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6xhbq1 | Why do street lamps' power cables run underground and not overhead like those between pylons? | It would definitely be easier to hang the cable over than dig trenches in between poles, and also use something like a third less of that precious copper cable, because the wire doesn't have to go up and down each pole. There must be a reason for this, so what gives? | Engineering | explainlikeimfive | {
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"I've been building and maintaining street lights for a decade or so. Unfortunately, the answer is that it kind of depends. Let's start with why cables are in the ground. There are several reasons. * a cable won't interfere with traffic. I.e, it will never hinder any kind of heavy machinery transports. You know the kind. They are typically too long, too wide, too heavy and in this case also too high. * A cable is, once it's dug down, very hard to steal. * As long as you don't interfere with the environment of the cable (i.e, as long as you don't go there with a digger or drill something) it will be well protected underground. Hanging cables are subject to weather-related issues such as sunshine, salty winds, stormfallen trees and something as simple as the wind making it grind back and forth multiple times a minute all day long, for more than a decade. * street light cabling is often a totally isolated grid. It's only powered on from dusk til dawn. So, the lamp post grid feeds along the roads, often branching off in a different direction. That means that you will pretty often have cables not only along the road but also CROSSING the road. It looks better, and it's safer to have a crossing that is dug down. Despite this, hanging the cable on a pole is sometimes the chosen method anyway. Mostly because it solves a few issues that makes it worth the drawback. * If you have to use dynamite to get the cable down, it's gonna up the cost of the project. Sometimes to somewhere in the vicinity of ten times as high a cost. All for virtually no gain. So, when you can't dig down the cable for practical reasons, it makes sense to consider hanging the cable on the poles instead. * When you have a faulty cable, you'll have to put in quite a lot of effort into finding not only which lamp posts the faulty cables goes between, but you also need to get a pretty exact location of the fault so that you start digging at sort of the right spot. The fault is typically located with a pretty heavy surge generator and a geo-microphone. By inducing a spark that ignites in the actual fault in the cable, you produce a sound in the ground that you can listen for with the microphone. It needs to be dead quiet when you locate the fault, so if your cable happens to be right next to the highway you need to close it down while you locate the fault. That is generally frown upon. A cable that hangs up in the air will instead shoot a visible spark, so the fault will be found in mere seconds. * Replacing a faulty cable between two poles that hangs up in the air is done in an hour, while digging down a new one takes at least a day. Sometimes it's simply not acceptable with the waiting time. And again, if this happens to be between the lanes on the highway it's gonna be a lot easier for everyone if the highway is closed for an hour than if it's closed for a whole day. * Sometimes you want lights in areas where you don't have access with skylifts. Yes. Those places actually exist. Think a narrow running-track in the woods, or an overpopulated island where you need a special permit to bring any kind of fuel-consuming vehicle, and when you get there you can't navigate around with a truck anyway because there is simply not enough space between the houses for one. If you got that kind of environment, your only option is to use wooden or composite poles so that you can climb them with tree pole shoes. And if you can't get a skylift in there for maintenance, you are gonna have a hard time when you want to dig up something too. And that leaves hanging the cable instead of digging. And, oh. If you look closer on a steel lamp post, you notice that there is a small hatch on it, about a metre up. The expensive cables end there, and a noticably thinner one runs up to the actual fixture. EDIT: I forgot to add that when you hang a cable, you also get all kinds of problems related to traffic accidents. They are really no fun then.",
"So the cost really isn't the copper. It's the labor to install them. So when a parking lot or street is being paved it very easy to go ahead and install the wires underground. What isn't cheap is repairing the lines if they are damaged. Let alone the liability of having hundreds of feet of live power lines above poles that if are hit by cars will be near pedestrians. Do it once right and you never touch it again."
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6xiw9i | How do cars know how fast they're going? | Engineering | explainlikeimfive | {
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"> How do cars know how fast they're going? They know how big their tires are and count how many times they turn.",
"If you change tire size, your speed will be wrong, unless you have a way to program it. I want to know how planes know how fast they're going.",
"Modern cars have a sensor in the transmission that counts how many times the driveshaft turns. There is a computer that uses this information to compute the vehicle speed by knowing the tire size."
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6xnb5u | Why would Reddit have their source code be open source? | Engineering | explainlikeimfive | {
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"Software developer here, That is because there's very little value in the software. The value is in the service, the intellectual property (Reddit's name), and the community fostered around it. Sure, you can take their source code, buy a domain, and fire up your very own clone, but who cares? No one. You don't have a community, you don't have partnerships, you don't have any means of generating revenue, you have nothing to distinguish yourself from one of the biggest internet communities, and you may suffer some negative backlash for being nothing more than a clone of Reddit using their software. There's little risk in opening their software, the website isn't where they're vulnerable, they're going to protect themselves by hardening their database, which likely isn't the open source part of their code, being considered an implementation detail and something they can fill with proprietary code.",
"A better question is why *wouldn't* they be? I don't know the details of Reddit's specific software situation, but they're not selling it; they're just using it. So there's no need to keep their code secret in an effort to prevent competitors from using it. Further, simply having the site code would not enable one to create a competitor site; Reddit's strength is its community, which they can only lose if they really mess up, or if some competitor comes up something *really* good (substantially better, therefore it won't be using Reddit's code). An open source product benefits from anyone being able to contribute to it, for no purpose other than to make a name for themselves or even to alleviate boredom. Whoever controls the project can accept or reject submissions, so its not like malicious code can be simply inserted into it (unless someone is being *extremely* clever). And one doesn't need access to the code to find vulnerabilities (as hackers prove all the time), but one *does* need access to the code to find ways to close those vulnerabilities, which is why open source code is often more secure than proprietary code."
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6xsetd | How do companies like Burt's bees produce bee venom products without killing millions of bees to harvest the venom? | Engineering | explainlikeimfive | {
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"Taken from Burt's Bees own website FAQ: > I am allergic to bees. Can I still use your products? > We do not use actual bee venom in our products – only bee by products such as honey, beeswax, royal jelly and honey powder. However, if you are allergic to bee by products, then we do not suggest using our products. We recommend that you contact your health care provider when changing your skin care regimen to find out which products are best for you. Short answer: they don't use bee venom in any of their products. Period.",
"I can't find something specifically burts bees, but some companies do offer bee venom products. Here's something I found on another website: > Historically, venom collection was lethal to bees, and was performed either by crushing them or by forcing them to sting plastic or rubber surfaces, which caused their stingers to get stuck (a bee dies from stinging only when its stinger is dislodged from its body). The modern method is kinder: Beekeepers start with fabric-covered plates that have conductor wires stretched flat across them. When a bee lands on the plate, the wires deliver a mild electric current that agitates the bee just enough to make it sting, causing the venom to drop onto the plate. Since the fabric on the plate is very thin, it doesn’t trap the stinger the way plastic or rubber used to do, leaving the bee free to fly away unharmed. “More venom is collected when other bees sense the chemical odors of the freshly-released venom, which signals them to start stinging, too,” says Karen Wassmer, a beekeeper and owner of K & W Apiary in Jacksonville, Florida. source: URL_0",
"A) [Burt's Bees doesn't make anything with venom in it]( URL_1 ). B) While it was once fatal, [we now have nonfatal ways to collect bee venom]( URL_0 )."
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6xt6qi | How are nuclear weapons tests underground without destroying the land around them or the facilities in which they are conducted? | **edit** FP? ;o Thanks for the insight everyone. Makes more sense that it's just a hole more than an actual structure underground | Engineering | explainlikeimfive | {
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"An underground nuclear test is essentially a bomb in a deep hole or mine shaft. It goes boom, a portion of the surrounding ground is vaporized, and a lot more is superheated. If the hole is deep enough (it should be, as we've done this sort of thing for a while) all the radioactivity and the blast is contained underground. Kind of like having a tiny balloon pop in your hands. The noise is muffled, the rubber doesn't go anywhere, and everything is cool.",
"I finally understood this when I visited the URL_0 in Las Vegas. An atomic bomb is a source of intense heat, what we normally associate with the explosion is the expansion of the surrounding air. In an overly simplified explanation, if there is no air you only get heat but not an outward explosive force. Yes rocks vaporize and all that, but his is less of a factor. In fact the area around the test device is keep in a vacuum, in the museum you can clearly see the vacuum vessel and vacuum pumps associated to maintain the neighboring area free of air and water. Water creates steam. It is important to keep water and things that can be vaporized away.",
"Compacted earth is incredibly heavy, dense and strong. According to [this site]( URL_0 ), 1600 kg per cubic meter. \"Cannikan\" was the largest underground test in the US at 5 megatons (equivalent to 5 million tons of TNT, or about 240 times more powerful than \"fat man\" which was dropped on Nagasaki. It was placed in a shaft 6,150 feet deep (nearly 1900 meters). So essentially, imagine a rock wall 6150 feet thick, and even something as powerful as a nuclear bomb has its work cut out for it.",
"Underground nuclear tests are performed by buttering the bomb deep underground. Larger bomb tests, such as the one North Korea just performed, cause earthquakes and significantly deform the land around the test site. Here are some videos of nuclear tests that show their impact on the surrounding land.[1]( URL_1 ) [2]( URL_0 )",
"Because it's not a little bit underground. Done (and depending on yield) correctly a underground nuclear test is several kilometers deep. There's also no facilities around them, other than the shaft the bomb is put at the bottom off. The hole itself is a write off, a solid chunk of the rock at the bottom will be vaporized, and any tunnels nearby will collapse. This isn't some specially built, hyper reinforced lab setting, it's usually just a repurposed mineshaft",
"i read somewhere, (can no longer find it, but if anyone can, please post). there was a test where the shaft was filled with water, and a massive steel door was put on the top, perhaps to just close it, or whatever. but what happened was that alot of that was was instantly turned into steam, hyperpressurizing the shaft, the subsequent blast sent the steel door into space at a rate of (if i can recall correctly) at about 6MPS or could have been much faster. it set the record for the fastest/largest/heaviest projectile sent into space, i'm pretty sure its still going because it would weigh so much and would escape earths orbit within minutes if not longer. i can't find the story anymore. the steam acted as a buffer and did not vaporize the door.",
"For those interested: Here is the US nuclear test site: URL_2 Here is where Pakistan tested its nukes in 1998: URL_0 And here is the secret Syrian facility the Israelis blew up: URL_1",
"What about the latent radiation to the surrounding soil, water, and microorganisms? I assume these factors are taken into account when choosing the site for detonation.",
"What can you learn from the test being underground vs above ground? What are they testing other than the boom.",
"The basic idea is the same as burying yourself in sand. If you're covered in a little sand you can still wiggle your toes, or pull yourself out. Eventually you'll get to a point where all you can do is wiggle a bit. When you get to this point someone really has to be looking for you to notice that something underneath them is moving. That's the general idea behind underground testing. You cover it up with enough dirt that someone really has to be looking for it to notice it. In this case we detect it using seismic sensors. Edit: Doing it underground also masks the radiation signature, which is a big deal if you don't want to irradiate your population or be caught.",
"How far down are they buried? Is there any concern for radiation leakage in water, etc?",
"Does this cause tremors nearby comparable to earthquakes?",
"[sometimes]( URL_0 ) they did blow the shit outta everything. Looks like friggin DBZ. Craziest part is, it's only that big because they miscalculated.",
"Underground nuclear explosions destroy everything in the vicinity, how much gets destroyed depends on the yield. 100kT or 0.4 PJ is pretty big, but not that big. The energy is mostly absorbed by the surrounding rocks being pushed aside (rocks are heavy so it takes a lot of energy to move them even a little bit) and melting (rocks have a high melting point so it takes a lot of energy to melt rocks), a fraction becomes acoustic energy which travels through the Earth and can be picked up by remote geophones operated by geologists watching for for earthquakes, as well as more sophisticated instruments operated by various government agencies and the CTBTO.",
"Can the hole be reused or does the radiation make it too difficult to set up the next nuclear bomb and they have to use another location?",
"Are the EMP effects of the bomb diminished?",
"Another question I'd like to know, did all the tests out in the ocean ever create Tsunamis?",
"What does the vaporized rock look like after the test?",
"[This]( URL_0 ) might not answer your question fully, but it does show test buildings with shock absorbers that seem to roll with the ground. Really cool to watch too.",
"On a related note, how do they scout these underground locations for testing? Are they all manmade? Seems like it require a lot of time and equipment to create a space large enough to be able to pass through all the equipment, material, and personnel needed to test a nuke",
"Not sure if it's been said elsewhere, but basically, it does. The device is lowered into a shaft with a full set of diagnostic equipment, the whole assembly is called a canister or a rack, depending on which lab you're talking to. All that diagnostic equipment is set up to record remotely, so you still get the data from the time of detonation to the point your diagnostics are destroyed. The tests we do now don't require us to destroy a bunch of equipment, so it's much cheaper in that sense, though the equipment is certainly more sophisticated."
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6xtbq4 | Why can't microwaves replace ovens? | Both can cook things, but I imagine produce differing types of heat or whatnot. Don't know much about the things. | Engineering | explainlikeimfive | {
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"Microwaves don't actually produce heat, they produce microwaves that rotate the water molecules inside of the food, in which the friction heats up the food from the inside essentially. Ovens actually produce heat with essentially a giant resistor that heats up the air inside of the oven, which then heats and cooks the food. Ovens are generally preferred because you get browned and tasty food, as opposed to rubber/flabby food from microwaving. It's a culinary preference.",
"Because you cannot get a nice tasty crispy texture on your food with a microwave, with a microwave its gonna be a soggy wet mess.",
"Microwaves effectively boil most food, and can \"rubberize\" starches (microwave a short stack of white bread for like ten seconds and then try to eat it), so it's just not suitable for baking or heating things in a way that browns them. Now there are special metal or metal-impregnated cookware that can translate the microwaves into high heat. The microwaves create little electric currents in the metal, which then gets hot, just like on a classic electric stove top (except the individual currents are random momentary circles that are very small). This is why there's a foil-looking plate in your microwave popcorn bag or your HotPocket pouch. So different heat sources are good for different tasks. You don't make sauce in the oven, you don't bake on the stovetop, you don't use a blowtorch liquid but it's great for browning sugary confections. Now a lot of food you eat, particularly in restaurants, has been microwaved as part of the cooking process. I don't mean that its been \"reheated\", the good chef knows how to use all his tools, so meat and root vegetables are often started or ended with conventional heat while being cooked through in a microwave."
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6xu9xs | Why the air humidity in an airplane doesn't condense on its windows? | My chem teacher asked me this question not long ago. I am interested in moisture forming proces, and why it doesn't occure on airplanes. | Engineering | explainlikeimfive | {
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"There are two layers of windows with a gap between them, providing insulation so the coldness outside the plane doesn't transfer to the inside layer. There are also dehumidifying air scrubbers for the air in the plane.",
"The air is then sent through a water separator, where the air is forced to spiral along its length and centrifugal forces cause the moisture to be flung through a sieve and toward the outer walls where it is channeled toward a drain and sent overboard. Then, the air usually will pass through a water separator coalescer or the sock. The sock retains the dirt and oil from the engine bleed air to keep the cabin air cleaner. This water removal process prevents ice from forming and clogging the system, and keeps the cockpit and cabin from fogging on ground operation and low altitudes. URL_0"
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6xuci9 | How do we assure that there are enough key/keyhole combinations for doors to be safe? | Engineering | explainlikeimfive | {
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"We don't, not really. Most of the doors in the USA can be picked with your average rake/tension wrench combo in under 5 seconds for anyone who has done it once or twice before. It's a really simple lock. Car doors have more tension in them, so you need a slightly stronger tension wrench to counter act it, and you might need a specialized pick, but they come in the standard pick set. Your various padlocks are also typically very insecure. High-end locks are much, much more precise than these cheap, common locks. Laser etched grooves and all-that being so accurate that they're nearly impossible to pick or bump. You need the key that goes to the lock, otherwise you're generally not getting in without breaking it.",
"By having just enough different combinations that the chance of lucking out is minuscule. Because really, someone who wants to defeat a lock isn't going to carry a hundred keys or try a hundred different locks hoping something good is behind them. Rather, they're going to try to cheat the mechanism - lockpicking. And so you make a lock safe by making it difficult to pick. So the lock on something important like a cash office or a computer closet will often take a key with not just teeth but also grooves or dimples.",
"A generic quickset door lock has ~7000 combinations. (6^^5 minus some because complex reasons) So the odds of your key working in a random door you try is about 1 in 7000. Those locks are very cheap, some can even be bypassed with a screwdriver and enough torque. Others can be picked with a bit of practice in just a few seconds. The part of the lock latches into is also usually a huge weakness. When a door is kicked in, that's what usually gives way. So really the number of key combinations aren't a weakness. Anyone that really cares to get around the lock has better ways of doing it vs having several thousand keys.",
"The standard lock on most homes isn't very secure as a person with a $20 kit and 60 minutes of practice could pick it in less than 1 minute (using YouTube tutorials. Look up \"lock bumping\") The amount of combinations isn't the problem, it's the type of lock that is the problem. Because the lock is so common, it's easily learned how to pick it. Making a lock more difficult to pick isn't too difficult, but will end up costing more if you're locked out. Most people \"feel safe\" knowing their door is locked. But in reality, a crowbar into glass tends to be the easiest method."
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6y178a | Why are we not supposed to rapidly turn lights on and off? | Engineering | explainlikeimfive | {
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"A lot of lights have a lifetime dependent on the cycle time. For example an incandescent light bulb have a tiny wire that heats up every time you turn the light on and produce light. But heating the wire also makes it expand which puts pressure on it which over time can cause cracks to widen and eventually go all the way though the wire and it will snap. So you only have a limited number of times you can switch on the light before it stops working. It is not true with all types of lights and electronics. You get incandescent lights which is designed for a high cycle count and modern LED lights often have no limits on cycle time. The lifetime and cycle count of a light bulb is often listed separately.",
"This came from incandescent lights. When you first turn an incandescent light it has a large mount of inrush current. This high current causes significantly more stress on the filament that normal operating conditions reducing the bulbs life. The high inrush current comes from a cold bulb conducting much better than a hot bulb. Once the bulb begins to glow and by association, gets hot. The filament conducts worse bringing the current to its normal operating level.",
"TL;DR: With fluorescent lighting, doing this will shorten the life of the lamps (the 'bulbs') by quite a bit. They can handle so only so many 'starts' before they will begin to fail. They will handle only so many running hours before they begin to fail. If you run fluorescents for about 3h (or more) every time you start them, then, generally, you will not reach premature end of life due to too many 'starts'. The lamps will fail due to too many running hours, which is the appropriate way for them to die. I do some lighting design for commercial, industrial, and institutional facilities. So I have a moderate background on lighting topics. And I can give a partial response to this question. Some commentors have mentioned incandescent lights. Yes there is some inrush when you turn the light switch from off to on, and yes it has some mechanical impact on the filament, and likely some impact on longevitiy of the filament. However, anecdotally, it is considered to be not particularly harmful to incandescent lighting to turn them on and off a bunch of times, once in a while, like kids might do at home. If the incandescent lights went their whole lifetime being switched on and off at random there would probably be a more noticeable shortening of life. But I am supposing this, I do not have any hard numbers on it.",
"Adding onto the other answers, LEDs can be turned on and off extremely quickly. In fact, if you have a device with an LED that dims, it's actually turning on and off extremely quickly."
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6y33zk | Why do modern vehicles headlamps turn off when the turn indicator is actuated? | I see this more and more. When I'm opposite the intersection of a vehicle with its indicator active, the headlamp is off. Midway through the turn, once the indicator clicks off, the headlamp immediately turns back on. Any explanation? | Engineering | explainlikeimfive | {
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"Daytime running lights, most likely. Most vehicles today will have their headlamps or front marker lights on as long as the engine is running for safety (better visibility to oncoming traffic). However, the car turns the lamp on that side off when turn indicators are active to make the indicator more visible (assumption). This is most noticible on vehicles with the LED strips around the headlight, that are used as DRLs instead of the headlamp or marker lights, as these strips sometimes double as turn indicators.",
"The new LED lights are so bright to incoming traffic that the turn signal wouldn't be noticeable. Due to poor placement and design, the manufacturers chose to have the LED turn off rather than moving the lighting arrangement around to allow both to stay lit and still be visible."
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6y6b3r | How does a tower crane remain stable when the load is moved to the end of the arm? | For those wondering, tower cranes are the ones you commonly see on construction sites. | Engineering | explainlikeimfive | {
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"They have a massive weight (like a huge concrete block, for example) as a counterbalance. As the load is moved towards the end of the arm, the counterbalance moves further backwards keeping the whole thing balanced and stable."
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6y82xb | Why no Front Wheel Drive Pickups?? | I've been in the auto business my whole life. I've never been able to figure out why small trucks aren't front wheel drive. | Engineering | explainlikeimfive | {
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"There have been some mini-trucks and what not that were front wheel drive, but it's not something that's done with full sized pickups. The situation where you need maximum traction in a full sized pickup truck is when you're towing something or have a bunch of stuff in the bed, which is a situation where there's plenty of weight on the rear wheels. About the only situation where you'd see a noticeable improvement in a FWD pickup would be in the snow, and if you're in an environment that's snowy enough that for this to matter they make plenty of four wheel drive pickups. There are some other practical problems: * It'd be really difficult to fit a big V8 and a pickup truck sized transaxle under the hood of a pickup truck that wasn't like 8 feet wide or 10 feet tall. * The solid rear axle that most pickups have is antiquated technology in a certain sense, but it's monstrously tough. It'd be pretty difficult to engineer a FWD pickup that wouldn't constantly be eating CV joints and what not. * Pickup trucks handle like shit with an empty bed in large part because of their unequal weight distribution. Taking the transmission and rear axle and moving them up to the front of the truck would make this worse.",
"VW had a small pickup back in the 80's and maybe early 90's that looked like a rabbit with a bed attached, it was fwd but it was small, think older Chevy s-10",
"Shout out to the Honda Ridgeline. FWD. Not a \"real\" pickup but cheap, indestructible, runs on gas, has a trunk in the bed, and can do 4x4 to get out of snow etc."
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6ybgnm | Why European fire safety standards are so lax compared to the US and Japan? | On my most recent trip to Europe I've noticed that the fire safety is appalling. Examples: Almost all business everywhere have inward opening front doors with no panic bars. My hotel in France requires a key to get out the door if it is locked. My Airbnb in Prague required an electronic release to open the front door of the building (what happens if it melts in a fire?) and multiple keys to get out of the door to the apartment and there was no secondary egress. The stairway at my grandmother's apartment in Denmark lights on a timer and no emergency lighting. The egress stair was under construction and had no functional lighting at all and no interim life safety plan was posted. Literally none of the outlets are grounded at all either (forget about GFCI). There has also been a chair on one of the landings for 20 years as one of the residents has a bad leg and gets tired. Why does this seem to be so common in Europe, which is typically way more progressive than the US and has generally much stronger consumer protection laws? | Engineering | explainlikeimfive | {
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"About Japan: Traditional is Japanese architecture is very easy to burn, using materials as wood, paper, plant fibres and straw. Adding to this the very high frequency of earthquakes and you have a while history of huge fires, many of them starting with earthquakes. That's why current fire regulations are very tight there.",
"Short answer: history. Most (not all) safety laws regard new construction. There are many buildings in Europe that have been standing for more than 300 years. New ideas get added on over time, but for the most part, there's no requirement to replace something that already exists. In the US, this is also the case to some degree, but the US has this habit of tearing down 15 year old buildings and building something new -- which results in the new buildings having to be built to code."
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6ycrgp | Why do lamps with the twist thing always tick twice? | Why does the twist thing on traditional lamps always tick twice to be turned on or off? | Engineering | explainlikeimfive | {
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"> Why does the twist thing on traditional lamps always tick twice to be turned on or off? They don't always click twice, they only click twice on lamps which are designed to work with bulbs that have two brightness settings. If you put a single brightness bulb it will still work but with the extra click.",
"Back in the day when we used incandescent bulbs they sold many with variable brightness filaments. Usually 50 75 and 100 watts (some up to 150 watts and some just two wattage settings) all integrated into a single bulb. So I would not be surprised if your lamp actually takes even three clicks to fully cycle."
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6ye15w | Why are ancient buildings (e.g. pyramids) build with such large stones? Wouldn't it be way easier to use many small? | Engineering | explainlikeimfive | {
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"When these ancient civilizations were building megastructures, they didn't have anything in the way of mortar or glue. This meant they designed and built these amazing, massive structures to press into themselves, so the sheer weight of the objects would keep them together. When they used smaller stones for detail work, they had to use a form of mortar/glue/cement in order to keep them from slipping. The products they had available just weren't heavy duty enough to hold 150,000+ pound stones in place. Hell, we don't even really have good enough glue for that today. The first post here; URL_0 describes other kinds of supermassive stone structures and how/why they might have been created by ancient civilizations.",
"Because stones have to be quarried and shaped. It was easier to cut the giant rocks out of the ground, work to make them roughly square and then send them down the river for construction. Conversely small rocks have so much more surface area that needs to be shaped for the same volume. Any bigger I guess the reduction in surface area would be outweighed by the extra difficulty in transporting the blocks."
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6ygnw9 | How can hurricane hunters fly into Irma and not get torn apart or thrown into the ocean in the 175+ mph winds? | Engineering | explainlikeimfive | {
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"It's a rough flight, definitely. But surprisingly enough, it's not as turbulent as you would think. The winds are fairly constant in speed and direction and there's not a lot of updrafts and downdrafts to toss you around like if you were flying into a summer thunderstorm. Sure, there's been a few times where the hunters from both NOAA and the AF Reserve planes have been tossed around good, but that's only been a few instances vs the hundreds of eye penetrations they've done.",
"Hurricanes have very strong winds, but those winds are basically parallel to the ground. There's no downward draft that makes flying through other storms so dangerous. So while the plane's path will be offset by the strong winds, there's not as much risk about the winds forcing the plane into the sea. And remember that many planes typically fly at speeds exceeding 200 mph and are designed to hold together at those speeds. The groundspeed might be low if flying directly against the incoming air, but as far as the plane is concerned, it's flying as normal.",
"If you were to roll down the window of your airliner and stick your hand out, the wind would be about 600mph. 175 is nothing, in fact it's about the speed those things takeoff at. They can barely fly with wind over the wing that slow. The thing with planes is, yes they make their own wind by flying fast, but they also drift along with whatever the local wind is doing. Imagine you're running indoor laps on an ocean liner. You run and run and the only speed you feel is your own, the only wind on your face caused by your own running (regardless of what direction your pointed, you are running laps), and you're completely oblivious to how fast the ocean liner is going because you're getting carried along with it. The ocean liner is to you what the jet stream or hurricane or any wind is to an airliner: something that carries you along that you don't even notice unless it abruptly changes speed or direction. If you stick your hand out while running laps or flying, the only wind speed you'll feel is your own. Now you won't feel the wind of a hurricane because you're drifting with it, but you will feel when it changes speed or direction because you'll get pushed and shoved until you're drifting in the new speed and direction, just like an ocean liner turning sharply might push you around uncomfortably. In a hurricane that speed and direction changes approximately once every constantly, so it'll be a bumpy ride for sure.",
"First of all, these are specially trained pilots. Second, they are in specially designed aircraft. Third, They are able to travel WITH the hurricane, whereas other aircraft are trying to get to a fixed point on the ground and have to fight against the hurricane.",
"Here's a great video explaining how the winds in a hurricane affect a plane differently than the winds of a thunderstorm: URL_0 Basically, a thunderstorm has incredible vertical wind shears while a hurricane has much more predictable, horizontal shears.",
"Since the question has already been sufficiently answered, allow me to input my reasoning just for shits and giggles: How can they fly into a hurricane and not die? Because the P-3 Orion is a beast, that's why."
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6yi6c9 | Why is the French Horn so difficult to play? If it is really hard to play why has it stuck around for so long? | Engineering | explainlikeimfive | {
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"It's stuck around because it makes arguably the most beautiful sound of any brass instrument. Substitute anything else for the horn, and you'll get an inferior result. You have to be really precise to get the right note. Due to the horn's narrow mouthpiece it's quite sensitive to what you do with your mouth."
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6yrx0u | how long can a typical commerical airplane cruise on land til its wheels give out? | Engineering | explainlikeimfive | {
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"Airliner main gear tires are usually replaced every 100-200 landings give or take. It depends a lot on the plane, its typical landing weight etc. When an airliner lands the sudden spin up to match the landing speed (150 knots+) will shed a bit of rubber, as if you're smoking your tires on your car. The nosewheel tires are replaced much more frequently. There's more weight on those wheels than the mains, also they scrub rubber when the nosewheel turns to steer the plane on the ground. If we're disregarding the scrubbing of rubber when the plane lands, this will extend the life of the tire considerably... but the tires on an airplane aren't designed for longevity like a car's, they're designed to be replaced frequently. When replaced they aren't tossed, they're retreaded and reused (the belted core is more expensive than a retread, so reuse that puppy). Having said that, well preserved airliners can be parked for years or decades on their tires just fine with proper maintenance. So if a plane is just taxiing in mostly a straight line on the ground I'd say the tires would last months to years? Again, the tires are designed to be able to take the max landing weight (plus significant safety margin) of the aircraft for 100-200 landings, so without that abuse they should hold up quite well. ed: NOT an aerospace tire expert, just applying what little I know."
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6yvjug | How do motorcycles differ when they have the same Kw (hp) but different ccm? | I am looking to do my motorcycle license, and will be allowed to drive a bike up to 35 Kw (48ps). But there are some bikes with 300ccm and some up to 700ccm, but they all have 35 Kw. What is the difference and what will I notice? (e.g. sound, acceleration, mileage, etc..) I am completely clueless. | Engineering | explainlikeimfive | {
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"The smaller engine will rev higher to produce the same power as the larger one. Acceleration will be better on the larger engine because it produces more torque, which is the force that gets you moving (this is a generalized statement as gearing would affect this.) It will also work less hard, potentially saving wear and tear. Fuel efficiency will most likely be better on the smaller engine. The larger engine will probably produce a throaty sound compared to the higher pitch smaller engine which is running at a higher RPM."
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6ywj3y | How large can you build something before you have to start accounting for the tendency of said structure to collapse into itself on account of its own gravity? | This occurred to me when I learned about Dyson spheres, which are hypothetical structures an advanced civilization might build around a star to harness its energy. Surely something so massive would simply buckle under the pull of its own gravity and collapse into a sphere? | Engineering | explainlikeimfive | {
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"Larger and more dense than anything we have ever created, and possibly would ever create so long as we inhabit only this earth. Gravity is a weak force and generating enough for it to be a structural concern (that acts in any direction other than towards the earth's core) is a materials science problem more than engineering. You'd have to build something on the scale of the Moon, and assuming you're using resources from earth alone you're going to have to take an equivalent amount of mass from the earth which is going to really fuck with literally everything."
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6yyp53 | Why do a lot of roads seem to curve for no apparent reason? | Engineering | explainlikeimfive | {
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"Before a road is installed, a number of surveys are done, one of them geological. The footing of the road has to be solid, not subject to settling or sinking. That sometimes forces a road to curve around a soft spot of earth. Sometimes the reason the road curves is due to private property. Rather than run the road in sharp corners around the line, it's easier for the drivers to do a curve, so road designers will make it a curve. The last possibility I can think of which I think may be uncommon, is there could have been a feature that caused the road to curve (building or tree) that is no longer there. I doubt that is common though.",
"Another reason for curves is to avoid costly topographic features that require additional excavation or fill.",
"Some highways are also built with curves to prevent drivers from falling asleep out of boredom if it were a super straight line."
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6yzar6 | Why are NASA spacesuits so bulky and Space-X spacesuits are so sleek? | Engineering | explainlikeimfive | {
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"The spacex suit you saw pictures of today is for transitions between craft, not full vacuum. Also they're brand new and NASA's aren't. But mostly the first thing.",
"There are two kinds of spacesuits: Pressure suits to keep astronauts alive inside the spacecraft in case it depressurizes, and EVA suits for when you actually go outside into space. The latter have to be much bulkier to protect you from all the hazards of space (debris, radiation etc) for a long period of time, rather than just having to protect you from vacuum for the time it takes the spacecraft to land. Also, EVA suits need a self-contained life support system (the backpack) rather than just getting air from hose connections to the spacecraft. The NASA suits are EVA suits, the SpaceX suits are not.",
"Nasa has a compairable one. Musk is just very good at reinventing the wheel then blasting social media and tech blogs with his breakthrough. URL_0"
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6yzphi | why do avoiding left hand turns save gas? | ups no longer does left hand turns. How does this save them gas | Engineering | explainlikeimfive | {
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"A computer determines the optimum route. It tries to avoid lefts because of safety and time savings. It does not mean they never turn left. If a left is the best choice, it will be mapped.",
"If you have thousands of trucks, avoiding the time spent waiting to make left turns across traffic can add up, especially if your planning routes with dozens of stupid. In your personal life, where you only have two or three destinations, your never notice the difference or even travel further.",
"In the USA, left hand turns means crossing the line of incomong traffic, UPS trucks are not known for their quick acceleration so left hamd turns often means waiting, and idleing the engine. engines at idle burn more gas then when they are actually movimg the vehicle (in most cases). it isnt a lot of fuel savings individually, but across their fleet of trucks it adds up. adds up to the tune of 200 or 300 million dollars"
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6z1y90 | Why are vacuum cleaners so loud? | Engineering | explainlikeimfive | {
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"To work properly they need to move a large amount of air. This means their small motors must spin impellers at a very high speed to create suction (loud). Also any sort of muffler to reduce the sound would impair the air movement making them less effective at creating suction. So, no matter the style the noise (with present technology) just can't be helped.",
"Actually, while it used to be a necessity for them to be loud, the technology exists to make relatively quiet vacuums. However, the general public is moronic and thinks that a quieter vacuum is not as powerful as a loud one. Thus, manufacturers purposefully build loud units so people think they're getting power.",
"Doesn't Reddit have a resident vacuum expert? An /u/earthquakeguy of vacuum cleaners. I wish I remembered his username.",
"My in-laws had an huge unit in the basement and you could connect a hose to several sockets throughout the house. Not as loud (except in the basement ;) But as someone pointed out you can only pick 2 and this was not a cheap system.",
"I refuse to let this ELI5 pass without referencing the Vacuum Repair guy AMA: URL_0",
"Fun fact. Vacuum cleaners over 80 dB are now banned in the EU, and anything over 900watts...",
"They use cheap universal motors which spin at high RPM because they're fairly small. Universal motors also have brushes internally which adds to the noise.",
"Vacuum cleaners displace a large amount of air to create a vacuum. That vacuum allows stuff to be sucked into it. Whenever a lot of air moves all at once, it creates a big sound kind of like a tornado.",
"Mufflers reduce suction power, its a trade off. Mufflers are also more effective the larger they are, so size is another trade off.",
"I remember reading a Batman comic where someone commented how quiet Batman's vehicle was. Batman then stated that 'noise was a byproduct of bad engineering'. I think he was referring to his bat plane or batmobile."
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6z49mm | How do investigators know which firearm specifically a bullet was fired from, do guns have unique fingerprints? | Engineering | explainlikeimfive | {
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"They don't and we usually can't figure it out to so much detail. Guns have different rifling patterns and you can sometimes tell a brand or style but CSI type shows overstate that capability tremendously.",
"Most guns push a bullet through a rifled tube by squeezing the bullet and changing its shape. That means the shape of the barrel and shape of the rifling is [imprinted on the bullet]( URL_0 ). The exact details of the barrel and rifling aren't exactly the same from gun to gun (even if the two guns shoot the same caliber and were made by the same manufacturer). So a careful examination of a bullet used in a crime and a bullet shot a few rounds later (because the barrel wears very slightly with additional shots) will show similarities that are different enough from other guns to make the round identifiable.",
"According to some, each gun will leave unique markings on a bullet allowing it to be matched. However, this is controversial. Forensic \"science\" is often done by cops in lab coats pretending to be scientists, rather than the results of an actual scientific process. An Oregon lawyer was incarcerated for weeks because top fingerprint analysts said he was an exact match to fingerprints connected to the Madrid bombing. The Innocence Project has used real science, chiefly DNA, to show how unreliable \"standard\" practices like hair, bite mark, and bullet analysis can be."
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6z49ye | How is software designed for cars and how does it stay accurate for the life of the car (e.g. 10-15 years) without failing like normal computers? | I was riding in my friend's car and they have a digital readout on their dashboard with speed, odometer, engine temp, etc. and I started wondering how the digital components of the car function. I would assume they need similar hardware compared to a computer, but how is the software designed? | Engineering | explainlikeimfive | {
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"They are actually made the same way as normal software, but with higher standards (sometimes) and more extensive testing. It helps that software used in cars has very clear and definitive objectives, as you said, read engine temp, display warning if it is too high and so on, in addition they are build a bit more sturdy as they are, well, built into a car. Basically, simple task and sturdy but simple hardware + software leads to somewhat reliable onboard computers.",
"Grandma can't click on ads, download malware, or play shady Facebook games on a car computer. The inability to significantly change anything about the system means it will likely never need maintenance. The fact that the set of tasks it has to complete will never get more advanced (games with higher graphical fidelity coming out) means the processing speed will never be too slow. Everything is probably stored on flash memory instead of a hard disk drive. HDDs have a lot of moving parts that quickly wear out, but flash memory should be able to last a looong time as long as the battery doesnt die (could the flash memory steal power from the car battery? Someone else might know.)",
"They don't change things, like letting you add apps or reconnect new accessories with cables. They only support a few configurations, and they test them to make sure they work.",
"True \"software\" inside of vehicles is a rather new concept. Vehicles have contained integrated electronics since the mid 1970s. The introduction of electronic fuel injection in the 1980s necessitated an engine control unit (ECU), and mandatory diagnostics in the 1990s made them a legal requirement. The ECU in most vehicles is a controller with a built-in ROM serving as a large lookup table. It takes a lot of sensory data such as engine temperature, intake manifold pressure, airflow mass, exhaust O2 mass, engine RPM, cranking status, fuel pressure, throttle position, etc... and controls things like the spark plug timings, AC compressor clutch, radiator fan relays, air-fuel ratio, fuel injector timings, throttle valve position, cabin blower power, etc... The ECU is also responsible for collecting diagnostic information and presenting it to an OBD/OBDII reader. Many enthusiasts modify the contents of the ECU's lookup tables in order to achieve better performance on fuel-injected engines. Early ECUs were very simple ASICs with no microcontroller component and thus no software to speak of, everything was pure hardware. Modern vehicles have numerous Electronic Control Units controlling virtually every aspect of the vehicle from the radiator fans to the trunk door. Note that I'm now using ECU to refer to Electronic Control Units rather than Engine Control Units, which are now one of many ECUs contained in modern vehicles. As you may imagine, this can and does add complexity to both the original design and subsequent maintenance. A modern vehicle may contain a dozen different ECUs with some ECUs having different microarchitectures than others and thus requiring very different control programs. As for how they're designed, it's no different than writing a control program for a CNC machine, an aircraft, or a power plant. It's done very, very carefully; it's validated by multiple engineers; then it's not changed unless it absolutely has to be changed. Each ECU runs its own program until the end of time. Programs written for personal computers do not undergo the same degree of validation as programs written for electronic controllers that are to be put in moving vehicles. Many design philosophies, such as agile programming, are absolutely verboten for good reason. Despite that, bugs and defects still make their way into vehicle software from time to time."
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6z4qaa | What is the difference between atmospheric, vacuum, gage, and absolute pressure? Visuals and analogies are welcomed. | Engineering | explainlikeimfive | {
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"Absolute pressure = pressure relative to vacuum (0 kPa). atmospheric = pressure of the air. 101 kPa, or ~14 psi. Atmospheric pressure is 101 kPa absolute (101 000 Pa above 0 Pa) vacuum pressure = atmospheric pressure - pressure in the vessel (pressure difference below atmospheric pressure) gauge = pressure in the vessel - atmospheric pressure (the amount of pressure MORE than atmospheric, it is also pressure difference relative to atmosphere). Tyre pressures are measured in gauge pressure. So if you put 32 psi in your car's tyres, you're putting in 32 psi gauge. In terms of absolute pressure you're putting in 32 psi + 14 psi = 46 psi absolute",
"* Atmospheric Pressure This is the pressure that's all around you right now. Air has mass, and because there's a layer some 20 odd miles thick (much thicker actually but the vast majority of the mass is in that first 20 miles) all above you, it exerts a pressure, which is normally agreed as around 14.7 psi, or pounds per square inch. * Absolute pressure. This is the raw value of pressure, if you like. The zero point on the absolute scale is nothing, no gas, absolute zero pressure, otherwise known as a perfect vacuum. You can't get any lower. So the atmospheric pressure talked about above (14.7psi), that's an example of an absolute pressure value, because it's looking at how much more pressure is there than zero. **Absolute pressure is relative to a perfect vacuum**. * Gage (or gauge) pressure This is a pressure value expressed relative to atmospheric pressure. So in other words, as I said before 14.7psi is atmospheric pressure, so that same pressure expressed as gauge would be 0 psi. Gauge pressure shifts the scale so the zero is at atmospheric pressure. If you add 5psi to that, the figures become 19.7psi (absolute) and 5psi (gauge). Make sense? **Gauge pressure is basically setting the zero at 14.7psia**. Why is it called gauge? Because most pressure gauges when you get them out the box, new, will display 0psi. Obviously it's not zero psi, we've already learned there's 14.7psi of air around you all the time. All that'll show is pressure *beyond* that starting point. That's why gauge pressure is a thing at all. * Vacuum pressure. If you got yourself an open gas cylinder, screwed a cap on it, then sucked out 5 psi of air from it, the pressure inside that is now 5psi less than atmospheric. In other words it has 5psi of vacuum applied to it. The same as 9.7psi absolute (because atmospheric is 14.7psi absolute remember). **A vacuum is any pressure that is less than atmospheric**. A vacuum pressure value can't exceed 14.7psi, because that's then 14.7 psi below atmospheric...which is 14.7psi. No more gas to remove beyond that. Does that make sense so far?"
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6z505i | Why do boats have circular windows? | Engineering | explainlikeimfive | {
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"It's easier to make a strong circular hole in something than it is to make a square hole. Corners end up being weak points in metal. If you bump a bit of metal with a square hole in it it'll definitely start to tear at the corners, but a circle has no corners and you can reinforce the whole thing cheaply."
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6z5a3a | Why is a 1HP engine rated at 1HP when a single horse (the animal) is still so much more powerful than that mechanical engine? | Engineering | explainlikeimfive | {
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"1 horsepower isn't the maximum of what a horse can do; it's the maximum a horse can sustain *indefinitely*. Prior to the adoption of engines, horses and cattle were the go-to for mechanical power production, thus it made sense at the time to advertise engines in terms of the number of horses you could replace.",
"The horse in question was a British mining horse -- a dwarf species bred to pull carts through the low-roofed tunnels in mines.",
"The unit was originally used to approximate the power of a horse in a specific work environment. I cant remember the exact industry. it never perfectly matched the power of horse, only the power of a horse doing that specific job."
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6z8x1o | If you had infinite gears, space, fuel, and nothing broke, could a car keep accelerating forever and never stop at a certain speed? | Engineering | explainlikeimfive | {
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"Just a normal car on a road on Earth. No. Eventually the power output if the car would match the resistance produced by the air etc, and you would not accelerate any more. It doesnt take that much power to reach 150mph. But to go to 200 needs about twice as much. To get to 220 take twice as much as that. The fastest cars with ~1000bhp stop accelerating mainly because of air resistance not because they don't have the right gear."
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6z9hfu | How do clocks compensate for the fact that a day isn't a full 24 hours? | Wouldn't they eventually be off and start displaying incorrect times? | Engineering | explainlikeimfive | {
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"A day *is* a full 24 hours, give or take a leap second every year or two. Until we invented atomic clocks, a day was exactly 24 hours by definition. Leap years are a separate issue, they correct for the fact that there aren't exactly 365 24-hour days in a year.",
"There's two kinds of days. A solar day is nearly exactly 24 hours. A sidereal day is 23 hours, 56 minutes, and change. There are 365.24 solar days in a year, but 366.24 sidereal days in the same time.",
"It's such an insignificant amount of time that it's not really noticable. That's why leap years are only every 4 years instead of more often."
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6zanlh | How do extreamly high voltage powerline workers operate on live wires without getting killed? | I was browsing youtube when URL_0 shows up. looks cool so I click. that got me thinking, you can clearly see that the wire is live as when he almost touches the wires with that antenna and you can see the electricity jumping. He then procedes to touch and operate on the wire. How can he do that, and why does he make sure that the electricity is jumping to that antenna? | Engineering | explainlikeimfive | {
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"Workers on the high tension lines, **insulate** themselves from the ground and then attach to the line. This brings them up to the same voltage as the line. Electricity only flows from high voltage to low voltage so if the workers are the same voltage as the line, then electricity won't flow into them.",
"He is not grounded... there is nowhere the electricity can go other than the wire . He is completely safe."
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6ze13n | How is renewable energy more feasible than the alternative if it relies upon rare-earth materials? | Ignoring the environmental impact for a moment, how is something like wind or solar energy a more feasible long term solution for energy resources vs. coal and oil when they use rare-earth materials such as Lithium for batteries? | Engineering | explainlikeimfive | {
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"despite the name, rare earth metals are abundant on earth (with exceptions). a quirk of their chemistry makes their elemental forms almost impossible to find in nature and their ores difficult to purify back when humanity was first figuring out this stuff. thus the name is largely historical. these elements are also (mostly) invested, rather than consumed. when you burn oil, it's not oil anymore, we can't realistically turn water and carbon dioxide back into oil. when you make a battery, 99.99% of the lithium is still there, even well after the battery is dead.",
"There are strategies for renewable energy that don't involve batteries, such as flywheels, or using available energy to pump water up a hill, and then using that to generate hydroelectric during peak usage. Plus there is a lot of active research in batteries. There's a good chance we will invent a better battery soon that doesn't rely on rare materials. Lastly, lithium isn't *that* rare. Even disregarding advances in batteries, there's enough lithium in the world to make all cars electric, for example.",
"1. You spend a lot more energy transporting coal and oil than you would for electricity. 2. Lithium and other chemicals used in battery production are not one time uses. It's not a perfect solution, but it's a better one.",
"Rare Earth metals are poorly named. They're more inconvenient Earth metals. They don't exist in easily harvestable veins like iron or copper and there are no large deposits in Europe or North America But China has a shitload of them! Harvesting \"rare\" Earth metals like neodymium is very similar to harvesting aluminum. You have to chew up large quantities of land and process the rock to separate out the grains you want, then process them. Neodymium is the 28th most common element in the Earth's crust, it is about twice as common as lead and 3/5th as common as copper. It's not rare, just crappily named Lithium isn't a rare Earth metal and isn't rare either, it exists as massive lithium brine fields that need processing. We've significantly ramoed up the amount of lithium we process over the last couple decades which is why battery prices have been falling",
"Every year, new forms of alternative energy and new designs are developed that make solar panels and wind turbines cheaper and more efficient with every passing year. For instance, solar panels have recently eliminated all of the rare elements needed from current designs that are rarer than silver (though many still use tellurium because for now it's cheap, even though it's rare, it's not actually necessary, just cheaper). If we were to fire all the scientists, stop all research, change nothing about our society forever, then you're right, eventually, we'd run out of rare earth minerals, we'd be recycling old solar panels, and hit an energy peak we'd never overcome. But we only need about 500,000 square kilometers of solar panel to power our entire world on current technology, and each square meter of panel needs 20g of silver. That means that a square kilometer needs 20 million grams of silver, and that the planet would need 1 trillion grams, or 1 million metric tons. As a species, we have 1.4 million metric tons of silver in storage though, so while that natural barrier without technological growth would exist, it wouldn't be insurmountable. But, as we said, these technologies change every year. For now, the materials required are adequately abundant that we don't need to consider changing them. Coal, while abundant, has become more expensive than solar, and it's technology is fully saturated, with no new research on how to get more power out of coal than we do now. There's also the important consideration that there are no side effects of solar power, whereas coal generates more and worse side effects the longer it's used."
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6zgo04 | Why aren't power lines in the US burried underground so that everyone doesn't lose power during hurricanes and other natural disasters? | Seeing all of the convoys of power crews headed down to Florida made me wonder why we do this over and over and don't just bury the lines so trees and wind don't take them down repeatedly. I've seen power lines buried in neighborhoods. Is this not scalable to a whole city for some reason? | Engineering | explainlikeimfive | {
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"Hi! I'm actually an estimator for a large electrical contractor, so I think I can comment on this pretty accurately. In large cities you're correct, there's a reason you don't see power lines draped across buildings in Manhattan. And even more affluent neighborhoods will have the lines buried. But there's one enormous reason that ALL lines aren't buried: cost. Now this answer had been given, but there's some details you might find interesting. The first is initial installation. Most underground cable at distribution voltage (4kV to about 35kV but that definition fluctuates) is installed in buried conduit, and basically every construction company can tell you that digging sucks. Even with a geotechnical report, some areas of the country are a total crapshoot as to what you'll find 3' down. In parts of VA it might be the water table, in parts of ID it might be lava rock. Usually the ground is either too soft and the hole/ trench doesn't hold up, or too hard and it takes forever to dig. Either way that means money. Digging also isn't very pretty, and most places have lots of rules regarding how you dig, when you dig, what you do with the spoils (dirt you dig up) and what you have to do to clean up afterwards. If you dig in the middle of nowhere this isn't bad, but God forbid you're in the rich part of town. Then on top of all this money you spent following the rules you now have to spend another big pile fixing landscaping (ya know that bush you dug up? The fourth one from the end that was almost dead? Yea, that was my great great grandmother's golden bush of infinite happiness! You owe me $5000 for it! No an almost identical bush isn't good enough!). Not too mention underground conductor is more expensive. The conduit it goes into is an added cost, but it pales in comparison to the price difference between underground wire and what you'd spend on overhead wire for a similar amount of current. Additionally this wire has to hold voltage that is desperately trying to release itself into the surrounding earth, so if you nick it when pulling it in, or damage the insulating jacket in some other way, congratulations you get to pull that wire in again! Because that electricity will arc that gap and the line won't work. If that happens later on down the road, it's also much more difficult to diagnose and fix. With an overhead line, you can usually tell what's wrong (hint: what parts that should be in the air are now on the ground?) But with underground lines you have to drag out the thumper. The thumper is a piece of equipment that applies a voltage to a line. The voltage goes higher and higher until it arcs through damaged insulation and makes a thump sound underground. Then a worker has to locate the fault (damaged piece of line) by walking the route of the line and listening for the thump. Now newer equipment is fancy enough to help you get pretty close without much work, but there's still a lot of experience and good luck to finding the fault quickly. By the time you add in the cost of the thumper, the crew's time to actually dig up and fix the line, and the outage time for the customers being fed, you're taking a pretty penny. Not to mention, mother earth is not kind. If you go to more remote places you can find lines that have been around 60 or 70 years. Not going to find many underground lines that old. There's also the fact that adding capacity to overhead lines is easier in most cases, but that's a bit too nuanced for this post. And finally, electricity is pretty easy to move overhead. Water, oil, gas, and sewage are not. In most places the ground where it would make sense to bury power lines is *crowded* and most of those companies don't want high voltage anywhere near their stuff. Hell they don't even want the pole in the ground because most of the poles are grounded. But any company that will even let you bury near them is going to, at minimum, want an inspector on site while you build, and you get to pay his wages while he's out there. Most companies would rather take you to court than let you build though. So most of the time, high lines are where it's at! Edit: All of my experience is in North America. I don't know why Europe manages to get everything underground, but as I mention below I expect its a combination of denser urban areas and government regulation. Some places in the US are experimenting with that, but others probably won't for quite some time. /u/thekbob linked a great study here: URL_0 That goes a lot more in depth about why underground electric utilities are better at some things, and still unlikely to catch on in the states. Also, I may have given enough information for some really dedicated soul to deduce who I work for. For the record I am not an official spokesperson for any company, any opinions expressed here or in other comments are solely my own and do not reflect the opinions of any other entity.",
"I work for a power utility contractor and we hear this a lot. Building new developments with underground power lines is easy. Before you put up the buildings, pour the asphalt for the roads, and plant the lawns, you can plan it all out and dig trenches to bury the electrical lines. It looks nicer, it's easier, and anyway, you're already digging trenches for water, sewer, gas, cable, etc... so laying another set of conduits in the same trenches isn't much additional cost. Look at most new master-planned housing developments, and this is how they do it. However, when you have a city that's already standing, buildings intact, streets covered with traffic 90% of the day, and water, gas, sewer, etc already crisscrossing underground, it becomes a lot more difficult to do. It involves getting easement rights from just about every land owner whose property you cross. It involves digging up existing streets, sidewalks, lawns, etc. It involves blocking traffic for several days to lay a couple hundred feet of cable. And then every transformer, switch, and other bit of equipment requires a bigger hole to be dug (some as big as 12'x15'x8' (4m x 5m x 3m ish for you metric folks). These require access manholes on the surface, vents, sometimes above-ground cabinets. More easement rights for these. Nobody wants a manhole in the middle of their lawn. So it's expensive. It's annoying to everyone in the area while the work is taking place. And while there are clearly benefits... there are downsides to underground power too. Vaults fill up with water and need to be pumped before workers can access them. If a segment of cable goes bad, it's much more difficult to test for the fault, pull it out, and replace it. And all of this work requires, again, traffic to be blocked, streets to be dug up and re-paved, all of the same hassles as installing them to begin with. And then consider the cost of replacing an existing overhead system with an underground one. Who pays this? The city? Fat chance. The power company? They're shelling out millions (billions) just on regular maintenance, hard to justify the cost of a project like this for dubious material benefits. The homeowners? Never gonna happen. And despite all this, it still does happen. Little bit by little bit, neighborhoods are getting converted across. Mostly it's suburban areas (it gets exponentially more difficult in tightly packed cities). Rich communities, for the most part. But to convert the whole country, even a whole major metropolitan area like Miami... would not be feasible, at least on any timeline not measured in centuries.",
"Burial is expensive and not always practical. For instance, Florida is crisscrossed with waterways, so not only would you have to dig through the dirt you'd also have to sink the cables underwater, which is insanely difficult and expensive for every feeder line. Plus there are specific laws that cover underground burial, which are different from the laws covering aerial cables, because most people or businesses do t need the airspace but do utilize the land.",
"Underground powerlines are only a solution for one problem. They mostly make sense when in a large metropolitan area where you've got conduits, and concrete/metallic sewers running throughout each building. Suburban areas have dirt, and are much farther away from switching stations, in order to replace the entirety of lines from above to below grade would require a tremendous amount of money, research of soils, and construction work to not only dig trenches, but also get civil utility planners out there to secure the ground space. For reference in Bellevue, WA; when replacing the power lines from above to underground for my apartment building, I needed to pay over 100k to service 4 buildings on the street, just for inspection, permits, and engineers. I then paid another 150k for the equipment, and the actual work cost another 60k, which required, yet another permit because it was in a city right of way. Since I was doing all that work in this area, I had to pay the entire bill. The work that they did afterwards was also pretty ugly, even though the lines were moved underground they still had to create a pole that stuck out from underground that fed to the existing buildings, because they weren't originally built with underground powerlines in mind. Update: Asked local power company and it usually costs nearly $1,000,000 per mile of power lines if you want them dug underground. Edit: 4 buildings not units.",
"Some good answers but I'll add my two cents. The answer is actually quite complex, and you actually touch on a few points that dont talk about reliability. Source: Am utility engineer in Planning now and was designer for the distribution network. So true ELI5: Cost a lot of money, presents new types of challenges for future, causes issues when the power does go out, and no one wants to pay for it. And now the longer, probably still 5 year old version. Just a quick note for those not in the loop (after I wrote this whole thing). OH = Overhead. UG = underground. 1.) The biggest is typically cost. Burying a line is a ton more expensive. You need sand backfill, have to open the trench somehow which usually involved a hydrovac (especially in town) and pushing under existing roads. Plus underground wires need to be bigger than OH wires for a variety of reasons. Mostly capacity. A wire in the air has a lot of surface area and is exposed so it can cool a lot better. A wire in the ground is either in duct or direct buried and gets less cooling effect, plus there is an insulating material on the cable, further reducing it. 2.) Getting location to 'convert' from OH to UG can be sometimes impossible. The location of switching points (take those big green boxes the police hide behind to catch you speeding) are massive. You need lots of those, plus underground pedestals, transformers, convert everyones house from OH to UG. 3.) Any new customers, new growth or upgrades are a lot harder. Wires in the road in front of your house could be old and designed when no one had cell phones, computers, 17 TV's and AC. Now, even thought their more efficient, electrical use is going up. Add in electric cars and other components and the amount of work to rebuild an UG line for capacity and OH line is quite a bit more effort. 4.) Restoration is a lot harder. So sure, the power might stay on (assuming it doesn't flood, it has happened and they shut the power off anyways) but when there is a fault it is a lot harder to find. For underground we have lots of ways to detect faults, but worst case you dig up the whole cable you know has failed until you find the break. On OH it is a lot easier, you drive along until there is a pole on the ground. So while the reliability is up, it can translate into a longer outage. Most utilities are measured on two metrics for reliability. SAIDI and SAIFI. One is the standard average duration (so 30 minutes) and one is frequency. UG usually has a higher SAIDI and OH might have a higher SAIFI. 5.) Cost, everyone bitches about costs as it is. I'd suspect a 100% increase (depending on what all got buried, did we go back and replace all the old OH or just new to UG) to your electric bill to accomplish this. 6.) Electrical characteristics. This isn't as easy but USUALLY UG cannot carry as much, for as far, so in town it isn't an issue but rurals can be a problem. 7.) Some components that we have for OH are a lot harder to get or a lot more money on underground. Certain things like regulators we only stock OH ones. So you have to be creative where we put those pieces as it is. To specifically point out your question about burying in residential subdivisions. There are really three major components. 1.) The disappearance of the back alley. Most OH lines were run in back alleys. Most new URD's (Underground residential developments) no longer have back alleys. 2.) It is for aesthetics, either driven by the municipality or the developer themselves. 3.) Cost, since the ground is already all dug up to put in gas, telephone, sewer, roads, and foundation. Plus no one technically owns the homes yet, so no one can complain about placement of facilities, it is quite a bit cheaper than browfield construction. Hope I cover it, I am sure there are variations depending on region and my area is not prone to hurricanes, but I'd be happy to answer more questions or discuss differences further.",
"Cost. It costs about ~~10~~ 5 times as much to bury power lines than to hang them overhead. Flooding also poses a risk to buried power lines, so that wouldn't be feasible for places like Miami, which is only 6 and 1/2 feet above sea level. So when comes specifically to a hurricane, when you're dealing with both high winds and flooding, there really is no guarantee that people will not lose power whether the lines are above or below ground. Edit: correction based on sources in below comments",
"Planned developments/neighborhoods these days are often built on undeveloped land. They're going to have to dig for water/sewer anyways, and can lay electric/phone/coax/fiber at the same time. Since the developer usually owns the entire site to begin with there are minimal right of way issues. Cities have generally been around much longer, and are not developed all at the same time with a predetermined layout. This leads to lots of right-of-way issues and people with existing structures get annoyed when you try to dig through their properties.",
"As this is my bread and butter I will answer however I won't go into too much detail as it will probably be buried. If this does end up gaining traction I will go into more detail or you can PM me. First is cost: Typically the average cost to bury a Main line primary feeder is about 3 million dollars per mile. This is just the Overhead cable not necessarily all the devices that allow it to go that far nor does that include secondary (which powers things normal consumers use like your house meter, street lights, traffic control signals and cell site equipment) Second is age: Please remember that in most \"established\" places electricity has been around for a hundred+ years and most anything pre 1990(excluding townhomes and certain subdivisions are fed overhead and to change it would be to require every homeowner to change their house configuration to go underground) and in alot of other places most of it used to be farmland and which brings me to my next point. Space. The amount of space need for the distribution system is mind boggling. Imagine Time Square in New York City. All the pretty lights and signals and billboards and stores are powered by something right? Well underground cables, but the amount of cable needed to provide that is sizable and so is the conduit that houses and protects the cable and the manholes that house the devices and allows people to work on them. Not to mention everything else in that street such as water, sewer, gas, fiber, cable, all of which also have mains and services branched off of the mains. Finally ease of repairs due to normal maintainance and damages. If we have a fault and even if we know it is between two manholes that are 200 feet apart. Well how do we know exactly where and how do we fix it. Tear up the road, pull the cable out an put a new span in? What if the conduit collapsed and we can't pull the new span and now we need to dig the entire road up and block traffic to fix it? Again OH is easier to see, easier to fix, easier to maintain and overall much more cost effective. However all that being said with better standards, materials, and technology putting it underground is becoming a more competitive option. Hope this helps!",
"Everyone who is saying that overhead lines require more maintenance are wrong. They last longer than underground lines unless you get a lot of tornados. Water ruins those underground lines quick. Also, it is ten times faster and cheaper to repair overhead lines. The only time underground is really beneficial is in densely packed cities where space is at a premium.",
"This fact hasn't been highlighted enough: The USA is huge! From Wikipedia: Area of the US: 3,796,742 sq miles. Area of The Netherlands: 16,040 sq mi Area of Great Britain: 80,823 sq mi Area of Germany: 137,903 sq mi The US is about 30 times bigger than Germany, 47 times bigger than Great Britain, and 236 times bigger than Holland. It is WAY cheaper to string lines overhead than to bury them underground. Many Europeans don't realize how big the US really is until they try to travel here. Burying the lines just isn't cost effective in much of the US.",
"Buried (No Pun Intended).. I don't have an ELI5 answer, but there is also an Engineering hurdle most people are unaware of. You can't just \"bury\" the cable without causing problems with the transmission of electricity, and potential damage to the cables themselves due to soil having wonky thermal properties. URL_0 \"Who could have foreseen that an electrical power engineer would need to be an expert at soil physics? Such knowledge is becoming increasingly critical, however, in the design and implementation of underground power transmission and distribution systems. Why? The issues are simple. Electricity flowing in a conductor generates heat. A resistance to heat flow between the cable and the ambient environment causes the cable temperature to rise. Moderate increases in temperature are within the range for which the cable was designed, but temperatures above the design temperature shorten cable life. Catastrophic failure occurs when cable temperatures become too high, as was the case in Auckland, NZ in 1998. Since the soil is in the heat flow path between the cable and the ambient environment (and therefore forms part of the thermal resistance) soil thermal properties are an important part of the overall design.\" Attempt to simplify: Power transmission generates heat. If you have cable exposed to the air, convection mainly solves your issue as there is plenty of air to help dissipate the heat and the overall environment is more predictable. If you bury the cable, the soil acts more like an insulator and can trap heat and damage the cable and/or make power transmission less efficient. This is compounded by the fact that soil is not the same everywhere and can be in various states that cause more issues (too wet, too dry, rocky, salty, sandy) and makes the situation less predictable and more expensive implement, service, and replace.",
"It is expensive to install and expensive to maintain, especially if the city was built before household electricity was a thing. It is often cheap just to fix and replace overhead lines. Also, natural disasters can damage underground lines as well, and it is much harder to get power back up again.",
"In addition to all the other answers given here: high voltage AC lines loose a lot of energy to the environment due to parasitic/stray capacitance. Think of the wire as one plate in the capacitor, and the earth as the other plate, with the air and other insulation as the dielectric. Also, a capacitor exists between each pair of adjacent lines. These capacitors charge and discharge once every half cycle, or 120 times a second in the US and 100 times a second everywhere else. So even minor losses associated with the charging and discharging of the capacitors will contribute significantly to power loss. Note these losses are greater with worsening dialectic. That is, worse insulation increase losses. Grid operators need to account for additional losses from a humid day. To give a quick overview, a capacitor can store more charge when you either increase the size of the plates (area in parallel with other plate) or move the plates closer together. The size of tje plates isn't going to change: the wire needs to run for the distance it does, so the length of wire being in parallel with both the earth and other wires isn't going to change whether the wires are suspended or burried however, if you stick the wires in the ground, you've now brought one \"plate\" of the capacitor much closer to the other: the earth. Additionally you'll likely need to take up a smaller footprint, so you'll likely need to bring the wires closer together as well. Of course, you'll need to use really good, really expensive insulation, but it'll be very difficult to overcome the additional losses of sticking the wire in the ground. Note at distribution voltages (under 40kV) this isn't really an issue, but at transmission voltages (above 100kV) it becomes a pretty big one. This is why you may hear about high voltage dc being used for transmission links where a line needs to be burried or put under water since you don't need to deal with the capacitive losses.",
"As said cost is high. Another reason is safety. Look how many times cable or phones went out of service for a area as someone dug without marking or something was missed. Now imagine that happening with very high powered lines. Repairing lines that are up in the air is also easier than in the ground. Easy to find the issue and repair. If it was under ground they would need to dig before getting to it and that adds more complexity.",
"FWIW where I live in DC the power lines are buried and once in a while due to heavy rain some underground box gets flooded, shorts due to environmental wear and tear, and the power cuts out. Point being that burying cables doesn't solve all problems and can introduce others. My FIOS line never has that issue, being above-ground.",
"My dad has been a lineman in Florida for about 35 years (he's actually out restoring power now), and I've asked him this question. He touched upon many of the topics in this thread: money, logistics, etc. My dad is also very much an old school lineman like his dad. To him, going up on a pole is how \"real linemen\" do it. At his company, the less-competent get stuck troubleshooting underground problems. Despite this, we are the only people in our rural neighborhood who have underground lines because my dad put them in when our house was built. We still loose power when everyone around us does because the feeder lines get damaged.",
"Hello! My job is to actually do exactly what you are talking about! I work for a firm which does the design work behind decommissioning residential power distribution and rebuilding it underground. The short answer to your question is cost. Much of the existing power infrastructure in certain parts of the US is very old. Many times the poles we scrap are from the 50's or earlier, have 'worked' so far so there hasn't been a need to spend on a huge overhaul. The cost of these projects runs into the millions of dollars and involves huge teams of people to manage property rights issues as well as the design, construction, management of the projects. It gets big and expensive quickly, and where the returns aren't really seen for years most of the time, it hasn't been as big of a priority. Now, however, there is a desire to improve reliability and decrease future maintenance costs by improving the grid via underground transmission and distribution.",
"As someone who works in this trade and builds overhead and underground lines, I can ensure you having ugly wires above your head is alot better then underground. Underground takes twice as long to trouble shoot issues and twice as long to repair. When things are built underground it's normally because the contractor or customer is paying for it, or it's existing and more practical, like in a downtown area where it's harder to get equipment and big trucks in to set poles. That being said, if anyone is reading this I'm going to take the time to inform everyone, just because a wire is down on the ground does not mean it is dead. It's not like the movies. Sometimes it just sits there and it won't move a milimeter and it won't make a noise. If you see wire down stay away and call 911. If you are on a job site and have a dig in, just because you separated the cable does not mean it's dead. Stay safe hope this answers some questions and feel free to ask me anything.",
"One. The power lines (in town high voltage stuff) isn't fully insulated. (pretty sure the distribution stuff doesn't have any)This is why trucks and cranes, balloons and hang gliders will create an arc when they touch them. It's not needed to fully insulate when it's high in the air, and it's easier to tell people to stay away. Burying the wire would drastically increase the size of the cable/wire, because you would have to fully insulate. Two. there's always water in the soil. In order to protect the people walking on the grass abouve, the wire would have to be fully insulated, and the conduit that is needed to protect it would also have to be water proof. Three. Mentioned in point two, the wire would have to be in a watertight conduit. The conduit would have to be large, (heat dissipation) . I wouldn't be surprised if the conduit was as big as 3~5ft for one line. There are three lines for every run. This makes for a bigger allocated space than water mains. Might be bigger than sewers. Four. You have to dig the trench. That means excavators, and trench boxes, which need to be installed and removed as you go. (for the workers safety) This is a long process. Time is money. more of a bonus point, than a genuine point. Five. If anyone digs, they will hit utilities under ground. Murphy's law. It doesn't matter if you have gps and lasers and drawings, and sonar or xrays.... Somewhere, sometime, someone digging a trench for a water line or internet or something will hit something that's already there. Having powerlines underground, means you could hit the powerline.",
"The answer to any \"Why doesn't the U.S. do *x* with utilities is almost always that we are a massive country with a massive population spread over a very large distance. Any simple solution becomes much more complicated when you factor the sheer logistics of doing it on the scale necessary to serve such a large population over such large distances.",
"Lineman apprentice here. Much easier to do the routine maintenance that occurs daily versus preparing for the one or two hurricanes that come in a year. Wire gets pulled down in a storm, you kill it at a transformer, splice the wire back together, fix the pole and turn it back on. Underground wire is safer in a storm but it's hard to work on every other day of the year",
"I live in the northeast and there are two reasons: cost and frost. It's mostly rural roads here and burying all that wire is going to cost a _lot_. And then there's frost heaves, when two areas with different soil composition freeze, there can be a big bump in the ground that forms. These frost heaves will gladly tear a road to pieces and I'm assuming stress or even shear off any cable you put down there. The solution is to dig a whole lot deeper and fill with gravel and stuff, which goes back to cost. Coincidentally that's why the roads here get destroyed by a single winter, and they could be fixed using the same thing except the cost of digging up and redigging the road beds deeper would be way, way too much.",
"I live in South Florida and was impacted by Hurricane Irma. Our power lines are buried but the power went out because the transformers and the electric substations are above ground.",
"My city has partially converted to underground, but not completely. A few towns over everything is above ground, and the other direction is the opposite. I don't think America is as homogenous in this as the images make it seem.",
"Most infrastructure questions in America come down to two things: 1. It's a big country. Geographically big. Building things in wide open spaces gets expensive fast. 2. We have a weird relationship between private and public. Private companies try to save money where possible. Public purses are also stressed.",
"There was a time when the US built dams, bridges, interstate highways, and all kinds of infrastructure. Now, we can't even afford to maintain them. There is no longer money available for the common good, because it might involve slightly decreasing the wealth of the plutocrats. It all started with Reagan. You want to see rational public engineering? Go to Europe and Asia. The US is a backwater.",
"After Hurricane Andrew, multiple counties started implementing 3 things. 1. Cement/concrete brick made houses with aerodynamic roofs 2. Power lines underground 3. Better drainage systems In Polk County, because T-storms always form over us and would take the power, majority of our lines are underground, but for smaller towns, it costs WAYYY too much to complete the jobs.....ps im sitting in the dark for a week.....send electricity plss.",
"Do you have the money to pay to rewire the entire grid? that's what I thought :)",
"Mostly, the US is just cheap. No one wants to pay taxes, so you have shitty infrastructure.",
"$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ Most times if lines are undergrounded, its a newer area and the developer of the area and/or the residents have agreed to pay extra for the service. They're also harder to fix if something does go wrong.",
"They are in some places. Where is grew up they started the transition about 10-15 years ago. I was quite young,. It is remember all the commercials telling people to call 4-1-1 before digging anywhere because they could hit power lines and Darwin themselves.",
"No one will ever see this comment but it is because (well at least for New Orleans) if you put the power lines below ground they would be destroyed if we ever had flooding like the one right now. Also the ground very literally moves here. Like we are built on swamps and it would slowly move and break over time.",
"Cost. Densely populated areas (e.g. city centers, concrete jungles) have manholes and cabling underground. Underground cabling is also more reliable in terms of not being susceptible to trees landing on them during storms and such. Reclosing (Protective function) on distribution lines with underground cabling is typically not performed due to this as an underground cable fault is not the type that will heal itself like effectively burning off a tree branch.",
"Very simple answer. Cost and logistics of moving existing lines underground is the reason. New developments typically have underground feeds, but not older ones. The cost of moving them after the fact is very high, plus three are other considerations, like designing along the existing gas, water, sewer and other utilities underground. The U.S. really needs to invest in their infrastructure, and improvements to the power transmission system should be a top priority.",
"As a mechanical draftsman who has had many opportunities to talk to electricians, I think one of the big things is the heat loads. Those lines give off a lot of heat which would obviously dissipate easier in open air than in the ground. Plus then you'd likely have to encase it in conduit and whenever something goes wrong you wouldn't be able to do a visual inspection, but would rather have to run system checks, followed by excavation, then reforming, tamping, etc. A lot of science goes into how those services stay put underground. My guess would be that the amount of repair needed to keep them in the air is offset by the huge cost of installation and maintenance of below-grade services.",
"I work for a large electric utility in a major US city. A lot of the reasons why we don't have underground everywhere have been presented already. Now, the reason most powerlines are buried in a large metropolitan area has a lot to do with how it looks, but it also has to do with load. The system we use in the downtown area is nothing like the overhead system as it was designed specifically for a load dense area (a lot of electricity in a small area). Looking at pictures from before the underground system, the poles looked like a bird's nest with all of the wires and this was back in the 1910s. Our underground system is one of the oldest in the US dating back to the 1920s. To put things in perspective cost wise, in my area the average home has an electricity bill of $150-$200/ month. In the downtown area, it is not uncommon for customers to have a $500,000/ month bill with some customers exceeding $1M/ month. Not only do these customers pay enough to support the cost of the system, they are also in industries that require uninterrupted power. These customers are typically high rise buildings. A few years ago, we had to recable about 2 miles on one feeder that cost $5M. While this sounds quite expensive, the job payed for itself because it was supported by the customer base.",
"I work as a utility arborist contractor for a major utility and hear this a lot. For one, To bury lines requires extensive engineering to take the existing utilities and put them underground. This requires locating countless other utilities and pipes that are underground and working around them. Lots of these also need replacing, which then becomes a major project as municipalities try to fix these at the same time. Digging is very expensive; its much quicker and expedient to put up a new pole. Only in new developments is it worthwhile to put in underground lines as the ground is still broken and there is nothing else down there that needs to be worked around. Also, trees have roots, and for property owners who don't like the way utilities trim around trees on routine maintenance (cause they think they \"butcher\" trees, digging tunnels through roots will invariably kill trees faster. Second, If something were to happen to the lines, such as a tree root or something breaks the insulation and water gets in, the time to repair and restore power is much longer than raising a downed pole and putting in a line splice. As bad as power lines are in a storm, it is very easy to locate the outage location (often a downed tree) on an OH system and repair it than it is to bring an excavation crew to dig up a faulted UG cable. To be fair, underground utilities SHOULD be more reliable than above ground, but the cost of installation + the cost of repair should something go wrong is the primary reason why we haven't put everything underground.",
"First you have to understand that there are two types of power companys, coops and utilities. Coops are member run and owned; so each member has a vote in how things are run. Utilities are usually city owned business' that sell power, water, and gas; while coops only sell power usually. Another important thing to understand is that underground power is a newer thing. If you notice any new housing developments going up in your area you may notice that most of the power in the area is underground. It's because of the cost. It's cheaper to place underground in New areas then it is in older simply because these are new and there isn't a need to tear up each existing members yard up. Keep in mind that even though the company may do all the work we still pay for it all due to the hike in power prices they would require to pay for the workers and materials. The cost for these upgrades will always be placed on the co-op membership since technically the membership owns and runs the business and the majority of power company's in the US are co-ops. On the otherside we have Utility companies. You'll actually find that in a lot of places, especially here in Minnesota, will install new underground utilities as needed when they tear roads up to redo them. Again this is done on the city side so is usually handled when you get the old city managers who have run everything out and new ones in, that's when it began in my area at least. Utility companies who are city owned simply have to fit it into a budget they have. And as we all know government and budgets don't ever get handled in a way that's bennificial to the local population because of politics. So for the most part it is simply because your neighbors don't want to pay higher prices to cover the cost to set the new system up and on the otherside you have politics that prevent things from being done."
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6zgq94 | Is it more fuel-efficient to drive a car fast so less total driving is involved and the engine runs for a shorter time or is it more fuel efficient to drive it slowly so the engine consumes less fuel? | Engineering | explainlikeimfive | {
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"Engines have an rpm efficiency range. No matter the speed you're going it's most efficient to run at a certain rpm that changes with every type of motor. We use gearing to keep us in this range as much as possible. It's most efficient to run continuously at peek performance range then to be constantly starting and stopping. This is why we get better highway mileage than city.",
"It depends on the specific car, but generally peak fuel economy is achieved around 50 miles per hour or so. You get more fuel efficient as you get faster, until you go *too* fast and it takes much more fuel.",
"Very generally, moving slowly is more fuel efficient over the same distance. If you've ever put your hand out a car window, you've felt air resistance, also known as drag. The faster the car goes, the more of its power is used to push against drag instead of simply moving forward. And the more power it needs, the more fuel it uses. Starting a car moving from a stop is more work than keeping it going, so you don't want to slow down enough to stop if you can help it. As long as the car is given enough energy by the engine to keep it from stopping, it will use less fuel at slow speeds.",
"I deal with this dilemma almost every day. Assuming really bad traffic for the commute home, I often have these options Route A is 13 miles and takes 50 minutes. Route B is 16 miles and takes 45 minutes. Which is best for gas?"
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6zhg2h | How did people from old times made hanging bridges between two mountains, unlike now, they didnt have helis so how did they manage to tie a rope from one end to another? | Engineering | explainlikeimfive | {
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"get a rope from one side to the other. if you can walk a rope from down the valley and up again. do that. if you can fire an arrow with a string from one side to other do that. use string to pull rope, use rope to pull cable. if you can fire a rope with a gun from one to the other, then use rope to pull cable. this is still the most common method today. the Navy uses it commonly when transferring supplies from one ship to another while at sea. URL_0"
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6ziaak | What is the difference between 4 wheel drive and all wheel drive? | Engineering | explainlikeimfive | {
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"4 wheel drive means the front wheels are powered together and the rear wheels are powered together or they are both powered together. cars/trucks with 4wd can generally turn it on or off since using 4wd can be disadvantageous in certain cases since 4wd effectively locks the front wheels to the same speed which is bad for turning. all wheel drive means that each wheel is powered independently and any combination of them can be powered at any given time. this system is active all the time. 4wd is generally superior in off terrain and at low speeds, it also is more reliable and has better mpg."
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6zjrip | Virtual Address Spaces | Why does all code begin at the same "fixed address for all processes" in a computer? What exactly is a virtual address space? The figures I've seen of this don't really help me understand. | Engineering | explainlikeimfive | {
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"ELI5: Processes can't directly mess around with the RAM the computer owns. The OS gives them a fake RAM to play around with as they please and behind the scenes manipulates the real RAM and prevents conflicts with memory the program cannot touch. The fake ram is called \"virtual memory\" and the addresses in it is the \"Virtual address space\". Eli10: All programs think they own the entire memory, apart from the little bit the OS reserves for itself. that means that in a 32bit system every program that you run thinks that it has unlimited access to 4Gb of RAM. The OS code is located on one end, the program code on the other, and then the actual memory the program manipulates is in the middle (along with some library functions and predetermined data the program needs). So, there are two things at stake: virtual memory and physical memory. The virtual memory is what the program, and by extension the instructions read by the cpu, works with. as stated, all programs think they own the entire RAM. They all start their execution in the state that every address, from 0x00000000 to 0xFFFFFFFF is under their control (barring the section the Kernel owns and is off limits). So if programs A and B both claim memory loction 0xDeadbeef they are both granted the request. This is called the virtual memory. The OS gives programs an \"virtual\" RAM, an imaginary memory they can do whatever with and not fear that they are messing with memory addresses other programs are using. Obviously programs don't own the entire RAM. The CPU has a special chip whose job is to translate from the virtual memory space into the physical memory space: It takes the address the program wants to access and translates it to the address the program actually is storing data. The program might request 0xDeadBeef and the CPU returns whatever is in 0xColdMilk"
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6zoyck | How do analog synthesizers work? | How do analog get their sounds and how does attaching quarter inch cables from input to another input change these tones? | Engineering | explainlikeimfive | {
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"Oscillators in the analog synth produce waves with specific shapes (sine, sawtooth, etc) using electrical energy. You can combine, mix, and match these waves by patching in, and the variations in tone and shape produce that distinctive sound when amplified. You can also futz with the wave shapes using sliders to adjust the ASDR, or use filters to cut out certain parts of the shapes (these are the harmonics). An analog synth has oscillators which generate these shapes raw (resulting in organic and unique sounds particular to that oscillator and its tuning), whereas digital synths play back the shapes using mathematical functions which are much less affected by the entropy and surroundings of the equipment.",
"Different sound waves, created through different electrical impulses (raw electricity), are routed (using these cables) through different filters, effects, wavetables, modulators to create dynamic, complex, sounds. Source: in my free time I use synthesizers to make filthy clean sounds."
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6zpbqb | What are the little holes on plugs for? | Engineering | explainlikeimfive | {
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"The little holes on the end of the prongs match up with little nubs inside the outlet. These help hold the plug in firmly and prevent it from working its way out of the socket.",
"They're detents to keep the plug in the wall The socket has a pair of blades that the plug slides into. At the deep end of each blade is either a bump or a flap that matches up with the holes on the plug to keep them from pulling out, unless you pull firmly on the plug"
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6zsk7o | Why are the zero to 60 times such an important piece of data in the car industry? | I've always wondered why this specific piece of information is of such interest to practically any medium that devotes itself to automotive reviews. Why is this so relevant? How and when did this come about? | Engineering | explainlikeimfive | {
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"It came from a man named Tom McCahill who was a road test editor for a magazine in the 40's. It became \"normal\" just as sort of a standardized test in that it was a good comparison. URL_0",
"I've only ever thought it some use when comparing performance vehicles. As a demonstration of acceleration only, I think it may have come from drag racing days before actual dragsters were really a thing, or from the days of stop light racing in the 50s, 60s and 70s (the 60s & early 70s being the hey day of muscle cars). You would probably notice the 0-60 figures are rarely listed for \"shitty cars\" (for want of a better term). For example I would be surprised to see a review of a daewoo matiz, or similar, listing the 0-60 unless it was for a laugh (0-60 in 28s, amazing, it tore my face off\" - Clarkson). Tldr: probably comes from the muscle car era. E: all praise u/HarrisJB78, the only one with what seems to be the right answer of the 0-60 origins.",
"60mph is your \"normal highway speed\" so it measures a vehicle's ability to accelerate to freeway speeds and safely merge with traffic. Because of this, it's become a pretty standard measure of performance.",
"It's a measurement of *acceleration*. Why a time over 0 to 60mph? the max acceleration varies a lot depending on your current velocity, so instead of giving a number of acceleration a time as a measurement of average acceleration when increasing the speed from 0 to 60 is more describing. Why stop at 60 and not 50 or 100? Probably because 60 mph is very close to 100km/h which is used in metric unit countries."
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6ztmqx | How are CD players in Cars made to not skip when the car goes over bumps? | Engineering | explainlikeimfive | {
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"\"No skip\" technology uses a memory buffer. The CD player can read and store a few seconds of music ahead of the current time. If the CD skips, it just keeps playing from the buffer instead of directly from the CD. Meanwhile, it keeps reading from the CD to \"catch up\".",
"It wasn't always so - when they 1st came out things were far form perfect. There's a few things they do - the mechanism is mounted on little rubber anti-vibration mounts / springs inside the unit, the CD is often read at 2x or faster and/or a few seconds of data is buffered in advance so it has time to pick up where it left off. Also they gradually improved the control software routines that move the read head so it doesn't fly off wildly when jogged and can pick up where it left off much faster."
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6zucxs | Why are there airbags attached to seat belts of older aeroplanes but not in newer ones? | I recently flew in a fairly old B777-300, and there were large, heavy [airbags]( URL_0 ) attached to the right seatbelt. However, when I flew in newer aeroplanes there weren't visible airbags (I didn't even know the clunky thing *was* an airbag until I read the little warning tag) on the seatbelt. Where are the airbags most often located nowadays, and why the change? I tried to look this up on Wikipedia to no avail, except for the picture ): | Engineering | explainlikeimfive | {
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"I suspect you flew in business class, or in an economy seat where there was no other seat ahead of you. Often seatbelts will have airbags (or a chest strap) if there is a hard surface directly in front (rather than the top of a normal economy seat, which is \"soft\" enough), or if the distance between seats is too great to brace against the seat in front. This mostly happens in fancy seats."
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6zvz76 | Why is is cheaper/more efficient to collapse a skyscraper than take it apart? | I see videos of high story buildings being collapsed instead of just taking them apart. Why is this the chosen way of doing it? Isn't there a lot of risk involved doing it this way? | Engineering | explainlikeimfive | {
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"The general answer is that it is faster and cheaper, which most people prefer, but leave it to Japan to do it in an interestingasfuck way: URL_0 I think in time this will be a preferred method as the cost of building materials keeps going up and this allows a lot more material reclamation. *also cleanliness. demolishing is a serious mess and fouls the air, not something most people like especially when they are older buildings.",
"There is no easy way to take them apart without damaging their structural integrity, risking an uncontrolled collapse that would be far more dangerous. Also, it is just a lot cheaper to let gravity bring all that material down to you rather than going up and getting it.",
"They are built extremely strong, so it takes a great deal of time to disassemble, especially to break up the concrete. (Have you seen how long it takes workers to jackhammer the road for just a small sewer replacement project?) Collapse does an effective job breaking up the concrete into chunks in seconds.",
"It's unsafe for the workers that are disassembling it as it will make the skyscraper unstable. Here's an analogy too to help you understand: If you have a jenga tower, is it easier to take down every little piece one by one or just knock the tower down, collect it together and clear it."
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6zywh8 | How are the bumps on the side of highways made? The ones meant to wake you up or make you pay attention. | Engineering | explainlikeimfive | {
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"They are usually milled or rolled. For milled rumble strips, a machine with a milling attachment (a drum with teeth on it) comes along and cuts the grooves into the pavement. The drum moves up and down as the machine travels along the road, so it makes a lot of small depressions instead of one long grove. You can often see the grooves of the individual teeth on the drum with this kind. For rolled rumble strips, while the pavement is still soft, a heavy machine with a drum on it, which has bars or pipes on the surface, just travels down the shoulder and the weight presses the bars or pipes into the pavement and leaves the rumble strip pattern behind."
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704myo | Why are cellphones now removing the 3.5mm headphone input? | Engineering | explainlikeimfive | {
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"It's not a function of outdated ports, headsets with 3.5mm plugs are still mass produced. The cynical view is they're forcing a change in periphery items they sell, forcing the end user to pay them more money for the new item. The beneficial side says they're upgrading to digital from analog, it's overdue, and they can make your phone thinner. The benefits of digital however are dubious to anyone who isn't an audiophile (they are more sensitive to changes in tone or pitch than others, resulting in hearing more imperfections). Also the associated technology, bluetooth, is not well setup for it. In layman's terms the technology lacks good traffic control and wireless speakers play things they shouldn't and then refuse to work when they should in an environment with multiple bluetooth devices. If every phone is broadcasting with bluetooth, then there's huge issues with the right devices getting the right information. Obviously I'm a cynic, the technology is nowhere near enough to force an industry wide upgrade unless it's because of money. My bet is that Android and Apple both fix the problem with new wireless technology that doesn't work with the other companies' items.",
"It's about trade offs too. Here's what the father of Android's team says: URL_0 Why remove the headphone jack? Some people consider it ‘essential’, what’s your team take on that? Headphone jacks are pretty big components and they don’t play nice with all-screen Phone architectures. We studied it very seriously, but fitting a headphone jack into our Phone required tradeoffs we were uncomfortable with. We’d have grow a huge “chin” in the display and reduce the battery capacity by 10%, or we’d need a huge headphone bump! We decided it was more important to have a beautiful full-screen display in a thin device with solid battery life. Then we made sure we to build ya’ll a high-quality DAC in a tiny adapter that can elegantly live on your headphones. – Dave",
"Partially what everyone else said- phones thinner, better display etc. I have an alternative theory that drove apple to remove the headphone jack. Apple's Apple Pay. Other companies provide you device to accept credit cards by utilizing the jack. With these new phones it's not an option therefore monopolizing the market on such devices, even if for a short period of time.",
"To make the phones thinner. The 3.5mm port is the thickest connector on phones so by removing it, you're essentially only restricted by the size of the next smallest port. Edit: Also, 3.5mm ports aren't particularly waterproof and by removing them you can make a phone somewhat more waterproof. Edit: Apparently this was really controversial? It's another hole in a phone that needs to be waterproofed. Yes, you can make reasonably waterproof phones with a 3.5mm jack and this is done all the time. They're just more complicated and expensive (pennies, but multiply that by hundreds of millions of phones sold). URL_0",
"1) Because fuck you. 2) Marketing and forcing people to buy their more expensive , bkurtooth hesdphones 3) to seem \"innovative\" it's much like \"wow look at us our phones are next generation and are totally wireless!\" I have iPhone friends who are about to get an s8 because of the lack of 3.5mm. not everybody has a Bluetooth radio and not everybody wants an extra adapter. The problem with Bluetooth is cost and the cost to quality ratio. You can get decent Bluetooth headphones but it's going to a decent penny. The best best for highest quality audio for phones are IEMS since they don't need an AMP and DAC since they're so low input but the majority of high end ones (500+) use the 3.5mm jack lol.",
"Agree that the size of a 3.5 mm jack has a large impact on mechanical design. However, recall that cell phones had 2.5 mm headset jacks a few years ago, and it was *Apple* that pushed it back up to 3.5 mm, while I think most expected connector technologies to continue to shrink.",
"Bluetooth devices are prevalent and cheap enough that they've started switching over to free up more space in the case. A 3.5mm jack takes up a pretty good amount of space inside so it's a good candidate for eliminating.",
"Are other cellphone companies removing 3.5mm jacks now? I thought (hope) that only Apple is dumb enough to do that. My car's sound system relies on that aux cord.",
"I would guess efficiency of internal phone design, waterproofing, and the end goal of making everything wireless. We can't make progress without a few sacrifices.",
"Marketing bullshit in my opinion. There are only two reasons worth considering, one is that that the 3.5mm port is too big, but there is a 2.5mm one which is more or less standard or even developing a new analog port would be better in my opinion (and Apple never cared about using standard ports). The other one is the analog vs digital thing. It sounds good to use digital signal, but in the end the signal creating the actual sound is analog and always will be, so there must be a digital to analog converter somewhere. There are minor advantages of putting the DA converter outside of the phone, but these will be only noticeable for audiophiles, maybe not even for them. On the other hand, leaving the 3.5mm port wouldn't prevent anyone in buying a bluetooth headset for (possibly) better sound quality. But hey, they can sell now a ton of overpriced headset and adapter, and they made a \"revolution\", it must be a good thing."
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705irq | why do cans of spray paint have balls inside of them? | Engineering | explainlikeimfive | {
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"It shakes up the mixture of the paint before it sprays. In just about every store that has a paint section, they have machines to shake up a can to evenly mix whats inside of it (especially if its been sitting for awhile. Paint is a heterogeneous mixture, so letting it sit will separate the molecules). Using spray paint, you dont have time to shake for long periods of time and mix up the paint; the ball is meant to help aid and speed up this process"
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70cnzu | Why are roundabouts so uncommon in the US even though research claims that they are safer and more efficient? | Could there be some particular reasoning to this like, is it something that isn't taught much in civil engineering schools or do American city planners just not give them much thought? They are much more prevalent in other countries and after having used some I've seen first hand how much better they are than the traditional 4 way intersection. Just boggles my mind. | Engineering | explainlikeimfive | {
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"Real estate developer here. I know we aren't excited about using them in a private development because local code requires up to 96' circumference of right-of-way for a cul-de-sac or roundabout vs 50' width (26' street and 12' of r-o-w on each side) for a street or 4-way stop. The fire department usually dictates this by the size of their largest ladder truck that may need to turn around. The economics don't compare when you're selling valuable land by the square foot. In a public project the city would have to buy more r-o-w which isn't popular. I envy how much smaller and dense everything is in Europe. We have so much more land in the states and the code takes full advantage of that.",
"They're only safer and more efficient if people know how to use them correctly and are used to using them. Because they're so uncommon, many drivers are not familiar with them or don't use them often, and even those that do often are not exposed to multi-lane traffic circles.",
"When they have been implemented in the US they have proven to be more dangerous here, not safer. now this could just be a function of the learning curve and they would be safer over time, but when first implemented they are more dangerous, particularly for pedestrians. Their efficiency is debatable. In general there is not much of a difference. And they take up a lot more space which means private citizens and businesses are losing more property and the city is buying more property. Both are things that many Americans do not like at all.",
"It entirely depends on the area. I live in Ohio, USA, and near me, there are several roundabouts, and it definitely makes traffic flow easier, safer, and better. I would like to think that we will continue to see more in the future. So much better than stop signs!",
"This is entirely anecdotal, but I live in DC and we've got a ton of roundabouts, and the traffic is absolute ass. They were put there specifically to make navigating the city more difficult. I guess city planners saw that and decided to not put roundabouts for that reason"
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70djm6 | How hard is it for a country to develop a missile | First things first, I'm drunk, so please don't crush me. I just had an argument about how hard it can be to develop a rocket with trajectory control. I'm either totally kruger-dunning that shit or don't get why you can't tell an engineer to look that shit up on the internet and just do it. Is that information you just can't get on the net because military doesn't want it public or is it significantly harder than I think, like too many variables in the equations so it requires years of tests? After all this technology is like 60 years old, isn't it? | Engineering | explainlikeimfive | {
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"It's expensive. If it's a choice between keeping 100 young men employed all year in the military instead of on the streets, it's a better return of investment to fund the standing army than expensive weaponry. It's not simple. Putting all that ordinance (even setting aside an armed warhead) inside a fast flying missile is not something just any engineer can do. Just the MATH on it alone started early 20th century. Liquid propelled rockets first appeared in WWII and Germany was focusing a fortune (massive) on weapons research, it took quite a lot for them to even get the V2 viable. And at that stage, it was arguable whether it was a better investment than air dropping bombs from planes (certainly there was more risk of pilots and bombers dropping them from planes though). Modern rockets have to fly fast and accurately to justify the investment, due to most major countries having SOME form of missile defense. So they have to be state-of-the-art enough to have a chance to get through, again, expensive investment. The missiles require a small army of trained personnel, and support personnel, and a guarded facility that is maintained. So again, one missile might cost so much that you could be looking at FAR more effective things a country could be doing with the money, in terms of defense spending. When you have a big country that already has a huge military infrastructure and trained engineers and scientists, and they are determined to remain the big boys in the playground, they have to do that. Countries with less generous budgets, technical personnel and support personnel, it's going to look relatively unattractive."
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70dzui | Why do trucks that carry liquids have cylindrical tankers? Wouldn't you be able to carry more volume in a rectangular container? | Engineering | explainlikeimfive | {
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"A cylinder doesn't create weak points, like corners or like the middle of flat sides (which can bulge). A cylinder uses less surface material to enclose the same volume, compared to a rectangle. (To help understand this intuitively: rounding off the corners saves a lot of material with only a small loss in volume.)",
"Mechanical Engineer here. Basically gonna repeat what's in [this fantastic video]( URL_3 ) by The Engineer Guy: Gases & Liquids want to change their \"parent container\" into a spherical shape. This is the most ideal for them. (Think of when you blow up a balloon). The problem with this is that spheres are not easy to transport (in fact, they're literally the [least-space-efficient shape in 3D]( URL_1 )). Like you said, rectangles (or cubes) would be the best. But cubes have corners and edges like some people have pointed out. These create weak points for pressure. A container of this shape would fail at much lower stress than a sphere. So we look at cylinders next - cylinders are much better: they're *relatively* easy to pack, but they also have fewer \"weak points\" (edges and corners). So we make one more compromise: we take the sphere that the gas/liquid wants to make naturally, split it in half, and put those on the end. Now we have created the best compromise between what will hold the gas/liquid the best and what is the easiest to pack/transport: a [pressure vessel]( URL_2 ). **In the specific instance of transporting on a truck:** Packing isn't really as important here. But a cylinder is still good for two reasons: you can easily just make a longer cylinder to fit a longer truck and, as /u/IgnoringHisAge mentioned, a liquid will easily funnel down to the bottom of the tank (especially if you set it up [like this]( URL_0 ))",
"You don't need to carry more volume. Tanker trucks can carry over 11,000 gallons of liquid. If that was gasoline it would weigh over 70,000 pounds. The maximum weight of a truck, including cab and trailer, is only 80,000 pounds. You're already there. Using a round tank gives you the max volume with the minimum amount of material. It would also be stronger than a square container. It will be easier to clean out (not so many corners) .",
"Very simple point that's been overlooked: when unloading a tanker, the cylinder allows for all of the liquid to pool at the outlet, allowing for a complete unload. Most tankers have a little belly or tilt to them that drains the fluid toward the valve. Your toilet and sink wouldn't be too great if they were rectangles.",
"Like others have said, it's all about pressure. A liquid pushes out perpendicular to the wall of the container, to simplify it. So when you have the corner of a rectangle there is equal pressure pushing down, against side 1 and against side 2 creating enormous pressure on that seam. On a cylinder it is equally distributed because perpendicular to the side is an arc, like how an arch Is so strong. Then you have a welded seam on a rectangle which can be a weak points whereas a cylinder is mostly just 1 piece rolled into a tank. There is probably a better way of phrasing all this.",
"It has to do with distribution of pressure, but also with the balance of the load. If it was in a rectangular container the load shift more due to more surface area. There is also a legal weight limit of 80,000 Lbs (truck+trailer+load) in USA, so it's not about maximizing volume.",
"cost vs performance, rectangular tanks would have more seams for one, which raises their cost, also makes them more peone to failure. Plus the cylinder is the second most efficient shape with regard of surface area to volume.",
"In rectangle as you're driving liquid can and will shift, making waves and since they can just reflect from other flat side, they get bigger and bigger, until eventually force of wave is so strong it flips the trailer. Round shape gets rid of that waves",
"For volatile stuff you want [egg shaped tanks]( URL_0 ) Its the shape with least surface area ([bird eggs being a prime example]( URL_1 )) As for trucks using cylinders, its a comprimise combination of the above (least surface area). And making sure the liquid dosnt splosh around when driving. And pressure control. (Same reason submarines are cylinders - in subs case, keeping the water out).",
"This may not be the most scientifically explained answer, but here is my contribution. I load dielectric fluid into tankers that are pulled on the road (aka tanker trucks). Most of the tankers that we load are limited not by the volume they can hold but by the weight of the fluid. Our tankers can hold 10,000 gallons total. We can only load 6,000 gallons on them to be shipped on the road. All this to say, even if they could hold more volume they may not be able to ship it due to weight restrictions.",
"Corners are stress concentrators so they would be weak points for mechanical failure. Having a cylindrical tank shape causes the tank to be able to withstand higher pressures and greater forces. This is also the reason that windows on airplanes are round and have no sharp corners.",
"TL;DR: You can haul more liquid in a cylinder than a rectangle when you consider weight and money. In order for a tanker truck to economically carry more it would have to be able to hold more liquid AND be able to safely haul more weight. First, consider the roads and bridges the truck has to drive on. There is a maximum weight that they can hold safely before trucks can cause them to fail. There is a practical limit on how big and heavy a hauler can be and still navigate reasonably. See URL_0 as an example of a truck being too heavy for a bridge. Next, you have to consider economy. Hauling is all about economy and in this case fuel economy. More weight means it takes more fuel to go the same distance. Engines have sweet spots where they operate most efficiently. You want as little dead weight as possible and the truck's engine running as close to its optimal speed as possible to conserve fuel and lower costs. A cylinder uses less material than a rectangle that holds the same volume. Less material used to haul the liquid the less weight is being dragged around that is costing you money to move instead of making you money. Time it takes to unload also costs money. You want this thing to be easy to clean out quickly to save on time spent unloading. Cylinders are easier to build and maintain as well. Again, money saved. So, if you want a container that is easy to clean out, uses a minimum amount of material to get the job done, and will improve your profit margin by saving fuel while letting you pull as much as a typical road will allow, you my friend want a cylinder.",
"Another thing is if it's food grade then the tank needs to be decontaminated after each load. It it's round there is nowhere for liquids to hide. You can clean and inspect the space easily.",
"Do an experiment! Take a cardboard box like a cracker box, and cut both ends off it so you have a long, rectangular, hollow \"tube\". Stand it on end, put a plastic bag in it that is larger diameter than the box you have it in. Start filling the bag with water. What shape does the box try to take? Rather than try to constrain this, the vessels are shaped this way to begin with. If you want to simulate a crash and toxic spill: seal the full bag, set the box on its side and jump on it. Preferably from the top rope or couch, depends on the nature of the crash. Check with your spouse or parent first. EDIT: wear a helmet.",
"Some guy has a video on YouTube explaining the design of the aluminum beverage can which I found surprisingly interesting, but that might just be me. However, he explains the shape well and it reminds me of this. I[Here's the link]( URL_0 ) for anyone who wants it.",
"Mechanical engineer here. You can carry more gas the more compressed it is. For example, natural gas can be stored ~600x as efficiently if compressed into a liquid. This requires high pressures. As many have pointed out, cylinders can hike more pressure than boxes because corners act as stress concentrators.",
"Any liquid in a tank will exert pressure on its walls. Pressure causes stress. Stress, over time, leads to structural failure. Corners collect more than their fair share of stress making them the weakest link and most likely point of failure, structurally speaking. Circular surfaces are able to disperse stress evenly, increasing durability.",
"There is another problem, not only the stress risers and the packing, if you put a dense liquid in a square box it would be around 2/3 full, at the first curve the liquid moves to one side, in a square section the desplacement of the mass center of the liquid is bigger than in a circular section, making easier to overturn.",
"Here is another aspect that may not have been explained. I am a former weighmaster. I had the job of filling trucks that pulled into the cement plant that I still currently work at. In most states there is also a weight limit that the state imposes. California is 26000 lbs altogether including the weight of the truck. Even though most trucks are more then capable of carrying more product, California likes to keep the weight regulated to conserve the quality of their roads. If I were to overkill a truck. There could be fines for both the driver and the weighmaster."
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70h777 | How did a 3.5mm jack get universal? | Engineering | explainlikeimfive | {
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"Short Answer: The Sony Walkman. Long Answer: The 3.5mm jack was created for use with transistor radios back in the 50s being a smaller version of the 1/4\" plug that was common in telephone and audio equipment beforehand due to a simple design and ease of use along with good quality. Sony, in creating the Walkman needed a small, but decent quality jack for their small portable tape player, so they chose the 3.5mm jack. It was somewhat popular already and had already been used in things like their transistor radios so it made sense to use. The walkman of course became incredibly popular to the point a lot of people would just call ANY portable cassette player a Walkman. This led to a ton of clones and headphone manufacturers going out and creating better 3.5mm headphones for use with portable tape players. This continued on with stuff like the discman, MP3 players, home computers etc. Why create a new jack when everybody already had a pair of 3.5mm headphones and it was small enough?",
"It was small and cheap. Initially, there were 1/4 inch plugs and jacks for telephone patching and headphones back in the 19th century. The 3.5 mm was a logical adaptation. Initially it was mono only and used on transistor radios. Then a ring was added for stereo, and later another ring for video (camcorders) and microphones (cellphones). There are TRRRS (tip, ring, ring, ring, sleeve) versions now.",
"It's compact, inexpensive, and most importantly, public domain, ie: there's no licensing. There might be a better design for a headphone/microphone connector for a mobile device, but any such connector would be covered by a patent for 20 years after its introduction, so it would need offer a huge improvement in functionality to be widely adopted.",
"Secondary question, for line-level signals is a 1/4\" plug significantly better or is it mostly for the strength and standardization with the higher-power outputs?",
"Old guy here. When pocket size transistor radios came out around 1960's not all mini phone jacks/plugs were interchangeable. This situation gradually resolved into 3.5 mm.",
"Same way that every other common port/plug became universal: It worked well, so lots of devices started using it, more and more, until it became standard."
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70im6j | Why do power plugs have multiple holes instead of using just only one hole? | Engineering | explainlikeimfive | {
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"The way electricity works is that electrons flow from one terminal to the other. You need a positive and a negative terminal in order for there to be a flow to power anything. That's why there are at least two holes in a plug. When there is a third it's ground, which is a safety measure to make sure that if something goes wrong the electrons go to the ground and not into you",
"I cant speak for other countries but UK plugs have 3 prongs as one is a safety feature. The top prong is longer and as you put the plug in it it essentially turns the socket on. If you stuck a knife into one hole of a UK socket you wouldnt get electrocuted."
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70jkh4 | why do we need to bleed the brake line? isn't a simple drain and fill the reservoir enough as a brake service? | Engineering | explainlikeimfive | {
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"You bleed the line to make sure you have no air bubbles in the line. If you have air in the line your brakes won't work then you crash and die When dealing with critical systems an abundance of caution is generally good",
"Hydraulic brakes work because when you press the brake, it pushes a piston that shoves hydraulic fluid through the brake line, which in turn compresses the brake calipers onto the brake disc (or shoves the brake shoes onto the brake drum if you have drrum brakes). The basic thing is that you're using a simple fact about hydraulic fluid (and many other fluids) to your advantage- hydraulic fluid is *incompressible*, meaning you can't make it smaller by squeezing it. So when you shove your brake pedal down, you're basically applying all the force your foot can muster- and that's a lot in most humans- to a tiny hose that in turn shoves the brakes down. Or you're sending a signal to a motor that's doing it with even more power than you. But it's still shoving an incompressible fluid through the line to transfer that power from the source to the brakes via the brake lines. Air, unlike hydraulic fluid is compressible. You can make it smaller by squeezing it; we do it with air conditioners and diving tanks and much more. So, if you get air bubble(s) in the brake line during the drain and refill process- which isn't hard to do- when you press the brake, you'll find they don't work well or at all, because those air bubbles are collapsing under the pressure and stealing the power you want to send to the brakes. Then your vehicle's brakes fail to operate and you're having a very bad day. Signs of air in the brake lines are a spongy feel in the brake pedal, reduced brake power, and (obviously) total failure of the brakes to operate."
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70jrw3 | How do they build buildings to be perfectly straight? | Engineering | explainlikeimfive | {
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"To be totally fair most buildings aren't perfectly straight. They're straight enough to stand, and that's the critical part. As others have mentioned, a plumb line or level is the classical way, today it's done with lasers and other technology to eliminate human and material error. But oddly, most really tall buildings aren't ever perfectly straight; they're constantly flexing in the wind and air pressure changes.",
"With a [plumb bob]( URL_0 ) you can create a perfect vertical line. It has been used since at least ancient Egypt in construction. And have worked fine sin Church spires over 120m high and have been used in elevator shafts in skyscrapers Today there are more advanced measuring equipment."
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70lz4y | Why do manufacturers have english and metric nuts and bolts in the same system? Isn't is cheaper to be consistent? | I noticed a lot of times when I'm working on a project that I'll have bolts that are 10mm or 15mm, then other bolts that are 5/8 or 1/2 inch. Sometimes it makes sense, e.g. my Toyota and Acura cars seemed to always have Metric parts and my bicycles (Huffy, Roadmaster) always seemed to have english. Lately, though, it seems that it doesn't matter what brand something is, I can never predict whether the bolt will be english or metric. I was working on an Oldsmobile and it had a 1/2 inch bolt on the front of a bracket and 2x 15mm bolts on the back. Is there a reason for this? It seems arbitrarily difficult and time consuming to swap out sockets all the time. | Engineering | explainlikeimfive | {
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"This happens when an American company uses European suppliers or even is jointly owned along with a European sister company and they share parts.",
"The US is still on its own measurements system despite (almost) every other country on Earth switching to metric decades ago. This causes problems and confusion any time there is an insistence on using US measurements."
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70p3zr | why do electronic devices, like TV remotes that are relatively the same size and perform the same function require different size batteries? What determines the type of batteries required? | Engineering | explainlikeimfive | {
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"The different-sized batteries have the same voltage, meaning that they can output the same amount of energy in the same amount of time. However, the size of the battery determines how long it can sustain that potential (how long it has until it dies). AAA batteries will generally die more quickly than AA batteries, but they have the same voltage. Three AAA batteries will approximately fit into the space of two AA batteries, but you can get more voltage with the AAA batteries because they're more compact. They will run out more quickly, though, which is why we add a bunch of them together. I hope this answers your question!"
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70phvh | how does an AC outlet charge a DC phone? | Engineering | explainlikeimfive | {
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"text": [
"There are special circuits that can take the high voltage AC and turn it into the low voltage DC that your phone needs to charge. That special circuit is what lives in the base of the charger (the part that sticks in the wall) If you want some non-ELI5 on how they work, Google \"buck converter\"",
"Your phone charger is an AC to DC converter. It takes the AC voltage from the wall, converts it to DC, and steps it down to the right voltage for the phone"
],
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5,
3
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|
70qzt5 | How a CD/DVD/BD can be read even heavily scratched? | Although the "bits" are so tiny, even a disk with many scratches will work just fine, How? | Engineering | explainlikeimfive | {
"a_id": [
"dn5afci",
"dn5ahx3"
],
"text": [
"They are recorded with extra, \"redundant\" information so that errors can be detected and corrected. This is called [forward error correction]( URL_0 ). On a two way communication channel, like a phone line or computer network cable, you might be able to detect errors and just ask for the information be sent again (requesting over a \"reverse\" channel) but there's no such recourse on a physical storage medium like CD so there's extra space set aside for redundancy.",
"The data is not written on the surface but is written on the metallic foil sandwiched inside the plastic. When the plastic layer is scratched, sometimes the laser used to read the data on the disc, can get through the plastic with little or know data loss. On other occasions the scratches in the plastic are profound and the data can not be read. There are products that can be used to resurface the plastic are remove the obstacles to light passage."
],
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6,
6
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"text_urls": [
[
"https://en.wikipedia.org/wiki/Forward_error_correction"
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} | [
"url"
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716m74 | Why does each system in a car require its own type of fluid? | Like, why does a car's brakes need brake fluid specifically, and why isn't there some universal fluid that we could use in everything? | Engineering | explainlikeimfive | {
"a_id": [
"dn8hoiv",
"dn8inod"
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"text": [
"Brake fluid is subjected to over 5000psi and sometimes hundreds of degrees Fahrenheit temps Antifreeze (coolant) only has to deal with < 300 degree temps but must not freeze and must maintain a consistent viscosity no matter the temp and must be good at conducting heat. Transmission fluid must maintain a higher viscosity than either of those and constant strain and pressure Engine oil must maintain its lubricating properties from -50f to 300f and not break down. And not foam up in the process of being churned up by the engine. Windshield washer fluid must not freeze but can’t leave an oily residue on the glass Gasoline must ignite at the precise moment a spark is applied no sooner and no later. Gear oil in your differential must lubricate the gears without running off of them since they aren’t submerged in it. So it must be a heavy weight oil",
"Because each system is independent and each fluid has different properties.. Let's compare it to your body and the different fluids in the different systems in your body. So you engine needs oil to keep the parts lubricated so they don't create friction, creating excess heat, and damage. The fluid also needs to be cleaned so it doesn't get thick and clog up the system. Our joints have fluid in between them to keep them lubricated and to prevent the cartilage and bones from scraping against each other. You need transmission fluid for the same reason you need engine fluid. All those gears need to stay lubricated so they don't degrade. You need brake fluid because your brakes use a hydrolic pressure system. When you step on the breaks, pressure increasses in the break lines to cause the break pads to clamp on the wheels. In this case it doesn't need to be a lubricant like oil. It needs to have properties that allow the transfer of pressure very quickly. You don't want a delay from when you tap the brake pedal to when the brakes activate. The closest system I can think of for this is blood. Our blood needs to transfer it's contents around the body very fast. The heart can be thought of as the brake pedal. Our blood pressure increases when there is increased demand for blood supply around the body. You also have antifreeze/coolant to prevent the systems from overheating in hot temperatures or freezing in low temperatures. This can't be achieved with wither oil or brake fluid. It needs to be easy to flow like water, but also be resistant to change in temperature. I guess there's no single bodily fluid that performs this task. But a variety of human fluids do like sweat, our kidneys, lymphatic system, and the thymus all work to keep the body within a certain temperature range. Then theres gasoline, this function is obvious. It provides the combustive force to power your vehicle. Neither lubricating oil, antifreeze, or brake fluid could do this. Gasoline is highly flamable and needs to be. The best analogue in the human body is food and the digestive system. Food is our fuel, the calories are burnt for energy. And I guess all that's left is windshield washer fluid. Obviously this is basically the same thing as windex. You wouldn't want to use this to lubricate your engine, and you wouldn't want to use oil to wash your windows. The best bodily fluid that matches this is tears. It keeps your view clean and clear. tl;dr Every fluid has specific properties that serve specific functions. The other fluids cannot meet the needs of all the systems in your car. If you tried to, you'd end up with either a substance that is mediocre at all of them, or you'd have a fluid that's good at one job and fails at all the others. Putting gasoline to lubricate your engine will cause your car to explode, and putting engine oil in your gas tank will ruin your intake valve."
],
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88,
3
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717jr7 | Why is downforce better than normal weight? | Engineering | explainlikeimfive | {
"a_id": [
"dn8oy2v",
"dn8p2rz",
"dn8p3eb"
],
"text": [
"Downforce provides extra downward force which gives you more grip, same as additional weight, but doesn't come with additional inertia which takes more force to accelerate and to hold to the turn. Being light with a lot of downforce will let you take high G turns, the same amount of downward force produced by weight will send you spinning out of control because it wants to keep going straight because it has inertia",
"Downforce provides traction at speed but doesn't actually add rolling mass to the car. That means that you get all the traction and straight-line stability benefits of weight over the wheels, but none of the body roll, sluggish braking, understeer, and labored acceleration you'd get from simply making a heavier car.",
"If you are going around a turn, your tires need to be able to have a certain amount of grip. Going faster or tighter means you need more grip, however, there is a certain limit to what the friction between the ground and the tire can provide before it starts slipping. If you increase the weight on the tires, you get more grip.This might make it seem that just adding more weight to the car would be good, but doing this would once again increase the amount of grip needed (F=ma), such that it cancels out the advantage of having extra weight on the wheels. Using down force keeps the advantage of having extra weight on the wheels without increasing the mass of the car (besides the mass of the aero package), so the necessary force to make the turn doesn't increase, but the available grip does."
],
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3,
3
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|
717t4n | how do noise cancelling shooters ears work? | I just bought a new pair of ears (long overdue) and I'm curious as to how they have a volume adjustment to hear outside the headphones at normal talking volume, but they can then cancel out louder gunshots. | Engineering | explainlikeimfive | {
"a_id": [
"dn8qvyp"
],
"text": [
"They work like regular ears to cancel out all sound. Then when you switch them on a microphone on the outside picks up ambient noise, processes it, and feeds it into the speakers in the ear cups. As long as that noise stays within a certain preset decibel limit it is allowed through. Any sound above the limit simply never makes it to the speakers. There is actually a very slight delay for processing time, but it's on the order of a few milliseconds."
],
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4
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} | [
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71bjl4 | Boolean satisfiability problem (SAT) and SAT Solver | Engineering | explainlikeimfive | {
"a_id": [
"dn9h2ke"
],
"text": [
"Boolean Satisfiability problem: I write down a formula defined on a vector of binary variables x=(x1,x2, ... x4). Can you find an assignment of truth values (like x1=T, x2=F, x3=T, x4=F) that makes the whole formula evaluate to True? A SAT solver is just an algorithm to solve problems of this type, that has been implemented in code. The problem is NP-hard, which means that in general nobody knows an algorithm that could solve it in fewer than 2^n steps (i.e. try all truth values). But in practice, SAT solvers can be very fast on some restricted types of formulas."
],
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5
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|
71c09a | After an earthquake, how do we tell if a building is structurally sound enough to re-enter and use again? | Is it possible for a building to have cosmetic cracks on the surface and still be structurally sound? On the flip side, is it possible for a building to have no visible damage, but be actually unstable and potentially collapse after being used again? EDIT: For Example, in Mexico several buildings collapsed so there must be a subset of buildings that were damaged but did not collapse. | Engineering | explainlikeimfive | {
"a_id": [
"dn9nhkt"
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"text": [
"If there's internal damage, there will always be some amount of external damage. The amount of external damage can be very small compared to the internal damage, misleadingly so, but there will always be some. And yeah there are a lot of things you look for. Small cracks (a couple millimeters) are expected in certain materials, and don't necessarily mean its unsafe. Other things are more obvious. If you see piles of debris, a lot of broken windows, huge cracks or the building is actually tilting, its best you stay away. For large buildings, they just don't let anyone go in until professionals can inspect the structure to see if its safe or not. With smaller structures and homes, you can have the people occupying it look for any obvious signs of problems, and make judgement calls until an inspector can get around to it (they'll be busy with more vital things like hospitals in the immediate aftermath, so it takes time to getto residential areas.) Ultimately, its usually pretty obvious if there are any major structural problems."
],
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6
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71cmbe | What’s the rationale behind not having the handbrake activate the brake lights on a car? | Engineering | explainlikeimfive | {
"a_id": [
"dn9prh4",
"dn9prvs",
"dn9pp5n"
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"text": [
"The handbrake isn't for normal use. It's an emergency backup to the hydraulic system. If the hydraulic system fails, it's probable that you are already jamming your foot down on the regular brake in a frantic effort to stop the car, so the brake lights would already be activated. The other time you might use it is if you are parking the car on a steep incline, and you want extra assurance that it won't roll away. So you wouldn't want the brake lights to be stuck on in that situation as it would run down your battery.",
"That's because you don't (or *shouldn't*) use the handbrake for braking, but rather to keep the car remain still once you've come to a standstill. There's no need to warn other traffic then.",
"Because you’re not supposed to use it while driving. You’re supposed to use it for parking, and you probably don’t want your brake lights sitting on for 5 hours while you’re parked."
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|
71dggv | Why does putting a hot piece of metal into cool water, such as the metal hardening process, cause fire to start on the surface of the water? | Engineering | explainlikeimfive | {
"a_id": [
"dn9w7i1"
],
"text": [
"Usually that's because it's not water, it's oil (some steels should be quenched in oil rather than water). The steel is often well above the oil's ignition temperature, so the oil ignites on contact with the steel."
],
"score": [
3
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|
71ejct | How do laptop trackpads work and how can some work even through paper? | Engineering | explainlikeimfive | {
"a_id": [
"dna766c"
],
"text": [
"The pad keeps track of where you touch it, kind of like battle-ship, where there are x-y coordinates. Some pads are 'resistive' types - where you touch the pad actually deforms it a little, changing the electrical resistance in such a way that the computer can tell where the focal point of the pressure of your finger is (to within some margin of error). Others are 'capacitive' and sense the change in electrical charge from when nothing is touching the pad, to when something conductive like a finger is touching it. Resistive tends to be less accurate, and needs more pressure, but will work through paper and with gloves on. Capacitive is smoother and sexier but won't work with just any touch material."
],
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3
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|
71hhm8 | Why are most cars' wheel arches curved inwards? | I am a car enthusiast and I love modelling cars in 3D. One thing I've noticed, but can't really think of a logical reason for is why most cars have wheel arches that tend to curve inwards the lower you go? Look at [this image]( URL_0 ) for example. See the bend? The wheel arch in the body shell isn't exactly straight, exposing some of the tyre tread, towards the bottom more so than the upper end. If you follow at the bumper seam horizontally all the way to the arch, you'd notice that the tyre and the arch are perfectly aligned. In contrast, when you follow the front splitter down below, the arch has now curved inwards exposing the tyrewall. Any specific reason behind this? | Engineering | explainlikeimfive | {
"a_id": [
"dnavk8u"
],
"text": [
"It's not so much the body curving inward but the wheels are. It straight vertical. Most cars are stances a few degrees."
],
"score": [
3
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71kefc | How does a gas home water heater stop the gas flow when pilot light goes out? How does it keep it open while the pilot light is burning? | Engineering | explainlikeimfive | {
"a_id": [
"dnbd66u"
],
"text": [
"It uses a device called a thermocouple. It sits right above the pilot light and generates a signal when it detects heat. The heat from the flame sends a signal to the valve to stay open - if the flame goes out, the signal stops and the valve closes. That's why you have to hold a little button on the valve down when you light the pilot - this overrides the thermocouple until you get the pilot started."
],
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3
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|
71l0o6 | With CPU chips having billions of transistors, What happen if a few go bad | So we know they jam pack billions of small transistors into a modern CPU chip. Does it only take 1 transistor to go bad to render the chip useless? Or can a few go down and the chip will still be functional. Is there some type of redundancy on them so that it can keep working. | Engineering | explainlikeimfive | {
"a_id": [
"dnbik0e",
"dnbia1w"
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"text": [
"Of course when such chips are made the manufacturing process isn't perfect and some errors may render transistors nonfunctional. The chips are designed with some level of redundancy so certain kinds of errors can be \"worked around\" but enough errors can render large sections of the chip inoperative. Instead of just throwing out this under-performing CPU the manufacturers perform what is called \"binning\". Chips able to perform at certain thresholds are separated into different product lines so a higher performance product which is crippled by broken transistors might be sold as a lower performance unit for less.",
"Chips are made with some spares, and before they are packaged the manufacturer checks them and might enable a spare circuit. Once it's packaged and sent to a user, a single transistor failure might make the part not work. Not always, as some features aren't in use at any given time, but it's certainly possible for the failure to be covered up if it's a transient failure. A hard fault might eventually be detected, unless the application doesn't need that feature."
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71liax | Why are there so many different kinds of wings on typical aircraft/airplanes? What are the pros and cons of the styles? | Engineering | explainlikeimfive | {
"a_id": [
"dnbm6zs",
"dnboskh"
],
"text": [
"The wings and everything are based on the needs of the aircraft and it's job. Long wings generate lots of lift at lower speeds, but will become damaged or even destroyed at high speeds. They're also not good for aircraft that make lots of sudden turns, like a fighter. They'd snap right off. Fighters and more agile aircraft need short wings, but that means that they have to keep going at a high speed otherwise they'll just fall out of the sky from no lift. There's also other factors to consider in wing design. One design may be very stable and keep the aircraft straight and level, which is good if you're flying a jet liner. But that same wing would keep your fancy fighter from being able to out maneuver the other guy.",
"There are a multitude of reasons for different wing geometries, angles, compositions, weight distribution. But mainly it depends on the flight envelope in which that aircraft must operate. It generally more complicated than just \"fast and agile aircraft need smaller wings\" I would recommend reading about fixed wing geometry if this topic interests you. It will be a lot easier to grasp that way rather than in a ELI5 comment but it is very intersting stuff. If you are looking for a book that covers this as well as control surfaces, aircraft geometry, weight distribution, landing gear, aircraft structure then I would suggest [Aircraft Design: A Conceptual Approach by: Daniel Raymer]( URL_0 ) We had to read this in 3rd year Aerospace and use what we learned to design a trainer aircraft concept for the RCAF that could be used to train potential F35 pilots (Irrelevant now lol) but it goes into great detail and does an excellent job describing otherwise complex concepts. Of course this is just the tip of the ice berg but IMO its a great starting point and you could easily apply this knowledge to small scale or model aircraft design."
],
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"https://arc.aiaa.org/doi/book/10.2514/4.869112"
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|
71qupu | how do power wires stay the same voltage when so many different homes and companies are drawing power from them? | Engineering | explainlikeimfive | {
"a_id": [
"dncqaat"
],
"text": [
"they don't stay same voltage. if you measure it, you'll see the voltage go up and down at a fixed position. if you move you'll also see it varies with wire distance to the distribution node. power companies are always monitoring the voltage levels and adjusting the power generators to match the expected demand."
],
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4
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|
71wzo4 | What is the science behind ICBMs? | Engineering | explainlikeimfive | {
"a_id": [
"dne367r"
],
"text": [
"The B stands for Ballistic, which means that the missile is boosted by rockets to a high altitude, then falls back down unpowered at an extremely high speed - something like 7 km (4.3 miles) per *second*. The sheer speed, combined with the lack of flames out the back, makes an ICBM extremely hard to track and intercept, by design. So the missile itself is fairly simple in principle, but getting it all to work is harder. If the missile's trajectory is set correctly during the boost phase, it means little or no correction is required during the terminal phase. Modern ICBMs have multiple independently-targeted re-entry vehicles - MIRVs -which separate from the missile and have their own rockets and guidance systems. The sheer speed of re-entry can't be over-stated. At 7 km/s, that means the warhead goes from 14 km up - 46,000 ft, higher than any commercial airliner - to the ground, in *two seconds*."
],
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12
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|
7215kh | How do civil engineers determine if a building is structurally sound after an earthquake? | Engineering | explainlikeimfive | {
"a_id": [
"dnf163j"
],
"text": [
"They would assess the structural components for signs of failure or serviceability issues. If they were looking at steel they could check and see if members or connections had yielded or worse. This might be evident through several different methods such as bolt holes being larger than they should be or members having localized sections with a reduced cross-sectional area and elongation. If they were looking at concrete they could check for unusual cracks, spalling, exposed rebar, or again a multitude of other things. They could also check member deflection. Typical floor members are generally limited to a serviceability deflection of L/240 under dead + live load. For example, if a floor beam was 20 feet long (240 inches) that beam would be limited to 1\" of deflection over the span length under this condition. If the beam is sagging 6 inches something is probably off."
],
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10
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|
721ywa | How can a cable possibly be stretched across the entire Atlantic Ocean? | Engineering | explainlikeimfive | {
"a_id": [
"dnf48c4",
"dnf497c",
"dnf4qz2",
"dnf4bu2"
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"text": [
"Very long cables, carried out on large vessels. They lay on the ocean floor where they dont see too much marine life. Even so, they have a thick casing to guard against animal curiousity.",
"Undersea cables are large and very well protected from the elements. Animals aren't a major concern. The ocean is miles deep, but that isn't really a problem. Cables aren't placed by divers or submarines, their unspooled off the back of a big ship.",
"Neal Stephenson wrote a cool article about the internet infrastructure that included a big section on putting down an ocean cable: URL_0 Search for \"ocean\" and it was the second hit that was in the section of interest, I think. The whole thing is very interesting, but long :)",
"Its really long and sits on the bottom. Its pretty well protected and its uninteresting to animals. They're as inclined to destroy it as the Titanic, its just an uninteresting hunk on the bottom. The cable isn't really *stretched* across the Atlantic, its just laid out on the ocean floor by a ship with a really really long spool of special cable"
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724qa3 | At a building site, it seems that the taller the building, the deeper the hole in the ground has to be - why? | Engineering | explainlikeimfive | {
"a_id": [
"dnfpgb6"
],
"text": [
"The ground is not perfectly stable. As the water flows though and as the temperature varies you have slight shifts in the particles that make up the ground. Even bedrock will move a bit over time. This can cause issues for fixed structures over time. If you build a normal house right on the ground and let it sit then every time the ground shifts the house will fall a bit deeper into the ground. After a hundred years it might be a few inches lower then when it was built. But if you build a heavier house then there will be more forces involved and it will sink into the ground faster. One of the most famous examples of this is the leaning tower of Pisa. You might prevent this if you are able to anchor your building securely to bedrock but this can be very expensive in some places. Another alternative is to build a proper foundation so that the forces on the ground is similar to the ground around it and also so you can use the ground on the sides as support."
],
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3
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|
728t77 | Why does soaking the seat belt from a child's car seat in plain water weaken it? | The manual for our child's car seat clearly states in bold that if you soak the belt in water it will compromise the safety of the belt. How does plain, cold water compromise the integrity of a nylon belt? | Engineering | explainlikeimfive | {
"a_id": [
"dngog3q"
],
"text": [
"> How does plain, cold water compromise the integrity of a nylon belt? It can allow them to stretch a bit which wouldn't of course let them break but may mean they don't hold securely enough in the event of a crash (unless adjusted again). Also they are impregnated with a fire-retardant chemical which could wash out and leave the belt out of compliance with the law, and by warning against such washing the company is in compliance with the law."
],
"score": [
6
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72blmw | How does destructive testing work? | I just watched [this]( URL_0 ) video and somewhere near the end he said that in destructive testing 'engineers purposely weaken parts of a structure to test how strong the other parts are'. Can someone explain how this works? | Engineering | explainlikeimfive | {
"a_id": [
"dnh8l95"
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"text": [
"Destructive testing is when you make an exact copy of the thing you are testing and then push it so hard you destroy it. This way you can find out exactly how much that component can take without worrying about having to stop short to save the component for actual use in whatever you're making. The opposite is non-destructive testing where you only use scanners and other instruments that don't break anything in the component."
],
"score": [
4
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72dy9g | What are these extra rails on the subway tracks here? | I'm waiting for a train at Flushing Ave station in New York, and I notice the train tracks have between one and two extra rails in the middle that start and end randomly (One of them has some little "x"s drawn on it, if that helps see what I'm talking about). Can anyone explain what they're for? Picture: URL_0 | Engineering | explainlikeimfive | {
"a_id": [
"dnhr1na"
],
"text": [
"They look like guard rails. Guard rails are an extra set of rails inside the normal rails so that even if a train does derail, it stays roughly pointed the right way. This is especially important on bridges and in tunnels, where the train going too far off the rails would lead to disaster."
],
"score": [
4
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72fdcs | How come railways in the UK risk buckling due to 'hot weather' but there are fully functioning train services in much hotter countries? Why can't the UK National Rail operate the same as those countries? | Engineering | explainlikeimfive | {
"a_id": [
"dni3ls9",
"dnirx43"
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"text": [
"The track is designed for a particular use case. When the actual plans for the railway are drawn we can look at history and see where temperatures have been and based on that we know the realistic limit we can operate in. It would have cost more money to make the U.K.'s railways able to withstand a temperature that the data suggested would never happen so they didn't design the system to work under these conditions. This probably has a lot to do with the railway being older than the concept of global warming. So simply put the reason it's designed that way is they never expected it to get that hot. If they would have known they would have spent the extra resources to prevent the issue.",
"When I lived in London there was literally an excuse every day for why trains were delayed or cancelled. Too hot. Too wet. Too cold. Staff are ill. Etc Really makes you wonder how the UK ever managed to take over the world back then when their infrastructure is so fucking ridiculous. I moved out of London and in six months, there was only 1 cancelled train."
],
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|
72i21p | ohms law | I'm getting into coil building for vapes and everyone says I need to understand ohms law and all I really know about it is how to spell it and it has something to do with resistance | Engineering | explainlikeimfive | {
"a_id": [
"dnipc9l",
"dnivqn0",
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"text": [
"V=IR. The voltage drop (i.e. the voltage your supply needs to be) across the resistor is equal to the amperage (i.e. the current that supply has to be able to put out) multiplied by the resistance of the resistor (which I'm assuming is a heating element, I don't vape).",
"You need to look a bit beyond Ohm's Law (V = I R) in to Power, because Power is what will determine the performance of the coil. Power is the rate energy is being used, per second, which will determine how much vaporisation gets done per second. Say you take apart an existing vaper and do some measurements. You have the battery voltage and the resistance of the coil. From those you can get a rough power usage figure for the coil in watts, using the formula P = V^2 / R. Now say you want to double the power for some reason - I'm not going to ask why. That formula has certain implications: You could half the resistance, and the power usage would double. But if you doubled the voltage, the power usage would *quadruple*, because it's related to the *square* of the voltage. So you wouldn't do that, you'd increase it by a factor of about 1.4 (the square root of 2). This is ignoring questions about the performance of the coil itself, which other posters have touched on. In my opinion, more voltage over the same coil would overheat it, so increasing the voltage would mean you'd have to increase the length of the coil wire too.",
"A lot of electrical things can be understood with an analogy to water. Voltage is like water pressure - imagine a dam holding a bunch of water back. That's like your battery. Resistance is how much the dam resists letting the water through. A battery that's not connected to anything has basically infinite resistance, and holds its charge. As soon as you connect it to a wire though, you've made a hole in the dam. The amount of water that flows through the hole is the current. Something with a very low resistance, like just a naked wire connected to both ends, is like a giant hole in the dam. Just as water would rush through all at once and cause a lot of noise, your wire will pass a lot of current at once and get dangerously hot. It's important to have an appropriate amount of resistance along your circuit so that the current goes through at a controlled rate to power your device. In your case, your heating element is kind of like a water wheel. You want enough energy flow to get it to work without overwhelming it. Ohm's law is the relationship between current, voltage and resistance and you can use it to ensure that you're getting the kind of flow you want. The current is always equal to the voltage divided by the resistance, or I = V/R, also stated as V = IR."
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72jm9w | Why do robotic arms for amputees move so slowly? How can we make them faster/more responsive? | Engineering | explainlikeimfive | {
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"We could, but the problem isn't the mechanical part, it's controlling the limb. There are a lot of different ways a prosthesis can interface with humans. Most of them are not accurate enough to allow faster/more responsive movements without destroying accuracy. Also, movements that require proprioception/some sort of feedback are a lot harder to do with an artificial limb."
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72q9ar | If rockets use controlled explosions to propel forward, why can’t we use a nuclear reaction to launch/fly our rockets? | Engineering | explainlikeimfive | {
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"URL_0 I think this is the wikipedia article you're looking for. There have been plenty of tests for a variety of nuclear propulsion drives. There are essentially three types. Nuclear Electric - You have a small reactor or nuclear battery and use the electricity generated from it to power some form of propulsion that relies on electricity, like ion thrusters. Unfortunately, nuclear reactors are quite heavy compared to solar panels, and ion thrusters are so slow they're not very practical for manned spaceflight. Nuclear Electric propulsion may have a future someday on a deep space probe that's too far out to rely on solar, but as far as I know nothing uses it today. Nuclear Thermal - Basically, you take a nuclear reactor and pump hydrogen into it. The hydrogen heats up, you let it shoot out the back, propelling your rocket forwards. It's kind of like you just spring a leak in the reactor's cooling system. Nuclear Thermal Rockets have real promise for providing very efficient thrust, and there have been several projects in the past to experiment or develop them, including a couple that are currently ongoing. But they have problems. Due to weight concerns, shielding for the reactor would have to be kept to a minimum. Most designs provide only for a shield dividing the crew from the reactor, meaning everything around the spacecraft would be bombarded with a lot of radiation. The exhaust is also radioactive. That's less of a problem if you only use it on an upper stage and rely on a normal chemical rocket to get you to space, but that's kind of putting the cart before the horse. They're also a pain to test, since you have to collect the exhaust or give cancer to your neighbors. You also have the shared problem with all of these designs- even proven rocket systems fail on a fairly regular basis. If you have enough material for a reactor go up in a high altitude explosion, you're going to be raining material down on a very large area. Even if it's over the ocean, you'll contaminate the food chain. It'd potentially be worse than Chernobyl. As an aside, I'd also recommend reading about project pluto. It was a nuclear jet engine on an aircraft, not a nuclear rocket on a spacecraft, but it used a pretty similar principle- it just heated intake air rather than hydrogen fuel. It would have been a nuclear bomber that could fly practically forever, and after dropping its bombs could have spent weeks flying at low altitude to kill more people with sonic booms and radioactive exhaust. Nuclear Pulse - This is the fun one. Basically, nuclear pulse engines are just shooting a nuclear bomb out the back, immediately setting it off, and riding the force of the explosion. They're utterly bonkers. They should be very efficient space propulsion, but they have added political problems. For some reason, launching a huge gun loaded with a magazine of dozens of nuclear bombs into space and having it orbit over everybody's heads doesn't make other countries happy.",
"That has been seriously proposed and investigated. ** URL_0 In theory it would be a way to get enormous loads into orbits, in practice it would be a way to make a whole lot of people very angry because you were setting of nukes. irradiating your launch pad the atmosphere and risking distributing your \"rocket fuel\" across the local landscape if something goes wrong. Politically and environmentally this simply would not work in practice. The physics are okay though.",
"We have a plan to do it, but its not environmentally friendly enough to use on earth, and lifting nuclear bombs into space to use as fuel isnt fuel efficient. If you are more interested though look up Project Orion.",
"So there's 3 options here: 1 is the \"nuclear thermal engine\" which is basically exactly what you've said. 2 is even madder, it's called an \"Orion Drive\" and it basically consists of having a huge plate on the back of your rocket and then dropping nuclear bombs behind you which go off, pushing against the plate. And 3, perhaps the maddest of all, a nuclear gun where you're the bullet. In all cases there's no insurmountable challenge but there are significant engineering ones, notably around building a spaceship strong enough. NASA got pretty close on the nuclear thermal engine, the rest are more conceptual. The two bigger issues are 1) fallout and radiation and its effect on planet earth meaning 3 is ruled out and 1 and 2 are only really viable options if taken as far as orbit conventionally and 2) the fact that at the moment conventional propellants work just fine for everything we might want to do. If we get serious about moving large payloads higher than Low Earth Orbit (say if we want to visit mars) we might revisit the idea, but at the moment conventional propellants are doing all the jobs we need doing just fine.",
"From a physics standpoint, we can! There are a couple treaties in the way, though. The Partial Test Ban Treaty says that nuclear weapons can only be tested underground. The Outer Space Treaty says that we can't put WMDs in orbit, on the moon, on any other celestial body, or otherwise in outer space. Project Orion or Daedalus type ships would run afoul of one or both of those.",
"To ELI5: PTBT (Partial Test Ban Treaty) prohibits it because any accident could irradiate the atmosphere and all the living organisms in it. It's a precautionary measure."
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72qbl0 | why is it food and beverage containers have empty space? Food/drink containers, why aren't they full to the brim? Bottles/canned goods seem to have wasted space, and it doesn't make sense if they can make the container smaller/more exact to the contents. Why isn't leave air? | Engineering | explainlikeimfive | {
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"Depends upon the product. Chips: The air is there so the bag prevents against shocks and broken chips. Soda: The air is there so that it can expand and contract with heat changes without exploding (if you really care, I can more fully explain). General products: tolerances are easier if you fill to 95% rather than 100%. If the line is moving at 20 mph things are going to slosh.",
"If the container is full to the brim, it will leak its contents all over the factory machine while the top is being attached. That makes for a very messy business.",
"You have to allow for error in the filling of something like a drink - you're never going to get the exact same amount dispensed, every single time."
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72qyse | Why is AC current better at long distances than DC? | Searching the internet I found someone saying that the above is not true, yet (on his word) when my father studied engineering he was shown through experimentation how DC current would not reach the stated wire length which was instead met by the same AC input. Not sure what to think nor how it works. | Engineering | explainlikeimfive | {
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"**AC power can easily be transformed to a very high voltage.** * By the equation P = U*I we see an increase in voltage (U) must lead to a decrease in current (I) for the same power (P). * With Ohms law I = U / R, we can calculate the power loss in a resistance (the cable) as: P_loss = R / (U²) or P_loss = R * I². In both forms in the second statement, we see it's beneficial to increase the voltage, and reduce the current. AC transformers exactly do this. DC transformers exist, but are still more expensive and harder to manufacture.",
"If you imagine electricity like water for a DC circuit you have to push water from the start, through the entire system and then back to the pump, figuratively speaking. In an AC circuit imagine two pumps one to pull and one to push and they switch back and forth at 60 x second so the water only moves back and forth slightly through the circuit. So imagine yourself trying to blow water through a long hose to the other side that is DC. If you have two people one at each end of the hose each alternatively blow/suck water through the hose that is AC. Kind of since this is explain like I'm 5. Plus DC suffers from long wire resistance and other more scientific reasons that are not listed.",
"The higher the voltage at which you transmit power, the lower the losses are going to be on the way. The reason behind that is difficult to explain without using physical formulas though. So power infrastructure uses very high voltages to transmit power over great distances, and transforms it down to more manageable voltages for local distribution, all the way down to the 110 or 230 V you get in your home. This is where AC has an advantage: You can feed an AC current straight into a transformer to increase or decrease the voltage, without needing expensive equipment and with minimal losses. DC current however can't be transformed, so you first need to turn it into AC current and then into a transformer, and then convert it back into DC. This makes the necessary equipment expensive and increases power losses, which is why almost all power infrastructure uses AC. But there is one disadvantage to AC: AC has slightly higher losses than DC at the same voltage, for reasons which again aren't exactly easy to eli5. When you have very long connections, these additional losses can offset the additional costs from converting AC to DC and then again to AC, which makes DC actually more efficient. So DC also has its uses in power transmission.",
"AC is easy to transform up and down in voltage. This is important since current and voltage are inversely proportional and the losses is related to the current and not the voltage. So if you increase the voltage to thousands of volts you will have very little transfer losses. You might have seen demonstrations of AC and DC being transferred along the same lines at the same voltage showing less transfer losses with AC but that may easily be a misunderstanding of how voltage applies to AC. Since the voltage is constantly changing the amount of power transferred is not as simple as with DC. It depends on the power factor of your load and if you are measuring peak voltage or something else. For long distances AC does have some issues with the capacitance and inductance in the wires causing more transfer losses then DC. However this loss can easily be justified if you look at the equipment in each end required to convert between AC and DC for a DC transfer line. So high voltage DC lines are more effective but are generally only seen with very long distance undersea cables and generally between two power zones that use different AC cycles so you need to convert it anyway."
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72tfd0 | Why is gas heating so much cheaper than electric heating? | Wouldn't it be profitable for the utilities to build more gas-powered electric plants, increasing the demand for gas and the supply of electricity, until the prices equalized? | Engineering | explainlikeimfive | {
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"no, there are numerous losses in electricity production and transmission. all along the way heat is slowly lost to the atmosphere. While we need electricity, because its a convenient form of potential energy to do all kinds of work. But if your ultimate goal is just to burn it as heat, we can do that ourselves on a small scale in our homes, so wed rather just take the raw fuel directly and avoid all the losses along the way. why dont we make our own electricity at home from a gas generator? small generators are inefficient and costly to buy, run, and maintain."
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7366kt | What prevents the wing of a plane from breaking mid air, under the pressure of wind/air? They seem so wobbly and unstable during takeoff... | Engineering | explainlikeimfive | {
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"The wings are capable of flexing quite a bit before they fail. This video shows engineers testing to failure, and you can see how far the wing can bend before it fails (catastrophically). The wing makes it to 150% of design load, which means that the engineers figured out how strong the wing had to be to perform safely, then included significant safety margins, and the wings as built far surpassed even those goals. URL_0 Here's an image of a 787 wing test: URL_1",
"They are built to be very strong while maintaining the lightness to fly, and a bit of bending isn't a big deal. You can tell how strong they are when they're just sitting on the ground - what other structures can you think of that can just stick out like that, 50-100ft, so thin without any support? (And heavy engines hanging off them to boot, along with fuel inside them). In flight, the roles are reversed, and the wings are basically holding up the fuselage."
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73bx8u | when you take a picture on your phone, how do you get rid of all location data on it so that it becomes untrackable? | Engineering | explainlikeimfive | {
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"Every phone has the setting to turn off the gps location in photos. You need to find that setting and disable it. If you have a pic that already has the info, then you need to edit the metadata and remove the coordinates."
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73ez74 | What is the difference between a propellor and an impeller? | Engineering | explainlikeimfive | {
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"An impeller is designed to push a fluid outward from the center of rotation (perpendicular to the axis of rotation). A propeller is designed to push a fluid behind the blades to produce thrust (parallel to the axis of rotation)."
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73f4qx | would someone please explain how a water tower works? | Where does the water come from? How does it get up inside of it? How long does it stay? How is it dispersed? Thanks in advance! | Engineering | explainlikeimfive | {
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"Water tanks are a solution for the \"need constant water pressure\" problem. You have a pump, but it's either on or off. When it's on, it probably moves more water than the area is using so it would generate more pressure than the pipes can take if you just pumped water into the pipes. The solution, is to build a water tower. When the pump is on it pumps water into the tower. This makes the water level in the tower go up. When the tower is full, the pump turns off. Everybody always sees the pressure generated by the height of the tower above the pipes.",
"They are basically big tanks of water on tall legs. The water is pumped into the tank, and then gravity pulls the water down into the system, although in some systems rain water is also collected. Usually the pipes to fill or drain the system are in the middle, but may be in the sides. The water may be filtered before and after, depending on the use. The gravity provides a consistent pressure without any equipment. This can provide entire cities with water pressure evenly through the plumbing by using pipes instead of motors. Pumping into the tank is far more efficient than trying to pump water to every eventual consumer of the water.",
"The water is pumped from a well up into the tower where the height of the tower then creates water pressure to keep the water flowing through that community. That's the quick and easy explanation."
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73idz6 | We have unmanned aerial vehicles, why aren't modern tanks unmanned? | Engineering | explainlikeimfive | {
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"I am a tank commander (Challenger 2) in the British Army Reserve. In my day to day job I am a pilot so I have a bit of experience in both worlds! So if we can have unmanned drones flying through the sky, why can we not have tanks remotely operated? The answer comes in three parts. Firstly, automating a drone to fly is really easy and is the reason they where the first autonomous vehicles. We've pretty much mastered the automation of the envelope of flight, so it wasn't too hard to put the actual controls of the aircraft outside the aircraft once fly by wire technology and reliable, fast satellite communication technology became a thing. We have been using autopilots and radio controlled planes for years, so the coming of the two together was pretty inevitable. Flying through the air is a lot easier for a computer than moving across the ground. The ground has obstacles and treacherous conditions that a computer struggles with. Moving through the air is pretty easy in comparison as aside from other flying obstacles, there is a lot less for the computer controlling the UAV to deal with. This is pretty much the same reason we do not yet have autonomous cars. The second reason comes down to capabilities. You might not believe this, but while a tank is equipped to go places a wheeled vehicle cannot, and is heavily armoured to protect its crew and its purpose, they are still pieces of machinery. And as a tanky, let me tell you I am being absolute truthful when I say that tanks are actually quite delicate bits of machinery. The maintenance required to keep them running is quite something and they are very prone to breaking in all sorts of imaginative ways. The number of times I have had a engine faults, suspension faults, track faults or otherwise been in a situation where a computer would have just thrown an error code and shut down are too numerous to count. Which brings me onto my third part...the human element. There is no computer yet invented that can replace the human brain for decision making. At some point a tank can and will find itself in a position where, without a human, it will be put in an awkward situation. A position where only a human, who can look at the situation and perhaps even jump out the tank if the need requires it and can effectively deal with this ongoing situation. This same scenario would never occur in aircraft as all a human pilot can do is look around and move the aircraft and make decisions from there. Having said all that, automation is coming to armoured vehicles. There is a number of automations in the works for tanks that while it will not replace the crew for the foreseeable future, it will be an aid to them. These automations take the form of automated turrets, allowing the crew to be located in the hull where it is safer (The Russian Armata utilises this), as well as remote control stations for the crew to operate the tank like a radio controlled car if the tactical situation requires it. There are even plans for tanks to be fitted with their own UAV's that feed directly back to the tanks weapon systems giving the crew greater tactical awareness. There is one last reason why you are unlikely to see main battle tanks like the Challenger 2, Abrams, Leopard and so on being automated to any degree, and I bring it up last because it makes me a bit sad. Like the battleships that once ruled the seas, their day is over. Just as battleships had to make way for the aircraft carriers as the new ruler of the seas, tanks are having to make way for...UAV's! Yes in the days of attack helicopters and UAV's that can carry the same ordnance as a manned plane like hellfires and such, the tank is no longer the master of the battlefield that it was during previous wars. No tank can really compete with something that is many times faster, more nimble and often more heavily armed than it is. That's before we even get onto the subject of man portable anti tank missiles (MANPATS) which if Syria has shown us anything has really brought the tank into question in an asymmetric warfare scenario. It's often rumoured that the current generation of main battle tanks that you see today are likely to be the last of their kind, making way for smaller and more versatile vehicles. Of course these will share the same reasons for not being autonomous that I spoke of earlier.",
"Different mission profiles and different advantages to remote control A UAV lets you have an aircrew somewhere nice, it can circle an area of interest for over a day while swapping flight crews out to keep them fresh, along with lots more people being able to review the intelligence it is gathering in real time. Not having a pilot also saves weight on life support which either extends duration or enables a bigger payload. You don't have a risk of someone getting physical access to the device because it is at high altitude so you can't literally break the antenna off. A tank is a big hulking behemoth, it needs a lot of space for a huge engine, big gun, and lots of ammunition. You have 5 guys at most in a tank, many don't have a radio operator so that's 4. You could put on an autoloader to get rid of the loader, that's 3.(Many newly designed tanks have autoloaders, they enable much faster fire) Even if you were to move the commander, driver, and gunner to be remote control you haven't shrunk the tank at all. It now weighs 59.9 tons instead of 60 and is at risk of someone physically gaining access and compromising the remote link, and now someone else has your fancy pants remote controlled tank. Its a similar reason to why we haven't fully automated freight trains, the crew provides a useful function at minimal costs, while in a plane having a remote crew provides *more* function at *less* cost",
"UAVs are used for asymmetric warfare, i.e., your enemy doesn't have access to nearly the same standard of weapons and technology that you do. Tanks are used against conventional armies. Any technological enemy is going to win against remote controlled vehicles by jamming their comms.",
"1. UAVs are very new. 2. UAVs are not totally reliable. 3. UAVs are up in the air where radio signals reach more easily. 4. Tanks use people to physically load the cannon, it's not fully automated. 5. Tanks are meant for use in very fast-paced battle where the delay in telecoms could mean failure."
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7ndz6c | What is a dual-clutch gearbox and how does it work? | Engineering | explainlikeimfive | {
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"Okay, forgive me if I go too basic here but I'm going to start at the beginning. Your standard manual gearbox has a series of gears at different ratios. All of these gears are spinning all the time, but only one set is actually connected to the engine at a time. The others are spinning freely because they're still connected to the wheels by way of the drive shaft. When you depress the clutch pedal, you disengage the engine from the gearbox. When you move the gear lever, you select a different gear set (which, remember, is already spinning at speed). This is where synchronisers do their thing and match the input and output speed of the gearbox up. You release the clutch pedal, causing the engine to re-engage, and your newly-selected gear takes over. Now, imagine you want to change gear super fast. The actual selection process (ie picking the gear to move to) can be done really fast mechanically, but the synchronisation step will always take time. Solution? Add another clutch! By nesting the clutch/flywheel assembly between two clutches that engage different sets of gears, you can engage one clutch at the same time you disengage the other. When you hit \"shift up\" in a double-clutch car, the next gear is selected at the same time as the flywheel moves from one input to the other. To visualise the sandwich clutch thing, try this. Put your hands next to, but not touching your knee with the palms facing in. Rest your knee on one palm. Each of your hands is a clutch, and your knee is the flywheel. By moving your knee away from one hand, you move it closer to the other. Source: Am automotive engineering student, wrote lots of papers on transmissions last year. Edited for clarity per comment below",
"Normal transmission: engine- > clutch- > gearbox- > wheels. Procedure is this when changing gears: clutch decouples the engine from the gearbox then the gears are shifted by a lever that moves a cog around and then the clutch couples that to the engine again. A dual clutch gearbox is essentially two different single clutch gearboxes with their respective clutches in one casing. Gearbox one is 1/3/5 gear gearbox two is 2/4/6. The advantage is that the next gear is already preselected in the other gearbox so you save the time it takes to move cogs around without the engine actually giving power to the wheels. You just select the other clutch",
"If you want detail, the two clutches are two multiplate wet clutches (like a motorbike clutch), the two sit one behind the other on the same shaft, but the shaft is a hollow shaft with another shaft inside it. One of the clutches sits on the hollow shaft servicing 1, 3, 5, 7 the other clutch sits on the solid shaft as it pokes out the hollow shaft next to the engine and services gears 2, 4, 6. Each gear is electronically pre selected, though this is where I'm a bit lacking, as I don't know how how it's decided which gear is preselected, one gear up or one gear down. Aside from that, the clicking of the paddle disengages one clutch and engages the the pre selected one electronically. To my knowledge, dual clutch transmissions can not be purely mechanical. There are various systems involved in reducing the speed of transmission, Mclaren for example used touch sensitive pads on the paddles to effectively pre select the pre selection process.",
"A dual clutch gearbox is two gearboxes in one. You use one gearbox while the next gear is lined up on the second. When it changes gear it just swaps between the two gearboxes one clutch out the other in."
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7niqog | What goes on at military installations near Death Valley? | Engineering | explainlikeimfive | {
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"If you follow that road further to the West you'll see it goes to [Fort Irwin]( URL_0 ) The desert is a lovely place for a military training center as it lets them build complete villages to train in along with providing plenty of space for exercises, both completely simulated and live fire without getting too close to anyone off base. Those roads you saw likely lead to the area where they perform these trainings, they don't want you going down that road and getting hit by a howitzer round when they're training.",
"That just looks like they are mining stuff. May be something as innocuous as gravel to build roads with. If it was something important, they would have ordered Google Maps to pixelate out that part of the satellite view."
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7nnsve | why there is so much iron and steel on top of bridges | Engineering | explainlikeimfive | {
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"The \"top of the bridges\" are significant in the support of the bridge. It's easy to think that the bridge is supported only by what is under it, but that's not really the case. Much of a bridge is \"hanging\" from the metal that is atop of the bridge, supported by the very heavy piers that come up from the ground, extend up above the bridge surface and from which additional metal (or wire in the case of a true \"suspension bridge) is then hung. I think you have in your head a sort of \"stacking\" engineering of the bridge, when that isn't quite right!"
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7nnxzg | What is the point of exhaust gas re-circulation in a gas engine? | I understand it has something to do with emissions? It sounds like a horrible idea to add exhaust back into the intake of and engine. Why do it? | Engineering | explainlikeimfive | {
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"When gas is burned on its own without additives, it burns very hot. When it burns this hot one of the products of combustion is NOx, nitrogen oxides, which is a serious pollutant, responsible for smog and a main contributor of acid rain. The most notable previous attempt to cool the combustion was leaded gasoline, which lead to airborne lead and serious health and pollution problems. So an EGR takes a little bit of exhaust and adds it into the combustion chamber. Because it's already exhaust it has less then atmospheric oxygen levels, removing a bit of oxygen from the mix, and the carbon dioxide helps cool the charge, reducing the amount of NOx produced."
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7noqtw | How does reverse thrust work on large airliners? (turbofan engines) | I've always been baffled by it. Do the propellers suddenly switch directions? Surely can't at such high RPMs. Does the blade pitch reverse? Does the exhaust suddenly act like an intake? How do they reverse the airflow so quickly without damaging the engine or flaming out? Thanks for any answers! | Engineering | explainlikeimfive | {
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"Actually, none of the things you've suggested. They work by having large bits of the engine, called \"buckets\", move into place behind the engine to deflect the exhaust gas so that the gas ends up going forwards. You can see an image of a couple of engines with the reverser buckets deployed [here]( URL_0 ).",
"the fan still blows the same way. but there's several flaps that redirects the jet thrust forwards instead of backwards."
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"https://www.researchgate.net/profile/Md_Haque80/publication/288737295/figure/fig1/AS:324709313990674@1454428141718/Fig-1-A-KLM-with-reverse-thrust-buckets-left-6-and-Northwest-DC9%27s-used-to.png"
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7npj99 | In video games, cars have a max speed. In real life if a car exceeds this max speed, what happens or could happen, if anything, to the car’s engine, chassis, etc.? | Engineering | explainlikeimfive | {
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"Depends on the car. Most real life street cars, the max speed is either an electronic limit (basically the gas pedal stops working once you hit it) or it's the actual limit that the engines horse power ceases to accelerate the car, this is more common in higher end cars. The max speed is thus the speed that air resistance (and other losses) matches engine horse power. Now what happens if you exceed that? Say you strapped a rocket to your sports car? The most common thing, if in gear, the engine may redline, and likely the failure mode is valve float (the valve springs are not strong enough to close the valves, and they may hit the piston), some engines the connecting rods might break from the forces. Those are the common RPM limit failure modes, and would result in a rapid unplanned disassembly of the engine. There are a bunch of other common failure modes (like lack of oil to the pistons, resulting in it seizing, and head gasket blowing resulting from too much fuel/air in the cylinder, but those are more common if the engine is supped up to provide more power than the engine block was designed for). Now if you pop the car into neutral and let the rockets power you, typically the first component to fail will be the tires, exceed their speed rating and they'll blow apart. At very high speeds, and if you have special super high speed tires, the next failure is aerodynamic, a bad bump or something and the front lifts up and you start flying. This depends a lot on the aerodynamics of the car.",
"Cars in real life have a max speed, its determined by the power of the engine and the aerodynamics of the car. Eventually the wind resistance equals the power from the engine and you can't go any faster Depending on the car, you can also hit a lift off point where any small bump will lift the chassis of the car, let the air catch under it, and send you flipping through the air. You'll sometimes see this happen during accidents in racing. If you can avoid lifting off and flipping then nothing bad happens to the car at high speed aside from burning through fuel and tires at a greatly accelerated rate."
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7npmsj | Why is it recommended to connect the black jumper cable to a bolt on the engine and not the negative post on the dead battery when jumping a car? | Engineering | explainlikeimfive | {
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"text": [
"Batteries generate hydrogen gas when the are charging. This can sometimes explode when connecting the battery cable as there are usually sparks. Ideally, connect the positive first, then connect the ground further away from the battery.",
"Because that final connection is likely to spark, and the battery can have hydrogen gas at the terminal (enough to combust, and flying lead and acid makes for a bad day for someone). Since the battery and engine are directly connected to each other, connecting the jumper cable to a large piece of metal on the car, accomplishes completing the circuit with less risk of a spark igniting any hydrogen gas that has built up near the dead battery."
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7nq1pf | Why can some 2000HP tuner cars beat million dollar hypercars such as the Bugatti Veyron? | Engineering | explainlikeimfive | {
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"text": [
"When it comes to cars, there's something important to remember: The more power it makes, the faster it breaks. A Veyron isn't impressive because it makes 1,000HP. Anyone can make 1,000HP these days. It's impressive because it makes a *practical 1000hp*. It runs on pump gas, without overheating in traffic, with reasonable oil change intervals, with an adjustment and maintenance schedule on par with a consumer car. It can go thousands of miles without issue, and be used every day. It's road legal, and passes the applicable tests. A 2000HP tuner car is a whole different story. That engine might only be good for a quarter mile to a mile at a time, before a full rebuild is required. It's going to run hot, you're NEVER going to idle in traffic and get away with it. These cars run for *seconds* at a time, they don't last *minutes* for a trip to the store or *hours* for a road trip. It's going to require constant attention and tweaking. It's going to require specialized fuel. It's going to require a start-up and shut-down procedure. It's going to have a massive peak of power and turbo lag that makes it a pain to drive in real life. TL;DR: They can, but, the engine would require too much maintenance and break too often while being unpleasant to use and impractical to live with the entire time.",
"Hypercars and supercars are designed to drive *well,* not just fast. Muscle cars can be much cheaper and go fast in a straight line, but when you try to take that speed around a corner, bye-bye car, you're a pancake now.",
"Yeah, but those ridiculous engines from top fuel dragsters and funny cars aren't designed for duability. They essentially get rebuilt every day at the track, usually even in between races. Because that much horsepower literally beats the stuffing out of the engine. While if you could afford a $2M Bugatti Veyron, you could afford to rebuild your engine several times a year, not everytime you drove it to the store. Those 2000 hp engines are designed for one thing: go fast, and go fast all at once. But not for long. Plus, your Veyron engine has to run well and smooth for the 98% of the time you're just going shopping and obeying the speed limit, but also be able to crank it up for the 2% of the time when you're on the Autobahn. While the Veyron's engine is not what I'd call fuel efficient, if you're doing normal road driving you'll get reasonable fuel mileage (for a hypercar). (at top speed tho, a Veyron will drain its fuel tank in 7 minutes) A dragsters engine will deplete its fuel in seconds.",
"Most of those cars \"beat\" the supercars in one particular aspect, because it's specialized. The Bugatti Veyron is specialized to get to the highest top speed in a production car, at the time it was built. That doesn't mean it will smoke everything else in a quarter-mile, because several other cars beat it in the 0-60 and 0-100, but don't have the top speed of the Veyron. Without knowing more about what the Veyron is being beat at or the car in question, it's hard to speculate, but it could just be that it's harder to mass-produce something like the 2000 HP tuner car."
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7nw1vg | - Why do soup cans have ridges? | At least some soup cans have ridges around their circumference all the way up and down the can. What is their purpose? | Engineering | explainlikeimfive | {
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"text": [
"Strength. It's the same sort of reason old metal fuel cans have the embossed X on the side of them. It makes the whole shape stiffer.",
"Resistance to bulging and collapse. In most situations cans are damaged by forces from the outside pushing into the can and denting them. The ridges act like a stiffener and help resist the damage that a smooth can would suffer. This is especially important when the can is on the bottom of a large heavy stack. If it fails, the whole stack might come down ($$$), so manufacturers have deemed it worth taking the extra effort and material to add the ridges.",
"Makes the can stronger to prevent denting from impacts on the side or collapsing from the weight of other cans on top. Soda cans don't have them because the contents are under pressure and because it's cheaper not to bother."
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7nwlz1 | How metropolises such as Phoenix, Tucson, Las Vegas, other southwestern U.S. cities, get enough water to supply the huge population with no lakes or rivers near. | Engineering | explainlikeimfive | {
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"ds50c7b"
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"text": [
"All these cities share water from the Colorado River under an agreement called [the Colorado River Compact]( URL_0 ). it is carried through the area by pipelines."
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