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991k81 | Why do space shuttles and other launch vehicles roll after launch rather than launching in their 'post roll' orientation from the start? | Engineering | explainlikeimfive | {
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"The position of the shuttle on the pad - and other rockets, too - is fixed by the design of the pad. As the rocket will launch in multiple directions, it will have to roll for at least some of them. When it comes to the Space Shuttle, the pad was created for the earlier Saturn 5 which launched from there, so they had to roll for all of their launches."
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991kvp | is it possible to use nuclear power for space travel? | Engineering | explainlikeimfive | {
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"Yes, absolutely. Project Orion was a proposed spaceship that would use nuclear bombs detonated behind the ship to push it forward. Initial small scale tests were promising but the ban in space detonations put a stop to it, also an accident at launch would cause massive problems. If it were implemented, a ship could theoretically reach a decent percentage of the speed of light (around 1%). Current probes use nuclear decay for power. A lump of plutonium is used for heat to generate electricity just by sitting there.",
"It's not just possible, it's certain, mainly because it's already been done! On any longer space mission, you need a source of energy that won't run out, and one that won't burden you with weight beyond your capacity, the lighter the better. Using combustible fuel isn't efficient because you just burn it away and would need to carry a lot of (heavy) fuel to go very far. There are already nuclear reactors in space being used to power long term stays in space because they're able to continue generating power for a very long time without requiring constant new fuel sources.",
"Sure. There are a number of theoretical and even some practical ideas that have been proposed and used. In a lesser form it boils down to using nuclear energy to make electricity and use that electricity to power your spacecraft. In a more extreme form you use nuclear reactions more directly to create thrust. In the most extreme form you just have a bunch of nuclear bombs that you detonate to move your spaceship. The problem with most of those ideas is that the place where you need the most energy to drive your spacecraft is the moment when you are trying to lift of from the planet and get to orbit. That is also the point where the people who live on that planet have the most to complain about. It doesn't help that the safer the ideas are the less thrust they give you. A nuclear powered rocket that irradiates everything in its path is not something that will find much love among the people in its path. The idea of literally using nuclear explosions for propulsion (the so called Orion drive) is really cool in theory but obviously not something anyone would be happy to see in their backyard. The safest method is the only one currently in use. A nuclear battery (not an actual fission or fusion reactor just a piece of radioactive material that keeps naturally warm as it decays) used to power the electrical components of a long range probes. It works and is reasonably safe. Still people have objections based on the fact that rockets sometimes explode during launch and would then distribute their radioactive material across the landscape. something that worries people. Of course a rocket that crashes or explodes and has debris raining down is a bad thing in general as rocket fuel tends to be the sort of hazardous chemicals that is bad for your health even when not on fire."
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992mni | How does bead rolling strengthen metal? | I watch a lot of car shows and whenever they have to replace the floorboards, trunk, etc, they always bead roll the sheet metal to strengthen it. How does what essentially looks like pinching the metal together strengthen it? Can this technique apply to other materials also? | Engineering | explainlikeimfive | {
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"\"Strengthen\" is not actually the correct term, stiffen is, although most car shows use them interchangeably. Thin material stock like sheet metal is really only stiff in one direction, that is it resists deformation in the direction with most material. Since this isn't usually useful, fabricators add features in different directions (like beads from a bead roller, or ridges from a stamp, or dimples from a die) to stiffen the sheet in different directions. This technique can be applied to any ductile material. Plastic bottles often have ridges for stiffness, cardboard has corrogations that add stiffness in one many different directions. You can experiment with this at home. Take a piece of paper and hold it by one of the edges, notice that it drops. Now fold the piece of paper and hold it by the crease, you will see it is much stiffer in this direction, even though you haven't added any material or reinforment."
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9997es | is it realistic whenever a brakeline is cut in movies? Why cant you just release the gas pedal like normal physics abiding citizen. | Engineering | explainlikeimfive | {
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"So there are a few things in place to avoid flying off a cliff if a line is cut. First, with one line cut at one wheel, you would still have some brake effort in two other wheels since there are generally two separate hydraulic circuits that control all 4 wheels. Then you have the transmission to help assist in slowing down. Automatics allow for down shifting through the manual gears by shifting into the \"L\" or numbered gears. These gears give you engine braking where \"D\" does not. Engine braking is when you let off the gas and transmission does not allow freewheeling so the resistance from the wheels actually slows the car. Do not throw the car in park. The parking pawl is a relatively small piece of metal and will just snap off if your at speed and just go to park. This brings us to the parking brake (or e-brake as some call it). Parking brakes are either cable or electrically controlled and are not part of the hydraulic brake system. The parking brake will work, but it only applies the rear brakes. If you lost all the hydraulic brakes, you would want to apply and release the parking brake in conjunction with down shifting to slow the vehicle to a stop. You dont want to lock up the rear wheels while driving as your car becomes incredibly hard to control with two wheels in a dead skid. Lastly, a person can use the steering wheel to stay on the road or ride in the shoulder to help slow the car. So it doesnt have to end like it does in the movies.",
"The brake system in a car works on hydraulic pressure. If the brake line is cut all the fluid leaks out and there is no pressure to apply to the brakes. At best you could coast down in neutral to stop, but you would need a hill to decelerate rapidly. The friction of the pads on the rotors assists in slowing the car down, but eventually the car would stop. In a real emergency just throw the car in park. You’ll kill the transmission but the car will stop.",
"Imagine trying to unscrew a bolt that is stuck, and you have two wrenches, one is made of metal, and the other is made of rubber. When using the metal wrench, all of the force put into pulling on the lever, is mostly transferred to twisting the bolt. The metal wrench actually bends a little, but not enough to prevent turning the bolt. But a rubber wrench would not transfer the energy of pulling it's lever very well. Instead of transferring that energy to the bolt, the wrench will bend, and that force is wasted bending the wrench. So in order to transfer energy, you need most of the work you do, to make it to the other end of the wrench. The same is true in a hydraulic system. Fluids do not compress very well, you can basically say they don't compress. All of the force of a brake cylinder pressing down, is transferred (minus friction losses) to the brake caliper cylinder on the other end. When a hydraulic system has air in the line, or the fluid leaks out due to a puncture, it is replaced by air, which is compressible. When the brake cylinder is compressed by the pedal, instead of transferring that force to the brake shoe caliper, it goes into compressing the air/gas bubbles in the line, and the braking force is considerably less. More of the work done at one end of the system is wasted and doesn't make it to the other end. When enough fluid leaks out of the system, none of the energy makes it through at all, because there is no longer any pressure. In the rubber wrench analogy it would be like the wrench breaking, and none of the energy making it to the bolt."
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99abi9 | How do nails pounded into wood create permanent walls for a structure? How do thin shards of steel in wood make a wall that lasts for so long? | You think that wind, or shifting or whatever would pop all the nails out within a couple years. Is there a physics reason why this doesn't happen? | Engineering | explainlikeimfive | {
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"Wood isn't rigid. It can be compressed slightly. If you compress it, it tends to expand back, like a spring or a piece of rubber. So, when the nail is inserted with force, the wood around it is compressed, and it presses back on the nail, holding it tight in there. If you pull out the nail, it won't slide back in easily, because the wood has expanded as you pulled it out. Other materials deform permanently, such as metals. Nailing a metal this was is not gonna work, because metal doesn't press back on the nail and doesn't hold it in place.",
"carpenter here. we use different types of nails for different nailing. the common types are 16p nails and 8p nails. 16p nails are long, and have a shear strength of about 500lbs. meaning one nail can hold 500 lbs. 8p nails are ring-shank. the shear is much less, say 100 lbs per nail. but the pull-out is incredible. it's nearly impossible to pull a ring-shank nail. btw, carpenters building houses use air-powered guns that can fire dozens of nail per minute. source: i fired a few hundred 16p and many hundred 8p nails today. edit: add a bit - 16p (p for penny. 16 penny nails) nails are used to build the \"bones\" of a house - the stuff that holds up the house. studs, joists, rafters, etc. fairly easy to pull out. 8p nails attach the \"skin\" on a house - the plywood that ties everything together. ring shank means the nail has lots of little ridges on the shank (shaft) of the nail, so once it's in, it's locked in, by the compression of the wood as mentioned by /u/Venic_"
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99cwkq | How does a sextant work ? | Engineering | explainlikeimfive | {
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"Sextants are designed to accurately measure the apparent angle between two visible objects. The key component is a semi-silvered mirror that allows half of the light through and half the light to be reflected. The reflected part is bounced off a second mirror that you can rotate. The idea is that you rotate the mirror until two objects are aligned. The angle scale on the bottom allows you to read off the angle between the two objects. Even though the mirror rotates through about 60 & deg;, the scale reads double the angle, i.e., up to about 120 & deg;, because the angle of reflection is double the angle of the mirror. For navigation the directly viewed object is generally the horizon and the reflected object is the sun, moon, planet or star. For the sun and moon there are dark filters that are used to avoid damaging your eyesight. Those objects are obviously also large, so generally you measure the angle to the bottom of their discs; trying to guess where the centre is is not precise enough. Sextants usually have a small, low-power telescope to view through but this is not essential.",
"For a Sailor, the most common measurement is the \"noon shot\" . An accurate clock is not needed, only the date is needed. Its done this way. Before local noon, the navigator will start taking sun shots. This is usually the angle from the bottom (limb) of the sun to the horizon. The measurement is repeated until the angle starts to decrease. The noon shot will be the maximum. From there a table is needed and there will be a direct lookup for that date with the observers latitude. The next most common for northerners is the North Star shot. The angle to the horizon is a direct read which is equal to the observers latitude. It sounds easy, but the boat is moving and if its too dark the horizon mat not be visible. Latitude is way harder. Thats why they invented clocks."
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99gft2 | What is a wind tunnel and how does it work? | Engineering | explainlikeimfive | {
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"It's a tunnel with a giant fan at one end. They're used to test the aerodynamics of various types of vehicles.",
"It's a tunnel that has very well controlled airflow through it. At specific points in the wind tunnel, there are little sensors that measure static pressure (how much force the wind is exerting on an area). Modeling these pressures allows us to build a velocity profile of the wind around different objects. We can tell when an object travels efficiently through the air because the pressure differentials will be small, which means the air spent less energy trying to stop the object. Forces like lift and drag can be determined by putting a force measurement device (load cell) on the object your testing, in the relevent direction."
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99hq47 | how do traffic intersections know what light to turn green when emergency vehicles are passing though? | Engineering | explainlikeimfive | {
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"There is a strobe on the vehicle, it pulses at a certain frequency. There are little sensors on each light arm, they can pick up the flashes and turn the required light. EDIT... These.. URL_0"
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99iwzt | How is power generated in antarctica during polar night? | Engineering | explainlikeimfive | {
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"same way it's generated during the rest o the year. big ass diesel generators and wind turbines. URL_0"
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99l2ws | How does a bong or a hookah work? | I don’t understand... | Engineering | explainlikeimfive | {
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"Both work by basically burning your ingredient, and then pulling the smoke of the burned ingredient (by you inhaling it) through water to cool it and to make it not as dry, so its more comfortable to inhale than just pure, dry, hot smoke",
"Imagine blowing bubbles into a glass with water. The bubbles that pop at the top of the water are your breath. Now imagine the reverse of that. A burnable item (weed, tobacco, etc) is packed into a bowl, heated up enough to create smoke, and the smoke is pulled through the devices tubes, through water, and into your mouth all through the inhalation of your lungs."
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99l4v8 | Is Storing Excess Electrical Energy as Cool Air Feasible? | Engineering | explainlikeimfive | {
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"How do you intend to use the cool air to produce electricity? You can convert electrical energy into cool air easily enough, what efficient way is there to convert it back into electrical energy? Is is more efficient than other storage methods?"
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99ob9u | Why do motorcycles have gears in this order? | Engineering | explainlikeimfive | {
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"While driving, you rarely need neutral, so making it easy to find isn't important. By putting 1st gear at the bottom, you can always easily find it when you come to a stop by shifting all the way to the bottom. Sure, with the old pattern, you could shift all the way down then one up, but that just adds a step.",
"From learning how to ride a dirtbike, 1 down, 4 up stuck with me. I never really thought about the why though. But it works well. I think its just so first is easy to find when you need it."
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99ojrh | A commonly touted problem with the Hyperloop is that the expansion/contraction of metal with temperature would make pressurisation impossible. How do conventional railways deal with this problem? | Engineering | explainlikeimfive | {
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"Answers so far are missing something important. Most modern railways don't use expansion gaps except at bridges. Instead, they use a continuous seamless welded rail. They solve the problem of thermal expansion by pulling the rail to *put it under tension* while laying it, so when it heats up and expands, you don't get compression and buckling, you just get less tension. This is important because it can solve the Hyperloop expansion problem: you could build it under tension too. However, the hyperloop's tube and support structure would have to be built extra strong to handle the forces. [ URL_0 ]( URL_1 )"
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99t9mw | Why can't you reuse needles on yourself? | Engineering | explainlikeimfive | {
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"It may not look like it but the tip gets significantly blunted the first time it penetrates the skin, and successive use of the same needle can cause scarring and damage to your veins. Also, proteins in blood form clots when exposed to air. If you pull a needle out, any blood on/in it will coagulate. If you reuse the needle you risk injecting a small blood clot into your circulatory system which could in theory kill you if it blocks off the right blood vessel in the right spot.",
"Needles are sterile when you open them, if you use them at least ones, one way or another you will get some germs, re using them you will introduce them in your blood stream and if you got a serious health problem you may end up with a lot of problems.",
"Because once you remove the sterile seal from the needle it slowly becomes contaminated with germs in the air. You could sterilize the needle and re-use it but after 2 or three insertions the needle will be significantly dull and develop metal spurs."
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99ufmz | Those round circles that you see in the ground right before you reach an intersection look like they influence the intersections lights, but how does that system work in general? | Engineering | explainlikeimfive | {
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"The work like a metal detector, but not exactly the same way but the indicate if a metal object move over them. You put down a cable in a loop in the ground. If you move a magnetic object close to a electric conductor induce a electric current in the conductor. So you have a sensor that detect the current in the cable that indicate that a car moved in over it. The information is used so the system know where there are vehicles and where it is not any so you can skip the one where no one is. It is quite common to have another loop some distance away from a intersection so it know if a vehicle approaches it so during the night on empty street the light will change when you approach and let you trough. The moving a magnetic object in a looped cable is how a electric generator work. A electric motor work the same way by applying current the the loop and move the magnet."
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9a0mhz | why are bathroom sink faucets frequently so close to the back of the sink basin, making it difficult to wet your whole hand? Why not have the end of the faucet closer to the front of the basin? | Engineering | explainlikeimfive | {
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"Bathroom sink faucets are kept back as far as possible so you can fill the sink with water and wash your face, among other things. For public washrooms, this design doesn't really make any sense; we'd do better with a touchless sink designed specifically for washing hands for 30 seconds."
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9ab5m1 | Do Extension Cords Use Power When Turned Off But Still Plugged Into Wall? | Engineering | explainlikeimfive | {
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"The only power consumed by the extension cord is from any status indicators and from resistance of the wiring (which is minimal even at full load and zero if nothing is flowing)."
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9agkf3 | How do monetary printing presses put different serial numbers on every single bill when they are flying down the line at blistering speeds? | Engineering | explainlikeimfive | {
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"[They use numbering blocks]( URL_0 ), wheels with numbers which can be automatically set and stamped into the bills. As they are mechanically actuated this can take place extremely quickly and with extremely low chance of error."
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9agylr | how do boat anchors work at sea? | Saw a YouTube video of people jumping off a US aircraft carrier for fun in the sun. I assume the boat was shut off and chilling. So, how do they know when to drop the anchor? How long are anchors? Do they not use anchors when the ocean is too deep? Is there a safety mechanism to cut off the anchor if shit hits the fan? Cheers, my semens | Engineering | explainlikeimfive | {
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"> So, how do they know when to drop the anchor? They have depth finders and navigational charts or GPS to know how deep the water is and if they can drop anchor. > How long are anchors? That depends on the ship and the conditions. The longer the chain, the more stable your ship will be but also you have to haul the thing around. Some quick research says you want about a 4:1 ratio ([or \"scope\"]( URL_0 )) on the depth of the water you'll be anchoring in (so 4x the depth) plus about twice the length of the ship (in good conditions; more chain for rough conditions). Some more quick research finds [this]( URL_1 ) which says [edit: of aircraft carriers]: \"The chain is 1,440 feet long and each link weighs 136 pounds.\" Keep in mind that for large ships, the anchor at the end of the chain isn't doing the bulk of the work to keep the ship still, the chain itself is. The chain is heavy, so it wants to pull straight down. When the ship moves, it will lift the chain off the bottom, which will try to pull the ship back. And it creates a lot of drag on the bottom, so the ship can't drag it around. Even on a small ship, you need to have enough line so that the force acting on the anchor is as horizontal to the bottom of the ocean as possible. Meaning, pulling directly *up* on an anchor is easy and will just pull it out of the sediment on the bottom. Pulling it *sideways*, through the sediment is very difficult. And if you're near the shore or otherwise above the continental shelf, you have to account for tides. Too little line or chain and the tide will lift your ship enough that it'll lift the anchor off the bottom. > Do they not use anchors when the ocean is too deep? They do not. But there's not much danger. If you're near the shore, you need to keep your ship from moving at all because you risk running aground or running into a reef or running into another ship. But in the open ocean if you're drifting slightly, there's nothing to run into, and everything around you is going to be drifting together. That means that if people are swimming around off the ship, the ocean currents will carry them in the same direction as the ship, so you'll stay more or less together (assuming there's little to no wind; if it's windy, it wouldn't be safe to be swimming anyway). Sailboats can do another thing called \"~~luffing~~ [heaving to]( URL_2 )\" which means putting the ship at an angle to the wind such that the wind doesn't push on the sails in any direction, the sails are just flapping. When done correctly, you can keep the ship fairly stationary. The ocean current (if there is one) and waves may push the boat in one direction, but as soon as it starts moving it moves relative to the air, which fills the sails a small bit and slows the boat down again. It's not going to keep you perfectly still, but it's good enough to hold still for a while in open ocean without an anchor. Edit: Several people have mentioned sea anchors, which are essentially a water \"parachute\" like device that creates drag in the water so the wind can't blow you around too much. Won't keep you still, but it would prevent you from going too far. > Is there a safety mechanism to cut off the anchor if shit hits the fan? Edit: I understood this question to mean \"The anchor is already down and the ship needs to GTFO\" rather than \"The anchor is on the way down in an uncontrolled fashion.\" The answer to the latter is definitely a \"no\". Depends on the ship and how likely it is that they'll need to get rid of it quickly. There are emergency brakes to try to prevent [this]( URL_3 ) from happening, although obviously they don't always work. I don't know for military ships, but I would think they would have a way to very quickly cut the chain and release the anchor if they had it deployed and needed to get gone in a hurry. That said, when military ships are deployed they rarely stop. Edit: Several people have pointed out the \"bitter end\" of the chain, which is where the chain is attached more or less to the ship. There is a pin that can be removed (with a sledge hammer and great force) to disconnect the anchor chain if needed, like if the anchor gets caught on the bottom and cannot be raised. Military personnel have also pointed out that the time it takes to recognize an incoming danger is sufficient to properly raise anchor, especially since you're not going to be dropping anchor where a fight is likely anyway. Edit: I'm definitely not a sailor or anything, I just did some quick research and tried to remember other things I've read over the years. I know I've made at least one mistake so make sure you do your own research, eh? Also, go read Chris A Jackson's *Scimitar Moon*: it's got pirates and magic and strong female leads, and Jackson grew up around sailboats and knows how to sail so the jargon is all accurate (I'm just dumb and haven't read it in a while).",
"Anchors are big heavy things that attach you to the seabed. The ship remains attached to the seabed by a long cable the length of which is usually determined by the size of the vessel. Usually a ship will move back and forth over the cable until the appropriate amount of cable has been paid out and it is the length of this cable, which on big ships is heavy metal, that keeps the vessel in position rather than the anchor itself which just attaches to the seabed. The moment a ship let's go anchor, it is obliged to indicate this to other vessels by showing a ball from its yardarm during the day or an all round white light at night. Naval tradition says that warships will also fly their jack from the front of the ship. The water can be too deep to anchor even for the big ships this is particularly true in large oceans, instead vessels can often drift with little to no engine power. The best places to anchor are called anchorages these are marked on navigational charts and you should use these as they are like parking bays for ships. It is likely that the ship was anchored in one of these places. A ship will have a depth sounder on board which shoots a sonar beam down to the seabed to determine how much water is underneath the ship. This, along with the information on the chart allow them to decide whether or not to drop anchor. Just like parking, there are rules and you can't just drop anchor anywhere, if you do you can get in trouble with the coast guard. In some countries you need permission from the coast guard to drop anchor or depart an anchorage, not dissimilar to air traffic control. Finally there is usually a way to disconnect from your anchor in an emergency although this means severing the cable and losing your anchor. EDIT: Added some more details",
"There also are sea anchors. Basically a parachute that opens underwater when it is too deep to use a normal anchor. Essentially it slows your drift.",
"I’ll just build on what others have already explained. The winch that lets the anchor chain out and winches it up is called the Windlass. These can be electrically, hydraulically, or steam driven for raising and lowering, and has a manual brake for releasing. The anchor is stored in and chain let out through the Hawse Pipe. The chain is stored below deck in the forecastle in a chain locker, these will have a false bottom to allow water and mud to fall off the chain while not in use. At the end of the chain(opposite of the anchor) the chain is attached to the wall of the chain locker by a Bitter End pin. This pin is accessible from the exterior so that in case of an emergency, such as the Windlass brake giving way you can hammer the pin free and the entire chain will be set free rather than potentially damaging the ship or personnel. In regards to how deep a ship can anchor, the answer is not very. The windlass is powerful enough to lift the weight of the anchor and a few shots of chain, but no where near the weight of the entire length of chain available. As people have previously mentioned, what’s actually anchoring a ship is the weight of the chain laid out in lines on the seabed, not just the anchor itself. In fact, while anchoring ships still move at slow speed while letting the chain out. If hypothetically someone were to drop the full length of anchor and chain out without touching bottom the windlass brake could potentially fail, and even if it didn’t the windlass may not have the ability to winch it back up, which is another scenario where the Bitter End pin comes into play.",
"The common idea of how an anchor looks is somewhat archaic. ⚓ The type of anchor in that emoji hasn't been commonly used for a while. One popular design consists of two parts, a metal shaft connected to a pair of flukes, shaped like, and conveniently named, a plow anchor. Boats like to anchor in mud or sand. As the boat tugs on the anchor, the anchor burrows deeper into the bottom.",
"Can confirm I was an echo sounder operator and maintainer onboard a Royal Navy warship for 8 years. We used echo sounder sonar which was a shallow & deep water sonar while entering and leaving harbour. This would sometimes be used to test the depth of water for “hands to bathe” or where the water might be unchartered or risky. Hands to Bathe is when the ship stops in the sea and us “Matelots” (RN slang for sailor) go for a swim. Often we would stop in 3-10000 feet of water with no anchor though, I used to love swimming in the Indian Ocean on trips to the Northern Arabian Gulf. If we were doing exercises off the south coast of England we would drop anchor in special places. Usually in Plymouth sound. Let me know if you have other questions I’ll be happy to answer them.",
"22 year US Navy here. When we do swim calls at sea, we are always in fairly deep water, deeper than our anchor chain length. We will come to a stop turning off our engines and drift, but we only do these on deployments, and maybe once during a deployment if we are lucky. As far as the anchor goes, we drop based on charted positions and depths. The process we go through allows us to fairly accurately drop the anchor in the desired position and then reverse slowly as we pay out extra chain to further weigh down the ship. Typically the anchor will stay put and the ship will turn around the anchor depending on the current. If we need to leave, we will pull up the anchor and get underway... As far as emergency procedures go, our engines are powerful enough to drag the anchor. We will pull the anchor up as normal, but could me making way away from the anchorage at the same time, even though I've never seen this done. Our desire would be to catch any potential problems early before we would need to do this. Military ships will anchor in ports without piers large enough to support us, and sometimes for loading weapons or fuel away from shore for safety.",
"Large vessels also typically have dynamic positioning. Essentially very accurate GPS along with small motors in different directions controlled by software. Computer constantly checks position and sees, oooo we have drifted a little south, applies correct motors to drift back North. These checks are being made several times a second and constantly micro adjusting",
"So I'm not exactly certain on an aircraft carrier, but when I lived on a 44 foot catamaran, we let out the anchor and it's chain about 3-4X what the depth was, more if it was rough out. So if we were in 20 foot water,we let out like 60-80 feet of chain. A boat would not anchor in too deep of water, cuz the ocean is thousands of feet deep and you can't carry that much chain. That's why you have to anchor near islands. One reason trans Atlantic crossings are so hard for small boats (one of many many reasons), you can't just anchor at night, you have to have someone on deck watching. The way the anchor works is it is more of a claw than a heavy object. The claw digs into the sand or mud, and if the wind shifts your boat will swing which is why you need lots of chain.",
"Do anchors actually go all the way to the sea floor, or do they just hang about in the water, dragging the chain down? I've been curious about this for ages because they look like hooks, but if a hook got caught on rocks or something there'd be no way to get it unstuck :/",
"An aircraft carrier creates a lot of drag due to its displacement (weight) So it's not really at fear of drifting in calmer currents too much. I've done swim call of a 225 foot Coast Guard cutter in the middle of the pacific and we didn't drop anchor all the time. No point. One thing people don't always realize is an anchor doesn't keep a ship in one spot but rather in one circle. The radius of the circle based on how much chain is played out vs how deep the water is. The majority of the chain is laying on the ocean floor creating drag and friction but the ship can still move and swivel about a circle depending on currents and winds. So during swim call, a ship can move around just as much at anchor as not at anchor in relation to the people in the water. As an aside related to anchors, The ship I was in was an ocean going buoy tenders, and some of the buoys we retrieved/set were NOAA 6 meter long buoys. They sometimes had 8000 foot long anchors =mostly made of cloth hawser (rope several inches in diameter) since chain would actually sink the buoy. This was attached to a giant concrete block. We would put the buoy in the water almost a mile away from where we wanted it to watch (the center of its drift circle), and then steam over to its watch position, paying out anchor line as we went. We would then lower the concrete anchor into the water, lower it to the limit of our crane and release it. The block would sink and you would see the buoy zooming towards you. These NOAA buoys though had about a half mile drift circle.. So even at anchor the buoy could be in any spot in a half mile radius circle.",
"> So, how do they know when to drop the anchor? We generally just pick a spot and hit it using GPS, radar, etc. If in a channel, the ports will have a designated area for anchoring that we will use. > How long are anchors? I was on a Cruiser and we had 2 anchors, 9,000 lbs each. The centerline (main) anchor we used had a chain that was 12 shots, or just over 1080 ft. long. The starboard anchor chain was 9 shots, or just over 800 ft. > Do they not use anchors when the ocean is too deep? We pay out 5-7 times the depth of the water (e.g. 60 ft. of water, we'll use at least 300 ft. of anchor chain). General rule of thumb for the U.S. Navy is we don't anchor in anything over 100 fathoms(600 ft.) > Is there a safety mechanism to cut off the anchor if shit hits the fan? The anchor chain is secured to the ship using a padeye in the chain locker and a shackle that goes through the chain and the padeye, so there's no button anybody can press that just let's go of the anchor. However, every 90 ft. on the chain is something called a detachable link. It's a link in the chain that is able to be easily broken in case an anchor needs to be slipped. This is obviously very simplified info, if you want to know anything that's more specific I'd be more than happy to answer. Anchoring is a major part of my job.",
"First of all when you initially plan to drop anchor you look for nearby anchorages. Most ports have either one or multiple anchorages closeby, these anchorages are designated zones on the chart where it is recommended to drop anchor. In a lot of places you can drop your anchor outside of these zones, but that is reserved for emergencies. When you are at the anchorage you reduce speed to almost full stop, either the captain or officer of the watch then decides how many shackles will be used and whether the port or starboard anchor will be used (you have on almost all ships). A shackle is a length of cable defined as 27,4 meters long, multiple shackles are connected to form the total anchor cable length (from personal experience anywhere between approx 6 and 14) The amount of cable you drop into the water depends greatly on the water depth: First of all, the anchor has to reach the seabed. Second of all you add approximately 2 or 3 shackles of extra length. for extra holding power and to make sure you do not start dragging your anchor when the first small wave hits your vessel. The vessel will be facing the current (bow of the ship towards the current) before the anchor is slowly lowered by the winch. This has to be done slowly to avoid dropping the entire anchor chain into the water (something something inertia, look up anchor fail on youtube). The shackles are marked with colored sections so you know how much you have in the water, after the previously determined amount has been lowered the chain is secured and the winches powered down. From now on the bridge is monitoring the position of the vessel by all available means (gps most of the time) and the waiting game begins for when you can heave again. Also on the other question, if you drop in too deep water the anchor will just go down. Pull along the entire chain if you are not carefull and rip it straight out of your ship. So best not to do that, or atleast check how deep it is using the echosounder on the bottom of the ship. And finally yes, there is something for when shit hits the fan, the last link of the chain is secured with a mechanism that can be released (not very easy though, definitely not something you want).But that would mean losing your anchor including the chain. Will not be a very nice call to the company. Hope this answers your question!",
"What you watched is Swim Call. Jump off the aircraft elevator, swim to the back of the ship, climb up a giant cargo net to get back on. You can't just \"shut off\" a nuclear powered aircraft carrier. They basically stop all the shafts and slowly spin the screws once every couple minutes. They don't use the anchor for swim call. Swim Call is done in calm waters. Itvs not like a 90,000+ aircraft carrier is going to get pushed around in calm waters. We did use the anchor once or twice, it works just like any other anchor. Just a huge version. Obviously it has to be in shallow enough water to work. Outside of foreign ports usually.",
"Former US navy surface warfare officer here. I think what many of these responses have failed to address is a clarification in your question. It’s not the weight of the anchor that keeps a ship in place but the weight of the chain. A ship wants to anchor in water deep enough to put out about 5-7 shots of chain, which is about 90 feet per shot, or 4-6 times the depth of the water. You want a lot of chain to weigh the ship down. But, the ship will have an allowance of how much it’s able to swing around the spot its anchored. If the ship goes outside that allotted space it’s called “dragging anchor.” And, really importantly, at the end inside the ship, the anchor chain isn’t attached. I know a lot of people have mentioned the windlass that controls the anchor chain, so imagine that goes on the fritz in the middle of the ocean. If it were to let out all the chain the anchor would be hanging hundreds of feet down. Worse comes to worst, the whole anchor and chain can be let go. It will throw the ship off balance for sure, but the ship can rebalance through water allocation (ballast). This info is just from my experience on military ships. Smaller vessels may use anchors differently.",
"I work in the merchant maritime industry. There are [charts]( URL_0 ) for damn near every navigable waterway in these United States which have designated “anchorages.” These anchorages are selected on various criteria that are well above my head but when ships come into a port with a [Vessel Traffic Service]( URL_2 ), VTS or just “traffic”, they coordinate with traffic as to where to drop their anchor in the anchorage, including how many [shots]( URL_1 ) of chain/wire in the water -usually 5x the depth of the water- and to determine maximum stay in the anchorage based on numerous factors-usually cargo, draught, and weather.",
"Former Navy here, fun story about hauling the anchor in my boat (LHA-4, last of it's kind on the East Coast). We were hauling it up one day, and when we do, we secure it with large hooks called Pelican Hooks. These things weigh a ton and basically go around a link in the chain and act as a failsafe in case something goes wrong and it comes loose. Buddy of mine was showing some new guys what to do and jt eas taking forever (as it always did), so I was getting bored and not paying too much attention. My position at the time was on our Sound-Powered phone connected to the bridge so I wasn't right next to them. All of a sudden I hear a CLANG and an AHHHHHH FUCK! One if the new guys had dropped the hook and the clamp had landed on my friend's thumb ripping the nail clean out. He made a huge show of it acting like the new guy had practically tore off his whole thumb (he was a rough red neck sob and this was nothing to him). Not exactly on topic but the question made me think of this and thought I'd share.",
"I can't speak to very, very large ships, but I've piloted my share of sailboats and know a bit. You only anchor when it's shallow enough to hit the bottom with your line. When you're out in the true blue open ocean and there's absolutely nothing else to hit... It's actually fine if you drift a bit. Even if there's stuff next to you, as long as you're not under power, you'll all basically drift in the same direction at the same rate. Wind aside, you're all under the same forces. Anchors work by pulling their hooks into the bottom of the ocean. You also use a length of chain off the end of the anchor to help keep the anchor pointed the right direction, and add extra weight. [See how the points dig in]( URL_0 ) - to make that work, the anchor needs to lie over on it's side. The chain makes sure the line (rope) doesn't float the anchor and prevent the points from catching and digging. You also need a nice long rode. The rode is the extra line you put out so that you're not right above your anchor. A good rule of thumb for a secure anchor is 7:1 rode - your rode should be 7x the distance from your tie-off point to the bottom. EG, if you're in 24 feet of water and your bow cleat is 6 feet above the water, you should put your anchor on at least 210 feet of rode for a secure, overnight type of hook. [There is such a thing as a \"sea anchor\"]( URL_1 ), which minimizes your movement, but doesn't actually anchor you the same way a Danforth does. A sea anchor is kinda like a giant parachute you deploy under water, and it's really used to help keep your boat pointed a particular direction when the weather gets really bad. If you can keep the boat pointed into the wind (and therefor into the swell), you're less likely to take a wave broadside and get really fucked by a storm."
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9alj15 | Why are two manhole covers sometimes separated by a foot or less? | Engineering | explainlikeimfive | {
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"They probably are for different purposes. One may actually be for the sewer; the other is probably for electrical, telecom, etc."
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9am63n | How do tuning companies perform ECU tunes on cars, in order to gain added performance (e.g. increased horsepower)? | & #x200B; | Engineering | explainlikeimfive | {
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"Since most modern cars have ECU-s that contain a certain map that specifies air-fuel ratio, every factory map is set up to work in every possible enviroment in the most efficient way possible. Lets say you drive in high altitudes, the sensors tell the ECU that the air is not very dense so the ECU makes calculations to compensate for it. Now since most cars are optimized to be efficient and spend the least amount of fuel necessary, changing the map of the ECU results in higher fuel consumption but also higher power output from the engine. It's simply tweaking the air-fuel ratio in the engines rev range that can affect the performance and life expectancy of the engine. You simply upload a modified map to the ECU and test the car to check for the performance. Some people do down-tunes, to actually decrease consumption, but that thing is rare."
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9amvpn | Why cant water enter the boat thru the propellers shaft? | Engineering | explainlikeimfive | {
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"We're really good at making tight fitting cylinders. If you think about it, every internal combustion engine has at least one - often 4 or more - cylinders-inside-tubes that are keeping not just liquids on one side, but exploding gasses. Unlike these cylinders, a propeller shaft just needs to rotate, which means we can even add oil to keep the water out. Oh yeah and if a few drops make it in we basically don't care. Water always makes it into boats, that's why you drain the bilge occasionally.",
"Because is has a shaft seal (or 2) to prevent it. There is loads of information about shaft seals on t'internet... Off you go! If you get a shaft seal wrong, you either have to have good bilge pumps or abandon ship. A famous military contractor fcuked up the shaft seals on some of the UK Navy's vessels the other year which cost them a pretty penny to replace....",
"Theres a stuffing box and gland nut you can tighten over the prop shaft packing. The packing is basically cotton twist strands coated in grease to provide a tight and waterproof seal. The more you tighten the gland nut, the tighter the seal, but also more resistance for the prop to spin through."
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9anpwg | How does pressing down on the accelerator make a car move forward? | Seriously, no idea. | Engineering | explainlikeimfive | {
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"The answers so far are imply that there's an actual cable or mechanical connection between the throttle and the engine, but that isn't the right story anymore. In older cars, pressing down on the throttle opens a valve that controls the degree to which air can enter the engine. More air means more fuel injection, and more power, so you accelerate faster. But most modern cars don't do this; instead they're \"drive-by-wire\". In DBW vehicles, your throttle is connected only to an electronic sensor that essentially registers a number between 0 and 1 indicating how far down you're pressing the throttle. It is not otherwise connected to the engine. The value of this sensor is passed to the computer running your engine, the Engine Control Unit (ECU). The ECU makes a decision about how much air and fuel to provide to respond to your pedal commands. In theory, this results in more efficient driving and lower wear on your engine, because the ECU can more smoothly transition between engine states in a way that would be difficult for human to manually control.",
"The pedal is connected to a cable that is connected to the throttle body. The throttle body is a butterfly valve located between the air intake filter and the intake manifold. It regulates how much air can go into the engine, based on driver input through the gas pedal. As more air flows into the engine, it injects more fuel, thus allowing for more power."
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9ap5gt | Why does driving feel smoother in the drivers seat? | Engineering | explainlikeimfive | {
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"When you know what will happen, your body prepares for it. Hard left, you know exactly when it will happen. Aceleration, deceleration are the same, you prepare for acceleration when you press gas pedal. Passengers are surprised when something happens, and their body doesn't react. Like in football, if someone slams against you and you expect it, you might even not even fall down. But someone surprise slamming into you while you are relaxed and standing on a street not expecting it, you will hit the ground so hard."
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9awgph | how does the fuel gage in the car measure how much gas is in the tank? | Engineering | explainlikeimfive | {
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"There is a rod with a floating plastic bobber on it. As the gas fills it floats to the top of the rod telling the gauge you are full. The position of the floater changes the gauge"
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9azpf2 | Why is the leaning tower of Pisa still standing? | Engineering | explainlikeimfive | {
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"The [inside]( URL_0 ) is hollowed out and filled with reinforcements supports holding it upright. Only the outside of the tower is original.",
"The tower was closed in the 1990 for performing corrective work which took a decade. This consisted mainly on the removal of soil from one side in order to straighten the tower, as well as some weight removal, placement of counterweights and clinching some cables to slowly pull the tower into the right direction. This is expected to keep the tower stable for at least another 200 years.",
"The tower of Pisa isn't leaning. It is upright. It is the rest of the world that's lopsided."
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9b005w | Why do touchscreens respond to my fingers but not, for example, to my gloves? | Engineering | explainlikeimfive | {
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"Fingers are conductive, and gloves are not. Fingers hold an electric charge. It's very weak but it's there. That's how you can use a touchscreen by hovering your finger just barely above it. The display can measure the change in the electrical field and use it to determine where your finger is, which is then used to make a button press or whatever. A glove can't do this as it doesn't conduct or hold a charge",
"There are two types of touch screens, resistive and capacitive. Resistive works by having multiple layers of glass and diodes, so when you push down on the touch screen, it activates the diodes underneath transferring a message to the CPU saying \"there's a touch in X,Y\". It works via pressure on the screen. Which is why you can use old ATMs with gloves, and could use literally anything as a stylus for your Nintendo DS. Capacitive touch screens are different in that they require an electrical conduit to register input, so tapping your finger against the screen allows the hardware to find where the current was completed and tell the CPU where the screen was touched. So why wont your glove work on a touchscreen? Simple, it's a capacitive touch screen and your gloves fibers don't conduct the electricity to complete the circuit. Hope that helps."
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9b1fmh | How does the military (any military) do air-to-air weapons testing? | Engineering | explainlikeimfive | {
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"They have drones. Sometimes there are purpose built drones like the [Chukar]( URL_0 ), sometimes they'll rig a mothballed old fighter from the boneyards in Arizona and remote control it. The 82nd aerial targets unit out of Tyndall AFB fly old F-4s as full size targets."
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9b3wpw | What's the difference between the voltage across a resistor, voltage drop, and voltage? | I am really confused on what is being measured and how everything correlates. | Engineering | explainlikeimfive | {
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"Voltage across a resistor is measured by the current through it, and the resistance of the resistor itself. Voltage is the potential across two terminals. So by measuring the voltage across each resistor, it should add up to the overall voltage. Voltage drop is also due to losses incurred in things like cables. So the current travelling through a cable will heat up and use power (P=i^2 *R), and a voltage is measurable from one end of the cable to the other. The voltage across the cable is the voltage drop, subtract this voltage from the voltage at the node in front of the cable, and you have the available voltage at the end of the cable node. Voltage is simply the difference in potential between two points. Using water analogy really helps in the fundamentals of electronics. Think of voltage as water pressure. The higher the voltage, the more current can be pushed through a resistor."
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9b80px | Why on cruise ships do drinks not spill when the ship is rocking? | Engineering | explainlikeimfive | {
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"Because the ship is wide enough that rocking doesn't affect the balance as much as it does a smaller boat. Take a 10 cm stick and balance it on your finger. lift one end up 5cm and it will probably fall off your finger. Now take a 1m stick and do the same. It will probably still stay on your finger. It's the same thing for cruise ships. Because they're so wide. Lifting one end up doesn't change the angle of the deck that much, as a result it doesn't shake back and forth violently. You would need much stronger waves to shake a cruise ship."
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9b8a55 | IVT's (infinitely variable transmission) | Engineering | explainlikeimfive | {
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"An IVT and a CVT are largely the same thing; the only real difference is that CVTs typically have a minimum allowable output speed (below which they disengage completely using a clutch). IVTs are continuously engaged all the way down to zero RPM output, which allows you to drop the clutch entirely from the system.",
"CVT and IVT are almost the same thing, but the gearing goes all the way down to zero for IVT. So theoretically, infinite input to output ratio is possible (not applicable in real life)"
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9bd2lp | What does Sport Mode do to my car (2015 Jeep Grand Cherokee, if you're familiar)? I just don't notice much difference... | Engineering | explainlikeimfive | {
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"It changes the way your transmission and traction control are set up. Sport mode will let your engine rev higher in each gear to get more power down to the road instead of being set up for fuel efficiency and your traction control will most likely turn off. In some fancy cars the throttle (gas pedal) and suspension will change to harsher and harder settings, but that’s not likely with a Jeep unless you have the SRT model. It’s just a slight change from regular mode because it’s not a sports car, but you should notice the Jeep accelerate easier in sport mode than in snow mode or auto mode."
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9bf945 | Difference between Power and Energy? | I've read multiple articles on this but I just don't get it. Please explain me like I if I was actually 5! Thank you all! | Engineering | explainlikeimfive | {
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"Consider speed and distance for a car. You want to reach a different town? If you drive fast you arrive there quickly. If you drive slowly you need more time. In both cases you drive the same distance. Power is a bit like speed and energy is a bit like distance. If a machine uses/produces a large power it uses/produces a lot of energy quickly. If it has a small power it needs much longer to use/produce the same energy.",
"Energy is the ability to do work. Work is the force applied on an object multiplied by the distance the object moved. Power is the rate at which work is done.",
"Power is the rate of change in energy. So looking at a phone as an example. The battery contains energy, but the phone uses power. In a hydroelectric dam the falling water has energy and spins a turbine which creates power."
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9bp7ti | Why tranquilizer darts have a fluffy red tail thing? | Engineering | explainlikeimfive | {
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"To increase drag on that end so the pointy needle end goes into the animal target. If the dart tumbles, like a ball or can of soup if you throw them, then the pointy end might not hit the animal and give it the tranquilizer shot. It's red in case you miss, so it's easier to find the dart (because darts cost money).",
"They don't always. If they do it is likely for visibility, particularly for the purposes of film which is where I suspect you are getting all your information about such darts. The presence of some sort of fluffy substance on the back of the dart has two purposes. First it blocks the barrel of the dart gun so that the gasses cannot easily slip around the dart, meaning it must be forced out the end of the barrel. Second it provides drag at the rear of the dart keeping it pointed forward rather than tumbling.",
"It's called [fletching]( URL_0 ). It's serves the same purpose as the feathers on the end of an arrow. It aerodynamically stabilizes the dart in flight, allowing it to fly straight and true."
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9bpmo4 | The No-Slip Condition | I am taking Fluid Mechanics this semester and one of the first topics covered was the No-Slip Condition, but the actual mechanics (?) of why at the boundary the fluid has a velocity of zero wasn't really explained. I understand that there's a frictional force, but is that it, the book mentions even in the case where the solid was completely smooth, non-porous, that the fluid would still have a velocity of zero. Fellow engineers, physicists or chemists, can ya help me out? | Engineering | explainlikeimfive | {
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"As a fellow engineer I will explain it to you in the best way I can: A joke. A math professor tells two students, an engineering student and a mathematics student, \"On the other end of the room is the prettiest woman in the school. You can kiss her, but you need to walk half way across the room, pause, walk half the remaining distance, pause, and so on.\" The math student says \"But according to Zeno's Paradox you could never make it across the room, isn't that right?\" Turning to the engineering student, who is already half across the room. \"You can't make it across the room\" says the math student. The engineering student shrugs, \"Eh... I will get close enough.\" When it comes to the math of engineering, close enough works. No, a fluids velocity isn't zero at the surface of the solid. But it is close enough that you might as well just assume it is zero."
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9br4zf | Having multiple motors | How do you use multiple engines to drive a vehicle? I’ve seen cars with two engines and such, but how would you connect the engines so they would work together? | Engineering | explainlikeimfive | {
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"There's two ways, make each engine control a specific set of tires, or make both engines go through the same transfer case or transmission. If both engines are independent, the gas pedal will be linked to all the engines to theoretically provide the same output at the wheels. In practice, variations in each engine, gear, wheel, and even the road or environment can make it less than optimal, if not dangerous in the worst case. If both engines go through the same drivetrain. This forces the wheels to all be sychronized with your gearbox, and the engines only need to worry about matching the gearbox. This is popular with electric hybrids, as the electric can seamlessly take over without changing the car's driving characteristics. If your question is more about hybrid cars, this goes over some different types. [Hybrid Drivetrains ]( URL_1 ) If you want a neat example of two petrol engines, going through a dual gearbox check out this guys 1600hp monster. [Golf GTI VR12 with 2 engines]( URL_0 )",
"Typically by using a *planetary gear set* which allows either of two drive input gears to advance the output gear. URL_0"
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9by8dk | What causes sinkholes? | Engineering | explainlikeimfive | {
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"Majority of sinkholes are caused by water eroding away material underground, causing the layers that are resting above to slump downwards.",
"As an example, my city of Ripon sits on a lot of gypsum, which quite commonly erodes due to water damage, and leads to the ground falling to fill the gaps eroded. The upshot of this is basically the ground 'settli g' for big old sinkholes in the ground. There are other minerals that are susceptible to this, but in Ripon it's gypsum. And Ripon is the sinkhole capital of the UK."
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9byu67 | Is more heat generated by air conditioning than cold air except that the cold air just goes where we want it? | Engineering | explainlikeimfive | {
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"text": [
"That's correct. Air conditioners don't generate cold at all. They are *heat pumps* that move the heat out of your room and into the outdoor air. And the actually create some more heat in the process.",
"Yes. Moreover, you are strictly increasing the total amount of heat in the world, since the air conditioner cannot run at the theoretical maximum efficiency according to thermodynamics."
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9bzevj | How do boat sails work if the wind is going the wrong way? | If the wind is going towards you, how are you going forward? It doesn’t seem like a very reliable system, same if there is no wind. | Engineering | explainlikeimfive | {
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"If there is no wind you're going nowhere. When there is wind your sailboat can move. Let's sneak up on the answer to your question by answering a few related questions first. Let's assume the wind is blowing from the North at 10 knots (about 10mph). How fast can you sail South? The fastest your sailboat can travel directly downwind is the current wind speed, in this case 10 knots. The fraction of this speed will vary greatly depending on your boat. Sailing directly downwind will make the wind feel very calm on the deck of the boat since the boat travels at the same speed and direction as the wind. How fast can you sail East or West? Counter intuitively you could sail East or West much faster than the wind speed. Why isn't the wind still blowing our boat South while we face East or West? It is because all sailboats have a keel. The keel is the big fin on the bottom of the sailboat. The keel allows the boat to slide forward on the water easily, but the boat is difficult to push sideways. The keel looks narrow from the front and wide from the side. How does this make us faster? When we were sailing downwind we could move as fast as the wind but no faster because we would run out of wind. When we're going sideways to the wind our sail collects the wind and pushes us. The keel keeps us from pushing sideways, so we push forwards instead. As that wind spills out of our sails there is new wind from the North replacing it, so we keep getting more and more power. We're not running away from the wind, so we don't run out. A good sailboat will fly when the wind is from the side. So, finally, how fast can you sail North? Well, you can't, not directly, but we can sneak up on it. We already learned that our boat is faster going East/West than South. What if we went a little tiny bit North of East? Well, our speed doesn't instantly drop to zero just because we're pointing a little bit towards the wind, we're still mostly going East where we're fast. We're not going as fast pointing a little North, but we are moving a little North (and a lot East). So, let's point a little more North. Now we're moving slower, but we're going a bit more North and a bit less East. We can keep on pointing more and more North until we lose so much speed that we stop moving. Somewhere before that point, often about halfway between North and East you'll find the spot where you're still moving well and you're getting equal amounts of North and East. All of the North travel is good. All of the East travel is wasted. At some point your sailboat gets too far off to the east. You'll turn your boat to the North West and do it in that direction. Your North travel is still good, and your West Travel is undoing all of the wasted East travel that you did before. This is why sailboats Zig Zag when traveling towards the wind.",
"You have to do what’s called tacking, where you zig zag back and forth using some of the wind with sails at 45 degree angle, then swing sail to other side to turn 90 degrees.",
"Oh I did this one a while back and found some neat diagrams. Wait a mo: Edit. Damn can't find it and Oh well here's an improv version with not as good diagrams. You can't sail in to the wind but you can sail at 45 degrees to the wind, and use this to zigzag upwind. In fact sailing against or sideways to the wind is faster than sailing with the wind, for reasons we will get into. When you sail with the wind the sail just acts as a bag pulling you forwards, but sail in any other direction and it acts more like an aircraft wing. The curved shape of the sail creates \"lift\" except because the sail is vertical not horizontal that \"lift\" is pushing you. [Like this]( URL_0 ) But that doesn't push you forwards, it pushes you sideways. But you've got a keel (to go upwind you need a big keel) and the keel pushes against the water and the water pushes you back, and that stops you from going sideways, so instead that water preventing you from going sideways turns that sideways motion into forward motion. [Like this]( URL_1 ) And it can do it faster than the bag effect can. Say you are going with the wind you can only go as fast as the wind goes. But if you're going against the wind you create your own wind by moving and so the \"apparent wind\" for you is stronger than the actual wind (because you're making your own wind) and so you can go as fast as *that* which is faster.",
"To sail up wind you basically zig zag. You set your sail and turn your Rudder to angle up wind slightly. Then turn around and repeat. It takes a while."
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9bzwp8 | Why dont front windscreens of cars have defogger lines like the rear window? | Engineering | explainlikeimfive | {
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"I'm not sure if I'm misunderstanding all the answers here, but a lot of cars absolutely **do** have defogger lines in the front window. They're just made to be a lot finer and are normally vertical so, sure, they don't distract, but also so you don't get the horizontal bands of gradually widening visibility when you switch on, it clears things a lot more evenly and quickly. [Here's]( URL_0 ) what a heated windscreen grid looks like close up.",
"Just a side note, Ford UK have been doing this for years. I had to drive an old Ford Transit connect (minivan) at work. 2004 model. Had vertical elements in the windscreen to deice/demist",
"My understanding, for the UK at least, is that it is under a patent owned by Ford. So you only get it in Ford cars."
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9ccdkt | How does red/blue-striped toothpaste always come out of the tube perfect and not with the colours all mixed together? | Engineering | explainlikeimfive | {
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"It's a paste. It doesn't flow very easily, so if it's put in the tube in such a way as to have the stripes, when you squeeze the tube the stripes don't flow through one another, they're just pushed away from the place you squeeze it. If you reach the end of one of these tubes, the stripes tend to be much less pronounced, due to the number of times they've been squeezed and mashed, mixing the contents."
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9cjn4q | how can a spark plug porcelain shatter a car window so easily? | Engineering | explainlikeimfive | {
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"text": [
"basically porcelain is very dense compared to glass it's also very sharp and comes to a small point normally, now when you apply all the pressure of hitting something (window) onto such a small point (end of the porcelain plug) it shatters the surface tension of the window before it can react , breaking the whole window because the tension has broken"
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9cmvzt | Why do most SUVs have a rear window wiper and cars do not? | Engineering | explainlikeimfive | {
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"Because the vehicle just sort of \"ends\" at the back window and goes straight down, it ends up creating a sort of suction zone at higher speeds that will pull water towards the vehicle, which ends up accumulating on the back window and blocking your vision. Worse, in muddy/offroad conditions this also ends up drawing airborne muck and dirt and grime onto the back window as well. Hence SUVs, minivans, hatchbacks, and other \"boxy\" vehicles will generally have a rear window wiper.",
"SUVs, wagons, minivans, and hatchbacks (or really any vehicle that has a window at the very back )have a pocket of air right behind the back window that usually swirls. On rainy days that pocket \"traps\" the mist of road grime that's kicked up by the back tire and that grime usually sticks to the back of the car.This usually makes for a very dirty back side of the car, especially the window. The grime on the back of a sedan or car usually gets stuck to the trunk area, but will pretty much never make it to the window. This is also why many new SUVs have a \"lip\" over the rear window. It helps to break up some of the swirling air and reduce some of that crap as well as drag."
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9cop7r | How do ethernet cables fail? They typically don't move or get put in extreme temperatures yet they still fail from time to time. | Engineering | explainlikeimfive | {
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"text": [
"Usually the failure point comes down to either being bent/twisted one too many times which damages the cable internally, or the cable getting yanked on hard enough to separate one of the wires from it's corresponding pin in the head. I work in IT and support around a thousand users, so I've seen every possible break scenario."
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9cqgsx | Does having a Hole/ Blow in your Exhaust Consume more Fuel, does position of the hole matter? | I was curious because recently my car's exhaust has been a lot louder and a friend says its bad for fuel. quick search found this article [ URL_1 ]( URL_0 ) but.. to lazy to read and dont have any mechanic friends. & #x200B; Thanks | Engineering | explainlikeimfive | {
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"text": [
"If the leak is in front of the O2 sensor then it can effect the mileage. If it's after the O2 no problem."
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9cs01s | Why does the Detroit–Windsor Tunnel run underwater and isn't just a bridge? | Engineering | explainlikeimfive | {
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"text": [
"Ships that navigated that waterway had extremely tall masts and it was feared that a bridge would be a hazard to them. A tunnel avoided that problem, and today such masts aren't an issue."
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9cu3e0 | How does an external battery charge a device with more power than itself? | If my external battery is nearly dead and my phone is near 100%, it stands to reason that the net charge of the external battery is lower than that of the phone's battery. How does the external battery continue to add to the phone battery's charge? If they form a circuit wouldn't the higher charge flow into the lower charge? | Engineering | explainlikeimfive | {
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"text": [
"Both your external battery and your phone have voltage converters in them. Essentially pumps to make sure the electricity goes in the right direction. The *actual* battery in your external battery's converter, if it's almost dead, will have a voltage about 3.0 volts. And your phone, if it's near full, will be about 4.2 volts. The circuit in the external battery converts the 3 volt power from the battery up to the standard USB voltage of 5 volts. The circuit in your phone converts that back down to the needed charging voltage of 4.2 volts. Both of these converter circuits are only designed to work in one direction."
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9cz7lb | Infrared Thermometers | Hey guys. Just watched the Great British Bake Off and Dan was using an infrared thermometer to measure the temperature of his chocolate. How do they work? How can you measure the heat of something by firing light at it? | Engineering | explainlikeimfive | {
"a_id": [
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"> How can you measure the heat of something by firing light at it? It doesn't fire light at it, it looks at light coming off of it. Everything emits light of a frequency related to its temperature, an example is how metal will glow visibly when very hot. Cooler things still emit light but not in the visible range.",
"The laser emitted by the IR thermometer is just to aim it. It it purely absorbing and interpreting the IR already being emitted by the chocolate. Hot objects emit more IR light than cold objects on a predictable scale. So the temperature can be inferred by the amount of IR being emitted. Night vision works on the same principle of IR emission."
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9czgww | Three leg tables don't wobble. Why aren't they more prevalent in restaurants and other establishments? | Engineering | explainlikeimfive | {
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"text": [
"I would have thought it was to allow for maximum area for weight distribution. On a three legged table you may run the risk of placing a load on the edge of a table (assuming its round) that may unbalance the table? On a four legged table that scenario should be impossible."
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9czlek | What are “pull-up” and “pull-down” resistors in a circuit? | What are these for? Why are they necessary? How do I know if I need to add one, when building a simple circuit, and how do I choose the resistance / value for it? | Engineering | explainlikeimfive | {
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"If you have an input to a binary circuit, that input at some point has to be decided on as either 0 or 1. If you leave that input 'floating', then random variations in charge can make the decision circuit unsure as to if the input is high or low. The solution is to provide a 'default' setting, which will overpower the noise associated with a lack of signal, but will be overpowered by an actual signal. So you can either connect it to ground, or power. You don't want to just directly connect it though, because it would overpower any input signal. You need a resistor. As for the value of the resistor, you can probably calculate it based on the characteristics of the digital circuit, but it's safe to say 1-10kohm. If you find your circuit still has noise, decrease the resistance. If you find it has trouble changing away from the pull resistor, increase the resistance.",
"They are so a wire have a know voltage if nothing is connected to it and the output is connected to for example a transistor. A simple example is a button that is open if not pressed and closed if pressed. You connect the wire between the wire and +5V. When you pres the button the voltage is +5V but what happens when you release it? If the circuit on the other end use no current like a MOSFET transistor that might be the input of a integrated circuit the wire can float and still be at +5V for long time. So to change the circuit to be 0V when the button is released you connect it with a resistor to ground. What size is needed? That is hard to say as a larger value result in slower change to 0V but a smaller value will let a large current trough it when the button is pressed. If what is connected is not a button with 0 resistans but something with resistance the pull down resistor will stop it from reach +5V and if it is to low value resistor the voltage might never get as higher as is needed. So the complex answer is that the value of the resistor depends. Look at values other people have used in similar design and understand your constrains."
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9d2nwt | How do light dimmers work? | Engineering | explainlikeimfive | {
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"They change the amount of power that is going to the lightbulb thus decreasing or increasing the luminosity.",
"Depends on what kind of dimming. These days it seems to be either DC control - so just increasing or reducing the amount of DC voltage the lighting system is receiving (popular for flicker-free backlighing on LCD panels); or PWM (pulse width modulation) dimming, where the lighting is switched on and off many thousands of times per second, based on a \"duty cycle\" signal received.",
"the real ELI5: the turning switch controls the voltage, less voltage in = less energy (light) out Eli~5: URL_0 visuals from here will help a lot.",
"If you switch an led on and off too fast it just looks dimmer. This might happen if, say, you're programming a microcontroller to flash a row of lights in sequence and didn't think to include a timer/countdown after each flash.",
"Older ones used a resistor, wasting some power as heat and sending the rest to the light bulb, but more modern ones us what’s called “PWM” which basically means they turn the power on and off very very quickly so that the lamp is on for less time in a second, therefore appearing less bright."
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9d777j | How does electric current "spins" the motor in an electric engine? | When you turn on a toy that has an electric motor in it, how does a current of electricity ends up as a spinning wheel? How is that energy transfered? & #x200B; | Engineering | explainlikeimfive | {
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"When electricity flows through a conductor it creates a magnetic field around it. As you know magnets can push and pull on other magnets, and a motor uses this to convert electricity into physical motion. The basic structure of an electric motor involves a couple of electromagnets which can be switched on and off, or even changed in polarity to cause a central core to spin.",
"In a brush motor, which is probably what you're talking about, there are permanent magnets and there are electromagnets. The electromagnets are given a polarity based on the direction of the current going through them. Power connect to these through \"brushes\" that run up against connectors to the electromagnets on the rotating bit. At the motor turns, the electromagnets will change their polarity in relation to the permanent magnets around them. So this always changing push/pull from the changing polarity causes the rotational bit to spin.",
"When current (charges) move through a conductor, they induce a magnetic field around them. This magnetic field can interact with other magnetic fields to produce a force, which causes movement. In a small toy, you'll have a brushed dc motor with permanent magnets on the stator (non moving part of the motor). These magnets are making a magnetic field going from one magnet to the other, through the rotor (the part that moves). The rotor ([image]( URL_0 )) has some coils of wire in it, a commutator, and brushes on the commutator. The brushes do not move, as they are connected to the stator. They are pressed to the commutator to allow current to flow. As the motor spins, a magnetic field is generated in the rotor in such a way that it is not aligned with the magnetic field going from one stator magnet to the other. So a force is produced. When the force is produced, it'll cause the rotor to spin a bit. As soon as it spins, the coils that were energized by the brushes are disconnected, and the next set are energized. So there's an effect like the donkey with the carrot tied to it's head, as it moves forward the carrot moves with it and the donkey never gets the carrot.",
"Electricity is like invisible water spinning around a wire. It does not push on you or the house, it only pushes on magnets. If you wrap wires around a magnet and give it electricity the magnet gets caught in the spin and start going around like the wheels on a electric toy. Most electricity comes from spinning the electric motor with different power, like big windmills. This spinning of the magnet near the wires does the same thing, it puts the spin into the wire which can then travel around and spin toy motors."
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9di4cq | why do modified late model cars backfire? I assume late model cars like BMWs aren’t carbureted but just saw one backfiring like a machine gun as they stop light raced. | Engineering | explainlikeimfive | {
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"It's probably not backfiring. It is likely an anti lag system that dumps fuel and air into the exhaust to keep the turbo spinning while the driver shifts gears. I don't think it's street legal, but I'm not 100% sure about that, and probably varies by area. URL_0",
"I think you are actually referring to anti lag, which for simplicity..... throws the exhaust gas out while it’s still expanding. It’s so the turbo spools faster (external gate).... side effects fire breathing monster that sounds like an ak47 URL_0",
"AFAIK there's a few things that contribute to maximum backfire. 1. As you may have noticed, this combustion happens when you let off the gas pedal, because this closes the valves, and creates a vaccuum in the exhaust system that sort-of sucks air back into the pipes. This air will meet with any unburnt gases in the exhaust system and then combust, creating a noise and sometimes a flame. 2. Air/Fuel ratio. If you're running rich (AKA too much fuel for the amt of air) more unburnt gases will be making it out of the cylinders and into the exhaust system, where they will meet with the air I mentioned above. 3. If you have removed your catalytic converters, then a lot more of the leftover unburnt fuel will be making it into the exhaust system as well. Hell, I get occasional backfires on my nearly stock G35 just because my exhaust is wider and sucks more air back in when I let off the gas pedal."
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9dl9qf | why are plastics straws worse than plastic cups? | As a restaurant worker, we are required by health code to have our own beverages covered by plastic and use a straw. I don’t know why this is, but why is there such a problem with plastic straws lately and no other forms of plastic containers? Other examples are pre-made salads that come in plastic bowls with plastic silverware and a plastic seal around the outside. Where’s the outrage for that? Are straws disposed of differently? Why can’t we recycle them? | Engineering | explainlikeimfive | {
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"Straws are small and thin. Because or their shape they might not be able to be handled by some recycling facilities as they'd clog the machines. So some facilities just sort out all the straws and send them to the dump. They are also small enough to be eaten by various animals, which of course causes issues.",
"Part of the issue is the fact that *most* people don't need straws. They can drink their beverage without them. So the real push is to get restaurants to stop giving them out by default, but rather only when a customer asks for one. However you need a cup of some sort, you need utensils, etc.",
"This whole plastic straw thing is green posturing started by a deeply flawed study done by a child that wildly overestimated they number of straws used daily. Since \"zomg we're using so much plastic for straws\" gained traction for some reason it became trendy to stop using them. Not only is it not based on valid reasoning, it's sometimes even making things worse. Starbucks replaced straws with a straw-free lid that actually uses *more* plastic than the old lid+straw combo used to. tl;dr - It's trendy to not use straws right now because people are dumb."
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9dobl0 | Why are Jet Engine Planes smoother rides than Propeller Planes? | I've seen models of modern jet engines, and since it's a different type of propeller, why are rides in jets much more smooth than the rides on propeller planes, even if the propeller planes use propellers on the wing than the single propeller on nose? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Jet engine planes tend to be heavier and go faster making them less affected by wind currents.",
"It has much less to do with whether the airplane is propeller or jet powered than it has to do with how much weight the wings of each type aircraft carry, given the wing size. In this case, large jet transports carry more weight per square foot of wing. This means there is less wing area (per pound of aircraft weight) for a gust (turbulence) to work against. This is called, \"wing loading.\" Fast moving aircraft (jets) can use their additional speed through the air to make up for having a smaller wing. They also typically need a lot of additional devices that can modify the shape and size of the wing to fly more slowly during takeoff, climb-out, approach and landing. At cruise speed and altitude, these are fully retracted and reduce the wing size. Slower aircraft don't modify their wing size or shape nearly as much. If you've sat at a window seat over the wing, you've probably seen these devices extend and retract when you take-off and land: Flaps. Slats. Flaperons. There are a lot of variations used on modern airplanes. Smaller propeller aircraft are designed to operate at lower altitudes and speeds, and typically have a larger wing area per pound of airplane being supported (they have less fancy devices to modify their wing size and shape during flight). That gives the turbulent air more wing area to knock around the same amount of weight on a smaller propeller aircraft, no matter how many propeller engines it has or where they're located. Non-ELI5: URL_0"
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9du2ns | How does a power bank "know" when it is connected to charge itself, and when to charge the connected device? | Engineering | explainlikeimfive | {
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"text": [
"There are logic boards in power bank, device, and charger that communicate, and tell each other what to do"
],
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9dv6xk | how toy cars convert your pull backwards into forward momentum over a longer distance. | It has always amazed me that you can pull a toy car backwards, let it go, and it will travel across the whole room. How does that work? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"When you pull it backwards it winds up a spring, then when you release it the spring unwinds sending the car forward",
"You pull it back slowly and not very far, but you’re pulling it really hard (lots of force) while you do so. If you do the math, this means you transfer a lot of total energy into the car. When the spring releases this energy back into the wheels, it’s able to turn them quite fast... it doesn’t face much resistance because the car itself is very light. This gets the car up to speed and it continues to glide across the room... on a smooth surface, there’s very little slowing it down. Your muscles could transfer the same amount of energy to the car quickly by, say, throwing it. But this would feel like more work, because our muscles are well-suited to a steady pulling motion (we do this all day to move ourselves around and pick things up) but aren’t as efficient at sudden, fast motion."
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9dxccw | How exactly does a fuse work in an electrical plug? Recently had one blow on an appliance. | Engineering | explainlikeimfive | {
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"text": [
"Think of a fuse like a water balloon. The balloon is the fuse and the water is electrical current. When too much water goes in to it, the balloon pops. When too much current goes in to a fuse it pops. For a more scientific reason and less of a 5 year old one, the fuse itself is rated to carry a current up to its limit. Electrical current also gives out heat and the higher the current the more heat is put out. The heat output melts the fuse if there's too much.",
"The fuse is made of a material that will pass the electricity, and get hot. It is calculated just right that it will melt from the heat if too much electricity goes through it. Once it melts, the electricity cannot go through.",
"Electricity heats things up as it passes through them. The more electricity flowing, the hotter it gets. A fuse is designed so that when it gets hot enough, it will either burn through (a traditional fuse) or it will bend enough to release a catch (a circuit breaker) Basically, the idea is, if something goes wrong and electricity flows more than it should, the fuse will burn out or break the connetion so the electricity can't flow any more. For instance, if you jam a key in an electrical socket, it gives the electricity a free path through your body into the ground, so ALL the electricity flows through you. The fuse gets hot and burns through, so now there's no path for the electricity, so it doesn't continue to flow and potentially start a fire(and, hopefully, it does it quickly enough that it saves your life as well- don't stick things in electrical sockets!)."
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9e5oy3 | how do rockets get fuel out of its tanks in microgravity? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"They accelerate. On the Saturn V there were small solid rockets, callel Ullage motors, on the bottom of stages two and three that fired just long enough to settle the fuel. The Command Service Module used the RCS thrusters to give themselves a small push is the right direction. The RCS themselves IIRC, used telescoping fuel tanks that were never any larger than the fuel inside required."
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9e7y96 | How is it that the Mohr Circle shows stress and shear stress in “all directions”? | What does exactly mean when they say that the circle shows all different general states of stress of an element in all directions, when in reality the element doesn’t turn or move? For example a cilindrical bar under a normal load is said to have shear stress at a “45 degree angle”. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It simply means that the circle shows the state of stress at each angle. If you wanted to find the tension and shear stresses at a direction of 15 degrees from normal, you could. It is important because sometimes the maximum stress of an element is not along the normal plane. For example, \"shear stresses is at a 45 degree angle\". This isn't the only location of shear stresses, but in this case it is the maximum. With a soft metal rod, if you just measured the normal tensional stress to predict failure you may end up having the rod fail in shear (along that 45 degree angle) long before the rod would've failed laterally."
],
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9e9mgs | How come the instant we turn off the heat to a boiling tea kettle, the whistling stops almost immediately. Shouldn’t the water continue to boil for at least a little bit more without the heat? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Liquids don't boil because there's heat, they boil because there's *an excess* of heat. They boil that excess away, leaving just hot, but not too hot water. In other words, boiling only happens when the energy is being continuously supplied.",
"Water turns into a gas at 100 C. That means there is almost never going to be anything in your kettle more than 100 C...anything hotter will shoot out of the top as steam. Once you turn off the heat, the whole system starts to cool. For a very brief period of time the water will continue to get hotter as it absorbs heat from the metal kettle, but after that any steam left will either condense back into water or quickly escape. Bear in mind it takes 1 calorie of heat to raise the temperature of one gram of water from 99 C to 100 C. It takes 540(!) calories to turn that gram of water into steam. That's a whole lot of energy, and once that heat spigot is turned off, everything else shuts down pretty quickly."
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9e9ulx | Why do torquey engines make their power at low rpms, but higher horsepower motors seem to hit peak power at higher revs? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"If you're talking internal combustion engines, a lot has to do with their bore (cylinder diameter) and stroke (how far up and down the pistons move). Engines with long strokes typically make higher torque at lower rpms, since to get a long stroke, the throw of the crankshaft is longer. Basically, a longer stroke gives the power stroke more leverage at the crankshaft. Engines with short strokes can be made to rev faster since the crankshaft throws are shorter. Since the torque at each power stroke is lower since the leverage is lower, these engines need to spin fast to make much power. Consider the formula for horsepower: HP= torque x RPM/ 5252. It shows how the same HP can be achieved by high torque at low rpm or by lower torque at high rpm.",
"besides bore to stroke ratio, already mentioned the other major contributing factor in when an engine makes power is valve timing and configuration. I'm going to assume you already know how a regular 4 stroke engine works, if you don't there are literally thousands of videos on youtube explaining it. Before the advent of variable valve timing you had to sacrifice low end power if you wanted to make more power at the high end and vice versa. To make build an engine that makes more power at high RPMs you need to make sure air can flow through it freely. This means making valves larger or adding more valves. The reason why this takes away from low end performance is at low RPMs air is flowing through the engine very slowly and there is no swirling action which helps vaporize the fuel better leading to a more powerful explosion in the combustion chamber, but if you have just 1 large intake valve instead of 2 as RPMs rise it gets harder and harder for air to flow through the valve. The other contributing factor is valve timing. When exhaust gasses leave the cylinder it leaves in 3 pulses. 1. When the exhaust valve initially opens the pressure equalizes and some gasses leak out. 2. The majority of your exhaust gasses leave in this pulse, it is caused by the piston rising. 3. This is where valve timing comes in. As the exhaust gasses travel through the exhaust pipes it has inertia. The inertia is so powerful it can draw out more gasses even though the piston has stopped moving up if the intake valve opens just a little early, this effect is called scavenging. The time both valves are open at the same time is called \"overlap\" and the more overlap there is the stronger the scavenging effect is. This comes with a very large performance penalty at low RPMs since the speed at which the exhaust gasses leaving traveling through the exhaust pipes is so low it has very little inertia and the engine ends up drawing in exhaust gasses during the intake stroke. This also leads to very poor emissions at low RPMs and the classic muscle car rumble. This is also why you don't want to oversize your exhaust system in your car."
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9ec60c | Why does the Kettle make noise in the process of bring the water up to boiling point? | Boiling water in a kettle makes a noise, however it doesn't make the same noise when boiling in a saucer on the stop top, why? and what process is generating the noise? | Engineering | explainlikeimfive | {
"a_id": [
"e5nqnuo",
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"text": [
"There is a great video by Thunderf00t, [link]( URL_0 ) But what it _boils_ (excuse the pun) down to, is that the bottom is very hot, so many bubbles get created, however they immediately collapse, and since there are a lot of them, it makes that sound. It stops when the bubbles don’t collapse anymore and rise to the top, in other words, the water boils",
"The loud nose that happens when the water is hot but not yet boiling is called cavitation. This happens because the heat is applied to the bottom of the kettle, making the layer of water on the bottom hotter than the top. Once the bottom layer of water has gotten to the boiling point of water, bubbles of steam form in the water and start to rise. Once the stream bubbles reach the cooler upper layers, though, their temperature drops, and the stream starts turning back into water, causing the bubbles to collapse. As the bubbles are collapsing, surface tension of the surface of the bubble also helps to forcibly collapse then. The way the surface tension slams the bubbles of stream closed is actually quite energetic and causes the rumbling sound."
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9eo80e | Can we use solar farms to also power steam turbines? How efficient would it be? | Engineering | explainlikeimfive | {
"a_id": [
"e5q860u"
],
"text": [
"This is exactly what [condensing solar tower plants do]( URL_0 ). Although more recently, they use the sun to heat a liquid metal like sodium - which can absorb waaaay more heat - which is then used to flash water to steam to drive turbines."
],
"score": [
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9eonsv | Why do brakes on a car hardly fail and you never hear about a car accident due to a brake failure/malfunction? | Engineering | explainlikeimfive | {
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"text": [
"There's generally brakes on multiple wheels, so in order for there to be a complete brake failure there needs to be some catastrophic failure that affects all the tires at once. If there's a partial failure or one single brake fails, it is extremely obvious that your car is not braking well and most people would get it fixed ASAP. Edit: Even in the case of catastrophic failure, usually it's not a \"one minute it's working one minute they do nothing\". As an example I've personally experienced, if the parking brake is used and not completely disengaged after use, you can slowly shred your pads. I noticed when trying to stop for a stop sign that I was stopping MUCH slower than usual, luckily I was only a couple blocks from my apartment at the time and by the time they had completely failed (3 or 4 brake uses later) I was slowly rolling into my parking spot and was able to stop with a shift to neutral - > Park.",
"In addition to what is being said about passenger car brakes, Air brakes on larger trucks are designed to fail in the \"braking\" position. They way they work is that air pressure holds them open, rather than fluid pressure from the pedal clamping them, so their \"default\" position is closed. & #x200B; If someone cut an air line, the engine shuts off, trailer disconnects from the cab etc. The brakes will default to a position of slowing down and stopping the truck.",
"Brakes are one of the most engineered components on a vehicle. The loads and stresses they experience are easily estimated and engineers may double or triple that criteria just because. For extra safety, brake systems are usually on separate systems too. That way for something dramatic to happen, all of the systems have to fail at the same time. On top of that, brakes usually take a long time to fail. This is literally why mandatory regular car inspections are required for license plates. Odds are pretty low that all of your brakes will fail between inspections. Once someone spots it, the car is deemed not-street-legal until the owner fixes them, usually as a set. With all this, when someone does finally line up all the conditions it takes for the brakes to fail and them to fly off the road, it's usually a non-story because the folks flying off the road are probably the ones that that knowingly cheated license requirements to knowingly drive around on a broken brake system.",
"There is a lot of engineering that goes in to building systems that don't fail much. As others have mentioned, brakes have a lot of over engineering. Not mentioned is that your car has two completely separate braking systems. One controls the right front and left rear wheel, the other controls the left front and right rear. Either system can fail and you'll still be able to stop the car. If the pressure in the hydraulic fluid in one system is different from the pressure in the other, this indicates a leak or a failure of one of the two systems, and that big red brake failure light on your dash will light up.",
"Honestly brakes fail all the time but most people find ways to avoid accidents an get it stopped in time then get it fixed. I see accidents all the time from brake failures but its just not somthing that does enough damage to make the news. Its kinda like how u dont hear about door dings in parking lots. They happen alot, but not alot of reporters jumpin on that story."
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9f03cp | How are fabric blends like 60% cotton/40% polyester made? | Is it that for every 100 threads, 60 are cotton and 40 are polyester? Or are the materials combined somehow before they are woven in the garment? | Engineering | explainlikeimfive | {
"a_id": [
"e5ssa30"
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"text": [
"To understand this, you need to understand how threads are made. Imagine many thin strands of whatever materials you use. These strands are very thin and only a few centimeters long. To make a thread, they roll a bunch of these together and pull. As an example, try pulling a few fibers out of a cotton ball and rolling those between your fingers. Now imagine you took a few fibers of cotton and a few fibers of polyester and rolled all those together. That’s how they blend materials for fabrics."
],
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9f29nk | Why do the front wheel rims of big vehicles like tractor trailers and buses stick out (convex) while the other rims are concave? | Engineering | explainlikeimfive | {
"a_id": [
"e5tben2"
],
"text": [
"There is a single tire in the front and doubles in the back. All tires are identical so a double tire are two tires with the convex part bolted together and attached to the axis. The reson that all tires are identical is because then you can have a single spare tire that can be used to replace any tire. The reson that the front are convex out is that so you can put the point you rotate it in the center of the tire to minimize the size of the wheel well."
],
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9f3000 | When you put a car in park then let off the gas, then turn the car off why does it rock after you’ve turned it off before completely settling? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"You are probably not using the emergency brake and parking on a slope. The transmission in Park gear locks the car in place, but it has a tiny bit of play and so the car can move a little before it locks the axles.",
"Automatic transmissions have what's called a [parking prawl]( URL_0 ). When you shift into Park, a metal pin slides into a toothed wheel on the output shaft to stop it, and the drive wheels, from rotating. The pin is ratcheted, so it does have some give into it. Which is probably why the vehicle rocks when you put it in park. Ideally, you shouldn't rely on the prawn alone. That's a lot of mass on a small piece of metal. Especially on a steep incline. That'll cause it to wear out over time. Replacing the prawl is expensive. They can also break if the parked vehicle is hit with enough force. The parking brake applies the normal vehicle brakes to the rear wheels, locking them in place. The brakes are a lot tougher than the prawl, and easier/cheaper to replace if they get worn or damaged. It's good to get into the habit of using it every time you park, even in an automatic.",
"When you put the car in park, that is inserting a pin into the gears to hold them in place. The car rocking is the weight of the car settling on that pin. This is a fantastic way to actually snap that pin off. Then, not only A) you have a piece of metal bouncing around in the transmission, but B) now your car is free to roll away. I've seen this happen a total of **4 times**. Never rely on the parking position alone. Use the parking brake to hold the weight of the car. That's what it's there for. The parking brake IS NOT an emergency brake. This pedal or lever mechanically engages your rear brakes. Your rear brakes are responsible for maybe as much as 20% of your car's total stopping power. Your front brakes perform 80% or more of your stopping power. When you brake, the car's weight shifts forward, putting more weight on the front tires, increasing grip and stopping power. So what happens if you set the parking brake while the car is moving? One of two things - either essentially nothing, because the parking brake doesn't have the friction force to actually hold a moving car, just a stationary one, or it'll lock up the rear wheels and you'll drag them behind you in a rear tire skid. You can still roll hundreds of feet at 55 mph like that. Using this as an emergency brake is a mistake. Oh, and people use it to drift their cars, because with the rear wheels locked up, you're very likely to induce something like oversteer, where the back of the car slides around to the front. Anyway, don't rely on a little metal pin to hold the weight of the car, use the brakes to lock the wheels in place when not in motion."
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9f7ewb | What is the advantage of dually trucks having two tires in the back rather than one wide tire? | Engineering | explainlikeimfive | {
"a_id": [
"e5u9shs",
"e5uatjr",
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"text": [
"In the event if one tire blew out, you could keep going until you get to a point to fix it. If you had one big tire and it blew out you'd be SOL.",
"To piggyback on what everyone else has already said, those truck wheels and tires are already heavy as shit. Having one large wheel and tire would be an absolute bitch to take off and put on. Plus dualies get serviced at normal dealerships and vehicle repair places. With the current setup no additional equipment is needed as the standard tire machine and balancer work with them. If the wheel and tire were one piece equal in size you’d probably need a seperate machine to handle changing and balancing them.",
"The dual tires are to support a heavy load, not necessarily to provide better traction for towing. Two \"normal\" tires means you have a total of four side walls to support all that weight. Additionally, they can provide failover of one gets a puncture. If you have a single super-side tire and it goes flat, you're pretty much screwed. But if one of two normal tires gives, you at the very least will have time to pull off the road and may even be able to get to a service station."
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9fodmj | what is machine learning ? | Engineering | explainlikeimfive | {
"a_id": [
"e5y1cl6"
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"text": [
"Traditionally, when you are programming a computer, a programmer will write out very specific instructions on what the computer should do in different situations. This works well for some tasks like doing arithmetic or searching for information, but can be incredibly complicated for things like recognizing photos. If you had to write a program to tell if a photo has a dog in it, it’s almost impossible to think of what instructions you’d write or how to describe what a dog looks like to a computer in a programming language. So instead, you can use machine learning. With this technique, you find thousands of photos of dogs and feed them into the computer, and the computer will figure out what details it thinks are important and build its own algorithm. If you show it enough pictures, it will get a pretty good idea what a dog looks like and will be able to tell if new pictures are of dogs."
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9fz6u0 | How does this remote control frosted glass work? | Engineering | explainlikeimfive | {
"a_id": [
"e60bbxu"
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"text": [
"I have this at work. The vendor told us that it works by passing electricity through a lcd film"
],
"score": [
3
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9fzki4 | What is it about the honey dipper’s design that makes it better than a spoon to get it out of a pot and why don’t we use it for anything else like jam? | What is it about the honey dipper’s design that makes it better than a spoon to get it out of a pot and why don’t we use it for anything else like jam? | Engineering | explainlikeimfive | {
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"It’s because of the consistency—or viscosity—of the honey. It’s properties make it hard to stay on a spoon. A honey dipper works because the honey gets into the grooves and stays there as you swirl it. Jam, on the other hand, has a completely different viscosity. Not only does it typically stay on a spoon just fine, it wouldn’t stay on a grooved dipper even (especially?) when it’s in motion.",
"You know, I've never seen a honey dipper in real life. Always, always used a spoon or fork."
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9g0k1h | Unlike other technologies which get obsolete in 20 years max, how does military technology have a service life of several decades? | Military aircrafts are inducted for 30-40 years. We are still using some equipment from the 80s. How do these machines stay relevant when everything around is evolving so rapidly. | Engineering | explainlikeimfive | {
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"Well, this is a newer effect. During both of the world wars, you can track how technology changed rapidly, in 1914 it was horse cavalry and carrier pigeon, by 1918 it was airplanes with machine guns, telegrams; in 1939 there were still biplanes in service, by 1945 there were fighter jets. During the cold war the major players were chasing any edge over the opposing bloc. As this continued the R & D costs grew and grew for even a small change. With the easing of tensions the need for constant development has eased as well (during the inter-war years there was serious atrophy of western militaries as well) and the money was pushed back to social programs etc and it became both less needed to replace military equipment and less palatable to politicians.",
"Real-world military maintenance guy here. Hoo boy. We're still using some equipment from the *60s*. Military gear has to get a job done, it has to do it reliably, and the total cost of ownership (procurement, storage, maintenance, and operation) have to be reasonable. I work mostly with munitions, so let's look at a heat-seeking missile. It's a solid rocket motor. There are better propellants today (less smoke) but the old ones work fine, too. The warhead still goes boom and airplanes aren't much more durable than they were 60 years ago. That leaves the guidance and control sections. Guidance is a seeker head and control is *flight* control, so moving your fins and wings. In the 60s, the seeker was a simple affair with a few transistors and a heat sensor on a motor around a mirror. It just moved the fins to point the missile toward the heat of an engine. Today, modern seeker heads are from the 80s and 90s and use actual computers. They don't really benefit much from being faster computers, they only have *one* job. But the rocket motors and fin controls and warhead don't need to change. Now, missile electronics also need maintenance and regular testing. As I said, the rocket and warhead are stupidly-simple, so a basic visual inspection is good enough to determine they should be good. Every so often, a test of one happens to make sure age and temperature or stuff like that don't wreck them, but we have a pretty good grasp of stuff like that by now, and one of the requirements for military gear is that they are robust in storage. Now, we *do* have test equipment that we use that gets more frequent updates, but they still have to be rugged for use in hostile environments. The original test equipment for some of these systems uses vacuum tubes, but we don't use any of them any more. Now, our most common test set is based on a 400 Mhz Celeron and runs a modified version of Win XP. Software updates for the actual weapons (because the GPS-guided kit actually runs fairly advanced software) comes in PCMCIA cards. Now, more modern weapon systems get introduced gradually, and they frequently use only slightly modified standards you'd see in civilian use. The computer that the \"modern\" test set is based on has USB, for instance. And the \"tail kit\" that turns a dumb bomb into a GPS-guided \"smart\" bomb is fairly modern tech. I guess the basic idea is, these machines do *one* job, and they do it *one* time. And the practical ability, regardless of how modern it is, to effect operations of a system indirectly is nearly impossible. It's not like most of these systems have wireless communication that lets them change their behavior. It's like trying to hack a Super Nintendo with your Android phone. The phone could be as advanced as possible, but without any physical way of interacting, the Super Nintendo is still going to play Mario World. And when your \"Mario World\" is really \"Go to these coordinates and then make this explode\" you can use it to win wars.",
"The military tends to refurbish their old equipment with new(er) technology from time to time. It boils down to, ships are expensive, so rather than build an entire new ship because we have new tech, let’s put the one we have up in drydock and retrofit some new(er) stuff into it. Due to the military’s procurement bureaucracy though there’s often a big lag between when new technology reaches the general public, and when the military adopts it.",
"I think the more intersting question is: Why is military gear so damn expensive for militarys to buy, when equivalent or much more advanced technology is available to the public at a much lower price (e.g. radios)?"
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9g4bbb | Why most of the motorcycle engines have their air intake on the back of the motor and exhaust on the front, only to wrap back? Why not design the engine (backwards) in a way that helps the air intake and reduce the exhaust pipe lenght (effectively reducing weight). | Engineering | explainlikeimfive | {
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"Because the back of the engine is where the seat goes. Take a look at [this]( URL_0 ) engine. It's a run of the mill. Japanese I4. The back is the intake. Thats also where the rider sits. Imagine swapping the two. You can't feasibly or practically put exhaust pipes there. It would be to hot/ or the turn would be way to sharp to avoid the rider. It's easier, and better for the engine exhaust flow to have a smooth length of pipe. Not too long. but not too short also. edit: to add on, there are also other things back there(under the seat) to include a battery, the frame, chain and swingarm. Those would get in the way of routing exhaust.",
"* Carburetor icing in cold weather * Carburetor + airbox + filter is a lot bulkier than exhausts"
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9gc14s | Would an airplane automatically fly after reaching a certain speed? | If I pulled an airplane like how you run with a kite, would it automatically lift after reaching a certain speed? | Engineering | explainlikeimfive | {
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"Yes. The point of engines on an airplane are to push it forward, not really pull it up. The shape of the plane's wings do that.",
"Yes, there are many examples of aircraft inadvertently lifting off in high-wind situations.",
"Sure. Airplanes have a certain speed they have to reach before they can take off. If you towed it at the speed and had a pilot making the right adjustments, it would take off. Even without a pilot, you get fast enough, the plane will leave the ground. That's how gliders work, BTW. They are towed by another plane so they can reach that take off speed."
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9gdqtk | What would happen if you switched off the ignition while driving at high speed -- let's say in a runaway, no brakes situation? | Engineering | explainlikeimfive | {
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"The anti-theft mechanism will lock the steering wheel if you turn the key off. Learned that the hard way goofing off in college.",
"For safety reasons your master cylinder maintains pressure even if the engine loses power so you can still use the breaks one more time to slow the car. You also have an E-brake. Assuming that you don't put the car in neutral your transmission will still be connected to the engine which will help slow the car down.",
"in a no brakes situation... it would have little effect, and actually be quite dangerous as without the engine running you're also now going to lose power steering (in a modern car). At speed, and in a straight line, you probably don't need power steering... but if you've never driven a vehicle without it: it WILL effect handling and you may not be able to turn the wheel enough for a required turn or straight-line correction. You will receive some benefits of engine-braking on the car, unless you put the car into neutral... but this will not be healthy for your engine. In reality... in a \"no brakes\" situation, it would make more sense to just shift into Neutral and disconnect the engine so it is not pushing the car anymore, and then you won't lose the benefits of the electrical/pneumatic/hydraulic systems that the engine is powering.",
"I've had this happen multiple times in a car I used to own. Engine shut off at 60mph on a 3 lane freeway with tons of traffic. Bit of a panic while I navigated to the exit that was 100 yards or so ahead (hard to tell at speed and a little stressed). Luckily merged to the exit based on momentum and made it to a safe place to pull over. Mechanic said it was a cable running to the battery. Replaced, didn't fix. I was young and rather than trying to diagnose further I just sold it back to the dealership and got a different car."
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9gjmav | Why are there so few examples of advanced, large scale contruction/engineering feats from anicent North America as comapred to the Middle East and Asia? | Engineering | explainlikeimfive | {
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"They used dirt and wood. The wood deteriorated but there are still many earthen mounds remaining. They didn't use a lot of stone. What they did use (usually covering an earthen mound) was \"repurposed\" by pioneers for buildings before the mound was razed. This is what happened in downtown Columbus, Ohio, the only thing that remains is the fact there is a Mound Street. Many were destroyed in the 1800s. Many sites like the mounds in Newark, Ohio, and the Serpent Mound in Peebles Ohio, where built in ways that they have alignments to celestial events like the equinoxes, so they did have adavanced knowledge in the sun and moon The Great Circle earthworks in Newark originally covered over 3000 acres but all that's been preserved is just over 200 acres. Marietta, Ohio has many remaining earthworks and some now have building built on them. There is a lot of info in this book, from 1848 before many sites were destroyed. Ancient Monuments of the Mississippi Valley, Ephraim George Squier. URL_0",
"There are many examples of such things. The issue is most of the ruins are in middle or South America where they don't have the money to put on nice ad campaigns. URL_0 Or for the Aztecs what about Tenochtitlan? The wonderful island City capital of the Aztecs which also featured large stepped pyramids, long bridges, and floating farm land.",
"There may have [been in Kansas]( URL_0 ). But why aren't there more? A major thing to consider is that N American pre-history was *very* unstable. The notion of the 'peaceful, land-loving indian' is a Disney/romance-era meme that's completely detached from reality. A more accurate description was that land in N America during the pre-Colombus era was constantly being fought over and constantly changing hands during a series of never ending wars/genocides and power grabs as whomever was locally powerful at the time sought to expand their empires. Life was brutish, nasty and short. This matters b/c building great works requires 1) stability and 2) socio-political & economic will. If you are an indian tribal leader, and you are constantly fighting off other tribes, you simply don't have the resources to dedicate to 'great works'. If you look at the Aztec, Mayan, Inca empires in Central/South America, they all experienced (relative) eras of dominance/peace that allowed for their building sprees.",
"As Jared Diamond argues in *Guns, Germs and Steel* basically farming, also access to easily farmed crops."
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9gjo9s | Are buildings (especially skyscrapers) always designed to fall "straight down" to minimize collateral damage, or does it depend on what type of damage it receives?? | Engineering | explainlikeimfive | {
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"No it's not an intentional safety feature. The twin towers used a non conventional load bearing system to open up the floor plans of each floor. They transferred the bulk of the weight to be carried by the out side walls and not a conventional internal frame work of columns. This allowed the company's to do more and remodel each floor to their choosing. The straight down collapse is called a pancake collapse. What made the towers continue their straight down path was that principal. And once the steel at the top failed it was only a matter of dominos falling over from the prior as each floor above hit the next floor down it exceed the working load of the floor below it. Since the collapse started at the top and not the bottom the pancake collapse was much more likely to take place over any other type of collapse. There is alot more about shear forces and beam strength under load and building floor load types. But this is the basics.",
"No they’re not, buildings are designed to stay up. Demolition experts spend an insane amount of time planning how to make a building fall straight down. (Controlled demolition) The actual chance of any buildings falling like the 3 towers did on 9/11 is ridiculously slim, especially considering the damage that they took (and in case of building 7, the damage it didn’t take.) This is often the basis of the conspiracy theories, mainly because of how perfectly all three buildings fell.",
"What happened in the case of the twin towers was the explosion and resultant fire in the floors that were hit weakened the structural integrity of the support system. While the “jet fuel” didn’t melt the steel beams, it made them more malleable, which is disastrous when they need to bear all of the weight of the floors above them. When the floors above can no longer be supported, they will collapse downwards, creating a chain reaction. The buildings were not “designed” to collapse like this, but this is in effect what will happen due to structural physics."
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9gn7ts | How do they make tunnels and how do they avoid the mountain collapsing on them? | Engineering | explainlikeimfive | {
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"Look up tunnel boring machine (TBM)... they come in different sizes and differerent flavours depending on what type of rock or soil they're going through. There's a drill face with rotating sharp grinding wheels which slowly dig out rock and soil. These slip through slots in the face and are collected in a conveyor system which takes them out behind the TBM where they're dumped into a standard rail car which an engine takes out of the tunnel to be disposed or dumped. Giant hydraulic systems slowly push the drill face forward. Once its moved forward far enough, precast concrete tunnel segments are brought forward and a new \"ring\" of tunnel is assembled. Behind this part of the TBM (which travels inside of the new tunnel as it builds it) are support systems to take away rock and soil, bring up new tunnel segments and crew facilities. The cutting part pushes against the tunnel segments it just laid. The shape of the tunnel is round - like any arch, they transfer the weight of the soil/rock above the tunnel _around_ the tunnel to the soil/rock underneath it. [Here's a really cool video.]( URL_0 )"
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9gx1ma | How exactly does the metallic coating on the inside of chips bags keep them crispy and why does it have to be metallic? Can some other material do as good of a job at preserving 'crispyness'? | Engineering | explainlikeimfive | {
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"The metallic coating is aluminium and it has the advantage of being completely impenetrable to oxygen (on account of reacting explosively if exposed to oxygen too quickly). This includes oxygen in water - metallic aluminium will strip the oxygen atoms from their hydrogen and produce enough heat to ignite the hydrogen in a secondary explosion - which means the two main reasons of chips going stale are kept out entirely as long as the coating lasts. In theory any airproof material could do the same job, but we have yet to discover any that are as cheap, light, and harmless to the environment as aluminium. Disclaimer: aluminium *production* is not at all harmless to the environment, but 8% of the crust is made of it so it does a lot less harm if dumped in the ocean than plastics, for example."
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9gyne7 | How do rotary engines work, and are there any benefits/drawbacks to it? | Engineering | explainlikeimfive | {
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"Here's a good basic [youtube]( URL_0 ) on the Wankel rotary, including running a see-through engine. simply put, the rotary engine spins, so it's already in a spinning motion rather than an up and down motion from a typical piston engine that then needs to be converted (via the crankshaft) into the spinning motion that can then (through gears and shafts) turn your wheels or propeller. The benefits are that it is small in overall size as well as displacement. It runs smoothly because it is not being forced up and down, it just spins in place. They can create a lot of power in relation to both physical size and displacement. The biggest disadvantage, particularly with more modern engines, is that they're just not nearly as efficient as a piston engine."
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9h8y47 | If surface area has no effect on fricton, why are some wheels so wide | Engineering | explainlikeimfive | {
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"While the friction is the same, the composition of the tires can be made differently for a tire with a larger contact patch (wider tire). A small narrow tire has to carry the weight of the car on a very small contact patch, which means the tire has to be stiffer and harder and must be run at a higher pressure to avoid wheel damage, and won't deal with the imperfections of the asphalt very well. A wide soft tire can carry the same load on a much larger area, allowing it to be of a softer composition and to be run at lower tire pressures without risk of damage or rollover. Therefore the tire will conform to the road or track much better than will a harder tire at higher pressures, and the larger contact patch will ensure good contact with the asphalt.",
"\"Surface area has no effect on friction\" is a simplification we tell Physics 101 students to help them grasp the material better. In the real world, it's not so simple. We're taught that friction is a function of the *coefficient of friction* times the normal force. The coefficient of friction is some constant that depends only on what the two surfaces are made of. But that's not always true. When you're dealing with compressible materials, like tires and asphalt, the coefficient of friction is not a constant. It's a function that depends on pressure. It actually gets smaller as the pressure increases, so to get maximum friction you want lower pressure. Lower pressure means wider tires."
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9hc73n | How does a blender mix all of its contents when it is filled to the top if the blade is only small and at the bottom? | Engineering | explainlikeimfive | {
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"When the blades spin they create a whirlpool which pulls everything in the middle downward. The ingredients that get pulled down go through the blade and get pushed down and then out. Because everything in the middle is going downward it also pushes everything on the outside to the top. This process repeats until the blender is turned off.",
"I'm pretty sure the blades are angled to push whatever they are blending downwards, causing the material to cycle",
"You've stumbled into the perimeter of wisdom. Ignore the other answers, they only apply to *good* blenders. If you are so unfortunate as to purchase a blender as you see on TV, you will find you're exactly right. The little blades whizz around the bottom getting all hot and bothered while the rest either sits around or rotates merrily without ever getting properly smashulated. Also, the smell of ozone and toasty electronics is apparently a sign of great success."
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9hicq1 | How does the ISS, satellites and probes and spacecrafts like the voyager deal with debris in space? | Engineering | explainlikeimfive | {
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"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. & #x200B; For something like Voyager, there's really no chance it will ever hit debris of any sort. Film Theory was going over the statement in the first Star Wars movie about how the Millenium Falcon in hyperspace could bounce too close to a supernova, and he calculated that would happen after travelling for several trillion years first (because Space is so empty). & #x200B; Satellites that are in low earth orbit do have to be careful. NASA tracks all of the satellite locations. The ISS and GPS satellites are at a different orbit and will likely never hit anything like that, unless one of the satellites explodes, sending debris out. As far as getting satellites into space, it's like merging onto the freeway. If you're standing still and looking at freeway traffic move past you, it looks fast and daunting. But if you're moving at orbital speed, it's like merging onto the freeway when you're already moving at freeway speed."
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9hjq72 | Why are the front-most rims of 18-wheelers and large trucks always convex, while all the rest of the rims are concave? | Engineering | explainlikeimfive | {
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"This is so that such trucks won't have to carry extra spare tires. The dual wheel pairs in the rear are all composed of identical wheels. Each metal wheel is offset further than the edge of the tire, so that you can just put a pair back to back to create a dual set with a slight gap between tires, with the concave sides of the wheels facing out. The front (steering) tires generally have a different tread pattern than the rears, but the wheels are identical, so you can install the spare anywhere. On the front though, they're installed concave side in.",
"They are all the same wheel just which way they are bolted on changes back wheels are dually so the are actually two wheels bolted next to each other the inside wheel it faces just like the steer axle wheel then the flip the out side wheel around so the two wheel faces touch when. The run the lug nut tight"
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9hn7j8 | how electric vehicles are more environmentally friendly than combustion engine cars. | I understand the reduction of greenhouse gasses etc. but I'm struggling to see how we're not just swapping one problem for another. Are we not just swapping exhaust fumes for piles of unrecyclable batteries? | Engineering | explainlikeimfive | {
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"> Are we not just swapping exhaust fumes for piles of unrecyclable batteries? Batteries can be recycled. It's not trivial, but it's not that hard either. Lifecycle analysis can be found for electric cars, and usually indicates they're somewhat more environmentally friendly.",
"An EV has a slightly higher manufacturing footprint then a gas powered car. But this is not as high as some people claim. In the Union of Concerned Scientists study below they estimate it to be 15 percent more then a gas powered car. But this extra footprint is made up quickly in operation since an EV is so much more efficient at using energy as a gas powered car. An EV is is 80 percent plus efficient at using a unit of energy. A typical gas powered car is more like 20 percent efficient. To put that into some kind of perspective. 1 gallon of gas has 33.5 kWhs of potential energy stored in it. If a gas car was as efficient as an EV it would be able to drive 141 miles on 1 gallon of gas (assuming the efficiency of the Tesla Model 3). So overall an EV has to use far less energy to drive a car for each mile. As for the battery. They are recyclable. But an EV battery will be used far longer then what people think. There has been lots of data collected on the big battery Tesla's and they will easily last for the lifetime of the car of the average driver. Then at end of life in a car they can be taken and used for stationary storage. Batteries don't just die usually. They degrade overtime. So this is why they can be repurposed for stationary storage where the amount of space they take up doesn't really matter. For more info there are lots of lifecycle studies you can check out. URL_0 URL_2 URL_1 URL_3",
"This is a somewhat tricky subject. There are currently many ongoing debates wheter an electric car actually is more environment friendly. It is true that an electric car produces no exhaust gases but unless you get the electricity for your car from a sustainable source, then it doesn't matter. Another aspect is the release of green house gases and the environment impact of producing an electric car. I read some report a while back that stated that a brand new current gen car can be driven for 15 years before it reaches the same impact as a brand new Tesla. The problem here lies mainly in the production of the batteries since they use up a lot of energy and resources, especially rare metals. So the main issue regarding todays electric cars are the number of electrical components needed and they are significantly worse to produce than a cumbustion engine."
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9hz8r9 | Why are large vehicles like trucks and buses not built with a streamlined shape like most cars? | Wouldn't it reduce drag and make the vehicles more fuel-efficient? | Engineering | explainlikeimfive | {
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"Fuel efficiency is measured a little differently for things like buses. They don't need the most miles per gallon, they need the most passenger-miles per gallon. If you lose the room for several passengers to gain a few mpg you might end up with each passenger still accounting for the same amount of gas. For example let's say on a certain trip a bus uses 50 gallons of gas and it carries 50 passengers. Redesign the bus to only use 40 gallons but reduce capacity to only 40 passengers and you've improved nothing. The same principle applies to trucks and their cargo capacity. Also, many buses are used only in cities at low speeds where aerodynamics aren't nearly as important.",
"Maximize carrying capacity you lose fuel efficiency. Maximize fuel efficiency you lose carrying capacity. The impact of losing fuel efficiency on net profit is much less than the impact of losing carrying capacity.",
"Their shapes are designed to allow the most carrying capacity and curves hamper carrying capacity.",
"It doesn't matter for buses. Most buses spend their time traveling at low speeds where air resistance is not the main factor in how much fuel they use. They're designed to excel at being a bus so they're great for their 95% use case, being aerodynamic would only be helpful for the small percent of time they're traveling at highway speeds Most small local trucks are similar to buses. The little UPS truck doesn't need to be particularly aerodynamic since it burns most of its fuel accelerating after each stop Big trucks that make long hauls on highways do have bits added to make them more aerodynamic. The curved bit on top of the tractor helps to direct air up and over the trailer, and you'll now see [tails]( URL_0 ) on some trailers which travel long distances. These tails reduce the drag which improves the fuel economy."
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9i1oqr | How does radio frequencies between walkie talkies and the FM-radio stations work? | I’m curious as to how these different systems work. Is it technically the same tech but with different frequency range or is there more to it? | Engineering | explainlikeimfive | {
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"There are two basic ways to transmit a signal using radio waves, amplitude modulation (AM) and frequency modulation (FM). Which one a walkie talkie uses depends on the walkie talkie. Some walkie talkies do use FM, so in that respect, they are just like the little FM radio stations. How does that work? Let me use visible light as an analogy. After all, radio waves are basically a form of light that we can't see. Light and radio are forms of electromagnetic radiation. All electromagnetic radiation can be described in terms of its *frequency* and its *amplitude*. In visible light, we perceive different frequencies as different colors, and different amplitudes as different brightnesses. A radio antenna is like a light bulb where we can precisely control the color and brightness of the radio waves. So, let's say we have this color/brightness-changing lightbulb, and we want to use it to send information to someone far away. We turn on the lightbulb and set it to a single color, let's say green. We have two different ways we can send information. We can alter the brightness, or we can alter the color. We can call these two methods for transmitting information Brightness Alteration and Color Alteration. OK, thesaurus time. Brightness = > Amplitude Color = > Frequency Alteration = > Modulation Brightness Alteration = > Amplitude Modulation (AM) Color Alteration = > Frequency Modulation (FM) That's basically how a simple radio works."
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9i8lr1 | what is stiff suspension and why would you want it? | I’ve heard a lot of people in the car and mountain bike worlds talk about stiff suspension. I thought the purpose of suspension was to absorb shock and make as smooth and comfortable a ride as possible. Therefore wouldn’t it be better at this if the suspension was spongy and not stiff? Why would you want a stiff suspension? Surely you could just get a fixed bike with no suspension if that’s what you want? | Engineering | explainlikeimfive | {
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"Imagine walking around with gigantic inflatable shoes. You aren't going to feel small bumps in the road, but walking will be a lot of work and you won't be able to be very precise about where you step or what direction you go in - that's very soft or 'plush' suspension. Now imagine walking around in a good set of running shoes. The padding between your foot and the road is still good, but it's hard enough that you can get some feedback. You can move a lot more precisely and 'feel' what's going on without feeling too much discomfort - that's stiff suspension. Now imagine walking around with wooden blocks on your feet - that's no suspension. Depending on what you want to do will decide how stiff or plush you want your suspension. Mountain Bike Racers and Racecar Drivers want very stiff, precise suspension. They want to go round corners and around obstacles fast and don't care about comfort. Old Mrs. Jackson in her Honda Accord doesn't need to go at 100mph to do her grocery shopping. She'd much rather a comfortable ride, so that her haemorrhoids don't flare up. She'd prefer plush suspension.",
"> I thought the purpose of suspension was to absorb shock and make as smooth and comfortable a ride as possible. That is part of it, yes, but the suspension also has to make the vehicle body follow where the wheels are going too. The circumstances where someone wants a stiff suspension are typically in sports cars or mountain bikes which are expected to deal with more extreme forces. In the case of a sports car you want to be able to take a corner without the spongy suspension of the car causing the car body to roll and rock. With a mountain bike it is likely strong vertical impacts need to be cushioned before the suspension bottoms out.",
"The art of \"dialing in\" a suspension is a science and an art form. Too soft and the car will bounce around all 4 wheels like it is riding on balloons. Too stiff and bumps would rattle your teeth and brains to mush! Lotus, a British exotic car manufacturer, is generally known for being the masters of this art. Soft enough that when you hit a bump initially, that 1 corner of the suspension 'absorbs' the energy and travel distance without upsetting the rest of the car. Yet you want it stiff enough that the suspension \"pushes\" that one wheel back down on to the road as fast as possible to maintain traction after hitting the bump. The other aspect to all this is momentum transition. If you slam on the brakes, the front of the car nose dives downward , or the opposite, accelerating hard transitions the weight to the rear of the car lifting up the nose of the car. Turn left, and all the weight transitions to the right side, lifting weight off the left wheels. If your suspension is too stiff.. you WILL lift the left wheels off the ground. Too soft.. and the car will just lean and lean, not really getting leverage down to the wheels to help grab the pavement.",
"One thing not already mentioned. After absorbing an impact a car or bike bounces up and down. A stiffer suspension will help it return to equilibrium faster.",
"> I thought the purpose of suspension was to absorb shock and make as smooth and comfortable a ride as possible. That is a secondary purpose, the primary purpose is to make sure the vehicle doesn't shake apart. If your vehicle is doing extreme things, a soft suspension can bottom out, which is hard on the vehicle, and in the case of a mountain bike, the rider as well. A stiffer suspension also gives you a better feel for the road, as the vehicle will more immediately react to small changes. In these cases, it can be worth it to trade off some comfort for better performance.",
"A suspension system will have a minimum and maximum length of travel. Depending on the springs stiffness, and/or the shock absorber the amount of force it takes to reach that maximum will vary. A soft suspension will allow you to easily glide over lots of small rocks, bumps, and other things without as much impact to yourself or the frame. It also helps with keeping your wheels consistently on the ground, and avoids \"flying\" or skipping over the surface when you need Traction to control yourself. A softer setting can also prevent your feet from flying off and allows you to comfortably ride down trails with light debris and bumps. A stiff suspension allows it to absorb bigger impacts without bottoming out and transferring all the force to you and the frame. This is usually done in places with lots of major jumps, or heavy landings. Since the human body can comfortably absorb most smaller impacts, as they become to explore bigger obstacles it will quickly reach a point of painful knees and ankles, sometimes other things too. A stiffer shock helps cushion these heavy landings enough to prevent major disruptions from ending your ride entirely. A shockless bike doesn't offer any absorption at all, and your tires will be pulling double duty. They tend to absorb some impact, but can easily bottom out on most bikes. Rims can bend or even break with a heavy enough impact, unless there's some kind of suspension to help absorb the impact."
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9i9r09 | What causes batteries to leak in a device when they don’t leak in their original packaging? | Engineering | explainlikeimfive | {
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"Batteries run off of a chemical reaction. Eventually as they age, whether they are used or not, this reaction runs and produces some gasses which put pressure on the battery body and causes leaks.",
"Batteries work by producing electricity with a chemical reaction. The reaction stops when no electricity is being used. In lower cost (zinc-carbon) batteries, the outer casing of the battery is made of zinc, and the zinc is actually one of the chemicals that reacts. This means that the casing of the battery actually gets used up as the battery is used up. When the battery is depleted the remaining casing is extremely thin and fragile, and can leak. Batteries which have never been used won't have gone through much of the chemical reaction so still have a reasonable thickness casing, so are tougher and don't leak. Better quality (called alkaline) batteries are less likely to leak because the casing is not part of the reaction. However, the reaction produces gas, and the gas builds up inside the battery. This build up of pressure can cause the chemicals to leak out through tiny cracks or holes in the battery."
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9iekg2 | Is glass railing really safe? | Engineering | explainlikeimfive | {
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"Glass can be surprisingly tough. Look at it this way, there is bullet-proof glass. Granted, the glass in the railings probably isn't as tough as that, but it would be tougher than normal glass. That and the panels are quite thick. That makes them a lot more solid. They may also be coated with or have a plastic layer inside (between two layers of glass) that makes then even hardier. If a laminated panel is hit, they can crack but are unlikely to give way. I once tackled someone into a window on the side of a building. The glass cracked and caved in somewhat, but didn't come free of the frame or drop any pieces. That railing glass would be like that, but thicker and tougher.",
"[ URL_0 ]( URL_0 ) looks safe to me :D & #x200B; & #x200B;"
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9ifjsv | What is the difference between horsepower and torque? | Engineering | explainlikeimfive | {
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"Torque is the rotational force output by the engine. It exists at 0 rpm or any other rpm. Think of it like how hard you can turn a bolt with a wrench. Horsepower is actual energy output. It's equation is (Rpm*T)/5252=HP where T equals torque. If you plug in some numbers here you can figure out your horsepower and a specific RPM. For instance if I have a car that produces. 400 ft/lb of torque at 5500 RPM that's (5500*400)/5252=HP. so (2,200,000)/5252=HP. About 419 HP. If you want to know why car guys favor more torque over more horse power I can try to explain that too.",
"Imagine riding a bicycle: High horsepower would mean you can cycle so the bike travels high speed. It could be in high gear or low gear, only the speed of the bike matters. The total amount of energy converted. High torque would mean having the strength to pedal the bike at the highest gear which is the hardest to pedal. The force exerted.",
"Horsepower is how hard a car engine can work to move the car. Torque is the measure of how strong the engine is turning the axle rod, but you can also call anything like that torque. For example, twisting a screwdriver, turning a door knob, or even spinning a top. In physics, torque is kind of like how much power you're putting into turning something, torque is even measurable when the thing you're trying to spin doesn't move at all. Hope my explanation helped, though I'm not overly well-versed in engines and horsepower."
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9ivgnc | If we have the ability to create tall skyscrapers, why don’t cities have a bunch of skyscrapers of the same height? | Engineering | explainlikeimfive | {
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"Each builder is going to do what they want. Google pictures of Beijing some time, they have entire large blocks of buildings the same style and height. They also are far more regulated about how they build. I imagine in a more free market economy, each builder wants their building to be \"their building\" and not like another one. Plus each builder has a plan, purpose and marketing approach to create a profitable building, and that's going to differ from developer/investor to developer/investor. You'd have to ask an engineer, but another short answer is the materials and design of the building will also dictate what is optimal. So again, with each design being different, making the building as tall as another building is just not going to even make the bottom of the priorities list for the engineer/builder/investor/developer teams.",
"It has less to do with engineering and more to do with politics. If someone proposes building a high-rise, there's liable to be all kinds of complaints from people who live nearby. High rises block peoples' views, they put pressure on infrastructure, they bring lots of people into the neighbourhood, etc. So city planners have to balance the willingness to densify their city with concerns that the residents might have.",
"Well.... because, each company wants their own building. think of it like buildings owned by different people, all who want their own looks, heights, needs."
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9ivrpq | what is the advantage of a car with rear wheel drive? | Engineering | explainlikeimfive | {
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"Better balance overall, and more unstable (and thus more responsive) handling under acceleration. You also get a good weight transfer onto the rear wheels when you're accelerating by the car rocking back onto its rear wheels, which results in more grip between your tires and the road and thus better acceleration. They're also generally easier to service as you're spreading out the important bits of the car across the entire vehicle, and your tire wear is more even because you're spreading out jobs to all four wheels (front for steering, rear for power) as opposed to putting all of the important jobs on the front wheels only.",
"Top Gear explained it best. When turning too fast/tight, front wheel drive cars tend to understeer (i.e. not turn as much as you want) while rear wheel drive cars tend to OVERsteer. Oversteer is fun and looks cool (when drivers talk about drifting, that's oversteer). Also, the other stuff people have said about spreading components around makes repairs easier, and torque steer. Torque steer is very annoying when passing another vehicle. As you speed up to get past them, your vehicle pulls towards them, and you have to countersteer."
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9ixu8h | Why do different countries have different shapes for electrical sockets? Wouldn't it make more sense for there to be the same one globally? | Engineering | explainlikeimfive | {
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"text": [
"Yes, it would. Now you just have to convince every nation in the world to agree to the new standard and change over every single pre-existing outlet and power cord to comply. That should be easy, right?"
],
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9iymfs | Why isn’t there a rover equivalent on the bottom of the ocean? | Engineering | explainlikeimfive | {
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"Exploring the bottom of the ocean is basically as hard as exploring space. The water is really heavy and the further you go down the more it pushes on your body, or the submarine or rover or whatever. The first problem is making the rover sturdy enough to survive that environment while still transmitting signals and data and whatever. The second problem is that if anything were to malfunction, it would likely be unrecoverable, or prohibitively expensive to do so. Also, the ocean is really really big and really really deep. It has about as diverse a terrain as the surface. Mountains, cave networks, currents, crazy hot magma vents. It’s probably not feasible to make a machine that can traverse all that, while remaining strong enough to withstand the pressure.",
"In addition to the previous correct answers, power supply is a big issue. Rovers on Mars are solar powered, but the ocean bottom gets no sun, and there's no fuel supply or electric supply down there. Atomic power would be your best bet (as on deep space probes), and that's expensive and hazardous."
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9j5vbd | How can there be millions of door/car keys that are different from each other? | Engineering | explainlikeimfive | {
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"Because there are different kinds of keys with lots of different combinations. Some of them are the same but not enough to be a problem",
"Same way there can be millions of cell phones different from each other...numbers. Let say your key has 8 notches in it, and each notch can have 6 different positions. That's 6^8 = 1,679,616 different positions. What's more, they don't have all be unique. You aren't going to run around trying your key in every car you see. So long as the probability of any two cars having the same key is very low, you are protected."
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9j9xn8 | what does it mean when a manual car as an "agressive" clutch? | Engineering | explainlikeimfive | {
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"An aggressive clutch has little slip so matching your engine RPM with your vehicle speed is more important and less forgiving. These clutches sacrifice comfortable drivability for greater strength for high powered vehicles.",
"So you can think of a clutch as a clamp, right? You’re essentially clamping your engine to your transmission. Normal road cars have “soft” clutches, meaning the clamping force is relatively weak. It’s much, much easier to actuate the clutch smoothly, because it isn’t trying to squeeze very hard. However, when a car makes a substantial amount of horsepower, this soft, smooth clutch no longer clamps hard enough, and the clutch can slip. This is where you install a more “aggressive” clutch. It squeezes much harder and it can handle the additional power from the motor. It will not slip. However, it will squeeze with so much strength that it can be very hard to engage it smoothly. This is what makes it feel “aggressive”."
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9jj818 | How are film projectors able to sync the two wheels up when one with a lot more film must have a much slower rpm than the one with a less film on it? | Engineering | explainlikeimfive | {
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"Only 1 reel is actually motorized. It is pulling the film off of the 2nd reel, which is free-rolling. It doesn't have to sync anything.",
"There is one motor that's turning the gears that feed the film past the gate where the light shines through. That motor runs at a very constant speed so the projector shows 24 frames per second (or 16 or 48 or whatever). Then there are two more motors, one for each reel. These don't work at constant speed, but they work at constant torque. One motor is applying just enough torque to the take-up reel so that it takes up the film as it comes out of main guts of the projector. The motor to the feed reel is actually applying a little bit of *backwards* torque to the reel so that the reel is resisting having its film pulled off. The motor in the guts of the projector is stronger, so it pulls the film off the feed reel despite that motor's resistance. This all keeps constant reasonable tension in the entire system so that the film doesn't start spooling off of a loose reel and wind up on the floor. Tape recorders work the same way. Source: head AV aid in high school. Edit: worth noting that better machines will run the tape or film past a roller that moves on a spring. That mechanism reacts to the tension on the tape/film and adjusts the torque on the motor accordingly, keeping the tension to the reel at a constant pre-set value."
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9jn4s7 | - How do we keep every bar code created unique? | Engineering | explainlikeimfive | {
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"text": [
"Each company that assigns bar codes has a unique prefix, the first part of the code. It's up to them to not put the same code on different products."
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