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60bixq | How do they put sponsors under the ice rink? | Engineering | explainlikeimfive | {
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"It's just painted or adhered to the floor beneath, and then water is frozen on top to make the ice surface.",
"A german show for curious kids (\"Die Sendung mit der Maus\") has a nice time lapse of how it happens: URL_0 Basically, you paint the ice and then put another layer of ice on it. In the video, the second step starts at 3:20. And yes, this has to be done all over every time they want to change something. Edit - A youtube mirror, should the other link not work in some regions: URL_1"
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"http://www.ardmediathek.de/tv/Die-Sendung-mit-der-Maus/Sachgeschichte-Eisstadion-Zeitraffer/WDR-Fernsehen/Video?bcastId=22380500&documentId=31634448",
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60bm0p | How does the gas meter on a car work, and why does it only work when the engine is on? | Engineering | explainlikeimfive | {
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"Depends on the year of the vehicle. My old 1975 ford had a mechanical float and showed the fuel level at all times. On newer cars and it's electrical there's most likely a float in the tank still except it's connected to a sensor. The reason it only works when the car is on is so it doesn't drain the battery. While it would be a small parasitic drain on the battery it would still be constantly drawing power. By having it only on when the vehicle is running the alternator would be charing the battery/providing energy to other systems.",
"What's interesting is watching the fuel gauge in older vehicles when you go over bumps or up hills. I had an old pickup where the gauge would go all over the place anytime the road was bumpy.",
"In the fuel tank there is a variable resistor connected to a float. A circuit passes current through the resistor and senses the resistance. In modern cars, the computer drives the fuel gauge. It drains the battery, so it is only enabled when the ignition is on. The engine does not have to be running. It could be done with a lower power circuit that could display continuously, but there is little demand for that."
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60br12 | How are pillars that support a bridge fastened to the ground under water | Like how do they start to make a bridge over a river? How do they get those pillars in the ground? Same for a dam. How do they start building at the river bed? | Engineering | explainlikeimfive | {
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"So imagine a metal roof panel but thicker. They drive these sheet piles into then river bed then form a good seal and pump all the water out. Then dump in a whole mess of concrete and steel to form the footer (there could we a steel of concrete pile driven in under the footer to support it). Then you pour a bunch of concrete and steel straight up to form the column."
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60bsu6 | How are manufactured products of measurement like measuring tapes, cups, scales etc calibrated. | What is the standard method. If you get a measuring tape from Stanley, Kobalt, or Black and Decker, baring any defects, the marks are all the same (of course) If I buy 5 scales, from 5 companies, i know they are all going to be conclusive. What standardized method do these companies use to make sure their table spoon is in fact a table spoon. | Engineering | explainlikeimfive | {
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"The rule of thumb is whatever process you're making, the standard against which you judge the product is 1 order of magnitude finer. If the finest discrimination of your school ruler or measuring tape is 1mm or 1/16\" (0.0625 in.), then those were made with tools that had to be accurate to 0.1mm or 0.006\". Because 0.1mm is 0.00254 inches, the finest precision there is about 0.001, so the *tools* used to make the rulers and tape were AT LEAST accurate to 1 thousandth of an inch or so. Those tools would've been made and measured to be accurate with calibration tools accurate to 0.0001\", and those calibration tools would be referenced against a tool-making standard like gauge blocks, which would be accurate to AT LEAST 0.00001\", and so on. Toolmaker's equipment often must be re-calibrated or evaluated for its accuracy. Tool-making equipment is often so precise that you shouldn't touch it without gloves: the contaminants and oils on your skin could affect it. Such instruments also must be kept in a temperature-controlled room to keep them from thermal distortions. Length is standardized according to the meter as the perfect ideal: it's defined as the wavelength of red light emitted from a certain elemental isotope. [Modern] Imperial length is based upon the Inch as the base unit, where the definition is 1 inch = 25.4 mm. Source: Manufacturing student.",
"Each manufacturer calibrates all of their instruments using a \"master\" instrument. This \"master\" instrument is sent out to be re-calibrated at the NIST (National Institute of Standards and Technology), using their very accurate \"master.\" The NIST sends their \"master\" to be calibrated at the International Bureau of Weights and Measures in France. Ultimately all measuring devices are calibrated using a single master device (of that type) kept in France under very strict storage conditions."
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60k12i | What can be used to protect a portable air conditioner from power surges, if a tag specifically states not to plug it into power surge protectors and extension cords? | Engineering | explainlikeimfive | {
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"The tag says not to plug it into extension cords because an AC unit uses up a lot of wattage, and a long extension cord would heat up from all the power that passes through it. The wattage is also why they say not to plug it into a power strip; those are designed for computers, 300-500 watts tops. You CAN use extension cords and surge protectors, but you have to find ones that are rated for 2000 watts (15 or 20 amps of current)."
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60o1a2 | In the event of an inevitable car crash, which part of the car would the impact do the least damage to the driver and/or the passengers? | Engineering | explainlikeimfive | {
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"Cars are built to take hits from all angles, but not all angles are created equally. The ideal case would be getting rear ended. Lots of crumple zone back there and while your trunk may get destroyed nobody should be in there. Airbags deploy and seatbelts restrain you from flying forward... you'll be as fine as you can be. Funnily enough, option 2 is a head on. Still super dangerous, but cars are designed to tank things from the front and back. Your engine block is actually engineered into the body in such a way that a strong enough impact *drops it out of the car* absorbing an enormous amount of force and getting it away from hitting you. Still super dangerous and painful but better than side impacts where there is far less shielding."
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60p3pm | How does bump starting a car actually work? | I know literally nothing about a car underneath the bonnet, I only know how to drive them. Question comes after bump starting my mates car the other day. Why is it easier in 2nd/3rd gear? Does it damage the engine to keep doing this? What actually causes the engine to tick over etc? | Engineering | explainlikeimfive | {
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"A cars engine is designed to be self sufficient once it is going. The revolution of the motor drives all the components, such as fuel delivery, electrical, lubrication, cooling, etc. when you start your car, an electric starter motor is used to get the engine turning and start the self sustaining process. In the case of a pop start, the electric starter motor is not used. You have to find a way get the crank shaft spinning so that it can drive all the components. By rolling the car in neutral, you get the transmission spinning. When you then dump the clutch, the clutch pressure plate will connect to the spinning flywheel, which in turn gets the crankshaft of the engine to start spinning (the same effect the starter motor has) and the engine will start. As far as starting in 2nd or 3rd gear it has to do whith mechanical advantage. 1st gear has the most mechanical advantage, meaning that in 1st gear one revolution of the engine produces the least number of revolutions on the tires. So it stands to reason that the opposite is true when trying to pop start a car. If you try it in first gear, the low gear ratio of 1st will translate into a slower spin of the crankshaft and may not be enough to get the motor to start. By selecting 2nd gear or 3rd gear, when the clutch engages it will spin the crankshaft faster and give you a better chance of spinning the crankshaft fast enough to start the engine. As far as damaging the engine, it really doesn't hurt the engine. The only thing it does do is add extra wear and tear to the clutch in your transmission. The clutch uses friction to link the spinning crankshaft to the drive shaft. When pop starting, the rotating clutch is smashed up against the stationary flywheel, which can wear down the clutch. It's not a totally damaging thing to do by any means, but it's wise to only do it if you have to.",
"Lets start with how an engine works. You have pistons which compress gasoline and then it gets ignited. The explosion drives the piston back, which cause a different piston to compress gasoline. But when an engine is stopped you can't compress the gasoline. Modern cars have when is called a Starter Motor, which is an electric motor that turns the engine to get it started. Old engines, or if your starter motor is broken, require a Bump Start or Push Start. The means turning the engine to till it starts. This could be pushing a car or spinning the propellers on a plane. Why you would do this in 2nd or 3rd gear is that it will take less force to push the car, but not a high enough gear that once the engine starts it would stall out at such a low speed."
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60rlle | If Hexagons are so efficient as a shape. Why are they not more commonly used? | Engineering | explainlikeimfive | {
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"There are many reasons for using the shapes we do... but one of the big reasons is that hexagons only stack well with other hexagons of the exact same size. Contrast this with squares and rectangles, which a bunch of non-uniform sizes can still pack well. Also the lines between hexagons aren't straight, while the lines between rectangles are. Last, rectangles generalize to three dimensions and remain stackable, while hexagons do not.",
"We build straight roads because they're the most efficient to drive or walk along, with right-angle junctions because they're the easiest and safest to negotiate. That means we make oblong (or square) plots of land, on which we build oblong buildings, in which we put oblong furniture. Smaller oblongs fitting inside bigger oblongs. Hexagons just don't fit.",
"I'm not sure if this has anything to do with the efficiency. Consider tiling many squares together. You can very easily end up with one large square. Tiling hexagons, however, doesn't make a large hexagon. You have a rough shape with protruding edges. Perhaps this is one reason it isn't used?"
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60sq5r | Why are there so many abandoned cities in China? | Engineering | explainlikeimfive | {
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"China has a problem; they have a lot of citizens and not nearly enough jobs to keep them all employed. One of their solutions has been to invest heavily in construction resulting in the building of cities for a population they just don't have.",
"First thing you have to understand is that there's a huge housing issue in China right now. Estate agencies are building house left and right and it's almost guaranteed to be sold out before it's done building as the need for them is ever so demanding. In an effort to resolve this, the local government may team up with Estate agencies to developing new district on the outskirts of the more popular region, and that includes schools, public facilities, apartment complexes, office buildings and such, once done, the population of the new district will start growing organically. Those things usually work out, but if the plan changes 3 years into development, or if it runs into financial issues, or if the new district simply doesn't have enough attraction, you end up with a ghost city. If the apartment complex has been completed, it might still draw some people in, but the public facility as well as transport will start becoming issues, and the nearest shop will be 30 minutes drive away, and as people starts leaving, water and electricity will be cut too, forcing the rest out (possible compensations from government will also assist in this process). Source: Am Chinese EDIT Added source and formatting",
"China has for years propped up their GDP by building towns they don't need hoping they will be filled one day."
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60sv7e | How/Why are game developers able to code anti-piracy measures like in pirated copies of ARMAII where the player seems drunk, but can't/don't just code the game to just not work or load at all? | I watched this video that showed some cool anti piracy measure game developers have done. Many of them were just trolly things messing with the user who has a pirated copy. I was wondering if they game developers can detect that copy is pirated and trigger something that makes the game run these ways, why can't they just stop the games from being played all together? | Engineering | explainlikeimfive | {
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"From what I understand, developers make these special versions and send them to torrent sites themselves. So, people who illegally download get a mostly working version that they think is bugged instead of intentionally tampered with. The more it seems like a mechanic or bug, the less they'll catch on and try and find a different torrent. And when it is more common knowledge, people will call them out for pirating when they post on forums for help.",
"There are basically two types of anti-piracy measures: 1. Anti-piracy measures build into the \"proper\" game, this means even legally acquired versions have them. These are not the \"funny\" measures you mention and they mostly lead to the game being unplayable (sometimes even for legit buyers), e.g. Drakensang which among other measures stopped spawning quest-important characters as soon as it detected piracy software running (e.g. Daemon tools). 2. Anti-piracy measures build into a \"fake\" version of the game which is intentionally distributed on piracy channels to send a message, confuse people and make the pirating experience worse. Most companies just decide to upload versions which trackers to nail pirates but other companies get more creative like you described. However these \"effects\" are not part of the \"proper game\" and they also don't trigger by detecting pirated versions, they are just a fixed part of them.",
"Honestly, if the game simply refuses to run, it makes it easier for the pirate to crack in the first place. Pirates often crack games by tinkering around with the game's executable file, deleting or replacing bits of code and then running the game to see if it works or not (Denuvo, which is the current go-to DRM for developers/publishers, works by preventing tampering with the executable file directly). If the game doesn't start up, then good, they've eliminated one option and they move on. If a game's anti-piracy mechanic consists of freezing mid-way into the final boss fight and deleting your save, with literally no changes to the game beforehand, well, that's a bit tougher nut to crack. How can you test something like that?"
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60tfus | What are the green lights for on escalators while walking on or off of them? | Engineering | explainlikeimfive | {
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"They are there to help you see the steps. Sadly, there is no special function/mechanism denoted by the light aside from increased visibility. As a kid I'd always thought that there must be a \"power converter\" or something there making all that light haha."
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60u2yk | Why can you switch gears without using the clutch? | New to this. A co-worker was trying to explain to me how he can shift without using the clutch, but I'm pretty sure he confused himself while confusing me. | Engineering | explainlikeimfive | {
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"Because on a mechanical level, when you can change gears without the clutch, it is because the input and output shafts are rotating at the same speed, and without tensions on the gears. The gears are able to move in and out smoothly. It can be potentially more damaging to the transmission in a vehicle with synchronizers to shift without a clutch, just because of how it's made. You do see floating gears a LOT in the trucking world (heavy duty) though. Truck transmissions do not have synchronizers, so double clutching or floating is required to change gears. Synchronizers, on a basic level, match the speeds of the input and output shafts, so the gears on each shaft don't grind when they interact.",
"In a modern manual transmission the actual gear wheels are in constant contact but freely spin on the output shaft, and the gear selector mechanically connects just one gear wheel at a time to the output shaft. An additional 'synchromesh' allows some slippage. It's only meant to match the gearbox speed to the road speed while the main clutch is depressed, and then releasing the main clutch handles matching the engine speed to that, but the synchros can be misused to do all the clutching. To do this smoothly the engine speed must be set appropriately by the driver using the accelerator, called 'rev matching'. Even then, imperfect rev matching when shifting without using the clutch will wear out the synchros. I advise don't do it routinely in a car you care about.",
"If you find the sweet spot in the rpm's, then the clutch becomes unnecessary. Since there is no tension on the gears it can shift in and out smoothly."
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60wrst | Does a larger engine capacity (cc's or Ls) translate to a decreased fuel efficiency and larger fuel consumption rate? What other SIGNIFICANT factors are at play in terms of efficiency and consumption? | SO a friend of mine was telling me her vehicle burns quite a lot of gas because it has a [large engine]( URL_0 ). I would like to know how the mechanics of engine size translates to fuel consumption and efficiency. Common sense dictates that a larger engine burns more fuel during combustion, but how does that combustion cycle correlate to covering a fixed distance per cycle (for example... how far would one cycle of firing all cylinders make the vehicle travel once static friction is overcome? 20 feet?) What other factors make a huge difference in performance? Tire pressure, oil levels etc? I understand that when all cylinders are firing, a 3 L engine would consume more fuel than a 2 L engine with the same amount of pistons. I'm aware that vehicles are engineered differently so it would probably be foolish of me to ask at what stage does the engine decide to fire all cylinders instead of a fraction of them etc... I'm asking this so that I can make a better informed decision in terms of fuel efficiency and fuel consumption when purchasing my first vehicle. Sorry if it seems like I'm all over the place/incoherent in asking the question. Thanks in advance for all your replies. | Engineering | explainlikeimfive | {
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"Internal combustion engines operate with a variable efficiency. At idle, all the energy is going to moving the car parts around, none is going to move the car forward. At high power output, lots of power is going to make the car move, but some is still used to just keep the parts moving around. A large engine is less efficient at idle, because the parts are bigger, and there might be more of them. It might have a higher maximum power output, but that's not an aid to efficiency. The other reason a large engine is less efficient is that it takes a minimum gasoline density for the spark to work. That means that there is a minimum fuel consumption needed to keep the car idling. The larger the displacement, the more air that needs that much fuel.",
"> I'm asking this so that I can make a better informed decision in terms of fuel efficiency and fuel consumption when purchasing my first vehicle. Used/New car dealerships have that information on the cars on a paper on the window. It'll usually have an average \"34 MPG\" with some ratio of city vs highway mileage, since highway driving is more efficient. Fewer stops, less idling in traffic, less acceleration. If fuel efficiency/consumption is your concern, MPG will basically give you the answer you want. Fuel flow rate is this, which produces that much power in these gears on the engine and it means you get the answer of 30 MPG on average. Efficiency is also affected by your driving. Flooring it from a stop to the speed limit is less efficient and harder on your car than a smoother acceleration. You'll also want to avoid idling because you're not doing anything, like waiting with the car on while a passenger goes into the store real quick. I've heard of cars (Europe, I think) that turn off the engine and turn it back on automatically when stopped, like at a red light."
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60yilv | Why do some cars have one exhaust pipe and others have two of them? | Engineering | explainlikeimfive | {
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"Just as a little refresher, [a standard 4-stroke engine has 4 phases]( URL_0 ): 1. *Intake* - piston goes down drawing air + fuel into the cylinder 2. *Compression* - piston goes up compressing air+fuel mix 3. *Power* - **EXPLOSION** drives piston down creating force 4. *Exhaust* - piston goes up pushing burnt fuel out of cylinder Everything but the power phase is \"wasting\" energy. The exhaust and mufflers on a car are there to cut down on the noise of all these explosions going on in the engine. Unfortunately, they create some back-pressure in the system making exhausting slightly harder and robbing the engine of power. A dual exhaust gives you two separate exhaust lines so that there's slightly less pressure, resulting in more power. Downside to dual exhaust is that they're more expensive. Most cars use singles because it's cheaper.",
"An exhaust system's function is to move exhaust gas from an engine's combustion away from the engine. Larger/more powerful engines need to move more air than smaller ones. This can be done 2 ways: a bigger pipe, or more pipes. Deciding which to use is pretty much entirely up to the car designer/manufacturer. So basically, it boils down to: because somebody arbitrarily made it that way.",
"It's an arbitrary decision by the car designer. It is true that the exhaust system creates some back pressure, and that thicker or more pipes would reduce this pressure, but if you look at the pipes under most cars, you'll see one pipe go from the engine through the catalytic converter towards the rear, at which point the single pipe splits into two pipes of the same thickness. Rather pointless, as far as pressures and exhaust gas movement. The decision is determined by aesthetics. We find things that are symmetrical a bit more pleasing than things that are not. Exhaust pipes on both sides of the back of the car = symmetry.",
"If not purely for aesthetics, then it's because of cylinder configuration. Inline engines will have one bank of exhaust headers, a v-shaped will have two."
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610pop | What's exactly the low humming sound that you can hear near high-voltage areas, like electrical substations? | Engineering | explainlikeimfive | {
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"What you are hearing is the vibrations of various metallic components, caused by the changes in the magnetic field of the alternating current carried by the power lines. Because the current is alternating at a certain frequency (60Hz in the US, 50Hz elsewhere) that frequency is carried over into vibrations, so all humming installations hum at the same frequency / pitch.",
"The term for that effect is \"magnetostriction\" and the frequency heard is actually double the mains frequency. The transformer cores (and other magnetic components) become powerful electromagnets twice per power cycle. Once N-S, once S-N due to the alternating current. TLDR : the sound is 120hz in the US and 100 hz in Europe."
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613acc | How do engineers figure out how much torque is the correct amount for a bolt when bolting something in place? | Engineering | explainlikeimfive | {
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"You can take the diameter of the bolt and the thread to calculate the tensile strength of the fastener. Once you know where it fails, you can then set the torque amount below that. I remember my auto shop teacher telling me to \"tighten it until it breaks, then back it off half a turn.\" He was obviously joking, but that is pretty much where the Torque specs come from: just shy of breaking.",
"There is a formula: > T = c * D * F T = Torque required F = Bolt tension desired (Axial Load) D = Nominal bolt diameter c = Coefficient of friction constant The idea is that the bolt has to take a certain load, and they never want the parts to relieve the tension, because then the bolt could shake loose. Your torque wrench preloads the bolt to prevent this.",
"While the torque can be calculated, for critical applications a torque test must be done. A very basic test consists of the joint stackup (the part you're threading into plus any parts that are clamped, plus the bolt/fastener) being torqued to failure while measuring torque and angle of rotation. Typically you would do 30 samples at minimum to get statistically significant results. Preferably you'd do more samples. Once you have data, you set the torque target somewhere between the joint starting to clamp and joint failure. Statistical analysis helps for this step. Source: am automotive engineer, have performed torque studies myself."
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6143al | What Happens To Electricity When An EMP Goes Off, And How Do People Store Electricity? (Bigger Scale Batteries?) | Engineering | explainlikeimfive | {
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"Large EMP could damage transformers and transmission equipment. The lights in your house are powered from a plant far away, and if the transformers that connect you to the plant need to be replaced, you're waiting in the dark. There isn't infinite supple of spares, because these transformers are very expensive, and it could take a year to get one. Batteries are one way to store electricity, reverse hydro is another, much cheaper way. The fraction of the grid that could be powered this way is very small.",
"Radio waves cause currents in conductors as they pass by and drag electrons with them. This is how radios work. EMP makes very loud radio waves and causes currents in many large metal objects such as power lines and antennas. This sends a surge of extra power through most of the items you own. Some items will never run again. Others might need to be rebooted but will be mostly fine. Items like flashlights with no cord, no antenna, and no internal circuit able to receive meter-scale radio waves will almost certainly still work."
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616dk7 | why do power steering pumps whine when the wheel is fully locked to one side? | Engineering | explainlikeimfive | {
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"The system is stalled and has to relieve pressure through a relief valve. Otherwise something would blow up. The pump will just keep building pressure until something gives up and fails."
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618cwg | What is going on when a light on old circuitry flickers several times before turning on? | Engineering | explainlikeimfive | {
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"In MOST cases this isn't due to the wiring but instead the light/fixture itself. In a fluorescent bulb, power \"sparks\" (arcs) through gas instead of flowing through a stationary wire. Once current is flowing the arc becomes a reliable/consistent path for current, but it can be tricky to start and maintain it in the first place. A component called a \"ballast\" limits/manages the amount of current flowing through a fluorescent bulb, and wear or failure of that component is a common reason the light would flicker instead of turning on immediately/correctly."
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61bphl | How potholes happen in roads | Engineering | explainlikeimfive | {
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"Canadian here. I live in Pothole Country. For us, we have the standard asphalt roads. Our winters are extremely wet (depends on where you are) and cold, like -44F cold. The second there is a crevice in the asphalt for water to seep in and freeze, you're going to get a pothole eventually. The water expands as it freezes, creating cracks. These cracks let in more water, meaning the crack grows rapidly. The earth around the crack heaves and settles as temperatures fluctuate and destroys the integrity of the surrounding material, which then breaks apart and creates a hole in the road.",
"Roads are made from asphalt. Little rocks suspended in a tar to create a hard surface. As you drive along the road, there is a tiny chance that one of the rocks gets picked up by your tire and flung at some guy's windshield. When that happens, the integrity of the road drops at that exact spot, making it easier for other cars to chip away at the road. That erosion causes a hole to form in the road.",
"It has a lot to do with the material underneath the paving, if one little spot of the fill material (gravel and such) wasn't compacted right, it settles over time under the paving and makes a little cavity. That hole cracks open, is subject to rain and other erosion, and you get a pothole. If there's a strong flow of underground water that isn't accounted for, great bit areas can wash away and hollow out, causing much worse sinkholes"
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61llny | How does a crematory not mix people's ashes together? | Do they power wash the inside before running another cremation? If not that or something similar, I would think remnants would be left over. | Engineering | explainlikeimfive | {
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"They often do get mixed up. What comes out of a crematory oven isn't ash, it's mostly bone dust and chunks, that get ground up in a big blender called a cremulator, and then bagged up. There are almost always at least traces of multiple sets of remains, though they do sweep out the oven every time. It's not considered to be a problem, because, like most such funerary information, people just don't want to know.",
"You could read this book 'Smoke Gets In Your Eyes'. It's a narrative by a mortician. Very enlightening and also well written and interesting, I learned a lot about the morgue life from it."
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61lx2h | Why do domestic (U.S.) cars have a reputation for being lower quality when compared to imported cars from Europe? | Engineering | explainlikeimfive | {
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"For a long time, American cars were often of lesser quality than Japanese and European cars, they had defects in manufacturing and used often substandard parts and processes to build cars--and they were known for it, everyone knew they just weren't as good, reliable, and such, even the companies making them, and they didn't do much to hide that. Producing cars, effectively, cheaply, and profitably is hard, and the process that was being used to make American cars produced a lot more quality issues than those produced elsewhere There is actually an entire field of quality management / production operations pioneered by the Japanese called Total Quality Management (TQM) [Also called Lean, or Lean Six Sigma, or the Toyota Production System] Who's whole purpose was that it was cheaper, better, and more efficient to produce goods (in this case cars) with as little quality issues as possible. That is produce quality goods with no defects, over and over and over. This system, through much investigation and research turned out to be crazy effective. And now it is used in manufacturing of just about everything across industries and around the world. This is the process that was used in Japanese car manufacturing, and to a degree, those in Europe as well Now back to american cars. Well, until the mid 90s, American cars were crap quality compared to many foreign ones, foreign cars used the system above and made quality cars with little defects, Americans did not, and had lots of issues. So the Americans took notice, and started changing their systems, the Japanese car companies even helped, it was a problem they all wanted to solve. By the mid 2000s American cars were as quality as made anywhere else, and today, American cars are often even higher quality than anywhere else (although everyone is making great quality cars, so differences are small) The stigma still sticks though, even though current, and last decade or so American cars are very high quality, and foreign cars are the same, American cars have not outgrown the old ideas that they are crap.",
"For what it's worth, in the UK at least the reputations are that Japanese and German cars are reliable and quality, whereas French and Italian stuff breaks down. The old bad British car companies, with workforces that spent a lot of time on strike, have pretty much all gone bust. American brands that make cars in Europe for Europe such as Ford are well-regarded, but actual American cars are seen as a bit rubbish. To be fair, we tend to look for different things."
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61og2g | Why aren't more electronics waterproof? | Engineering | explainlikeimfive | {
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"It is significant extra expense and engineering challenge for something most users don't need. Most of your life is in a dry environment, why spend a lot of work so you can dunk your laptop in the tub?",
"Because it can cost a lot. Most electronics needs to be opened up to put new batteries in, for repair, or ease of manufacturing. Closing all the holes that water can get in while allowing the above three costs money for features most consumers dont care about."
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61onw4 | Why is the triangle the 'strongest shape'? | Engineering | explainlikeimfive | {
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"Because you can't change the angles without change the lengths of the sides. With a square, it can deform into a rhombus without bending or otherwise changing the lengths of the sides. With an equilateral triangle, you have to do both.",
"Technically a perfect circle is, because there are zero weak spots, because there are no corners. It's because there are three corners, so therefore less build up of pressure than there would be in another shape, so each point can handle more pressure.",
"Because the lengths of the sides of a triangle are enough to define the shape. With a square or rectangle you can maintain the side length and still distort the shape into a rhombus or parallelogram. In other words, maintaining a square shape is relying on the strength at the corners to maintain the angles but a triangle only relies on the strength of the sides to maintain their length."
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61papi | What makes a telescope different than a telephoto lens? | Besides the obvious mount for a camera, being made to withstand rigors of the road, and a logo on the side, what's mechanically different about a telescope that makes it so special? | Engineering | explainlikeimfive | {
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"A telescope and a long focal length camera lens do pretty much the same job, but there are some differences: * Camera lenses nearly always use just lenses. Telescopes can use lenses, mirrors, or both. * Camera lenses are designed to focus over a range of distances, which can mean compromises. Telescopes are designed purely for focusing on distant stars, 'infinity' in photography terms. * Telescopes are designed to capture as much light as possible. That usually means just two or three glass elements because each surface loses some light. Camera lenses don't worry about that so much and often have lots of glass elements. * Camera lenses are designed for use with variable aperture - the diameter of the opening for light to go through. They may compromise sharpness at wide aperture, and they need a clear light path down the middle for small aperture (which is one reason they rarely use mirror designs). Telescopes are generally designed for use 'wide-open' only and need to perform well at it. * Long focal length camera lenses invariably use the 'telephoto group', a lens arrangement to make the focal length longer than the physical length. Long focal length telescopes are often physically long, although not always. * Telescopes get physically much wider - again, it's light transmission. For example the Skywatcher Skyliner 300P is a £1000 amateur telescope with a 300 mm (12 inch) diameter main mirror. In camera terms it's a 1500 mm f/5 (mirror) lens, and a comparable camera lens would cost over ten times as much. And that's just amateur stuff - professional astronomers use telescopes with main mirrors several *metres* across. * Camera lenses have autofocus. Amateur telescopes usually have manual focus. * For photography, normal photographers use exposure times of fractions of a second. Astronomy photographers use exposures of several *minutes*. That means the mounting needs to be rock solid, far more so than a typical camera tripod, and also compensate for the Earth's rotation. Because of the 'bang for your buck' performance, terrestrial photographers interested in extreme telephoto shooting often turn to amateur astronomical telescopes despite the drawbacks."
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61qa3v | why do wood fires burn so slowly, but house fires with even greater area to cover seem to be rather quick? | Whenever I'm camping and light a fire, it generally takes a hours until the wood burns completely through, but whenever I hear about a house fire on the news, it seems like houses can almost completely burn down before the FD even gets there. Why is it that the wooden structure of a house burns so quick when camp fires don't? | Engineering | explainlikeimfive | {
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"The wooden structure itself actually doesn't burn that fast, and if you look at the remains of a structure fire, you'll notice that a lot of the wood is mostly in tact. The fire just weakens it enough for it to collapse, if it does at all. It's the furniture, carpets, etc. that burn so fast. Especially curtains. Curtains are a HUGE fire hazard.",
"In addition to the other comments, the structure of a standard campfire (3-4 logs making a triangle into each other) contributes to it. In this campfire, the logs burn, some of the heat radiates into the other logs, but most of it rises, away from the campfire, and into the air. This heat is lost, and it flies away. The flames on the log crawl up the log at about a 45 degree angle, where they contact a small amount of neighboring wood, and a lot of air. You may notice that as the logs ember, they drop coals in a pile under the logs. These embers sustain the fire by radiating the heat upward (into the logs) and empowering the flames on the underside of the logs. In a housefire, the fire doesn't radiate the heat away. (until you breach a wall, or ceiling) The heat radiates into nearby furniture, walls, whatever, retaining that heat. This spreads the fire much faster by having everything heat up. For flames on a vertical wall, the actual flame is in contact with the wood directly above it, far more than a log at 45 degrees, which accelerates the burning of that piece of wood. In a housefire, there is also a much greater quantity of fuel. As the wood starts embering, there is simply so much more fuel to burn. The embers land, spread their heat to their surroundings and then those surroundings burn and ember and so forth. The fact that a house is a box-like structure means that it contains the heat and accumulates it, like an oven, whereas an open campfire is always losing heat to the air and wind. TL:DR - fire burning things is a reaction that is controlled by the amount of heat being retained, the amount of fuel in contact with flame. Houses on fire hold the heat, spread it more effectively, and are simply larger.",
"I'm a person responsible for fire testing of architectural products and here is my take on it. A commercial or residential window shade will burn if in the path of a flame, otherwise it self extinguishes. Similarly the walls and furniture will burn if in contact with a flame from a source like a carpet or other flooring surface. Ceiling tiles will burn if in path of a flame off of desks and sofas. The intensity of the fire will determine the flame height and the materials in the room affected by the flame. The reason the campfire takes so long is because the logs were not stacked in order to enable the lower burning logs to ignite those above them. Next time try slicing the log with slits in it and see how much faster it burns. It has to do with accessibility to air. A solid log burns slowly while the slit logs burns faster because the air reaches inside the slits. Any burnable surface in contact with both air and a flame will burn quickly.",
"I work wit a volunteer fire fighter. We were talking about the speed difference in modern and old houses. Modern houses are filled with plastic and synthetic material so burn damn fast! Old wooden houses are much slower.",
"Its about surface area as much as anything else. Yes there may differences in flammability but surface area is much more important. The greater the surface area the greater the exposure to oxygen.",
"I think the real answer is that you are comparing the acceleration of a fire to complete consumption. If a house fire was to lead to the complete consumption of the available fuel it would take a very long time."
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61rnal | Why are German products higher quality? | Engineering | explainlikeimfive | {
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"Germany was one of the first countries to get mass amounts of high quality steel by way of Krupp steel. This led to the development of higher precision machine tools and higher quality metal goods. This reputation has survived largely because of this history but now Germany can't compete in the cheap markets where Asian business dominates. Instead they stick with premium goods at a high price.",
"it's certainly not true for all german products, but it's just good business to maintain an expectation of high quality to build customer loyalty",
"I wouldn't say it has anything to do with any crazy engineering or anything. Germans just don't settle for shit. If something breaks or is unsatisfactory, they will let it be known. I think that is the main reason. If you are complacent and accept it, of course its going to keep happening.",
"Because they can't compete in price. So they have to use higher quality to distinguish themselves. I think it's also partially a cultural thing.",
"Hopefully someone will expand on this in greater detail because I'm on the toilet at work on mobile right now, but here goes. IIRC German engineering grew into the powerhouse that it is today, following their defeat in WWII. One of the provisions within the Morgenthau & Marshall Plans (basically a plan giving Germany the finger for being huge DB's during WWII, while trying to make sure they wouldn't ever be able to go for round III) was that Germany wouldn't be able to spend anything having to do with military operations or development. *Obviously this is a gross oversimplification, but I'm going off memory and I'm on the toilet so cut me some slack.* Consequently all of the engineers and businesses that had been part of the German war machine transitioned to private industries. Since the money that the German gov. had previously been spending on being dicks to all of Europe was now just laying around (not counting all the money they had to pay out for reparations), they decided to invest in domestic infrastructure. All of the aforementioned factors [many omitted], in addition to the efficiency of German production, and absolute necessity were driving forces in Germany's post-war reconstruction. Tldr: Germany wasn't allowed to make shit that went \"boom\" after WWII, but the engineering nerds who were previously working in the war effort still needed to make money. Instead of designing/producing weapons & war machines, they began focusing on making cars & shit to sell to the chumps across the pond in Freedomland. This is all going off what I remember from a one day section in my AP Gov class during my junior year of high school. There's probably more holes in this crude account of history than Swiss cheese, so hopefully one of the kids I used to copy off can pop in and clear it up for you.",
"What I was taught in Design History was that German products used to be of lesser quality before the 20th century, so they formed the [Deutscher Werkbund]( URL_0 ) , an association of industrialists, craftsmen, architects etc. to make better products and rebrand \"Made in Germany\" as a sign of quality. There was a TIL I think a few days ago about the Made in [Country] mark, saying the British invented it (near the end of 19th century) to mark foreign goods which were generally of inferior quality. Another aspect of their current quality is the coupling of specialist high schools with the industry where they basically train their employees from day one. *disclaimer: I am a trained industrial designer, not a design historian, so I welcome any addition/correction to this*",
"You're assuming they ARE higher quality, which I'm not sure is the case. For example, here's a 2016 vehicle quality study: URL_0 Porsche is near the top, BMW, Audi, and Mercedes are just above the middle, and VW is down near the bottom. Edit: I've had several replies about the minutia of my post, without addressing my point: that OP's premise isn't necessarily a good one, so it's hard to explain.",
"In 2006 I visited a manufacturing facility in Germany that was recently purchased by the company that I worked for here in western PA. While standing on a mezzanine deck overlooking the shop floor, one of the German engineers proudly asked me if I had ever seen an operation quite like his before. When I answered that it looked very much like the operations that we had back home he seemed very disappointed. I was just telling the truth. Their manufacturing floor and the one back home pretty much looked and operated the same. And I already knew the western PA work ethic and work quality was outstanding.",
"Most products aren't actually higher quality. People just assume they are because they're imported (which often raises the price) and from Germany. It's kinda like how people assume that Italian cars are high quality cars because everyone knows Maserati, Ferrari, Lamborghini, etc, but anyone that's ever actually driven a Maserati or Ferrari knows that they're crap and you're really just paying for the emblem on the front.",
"They aren't. The 'brilliant German engineering' trope appeared around the 60s and 70s when Germany went through an economic boom fueled by post war investment. Manufacturing industries flourished and German cars in particular became a huge export. These cars were good and the marketing team advertised them as premium vehicles overseas. In Germany they were just normal cars. Despite this, Germany began building a public image of having the best engineers in the world. Before and since then the trope hasn't really applied. There are plenty of shockingly back German cars around, and other terrible German products. Also plenty of great German cars and products still. However some clever marketing from 50 years ago has stuck.",
"The German national ethos includes a penchant for attention to detail. Germans don't say, \"ah, that's good enough.\" Instead they say \"How can we make this better?\" I'm generalizing of course, but geez, they've had laws about beer purity forever. If you're so serious about beer, how serious are you going to be about cars, train schedules, and firearms?",
"As stated above not all german products are higher quality. I think one reason for better quality in some areas, despite the histroy, is the legislation in Germany, the consumer organisations and quality seals, which carry a lot of weight. For example the [Stiftung Warentest]( URL_0 ), a independent organisation, that tests products and compares them or the product liability as a EU directive ( EG-Directive 85/374 EG.)"
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61sn1k | a major problem with renewable energy like wind and solar is storing energy when the source (wind or sunshine) is not available. Why can't they just use water? | You could use excess electricity to power pumps to pump water to a higher elevation, and when there is less power than normal let it fall back down and power a turbine or something. Obviously this wouldn't work for something mobile like a car, but why couldn't it work for a stationary power plant? It seems a lot more practical for storing huge amounts of power than huge arrays of lithium or lead batteries. Hell, even if it's inefficient it's still probably cheaper and more environmentally friendly than mining all that lead and/or lithium. | Engineering | explainlikeimfive | {
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"This is called pumped storage and it's commonly used wherever there is a good place to put a reservoir in. But there are many places in the world where there isn't a convenient large hill nearby, and because of the huge amount of water involved it's not possible to build something from scratch on flat ground.",
"This is being done. If you look at the new additions to the high power grid of Europe a lot of the new lines are between mountainous regions in the alps and Scandinavia where they have a lot of hydroelectric power plants and flat areas where there is more wind and solar as well as more cities. This is in preparation to go away from coal and gas. But even this might be enough. The problem is with high speed pickups. When you switch on a kettle that energy have to be already in the power grid. It is not enough to have it in form of water on top of a mountain. In traditional coal, hydro, gas or nuclear power plants there is a big heavy turbine that contains a lot of energy. When you switch on your kettle the turbines will move a tiny bit slower as you use their energy. To keep up the speed there is a need to change the flow of water to the turbine but this is a process that takes seconds. The turbine have lots of energy that is available in milliseconds to anywhere in the grid where it is needed. So to keep a pumping hydro plant working you would have to run the turbines all the time to keep them spinning. And the pumping is not going to be as efficient as you might think. Nuclear power is a very good option and does complement the existing hydro plants and allows for more wind and solar as well. We have mastered the safety aspects of it and can make very safe reactors if we are able to respect it and manage it properly."
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61we9a | how can f1 cars rev so high yet production cars cant and or wont? | Engineering | explainlikeimfive | {
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"The bore of each piston is much larger than the stroke, meaning less stress per revolution as the length of the rod (the stroke) is shorter. This means larger intake and exhaust valves and essentially more useable horsepower. This however means a significant reduction in reliability (many motors are only run a few races or even a single race before rebuilding) and of course a major hit to economy of fuel. The balance point is reliability and economy of fuel over raw power, as most of it simply not be used under normal circumstances."
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61xw8m | If AI is so dangerous, why is there little to no legislation on this topic? | Engineering | explainlikeimfive | {
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"> I've been told the UN ranked AI first among the possible causes for human extinction, higher than climate change and nuclear warfare. So why are both of these things so heavily regulated when AI isn't? Lawmakers don't have magic \"Regulate this topic\" button they can press. You have to tell exactly how do you propose this thing should be regulated. Even if we assumed we got together world government, made you the dictator of the world and let you decide all the policies, laws and regulations, you'd still have to say exactly what you think world government would do about AI and risk it poses. Do you make AI research illegal? Beside being obviously an extreme measure, you're gonna run into trouble as we now kinda have to worry about drawing a line between what is AI research, and what is math or computer science. Universities and companies like Google would depend on this distinction. Does Google search engine count as illegal intelligence? You'd have to draw a line here. What other methods of regulation are you thinking?"
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620oc9 | Why is all glass not safety glass? | Just dropped a beaker at work and it got me thinking why all glass isnt configured the way lets say a windshield or window is. | Engineering | explainlikeimfive | {
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"for general use, cost. car windshield glass is laminated. it's actually two pieces of glass with a clear glue in the middle. it doesn't shatter into million pieces when it breaks. windshield glass also needs to be mostly distortion free. you'll note that windshields are bent, but when you look thru them, the image is not bent. car side window glass is not laminated, but it's still special glass. it's tempered. it's stronger than just \"normal\" glass. but it shatters into many pieces when it breaks. then there's glass made for ever other specialty application. optical glass doesn't need to be super strong or not shatter. it needs to be very clear and very distortion free. gorilla glass is very scratch and shatter resistant. and very pricey. UV protection glass filters out UV light. residential window glass is treated for filtering our both UV and IR light.",
"Most probable reason? Price. Plain glass is much cheaper than shock resistant glass, or even scratch resistant glass or so. All these improvements make the product a tad more expensive and sometimes this difference gets bit enough to matter. We could also say that in some situations a heat tempered glass piece is just plain stupid. Imagine if a window in you house got hit by a sharp rock. If it was a heat tempered piece it would shatter in a million pieces and cleaning that would be a pain in the butt. Now, if we use plain glass it just breaks into big chunks near the impact. See? Its much easier to clean and sometimes can be \"fixed\" with a piece of tape till the next day, while if it was HT glass you woudn't have a window anymore, just a hole in your wall."
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6215d2 | Why isn't the power grid underground like plumbing/sewers/water lines? | Wouldnt this reduce outages since there are no poles to knock over or power lines to get hit by falling branches etc? | Engineering | explainlikeimfive | {
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"It is sometimes. Running power underground is expensive, but will fail less often. But when it does break, it's expensive to repair. Running power overhead is cheap. It's more fragile, but also quick and easy to repair. Water and sewer lines are underground for some key reasons. One, they are heavy. Very heavy. So not only do you need very strong towers to hold them, if they fall they can do some serious damage. And also, they are gravity driven. Especially for the sewers, those lines need to be below that of your house so that things will drain away. Electricity doesn't care about gravity.",
"Especially with high voltage (carrying over long distance) lines, there is an immense cost in underground lines. One of the reasons is that air is actually a pretty good insulator. But it can't be used as an insulator in buried cables. To insulate those high-class lines, a lot of material is required, which also means the cables will be quite large when buried. In addition, underground cables are prone to damage, from natural causes or accidents, and are difficult to maintance.",
"The power lines in my neighborhood are buried. A few years ago I lost power, and the power company told me that one of my lines had broken due to the soil shifting over time. Because they were buried, they were *my* responsibility to repair, where if they had been aboveground the power company would have repaired them. So I had to spend $3000 to have new lines put in. Exposed power lines are a PITA, but buried power lines are very expensive to maintain."
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622sqe | Why is it that only hatchbacks/SUVS have a rear windshield wiper when they're the ones that need it the least? | I had a subaru outback for awhile and absolutely loved it. One funny thing I noticed was that I had a rear windshield wiper, but never ever had to use it for more than one swipe. If my car had been out in the rain or snow, I would swipe it once then drive around and no rain or snow would accumulate at all so I would never need to leave the knob switched "on." Then I began to notice that ONLY SUVS and hatchbacks have this thing. What the fuck? Why? I've yet to see a car with a slanted rear windshield that has one and I have not been able to figure out why | Engineering | explainlikeimfive | {
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"They aren't the ones who need it the least if you think about dirt. Cars with a trunk and a more angled rear window will see more rain hit the window, but cars with a flat rear end will see maximum air pressure pushing up dirt/grime into the back of the car. For this reason, these cars often have rear windshield wipers.. for the dirt that is more likely to accumulate, etc.. not necessarily for the rain.",
"Aerodynamics can be counterintuitive. The flat vertical back of a hatchback or SUV creates turbulent air behind it that can then deposit dirt on the rear window. I drive a hatchback and it's true I tend to just use the rear wiper for one or two wipes, but that's one or two more than zero!"
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6244o2 | How is an engine affected by +/- degree(s) of timing? | I've always been into the car scene and have modded my car quite a bit. I've seen others have their cars modded and say something like "I'm running +3 degrees of timing." or something like that. What exactly happens to the engine when you run more or less timing? Edit: grammar | Engineering | explainlikeimfive | {
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"There are two type of timing: ignition timing and valve timing. When you see someone talking about adding/subtracting a few degrees, they're probably talking about ignition timing. Ignition timing is when the spark plugs fire in relation to the position of the piston. Getting it right is a balance between igniting at the highest compression (closest to Top Dead Center for the piston) and making sure the spark has enough time to ignite the air/fuel mixture. Getting closer to TDC will increase power, but advancing the timing can cause the spark to start so late that the fuel doesn't completely burn, causing a reduction of power and drivability issues. Since stock engines are usually tuned very cautiously, advancing the timing a little is generally a good way to get some extra power. Granted, there's WAY more to it than that (vacuum advance, ignition at different RPMs, computer controls, the effect of different manifolds, etc.) to really understand how to use timing to tune, but that would turn this into \"Explain Like I'm an Experienced Engine Builder.\""
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625fc8 | Why do we have a space station when we could have a moon base? | Engineering | explainlikeimfive | {
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"There are some great images from XKCD's What If blog that I'm gonna shameless steal from: [This is probably what you imagine when you think of space]( URL_1 ) But in truth, it actually looks [more like this]( URL_0 ) The international space station is 400km away from earth, that's about forty times higher than the maximum cruising flight of most aircraft. The moon on the other hand, is over 380,000km away from earth. Almost a thousand times further away! Worse still, it has its own gravitational field so getting back to Earth requires a huge amount of fuel, whereas a shuttle leaving the international space station only needs to slow down a bit in the opposite direction of its orbit to re-enter Earth's atmosphere.",
"The moon is significantly further away. The ISS is about 250 miles away from Earth. The moon is about 250,000 miles from Earth. Every planet in our solar system can fit between the Earth and moon. It's about 10 times the circumference of the Earth.",
"In addition to the practical issues with building a moon base, a major purpose of the ISS is to do experiments to see how things behave in zero gravity. You can't do that on the surface of the moon, you have to be in orbit.",
"Traveling to the moon would take a lot more fuel and weight and the more weight, the more fuel that is needed; which costs money... a lot of money",
"Because of the Space Shuttle. The space huttle was the primary means for constructing the space station, but it can not leave Low Earth orbit. As such, there was no way to have a moon base.",
"The ISS is close enough to not require huge amounts of fuel, money, and time to get to. Other than geology, there isn't much more that could be done on the moon that can't be done on ISS.",
"Why would we have a moon base when we can have a more useful space station instead? The space station allows for microgravity experiments which you can't do on the moon. It's also nice and close (relatively speaking) so we can fairly easily shuttle things up and down to the space station. Getting things to and from the moon is a lot harder as the moon is 1000x further away and has its own gravity so you need rockets again to land there and get away from it again. Plus, there's not much interesting stuff we could do on the moon that we can't do either in space or on Earth."
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62bxa2 | Why cant we build a bridge from Key West to Cuba? | Regardless of either countries relationship status, would it even be possible to build such bridge? It would only be 90 miles or so? | Engineering | explainlikeimfive | {
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"the longest bridges in history are usually built over relatively calm bodies of water. The challenge isn't how far we can build a bridge, its can we keep it safe/stable enough for cars to drive over it. The Depths of the Caribbean Sea are somewhat extreme, and for many miles of that distance, we are talking about over 1 mile of water. We can't very well put supports on that, so we'd be talking about a floating bridge... While the technology for building a floating bridge does exist, building one of that scale, in an area that is routinely plagued by the hurricanes that visit the region on a yearly basis would make it very implausible to construct, maintain and keep safe a bridge that spans such a very long distance. Also, as far as accidents go, people are stupid. One accident would back the bridge up for.... the entire bridge. 90 miles of traffic jam due to an accident would be unsolvable. You've also got to look at how many people would actually USE the bridge. Theres only about 5,000 registered vehicles in Cuba, and mainly the use would either be tourists or travellers. 90+ miles for businesses is more easily done with a plane-ride than in a truck due to sheer speed alone. Taking a prop plane at 450MpH would beat a truck @60Mph multiple times over.",
"> only be 90 miles or so You're misjudging the difference in conditions. As u/uchihakengura42 said, 90 miles over the Caribbean Sea is *very* different from 90 miles over land. Marine conditions can change by the minute, and any accident backs up *all* traffic behind it. One of the [longest traffic jams in history]( URL_0 ) happened a few years ago, and that was on land. Imagine 50% more of that, and over water. That could easily end up [going very badly]( URL_1 )."
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62d42v | The Verrazano-Narrows Bridge was designed to curve along the earths. Yet, the water under it stays does not curve along the earth. How could it be if the earth is a sphere? | Reference: URL_1 Image: URL_0 | Engineering | explainlikeimfive | {
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"While it may have been designed to curve concentric with the Earth, the arc you see is because suspension bridge are also designed to be hump shaped so that they go flat when heavily loaded. The Earth's curvature is much\"flatter\" than the arc you see in the bridge. The water has the arc of the Earth.",
"The water does curve, but it's a much smaller curvature than that of the bridge, which is exaggerated for the structural reasons mentioned already. The bridge as a whole does take the Earth's curvature in to account e.g. the two towers are not parallel to each other, but that doesn't mean that the roadway has to follow the precise curvature of the Earth. The structural reason for the exaggerated upward curvature of bridge roadways goes something like this: with the roadway curved upwards, when you load it with cars and trucks, the forces generated are translates sideways, so that the roadway pushes outwards against its buttresses, which are built to take that. If the roadway was sagging below level at any time, that would mean *tension* (pulling in) at the ends, which would be a really bad thing, structurally - it's much harder to handle tension in the ground. So the upwards curvature is exaggerated to make sure that the roadway could never sag, under any conditions."
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62il5i | Why does road construction take so amazingly long? | I lived in Florida for almost 20 years. Road construction was awful and would take forever. Why is this? | Engineering | explainlikeimfive | {
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"The simple answer, is that building a road is pretty easy. But building a road that support trucks that weigh several tons, constant beating from various weather conditions, and won't sink under its own weight is much harder. They basically tear up the ground and the rebuild it layer by layer, to make sure it can drain and take the weight. Then build a multi layer road on top of that. Add in the bureaucracy that it takes to make sure the road goes over only the correct property, lines up with waster water drains and power lines, and a dozen other things I probably have no idea about and it ends up taking a long time.",
"Because a watched pot never boils. Also tons of days in Florida get rained out and they can't work on the construction. Source : also a Floridian"
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62jqwe | The concept of engineering a bridge | Incoming civil engineering double major student with several questions: URL_0 the engineers do the drawings and calculations, then a construction company is hired to build it? 2. Does the lowest bidder usually get to build it? 3. How do they calculate the max load the bridge can take? 4. How do they know how much concrete to use? 5. What principle in engineering do they use for bridges? | Engineering | explainlikeimfive | {
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"Most bridges are owned by the Government. The government hires an engineering firm to design the bridge, taking into account many variables that would impact the life of the bridge. Either the architect, or the government will ask contractors for pricing at a certain time and day. The bid will have wording to make sure only good contractors prices will be used. The government and architect review the pricing and determine if it's reasonable. A contract is issued, then work begins. There isn't a single bridge design that is always used, the design varies based upon length of the bridge, expected weight of things using the bridge, height, etc... I skipped many steps, but this is ELI5"
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62kv4k | how do plane formations (specifically jet display formations) keep their speeds identical for extended periods of time? | Is it as simple as super-sensitive speedometers? | Engineering | explainlikeimfive | {
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"This is a big part of my job. To directly answer your question, it's as simple as trying to drive the same speed as a car next to you on the highway. Add more gas if you're getting behind him, reduce it if you're getting ahead of him. You can do this on a bike or even walking next to a stranger. In jet formations, the leader of the formation tries to make it easy by keeping the same speed. As promised, a little more in depth... Flying in formation requires no instrumentation or advanced aircraft systems or computers. It breaks down into a few simple components. **1) Knowing where you want to be relative to the other plane.** In formation flying, the position you need to be in depends on what you're trying to accomplish. It can be arbitrary or have a specific purpose. You can try to be directly side-by-side, at an angle, behind and above/below... it's only limited by how easily you can see the other plane. As an example, the most common formation you will see is called parade. It's a tight formation that's used for things like flying together through low visibility, checking the other jet for damage, etc. [To fly perfect parade F-18 pilots have reference points.]( URL_0 ). For position, the pilot is trying to put the tip of the missile launcher rail of the jet he is following (in orange) on the headrest of that jet. The red line shows how they line up. For distance, he is trying to line up with the end of the exhaust nozzles (green line) For other formations, there are other reference points. For planes or positions without defined reference points, a pilot can use his own cockpit for reference, create ones when he gets close, or use intuition. **2) Recognizing when you aren't.** When things don't line up, it's pretty obvious. If, from your perspective, the tip of the launcher is in front of the headrest. You are behind, and need to move forward by \"moving\" the rail back. If the rail appears above the headrest, you are low, and need to pull up to \"move\" the rail down. A big part of this is seeing the movement before it gets too big. To be precise, corrections are made before the error becomes too big. **3) Knowing how to get from where you don't want to be to where you want to be.** This will totally answer how speeds can be matched between two planes. Let's use the above example. The tip of the rail is forward of the box. We need to move it back. [Reference this image]( URL_1 ) Add enough power to go a little bit faster than the other jet. Once the tip is about to touch the box, bring the power back JUST enough to stop the movement. If you've gone too far, you didn't catch it in time and need to add power to move the rail forward. Since you're never going to do it perfectly, the alignment will keep changing. With practice, you will only need little power movements to stop those alignment problems from getting too big. When the reference points on the aircraft are moving very slowly, you are almost perfectly matched in speed. Similar corrections can be done to fix up/down and left/right alignment using your stick and rudders."
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62kz2q | . For the "Door to Hell", if it's been burning so long, why hasn't a company/government taken advantage of it and use the heat as a source of energy or drill below to syphon the gas prior to ignition? | Engineering | explainlikeimfive | {
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"It would be an extremely difficult and dangerous way to get at the energy, and the natural gas. There are plenty of sources of natural gas in the area that ARE NOT currently on fire.",
"It's in the middle of a desert (The Karakum). There's no infrastructure there. A village is nearby, but it only has a few hundred inhabitants. Natural gas is typically collected and then transported to a place where it can be burned in a controlled and regulated environment (a power plant). This is done for safety and efficiency. It's better and easier to transport the natural gas than it is to transport electricity (across power lines). Building a power plant over top of the gas crater would be unsafe and inefficient. A few years ago the government of Turkmenistan said that the burning should be stopped because they want to exploit the natural gas and not have it just burning off into the atmosphere. But I don't know if anything has been done towards that end.",
"The fuel it contains is on fire far beneath the ground, and impossible to extinguish, making it impossible to exploit for energy. For the same reason it would be too dangerous to construct anything around it to capture the heat.",
"From an environmental perspective it's far better for the planet to have gas burning (turning into CO2 and H2O) than to vent all that methane into the air, since methane is a powerful greenhouse gas.",
"Turkmenistan has a lot of gas that they are already harvesting and selling as much and fast as they can. It's not a particularly well-run country, so there's no rush with doing anything with problems that only exist outside the view of the president. They have made a few attempts at coming up with a plan for fixing the problem, but all theories seem to conclude that the gas will find its way up to the surface no matter what they do, so they might as well leave it in the known location, where it doesn't bother anyone directly. So, the short answer is that they don't do anything with it, because they don't have to. Besides, many Turkmen believe that it has already been dealt with. When I visited and later met locals in Ashgabat and told them I had been there, they were puzzled. Mainly because I had chosen to Turkmenistan voluntarily, but also because the local news a few months earlier had reported that the fire had been stopped thanks to heroic feats by Turkmen engineers ..."
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62lq1k | How is a piece of wood made into a thin piece of white paper? | Engineering | explainlikeimfive | {
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"Grind raw wood into a pulp with your desired method, such as a grinding it with a machine. The pulp will contain cellulose, lignin (natural polymer), water. Chemicals are used to separate the lignin from the cellulose. Here you can bleach the pulp. This will leave a watery mixture of pulp which is then sprayed onto a mesh screen to make a layered mat. This is then goes through several processes to remove water. Then, heated rollers will remove any leftover water and compress it into large continuous sheets of paper."
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62lusr | Why are old houses built better than new construction? | I own a home built in the 30s and everything in it is solid. Every door is made of real wood and has some heft to it. I have beautiful real hardwood in every room. There are little character details everywhere like special trim and a built in bookcase with cool matching arches on the doorways. Note, I do not own this great mansion or anything. It is just a classic American Foursquare, a very typical middle-class house during the time it was built but it has all of these great qualities built in. One of my friends just bought a house from the 90s and everything feels...worse. Not that the house isn't nice, it probably cost a good deal more than mine and is much larger, but all the doors were very light and just looked cheap. No hard wood floors only laminate that looked like wood (but obviously not), tile, and cheap carpet throughout the house. There was also absolutely zero character or even design to the house, except some sky-lights in the kitchen which were admittedly kind of cool. Why are things that were built in the first half of the 20th century seemingly much better than what came after? Or is the newer stuff actually better and I have no idea what I am talking about? This could be true, but it doesn't seem that way to me. | Engineering | explainlikeimfive | {
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"You're not wrong, things were built better. Your house cost ~$7,900 in 1930s money, or $115k after inflation in current currency. But things were built differently, we didn't have the mass production we do today, companies didn't have the capability to minimize their product to the minimum acceptable while marking up their consumer price to the maximum the market would stand. We didn't have a disposable economy where everything is expected to be shit and you just throw it away. I remember way back in high school taking a few years of CAD and architecture (I'm so glad I didn't pursue it further), and we learned quite a bit about minimizing materials. Back in the day, a 2x4 was a lot closer to it's rough cut dimensions. Now days, they're typically actually 1-1/2\" x 3-1/2\" or less. Engineers are hard at work determining just how little is actually necessary to frame an acceptably sturdy and load bearing wall. Joists used to be 14\" OC, now they're 16\". And this much I can say for sure: cookie cutter new construction houses, built as starter homes for first time buyers, are designed by people who had never given any thought to actually living in that house themselves. They're designed to be both easy and cheap to manufacture, fast to erect, and have sale appeal. The living spaces typically aren't actually usable, but the model homes are staged perfectly, because their layout was designed by the architect at the beginning. This is how we were taught to design a house. As late as the 70s, all houses had hardwood floors. It's what you did. And THEN, they would cover it in carpet, because carpet back in the day was a lavish extravagance. Now days, they put carpet right over the subfloor (admittedly, it makes the most sense). Beams are undersized. I remember this. Even my instructors said if they architected their own house, they would upscale the size of their main support beams and use older standards to over-specify the construction of their floors and footings. You know how to test you have a shithole constructed house? Walk across the room, does the china hutch rattle? On the other side of the house? This whole subject just makes me angry. I've been looking at some new construction that starts even above my price range, and I see a brand new house, not even a year old, with substantial sheer cracking in the foundation, enough that this brand new house will need to have the crack sealed at the very least, and likely the foundation cut and replaced in 10 years. Concrete cracks, yes, it's supposed to, foundations settle. But this is bullshit. If you want a quality house, you're going to spend a lot of money to get it, and it's difficult to evaluate contractors for suckage.",
"\"Better is in the eye of the beholder\" Compare an American door latch to a German door latch if you'd like a real shock. German door and window hardware feels like it will be completely serviceable in 100 years. Frankly it looks a lot like the 100 year old stuff in the older part of town. Folks aren't heading out to the Home Depot every few years to get a new door latch. Making things plentiful at lower initial cost while ignoring the life cycle cost implications is a hallmark of US marketing.",
"Your house also may contain lead paint, lead pipes, asbestos insulation, lead pipes, wiring that would make an electrician weep, no central a/c ducting, etc so \"quality\" is subjective. New construction may also use lighter composite materials that are engineered to be easier to work with and cheaper, so they may not be as long lasting, but the trade-off is cost may be worth it",
"Easy answer...old was built to last but new was built to keep costs down. Cheap house, cheap material but expensive in todays dollars",
"> everything feels...worse Totally subjective feeling. Lighter materials have their benefits, \"Cheaper\" options like laminate and cheap carpet aren't bad because who would want to finance fancy carpet for 30 years? Just upgrade the stuff you want.",
"Some homes were built better back then, because the only people who could afford homes were more well off (pre-30 year mortgage), and because there was no minimum wage, lots of cheap immigrant labor. But there is also a confirmation bias at play... the only homes still standing 90 years later are the best built ones. For every well built, solid brick home from the 1920's there were also others that burned, fell apart, or were torn down for something more modern in its place.",
"The pretense isn't really correct. Maybe new houses come with laminate floors, but they have better insulation, better framing, electrical systems, and such. When I worked for Hometime they remodeled a foursquare and found nice woodwork but shocking deficiencies in the framing. You can still commission a house with real wood floors and such if you want. In the old days cheaper finish materials weren't available and real wood and the labor to install them were cheaper. Oak is really expensive now, but it didn't used to be; my 1960s house has oak trim with cheap tile floors.",
"In college I lived in a house that was built in the early 1900's (somewhere between the 20's and 40's in the Midwest). It is not that it was necessarily built better, but they did not have the same materials we have today. What you are seeing is known as survivor bias. Just like we say that \"Look at how all of these monuments/bridges/buildings lasts from the first millennium\", but you have no idea how many building were destroyed since then. By the 90's came around lots of construction developments have been made. One example is the pre-fabrication construction. Other things include door materials (the fiber board). Your friend probably got a base model house, while you got a house that, when it was new, was embellished. Houses now can be erected in a few weeks. Compared to a month or more of work. Each house will have their problems, but the older the house the more issues you are going to have with a variety problems. Cracking foundations, warping wood, and poor wiring are just a start. So your house will feel like it is more homely without as much furniture or decoration, but your friend's house will be more sound 'behind the scenes'.",
"I do see homes with hardwood floors. Ours does, and it's not a high end home, but hardwood is popular in Boston suburbs. On the flip side, unless it's been upgraded or the builder was at the leading edge, that 1930s home probably has knob and tube wiring, or at most two wire wiring, with maybe one or two outlets per room, and a fuse box instead of circuit breakers, and maybe just 60 amp service. GFCI outlets would be an upgrade. The bathtub might not have had a shower originally. One thing people haven't mentioned is that labor was proportionately cheaper back then. Homes use sheetrock now because plaster skimcoats require more skill and labor. A good hardwood floor requires some expertise for the finish coat; laminate or prefinished hardwood is cheaper.",
"This was a big deal when I was a volunteer firefighter in rural Ontario. The local area had a pretty big stretch from homes and shops built in the 30's and 40's, to new ones still going up. Partially it's the difference in the availability of materials and cost; such as readily available hardwood trees back in the day, that would be large and strong enough to span a roof, that just aren't around any more. I've seen center roof beams and floor joists that that are a single board, a foor thick in both directions. Modern construction replaced these with MDF board and manufactured wood I beams (think beaver puke). The other part is the engineering knowledge at the time. Back in the day, everything was over-engineered and oversized because the science and knowledge just wasn't there. Think about it the same way old cars and trucks were built, compared to modern ones. Bigger, heavier, more resources."
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62pvnb | Why is Gmail still not end to end encrypted | Engineering | explainlikeimfive | {
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"Because it is email, and email cannot be end to end encrypted, without bringing in other technologies like PGP encryption. If you use HTTPS and/or SSL IMAP to access Gmail, the connection is \"end to end\" encrypted between the computer and the server. However the server can read the contents of your email because that is how the email system was designed.",
"1. GMail is an email provider, and has to work with other email providers. Even if they implemented end-to-end encryption, they couldn't use it with other providers unless those providers also used the same system. 2. GMail's servers read your email to see whether they are spam, and to target adverts at you, and to provide fast, high-quality search of your emails. All of these are impossible if GMail can't read the email because it's encrypted. 3. If GMail stored your mail encrypted, as well as being unable to search it, it would all be unreadable if you lost your private key, or if you moved to a computer where you didn't have access to it. Storing it in the cloud would require another layer of interoperability (you'd need a way to get the key into GMail), unless Google itself stored the key, in which case Google could also decrypt your emails. If GMail stored the email unencrypted, there would be no point. It's good to compare the service with WhatsApp. WhatsApp does everything through your phone. If your phone is off or without internet, it doesn't work anywhere. This means they can store your key on the phone and have it only decrypt stuff on the phone. Because it's their own protocol they can build the key management right into it and don't need to worry about some other service not supporting the way they do encryption.",
"If it was end to end encrypted, either you'd have to manage the key yourself (and your email would all be lost if you lost the key) or the key would have to be stored on Gmail's servers encrypted with your password (and all of your email would be lost if you forgot your password- no such thing as a password reset for this). There is no way to make it \"just work\" with end-to-end encryption, and it turns out that ease of use and password resets are more important to more people than end-to-end encryption.",
"If it was, Google wouldn't be able to read through it to help figure out what kind of ads to show you. That's the whole point of Gmail.",
"There are several reasons. One huge one I haven't seen mentioned is spam. A big selling point of Gmail is their great spam prevention, which only works based on Google's ability to read emails en mass and get feedback (whether from automated AI data mining or manual user reports) about whether or not certain types of email are spam. If they couldn't access the plaintext of your emails, then spam prevention could only be done client side, which would be much less effective (less processing power, delays incoming mail, can't share results with other users as easily, etc).",
"Encrypting e-mail is easy, addon like [enigmail]( URL_0 ) for thunderbird do the job. The problem is that nobody uses encryption. If I send an encrypted e-mail te Jeanne Doe, she needs to be able to read it. It's not that hard (2 Buttons in enigmail) but already to complex for the average mail user. The only encrypted e-mail I sent was something like \"*test post, do not answer*\" and the encrypted answer from my friend was \"*it's working*\" For Gmail the Gmail crypt plugin will do the trick, but again if none of your friend use it your screw.",
"Your emails hosted on Gmail have to be able to send to other domains too, so none of those would be compatible. Likewise you receive emails from other domains, which also wouldn't be encrypted.",
"This is as close to I have found to encrypted email: URL_0 When I got the account I was on a waiting list for over a year."
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62st77 | Why can't magnets create perpetual motion? | Engineering | explainlikeimfive | {
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"It won't swing forever, it'll just swing until it loses momentum due to air resistance. It's not being powered, it's just a variation on a pendulum, and like a pendulum, it can only put out the energy that has been put into it, minus what it has lost from air resistance.",
"Man some of these responses are way off base. First, there's nothing in physics that says you can't have a perpetual motion machine. You just can't extract any energy from it and have it move forever, because whatever you're using to create energy will add resistance to the system. A perfectly frictionless pendulum will have perpetual motion. You can also go into deep space and spin a drumstick like a rock star and that will spin forever (unless act on by another force of course). In your example, even if you ignore friction and air resistance, you wouldn't have perpetual motion. This is because of something called an eddy current. When you have a conductor moving through a magnetic field, a current develops that creates a magnetic field in the opposite direction of the existing field. The magnets in your example both create the magnetic field and act as conductors. Thus, as soon as you start spinning the magnet, the eddy current will create a magnetic field to counter that movement and stop the motion. Eddy current braking (as it's called) is used as a brake in electric motors, such as in your power drill. My guess for what would happen in your example is you give the magnet on a string an initial push, it stops almost immediately and bounces around on the string until finding its equilibrium in the repelling magnetic field.",
"Are you a memeber of insane clown posse?",
"You can create motion for a while, but you'll never be able to create more energy then it took to create the magnets. Eventually magnets lose their magnetism, even \"permanent\" magnets.",
"It won't swing in circles. It will find the point where all the forces are cancelling eachother out and stop. But even if it would swing forever, you still won't get any energy from it as it will cause it to stop. The best case scenario is getting the same amount of energy back as you put in when you first set it in motion. There's nothing spectacular about making something go forever, just look at the planets orbiting the sun. But this doesn't mean that there's an infinite amout of energy to extract. Any energy you take out of the system will cause the objects to slow down.",
"My past experience with eli5 has been pretty bad. Try asking r/science. That's what the mods here told me to do. Probably get more complete answers there.",
"The magnet doesn't add any energy. Even in a frictionless vacuum, it keeps circling at the same speed, the same kinetic energy. You can't get energy from it without harvesting that kinetic energy, and you only have so much if it.",
"The repulsion cannot be harnessed. Attempting to connect anything to the spinning magnet will cause it to stop because the repulsion is no longer strong enough to push both the magnet and your mechanism. There's a great [Captain Disillusion episode]( URL_0 ) on it feat. Beakman.",
"The first two laws of thermodynamics; 1) Energy cannot be created or destroyed in an isolated system. 2) Entropy of any isolated system always increases. Magnets can not add energy to the movement for they have no energy of there own that is coming in. They are a constant force. In this system the friction of the pendulum will stop it and it will hit a point of equilibrium."
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62ut9h | what parts of subway tracks would kill me if I touched them? | Engineering | explainlikeimfive | {
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"In three-rails systems, two obvious tracks will be for the wheels of the cars themselves. One \"third rail\" is electrified. In two-rail systems, don't touch anything. Wikipedia page on the third rail, for further reading: URL_0"
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62x3wv | How did the western world lay underwater telegraph lines as early as 19th century with their level of technology? | Engineering | explainlikeimfive | {
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"The Victorians (as we call them this side of the pond) were actually pretty good at organising large scale engineering projects. These were the same people who built railways across the world too. Without underwater cables it would take weeks or months to have a decent international conversation so given the importance of a telegraph link, and the fact that the technology existed (The first telegraph was about 100 years earlier, and the first transatlantic ship was about 300 years before that), the rest was a question of will.",
"They has steamships, and with big spools of cable they could lay underwater cables. Specialized ships even allowed cables to be retrieved and repaired.",
"They basically did it the same way we do it today -- send out a ship with a huge amount of cable on a spool, and let it gradually play out and sink to the bottom. The main advantage we have today is the use of submarines so that maintenance can be carried out if necessary, but by-and-large once a cable's resting on the ocean floor nothing is going to disturb it anyway, so even without submarines they were able to run underwater cabling quite successfully.",
"They'd already mastered telegraph lines on land, so what they needed for underwater cables was a way to waterproof them. Unlike today, when we have all kinds of artificial substances, they could only use natural ingredients. So one of the vitally important substances that allowed them to do this was gutta percha, which allowed them to waterproof the cables. It comes from a tropical tree. Once they learned this waterproofing technique, they used existing tech to lay the cables. It was dicey at first and there was a lot of trial and error. By the way, if you want to read about this in depth, Neal Stephenson wrote about the history of trans-oceanic cables in his book of essays, *Some Remarks*.",
"It was very difficult but possible with the level of technology available in the 19th century. However, the potential payoff of linking continents by near instant communication was huge, big enough to prompt people to do it multiple times. The cables were similar to what is used today, a very thick armored sheath covering a few wires ( URL_2 ) (nowadays, fiber optic lines have replaced the signal lines). Massive reels of this cable were loaded on the biggest available ships and slowly laid down (an early steam powered cable laying vessel: URL_1 , and an illustration of one of the giant cable reels: URL_0 ). Cable breaks happened (as they do today). The earliest ocean cables were laid by sailing ships, but steam powered ships became common not long after. The break could be roughly located using the electrical \"echo\" that occurs when sending a signal down a long wire. A repair ship would sail out and dredge up the cable, where it would be repaired. The technology didn't come out of the blue. Long distance land telegraph lines were already common. There were some early underwater lines which ran for much shorter distances (like between England and France). This helped establish the basic technology before ocean crossings were attempted. There was no in-line repeater/amplifier technology at the beginning, so the extremely powerful signal sent on one end of the cable was extremely weak on the other end. There was no widespread electrical grid. The telegraph would be powered by large lead acid batteries. Because of the extremely long distance weak signal, non-standard equipment was used. A \"mirror galvinometer\" used a small mirror and magnet hanging from a string, which could be deflected by the tiny signal that made it through the cable to \"read\" the signal. Non-standard signals were used as well for several reasons: 1. Morse code was not yet the universal standard it became 2. Many cables linked to non-english speaking countries which didn't use Morse code anyway 3. The poor signal quality over the extremely long cables made other signal systems more attractive. The earliest cables could send only one signal at a time. Each end would have a schedule and would swap \"sending\" and \"receiving\" rolls at prearranged intervals. The code had to be sent slowly as well, since the signal was very weak. Given the very limited bandwidth, sending a trans-oceanic message was extremely expensive, writing a letter and sending it by ship was much more economical but far slower. Most signals would have been business or government messages as opposed to personal. Technological improvements gradually increased the capability of the trans-oceanic cables: 1. The invention of electrical amplifiers improved signal quality and the speed at which messages could be sent on a cable. 2. The invention of multiplex technology allowed one cable to send and receive at the same time instead of switching rolls. 3. Cable design improvements reduced breakages and allowed for more than one wire per cable. 4. Human operators initially did all sending and receiving. Eventually, mechanical punch card reader/writers replaced direct human signalmen and allowed for signal speed increases."
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62zbdo | why sometimes when you put food in the microwave you hear lots of sparking sounds, then take it out, and your food is still cold/warm | Engineering | explainlikeimfive | {
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"Microwaves don't really heat food itself, they mostly heat the water *inside* food. But microwaves don't heat the water evenly. It gets heated in little sections, and those hot parts spread heat to all the cold ones. That takes time though. When food snaps but doesn't get hot its because the water in those hot parts started boiling (that's the sound) but it hasn't been long enough for the heat to spread out (that's why its cold). This is why packages say to let the food sit for a few minutes after cooking. Or you can run the microwave a few seconds on and a few seconds off to spread the cooking time out, which is the same exact thing the \"power\" setting will do.",
"If the food has thin areas, they will heat faster and sizzle/pop before the thicker part is heated. You can either bunch the food together and use lower power level/longer time, or spread the food into an even thin layer and use high power. Stir halfway through and after heating to even out the temperature.",
"Well according to [this]( URL_0 ) Popping or cracking noises can be caused by the following: • The food item you're cooking in the microwave. Dense foods or foods high in fat content can cause more noise. Covering foods and piercing the skin of potatoes and other vegetables will help reduce this. • Food spills can also cause popping noises. Clean up spills in the microwave as soon as they occur. • Operating the microwave empty can also cause popping and can damage the interior. Always have something in the microwave when you run it. • Using metal or metal-trimmed cooking utensils causes arcing in a microwave along with popping or crackling sounds. • If you are using the metal cooking rack, having the rack installed improperly can cause popping or crackling. Make sure the rack is firmly in place and not upside down.",
"Microwaves do not heat food evenly [due to the presence of standing waves in the microwave]( URL_0 ). Certain sections of the microwave will get hotter than others, since the standing waves are, well, standing (i.e. they aren't moving). These hot areas can start boiling before the rest of your food is hot - especially if your food cannot dissipate the heat from these hot areas fast enough. This is one of the reasons why microwave food will oftentimes tell you to leave your food in the microwave for 1 minute after cooking is \"done\" - to allow the heat from the hot areas of the food to dissipate and even out.",
"There are a lot of people in here explaining how microwaves work but in this case I think we maybe need to talk how microwaves fail. If the microwave is sparking and not heating you could have a blown out magnetron antenna. Sometimes the magnetron can fail in such a way that all of its energy runs straight to the chassis of the microwave like a lightning bolt. It makes a weird electric sound and the food heats very little or not at all. You likely need a repairman. Source: am repairman.",
"This can happen if you put completely frozen foods in the microwave. The microwave works by rapidly alternating the orientation of water molecules and uses that friction to heat up your food. So if your food doesnt have a high water content (or all the water is completely solid), it won't heat up as well as it should. You can fix this by sprinkling some water on top, wrapping with a damp paper towel, or placing a small dish of water next to whatever you're heating up.",
"So all of these responses are generally correct, but dont fully explain. Microwave Ovens use Microwaves to heat the food. Microwaves heat through radio waves, which pass through your food causing small particles to vibrate and heat. I believe most microwaves use a wide range of frequencies, so certain areas will be affected by multiple waves, some by none. Microwaves trust that they will heat enough areas that the heat will diffuse through conduction (heat transfer through a solid), but what you hear is the initial boiling of water or fat within the object on a very small scale. These tiny boiling areas serve to heat all of the cooler ones around it, but it also means microwaves can really destroy parts of your food (this is why microwaves tend to make meat tough and dry out your food).",
"Microwaves don't heat food evenly. What your hearing is the food that is in your microwaves hotspot that have cooked. This is one of the reasons people aren't supposed to heat bottles in the microwave.",
"The sounds is evaporating water that boils quicker than the fat and solids in the food itself. The way microwaves work also creates points of more intense heat where the waves used to cook amplify each other simular to how a ocean wave can make another wave bigger with the right timing. The sound you hear is similar to the sound firewood makes when being heated, before it actually burns, as the gasses in the wood evaporate and push out of the wood creating the odd hissing sounds.",
"I ditched the microwave 5 years ago, never had once since. Its not because I worry about cancer or anything like that. I just genuinely think food out of a microwave tastes like complete shit. Only thing I miss it for is melting butter.",
"It sounds like you put metal in the microwave. Either that or your microwave is just broken. It shouldn't be doing that.",
"**Salt!** Something no one seems to have mentioned yet is salt. Along with metal, microwave energy can generate an electric charge in particularly salty spots within the food. When this charge arcs to an adjacent salty spot, or simply to the metal interior of the microwave, you hear a pop. Bonus Experiment: In a medicine cup, combine enough salt with water so as to make a paste. Consistency should be a bit goopy. Place the cup of salt paste in the center of the microwave, and cook for 10 mins on high. Patiently wait for the resulting light show.",
"Well, is it frozen peas/carrots? Or a small amount of bacon? In that case the cause is: too little water, not enough microwave-absorption ...and this *converts your microwave into a Tesla Coil.* A nearly-empty microwave easily generates tens of thousands of RF volts (RF radio frequency.) This easily produces electric sparks between small food items. If sharp points are present (such as crusty charred bacon edges, or the pointy bits of frozen carrots,) it can even create blue-white flashes of corona discharge. If you don't like the visible flashes and cracking sounds, just add a small glass of water (or a large glass with an inch of water.) Now your microwave has something to absorb the waves. It will prevent the standing-wave from building up into \"Tesla Coil mode\" high voltage."
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62zo55 | How can bombs be unexploded? | Recently saw an article about the Oxford-Cambridge boat race possibly being postponed because of an unexploded WW2 bomb. I was just wondering how bombs can land and not explode. Also how can bombs as old as these still be active and dangerous? | Engineering | explainlikeimfive | {
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"WW2 bombs (like pretty much every bomb) require two parts - the ~~combustible~~ explosive material (what goes boom) and a fuse (what makes it go boom). The fuses were usually set based on the bombers height to make the bomb explode as close to the impact time as possible (so people couldn't run away). There are various ways that the fuses could be started - either when the bomb was dropped, when the bomb reached a certain speed (using fans in the nose) or trigger bombs (that would explode when contact was made) Sometimes these fuses would fail and the bomb would land but not explode. They can still be incredibly dangerous because the explosives in them are still active and if exposed to anything that would cause them to ignite will explode. The old trigger bombs are (obviously) the most dangerous because all they need is for somebody to hit the trigger (assuming it hasn't rusted over) and they can explode.",
"As a further twist to fuse failure as already discussed, it was discovered during the Spanish civil war (pre-WWII) that bombs that did not explode due to fuse failure caused more disruption than the ones that did explode -- the area around the bomb would have to be evacuated until the bomb was rendered safe. The Germans then started installing fuses that had a long delay-time, hours or days even, to cause this sort of problem. An entire military specialty, Explosive Ordnance Disposal (EOD), was devoted to finding and de-fusing these bombs. Twist number two is that the Germans then engineered fuses that were specifically designed (booby-trapped) to explode and kill the EOD officer trying to de-fuse it. There is an excellent British mini-series about this WWII experience, DANGER UXB. Highly recommended. A movie on the same subject in the modern era is THE HURT LOCKER. [EDIT: spelling]",
"Sometimes the mechanism just fails and there is no explosion, it's still dangerous because if the contents ignite the bomb will still explode."
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62zrs6 | Why, if petrol is more volatile and burns hotter and faster, are diesel engines more efficient in engines of the same size? | In Europe particularly, diesel cars are much more popular now than petrol. A new diesel 1.6 engine burns much less fuel than a 1.6 petrol, for example. How can this be when petrol is much more volatile? Surely if it explodes at the rate it does, petrol can generate more power? Petrol cars are faster, but so much less efficient comparably. | Engineering | explainlikeimfive | {
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"As said before diesel fuel has more energy per volume, but that's not the whole story. The 'burn' in a diesel is more powerful not only because of the fuel type, but also because the compression ratio of a diesel engine is much higher than a gas engine on average. It's so high that a diesel engine does not use spark plugs to ignite the fuel mixture, the burn happens from the force of compression alone (except in startup situations and/or if you have a tricked engine management system where the 'glow plugs' are activated to aid the combustion process). Higher compression ratio typically gives you an increased volumetric efficiency and ergo yields more power output. Now all that said, these new direct injection gas engines are getting up there with relatively high c:r, but still not quite near a diesel yet.",
"Diesel fuel contains more energy per unit volume than does gasoline. That's really all there is to it - there's more go in the go-go juice the big trucks use."
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630hs7 | When jumpstarting your car, why do you connect the black cable to the engine block instead of the black/negative terminal? | My mother needed a jump start earlier today and insisted on connecting red to red and black to black. Looking at the instructions on the cables and, later, on the internet you're supposed to connect the black cable to an unpainted section of the engine block of person's car with the dead battery. My mother insisted on doing it her way because she's done it that way before and it worked. I wasn't going to win the argument so I went along with her. Fortunately, the were no electrocutions or explosions. this time. So why do the instructions on the jumper cables say to do it their way and what could happen if you continue doing it incorrectly? Thank you in advance. | Engineering | explainlikeimfive | {
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"Sparks near the battery can cause hydrogen fires. Sparks near the engine block are much safer. That said, modern batteries are sealed and pretty safe, but safer is always better."
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6314bc | How does a fire cause a interstate highway to fall | How did the fire lead the highway in Atlanta falling. Why does it look like such a clean spit? | Engineering | explainlikeimfive | {
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"The portion of the interstate that collapsed is made from precast concrete beams. A bunch of steel reinforcement bars (rebar) are shaped and welded into a beam and it's placed into a mold into which they pour the concrete. Those beams are then placed between structural supports and metal decking is placed between them. The concrete roadway or road bed is then poured on top of the metal decking. This is all made of material that contracts and expands with heat so at both ends there are expansion joints. In this case it's just a giant compressible rubber gasket that's about 4\" wide. Concrete is extremely strong when undergoing compressive forces but not so great when it's under a flexion load. The beams are cast in an arch so that when they are loaded(heavy stuff on top), the concrete is under a compressive load. The fire burned under the entire bridge and was hot enough to weaken the rebar. Think about the bridge like a long board that's supported by two chairs; one on either end. The roadway on top of the beams is \"really heavy\" and the weight is mostly evenly distributed among them. The weakened rebar caused the arch shape in the beams to deform enough to where the load on the concrete moved from compression to flexion. In the board analogy if you put enough weight on the middle of the board it'd sag. Keep adding weight and it'd deform enough to where the ends would slip off of the chairs. TL;DR The fire did NOT melt the steel; it just got it warm enough to where it was bendable. It bent enough to where the bridge beams slipped off of the supports on the ends"
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633r5e | Would a refrigerator act like a heater if placed outside in subzero temperatures? | If not, do they specifically design refrigerators to work in places such as Antarctica? | Engineering | explainlikeimfive | {
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"A refrigerator would NOT act as a heater in sub-zero temperatures, it would simply turn off. The refrigerator has temperature sensors inside that turn it on and off based on the temperature inside, and normally what happens is the heat from outside seeps into the refrigerator, making it hot, and activating the temperature sensor. If it's cold outside, then the heat inside the refrigerator will seep out, and the refrigerator contents would get cold. Temperature sensor would detect this and turn off the refrigerator to conserve energy. In addition, the refrigerator transports the heat using a gas that turns to liquid at a certain temperature; because of the cold outside, this gas would stay liquid or even possibly freeze, and the refrigerator wouldn't function properly. For Antarctica, if they need a refrigerator inside a (normally warm) kitchen, they probably use a regular refrigerator. They're designed to work in normal temperatures that you find indoors. Or, they could have some outside storage sheds that would be very cold because of the environment, and thus use no electricity to freeze meat or whatever.",
"Any sort of heat exchange machine always outputs a net surplus of heat because they consume energy to operate. A refrigerator operated in any environment will output heat. Refrigerators are not usually designed to work in places such as Antarctica because all the need is that the heat exchange coils on the outside of the refrigerator are warmer than the surrounding environment. It being too cold outside isn't really a problem in any way. Furthermore most consumer refrigerators dump heat from inside themselves into the room in which they reside. Even if in Antarctica if the room is a similar temperature to normal then the refrigerator doesn't care at all what the outside temperature is. Finally if it is super cold outside all the time people don't care about refrigerators, they just put things they want kept cold outside. Cooling things down isn't a problem when there is ice everywhere."
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63443g | Why do guns recoil up instead of down? | Engineering | explainlikeimfive | {
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"The axis of the cartridge lies above the fulcum created by the shooter's hand, so the recoil acts to torque the firearm muzzle up.",
"principles of the lever. the force in a standard firearm is backwards at the chamber. this position is forward and above the fulcrum, usually the shooter's wrist. this is true for a normal handgun. weapons that do not have the chamber above the fulcrum will not exhibit this behavior much. a shouldered AR15 will rise much less. the chamber is basically directly forward of the fulcrum (the buttstock). however it's still the top half of the buttstock that unevenly absorb the recoil.",
"It has to do with the shape of the gun and the way it is held. The action takes place in the upper portion of the weapon, and the hands are around the grip which is pointing downwards. If you were to fire the gun upside down, it would recoil down.",
"The location of the barrel at the top of the gun, above where the shooter is gripping the firearm. If the barrel was on the bottom, the gun would recoil downward. The Mateba unica 6 and Chiappa Rhino revolvers have barrels that align with the bottom of the cylinder instead of the top. This directs more of the force backwards into the shooters hand and reduces recoil- induced muzzle flip.",
"ELI5 explanation. The barrel is above your hand. Try holding a toy pistol (or a banana, or anything else pistol shaped) in one hand. Then, put a finger on the \"muzzle\" and push back. It will try to rotate upwards, because your grip is under the point you push at. That is why many modern rifles have the stock extending backwards exactly along the length of the barrel. The force of the recoil will then go straight back against the stock."
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6355d2 | how come microwaves only heat the water in foods and not the food itself? | Engineering | explainlikeimfive | {
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"They don't strictly speaking heat \"water in foods and not the food itself\". /u/jaa101 touched on this in his response - microwaves aren't tuned specifically to water. Microwaves work by creating oscillating waves which induce movement in polar molecules, which isn't an ELI5 answer, so stick with me. A polar molecule is one where the overall charge is not fully balanced and there is a slight variance in the charge on different sides of the molecule. Here's a quick text-drawing of a water molecule to demonstrate: H H \\ / O The bond between the H and the O has a positive and a negative end - the H \"side\" is positive and the O side is \"negative\", and because of the arrangement of the atoms in the molecule, the side with O on it has a bit of a negative charge and the side with the H has a bit of a positive charge. We know that opposite charges attract, so if you can induce a negative charge on the bottom of that drawing, the O atom is repelled and the H atoms are attracted, so the molecule rotates and becomes: O / \\ H H If you keep the source of charge oscillating (so that the source of negative charge changes position around the molecule), the molecule will spin. The spinning molecules will bump into other molecules which passes the energy from the spin onto them - and this energy is observed as heat. The fact that this works on water shouldn't be mistaken for only water being heated - fats, sugars and other molecules can also be heated. The key bit is that to be heated, the molecule needs to be polar. Edit: Formatting"
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6367b1 | Manual Cars | Literally just explain what the clutch does to let the car change gear. And like how the gears move in and shit. Just explain a manual engine like I'm 5 | Engineering | explainlikeimfive | {
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"The rotation of the motor must be transmitted to the rotation of the wheels. What the clutch does is connect the rotation of the engine with the rotation of the wheels. Inside the car you have several gears with dog teeth connected to one another [like this]( URL_0 ). The engine is rotating, makes the green (and inevitably the red and the blue) turn. But the blue are turning blind, they are not connected to the yellow rod. If your engine is off and you're rolling downhill, the yellow rod rotates, but all the gears are still. The yellow rod is only connected to the purple and it's what makes the wheels of your car turn. With the clutch and the knob you can move the purple and attach it to whatever you need. When the purple is attached, you have a direct connection between the engine and the yellow rod (and eventually, the wheels). The reverse has an additional gear, so the rotation of the engine is transmitted backwards to the wheels. And gears work in the same way as in a bike. You can pedal a lot (high rpm, but get not a lot of displacement for all the pedaling you're putting in) or pedal less and make the engine (you) more effective. Now, on a bike you usually choose to be less tired (pedal a lot) at the end of the day. But in a car you're looking for the most effective and less fuel consuming gear."
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636zeo | How does data recovery from formatted SD cards work? | Like if I formatted an 8GB SD card which had, say, 5GBs of data, then the computer shows me that's I now have 7GBs of free space. Then where is the previous data stored such that it can be recovered? And if it can be recovered from the 1GB of space(which means it can fit in 1GB space and didn't really require the 5GBs of space) then why wasn't it stored in just 1GB rather than 5GBs to begin with? | Engineering | explainlikeimfive | {
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"The difference between an 8GB card vs a 7GB card has to do with how cards are marketed vs how computers count data. It's kind of fucked up that it's allowed, but it's the way all data storage is sold. A card retailed for 8gb contains 8,000,000,000 bytes. Except computers don't count in base 10, they count in base 8. So 8 GB in computer talk is 8,589,934,592 bytes. This is stupid, but it's the way storage has been sold since forever, so that's just the way it is. 8,000,000,000 bytes is around 7.4 gigabytes. You might also lose a little because there's some overhead. So that takes care of your missing space. The recoverable data is not in that space. So the way computers store files are in 1 looooooong string is 1's and 0s. The computer then makes an index that says FileX starts at position 362 and runs to 492. So it makes note of where it stores the file, what storage positions the file occupies. So when you delete a file, all that happens is it removes that file from the index and notes those areas as \"available\". It does NOT actually go back and change the 1 or 0s to some other value. It just kind of abandoned the file and notes the area as empty when it's really not. When you want to store a file in that so-called \"empty\" space the computer just over rights whatever is there with the new data and makes a note in the index. File recovery ignores the index and goes directly to where the storage is, it looks at all the 1s and 0s and try's to identify what is actually stored there, as opposed to what the file index table says is there. So if the table says positions 1 to 10 are empty, the recovery program looks at 1 to 10 and finds that there's actually a picture stored in 7 & 8, 1-4 are a video. 5 & 6 are part of a video and 8 & 9 are part of a picture."
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637nfc | How could Japan fix that masive sinkhole in the street in two days, but Atlanta is going to take months to repair an overpass? | Engineering | explainlikeimfive | {
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"The road that got the sinkhole was supported by the earth. The elevated freeway in Atlanta was supported by concrete posts that were weaken by the heat and the stress of the collapse. New posts must be formed, and then a new roadway fitted above them. It will take months.",
"Fixing a sinkhole is much, much easier than fixing the overpass. A sinkhole just has to be filled in an paved over. The overpass has to be thoroughly inspected for fire damage in every section before construction can even start. They determined that the fire irreparably damaged the adjacent bridge, meaning they have to demolish it. After all of the inspection, cleanup, and demolishing is done, they still have to build a huge concrete structure, which isn't easy."
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638clk | For the love of Graham Bell! Why have cell phone manufacturers not devised a way for a camera to shoot in landscape mode while the phone is vertical? | Engineering | explainlikeimfive | {
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"Software solutions exist for this (see the [Horizon]( URL_1 ) app), but the vertical vs horizontal problem is a hardware constraint that can only be partially solved by software. Just like film in a camera, the sensor that is used to capture an image is _physically_ a rectangle. For usability, purposes the manufacturers align the rectangular shape of the sensor to the rectangular shape of the phone. I.e. the long axis of the physical sensor is parallel to the long axis of the phone. EDIT: I can't stress the usability issue enough. Having the long axis of the phone parallel to the long axis of the handset means the orientation of the phone _represents_ the orientation of the sensor (and thus the photo). If the long axis of the phone were perpendicular to the long axis of the sensor, that would increase the cognitive load on the user. That means, in a phone that is held vertically (the long axis *of the phone* on the vertical), there are **only three solutions** to taking a photo with the long axis *of the sensor* oriented horizontally: 1. Manually turn the phone 90 degrees. Duh. 2. Leave the phone oriented how it is and mechanically turn the sensor without the phone being moved. This is certainly mechanically possible, but would require additional components and a tiny motor to rotate the sensor inside of the phone before the photo is taken, either automatically or on demand. This doesn't happen because the value of doing this (over #1 above) isn't worth all the extra space in the phone this kind of physical mechanism would take up. 3. A software based solution, like the aforementioned Horizon app, which uses the phones' accelerometer to determine tilt and adjust _which_ pixels on the sensor are being used to capture the photo. The downside to this approach is when the phone is held vertically (long axis of the phone on the vertical), the long axis of the photo sensor is still on vertical. The way the software gets a photo with an aspect ratio with the long axis of the photo on the horizontal is to ignore large portions of the sensor data. So when you're holding the phone vertically (or on an angle), an app like Horizon is only using a sliver of the middle section of the sensor to maintain the aspect ratio and orientation, and throwing away the rest of the sensor data. So you're giving up picture resolution and detail in favor of maintaining orientation. EDIT: [this demo of Horizon]( URL_0 ) makes it clear what data is being left out.",
"It's not that far out there, but as someone mentioned, the sensor is an issue. Sensors are rectangular, not square (assuming they are doing what most cameras do). So to shoot landscape while holding portrait, you'd need a bigger sensor. Then you'd need UI controls to determine when you wanted to do this, because sometimes you might want to shoot portrait, so it couldn't be an \"all the time\" situation. More trouble than it's worth, I expect."
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6398rw | On a given construction site, why are there usually 4 people standing around doing nothing or watching someone work, for every 1 person actually working? | Engineering | explainlikeimfive | {
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"The people that you see standing around doing nothing on a site 'doing nothing' are all working. Let's pretend that the crew is fixing an underground pipe, and name the crew members and their jobs. Normally a survey crew marks out where the pipeline is, and where other utilities should be. Now for the working crew... First you have the equipment operator, the guy sitting in the excavator. He moves most of the soil, and is responsible for hitting the gas/sewage lines. Next you have a crew of several people with shovels to do delicate soil removal, and other general labor. They take shifts spending time in the hole. Space is very limited for both personal and equipment. Have you ever spent 10 hours digging a hole, or managing a 8\" angle grinder for weeks straight? It is exhausting, they have to perform this hard manual labor for weeks on end in the raw weather. They need their rest. The hole that is being dug is a dangerous confined space area. The sides can collapse, or oxygen levels can be lower then normal. A safety officer should be on hand to monitor the soil conditions and quality of the air. He is to protect the lives of the crew, and makes sure that this construction project never makes it to the 5-o'clock news. Pipefitters are tasked with removing the damaged section of pipe, and installing a new pipe section. There can be lot of prep work and rigging involved to remove and install these heavy pipe sections. If this worksite is on an active road, a crew is needed for traffic management. Each trade can have their own foreman, or their can be a single supervisor for the entire construction crew. This work site can have various inspectors for each trade, inspectors for the local city, reps for other utilities, and civil engineers can all appear on this site. These workers do all the paperwork, record keeping, and assume the liability for this job. Even though there are a dozen or more people on site, only three have shovels. Everyone is working hard at their own speciality. At any instant there are more people employed to ensure the smooth workflow of the repair and protect the lives of everyone involved, then getting sweaty and getting their hands dirty. They are all working.",
"Construction worker here. Sometimes there is nothing that needs doing, especially if you're a laborer. Sometimes the task is a one man task and the other workers are not needed. Sometimes the people standing around are foremen. Sometimes something arrives on site that halts business, like a crane lifting huge panels, so everyone is either helping the crane or watching it. Construction sites are pretty busy places, and skilled workers often skip breaks or go for longer. There usually aren't many lazy construction workers, just lazy sites.",
"Task-specific expertise. Most jobs on a construction site *aren't* just dragging heavy things around, most of these guys are skilled tradesmen who know something specific (electrical, plumbing etc) who need to be on-hand to jump in. They're needed regularly enough to hang out on-site, but since they have specialized training shouldn't be touching stuff that isn't their field."
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63fih0 | Why are semi's not more streamlined? | Why is it when I see a semi 90%+ of them are very boxy? I feel like when hauling long distances, you'd want to be as aerodynamic as possible to save on fuel costs. | Engineering | explainlikeimfive | {
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"In the US trucks used for long haul work usually are pretty streamlined. They need that large flat grille to suck air into the radiator during the summer, but the rest of the cab angles back. Some companies even put fins on the bottom and back of the trailers to disrupt vortex formation and lower drag. Trucks that do more local hauling don't usually go fast enough to warrant any aerodynamic improvement, so other concerns like cost, maintenance accessibility, and length determine the shape.",
"I'll add that the tractors in Europe are boxy (flat in front, with the cabin above the motor, not behind like the typical American truck) because of length restrictions covering the whole vehicle, instead of only the trailer.",
"They are designing more aerodynamic truck portions, but the trailer portion will be either box or open topped due to the nature of the semi trucking industry. Boxes allow for stacking and easily standardized sizes, as well as maximized carrying capacity per space allowed. That would be my guess anyway."
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63fixg | What's the difference between a well optimized computer program, and one that's not well optimized? | I'm a Computer Science Major, but still a Freshman in College. (Within C++) I've recently learned about "pass by reference" in relation to "pass by value", and it got me thinking... Passing by reference (even when not modifying the variable) makes it so no extra copy is made of that variable, thus making the program require less memory to run. Is it little things like this, when done thousands of times, that makes a program well optimized? I'm very curious. Will someone smarter than I please enlighten me? | Engineering | explainlikeimfive | {
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"Pass by reference vs. pass by value is one of the many optimizations that people consider when looking to improve performance when using C variants where this functionality is exposed. In other, higher level languages, this functionality is performed by the compiler and therefore isn't exposed. Instead, when people discuss optimization they are usually referring to how a task is being done and whether it makes sense. Loops are expensive, especially over large data sets so a lot of optimization revolves are minimizing the number of times you have to perform that loop or figuring out a way to segment the data so that each loop is smaller. Optimization may refer to how data is organized either in memory or in the database to limit the amount of information that needs to be passed around or worked on.' And then there is really low level optimization where you may opt to implement a piece of functionality in software on a FPGA or custom built chip instead of in software on commodity hardware. It all depends on what level you're working at and what your most expensive operations are."
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63m7fx | What goes on mechanically in a speaker when you turn down the volume of music? | Engineering | explainlikeimfive | {
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"A speaker pretty much consists of a cone, an electromagnet, and a permanent magnet. You can see the cone, usually, although sometimes it's covered in fabric or metal mesh. To produce music, an electronic signal is sent to the electromagnet, telling it what direction to produce an electric field. So it either moves closer to the permanent magnet, or it moves farther away, and this causes the cone to vibrate. As the cone vibrates, it causes vibrations in the air around the cone - and that's how sound travels. Sound is just vibrations in the air. The frequency of the vibrations (how fast the cone is wiggling back and forth) dictates the pitch - higher frequency, higher pitch. When you turn the volume down, the electromagnet is still causing the cone to wiggle, but it causes it to wiggle less. The amplitude of the wiggling goes down when you turn the volume down. So the sound isn't as loud, but it's still the same pitch. If you have the kind of speaker where you can see the cone, and you turn it up really loud, you can actually see the cone moving."
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63mgy2 | Razors - why does the little blue lube bar come after the blades? It goes squeegee, blades, lube strip, instead of the opposite - why? | Engineering | explainlikeimfive | {
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"~~The squeegee is to clear excess shaving cream before the blades get there.~~ Since you presumably have some sort of shaving soap or cream you don't need to moisturize more before the blades do their job. The moisturizer bar comes afterwards to help re-moisturize once the blades clear away the cream/soap. Edit: The squeegee thing is actually called a guard bar and prepares the skin for shaving by smoothing it and making it taut.",
"According to this [Gillette video]( URL_0 ) the average guy takes 170 strokes or more to properly shave. From my experience, the reality is that you never get a clean shave in a series of single passes no matter what blade you use. In my case it takes multiple passes in different directions to get what I consider a clean shave. The first pass removes the shaving cream and some of the hairs and the lubricating strip ensures that the next pass glides smoothly. It also may have some impact on the angle of the cutting action. Then consider that as the lubricant wears off the angle changes and the razor may not cut as well over time as the angles gets ever more flatter. How hard you press the razor into your skin may also affect the angle and at what angle you hold the blade may impact its effectiveness if the lubricating strip acts as a fulcrum to lift the blades away from the skin surface."
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63mya5 | Why do we drive using our right foot for both the accelerator and brake instead of using our left foot for the brake? | Engineering | explainlikeimfive | {
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"You are taught to use the right foot for gas and brake for two reasons: 1) If you drive a car with a manual transmission, you need your left foot for the clutch, because you have to clutch and brake at the same time to avoid stalling the engine, and you always either have to have the clutch engaged or the gas pedal down when the car is running (or else you stall the engine). So you need a clutch food, and a gas/brake foot. 2) Even if you drive an automatic, if you use two feet, you might accidentally panic and put your brake foot down before you take your gas foot off. It's bad for your car to have the brakes on while the gas is on. Damages your engine.",
"By using one foot, you can't \"ride the brakes\". This bad behavior comes when resting the foot on the brake pedal engages them just a little bit all the time. It makes your engine work harder and your brakes very hot. They wear out faster and hot brakes have a much larger stopping distance in an emergence. Simply training drivers to use the same foot to hold down the accelerator and press the brake pedal keeps them from doing both at the same time. You might need the left foot to press the clutch, but that's not the reason for using the right on the other two.",
"Are you talking about an automatic or a manual? in England we drive mainly manual (stick) transmissions, which requires our left foot to operate the clutch. The fact that automatic drivers use their right for both is a holdover from when automatic didnt exist. It also encourages the good practise of having brake OR accelerator, but not both at once.",
"because of manual transmissions. your left foot had to operate the clutch, leaving the right for gas and brake. enter automatics, and the right foot still does double duty and the left foot goes on vacation.",
"Of not race drivers (eepecially in cars with paddle shift) do exactly this to avoid transition time and let them do some advanced techniques in specific circumstances where you might want to use both at the same time. For road users its not recommended. The threads gone into why already.",
"Probably a few reasons: You should not use both the break and accelerator at the same time- using the same foot for both prevents this. Cars with manual transmissions require a separate foot to operate the clutch since it is frequently used at the same time as the brakes or accelerator. Wouldn't make sense to learn to use the left foot for brakes if automatic but right for manual transmission."
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63o38a | why is the gas tank at the rear of the car(for most cars) if gas needs to get to the engine? | Engineering | explainlikeimfive | {
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"Just a few thoughts but 1. It's safer; A vehicle fire is likely to break out at the front of the vehicle so the farther away the gas tank the better. 2. There's no room; There are a lot of things that HAVE to be in the engine compartment or the front of the vehicle leaving little wiggle room for something as massive as a 15 gallon tank 3. Balance (this is probably more unintentional than anything else). The more unbalanced a car is the more likely it will be tail happy, so adding a bunch of weight to the rear never hurts 4. Ethanol, a component in a lot of different gas products, evaporates, so the cooler (farther from the engine) the better",
"Engines get hot, as does the area around the engine. It's probably not a good idea to put *all* the flammable liquid near such a source of heat. Probably best just to send over a little at a time as needed."
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63qkas | How can you launch a heavy nuclear missile and be certain that it will hit some exact spot 9000 miles away without manually steering/piloting it or anything? | Engineering | explainlikeimfive | {
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"text": [
"Math. Lots and lots of math. Physics is not magic. Even launching a extraordinarily heavy object thousands of miles (\"rocket science\") is still just a matter of getting the calculations right. Lift velocity, aerodynamic stability, friction, gravity...it's just numbers. A lot of numbers, but numbers nonetheless."
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63qlbt | Are diesel cars better or worse for the environment than petrol cars? | As I understand it, diesel is worse for the local environment as they cause more air pollution. So if all the cars in your city use diesel, you will have lower air quality than if all the cars in your city used petrol. On the other hand, diesel cars have better mileage than petrol and so contribute less to climate change. Netting these two factors, are diesel cars greener than petrol ones? | Engineering | explainlikeimfive | {
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"It is an ongoing debate whether diesel or gasoline causes more pollution. Diesels often seem to cause more pollution, as they release more of the visible pollutants, like NOx and soot. However, they release fewer hydrocarbons and carbon monoxide, things you can't see as easily. They also don't release lead, which is less of concern in places that mandate unleaded gasoline.",
"It depends on what you're looking at. If you're just taking the engine into account, and nothing else, Diesels are considerably cleaner. Spark Ignition vehicles typically operate in such a way that they have an immense amount of partial combustion, which produces all sorts of hydrocarbon compounds (which are typically both bad for you *and* the environment), as well as carbon monoxide. Diesels, on the other hand, generally burn pretty cleanly, because they generally operate with spare oxygen in the cylinder (if they're not, you're literally shoving fuel out of the exhaust). **However**, there are two major caveats. First, it's actually surprisingly easy to clean the exhaust from Spark Ignition engines. We use catalytic materials to actually promote this cleaning process, and those catalytic materials generally perform better when they have all sorts of chemical species to work with (particularly, hydrocarbons). Normally, this wouldn't be a big deal until we get to the second problem. Diesels have what is called the NOx-PM tradeoff, whereby every diesel will either make particulate matter (PM), which is basically just fuel droplets that didn't burn completely and are shoved out the exhaust, or oxides of nitrogen (which are, collectively, NOx), which are some of the worst compound to come out of your engine that aren't the hilariously bad things like BTEX compounds. The tradeoff exists because you can't really run the engine without producing one or the other without getting into particularly interesting engine cycles that are kind of difficult to control. PM we can sort of deal with, but you generally don't want to be making PM (as you're literally just shoving fuel, and therefore money, out the tailpipe), so we generally end up making NOx instead. The big issue with this is that NOx is **really** hard to clean up in diesels. There are various convoluted methods to do so (the gold-standard of which is Selective Catalytic Reduction, or SCR, which typically requires urea injection). Note that Spark Ignition engines will *also* produce NOx, but the same dirty exhaust helps in cleaning that NOx out through normal catalysis. In diesels, the exhaust is extremely clean already, so we can't take that path. So, as for which one is better...Diesels. Diesels are far more efficient, in that you'll get more energy per liter of greenhouse gases emitted by the engine, but they make NOx and PM. Both NOx and PM can be cleaned, but that makes the engine more expensive upfront, and can eat into the cost savings from having lower fuel consumption. If you're okay with the added costs, then diesels are considerably cleaner. FWIW, what VW did was try to use the tests to justify their deletion of their SCR systems, which costed a significant amount of money, and thus forced them to raise the prices, which in turn hurt sales. The specifics of how they did their cheat are actually hilariously easy to pull off, such that I wouldn't be surprised at all if most of the other diesel manufacturers in the US and the EU hadn't at least considered attempting it. Source; Two degrees in Mechanical Engineering, working on a third, research includes diesel engine combustion and emissions."
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63qqh5 | in a building collapse, where would you be the safest? | Engineering | explainlikeimfive | {
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"text": [
"Not in the building > next to main support beams > standing in door frame > under a sturdy table"
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63tp8n | How does a gyrotheodolite work? | Engineering | explainlikeimfive | {
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"text": [
"An internal gyroscope will point north when it has freedom to spin. So you hook that up to surveying equipment and you can determine with some accuracy which way north is, in situations where you can't use GPS or other methods (such as building a tunnel or mining). It's not the world most accurate thing (within 10 arc seconds), since there are issues with Earth's spin and such, but you hook one up to a theodolite (that surveying thing people look to to determine angles on horizontal and vertical planes you've seen on the side of the road), and you can get an idea of where you are when you have no other options to know where you're going."
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63ul3z | How do civil engineers ensure the on-ramps and overpasses supported by manmade dirt slopes never collapse? | I've always been curious how these last without issue. Is the dirt just packed really hard, or is there more to it? | Engineering | explainlikeimfive | {
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"text": [
"A pile of granular materials has a property known as \"angle of repose\" which is the angle the side slopes of a pile of that material spills to when left alone. Embankment sideslopes are designed at an angle less than this angle of repose to keep the sideslopes stable. Secondly, the material is compressed, this tends to lock the edges of the grains together and it also tends to remove voids. Remove the voids prevents water from running between grains which could destabilise them. Compacted earth is often also vibrated as it compacted so that the grains move around and fit together better - as an experiment, try gently shaking a coffee jar, and you'll see the level of the coffee drop as the grains fit together better.",
"They are not generally supported by dirt slopes. They are supported by concrete and steel pillars that go down into the ground all the way to bedrock. The packed dirt is simply there to help the pillars not shift and to be more aesthetically appealing."
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63w92q | why does a 4 legged table wobble whereas a 3 legged does not? | Engineering | explainlikeimfive | {
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"text": [
"Since any 3 points define a plane, it's guaranteed that the bottoms of any 3 legs can touch the floor at the same time. This cannot be said of any 4 legs.",
"A three legged table is a tripod; very stable. If someone were to try to balance it on two of its legs, they would find it tries to lean to one side (since most of the weight is to one side of those two legs); it \"falls\" until the third leg touches the ground. Adding a fourth leg is a bit trickier; it has to be exactly long enough to touch the ground with the \"tripod\" of the other three already supporting the table. Otherwise, the table will tend to alternate between the two most stable tripods: both with the two longer legs, and each with one of the shorter legs. It will, thus, wobble."
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63ykl7 | Why is 95 gasoline powerful than 92? | Engineering | explainlikeimfive | {
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"text": [
"Are you talking about octane rating? If so, it's not more powerful. Octane rating indicates how much compression the fuel can sustain before it ignites. A high octane rating can be compressed more, thus high-powered engines that compress the fuel more need it in order to avoid it igniting prematurely, causing knocking and engine wear. If your car doesn't have one of those engines, any octane gasoline will work just the same for you."
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640u6l | How would a hyperloop logistically work? i.e. Safety at high velocity, boarding, exiting, etc. | Engineering | explainlikeimfive | {
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"It doesn't. The hyperloop test track is about a quarter mile and about 4.5 feet in diameter, and by volume is the second largest vacuum chamber on Earth. There's a shit ton of energy in a vacuum, as the test track has ~14.6 psi on it which is nothing to scoff at when you have ~19,000 sq.ft (Edit: 2,736,000 URL_0 , to keep consistent with the units - that's 39,945,600 lbs of pressure on the vessel) of surface area. Any falter in the structural integrity anywhere will cause a cascade implosion failure along it's entire length until the vessel ruptures and vacuum is lost. The thing is wildly dangerous just to stand next to it. (Edit 2: rapid loss of vacuum is about as deadly and destructive as the implosion itself.) But of course they said it's only a partial vacuum, but what they didn't get into was that their partial vacuum is ~99% to a perfect vacuum. The difference is irrelevant when you're talking a chamber this large. The second prototype is currently using steel so thin it can't even support it's own weight, and they want to suspend it on pylons. And the suggested plan is to run this thing in a loop the length of California? Any earthquake, any car crash into a pillar, any punk kid who throws a brick at it, any significant falter in it's construction or due to weathering, and the thing can implode. Thicker steel and more structural support can only offset the danger until the construction is too expensive to be feasible. Boarding would require chambers to hold the vacuum in the whole system while the train is accessed. Then it has to be sealed and vacuumed. They will have to build the biggest vacuum system in the world to pull a perfect vacuum in an appreciable amount of time and keep the whole system under vacuum, because the test track took about an hour per, and they had to pressurize the whole thing every time the opened it. It currently takes longer to pull a vacuum than it would take to travel the length of California by more conventional means. Trains are not cost effective for passenger travel because the maintenance costs are astronomical and commuter needs are at odds, too many stops, and it's not time effective and will drive away customers, too few stops and you won't have enough customers to be cost effective. High speed trains are ever more so expensive and dangerous. In an airplane at 640 mph, any sort of bump, and you have miles space to gracefully dampen it. Any bump in a bullet train, and no matter what, it has to remain on it's rails, and now it has to remain on its rails and not hit the walls of the vacuum chamber. Overall, the thing is insane and the liability is huge. No one would seriously fund this project and no government safety regulators would ever allow it to go into production. But I appreciate it for what it is, and that is to get engineers and students thinking outside the box. That's all. This is a publicity stunt and they know it, but it's also a prospect for innovation they might scoop up and invest in.",
"Wow, some serious negativity here. First of all, most tech starts out like this, doesn't it? Once upon a time people said \"You can't travel underwater/over 100MPH/through the air/in outer space, it's too expensive/dangerous/the tech can't handle it!\" I guess it's a good thing not everyone said \"Yeah, you're right, let's drop the whole thing\". Just because we can't do something *today*, or it isn't perfectly efficient/safe/etc., doesn't mean it shouldn't be explored and developed.",
"The speed gains over conventional high speed rail are negligible. The construction and operating costs are **way** higher (making a near-vacuum takes a *lot* of energy). And safety... Well, you've got a positively pressurized vessel inside a negatively pressurized vessel, and they're moving relative to each other at the speed of sound...",
"In a nutshell; it won't work. The youtube channel Thunderf00t has several good videos which breakdown exactly why. Start here URL_1 (commentary begins at 1:36). Or his most recent video on the topic URL_0 (edit: added extra link)",
"Stuff You Should Know did a pretty good podcast covering the in's and out's of the Hyperloop. Pretty recently too, as of 03/23. Enjoy! [Hyperloop / SYSK]( URL_0 )",
"Unfortunately the hyper loop has a few problems; known, speculative and assumed. We know the cost due to the price of steel and manufacturing, the well known phenomena of [cascade collapse]( URL_0 ), material expansion due to heat (he chose a desert of all places!), and energy costs, [dangers]( URL_1 ) and time of producing a near vacuum. We suppose that the hyper loop would have problems with multiple destinations, turning and basic commuting. We assume that there will be some radical who sees the hyper loop as a target and protecting all 600 miles will be infeasible. Hope this summarized everything nicely! I included videos just as an example of what I'm talking about.",
"Allow me to sum up the comments. Most posts ... Reasonable points show this is dangerous and that i see no way of over comming. Other posts with no real facts mock the first set as being downer. Believe whicj posts u want. Ill take science and common sense on this one.",
"> ... , boarding, exiting, etc. That doesn't begin to touch the hurdles. Howzabout: Switching? Look at those maps from Denver and all the branches. Do ya hafta slow down to go around \"corners\"? Can they put more than one capsule in the tube at once? How? (Airlocks??) Does one capsule have to go B- > A for every one that goes A- > B? Think commuting here.",
"Maybe it could be used as a cargo transport at first. I'm sure delivery services have a need for products to go places that fast. You could order a St Louis style pizza from Kansas City and it would be there in 20min. I just wanted to lighten the mood. It's pretty intense around this post."
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642zmi | Why is the Boeing 737, a 50 year old airframe with 4500+ on backorder still so popular? | I've been flying a bunch lately and I flew with the 737 (9400 built ad 4500 still on order) and it made me think why such an old airframe still being built 50 years after introduction, of course there has been major upgrades like avionics, glass cockpit, engines but what made it so successful while Boeing 757 have been discontinued (IIRC 747 is still being built for air cargo) 767 is still being built but barely 1100 built | Engineering | explainlikeimfive | {
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"It does it's job really well, and at low cost. It's design also allows it be upgraded easily and at low cost. It is also versatile. It's small enough to work for short hops, but efficient enough to make a longer journey if needed, all without major modifications to the aircraft.",
"\"It it ain't broke don't fix it\" is pretty much the running platform for anything involved in throwing objects through the sky.What incentive do they have to replace an easy to make, affordable airframe with something else? People flying only care that it safely gets them from A to B. As well, Realistically the only improvements that can't be made to the existing design are involved in Concord style faster-than-sound airflight. There's nothing better than the 737 that can't just be put on the existing 737."
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646xvk | Why do cars tick when they're hot after stopping? | I have noticed that cars, particularly more modern sports cars, tend to make a ticking noise when cooling down after being driven hard. Is this due to the cooling system itself or just a byproduct of the engine being hot? | Engineering | explainlikeimfive | {
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"My understanding is that it is the hot parts on the car expand and contract based on how hot they are. So as the parts cool and shrink a bit they move ever so slightly and make a small noise. Alot of the time it tends to come from the exhaust system as it changes temperature the quickly and is made of fairly thin metal, so it works like a bell when any small thing changes. Think of a house creaking at night when the temperature drops. Additionally, depending on the engine it can be cause by the block and heads being different metals that expand and contract at different rates. Most new cars have aluminum engine blocks and heads so this wouldn't effect those but other cars like my 03 mustang GT has a Iron block but aluminum heads. Not 100% accurate but best I can do in simple terms"
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649jqv | Why are Earth solar panels blue and Space solar panels orange/brown. | I was looking at some images of the space station and noticed that their solar panels were orange/brown. Most satellites and probes have orange/brown solar panels as well. Why aren't they blue like here on Earth? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The orange color of the panels around the ISS and some other space applications is [Kapton] ( URL_0 ), a polymer (polyimide) that is space rated for holding together electronics. We used to use it a lot when I worked for NASA. The solar panels around the space station are covered in sheets of flexible Kapton so they could be folded and unfolded for delivery."
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64bjmb | why do so many more small planes crash compared to large planes? | Engineering | explainlikeimfive | {
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"text": [
"1. Pilots of larger aircraft do this day in and day out; they know what they are doing and are very unlikely to find themselves \"out of their depth\" This is not the case of hobbyist pilots 2. Larger aircraft have significantly more advanced functionality to assist the pilot when they are out of their depth 3. Large aircraft are properly maintained along stringent schedules with very high bars as it relates to flight ready.",
"* there are a lot more of the smaller planes * they are flown by *far* less experienced pilots * they are not maintained as thoroughly, and they people who work on them are in general less skilled and experienced * they have fewer safety features...like only one engine * they fly the same very familiar routes over and over Anyone with a few thousand dollars to spare and some free time can join a flying club and have their pilot's licenses in a few months, and then rent a plane for $100/hour. It takes a whole lot more than that before someone is going to let your fly a multimillion dollar plane with 200 people on board."
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64crhx | Why do power tools (especially ones that need high torque) often employ a motor spinning at a ridiculous speed and then a deep reduction, instead of a motor spinning directly at the tool's speed and higher torque? | Engineering | explainlikeimfive | {
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"An electric motor works by having magnets and electromagnets arranged around the axle, which attract and repel each other in succession to spin the motor. To get high torque you need to have very strong magnets and/or very strong electromagnets. Increasing the strength of the magnets and/or electromagnets by 20 times you will have a motor which is 20 times as big and heavy. On the other hand, electric motors can naturally spin at very high rates. A reduction gear which increases torque by 20 times (and reduces RPM) will be smaller and lighter than the motor you attach it to, making this a far better solution to get high torque at low RPM than building a bigger motor would be.",
"essentially the way the motor works is a bunch of electromagnets pulling the axle around in a circle. if the axle was spinning slowly, the resistance from the load (whatever you're drilling) would stop the motor and it wouldn't get to the next coil. by having the main axle spin fast, it is more stable and therefore can have more torque.",
"The power of an electric motor is mostly limited by overheating. Making the motor spin faster makes it easier to cool it. If you tried to input so much power into a slowly spinning motor, you would melt it. Some large motors can also be designed to work at precisely defined speed, so you need reduction to make them work correctly."
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64dx3w | Why are dome-shaped housing structures not more commonly used in modern architecture? | Engineering | explainlikeimfive | {
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"theres several reasons 1) complexity: a dome is somewhat more complex to build than a box. a one-story house can be completely framed within one, maybe two days, then sheathed/roofed in another two. you dont need to make weird cuts- the raw material comes in rectangular shapes, and downsizing is easy. domes require lots of oddly shaped pieces that take more time to cut and assemble- raising the cost. 2) space: most of your furniture and appliances are square or rectangular. you cant hang a standard door into a curved wall. a rectangle-based floor plan offers more effective space. to get the same livable square footage, you would need a larger dome, particularly if you want a usable 2nd floor- a box is easy to expand upward. a dome has to get bigger in all dimensions. 3) tradition- we were building boxes long before domes. and those box-homes work pretty well."
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64e3qc | why is making the bottom of a soda can a dome makes it use less metal? | URL_0 at 3:02 | Engineering | explainlikeimfive | {
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"By making it a dome the force of pressure inside is born by the compressive strength of the metal and not by its resistance to bending. This allows a thinner metal to be used.",
"It allows you to make a thinner can, because the dome evenly distributes the load as opposed, just as in architecture. This is a pretty good video if you're interested in learning more: URL_0",
"Former structural engineer here, but this is close enough of an analogy. The dome shape is intended to reduce unwanted stresses in the metal. By arranging the very thin metal as a dome, it reduces the bending stress, favoring pure compression/tension. The reason we don't want bending stress is the way the material is asked to respond. Bending means that the can's wall needs to develop a thin zone of compression on top of a thin zone of compression, that taken together result in bending. Think of an I-beam in a building: if you look at its cross section, it is optimized to develop these tension and compression zones **way** out at the top and bottom. Compare an I-beam cross section to the cross section of a can wall (just a rectangle a mm thick) to understand why thin metals do **not** want to be bent."
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64esmm | Why are the parts on the bottom of a car always exposed? | Engineering | explainlikeimfive | {
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"text": [
"What would be the point of that? Where it is needed (offroad vehicles mostly) there is a metal shield/skid plate that protects the more sensitive bits of the undercarriage. However on normal street cars it just isn't necessary."
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64g0an | How was Venice built? | Engineering | explainlikeimfive | {
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"text": [
"Venice was originally a sanctuary for those fleeing the barbarians plundering the remains of the Roman Empire, around 400CE. It was a swamp that the hordes couldn't be bothered to slog out into. The city itself was built using pilasters of wood pounded into the ground. The lagoon itself is mud for a fair distance below the water, but it turns into bedrock and bottoms out eventually. Think of it like a series of toothpicks stuck into clay. If you get enough toothpicks you can hold up an entire book. If you get enough pilasters you can hold up a building. The weight distributes evenly and it's a city on stilts. A lot of our modern building have foundations like this, either pilasters or caissons. In recent decades the city has drilled into the bedrock, for stability in its modern construction and for fresh water. This has comprised the integrity of the bedrock on which many of these now ancient pilasters rest(although they're occasionally replaced), causing a sinking effect. The \"sinking\" of Venice has slowed since the city has restricted well and structural drilling. Source: I'm an architect that worked in Venice for a short time."
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64j7zl | What's the likelihood of a battery in an electric car, like Tesla, to blow up, like the Samsung phones? | Just saw this CNG explosion and thought to ask about the inherent dangers of electric vehicles: URL_0 | Engineering | explainlikeimfive | {
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"In the same way as the Samsung phones? Next to none. The trouble with phones is that phones are small, and the industry (and consumers) are obsessed with thinness. As a result, manufacturers keep trying to cram the maximum amount of battery capacity they can into the smallest amount of room. Lithium batteries have safety mechanisms, but those also take room, which is extremely scarce in a cell phone. By comparison, a car has way more room in it. Protection circuitry is tiny when you compare it to the size of a car, but far more significant when you compare it to the size of a phone. So while in phones there is a lot of incentive to go to extreme lengths to squeeze the last 5% in, in a car that's much less of a problem. Tesla not only has room for better monitoring circuitry than a phone does, but also has good physical shielding for the battery. Another difference is the use they make of the battery. Phones are effectively disposable -- the battery only needs to last a couple years. Car batteries however cost on the order of $10K and are supposed to last for more than a decade. So Tesla cars handle their battery way more carefully and don't actually use the entire capacity to maximize battery life. This also stresses the battery less than a phone would. None of that means a Telsla battery can't be made to catch fire -- that can be done if you physically damage for instance. But people poking a hole in the battery wasn't what the problem with the phones was."
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64mj0x | Why do apps like Alien blue become unstable when support is discontinued? | Engineering | explainlikeimfive | {
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"text": [
"They don't, immediately, but the technology around them changes and there's nobody to update them, so they don't keep up. Android breaks *something* with every new OS version, and the same is true of IOS; some frameworks are updated much more frequently and will occasionally change the \"right\" way to do things as well. For something like Alien Blue that's dependent on a service not running on the phone or tablet (in this case, Reddit) the server software will change over time as well. Little changes add up, and unless the app is constantly updated to match, which it can't be if support has ended, eventually they're too significant for the app to work."
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64njho | Why does the space shuttle or the soyuz need special tiles to reenter the atmosphere but spacex falcon does not? | Engineering | explainlikeimfive | {
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"text": [
"Are you talking about the Falcon 9 first stage, or the actual Dragon capsule? If you're talking about the Falcon 9 first stage, that's because it separates from the rest of the rocket at a relatively low altitude and speed, and thus there's less heat during reentry. It also burns it's engines to slow down to further reduce heating. If you're talking about the Dragon capsule, it does have tiles. The shuttle and Dragon have reusable tiles since the shuttle was reusable and so is the Dragon. The Soyuz does not have tiles. It has a simple ablative heat shield because the capsule is not reusable. Once it lands back on earth, its job is done, so the heat shield does not need to reused either.",
"The falcon is just the first stage rocket and never gets anywhere near the speed needed for orbit. Thus, it does not heat up nearly as much during the landing phase.",
"Don't think about the heat tiles as being about heat. Think about them being brake pads. Crazy right? What the heat shield is ACTUALLY doing isn't protecting the ship from heat, rather it is slowing the ship down from EXTREMELY fast orbital speeds to basically conventional falling speeds. It does this breaking through air friction (the aerodynamics involved are a lot more complicated than simply saying friction but really that's what it boils down to). The friction (and those other aerodynamic effects) are what cause the heating. But really all that energy that was put into speeding the spaceship up enough to orbit the earth and raise its altitude enough to get into space, that energy needs to be shed before landing, and the heat shield is how that is done."
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64nwkf | Master and Slave Cylinders in cars | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"A master cylinder pushes hydraulic fluid through a hose. A slave cylinder is attached to the other end of the hose, and is pushed by that fluid. This is a clever, simple mechanism for transferring motion from one place to another. For example, the master cylinder might be under your foot (at the brake pedal or clutch pedal), while the slave cylinder might be far away (at the wheels or in the engine compartment)."
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64nx5y | Why is Asian steel considered inferior to American and European steel? | Like I hear how katanas needed to be forged in a certain way to overcome their metal and that even then they were inferior to European swords. Or the fact you could make a rapier from the same amount of steel as a katana. I have heard this even going into the world wars with the Japanese making guns out of inferior metal. And the whole thing about chinese steel sucking. Why is this? Does that part of the world just have bad iron? And if so Why? | Engineering | explainlikeimfive | {
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"text": [
"It's not Asian steel, it's Japanese steel (remember that Asia is a huge continent with more than half of the global population). As for why, it mostly comes down to bad luck. Japan is simply not blessed with good sources of iron (that's part of why they were so hard up to invade China before and during World War II). Traditional Japanese swordsmithing used iron sand, and with the smelting technology of the day that produces a very impure and comparatively low-quality steel. The folding and hammering that goes into making a traditional sword was partially to counteract the poor-quality materials. As for Chinese steel, that's really the same as Chinese products in general being cheap and low-quality. Apparently manufacturers sometimes try to pass off low-quality metal as prime steel. There's nothing really special about China in that respect; it's just that right now they're the foremost producer of cheap stuff. 50 years ago Japan was in the same boat, ironically. 150 years ago it was Germany.",
"\"Additives in some Chinese steel used to reinforce concrete can affect the metal’s strength when it is welded and now UK industry is highlighting the dangers posed by it. Chinese steel makers sometimes add boron to their products to get a tax rebate as it was classed as an alloy. When the steel joined by arc welding, boron can make welds more likely to crack, weakening structures. The risk comes from current regulations not requiring steel-makers to specify how much boron has been added if the steel is used for reinforced bar – or rebar – which is added to concrete to strengthen it. If steel contains additives, different welding techniques have to be used so eliminate the risk of cracking.\" Source: URL_0",
"I think you are mixing two things: Katanas were made of Tamahagane which was a kind of steel made from iron sand (satetsu) which was not a very good iron ore to begin with so the result was a somewhat impure heterogeneous steel. Nowadays the steel companies are not necessarily (mostly not) the ones that extract and/ refine the iron. The process of making a good steel is something that has to do not only with a proper mixing of ingredients but also with the treatment of the resulting material in different stages of cooling. This is because steel is actually a crystalline material. This crystals can very in size and length. In order to make a resistant steel u need to produce long shaped crystals so that it is harder to brake when bent. This knowledge is not necessarily sheared by big steel companies that also have been doing this for centuries in some cases. So that's why Asian steel can be of less quality nowadays. EDIT: a typo"
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64o3rk | why do cheap iPhone chargers work great at first but break in 2 weeks no matter how careful you are? | Engineering | explainlikeimfive | {
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"text": [
"Quality control probably plays a part, they contain components that have flaws or values that are out of tolerance. But I think the bigger factor is that they're just under-engineered and overheat. That said, I don't know why Apple chargers cost so much, and why you can't find quality alternatives for 30% less. It seems like there are only crappy alternatives for 60% less, no middle ground."
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64pa2v | How do seat warmers on ski lifts gain power to operate? | While on our last ski trip, during the boring ascents, a couple of friends and I tried to figure out how the chairlift's seat heating works. Ideas ranged from the chairs packing a battery which provides power for an entire operating day, or having the main cable under power. | Engineering | explainlikeimfive | {
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"I've never been on a lift with heated seats, so your question got me curious. Basically an Express chair jumps on to a separate track at the bottom and top of the lift to slow the chair down for people to get off. With heated seats it seems there is a power rail on the bottom lift track. So while it is on that track it uses the power to quickly heat up the seats and they radiate it out on the ride up. Video showing the process: URL_0"
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64rcoa | Why hydraulic presses are so strong. | Engineering | explainlikeimfive | {
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"text": [
"Hydraulic presses have very large mechanical advantage. When you have gears, connecting one gear to another that's twice as big gives you twice as much force. To get a lot more force, you need a pretty bulky mechanical contraption. In a hydraulic press, it's the ratio of the area of the big piston to the area of the little piston. Area is the square of dimension, so a piston that's 5 times bigger applies 25 times more force. That lets you apply a lot of force with a smaller gizmo."
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64uzgj | why aren't traffic signs and lanes around the world universally the same? | Engineering | explainlikeimfive | {
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"text": [
"Two reasons: 1). They were all developed individually and there is little incentive to go uniform. And if there was, who's would you adopt? Any attempt would likely be ignored by the US anyhow. 2). There are going to be differences anyhow due to things like different road conditions and localization. Counties Luke to control these things and as long as the local population understand it that's all they need to know. Visitors can accommodate like they do with anything else.",
"There is a UN convention that sets out standard street signs, so they are standard in most of the world. As far as I know, the US and Canada are pretty much the only major developed countries that haven't adopted the UN system. Probably because by the time the convention was created, the US had already put up signs all over the place and didn't want to replace them. Also in North America, street signs are a state / provincial responsibility so it's difficult for the central government to get the states / provinces to cooperate. URL_0"
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64wi01 | Why are blueprints blue, and not another color? | Engineering | explainlikeimfive | {
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"Actually modern blueprints are black on white, but the name came from when they were white on blue. This was because one of the earliest copy process resulted in white lines on blue background. With architectural and engineering drawings where there a re lots of little details and accuracy is very important, making exact reproductions can be complicated and alternatives such as redrawing the entire thing with a pantograph or similar is not the ideal solution. This is why such chemical copying processes where used in this area first before better methods that reproduced black on white as black on white where invented.",
"Originally blueprints were the only way of making copies of technical drawings and the process involved exposing the special paper to ammonia. I imagine that the interaction between the chemical coating of the paper and the ammonia produced the blue color, but I can't tell you the exact reason for it being blue and not another color. edit: Here is why they were blue: In 1861, Alphonse Louis Poitevin, a French chemist, found that ferro-gallate in gum is light sensitive.[4] Light turns this to an insoluble permanent blue. A coating of this chemical on a paper or other base may be used to reproduce an image from a translucent document. URL_0",
"well it would be a little silly if blueprints were green now wouldn't it?",
"As a side note to other people's correct answers the technical term is actually \"schematics\" and *blueprint* was just the early printing technique that was commonly used so the terms became synonymous.",
"The process used to make blueprints is called Cyanotype. It works using a greenish blue solution of ammonium Iron citrate and potassium ferricyanide. These 2 chemicals in solution are painted or soaked in to a surface, usually paper. Next, the design to be transferred is drawn on to transparent acetate film in black. Back before printers and computers engineers used to draw these by hand. The soaked paper and acetate are placed in an exposure machine which blasts the paper with UV light, but the areas which have been drawn in block the light. UV light makes the 2 compounds react. The important thing about the reaction is that it makes the parts exposed to the light harden and become insoluble in water. The parts that are covered don't react and can be washed away. Long story short blueprints are blue because the cyanotype process makes *blue prints*! Simple as that. Nowadays this process is not used in the engineering world because we have fancy computers to do the work for us, but many artists still use it for a particular a e s t h e t i c."
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64y9vw | What's the difference between quarantine and deleting files from anti virus? | Why wouldn't you want to delete an infected file? what does quarantine do and what's the difference? | Engineering | explainlikeimfive | {
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"Quarantine is just storing the infected file in a protected folder, where it should not be possible to be executed. The idea behind this, is that you may want to recover your data. If you work an a 400 pages PDF, and it got infected, you may be able to recover your 400 pages pdf instead of loosing everything (yes, you should have a backup, but well, you know....) For many malware, you have a way to revert the things back. Maybe not when the virus just get out, but waiting a bit of time your anti-virus may be able not only to delete or quarantine the file, but also to recover it."
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"score": [
4
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64ykvt | What is that *hiss* when a bus stops or opens its doors? | Engineering | explainlikeimfive | {
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"Either the air brakes bleeding off air from excess pressure, or the pneumatic operators for the door, or the pneumatic lift (if equipped)",
"Large vehicles like buses have air operated brakes. When a driver is ready to move the vehicle from the parked position, he depresses a button that applies air to release the parking brake. When comes to a stop, he pulls the button out to release the air and apply the parking brake before opening the door. That's the loud \"pshhh\" you hear. The brakes on these vehicles are designed to be applied unless the air pressure is sufficient enough to release them. If the vehicle develops an air leak, the brakes will automatically apply. This design is a failsafe. If they used air pressure to press the brake shoes against the drums, and they lost pressure, there would be no brakes. It's actually a simple design. A compressor on the engine pressurized multiple air reserve tanks. At each wheel, there are devices that contain powerful springs. These springs keep constant pressure on a lever that makes the brake shoes contact the drums. When the driver releases the parking brake, these devices fill with air and compress the spring, lifting the shoes from the drum and freeing the wheel so it can travel. When the driver presses the brake pedal while driving, air pressure is released allowing the spring to apply pressure to the brakes. This is a simplified explanation, but you get the idea. Source: I hold a Commercial Drivers License, which requires training on air brake systems. I'm also formerly an ASE certified diesel mechanic."
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64yt6q | Why is height the only biometric used to determine if you can ride a ride. | Carnivals and theme parks will often say "you have to be this tall to ride". Why is height the only important factor when riding a ride safely? Wouldn't many other metrics also be important? *EDIT* So it appears that the other biometrics are considered when allowing someone to ride. The height metric is more visible due to lack of offense. Others have pointed out that too tall, too heavy, too wide of a waist, and more are all factors that can prevent a rider from riding. | Engineering | explainlikeimfive | {
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"Height varies a lot and very short people - children, usually - won't be properly held in by the ride's restraints. Very tall people and very fat people also might not be able to ride, but they will be a lot less common. But theme parks are full of children who might not be tall enough for some of the rides.",
"There are many others. Many rides have a long list of conditions that prevent one from being allowed to ride. Things like pregnancy or recent surgery, weight restrictions. Height is just the most commonly known one.",
"It's a very simple metric to check. All they need is a sign people walk next to and you can determine who will be able to ride a ride. In contrast, almost any other measurement would need to be invasive or handled on an individual basis.",
"I worked at an amusement park, and got some insight. You experience a variety of not often experienced forces during your day at the amusement park. Height is good measurement to determine how well you fit into the safety specifications of a ride. It is also quite consistent, and quick measurement that can be applied to all rides.",
"It's not the only important factor, and some amount of additional discernment may be called upon by the operator. That being said, height is useful in two basic estimations, 1) if the safety equipment is likely to fit you, 2) your age, and hence expected maturity when dealing with the ride."
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64zjrd | Why is the default background on BIOS/command prompt black but on pretty much everything (webpages/text document/google etc) it's white? | Engineering | explainlikeimfive | {
"a_id": [
"dg67nyv",
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"text": [
"In a BIOS, it's because this requires the *absolute minimum* of processing power: a monitor receiving a blank signal displays it as black, so only the bits that need to be seen have to be \"drawn\". When the BIOS has to run even if there's no graphics card present, saving graphical processing is useful. TTYs (text shells outside of graphical environments) on Linux and the rest of the Unix family tend to be white-on-black for much the same reason: it turns out to be the option that requires pretty much the least graphics-processing, which means it's likely to work pretty much universally - great if your GUI subsystem breaks. It's also due to the Unix heritage of dedicated terminals, which would have been entirely text-based with a dark background. This doesn't apply to terminal emulators, which can be configured for any colour scheme - whether under Linux, BSD, or Mac OS X. The Windows Command Prompt is white-on-black largely because people and applications *expect* it to be. The DOS prompt was so for the same reasons that text mode on Unix is, and the Command Prompt in Windows started as a way of accessing that even when graphical programs are running. Microsoft have started to allow much more flexible colouring with PowerShell, though. Meanwhile, most graphical-mode content is dark-on-light largely because of the desktop metaphor - if webpages and so on are *documents* then people expect them to be presented like physical documents, and the latter are usually printed on white paper. People are used to it. There's a certain amount of evidence that on backlit displays, we'd actually have an easier time if we switched to light-on-dark colour schemes, but dark-on-light is so entrenched that it's not going anywhere any time soon.",
"Because that's how it is programmed by the programmers. No real reason. Traditional bios have been blue, green, sometimes yellow. Application/desktop white background comes from trying to mimick a traditional paper view. Alot of people benefit by switching to black or grey background."
],
"score": [
8,
3
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64zsyr | Why are batteries like AA and AAA almost always inserted in opposite directions for polarity? Why not just create wiring so they can be inserted in the same direction? | Engineering | explainlikeimfive | {
"a_id": [
"dg69ec0",
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"text": [
"A few inches of wires costs a lot more in parts and labor/machining than a few extra square mm added to a shim of metal (and the enlarged metal shim can actually reduce the number of parts in an assembly). For a lot of purposes you would find this kind of setup, every saved penny in manufacturing costs contributes a huge amount to the profitability and final cost of the product.",
"Batteries need to be connected in series. That means negative to positive ends. Putting batteries facing opposite sides eliminates a LOT of unnecessary wiring.",
"You can do that. But you need more wire. Imagine that it costs a penny more to wire it that way. Not much, right? Now imagine that you're making ten million of the devices. Odds are you'll value $100,000 more than any OCD-ness you may have about having them all face the same direction."
],
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650nb3 | Why are currently used guns (by the military) so "old"? | An example is the [Heckler & Koch MP5]( URL_0 ) widely used firearm, it has been produced since 1966, and is still used by the modern military to this day. Is/was there no way on improving this - or other firearms - in the 60 or so years that it has been in service? | Engineering | explainlikeimfive | {
"a_id": [
"dg6h4zo"
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"text": [
"the basic design of firearms hasn't changed all that much over the years and although the basic design is old, there's still a lot of room for customization. as long as the weapon meets the requirements, why change it? military use specifically is unique as for logistical purposes, you don't want to change your platforms too often as you often order in the millions. and any change can create a logistics nightmare."
],
"score": [
6
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650spz | Why do buildings use revolving doors? | I'm from a city were practically no buildings have any revolving doors. Anytime I go to a city that does have them, it always strikes me as odd. So what are they for anyways? | Engineering | explainlikeimfive | {
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"text": [
"Revolving doors limit the heated or cooled air lost by people exiting and entering a building. They are most useful in very hot or very cold climates",
"They're meant to eliminate the social expectation of holding the door for people behind you.",
"it's energy efficient as they don't create drafts and they allow mutliple people to enter/exit at the same time. it's basically like an airlock",
"Revolving doors are energy efficient as they prevent drafts (via acting as an airlock), thus preventing increases in the heating or cooling required for the building",
"If the air in a tall enough building is either warmer or cooler than the surrounding air, there will be a pressure difference at the base. This can be enough to make normal doors physically difficult to open and prone to violently slamming shut. Even in a smaller building, winds can have a similar effect if there are doors on multiple sides. A revolving door is not affected by this pressure difference."
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