU you can start a large engine. Before you had a APU jetliners required ground based equipment to start and that is a problem on small airport. So with a APU you can operated independently of ground power. Air conditioning on airplane need compressed air so you need the large engine or the APU running to keep a large airplane cool. Even if it was a option to use the engine they are inefficient if you only need a small amount of power so using a APU reduce fule usage a lot."
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9q8ntz | Caching-Write through policy | Can someone explain where is "Write Through" policy used in Caches? Writing to Main Memory every time when written to cache doesn't seem to be a good option. If Write Back does a decent job, why bother having this policy at all? | Engineering | explainlikeimfive | {
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"There are some demanding uses of computers, where *any* data loss is intolerable. Write-back writes only when necessary or after some interval, but if the power goes off in the meantime, what was in cache is lost. Imagine it like autosaves in games where every 10 minutes it saves. What you did since the last save might be lost. Now in things like banking, data loss of any sort could mean big trouble. Imagine if your direct deposit check was in the middle of being updated in your account and the bank lost power. Might have just lost that transaction! Write-through is more demanding of computer resources, but it's okay because the reduction in potential data loss is more important."
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9qgpwt | How is power restored after an outage caused by damaged poles or power lines? | Near my home this morning, a car crash occurred at an intersection, and a power pole was hit and split in half. The power company said there were power lines in the road. This caused a power outage to about 1300 people. After about an hour, crews had restored power to those affected by the outage, but they said that they still needed to repair the broken pole and equipment. If they didn't fix the pole yet, then how was the power restored? | Engineering | explainlikeimfive | {
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"They fixed / replaced the wires that were broken, and strung them up between the poles that were left intact, with perhaps a temporary pole or suspension wire to hold them in place until the full sized permanent pole is ordered and placed into the ground. A residential area is also a \"grid\" (that's why it's often called the power grid), which means that there are multiple connections available and they can re-route the electricity much like they re-route cars to go on alternate roads until the main road is re-paved or whatever.",
"So there are a 2 ways that this can happen. 1. Temporary line failure- when an object is obstructing the line such as a branch falling on it or something like that. The line itself is not immediately damaged and service can be restored once the obstruction is removed. Newer power lines have special sensors that can shut off the voltage in a line section if this happens, so that the line doesn’t burn out. 2. Permanent failure- when the line itself is damaged and must be repaired or replaced to restore power to the line. Caused by the line burning out or being torn down in a storm. This method of failure will take longer to remedy. However, in both cases power is restored by rerouting power from other lines. It is easier to picture from a drawing but I will do my best here. In general, power lines are very redundant and can be routed in many different ways to accommodate different electric loads. Think of it as train tracks with the power being the trains. At any given time, the tracks are oriented so that each track is continuous, but the tracks can be realigned at certain junctions to allow trains to transfer to a new track. If a section of the track is damaged, anything farther down that track can not be reached by a train. But then the track next to it is switched later on down the line so that trains from that track can transfer and reach the original destinations of the first track. By rerouting the trains, only the damaged section can not be reached by the trains. The tracks will stay in this orientation until the track is fixed, then it can be returned to normal. In your particular case, your power was likely not directly attached to the damaged section so you were able to receive service from a different power line that had been switched. There were probably some folks who had to wait until the power line was fixed because they were directly attached to it."
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9qibjc | What stops the flame travelling back down the gas pipe on a gas hob? | Engineering | explainlikeimfive | {
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"there's isn't any oxygen in the pipe, it's 100% gas so it won't burn. if you held a match far inside the pipe the flame would go out.",
"For one, there typically isn't oxygen in the pipe, so there can't really be an explosion. *However*, there is also typically a device installed on the line called a flashback arrestor, which ensures that gas only travels in one direction, and that shocks, flames, and high temperatures don't travel back up the line."
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9qiwvi | why do some countries have such superior internet speed and connectivity compared to others? What are these speeds based off of? | Engineering | explainlikeimfive | {
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"Network Admin/Engineer here. It's hard to be certain about specific countries because I don't know how their internet is set up. What I can answer is how various speeds work in general. Essentially internet in high density areas is faster because of the framework that is built. Imagine it like a plumbing system. An apartment building has many pipes filtering into a single big pipe. This big pipe is the internet and the little pipes directing your poop is your network connections being filtered and forwarded into the internet. The internet is kind of like this magical cloud that people tap into but it's not *really* there. What is really there is all the wiring and routers and switches directing traffic in various ways. An area like a city has a very big network of cables directing packets to even bigger centralized data centers that host and store data from the internet. An area like a farm, the country, or less developed countries have further to send that data. The easiest way to explain that is if you have a router and you have a computer plugged into it with a 6 foot cable it will have a faster connection than if you used a 100ft cable. It might not be that noticeable when you are on a LAN but imagine being miles away from the data centers and you can see why it's even slower. Some countries might have to travel via satellite or hundreds or even thousands of miles away from the host connections. This gives you entire countries with slower connections. And finally just because I feel like this might also be a follow up question - why can I connect to the same website in Europe and it's just as fast in America if these websites are being hosted in other countries? Well bigger companies that can afford it actually have servers in multiple countries hosting the same content to have faster speeds in other markets. So something like Blizzard or Valve will have their sites hosted in multiple countries and even though you are still going to URL_0 their servers have packet filtering set up to automatically pick the faster server for you based on your IP address.",
"I can't speak to other countries but here in Australia our internet speed is largely based on how fast our network technician can turn the crank on the internet box. Speed varies generally based on forearm strength of the operator. Sometimes I can load any webpage in under 12 minutes which is why the majority of my salary gets funnelled into paying for this amazing service.",
"Answers so far discuss latency (time for a packet to travel between A and Z). Internet speed is more about bandwidth though (how many packets you can get from A to Z in a given amount of time). Some countries have prioritized getting fiber installed to homes and getting competition on that fiber or getting a municipal or other ISP that answers to the users instead of to shareholders. There are pockets of that in the U.S., but in much of the country it's large ISPs that squeeze their customers for every penny, have captured much of the government that could regulate them, and only upgrade when forced to."
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9qk271 | Why is airplane fuel measured by weight instead of volume? | Engineering | explainlikeimfive | {
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"Many aircraft are limited by their “maximum gross weight” for takeoff and/ or landing. It makes the math easier when you don’t need to multiply the gallons by the specific weight of the fuel / gallon. Make sense?",
"Volume doesn't really impact the flight capabilities of the aircraft; any fuel it is carrying will obviously fit into its tanks, and it isn't like the aircraft can swap out fuel volume capacity for anything else. How much weight the aircraft is carrying is important though because for example it impacts how it can safely land, or how much fuel it burns to stay aloft. So weight is much more useful and relevant than volume.",
"Aircraft are regularly weighed because their weight affects the aircraft's performance, especially during take off and landing, the aircraft needs to be within the Maximum Take Off Weight allowed for that specific aircraft. The fuel is measured into the Take Off Weight, and it is much easier for the fuel to already be in weight units. Weight is also a better unit of measure when dealing with fuel because it is an indication of mass which is more relevant when considering it's chemical energy. And finally, volume changes as temperature changes, but weight will not, and therefore weight is a more accurate measure of how much usuable fuel there \"really is\".",
"Volume changes with temperature. By using weight you can calculate everything better, from mass & balance down to fuel flow and therefore endurance, fuel required, everything pretty much."
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9qlmhx | How do astronauts aboard the ISS always have an oxygen supply? | Engineering | explainlikeimfive | {
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"They have some plants which helps, but they're not really there to generate oxygen. Most of oxygen is generated by electrolysis, take water and break into hydrogen and oxygen. Collect the oxygen and vent the hydrogen into space. resupply runs bring water along with other cargo. And water is reclaimed from the air and urine of astranauts.",
"With the a carbon dioxide removal system (CDRA) which removes CO2 from cabin air. When we exhale we release CO2 and a reduced amount of oxygen. In a closed system (like the ISS), CO2 builds up as the astronauts exhale. However, the CDRA \"scrubs\" the CO2 from the air and helps keep oxygen in the ISS at a sustainable level.",
"Through electrolysis of water. The station's solar panels generate large amounts of electrify, which when passed through water, splits it into hydrogen and oxygen. The hydrogen is vented into space, and the oxygen is used for breathing. Resupply spacecraft regularly deliver water. There are also chemical oxygen generators that can be used in emergencies."
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9qmo50 | Why do car companies build engines with overhead cams instead of with pushrods/overhead valves when there does not seem to be any benefit for the added complexity? | Engineering | explainlikeimfive | {
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"\"The main disadvantage of an OHV design is that it's difficult to precisely control the valve timing at high rpm. The reason for that is the higher inertia caused by a larger amount of valve train components (lifter-pushrod-rocker arm). This means, that an OHV design is better suited for V8 or larger engines, where large engine volume offers higher torque at lower rpms. It's also technically more difficult to install more than 2 valves per cylinder, or implement Variable Valve Timing - something that could be easily done in a DOHC engine.\" \"A typical DOHC engine has two camshafts and 4 valves per cylinder. One camshaft operates intake valves that are installed on one side, while another camshaft controls exhaust valves on the opposite side. With this design, camshafts can be installed further apart from each other. This allows the intake valves to be at a larger angle from the exhaust valves, which results in a more direct air flow through the engine with less obstruction. In other words, a DOHC engine can \"breathe\" better and thus produces more horsepower out of smaller engine volume. \" \"Technologies like Direct Injection, Variable Valve Timing and Variable Valve Lift can be easily implemented in a DOHC engine, further improving fuel efficiency.\" Taken from source"
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9qnsz1 | Can a mason jar valve work for something like hyperloop? | cars, trains compress air when traveling, could we use something like a mason jar valve so we release that pressure thus having lower than atmosphere pressure in a vacuum tube? | Engineering | explainlikeimfive | {
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"The mason jars works as a one way valve. If the pressure inside the valve increases above ambient pressure the air is released into the atmosphere so that the pressure in the jar drops to ambient pressure. However if the pressure inside the jar drops to under ambient pressure the valve seals shut. Normal tunnels do not usually have these types of one way valves. There are usually ventilation shafts in the tunnel which will equalize the pressure. So when a car or train goes past the air will first rush outwards and then rush back inn when the train have passed. If you were to use a one way valve in the ventilation shafts then the valves would shut as the train passes. This does keep the pressure behind the train at slightly lower then ambient pressure. This will slow down the train and create extra drag as the vacuum sucks the train backwards. And as the tunnel is not sealed the air will just find other ways to enter and the pressure will equalize when the next train comes along. & #x200B; The hyperloop concept is a fairly old idea that people have been working on for decades. The idea is to seal the tunnel and make it into a vacuum chamber so that you have lower air resistance. There have been small scale \"rocket sled\" experiments but nothing bigger. There will likely be some one way valves to prevent the pressure from going high in a catastrophic event. However during normal operation the pressure in the tunnel will always be far bellow ambient pressure in the air. So the one way valve will always be shut."
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9qob4d | How do escalators maintain the same speed regardless of how many people are on them? | Engineering | explainlikeimfive | {
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"Whenever electricity is involved it can't be truly ELI5 but I'll try by skipping over the details. I'm a winder electrician, which means I build motors and motor systems. They are driven by induction motors that always turn at a constant speed linked to the 60Hz frequency of the electric lines. Every time the electricity changes polarity, the motor moves on to the next magnetic pole (simplified). Typical speeds are 1200/1800/3600RPM for 6/4/2 pole motors respectively. As the load increases the motor will draw more power up until it stalls. Until then it won't slow down much. Real speeds are actually a bit lower due to \"slip\" of the rotor but true synchronous motors do exist and are used as generators and in heavy industry. The only motors that vary in speed greatly due to load are the brushed sort usually found in tools and small appliances. For reasons I won't go into, they are not linked to the frequency of the power, and can often run on both AC or DC power.",
"In a motor torque is proportional to current. If you need to lift more people, increase current to increase torque. Add a sensor to measure motor speed. Use a small computer to control current based on desired speed. Edit: Many are saying you don't need a speed controller for AC motors on an escalator, sweet.",
"There is a motor always running at the same speed ~1800 rpm attached to a gearbox to slow down the rpm's and create torque. The motor is large enough to carry a fully loaded escalator. It will just draw more amperage when fully loaded than when empty.",
"The real question is, why aren't escalators faster?",
"It is using an Alternating Current motor that runs at a constant speed, the speed is directly related to the frequency of the AC power, 60 Hertz in North America. The motor is sized with enough torque for full load. Running it at no-load it will run at the same sped as full design load, just drawing much less current (power) from the source. Kind of like pedaling a bicycle in a low gear on flat ground, really easy to push the pedals. As load increases the speed will remain the same but the motor will draw more current, like pedaling up a hill. If the load exceeds full design load and the motor should trip the Overload Protection device. like a hill too steep to pedal up, you slow down and stop. The motor should trip the O.L. long before it gets to the point of slowing down. Not exactly for a 5 year old I think.",
"URL_0 I'm a more visual learner, and just happened to watch this yesterday. You can view the type of chain system that drives the entire stair carousel.",
"Heavy-duty synchronous motors. They run at a constant speed, but draw more power as the load increases. The older ones? Those escalators probably used governators. Seriously. A \"governor\" is a mechanical device intended to adjust the speed of a motor that it is constant.",
"The escalator is designed such that it has enough power to carry way more people than can possibly fit on it without slowing down. Therefor, the question is really, why doesn't it speed up when less people are on it? It is because the motor and gears can spin only at one speed. So when less people are on, it just does so without using as much electricity."
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9qqize | Who are those guys with the yellow tripods and what are they measuring? | Engineering | explainlikeimfive | {
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"They are land surveyors and typically the tripod holds a laser. There is another guy at the other end of what they are surveying with either another tripod or a pole with measurements on it. They are checking slope for the given distance by shining the laser at the measurements and reading where it hits.",
"They are surveyors. They're measuring distances and differences in height. Two common reason, for example, is to determine property boundaries. Hidden in many areas are marker points as a \"starting line\" for surveying, or they may use natural features or something else that isn't likely to move or change. A local courthouse or other government building contains instructions on what the exact boundaries of each plot of land are. By working from a reference point, surveyors can measure and mark the exact property lines for things like fences, or if land was purchased to build a new highway (so they don't go off into land they weren't planning on or something), and so on. Differences in height can be useful when planning a road or railroad track or something, to make sure they can properly build the grade and that whatever traffic is on it can actually use it.",
"Land surveyors! The go out and double check property lines and areas where to and where not to build houses and other structures. I'm sure someone will come a long with a much better detailed answer, but that's a start anyways :p",
"they're survey crews. They're basically measuring the land - how far from point A to point B and their difference in elevation. This allows engineers to build detailed maps of an area for use in building roads, bridges, drainage systems, building foundations, etc."
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9qrqm7 | Why wheels of some wheelchairs are slanted? | I seen slanted wheelchair frequently in Para Olympics. | Engineering | explainlikeimfive | {
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"The slant allows the wheel to have a wider base while still maintaining a close grip at the top for the user. This prevents the player from falling out of the chair or flipping as well. (This is in most instances; watch wheelchair rugby highlights) I believe the design also allows for quicker and more fine cuts and turns. I took a class last semester that involved disability sports."
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9qxmiu | Can we make the switch to 100% sustainable alternative energy sources without nuclear power? | Engineering | explainlikeimfive | {
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"The main problem with solar, wind, and tidal is that the energy is not always available exactly when you need it, which is quite a big problem. Hydro is much more stable, but environmental agencies prevent most large dams from generating as much power as they'd like to. These are all considered \"peak load\" energy sources, which help to offset seasonal energy demands for things like cooling and heating. Nuclear power is much more reliable and extremely safe, aside from the ore mining (which is extremely dangerous). It, as well as things like coal generators, are called \"base load\", and it's a good idea to run them pretty much year-round. Maybe in the future, we'll have so much power infrastructure in place that cloudy or windless days won't be as devastating to solar and wind generators, and we can make the transition towards those more fully. But until then, we're stuck with at least a little bit of coal or nuclear power."
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9r0jt4 | Why can you stop in an automatic car without putting it in neutral but if you try in a manual the engine will die? | Engineering | explainlikeimfive | {
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"In an automatic car, the engine is connected to the drivetrain using a torque converter. It's essentially a casing that contains fan connected to the engine submerged in a fluid. On the other end is another fan connected to the drivetrain. When you step on the gas, the fan connected to the engine will cause the fluid to swirl which pushes on the other fan, this causing the wheels to spin. When you're idling, the fluid can't impart enough force in the drivetrain side. It does push a little bit, which is why your car creeps forward when in drive. For a manual transmission, the engine is connected to the drivetrain via a clutch. When you engage the clutch, it makes the engine and the drivetrain spin at the same rate. If you are stepping on the brakes, you are preventing the engine from spinning as fast as it wants to, so it stalls.",
"You can stop in a manual transmission car without putting it in neutral, you just have to engage the clutch. The reason why you don't have to do anything in an automatic is because the \"automatic\" part of \"automatic transmission\" is automating the operation of the clutch and gear changes, so when the car is braking, the clutch is automatically engaged to prevent the engine from stalling.",
"Cars with automatic gear boxes have a torque converter where the clutch would be in a car with a manual gear box. The torque converter allows the engine to spin even though the gears in the gear box is stationary. It transfers the torque without a direct link between its input and output. This does mean that there is some energy loss so that an automatic car is not as powerful as a manual car. So in a manual car as you need to actively change gears manufacturers install a clutch which is more efficient then a torque converter but require the user to push a pedal to activate it. You do get vehicles with a manual gear box and a torque converter or a clutch and an automatic gear box but these are very specific use cases which you normally will not see except on very specialized equipment.",
"This video explains it well if you have 12 minutes [Fluid Coupling: Principles of Operation (1953)]( URL_0 )",
"Most automatic gear boxes uses a torque converter that is a hydraulic and decouple the engine from the rest of the gear box at low speed. A manual gear box used a mechanical clutch to decouple the engine from the gear box. So you need to press down the pedal manually. Both are used when you start the car so you slip on the clutch or use the torque converter when you start the car and the engine is faster then, A torque converter can lock to the rest of the gear train when you are at higher speed. There are other automatic gear boxes design that used clutches that is engages automatically."
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9r4td5 | How does a bomb suit protect a bomb technician during an explosion? | Edit: Thank you all for the responses. They very very clear! | Engineering | explainlikeimfive | {
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"There are three big dangers that typically come from a bomb explosion: heat, shrapnel, and shockwave. A bomb suit is designed, as much as possible, to protect from those three things. It's got thick layers of padding and kevlar to keep shrapnel from the bomb from piercing and harming the wearer. It's thermally insulated so that heat can't get inside the suit and burn the wearer. And it's got layers of material with a high acoustic impedance and soft foam layers to keep the shockwave from exerting too much pressure on the wearer. The shockwave is the biggest danger to the wearer if they're close to the bomb, and the hardest to protect against. A light suit can protect very effectively from shrapnel and heat, but might not be able to withstand a close-range shockwave that could still cause a lot of internal damage. Heavier suits are more able to withstand that pressure, but it's the hardest factor to protect against.",
"The bomb suits are not magic force fields. A large enough bomb close enough to the guy wearing it will still result in injury or death. However, bomb suits do offer a large degree of protection. They protect from light fragmentation and heat as well as reducing the blast overpressure experienced by the wearer. In addition to the testing these suits have undergone, bomb techs have been blown up while wearing them.",
"Thick kevlar and padding both help to stop shrapnel and dampen the shockwave, but not by much. Chances are if you're close to an IED a bomb suit wont help much",
"If they don't work, do you get your money back? & #x200B;",
"I worked with EOD. The suits don't do a whole lot of shit, unless it's a poorly made IED. If it's a 155mm round, it's over no matter what. If it's a pipe bomb, you can walk it off. They use robots more now, but guess how often those robots work? For $200k you'd think it would work. A lot of the times, they just go pick up said IED, and then go blow it up in another place(after they've traced the detonating device). I've seen and done this with them. The suit stays in the MRAP unless the CO tags along."
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9r729w | Why does an Airfoil (cross section of wing) have blunt edge face the front instead of the sharp edge. | Engineering | explainlikeimfive | {
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"In general, for subsonic flight, more lift is created by a greater variation in thickness. Having a rounded leading edge allows for the airfoil to have a greater variation in thickness. A lot of other things also effect the lift, such as camber and viscosity, but we'll ignore those for now. However, airfoils you see on a supersonic aircraft, such as the F-104, have a sharp leading edge. This allows the shock wave to be attached to the wing in flight instead of forming a bow shock in from of the wing."
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9r90oy | How do cars in the USA accept petrol which is a lower octane level than 95? | Engineering | explainlikeimfive | {
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"It's two different measurements. In Europe they use a measurement called \"Research Octane Number\", or RON. In the USA they use a measurement called \"Anti-Knock Index\", or AKI, which is the average between RON and another measurement called \"Motor Octane Number\" (MON). MON is usually about 8-12 lower than RON, which makes AKI about 4-6 lower than RON. Additionally, in higher elevation areas you can use a lower octane because the engine draws in less air.",
"Engine performance is TUNED according to the market that is sold in. Your car's ECU (Engine Control Unit) manages your vehicle's performance according to a fuel map. If you had to take your car over to the US and put in regular gas you are likely to noticed decreased performance as well as higher fuel usage because your car's ECU will be set for a higher octane number. However when filling with premium your car should run as normal. But yes it should be noted that because of the method of Octane rating AKI as used in the US is 4 to 6 octane levels lower than equivalent petrol per the RON rating however regular gas in the US is 87 Octane (AKI) which still works out to be lower octane than regular unleaded petrol at 95 Octane (RON).",
"What would be a 95 in the US?"
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9raczt | How do they isolate the heating coils in a toaster? | I was just looking at my toaster, and the coils run through what appears to be tin, or some type of metal. Wondering if they are isolated them from the rest of the metal, or just higher resistance than the rest of the metal and so more of the heat centralizes there. | Engineering | explainlikeimfive | {
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"Most toasters use [mica]( URL_1 ) sheets as the insulating material. Mica is an electrical insulator and can withstand extreme heat: URL_0"
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9ratsg | How does a Total Containment Vessel, or 'Bomb Truck', work? | Other than just being 'really strong', how are they designed to withstand an explosion in such a confined, sealed space? | Engineering | explainlikeimfive | {
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"Their main goal is usually to contain the shrapnel that an explosion would cause. They do this by disappating the energy of the explosion and shrapnel. On the inside there are layers of materials like kevlar that catch small debris and layers of metal to stop/break up larger debris. The outer shell of metal being the last layer to stop anything that gets through. All these layers spaced out is what tends to make these devices large and bulky. They also can't completely seal. An explosion creates a lot of hot gases that want to expand and containing the gases leads to big shockwave and more debris so the bomb vessels would need a way to vent gases so they don't become the bomb themselves. (Although I'm not sure how they deal with the situation of a biohazard bomb)"
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9rbe4c | why do train tracks have horizontal slats when the train wheels only use the side parts ? | Engineering | explainlikeimfive | {
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"Beyond acting as a spacer, they anchor the rails firmly inside the gravel. Otherwise trains wouldn't move forwards but just eject rails behind them.",
"Railroad ties are uses to distribute and transfer force to the ballast material (often ballast stone). Without it you would have alot of force concentrated in one area",
"To keep the rails a fixed distance apart?",
"To keep them in place. If they didn't have spacing boards they could drift apart or closer together causing damage and accidents to the train."
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9rdiqi | What is the reason why cars are made FWD/RWD? | How do car manufacturers choose between FWD and RWD in their design? Is there a reason behind that? | Engineering | explainlikeimfive | {
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"RWD cars are good for performance, because when a car is accelerating, its' inertia pushes weight backwards, which gets caught by the shocks into essentially transferring that mass down onto the back tires (regardless of what wheels are driving the car), leading to greater traction for straight-line acceleration. FWD cars are typically lighter, and thus more fuel efficient. AWD cars give you the best handling, but you add a lot of weight because you have 3 differential systems instead of the typical 1. They're also typically more expensive due to the added parts, and wear tires faster in everyday driving conditions. FWD cars also tend to not oversteer (your typical fishtail-type skid), and will understeer instead (you keep going somewhat the way you were going before turning), and are less prone to losing grip overall, which makes them favored by inexperienced drivers (more experienced drivers who routinely push their cars to skids tend to prefer oversteer, though.) Typically, FWD cars are going to be your economy models that are focused on saving fuel, and your newer standard sedans. RWD cars are going to be more sporty cars, and AWD cars are going to be either higher-end performance cars, or certain wagons/sedans made to do better in rain/snow/etc.",
"Like most decisions for a car design (or any consumer product really), cost of production and intended audience play the biggest role. The goal, in simple terms, is to minimize cost of production, while maximizing interest from the intended audience. As a car company, you want to add features that add value to your audience, and nothing else. No one will pay more for features they don't care about if a more affordable option that forgoes them exists. In order to understand which drivetrain to include in a car, let's compare the advantages and disadvantages of each. FWD: Least expensive to produce, maximizes interior space (no transmission tunnel necessary), cheaper to maintain (fewer and smaller parts), tires last longer (rear tires almost don't wear, can rotate more frequently), higher fuel economy (less weight, possibly lower drag), provide more control in wet pavement. However, it's has poor weight distribution (front heavy), poor traction in turns, worst traction while accelerating forward, worst breaking performance. RWD: Excellent weight distribution, higher power capacity (as drive shafts and transmissions can be made larger and more robust), simple (transmission is usually separate from differential and drive shafts), great acceleration in straight lines, good breaking, best cornering. But it's more expensive to produce and maintain, robs the cabin and trunk of some room, generally less efficient (as the rotating assembly is heavier) and offers poor traction in wet/snow. AWD: Best traction in any condition, redundancy in case of driveline failure, predictable handling. However, it's the heaviest configuration, most expensive, most complex, requires most room, has worst efficiency. So, if your audience is comprised of working class families, you will add different features than if you're appealing to young enthusiasts. These are things like interior space, low cost of ownership, good fuel economy, reliability. In this case, FWD is unquestionably the right choice. If you want to sell a go anywhere fast car, than AWD is probably the right decision. If you want to sell a small high performance car, RWD is the best choice. The same process can be applied to transmissions, interior features, size, pretty much any voluntary design aspect of the car. TL;DR: Companies want to spend the least amount of money possible to make an attractive car. A family will be attractive as a FWD. A performance car will be more attractive as RWD."
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9roe48 | How do tanks (and similar vehicles) turn left/right? | Engineering | explainlikeimfive | {
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"The left and right tracks turn at different speeds. The engines have enough strength (torque) that they'll scrape across the ground as they rotate",
"One turns forwards, the other turns backward (or just forward but slower), creating a spinning motion."
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9rp1c1 | Why do touch screens react to fingers and touch pens but not other materials? | Engineering | explainlikeimfive | {
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"Touch Screen react to Hotdogs and Slim-Jims... which just proves that humans are nothing but meat-tubes with natural casings. The real reason is capacitive touch screens. Smart phones required a touch that dissipates an electrical charge, a human finger conducts electricity naturally. A pen does not. Even if it can conduct electricity, it doesn't disperse it like a human finger does. The phone looks for the charge to be dispersed, and registers a touch."
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9rq9m2 | Why is plugging mulitple power strips into each other a bad idea? | Engineering | explainlikeimfive | {
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"The strips are rated for a certain amount of current through them based on the number of sockets. By chaining them together the socket total can be increased arbitrarily leading to potentially stressing them beyond the point of failure.",
"Electrician here, and I'm seeing a lot of bad answers. To start, as long as your circuit breakers aren't malfunctioning, daisy-chaining power strips won't magically allow you to run several hair dryers or microwaves. If the outlet is on a 15 amp circuit, the breaker will trip when it gets there, regardless of the number of power strips. The real problem is two-fold. For starters, power strips tend to be cheaply built. They don't handle high loads as well as a normal wall outlet does, so overloading the strip creates worse consequences than you would get from drawing the same wattage from a wall outlet. Second, because a power strip lets you use more things than you could before, it means that you can more easily load your circuit to just under its max capacity. As a general (and literal) rule, circuits shall not be loaded to more than 80% of their max capacity for more than 3 hours. We have to take this into account when sizing up circuits for appliances. For instance, a fridge using 10 amps can run on a 15 amp circuit, but a fridge using 13 amps (more than 80% of 15) would require a 20 amp circuit. These rules exist so that the wires don't overheat from extended use. By using multiple power strips, you're effectively bypassing the rule and running a risk of overheating the wires or burning up the outlet. Think of it like a car. Sure, you can run it at high/max RPMs for a little while, but keeping it there for too long can damage it. Power strips make it easier to \"redline\" your circuit for too long. Don't buy cheap power strips, and be mindful of how many amps you're drawing."
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9rqsmd | Why should I care that a bridge freezes before the road's surface? | Engineering | explainlikeimfive | {
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"Because you won't be driving according to slick bridge surfaces on a street. There is a bridge by my aunt's and it freezes up before the roads so people heading out of town have good traction accelerating until they get to the bridge. The ice catches them off guard and they slide and bounce off the railings and end up hitting power poles after they finish ice skating. Because the frozen bridge will catch you off guard and you'll crash on it.",
"Ice will form on a bridge before a traditional roadway. And ice covered road provides less grip to the tires. Friction = grip. A sudden transition from a high friction surface to a low friction surface can cause you to lose control of your vehicle.",
"The transition from a surface that has good traction (the road), to one with poor traction (the icy bridge deck) can cause you to slip."
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9rr5zt | Why are Some Bus Wheels Concave While Others are Convex? | Over the past year, I have seen buses with concave and convex wheels and I am wondering why this is, Is it something to do with the axles? & #x200B; [ URL_0 ]( URL_0 ) | Engineering | explainlikeimfive | {
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"The inside wheel or the only wheel such as the front axle will be convex to clear the brakes. Axles with dual tires will have a convex (inside fitting over brakes) and a concave on the outside. They run the same wheels on duals so you don't have to have a specific inner and outer wheel.....you just flip it around it is a concave and convex wheel all in one.",
"It's the same rim. The convex wheels would normally be the \"inside\" set of tires on the rear wheel. The rear wheels are dual and that convex set butts up the concave and creates a budd spacer"
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9rwvbk | Automatic transmissions | Engineering | explainlikeimfive | {
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"The torque converter replaces the clutch with a fluid link. It's like a pair of propellers in a bath of oil. When the propeller connected to the engine spins, it whirls the fluid which then makes the propeller attached to the wheels spin. This has the advantage that the propellers don't need to be disengaged when you slow the car to a stop; the engine can keep turning against some resistance in the fluid rather than stalling."
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9s76y6 | How does the seatbelt know that it's being pulled fast (crash) and stop extending but still extends when pulled slowly? | Engineering | explainlikeimfive | {
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"true eli5: imagine standing in a very small room. Relax your arms and turn slowly. Your arms will stay close to your body. Now turn fast. Your arms will move away from your body and hit the walls slowing you down.",
"It uses what's a called a centrifugal clutch. Inside the spindle there is a mechanism with 2 grips. When the spindle spins quickly the grips are thrown outwards (just like you are on a merry go round) and stop the belt extending. When you pull slowly the grips don't engage.",
"It looks a bit like a pendulum that, in cases of rapid acceleration/deceleration, swings forward and locks the belt in place. Simple and ingenious. Very skookum.",
"Along with the other replies in this thread, some mechanisms also include a magnet and a large steel ball bearing, known as an inertial switch. If the inertia of the ball overcomes the force of the magnet on the ball, the belt locks up. This is also used in ever Ford fuel pump cut off switch.",
"My time to shine! Seat belt retractor design engineer checking in! There is a sensor sensing the ACCELERATION of the webbing extraction, there is also a sensor sensing the car acceleration. This ball someone mentioned that senses if the car is accelerating above a certain g in any direction, this sensor will lock the retrctor in a roll over accident. This acceleration sensor is not a centrifugal clutch as this would sense the velocity of the webbing and not the acceleration. This sensor is roughly a mass that will by it's inertia \"stay\" in it's place and initiate a locking. This applies to EU legal requirements, US only requires one sensor and might not have the webbing acceleration sensor or have it but it will lock at a much higher g. There is a \"Better call Saul\" episode, the one we're he gets a Mercedes were this is well shown, someone used to a American webbing acceleration gets in to a European car. He manages to lock the webbing several times before he calms down and pulls slowly. Please don't watch YouTube seatbelt repair videos to help you \"fix a broken\" retractor. I have seen alot of them and as seatbelt design engineer my judgement is that most of them are plain wrong and makes the retractor dangerous.",
"OT: for people who don’t know, there is an extra mechanism where if you fully extend the belt, it will only be able to go back inside (you can hear the extra clicks all the way until it’s fully retracted). This is useful is you have to put a seatbelt on a piece of equipment or a child seat, as it will not have that helpful slow extension.",
"Inside is a roller with hooks that rotates when you pull your seatbelt. The more speed they receive more centrifugal force which causes the hooks to extend up to the point of getting caught (a piece of metal in the path)",
"Some seatbelts, usually older ones if I'm not mistaken such as my 2000 Chevy cavalier, have both the centrifugal clutches, but also a little ball that sits on a platform that when the angle that the car is sitting at or the angle at which gravity is enacted on it get too high, then it falls to the side of the platform and engages the clutch too. I imagine it is designed this way for the situations when your car is moving slowly in a way the would flip the car and it prevents you from moving around too much when the airbag wouldn't be engaged."
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9s91b1 | How do the things that lower to stop traffic when a train is coming know when to lower and raise back up? | Engineering | explainlikeimfive | {
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"There are sensors next to the tracks and on the trains that communicate with each other to make that stuff happen. I actually work at a facility that makes those systems but I'm just a guard and dont know enough to get more detailed than that. I'll ask next time I work and if this is still here I will give a better answer.",
"As I’ve understood it there are mechanical switches along the tracks before and after the station so as the train rolls in it triggers the gates and all going down and as it leaves the opposite will happen. Don’t know exactly where they are or more technical details maybe someone else does"
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9s9mrz | what are those hissing sounds made by large vehicles? | Engineering | explainlikeimfive | {
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"Two things; Brakes in trucks work differently than in cars. On big trucks the brakes are always applied, the engine drives an air compressor that uses compressed air to push the brakes off the wheels. When you push the brake pedal it lets the compressed air out of the system and applies the brakes. In the event of system failure the brakes are automatically applied and the vehicle stops. If the air leaks out it can simply be replenished. The vehicle won't move if the system is too damaged to function, unlike hydraulic brakes which will still allow the vehicle to move if the system is malfunctioning. Air brakes are safer than hydraulic brakes. In addition to the brakes needing compressed air to release, the engine also uses compressed air. Combustion needs air and fuel. The more air you have, the more fuel you can use. The more fuel you use, the more power you generate. Trucks need to move a lot of weight and that takes a lot of power. The engine uses a different air compressor called a turbocharger. Turbochargers use exhaust gas to power a turbine that compresses air. When you decelerate suddenly the extra pressure in the system needs to be vented or it causes a back pressure surge which can damage the system. This air is typically recirculated, but can be vented to the atmosphere, by way of a blow off valve, causing a loud \"whoosh\" sound. This system can develop small leaks that are loud but are otherwise unnoticeable. It's likely that the hissing sound you are asking about is the brake system leaking air. Trucks are allowed to leak a certain amount of air and the system will still be functional.",
"You may also be hearing a waste gate on a turbodiesel. Blowing off excess turbo pressure. Does it happen around shifts/during acceleration?"
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9saauz | why do cars normally have front wheel steering instead of rear wheel steering and why do some cars like the forklifts have rear wheel steering? | Engineering | explainlikeimfive | {
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"Its more stable at speed to have front wheel. Im not sure if youve ever gone fast in reverse and turned, but it is very easy to go too far. The forklift requires a very small turn radius that is more easily accomplished with rear steer.",
"Forklifts have rear steering wheels for a few reasons but the most important is the working load at the front. If the front wheels steered then it would be very hard to position the pallets precisely and almost impossible to position them close to walls. Just like you can't parallel park a car in a tight space other than by reversing into it. Cars have their steering in the front because it's easier to stabilize the vehicle in a lane. The driver sees the effects of his wheel turning immediately because the front turns first. They just keep the visible front in the lane, the rest of the vehicle follows. They also don't run the risk of hitting something with the back of the vehicle on a tight turn (which can happen easily in a forklift). Sure, they could scratch the side instead, but that is easier to see. & #x200B;"
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9sd46g | Why do drinking fountains have two separate jets of water that combine to form one arc? | Engineering | explainlikeimfive | {
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"Two separate small jets running parallel with each other produces a less chaotic flow of water than a single large jet. You can notice this in those elaborate fountain shows: each jet is actually a bundle of smaller jets that combine to form the big \"ribbon\" of water.",
"It's like putting hair into a braid. If you have just one handful of hair, it will eventually spread out and get messy. If you twist different handfuls together, they stay organized for longer.",
"The surface tension snaps them together and they 'braid' and prevent splashing and spraying. Keeps the stream tidy.",
"From URL_0 In 1896, Halsey W. Taylor lost his father to an outbreak of typhoid fever caused by a contaminated water supply. This personal tragedy led the young Halsey Taylor to dedicate his life to providing a safe, sanitary drink of water in public places. … The historic Double Bubbler projector [spouter] was designed by Halsey Taylor himself, and still ranks as the most important innovation in the industry’s history. It projects two separate streams of water, which converge to provide an abundant `pyramid’ of water at the apex of the stream. This gives the user a fuller, more satisfying drink.” The folks at Halsey Taylor are being polite here. What they mean is that the Double Bubbler enables you to take in more water and less air when you drink. As a result, you don’t burp. Think of all the delicate social negotiations you’ve been involved in that have gone awry because of an ill-timed eructation (that’s belch for you dropouts). Had you been drinking from a Double Bubbler, that fat contract (job, babe, whatever) might have been yours. The Double Bubbler serves other purposes as well. You get less spraying, presumably because the water slows down when the two streams merge. The double streams also act as a sort of pressure regulator. If the water pressure is unusually strong one day, a single-stream fountain might give the unwary sipper a shot in the eye. When the twin streams of the Double Bubbler meet, however, their upward momentums tend to cancel out no matter how high the pressure gets.",
"I don't understand. What type of drinking fountain has two separate jets of water?",
"It's the most basic of laminar flows. Those jumping fountains, and the ones that make globes of water come from laminar instead of turbulent flow. A whole container of drinking straws filling a pipe will make the water coming out more laminar than if if just allowed to do whatever chaotic turbulent nonsense it wants. Real, turbulent... juice! EDIT: Turbulent means \"swirly\" and Laminar means \"not swirly\"",
"Where on earth are those type of drinking fountains common enough for the OP to phrase the question as if that's the norm? All my life I haven't seen any such drinking fountain until seeing the 500$ picture someone posted in this thread.",
"Laminar flow means fluid flowing smoothly. The bigger the pipe, the more pressure it will take to make things smooth because of scaling effects. Using smaller diameter holes makes things smoother. I've seen four small holes frequently in drinking fountains, it can be more than just two. Straws tend to be as narrow as possible. The only times straws are made bigger are for tapioca teas and thick milkshakes. If you have ever tried to suck on the larger straws, you realize it is a jerky and less enjoyable experience of drinking the beverage. Even when not blocked, the fluid can arrive unexpectedly slower or faster, forcing you to adjust the pressure with your mouth."
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9sfjuc | How does putting the keyfob to your head extend the range when unlocking car door? | Engineering | explainlikeimfive | {
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"A key fob usually have a too small antenna. Car locks usually use the 433MHz radio frequency which have a wavelength of 70cm that would require a minimum antenna size of 35cm or about a foot. Nobody wants to have such a big antenna as they key fob. They do a few things to get as big of an antenna as possible. First of all they use the actual key as one end of the antenna. Secondly the button or the frame of the key fob is the second half. High frequency electricity like the ones for the antenna can go through plastic using the capacitive effect. So when you are holding on to the key fob with your hand it acts as one half of the antenna. You can do the same with the other half if you hold this to your head. So your head is one half and your hand is the other half. Now you have an antenna which is technically too big but that is much better then a too small antenna. This gives the radio in the key fob a much better antenna and therefore much better reception."
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9shi5w | How do you cool something other than radiating away it in space or using a coolant? How do you cool a coolant? | How do you cool something other than radiating away it in space or using a coolant? How do you cool a coolant? | Engineering | explainlikeimfive | {
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"A coolant is generally just some fluid which is used to carry heat away from a device or location, which as you suspected needs to be cooled itself. The only way available in space is by radiation which is why the ISS has giant radiator fins in order to cool their ammonia coolant. Another method of cooling could be to transfer the heat into a substance and then jettison that substance. The engines on some rockets use this by pumping their cryogenic fuel past engine parts to cool them down, then into the engine to be burned and the exhaust thrown out the back (along with whatever heat they absorbed from the parts). But of course that cannot last very long as you quickly run out of material."
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9si99k | Why are phone charging cables only 10ft at their longest? Why are they not longer like extension cords? | Engineering | explainlikeimfive | {
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"text": [
"Often, the resistance of the cable becomes a more notable issue. Due to the low voltage used by USB (5v as opposed to 110v), the portion of the energy supplied that is lost to cable resistence is greater).",
"Just buy a longer one? I have a 12' USB-Micro USB cable to charge my phone.",
"The usb spec limits low speed cables to 3 meters and high speed cables to 5 meters. Past that you have issues with signal degradation and such.",
"Typically low speed devices (those powered by the USB cable itself) cannot be connected beyond 10 feet due to their signal and power delivery degrading over that length of cable. Extension cords can be much longer because the amount of power transferred through them is much greater (you cannot run an angle grinder off of USB for example) and they don't carry data at all."
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9sme2p | What is first and second order system ? | Engineering | explainlikeimfive | {
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"text": [
"Do you mean control systems? A first order system is one where the output/input relationship is a first order differential equation (eg y = dx/dt + x + 1.5). Second order systems have second order differential equations (eg y = d2y/dx^2 + dy/dx + 2x + 1). Most systems can be modelled using 2nd order systems, very rarely will you need to go up to 3rd order systems or higher. Edit: sorry it’s not ELI5, but the concept of control systems is very theoretical. I can give some examples of where the systems are used though. For a lift going up, it needs to stop exactly at the same point each time, preferably smoothly and not jerk around. A 1st order PD controller can be used here. For a drone flying, you need to control its position and speed. Such a complicated control (3 directions instead of 1, as well as 3 tilt directions) needs a 2nd order PID controller. The higher order the controller, the better it can control something, but the harder it is to create and use. I have not seen/heard of a single 3rd order system controller, maybe it can be used for situations where you need to control jerk."
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9spu02 | How machine guns on old panes were shooting through propeller without damaging it? | Engineering | explainlikeimfive | {
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"text": [
"There was a little notch on the drive-shaft of the propeller that lined up with the blades and was connected to a shut-off for the guns and disconnected the gun's trigger from the firing mechanism while it was engaged; [here is a diagram]( URL_0 ) of one such mechanism; the overall mechanism is called a Synchronization Gear, and the [wikipedia article]( URL_1 ) goes more in depth.",
"It is actually pretty clever, they used a cam (a mechanical component) on the propeller shaft to time the shots so that it would fire only after the propeller has passed or just interrupt the fire whenever a blade was in the way",
"Its called an interuptor gear, basically the gun had somthing similar to a second trigger, or more accurately a safety. Either way the gun would not fire until the propellors were out of the field of fire. They did have the issue of pilots destroying their props in the early days of air combat. Even earlier to that they would almost joust in the air firing their service pistols at one another. Before even this they would politely wave and greet eachother but the war on the ground got more viscious and thus the war in the air did likewise."
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9svmlm | How does the water level in a toilet remain same even if you pour buckets of extra water into it? | Engineering | explainlikeimfive | {
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"text": [
"The toilets have a u-tube; it curves up a few inches and then turns down. So that the water doesn't drain away completely. This way, the excess water flows out, but there is always some amount of water, so that it won't start to stink. It also makes cleaning easier.",
"Think of your toilet like a tilted letter J. The toilet bowl is the long part of the J. Your \"stack\" ( the vertical part of your sewer that is connected to the toilet) is connected at the little end. You can pour water into the top of the J but unless it gets clogged gravity will always make the water fall into the stack at the height of the little part."
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9sxstg | How did we get more precise rulers only having primitive rulers in the first place? | Engineering | explainlikeimfive | {
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"text": [
"If you use a [pantograph] ( URL_0 ) or some other form of leverage, you can control something with greater precision than you can deliver to the control arm.",
"So basically we tried a bunch of different ways of defining what the \"right\" amounts were, until we all agreed on some good rulers. Then we spread those good rulers everywhere so you could compare your own rulers with them. [Check out this video]( URL_0 )"
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9t25em | Why not just eject airplane black boxes before impact? | We witnessed the ejection of two astronauts on Oct 11 when the rocket signaled failure. Why can't we do the same for airplane black boxes? During an emergency, can't we have a system where the pilot flips the "ohh shit" button to pre-stage an ejection and if the airline detects an altitude of less than 100 feet, just eject the black box, with a small parachute. Maybe even a kiddie-style pool arm band to keep it afloat for a while? | Engineering | explainlikeimfive | {
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"text": [
"The US Navy has been using such a device since 1993. A combination Flight Data Recorder, Cockpit Voice recorder, and ELT (Emergency Locator Transmitter) that is automatically ejected from the aircraft by sensors and can be recovered using a satellite signal. Attempts have been made to make such a device mandatory for all civilian aircraft but the cost to retrofit such a device is extremely high and the laws have so far failed to pass congress. There is also a benefit to keep the device in the aircraft in order to record details right up until the moment of impact. To resolve this the Navy has 2 devices in the aircraft, an ejectable device, and a non-ejectable one. It's also important to note that flight data recorders are remarkably resilient devices so the benefits of ejecting the device would only be to speed up recovery, but that can also be accomplished by adding a homing beacon to the device itself. Modern ELT's phone home using a satellite signal so the location of a crash is known almost immediately anyway. Given modern technology it's possibly more practical to keep the recording devices onboard the aircraft and instead to transmit a copy of the data back to manufacturer over a data-link in real time.",
"Since black boxes are made very strong and are very likely to survive flames, explosions, and most damage a plane incurs in a crash, it (usually) preserves the integrity and makes the black box easier to find knowing that it'll be nearby or inside the downed plane. Ejecting it would more often than not make it harder to find, because it would increase the area you'd have to look for it in. Situations like this more recent one are more an anomaly than the norm.",
"The purpose of the black box is to record ALL of the flight and electronics data so that in the event of a crash, they can determine what went wrong and potential fix it so that it doesn't happen again. If something were to happen in those last 100 ft, it would not be recorded. Aerial mishaps rarely have eye witnesses. The investigators have to work backwards from the crash to figure how things went wrong. If they're are missing the last minute or so of data, it's a huge crutch they'd have to overcome. Making the black box easier to find is pointless if they can't use the data inside.",
"The black box records data to help learn why the crash happened and to help prevent future crashes. Data about the impact itself can be important, so ejecting the box before impact is not a good idea."
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9t3jjy | What makes security glass so strong, opposed to normal glass? | Engineering | explainlikeimfive | {
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"text": [
"Thickness and material. Many safety glasses are make with transparent plastics or are covered in a stiff laminate to prevent failing, even when the glass is shattered. And by making the glass thicker, it can withstand more of an impact without breaking. Use a combination of both techniques, and you can have glass that withstands incredible forces.",
"Multiple panes of tempered glass, layered over a plastic film insulation in between panes to provide support, durability, and resistance to striking forces. Not completely heat resistant, as heat can melt the plastic layers in between panes, causing a cavitation effects at certain temperatures making breaking easier.",
"In addition to just using thick layers of glass laminated by plastic sheets you can also tamper glass. Glass is very good at tensile forces but not good at compression forces. So when try to bend a sheet of glass the inside will stretch which the glass can handle but the outside will compress causing the glass to fail. Tampering the glass uses heat and salts in a special process to make it so that there is lots of built up stress already in the glass. This stress is all tensile which the glass can handle very well. When you try to bend a tampered sheet of glass the inside will stretch which adds more tensile stress to the already existing stress in the glass but it can handle it. However on the outside the glass compresses which relieves the tensile stress. So you can apply a lot more force to the glass before it breaks. The downside is that when tampered glass breaks all the internal stress of the glass is released and the entire piece of glass shatters all at once."
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9t9lj5 | How are we able to control Space Shuttles or Robots when they are in outer space? | Space Shuttles excluded* With Robots i mean those research robots that we send to planets for research | Engineering | explainlikeimfive | {
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"text": [
"Mainly because there's someone IN the shuttle... But we also use radio waves (think \"RC car\", but way more powerful) to send it a signal to control movement, etc."
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9tatdw | Why do airplane black boxes have to be kept in water after they are removed from the sea? | Following the latest Lion air plane crash, I saw a video of the black box being retrieved. Upon taking it out of the water it was immediately thrown and kept in a bin of water. | Engineering | explainlikeimfive | {
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"Black boxes have to be kept in water basically to avoid corrosion. Let’s say the plane crashed into the sea, and the black box was drowned in salty sea water for some time. When retrieved, it will be thrown immediately into normal water to avoid corrosion so the people will have more of a chance of recovering the data.",
"I'm involved in the marine side of black boxes (VDR) but the leading manufacturer of VDR capsules is also the leading manufacturer of the final recording medium of airplane CVR/FDR. & #x200B; Snipped from the accident data recovery manual: [ URL_0 ]( URL_0 )",
"What is the longest period of time a black box has been recovered and the data along with it?? Don't they stop working after a week?",
"I think it’s distilled water and it’s used because it won’t cause more corrosion. I work with cameras and when they get saltwater infiltration we immediately or ASAP give them a soak in distilled water to dilute the corrosives found in seawater to attempt to mitigate as much corrosion as possible. This is actually a technique that Sony Corp. suggests when dealing with cameras and (way back in the day) VTRs were hit with a wave from the reporter at the beach live shot. It works probably about as well as it can as there’s instant corrosion on things like copper and gold when seawater hits it.",
"Why don't they make the whole plane out of black box?",
"If it is taken out of the water and allowed to dry, the salts in the water become concentrated and deposited on the surface. The concentrated salts can cause damage where dilute salts might not, and with ones that use magnetic tape, salts drying onto the surface of the tape will definitely damage it. Storing it immersed in fresh water will start the process of diluting and flushing out the salts, and prevent anything from drying out before it is properly cleaned.",
"Why don't they make black boxes that float?"
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9tc7s2 | Why do dams actually work? | Engineering | explainlikeimfive | {
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"text": [
"That's actually exactly what we want to happen. Let's say that there's a river we want to dam. The first thing we do is find a logical spot to place the dam. As soon as we dam a river, the water has nowhere to go and the river will start to flood the area behind the dam and eventually create a lake. A reservoir. That means the location we choose for the dam will be sacrificed to create the reservoir. Once we have a reservoir, we can use it for a variety of purposes. * If you build the reservoir in a region that has wet and dry seasons, the reservoir can act as a water supply for the dry season. * A river takes the path of least resistance but your reservoir can be diverted into channels for irrigation in agriculture. * If you want to transport water uphill using an aqueduct, you need water pressure. Your reservoir can provide that. * A modern use for dams is generating electricity. A hydroelectric dam incorporates turbines. When water is let through the dam from the reservoir, the water pressure will turn the turbines and generate electricity."
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9ted2k | How does a massive site like flickr transfer everything to new owners? | Engineering | explainlikeimfive | {
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"text": [
"Usually you'd expect the infrastructure to be part of the buyout, i.e. flickr servers become smugmug servers. Its quite possible that the servers (and storage) are rented, rather than owned, in which case the new company takes over the bills and the access to the servers."
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9tegwh | Why are all touch screen displays so reflective? | Most regular LCDs are non reflective. However, pretty much all touch screen displays use glass for the top layer, which makes it very reflective. Why can't touchscreen displays be manufactured with a material that isn't reflective like how regular LCDs are? For example, my Chromebook which is touchscreen has a very reflective screen and I don't like how it is hard to look at the screen when the screen is facing a window, or when I turn on a desk lamp because of the reflectiveness. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Because a touch screens use case involves touching, it needs to be durable. Glass is stiff thus able to spread pressure evenly (you could kill/damage the pixes of an lcd if you push on them hard enough). They also need to be resistant to scratches, plastic screens have been used on plenty of devices but they scratch easily. A tempered glass is hard and resistant to scratches (a level 6 or 7 on the scale of hardness I believe). Now the glass used on touch screens could be 'frosted' (that would reduce the glare on a screen) but that would probably made them a fair bit more expensive to manufacture compared to maintaining the smooth surface. Now a standard lcd like that on a tv doesn't have a need for much protection, it's easy to throw a thin layer of plastic over it and for the most part that plastic is 'anti-glare' because it offers a better user experience at little cost. Tldr: glass is used for touch screens because it's tough and resistant to scratches. Glass is reflective."
],
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9tekxd | When they found the back box for the Lion Air plane that recently crashed, why did they keep it in a bucket of water after retrieval? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Salt water is very, very corrosive. The higher the salt concentration, the more it damages connectors. If you leave it out, the water evaporates, raising the salt concentration and possibly corroding the connector you need to use to get the data out. Put it in a bucket of water, and add more fresh water as you bring it back to base, and you can avoid corrosion."
],
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|
9teuxp | How are giant statues (like the new one in India) built? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Usually there is a supporting structure inside, these days made out of structural steel. The Statue of Liberty for example is copper sheeting over stainless steel bars attached to the internal framework. Individual sections are built and put in place at a time, eventually forming the completed statue. Beyond that it is a bunch of money."
],
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9ti49x | Why can't we just build telescopes with a mirror diameter of 50/75/100m? | Are there construction issues? Technical Issues? Is there a cap on the telescope size where there are no more benefits? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The precision used to make telescope lenses is insane, so making a lens that big without any flaws would be next to impossible. Not to mention how exactly would you move a lens that’s 100m wife safety to the observatory (since they’re usually located in the middle of nowhere to avoid light pollution)",
"The JWST has hexagonal mirrors, I don't see why it wouldn't be scalable for ground usage. ESO's VLT is using adaptive optics for nanometer precision shaping of mirrors. It's not impossible like some people say. URL_1 URL_0 P.S. I'm on mobile, sry for errors and poor formatting."
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"https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope"
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9tjb5t | How did we discover oil in the ground? and without refining it, how did we know it would be Useful? | Engineering | explainlikeimfive | {
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"text": [
"People have known about crude oil since ancient times; there are places in Asia Minor and other spots around the world where crude oil bubbles up to the surface. The word “petroleum” literally means “rock oil”, and it was one of many kinds of flammable oils that people used to light lamps or fuel fires. In the mid-19th century, chemists started figuring out how to distill or process crude oils, tar, and other types of petroleum into lighter oils that could be used for various purposes as lubricants or fuels. Engineers invented various forms of internal combustion engines shortly afterwards, and from then on people started to drill for oil. So, basically, we’ve always known about oil and its flammability. Drilling for it was just a natural extension of looking for more.",
"Surface oil deposits in Babylonia were used to build roads. There are many places in the world where oil in on the surface and even forms lakes. From that, you just dig deeper as the surface supply runs out",
"It used to just come out of the ground in many places. We've since exhausted most of that oil. The oil used to be used as medicine as it doesn't burn very cleanly as raw crude. In the US they discovered it in salt mines in Pennsylvania, they had so much they didn't know what to do with it. Chemistry was a big thing back in the mid 1800s so they started playing around with distilling it (similarly they had distilled coal gas). Originally they just had kerosene but gradually learned how to make other things from it.",
"You see there was A poor mountaineer, barely kept his family fed, And then one day he was shootin at some food, And up through the ground come a bubblin crude.... & #x200B;",
"The first oil deposits we have found was before human writing so we do not know how this came about. We do know about primitive refining technologies to separate oil into different types. Heavy oils were used for roads while lighter oil were burned for heat and lighting."
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9tjga7 | How do ATM/cash deposit machines know which denomination of notes you put into it? | Let's say I put in $10. How does the machine know that I inserted $10 and not $20 or $50? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Modern machines use similar technology to vending machines and read the bills. Older machines usually use envelopes and are physically verified by a bank employee before the deposit \"clears\" your account.",
"When they first came out, there was a bank that gave out 5's and 20's. One weekend at a particular machine, someone put 20's in the 5 compartment and it spit them out to several lucky people before Monday rolled around and the error was discovered. Surprisingly, when they tracked down those who had used the machine, no one mentioned having any issues."
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9tkuw8 | Why do windturbines have 3 blades? | Engineering | explainlikeimfive | {
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"text": [
"Short answer: balance of stability and reducing resistance. The more blades you add, the greater drag. One blade would be unbalanced, two would be balanced, but prone to gyroscopic precession (and would be wobbly). Three gets beyond this hump of instability issues and adding any more increases drag and reduces efficiency. For more you can read here: [Interesting Engineering]( URL_0 ) make sure you have your parents' permission to go online and visit this site."
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|
9tnxcc | How do WiFi signals get transmitted and received by that specific device? | If there is a room of devices connected to a router all using the WiFi connection, the signals are all over the place right? How are the signals transmitted to be received by device A not being captured by other devices? Or are those signals also being received by the other devices, but discarded when it's determined that it was not meant for their IP? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Every network device have a unique MAC address designated to it. Each transmission includes the MAC address of the sending device and the receiving device. If the receiving MAC address does not match the MAC address of the device it is ignored. You can get software that can, depending on the network interface, sniff all data and display it to you. If you are using encryption the data is also encrypted with a unique key for each device so that anyone else would just get encrypted traffic."
],
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9tquwr | Why do wind turbines obscure radar? | I don't have a link but I read somewhere that wind turbines obscures radar in that specific spot regardless of the height of aircraft, radar or turbine. But I have no idea if it is true or not. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Radar engineer here. We hate wind turbines! ELI5 version is radars are really good at detecting physical things. Planes, buldings, mountians, all things. But we only care about moving things, so there are filters that throw out stationary objects and only show moving objects on the display. Wind turbines are tall enough to be in the radar beams path, and they have a moving signal so it shows up. A whole field of them will look like a field of helicopters just hovering. And a real plane flying over would just blend in."
],
"score": [
19
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9tz6m0 | Why aren't car tires just solid rubber? | Engineering | explainlikeimfive | {
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"text": [
"Too soft and would wear out and blow up easily. You can engineer a better ride and handling with belts and other materials in them. Rubber is for traction not strength. Car tires have always had some type of carcass inside the rubber.",
"Asked 16 days ago in this same sub: URL_0"
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|
9u0zbu | Why dont they separate and reuse the oil during an oil spill? | Engineering | explainlikeimfive | {
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"I'm from Louisiana and oil spills can be a big topic there. Here is what I know: Oil is collected and used but not all of it can be. You see, the ocean can spread the oil deep and far, meaning not all of it reaches the surface right away. After the BP spill tar balls washed up on the beaches along the gulf coast long after the spill stopped. Sometimes rough seas will break up a large slick so it's a lot of small oil bits making it difficult to contain and reclaim. But, let's say we have an oil spill on calm seas so it's all in one place and will be for awhile. Coast Guard has contained it with booms and now its waiting to be collected. Under these ideal conditions, the oil still can't be as fully utilized as uncontaminated oil. It will have uses but salt and other stuff in the oceans render it less than ideal. This is, of course what we can get right away. The longer it stays in the ocean, the more it deteriorates. Once it reaches the stage of the tar balls I mentioned earlier it becomes useless bad has to be safely disposed of. All in all, from an oil spill we can only recover a fraction, maybe a fourth of it max in some useable form.",
"When millions of barrels of oil spill out onto the ground or into the ocean they would certainly like to be able to separate it out and reuse it. However, you seem to be ignoring the issue of it being **spilled out**. How do you think they are going to snatch up a million barrels of oil out of the ocean? What mechanism do you think is available to perform such a trick?",
"My environmental professor told us 10000 times... currently the solution to pollution is dilution"
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9u60it | What is the difference between different grades of gas for my car? Is it worth paying more to keep the engine cleaner/running better? | Engineering | explainlikeimfive | {
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"The octane rating has nothing to do with the quality of the gas. Octane is basically how fast it burns, with the lower the octane the faster it burns. Cars with high compression, generally your turbo or supercharged cars, run better on higher octane gas. You are best off using whatever octane your cars manufacturer recommends.",
"Octane rating is about how much compression fuel can take before it detonates. Early detonation (combustion before spark) is called knock. So the higher the octane the more knock retardant the fuel.",
"Octane is not the quality of gasoline. Running higher octane fuel in your car than it needs is just a waste of money. In order to produce power from gasoline it must be burned with air. More gasoline requires more air, and these are mixed within the cylinders of an automobile and ignited. If you want more power you must burn more fuel and use more air, and if you want to do that in the same sized space it means you must compress them more. Compressing air heats it up and a mist of fuel will eventually explode on its own instead of being set off by a spark. The delicate timing of an engine requires that it ignites exactly when needed and not before, and by adding certain chemicals to the gasoline it can be made more resistant to igniting from the pressure. Octane is a measurement of this resistance, higher octane being more resistant. This is why high performance engines such as in sports cars where the engine needs to be small yet produce a lot of power will be high compression and require higher octane fuel. A normal car capable of running on normal octane fuel gets absolutely no benefit from the higher octane fuel as its ability to avoid detonation at high pressure is pointless."
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9u8z3s | what are the quartz crystals on computer cpu's. | I have three questions pertaining to the crystals used to measure clock speed. 1. When I searched the sub, I found that there are electrical signals passed through these crystals that make them vibrate but I was still left wondering how are these vibrations measured and how can ambient shaking of the device not mess with this? 2. How are they mined/produced? Are they grown like mono-crystalline silicon or are they taken from the earth? 3. What do they look like? Are they embedded in the silicon in the circuit board or are they placed on top like other circuit elements? | Engineering | explainlikeimfive | {
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"A quartz crystal is used along with an amplifier to make an oscillator. The crystal tends to vibrate at a single frequency when a pulse of electricity is applied or if struck with a micro-hammer (like a bell or piano string). That frequency is called its resonant frequency. Unfortunately, pulsing it would not produce a steady frequency. Instead we use it in the feedback of an amplifier so that some of the output is applied through the crystal to the amplifier input. It will then oscillate at the resonant frequency of the crystal. The output of the amplifier is the clock. No further measurement is needed. Shaking the device can affect it, but they are mounted to minimize that. Plus the frequency of electronic vibration is much higher than the frequency of mechanical vibration."
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9udcr6 | how does the 1.3km zipline in Philippines cable stay tense enough for passengers with no colums supporting it? | Engineering | explainlikeimfive | {
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"It's under tremendous tension, putting a static load of thousands of pounds on the anchor points. There is sag of course, but as long as the finish point is sufficiently below the start you're not going to notice it. The weight of the passenger is fairly inconsequential here, that span would probably need 3/4\" or greater cable so the cable itself weighs 4300+ pounds. Looking at a few tourist photos, it does look like a pretty heavy 3/4\" or 5/8\" cable."
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9ufccx | Why are you not supposed to change your transmission fluid once it gets dirty enough? | I've been told numerous times by numerous people that if your transmission fluid is too dirty, you can no longer change it out because it puts your whole gearbox at risk of failure. I just can't seem to understand why. Why is this? | Engineering | explainlikeimfive | {
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"The detergents in the new fluid will eat away the friction plates. And stir up any trash that is in there. Then you have trash going everywhere which isn't good for the valve body. Useless your trans hasn't been overheated and the fluid red your good. I was a ASE Trans guy for 10 years."
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9uj0uw | How does the automatic wiper blades works? | Some cars have a system in wich the wiper washer auto activates when is raining, and adjust itself to how hard it's raining. At the start I figured it can work with some kind of system that measure the water that falls down the windshield, but when you throw water into the windshield it seems to start working before the water reach the bottom of the windshield. I know it seem a silly question, but have been bugging me for some time so... is there any car engineer in the room? | Engineering | explainlikeimfive | {
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"Most have this clever system that relies on how light bends when it goes through stuff like glass & water. They project some infrared light through the glass at a 45 degree angle. if the glass is dry most of it gets reflected back to a sensor. But if there are rain drops on the glass some of it will be scattered. The more rain drops there are the less is light reflected back. The system will turn on the wipers if the amount of reflected light reaches a low enough level. It also keeps sensing between wipes & if it detects too many rain drops building up between sweeps it will increase the frequency.",
"Im no expert but from what I know if existing sensor technology I can guess: Probably measuring the capacitance of some surface layer, when it changes in a recognizable way, like when a conductive liquid (i.e. water) is on it it triggers a response that scales with the change in capacitance.... It's how our touch screens work on our phones and tablets, so it's probably similar - likely with less granularity than a phone though."
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9umgst | Why do astronauts use special pens, ie. anti-gravity pens? Why can't they just use pencils. | Engineering | explainlikeimfive | {
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"NASA did indeed use pencils right up until the Apollo program. It was at this time they switched to space pens. When Fisher contacted NASA to try out their pens, they were so impressed that they bought enough of them in bulk to be used on all future space missions. Russia would soon follow suit. By 1969, both America and Russia were using these pens in space. Pencils have a habit of breaking, shattering, or leaving graphite dust. Don’t forget that pencils are made of wood which may have been treated, and is itself flammable. This would prove to be a serious fire risk in the pressurised, oxygen rich capsule.",
"Pencils create carbon dust and with zero gravity this dust floats around the ship and might end up short circuiting electronic components.",
"There are several reasons astronauts don't want pencils in space. Graphite is very conductive of electricity, and in space, because there is no gravity, things like crumbs, dust, and pencil particles have a tendency to fly all over the place and get into places they don't need to be. If small particles of the pencil graphite were floating around, it could make its way into the intricately designed electronics and cause damage by shorting them out, or cause fires and explosions due to the nature of graphite's conductivity. There is also a risk of fire because of the wood and pencil shavings that come off of the pencil. Another reason is because pen ink is permanent. Pencils are not. Often, there are times when using a pencil isn't a good idea because you want whatever you are documenting to be written permanently. By using a pencil you run the risk of whatever important document you are writing in outer space getting smudged or messed up or even manipulated. Also, it's much easier! With a pen, all the astronaut needs to do is start writing. There is no finding a pencil sharpener, sharpening the pencil, and trying to make sure the shavings don't float away. It's just grab and write."
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9ur2nr | how does electricity get into a battery | Engineering | explainlikeimfive | {
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"The electricity starts as chemical energy. When a regular one use battery is built it has two different salts that will react with each other loaded into it separated by a porous membrane called a salt bridge. Electrodes are placed into each solution of an appropriate type for the salts being used. The reaction doesn't take place until something connects the two electrodes, because in order for the reaction to happen electrons need to flow between them. Generally one of the electrodes is slowly turned into more salt and the other collects more metal from the salt. How much the reaction wants to happen is what \"pushes\" the electrons through the wires making electrical energy. For rechargeable batteries plugging the battery in to charge forces the electricity to run the opposite direction undoing this reaction and allowing it to happen again when it's unplugged.",
"It doesn’t get into the battery, that’s what a battery is. By combining different elements that undergo a chemical reaction that produces extra electrons. There’s a natural “pull” whenever an imbalance of charge exists and that’s what allows the current to flow.",
"Imagine a magical scoop of ice cream. As it melts, it can push electrons around, which makes it melt. Once it is all melted, it can't push electrons any more. But you can put it in the freezer and refreeze it and form it back into a scoop. Now you can melt it again so it can push electrons around again."
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9uwluv | Why do furnace filters have to be installed with the arrow facing the furnace? | All the sites I've visited say the inlet side is more porous than the outlet and the air needs to hit the porous side first to filter the air. If the filter is installed backwards, with the less porous side facing the incoming air, it will cause a blockage in the air, reducing efficiency and causing the blower to work harder. I don't understand why this matters since the air will have to move through the less porous side one way or another. Why is there no airflow blockage when the air flows through the more porous side first? | Engineering | explainlikeimfive | {
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"Because the larger particles will collect on the more porous side while still allowing airflow. As you get deeper into the filter it is more condensed and traps the smaller particles. This allows a more even distribution of dust. Installing it the other way around will trap all the particles on the surface. This will restrict airflow because all of the particles are trapped near the surface rather than being distributed throughout the different density levels of the filter."
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9uz0nk | How is a single speaker able to produce the sounds of multiple instruments at once? | Engineering | explainlikeimfive | {
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"text": [
"Your eardrum is a reverse speaker - do you ever wonder how you can hear multiple instruments at once? Anyway, the different waveforms just add together and all of the different frequencies are still present. If you look closely at the grooves of a record, the vinyl is just cut to represent that complex shape. When you turn it back into sound, via an amplifier and speaker, the original sound is reproduced with high fidelity.",
"If you are more interested in this topic look up \"Fourier transform\". In short, all sounds are composed of multiple sine waves. They just add together to form more complex signal which you then precieve as multiple sounds"
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9uz0yp | How does a gas fridge keep things cold by making heat? | Engineering | explainlikeimfive | {
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"text": [
"Gas-powered refrigerators are [absorption refrigerators]( URL_0 ), which as actually an older design than the compression refrigerators powered by electricity which we're used to. The single-pressure variant uses three different refrigerants (water, ammonia, and hydrogen) and depends on somewhat complex changes of the partial pressures between these in different parts of the system. But the main idea is that the heat from burning the gas (usually propane) is used to heat up an ammonia-water mixture to extract the ammonia. This goes through a heat exchanger, dumping its heat to the outside and codensing. The now liquid ammonia can be used to cool down the inside of the fridge, after which it is absorbed by water. Then it returns to the gas-powered boiler."
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