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6b1wyq | what is the purpose of the grooves in gravel roads? | Whenever I drive on a gravel drive my car hits grooves that are perpendicular to the roadway across the entire road. What purpose do these grooves serve? | Engineering | explainlikeimfive | {
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"The phenomenon is called \"[Washboarding]( URL_0 )\". It's caused by the wheels of cars bouncing on the road gradually moving the gravel, sand, or even clay around.",
"They don't have a \"purpose\". It's how the road wears. When the gravel road is first laid down (or regraveled), the grooves aren't there. They form over time as the road wears. Why the road wears in that pattern I cannot tell you for certain. I suspect that it is due to the grader blade catching and jumping a bit as the road was first made. But I don't really know.",
"Its washboarding, like tsuuga said. Its caused by vehicles either bouncing on uneven rock or spinning their tires on loose gravel. Water accumulation from rain on a gravel road that isn't properly crowned can lead to improper drainage and water sitting on the surface and washing out the fines (very small rock/sand) that helps to bind the bigger rocks together, which can also lead to more bumps or potholes. Then it just compounds on itself, as more vehicles travel over one of these bad spots, it will lead to vehicles bouncing or spinning tires more and more and more loose rock and bigger holes and it will just keep increasing the problem exponentially (not really that fast, but almost). Gravel roads will never stay perfect, no matter how well they are designed and compacted, eventually someone will spin a tire and everything will just go downhill from there. They require regular maintenance (grading and sometimes compacting), depending on how much use the road sees, and if its regular cars, or loaded log trucks. Its cheaper to build a gravel road and maintain it for low volume travel than it is to build a paved road. Forest engineer here, I design and layout logging roads (gravel roads) for a living. I also used to maintain these roads with heavy equipment (grader operator). Any other questions, let me know"
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6b2iha | What causes some images to be wavy for a moment but then render correctly? | For example: URL_0 Both are screenshots of the exact same thing; the left immediately upon loading, the right shortly thereafter. What causes the wavy pattern, and why does it go away on its own? (Forgive the misleading timestamps, it took a few tries to get the left screenshot) | Engineering | explainlikeimfive | {
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"There are two things going on here. The first is that this is a photograph of a TV screen. The TV screen has pixels, and so does the camera that took that photo, and so also does the device you're viewing the image on. The different sets of pixels don't necessarily line up perfectly, and under certain circumstances when this happens, the result is regular or semi-regular patterns, which can often look like wavy lines. This effect is called \"moiré\". The second is that the image is most likely saved in a \"progressive\" format. The image downloads in stages, first with really big pixels which gives you a blurry version of the image that displays fairly quickly, and then more detail is added, making the pixels smaller to give you a much sharper image. So on the left, you have the partially-downloaded image with the big pixels, and due to the respective resolutions of the TV screen, the camera and your device, that just happens to give you that moiré pattern. On the right, the image has completely downloaded: the moiré pattern is still there if you look closely, but it's much finer."
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6b5ryk | What's the difference between a powerful (semi truck) and fast (racecar) engine? | Engineering | explainlikeimfive | {
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"The difference all boils down to torque. That is how much turning force an engine can put out. Torque is arguably a more important number in determining engine performance than horsepower. Now there's two ways to increase torque: raise the pressure inside the engine, or increase the number of cylinders. In the case of a truck, you're dealing with a heavy object that needs a lot of torque to get moving. So you want your peak torque to all be at the low end of your RPM band. To do this, we turn up the pressure, aka the compression ratio. The piston will squeeze the air/fuel mixture more before it ignites. When you compress the mixture, it generates heat. If you compress it enough, that heat will cause the fuel to spontaneously ignite, slamming the piston back down with a lot of force. That force is transferred to the wheels, which helps get that heavy load moving. This is why trucks use diesel engines. Diesel fuel stands up to high pressures without igniting too quickly. So you can get pressures in the cylinders really high, meaning lots of low end torque. The downside is that due to the high pressures, diesel engines have to be built strong. That makes them heavy. A heavier engine can't spin around as fast. Nor does it like to change its rotational speed very quickly. Gearing can help, but you're ultimately limited how fast you can go, and how quickly you can accelerate. Now gasoline/top fuel engines use lower compression. They can be built much lighter since they don't have to hold up to very high pressures. So the engine can run faster. If you want more power, you just dump more air/fuel into the system. So they produce more torque the faster you rev them. Great for racing, because you're going to be running high RPM at full throttle. But even if you dump more fuel in, you're ultimately limited to how big the engine's volume is. So we need to go bigger. Now you could make one big cylinder, but that's going to require more momentum to get it moving. It's also less compact. So instead you work with several smaller cylinders. To increase torque, just increase the number of cylinders. You can increase power without having to increase the mass or work done by one piston. And you can just keep adding pistons. Petrol aviation engines will have 12, 24, even 36 cylinders and run at thousands or horsepower. A diesel can do the same with far fewer cylinders, but it'll run slower. Think of it like dragging a cart with a rope. You could get one big dude (think The Mountain) and he'll be able to efficiently pull it by himself without getting too tired, all be it slowly. But if you have four skinny guys, they can each share the work and move it faster, but they're going to tire out faster because they have less endurance. Of course there are gasoline engines that can run at higher pressures to increase torque. But these are more complex than a diesel, and also require specially formulated fuel. That is because gasoline self ignites more readily at lower temperatures. If it ignites prematurely, it can severely damage the engine in a phenomenon known as \"detonation\" or \"knocking\". They will use these more complex engines in race cars to help improve low end acceleration while keeping high end torque. However, it's not that common in road cars except high end ones. So what if you need the best of both worlds without increasing complexity, or making the vehicle prohibitively expensive? That's where electric come in. An electric motor produces consistently strong torque at all RPM bands, in a lightweight package. You'll see them used in vehicles like trains, which need to pull very heavy loads, but also need to go fast. Or Formula E race cars, which can accelerate very quickly.",
"Horsepower is how fast you hit the wall, torque is how far you move that wall. Semi's have to move a lot of load, so they're built to supply torque. Race cars just have to go fast, so they're built for more horsepower.",
"Most of the answers so far have mentioned only torque vs horsepower. Just to be complete, HP is calculated from torque...so it is a derived unit based on RPM. There are a lot of other differences that you might be interested in. A racecar engine is designed to have the highest possible power-to-weight ratio... it needs to be as light as possible to keep the weight of the car down. It's also important to keep the moving parts very light, as heavy parts have more *momentum* once they are moving, and more *inertia* if they are stopped. This is important in race engines (especially F1) because the engines are required to run very fast, then slow down quickly, then speed up again... thousands of times in a race. Because these moving parts are so light, they need to spin *very* fast to have as much power as a heavier motor spinning slowly. This is the main reason race engines need to spin at very high RPM to generate a lot of power. All the parts are optimized to be light, and very well balanced. Only the very finest materials are used. The *tolerances* (spaces between moving parts) are extremely small. An F1 engine can cost between 8 - 10 million dollars. Each. That semi-truck engine? Lots of torque...but it does not spin very fast. Compared to a race engine, they are quite crudely made. Many thousands are built...and they are designed to be easy to assemble, and last a reasonable time, with minimum maintenance."
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6b7hv3 | My nearest major city has a road grid that is *slightly* angled off East West. Is there a practical reason for this? | URL_0 Is this deliberate or just a continuation of the infrastructure originally installed in the city's infancy. Edit: Melbourne Australia is the linked map though I'm assuming the design considerations are also applied elsewhere in the world. | Engineering | explainlikeimfive | {
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"From what I can tell of the [article on the \"Hoddle Grid\"]( URL_0 ), it's not a continuation of the original infrastructure, which has a different angle meant to match with the Yarra River. That same article implies that the *slightly* off angle of the rest of the city is aligned with what magnetic north used to be, 8 degrees off true north. But that's not really cited so I don't know if it's definitive or just a guess."
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6bhsn8 | why space rockets do not tip over at T plus one second? What keeps them in vertical position? | Engineering | explainlikeimfive | {
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"The engines at the bottom of the rocket are mounted on gimbals that can adjust their direction. The rocket has very precise sensors that can detect if it's starting to tip over, and its computer will react by angling one of the engines to push back the other direction. It took a lot of engineering and fine-tuning before we got the sensors and the engine adjustments right. Back in the '50s, a *lot* of rockets blew up on the pad or shortly after launch. [Here's one compilation]( URL_0 ) of some early rocket failures.",
"Gravity affects the entire rocket more or less equally (the distance between the furthest and closest point to said gravity on the rocket is too small to really affect anything), so being properly upright to begin with is a major help. With a perfectly aligned axis of thrust, there's nothing to torque the rocket off either. Of course, to help make sure everything does operate properly, as nothing's truly perfect and there's also air currents to worry about, the rocket itself has some active stabilizers. Used to be tiny jets of air or other materials to help provide thrust counter to whatever direction it might start tipping towards, but nowadays all of the engines are gimbaled: Effectively the rocket uses limited thrust vectoring to make tiny adjustments and keep itself perfectly on course. Once it's actually picked up some speed, rotational inertia will also add in to the list of things keeping it going nice and up."
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6bhwj7 | Why are radio waves preferred for long distance communication? | From my understanding, most communication sources from Wifi to long distance radio uses radio what. What properties of radio waves make them suitable? It you can link a more technical explanation, that'd also he great! (AskScience never accepts my question, but I'm also looking for a somewhat technical explanation) | Engineering | explainlikeimfive | {
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"Nice properties of radio waves: 1) The go through walls, unless they are made of metal. 2) They are bent by the upper layers of the atmosphere, so a radio message can go from the US to Europe. 3) Very sensitive receivers are mass produced at very low cost, so that only a very small part of the signal is needed to produce long distance communications.",
"Cable is preferred for long distance communication if you don't have to move around. Are you asking why radio instead of x-rays or infrared?",
"> Why are radio waves preferred for long distance communication? They aren't. The preferred method is trans-continental fiber-optic cable. At $50-400m (not including launch insurance or the cost of the launch itself), 288 strand fiber is cheaper per mile at ~$6/ft than a satellite, it doesn't suffer from interference, the signals are extremely difficult to intercept, since it's terrestrial it's relatively easily maintained, and latency is much shorter. Satellites have a typical theoretical maximum bandwidth of 155 Mbps, but in practice they get much less than that, whereas single mode fiber can achieve 10 Gbps per strand, and multi-mode is regarded as effectively near limitless at distances less than 100m. DWDM can achieve up to 16 Tbps, or more bandwidth on a single fiber than all operational communications satellites. Microwaves are used for point to point communication between two towers, using directional horns or parabolas, and have some specific application, enough that you still see them in use often enough, I suppose. From personal experience, I can tell you you're not supposed to stand in front of a horn because you can get yourself cooked from the inside out at those radio frequencies and amplitudes. For broadcast public radio, certain frequency bands have desirable propagation properties that make them cheap to operate and achieve wide coverage. Radio is typically the preferred method of communication when you don't have access to a physical line. A single satellite can provide line of sight coverage as far as to the horizon of it's purview from it's orbit. Antenna towers are preferred to be as high as possible for a similar reason, line of sight coverage. Different frequencies have different propagation characteristics. It's not an arbitrary decision that WiFi is in the 2.4 GHz band, those frequencies at typically 100 mW will scatter and be absorbed within a few hundred feet, perfect for local area coverage. These properties have helped dictate aspects of FCC regulation regarding things like tower height, maximum output, and frequency allocations."
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6bkchf | Why does the typical wooden house built today (or buildings I've seen built as new developments) look like there isn't enough there to hold it up, yet stand to hold a fair amount of weight? | Background: I'm in the process of buying a house that is being built and have been tracking its process, week by week. I've also seen multiple apartment homes built recently and noticed that a a good chunk of the building is wooden, despite being many, many stories tall. I'm sure I have an irrational fear of it all collapsing upon itself (too many games of Jenga bias my opinion, I'll admit) out of the sheer fact that I misunderstand how structures are built today. Explain like I'm 5, just how it looks like so little wood can hold so much weight and won't collapse while I'm sleeping at night. | Engineering | explainlikeimfive | {
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"Civil engineer here. There are two parts to this: 1. There has been a shift in the way things are designed over time. When we started building things centuries ago, we didn't quite understand material properties, so we over designed our structures i.e. we put in extra to make sure it would stand up. That's part of the reason many ancient structures are still standing, they are far stronger than they need to be. As we have tested and learnt more about materials, we are able to design structures closer to what they need for their purpose. This was mostly driven by cost during recession periods, where work was more competitive, so being able to build the same structure with less material meant you could bid a lower price on the job, so you were more likely to get selected. 2. For wood in particular, we have always known it is strong (100ft redwoods for example), but the problem has been knowing how strong a particular piece of wood is. For concrete or steel, you can try a particular method of manufacture, test the product to destruction, and know with reasonable certainty that if you use the same method again you will get a product of a certain strength. Wood is grown, so every tree will be slightly different, so when we used wood before, we over designed to make sure it was strong enough. Then we developed glulam, or laminated sheets of wood that were glued together to form structural members. This allowed for more certainty in the strength, therefore we can design wooden structures more efficiently. TL;DR - cost pushed us to design more efficient buildings, and wood was made more reliable by gluing sheets of it together instead of just cutting trees to the required shape."
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6bmt55 | Is it better to leave a car running while idling or to turn it off and on when you need to move? | Engineering | explainlikeimfive | {
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"It depends. Each time you start a vehicle you increase wear on the starter motor, which is a heavy-duty motor near the back of the engine that is powerful enough to spin the engine without using any petrol. This wear and tear isn't all that important, but the starter motor uses a lot of electricity to work and will therefore drain the car's battery very quickly. The battery gets charged when you drive around, but this takes quite a long time, so if you keep turning the engine off and on, eventually it'll go flat and won't be strong enough to start the car. To reduce pollution and save fuel, lots of modern cars have something called stop-start technology. This means that the engine will stop in the best position to restart, using the least amount of fuel and electricity in the battery. And the car is clever, so it knows if the battery is almost flat and will keep the engine running to charge it back up. The short answer is, if you don't need any heat or aircon and you know you're going to be idling for more than a few minutes, turn the engine off. If you're waiting at traffic lights, or in light congestion, keep the engine on.",
"It depends on the engine and the time. Starting the engine uses more fuel for a short time than to keep it running for the same time, especially with older engines. But this is for something like 5 to 10 seconds. If you know you'll be waiting longer, turn it off.",
"There are now quite a few cars that turn off your engine while stopped and then restart it when you press on the pedal. This can increase fuel economy in the city by about 1-2 mpg. Of course those cars are designed to do that so I would not recommend doing it with a car not designed for it. Overall idling is better for the engine but you do waste fuel, and only turning it off for a little bit and then starting back up while everything is still warm and lubricated won't hurt the engine much if at all. Yet it is not something you should continually do since your car is not designed for that kind of use (specifically your starter motor and possibly battery usage)."
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6bn96x | Why did cellphones only become popular recently in the last decade when walkie talkies and transistor radios were available long before? | Cellphones only started to become popular after the mid 2000s but as a kid in the 90s we had walkie talkies. Did it take a long time for the technology of radios used by the army to become available for home use? | Engineering | explainlikeimfive | {
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"The main problem with walkie talkies is range. Walkie talkies are only limited to a few kilometers, and they need to broadcast a very powerful signal. The farther you are, the more powerful the signal needs to be. The main innovation of cellular phones is the cellular part. When you call someone, your phone doesn't directly connect with their phone. Instead, your phone connects to a cellphone tower in its vicinity, while the recipient is also connected to a cellphone tower in their vicinity. The two cellphone towers are physically connected through a series of wires (well, not directly, they pass through a switching center). This way each phone only has to have a signal powerful enough to reach the closest cellphone tower.",
"> Did it take a long time for the technology of radios used by the army to become available for home use? No, but it took a long time for the price of cell phones to drop and it also took a while for cell carriers to have coverage in enough places to justify the cost of the device and the calling plan that came with it.",
"Up until 80s when the first cell phones became available, radios and walkie-talkies weren't common. Police cruisers would have a radio, but individual police would not. This is because they were so large and required such large batteries that they would prohibit certain movements. Hence why early cellphones were car phojes and bag phones, never meant to be truly mobile but keant to be transferred from home to car with a few minutes of life away from a power source. It wasn't until the late 80s and into the 90s that they became smaller and powrr sources became more efficient that you could have them on your person and not be prohibited by the size and weight."
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6bpptd | Why do some establishments and government departments not upgrade their computer's OS? | Engineering | explainlikeimfive | {
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"Usually it's because they have some old app that, due to a design problem, does not work right on the modern version of the OS. Sometimes it's because their IT department does not have enough staff to upgrade their numerous computers; everyone is busy. Sometimes it's because the bosses would not allocate the budget for needed upgrades, if they were not free of charge.",
"Resources mainly time and money. The training for the new interface. Different programs that they use do not have compatibility with the OS. Most companies or groups do not delay advancement out of choice, but rather that they are waiting to confirm that advancing will not hurt their production activities.",
"In addition to the great answers here about cost and support of old hardware/software, there's also the question of security. The Army, for example, spends a great deal of time and money doing everything they can to lock down workstations and keep them free of viruses, and to limit access by people who shouldn't have access. If they spend five years patching security flaws in, say, Windows 7, and then finally manage to get everything just the way they want it, why would they then switch to Windows 10 and risk re-opening all those security fixes, or opening entirely new ones? Does Windows 10 offer them some inherent advantage that makes it worth the trouble, or is upgrading something they'd just be doing to keep current, because reasons? If there's no clear advantage to spending the money, time, and resources to upgrade and then fix all the things that are going to go wrong, there's no good reason to bother. If everything is working perfectly on Windows 7, why should they upgrade to Windows 10?"
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6bqkkb | why could old mopeds (before many antipollution laws) get insane mileage while new "ecofriendly" ones can't? | Engineering | explainlikeimfive | {
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"The very short answer is that they were tuned differently. By increasing the amount of oxygen present during the combustion cycle, you can extract more power from the same amount of gas (or the same power from less gas), which increases fuel economy. However, oxygen-rich combustion (or *lean* combustion) is extremely hot, which produces more pollutants (specifically ~~hydrocarbons~~ oxides of nitrogen, as /u/tminus7700 corrected me below). In order to be \"ecofriendly\", new mopeds (or any Carnot cycle gas engine) has to meet a certain emissions threshold. To reduce the number of pollutants, they have to cool down the combustion. To cool down the combustion, they have to use less oxygen. Using less oxygen means they extract less power from a unit of gas, which means you need to use more gas to propel the vehicle."
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6brk1d | Refrigerators versus air conditioners | From what I've learned from thermo classes, refrigerators and air conditioning systems work by using the same principle of using work to move heat. My question is why do air conditioners (both home and auto) require service every 5-10 years to recharge refrigerant, but my refrigerator in the basement has been running constantly for 30 years with no service or refrigerant exchange? | Engineering | explainlikeimfive | {
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"Your refrigerator is only really running every once in a while. Once the door is closed, the temperature inside will pretty much stay the same until you open the door again. So the cooling part of the refrigerator only has to run every so often to maintain the internal temperature.",
"Home systems are hermetically sealed should not need refilling. If they do, there is a leak. Cars have a belt driven compressor and rubber hoses with fittings. The seals in them wear out and tend to leak. Refrigerators do need periodic cleaning of their condenser coils. I've spent more time doing that than cleaning my house's AC."
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6bs8ey | How does forcing laptops to be in checked luggage prevent bombs hidden in laptops? | URL_0 An altimeter (built in to laptops), GPS, Bluetooth, or other RF detonator can still set it off... So, if there is a bomb in a laptop, does it matter where it is on the plane? What is the point of banning them in the passenger cabin? | Engineering | explainlikeimfive | {
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"The idea is that a laptop bomb is usually going to be used in an attempt to depressurize the plane by detonating it next to a window. If the laptop is stored with cargo, it will be dampened by all the other stored cargo and probably won't have any devastating effect except to the luggage of the unlucky people who got the storage space next to the bomb.",
"You are looking for sense where there is none. The entire set of security rules is just a random patchwork of unsubstantiated fears.",
"Many things about Airplane/Airport security don't really make much sense - a couple likely reasons are that a Laptop's removable Lithium Ion Battery, if handled the wrong way can explode, and as a result makes a good improvised bomb, placing it in checked luggage makes it easier to detect and prevent from being loaded onto the plane a battery or laptop which has been tampered with, as the owner won't have access to it in order to take a normal battery and convert it to an IED on the plane. You mention C-4 and RDX in a second level comment, it is possible that the intent is to give airport security a chance to run a bomb dog over the luggage, but I doubt this has anything to do with reducing the amount of damage a plane takes if a bomb goes off, and more to do with preventing bombs from getting on in the first place."
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6bwkz4 | What does it mean when software is open source? How come others can't just look at the coding of closed source software? | Engineering | explainlikeimfive | {
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"Think of software as a delicious cake. Think of source code as the recipe for the cake. For both open source and closed source software, you get to eat the cake. For open source, the recipe is available to you. For closed source, the recipe is a secret kept by the people who sold the cake. You can take a closed source cake and attempt to figure out a recipe from it, but you don't really get the recipe.",
"Source code is what software is initially written in by a human programmer. The programmer selects a language (or, in some cases, multiple languages) and uses it to create the source code of the program. Depending on the language used and the skill of the programmer, the source code could be very easily readable by a programmer, or it could be nearly impossible. Most software source code lies somewhere in between. This source code represents the logic of the program, but it can't be \"run\" directly. Another program needs to either compile or interpret it. Compilation is the process of turning source code into byte/machine code, which the hardware knows how to run. Interpretation is the process of reading through source code and converting the source code instructions into into a running program \"on the fly\". Programming languages are often, at a high level, divided into \"compiled languages\" (like C, C++, or Java) and \"interpreted (or scripting) languages\" (like JavaScript, python, ruby, perl) depending on which route is used. For (closed-source) compiled apps, only the byte/machine code is distributed. There is no deterministic method of reversing the compilation process back to get the original source code. There are many reasons for this but two stand out: 1. Optimization. The compiler is much smarter than human programmers so when it compiles the code, it makes changes to the actual logic. This produces the same result that the programmer intended, but performs the task much more efficiently so that the code runs faster, uses less memory, or both, compared to what the programmer actually wrote 2. There's More Than One Way To Do It. Programming languages are much more verbose than machine code. There could be thousands (or even infinite) ways to write the same program in a given high level language, that all compile to the same machine code. There would be no way to know which one of those alternatives was intended, given the machine code, so reversal is impossible. On the other hand, for interpreted code, the source code is generally what's distributed, because there is no intermediary phase of compiling to machine code. Most developers of such software stick to an open source model for this reason, but for others, there are alternatives, such as obfuscation (turning source code into intentionally less-readable source code prior to distribution). Editing to add: one of the big reasons why source code is verbose and machine code is not is that in source code (for most useful real-world languages, anyway), things have names: variables, constants, functions, classes... all of these things are named (hopefully) to indicate what they're for, what they do, what they mean. When the source is converted to machine code, all of this naming is automatically lost. In the machine code, all those things only have numeric addresses -- there's no context of what things mean. The same thing can be accomplished through obfuscation: change every variable name to vNNNNN and every function to fNNNNN and your code will be nearly uninterpretable (to humans) without any change to its meaning to the computer.",
"The key word here isn't \"open\" or \"closed,\" it's \"source.\" Source code is readable, logical, full of structure and flow. But the computer doesn't run that (well, it does if the language is *scripted* or *interpreted*, but those have huge tradeoffs). The source code is *compiled* into a program that your computer can run directly. **Almost all of the content of the source code is thrown out, when compiling. It's there to direct the compiler in making a finished product, not to be *part* of the finished product**. So you can take the finished product and try to reverse it back into source code, but there's not much left to work with. In Open Source software, you can see that original source code, and work with it. In Closed Source software, you only get the compiled bit. They keep the code private."
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6c0wpl | Why are houses in the United States built out of wood instead of stronger materials, specially in the middle of hurricane and tornado country? | Please spare the "cheaper" and "faster" explanations. Houses in most third world countries are made out of concrete blocks (lower middle class and above), and I've been part of construction crews building cinder block housing, so building a wood house is probably just a week faster. | Engineering | explainlikeimfive | {
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"Wood is plenty strong against most problems, and where it fails (like in tornadoes) so do \"stronger\" materials. The biggest danger in hurricanes is flooding, where concrete blocks or bricks are just as bad. Block construction, while stronger in compression, is weaker than almost anything in tension and shear, like you get with strong winds or earthquakes. Block buildings are some of the *worst* construction in earthquake-prone areas. This has been a serious problem in several disasters in third world areas. They can be reinforced well enough to be acceptable, but in many cases that means building a double-wall with framing as a separate reinforcing layer, making it not really a pure block construction at all. Lastly, block walls are harder to insulate against serious cold. Altogether, framed walls (wood or steel) are a *good* design choice for a lot of the conditions around North America.",
"Sorry, Cost is the answer. It's a tradeoff between the cost of materials and the cost of workers. Houses in hurricane districts in Florida are made of concrete blocks or poured concrete. It's 50% more expensive that wood frame construction, when you factor in what construction workers in the US are paid.",
"Concrete blocks and bricks are just as susceptible as a wood house when it comes to getting hit by tornados for one. Also, there are still windows that can break creating a vacuum of pressure even if you did avoid the stick frames. Better question is probably why arent block and brick houses built where wild/forest fires are prevalent?",
"Tornadoes will erase a cinder block house right at ground level. Most damage from hurricanes is from flooding, or from roof failures. You still need a roof on a cinder block house. Most third world countries suffer way more casualties from weather than the U.S."
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6c7bj5 | If traditional locks are easily picked, why do we still use them? | What are the great advantages of tradicional locks over other designs? Security doesn't seem that great... | Engineering | explainlikeimfive | {
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"Physical locks are not meant to make things impossible to get to. They just make it hard to get to. No amount of physical locks will ever make something 100% secure because even if they are unpickable, and there are some unpickable locks, physical things can be broken. The point of physical locks are that it takes the robber time and energy to get around them. If it takes more time and energy to do it most robbers will just go to the next location and hope there is less security. because of this most people just need convenient locks. Ones that do not take up a lot of space or time to open. It is only when we see extremely valuable things that the higher tech locks that take a lot of space/time/energy to work with.",
"No point in having amazing locks when you can just kick a door down or bust a window. Locks on homes just need to be enough to keep out lazy casual thieves and curious neighborhood kids. Most residences aren't specifically chosen because a burglar wants something specific in your house, they're chosen because it's easy to get inside & take whatever might be valuable. If you're trying to secure a place that has things of particular value, you'll have far more robust security measures in place. A gun store, for example, will have bars on the windows, multiple heavy duty locks, reinforced doors **and then** also have all the guns locked up in safes overnight.",
"It falls under one of four objectives in reduction of crime: [increasing the perceived effort of crime.]( URL_0 ) Most petty crimes are crimes of opportunity, aka: easy to get away with and little risk involved. If you have a padlock on your shed a thief needs to pick it before you or your neighbor glance out the window and see him doing it. If there was no lock to mess with the thief could go right in and take what he wanted in a matter of seconds. Funny story, I lived in a house awhile back, and the bank was selling the house next door. There was a metal shed in the back. After awhile the Realtor sign said \"sold.\" A few days later I saw some guy in the neighboring house's backyard with a big white pickup, disassembling the shed and putting it into the back of the truck. It took him about three days to do this. At the time I thought he was just working for the Realtor cleaning up the place. About a week later the man who bought the house yelled at us demanding to know why we didn't call the police on the man who stole his shed.",
"Most locks are designed to stop the casual thief, not the professional. So, they barely need to work at all to be 99% effective.",
"Security and price. While they aren't very secure (I have learned to pick locks and know how easy they are to pick) it does provide protection to the vast majority of people who don't know how to pick locks. A example would be a convertible on the street with it's top down and $300 sticking out of a wallet. Super easy to just reach it, grab it, and keep walking. A non-convertible with an unlock door more secure, but you'll have some people pulling the door handle to see if it's unlocked and grab the wallet. While a thief who knows how to pick a lock can easily grab it, the risk of getting caught sticking some tools in a door to get it to open would pose more risk.",
"If someone wants to get into your house and steal something specific, it's not that hard to pull off. But most break ins aren't that targeted. You would typically patrol a neighborhood and look for houses that are easy to break into. If your house is locked, burglars are more likely to just move on to a different house. Locks prevent that sort of crime.",
"They aren't \"easy\" to pick per say. If you invest some money in a set of picks and some time in learning how to do it it isn't the hardest thing in the world - assuming it's a basic 5 or 6 pin tumbler with no additional security measures - but even 1 or 2 security or mushroom pins in a tumbler will give even an experienced locksmith a run for their money. Introduce things like dimple pins into the mix and it becomes even more difficult to pick a lock open. 9 times out of 10 it's easier to drill a lock out or snap the barrel or even break the door down, depending on why you're doing it. The reality is, if someone wants to gain access to a locked door, they will regardless of how hi-tech your lock is or how strong your door is. Short of you having like a bank style vault door there's no real upgrade to the doors/locks we use now. Source: I used to work for a locksmiths that primarily gained access to homes that the tenants were being evicted from for the local council. We almost always snapped or drilled the barrel of two way tumbers and shimmed latch locks. Picking is slow and unreliable in comparison.",
"First, traditional locks are not easily picked, they require a degree of skill. I know how to pick a lock, but it would be much faster for me to just use a crowbar or a brick. Second, the purpose of a lock is not just security. Circumventing a lock shows you had intent to break a law, and didn't just make a mistake and walk into the wrong house."
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6cau4e | How do 20 speed transmisions work? What vehicles use a 20 speed? | Engineering | explainlikeimfive | {
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"Think of it like a 4-speed transmission hooked to a 5-speed one in series. The 4-speed gives coarse control and the 5-speed fine tunes between the coarse steps. I can't imagine anything but a long-haul trick using something like this. There are a lot of parts, and that costs money. The precision adjustment would never pay for the parts. In lighter cars, they use continuously variable transmissions for this sort of thing, so it would have to be a high-torque application.",
"My semi has 10 speeds. Unlike most passenger cars, my 15 liter engine only has an operating range of 500 rpm. 1000 RPM-1500 RPM. For some perspective my Suburban has an operating range of 500 RPM - 5500 RPM. The rotating assembly in my semi has so much mass that if it spun too fast, it would literally fly apart.",
"Typically anything with more than a dozen gears will have two gearing systems, similar to how a multi-gear bicycle works. They are typically used only with large cargo trucks. A semi tractor without a trailer might weigh 5 tons, while fully loaded it might weigh 40 tons. The transmission needs to have enough range to handle both loads over a variety of speeds and inclines."
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6cjcyx | Why Moore's Law works, and why it will stop being applicable in ~2020 | What I'm most confused about is that it says computer power increases because of the number of transistors on integrated circuits doubles every two years. But isn't this a physical thing? Aren't we constructing them smaller? If it will stop in 2020 because it's impossible to make transistors more compact at that point, why couldn't we have constructed them that way from the start? It sounds like more of a machinery thing than a processing power thing. | Engineering | explainlikeimfive | {
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"Gordon Moore of Intel gave an interview in 1965. He made the observation that the number of components per processor had been doubling about every 24 months. Over time, the doubling rate actually turned out to be about every 18 months. In practice, as the number of transistors per IC doubled, so did the density. Smaller transistors can switch faster. More transistors means you can do more stuff. One interesting thing is that people have been saying Moore's Law will be over since the 70s. Continuing to shrink the dimensions of transistors has been expensive and has required enormous technological development. Many limits that people thought were fundamental have been worked around. However, right now we're approaching the point where transistors would have to become smaller than atoms. That's pretty much impossible. So the next evolution will have to be based on a new device that's fundamentally different from the silicon transistors we know now. In order to fully understand the issues, you have to know a bit about how integrated circuits are made. The ELI5 version is that they're made in a photographic process that involves shining light through a patterned plate onto a piece of silicon. Generally, the smallest image you can clearly see (or pattern) using light is limited to about half the wavelength. Visible light has wavelengths around 400-700 nanometers. Early transistors were hundreds of times larger than the wavelength used to pattern them. As transistors were made smaller, dust particles became large enough to disrupt the patterns. People invented filtration technologies and moved IC fabrication into clean rooms. Eventually transistor sizes starting getting close to the wavelengths of light. The industry started using single-wavelength sources for better resolution. The industry moved from 436 nm to 405 nm to 365 nm.. and so on. Short-wavelength light sources are harder to make with sufficient intensity. In the 1990s the industry was using 248 nm excimer lasers (not cheap!). Then they moved to 193 nm lasers. All the while, the industry found ways to \"cheat\" and make features even smaller than half the wavelength. Some tricks they developed: - Modifying the chemistry of the photo-sensitive materials used to pattern the chips. - Using oil or water in between the lenses used to focus the light and the chip surfaces to make a small lens behave like a bigger lens. - Optimizing the patterning mask geometries - Exposing the patterns in multiple steps The industry has been stuck at using 193 nm lasers. Using all the various tricks, they can currently pattern features around 20 nanometers. It's got to the point where they're making devices about as small as they can be made with out moving to smaller wavelengths. The problem is that below 193 nm, most materials absorb light very strongly, so they'll have to move from using lenses to using mirrors to focus the light. Also, making bright enough light sources has been very difficult and still hasn't been perfected yet. The industry is expected to eventually move to using extreme ultraviolet, or EUV (~14nm wavelength). To keep improving performance, Intel and others have started introducing enhanced transistor designs. Until recently transistors in CPUs were basically planar. Now, they're moving to 3D designs that can switch more efficiently. The reason we haven't done all these things from the start is that we didn't know how in some cases and that many of the technological developments have been extremely costly. We've known how to make 20-nm transistors for at least a decade using electron beams instead of light. The problem is that process is still way too slow to ever be used in production. Developing to the state of the art we have today has probably cost in the trillions of dollars or more by this point. A single EUV exposure tool is expected to run 100 million dollars when it becomes commercially available. That's 20X more expensive than a state-of-the-art tool 20 years ago. So, in short, it's a combination of economics, technological limitations, and physics.",
"Moore's law is just a rule of thumb, really. Transistors are *so damn tiny* right now that we have to invent new technology at every single step to get them any smaller. There's no way we could have made them that small back in the 60's. For one thing, we lacked computers powerful enough to design the very transistors they needed to run. The ultimate end of Moore's law is not our ability, but rather the laws of physics themselves. With transistors and wires that small, there is a nonzero chance that electrons will quantum tunnel out of their wires and into nearby wires, and suddenly 2+2 gives you 8 and computers can't work. You cannot make a computer smaller than that."
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6cjgn3 | How UPS drivers save gas by avioding left turns. | Engineering | explainlikeimfive | {
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"UPS drivers drive a large and not very agile box truck. This means that for a left turn, they must wait, idling the engine, until a rather large gap is open across both directions of the road. (In the US, the left turn crosses to the far lane.) If their route only involved right turns, and it was the same length, then they would use less gas idling, because they would only need ot wait for a gap in the near lane. Computer software can arrange that, and thus they make left turns only when the distance traveled is significantly less than could be achieved with right turns. In the US, road networks are dense and one-way roads uncommon, this turns out to be almost never making a left turn.",
"You get the most mileage out of your gas by travelling at faster(-than-stalling) speeds. In addition, whenever you brake, you are taking the energy you had from your gas and turning it into heat via friction with the brakes. Then you have to accelerate back up to speed again after you are done stopping. When you make more left turns, due to having to stop to wait for a break in the oncoming traffic, you stop and start more often. Turning right, on the other hand, only requires that you slow down very slightly since there's no oncoming traffic to avoid.",
"Why is this marked NSFW? Is it because of [this?]( URL_0 )",
"In most US and Canadian jurisdictions, you're allowed to make right turns at a red light. You just have to yield to oncoming traffic. And if the light is green, you don't have to wait at all. Just make your turn. In the case of a left turn, you have to sit and wait at the red, then yield to oncoming traffic unless there's an advanced green. When your vehicle is sitting idling like that, you're getting somewhere in the ball park of 0 miles per gallon. You're burning fuel to go nowhere. Now for one truck, only making right turns is going isn't going to save a whole lot of fuel over the course of a day. But if you multiply that by thousands of trucks on the road all day, every day, it adds up pretty quickly."
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6cjq7d | Why was the Light Emitting Diode (LED) so late entering into the game of being practical & widespread? | Engineering | explainlikeimfive | {
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"In comparison to fire? Or filament lights?? The quantum mechanics that predicted the performance of LEDs, and thus started the search to make them affordably, was a recent scientific discovery. Moving to shorter wavelengths, like blue, took years longer than the red ones. The key to widespread is practical. LED light bulbs in white are still 5-10 times as expensive as their incandescent counterparts.",
"Blue is the key. If you want white light, you need a light generator that can produce a full spectrum. We were pretty good at making red and green ones LEDs, but blue was another story. The trick was finding the right combination of advanced semiconducting materials to pull it off. Blue LEDs were first developed in the early 70's, but they weren't very bright. Nowhere near bright enough to function as a practical replacement for conventional light bulbs. The next two decades were spent trying to develop a suitable material that could produce bright blue light efficiently. Key breakthrough were made in the 80's that laid the groundwork. The first high brightness blue LED wasn't invented until the early 90's by Shuji Nakamura. Two other physicists, Isamu Akasaki and Hiroshi Amano were also working on blue light using Gallium Nitride (GaN) semi-conductors. A process for growing GaN on silicone wasn't successfully demonstrated until 2001. The three men went on to win the Nobel Prize for Physics thanks to their discoveries. Once we figured out how to make blue LEDs, we now had the pieces to make white ones. You do this by coating blue LEDs with certain phosphors to get the colour temperature you want. A common one is yttrium aluminium garnet, which produces the warmer yellowish-white light we humans tend to prefer. It really didn't take long after the successful silicon process was demonstrated before they entered mass production. Though early high brightness bulbs were expensive and had large, ugly heatsinks to help increase the bulb's life span and efficiency. It's only in the last 5 or so years where they've become cost competitive with florescent and incandescent lighting."
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6cnzwj | With so many people on a small airplane, how does the plane not run out of oxygen? | Engineering | explainlikeimfive | {
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"It pumps air in from outside. Air is compressed (the pressure outside is lower than people like) and warmed up (it is very cold outside a plane) in the engines before being pumped into the cabin. Excess air is exhausted to keep the cabin air fresh.",
"The oxygen is circulated from the outside of the aircraft, like air con in a car but the aircraft is kept pressurised like a can of soda, by the engines. This is so people don't die of asphyxiation (where the brain is starved of oxygen) as the high altitude air has less oxygen. The pressure is maintained automatically by the aircraft at around 8000 ft above sea level."
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6coecd | Why do they have to replace the (whole) transmission? Isn't there just a part inside they can fix? | Engineering | explainlikeimfive | {
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"Transmissions are very finicky fine tolerance units that require specialized tools and know-how. Average mechanic doesn't want to to open it up and dig in. It's much quicker to replace the unit than spend hours to fix a $10 inside part..",
"Without more context I can't give you any insight. It depends on the nature of the damage, where it may be so extensive it's cheaper to replace the whole unit than it is to pay for the man hours to disassemble and reassemble, which is a complicated, tedious, and precision based task.",
"Like the others said, normally it's a lot easier, quicker and cheaper to replace it than try to fix it, maybe find out what's wrong, then putting it back again. The time alone would often offset the price difference between fixing it and replacing it entirely. And even then it's not even a guarantee that it'll last long or even work. I take the same approach when fixing computer problems. I can spend hours trying to locate and fix it, but most often it's a lot easier on my sanity to just reformat and start over. Disregarding a hardware problem, that fixes it.",
"Also Am mechanic. Alternative: take it to special transmission shop to fix it. This is only a good choice is if their quote is half the price of a used one or similar one. ( You don't own a very rare car)"
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6conpv | Why does the fridge have a lightbulb in it but the freezer compartment doesn't? Is it too cold for the filament, would the bulb heat it up too much? | Engineering | explainlikeimfive | {
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"Both of my freezers have lights. Although now that I think about it perhaps the older style \"fridge in the bottom, freezer on the top\" ones might not have had a light in the freezer compartment. Perhaps it was a heat issue and this has been resolved with the advent of LED lights?",
"It's only really low end fridges that don't. Probably as a cost cutting measure since the freezer compartments in those fridges are usually small, and you're not going to be going in them as often. Cutting out the switch, socket, and associated wiring is going to save a couple bucks on each unit, which can add up on bulk orders. Most-mid to high end fridges do have a light in both compartments these days. Almost all stand alone chest freezers also have a light."
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6cpzja | What exactly does brake fluid do? What makes it work more than another substance, say something like water? | Engineering | explainlikeimfive | {
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"These are glycol-based hydraulic fluids that are not appreciably compressible, non-toxic, biodegradable, hydroscopic, and have extremely high boiling points. That's key for a system that converts motion into heat through friction. Your brake system can easily hit several hundred degrees, and the hydraulic system can itself rise a couple hundred degrees through conduction and radiant heat. Water will boil and turn to steam in your brake system, which becomes a compressible spring. That doesn't mean you get an additional spring force pressing on your brakes, that means you have a spring absorbing all the force you're applying to the brakes. This is a foot-to-the-floor-and-you-ain't-stopping sort of problem. This is why it's important to keep that cap on your master brake cylinder - your brake fluid will actually pull moisture out of the atmosphere. Also, don't keep bottles of old brake fluid around, they, too, can collect water from the atmosphere.",
"It has a high boiling point so it does not vaporize in your brake lines like water would do.",
"Brake fluids biggest advantage is that it takes a lot of heat to boil. The liquid isn't compressible (or not nearly as much) but if it were gas it would be. It also acts as a lubricant for the breaking system.",
"The brake pedal compresses the fluid which in turn pushes on the brake pads and drums, creating friction with the spinning wheel thus slowing it down. The friction of braking creates a substantial amount of heat, and the fluid must have a high boiling point to prevent vaporizing in the hydraulics. Water would boil, creating vapor in the line that would disrupt the hydraulics, thus causing the braking system to fail. The fluid also must maintain a stable viscosity at different temperatures and not corrode parts it comes in contact with.",
"Now is my time to tell it how it was. My stepdad and my first new car (5mi off the lot, just a Malibu, but still) in his great genius decided that my brake fluid was low...^^because ^^he ^^drained ^^it. But, he had some power steering fluid and decided since both are \"hydraulic fluids\" that they should work interchangeably. Long story short, a month later I had to have the entire brake line system removed as the steering fluid corroded them. I've got lots of stories about his smarts. This was one of my favorites.",
"Brake fluid is basically hydraulic fluid but with several properties that make it useful in automotive braking systems. Needs to be non corrosive Needs to be thin enough to flow easily in small tubes but thick enough to prevent foaming or break up. Needs to be stable at a variety of temperatures. Water would corrode the metal of the brake system and it would be unstable and freeze at low temperature, and might boil off or explode at high temperature. Regular motor oil would be very good at preventing corrosion or being sensitive to high temperature but it may be to thick to flow properly through small brake lines especially when cold. So brake fluid is engineered to have these properties as well as as not attacking seals and gaskets in the reservoir."
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6cqjzm | What engineering limits are keeping modern passenger planes from going more than ~600 miles per hour? | Engineering | explainlikeimfive | {
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"The biggest one is actually political. Breaking the sound barrier makes a lot of noise and makes people grumpy. That's the main reason we haven't done it again since the Concorde, there's just too much pushback; though companies are working on quieter supersonic jets to help with it You'll notice that most commercial jets top out around mach 0.8, there's a reason for that! Between Mach 0.8 and Mach 1.2 you're in the \"transonic region\" and the math gets icky. Some parts of the plane have air moving over them at the speed of sound, others have it moving slower, its not a good place to be so you want to fly faster! The Concorde did Mach 2.0 meaning it was only briefly in the transonic region before getting into full supersonic A supersonic plane needs a much different shape than a subsonic plane. Lift doesn't work the same at those high speeds, big wide wings are just going to rip off, you end up with swept wings that are closer to the body and narrower which reduces drag at high speed, unfortunately this means that your plane isn't very good at subsonic speed And we're back to point #1, politics. You can make a plane good at being supersonic or you can make a plane good at being subsonic but you can't make a plane good at both so you either have a plane you can only fly over the ocean that goes really quick, or a plane you can fly anywhere that goes slower, but you can't have a really quick plane that flies anywhere right now.",
"The speed of sound is a mofo. Some of the design problems are here: URL_0 The problems are solvable, but not efficiently. In general, it's not just that the cost needs to come down, but that it needs to come down relative to subsonic flight, so that people will pay for the express.",
"1. Supersonic flight burns a lot of gas and this means tickets are going to be expensive. 2. Burning a lot of gas means that you can't do the real long haul flights like LA to Tokyo or whatever, which is where being able to go really fast would give you the greatest benefit. Also, the noise from the sonic boom means that supersonic flight is mostly going to be over the ocean. 3. Unless you're on one of these real long haul flights (which supersonic airliners can't do) then it's entirely possible that most of your journey is going to be spent in a cab going to the airport, then dicking around in line at the ticket counter, then going through security etc etc etc rather than actually in the air flying. 4. The fact that you can lease an executive jet these days means that the kind of people who could regularly blow thousands of dollars on a supersonic flight have another option that costs about the same, takes about as much time (considering the whole journey) and is vastly more comfortable.",
"Cost benefit ratio. Air resistance increases exponentially the faster you go which means exponential fuel consumption. And also breaking the sound barrier also causes other problems itself too.",
"Limits of fluid dynamics as result of laws of physics. The faster you go, the more air molecules you have to shove aside. Fuel isn't free. Nobody cares to pay $10000 a ticket to get there 5 hours sooner.",
"The faster you go the more air resistance that you meet. The more air resistance the more fuel you have to burn to maintain that speed. There is nothing necessarily stopping commercial planes from going super sonic except for some laws about super sonic flight over populated areas, but its just not economical.",
"There are a lot of changes that occur as a plane hits supersonic speed. The flow of air through the engine, the heat generated by air compression, and the vibrations of the shockwave all have to be incorporated into the design of the aircraft for it to survive supersonic flight. And even if you do all those, fuel efficiency plummets."
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6cvry3 | Can you detonate a bullet with blunt force? | If a bullet isn't in a gun, can you hit it hard (like with a golf club or hammer) enough to make it fire? If not, what exactly is the striker doing? Edit: Thanks guys, my question's been answered succinctly and quickly. You guys are the best. | Engineering | explainlikeimfive | {
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"Yes you can, and the danger isn't so much with the projectile on this one as it is with the metal fragments of the case. It's not guaranteed to shred open but since there's no chamber rugulating it, it gets a little crazy sometime's. Without a chamber it's not as powerful either, so you wouldn't be able to use it to hit stuff very easily, but it could still hurt you and has a better chance of being unpredictable.",
"the primer on a bullet contains a crystaline form of mercury fulminate. in a rim-fire bullet, this is in the base of the cartridge. to fire the bullet, you need to hit the primer hard enough to break the crystal of mercury fulminate, at which point it will spontaneously decompose, releasing a LOT of heat, which will then detonate the powder charge. it's totaly possible to detonate a bullet by handling it incorrectly. i've detonated .22lr by dropping it off a table. the brass of the primer is there to hold the mercury fulminate in place, AND protect it so that only a carefully placed blow will detonate it.",
"Yes. That's what your gun does. A gun works by striking a bullet with blunt force at exactly the right spot. If you did the same you could trigger ignition without a gun. Most bullets are designed to make this difficult for safety. But if you mimic the action of the firing pin striking the bullet it will go off.",
"> can you hit it hard (like with a golf club or hammer) enough to make it fire? This would be much easier with a rimfire cartridge as centerfire would have the primer more protected in the center of the back of the cartridge. Whacking it hard enough should dent it and set off the round. Keep in mind that as it isn't contained in a firearm barrel it would probably just explode, throwing small amounts of casing shrapnel around."
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6cx93t | What exactly does it mean for something to be scalable and why does it have to be this way? | Engineering | explainlikeimfive | {
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"If your business is scalable then it has solved the tradesman's problem. Consider a chef. To make the world's best food, you have to know exactly when to flip the steak at just the right time and temperature. That's a unique skill that not just anyone can do. Being the best at it allows you to charge a hefty premium and make more money per-steak. However, you're limited in how much more you can charge because eventually the 2nd best guy will be good enough. You can't open a second location because the guy flipping steaks at that location doesn't do it as well as you do and therefore can't justify the obscenely high price you do. A business that is perfectly scalable doesn't depend on any one particular person, place, or resource. It works anywhere and everywhere, and only requires $X to get started, and can expect Y% return, provided you find people that are generally good enough to do their jobs and fit into your model.",
"Scalability is the capability of a system, network, or process to handle a growing amount of work, or its potential to be enlarged to accommodate that growth. A system whose performance improves after adding hardware, proportionally to the capacity added, is said to be a scalable system. As far as why it has to be that way, I'd say the description of that type of system is pretty self-explanatory.",
"Let me put it a different way than /u/Ameos: A scale-able system can be upgraded to handle more work. A system that is not scale-able would need to be replaced in order to handle more work."
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6d238v | Why are most boats operated/captained from the right side, but autos and airplanes on the left? | Engineering | explainlikeimfive | {
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"It has to do with where the rudder oar was placed on boats before fixed rudders were invented. That oar was on the right side so that side was the Steerboard (later starboard) side. The left side was therefore the side that went next to the dock (port side). As for cars. That has to do with the driving practices of wagons. Originally you sat in the middle behind your single horse. As teams of horses got bigger you eventually had them running two abreast. So you had to choose which one you wanted to be the lead. Some countries made the front left horse the lead, some the front right. You sat on the appropriate side of the wagon for the placement of the horse you were directing. That became the side of the car that you sat on when they were invented. With planes you sit in the middle, unless they are large enough to have two pilots seats. Either can control the plane.",
"I'm not sure the assertion that most boats are operated on the right side is true. It certainly is true for most recreational powerboats that have side by side cockpit seating, but a large number of powerboats are also center console. Sailboat cockpits are also mostly centered. And many larger boats have multiple control locations. For recreational powerboats, one of the main reasons is throttle location. Most people are used to controlling throttle with their right side of their bodies. On most motorcycles, jet skis, etc., the throttle is on the right-hand grip. In automobiles, the gas pedal is on the right. For powerboats, the throttle is generally to the right of the steering wheel. So for small, bow-rider style power boats when it comes to choosing left or right side, most will go with the right side so the throttle can be to the right of the steering wheel. If it were to the left, by the pass-through, people could accidentally hit the throttle which would be a safety concern."
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6d72fh | if locks and keys have specific grooves so only certain keys work, how to GM keys work? | Engineering | explainlikeimfive | {
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"Bluecollarbiker is right. But I just spent 20 minutes trying to figure this out for you, and a little extra detail couldn't hurt. When you open a door, you put the key in a cylinder. When the cylinder turns, the lock opens. A lock has a set of metal pins (tiny rods, basically). The metal pins enter the cylinder, and they also go into a part of the lock that doesn't turn. The pins prevent the cylinder from turning. Every pin is actually divided into two parts. If it was just one solid piece, you could push it up as far as it would go, and the cylinder would turn, and your lock would suck. Each groove of a key pushes up enough so that the top half of the pin leaves the cylinder. The bottom half of the pin remains, but since it is totally within the cylinder, the cylinder can turn. If you went up any higher than that, the bottom half of the pin would push out of the cylinder, and the lock wouldn't open. With a master key, they add what is called a master wafer between the two halfs of the pin. Basically, it's a tiny metal hockey puck. What this means is that each pin is effectively three pieces. Because it is three pieces, there are two breaks in each pin. If you raise the top part of the pin AND the wafer, the bottom part of the pin remains entirely in the cylinder, and the lock opens. If you raise the top part of the pin, but NOT the wafer, the wafer and the bottom part remain entirely in the cylinder, and the lock opens. So each pin has two possible ways to open it. One possibility will be the same on every lock, and the other possibility is unique to each lock. Normal keys open the unique possibility, and master keys open the shared possibility. I think (might be wrong), that a grand master lock would have two wafers, thereby creating three possibilities on every lock. For every lock, possibility A will be the same, so the grand master unlocks it. Possibility B will change, with one unique configuration for each master key. Any lock opened by a particular master key will have the same B possibility. Possibility C will be unique to every lock, and can only be opened by the regular key."
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6d86hj | Why are purely mechanical machines seen as more ingenious than their electronic counterparts? | Engineering | explainlikeimfive | {
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"Because you can actually see what's going on. You can see all the parts moving. A microprocessor is doing some very complex stuff, but it doesn't look as \"impressive\"."
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6d8kb6 | What use do multiple exhausts have on automobiles? | Engineering | explainlikeimfive | {
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"Primarily their function is to move as much volume of exhaust as possible. In the case of cars with larger engines this means larger amounts of exhaust are created. Instead of having one single pipe with a big diameter, they use multiple pipes with smaller diameters to create the exhaust. This is a ELI5 so i didnt go into other functions like newer cars will regulate how many of the exhausts are being used to control backpressure at different RPMs/throttle levels, and also to control the sound, efficiency etc etc. But still TL;DR:, primarily, more power = more explosions = more exhaust created = more exhaust pipes.",
"It's worth meantioning too that ground clearance is at a premium in cars. Four 4 inch pipes gives you far more clearance than one big 8 inch pipe."
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6dafkd | How do they build underwater tunnels and seal them? | Engineering | explainlikeimfive | {
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"underwater tunnels are often created with humongous tunnel-boring machines (TBMs) — sometimes called moles. These machines cost millions of dollars, but they can create large tunnels in a very short time. A circular plate with disk cutters rotates to cut through rock as the machine inches forward slowly. As the machine excavates the tunnel, it also helps to build the walls that will eventually support the tunnel. France and England used 11 massive TBMs to create — in just three short years — the three tubes that make up the 32-mile Channel Tunnel. Also called the Euro Tunnel or Chunnel, these tunnels now connect the two countries under the English Channel. Another new method of creating underwater tunnels is the cut-and-cover method. To use this method, builders dig a trench in the riverbed or ocean floor. They then sink pre-made steel or concrete tubes in the trench. After the tubes are covered with a thick layer of rock, workers connect the sections of tubes and pump out any remaining water. This method was used to create the Ted Williams Tunnel, which connects the southern part of Boston with Logan Airport."
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6dcfm2 | why can't we eliminate traffic jams on major highways? | It doesn't make since to me, with all of our advancements in technology, that we can't eliminate traffic jams. I mean everyone knows there will be heavy traffic at certain times everyday and we can predict it like clockwork. So why can't we fix it? Have we just decided as a society that a certain level of traffic stoppage is acceptable? Why can't they just build a couple additional lanes or anticipate the traffic and build them bigger to begin with? | Engineering | explainlikeimfive | {
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"Okay, I'm an engineering student (aerospace/mechanical), but I do a lot of studying of it on the side. Let me tell you, this is something I'm passionate about. & nbsp; **There are are few things that cause traffic on highways: (And this is the tl;dr)** * Merging * Number of Lanes (see merging) * Amount of bypasses * Backroad availability * Car spacing & nbsp; & nbsp; Let's look at **merging**. In my opinion, this is by far the biggest issue. I live in Orlando, and if you have been here recently, we are expanding I-4 to contain - I believe - six lanes on each side. This is a *horrible* idea. It is a two-dimensional idea; if there are too many cars on the road, building more lanes will allow them to flow better, yes? Well, no... not exactly. The reason behind this is merging. The biggest causes of *any* car accident is either: merging, rear-ending (touching that later), and backing up. The latter is almost completely irrelevant to highway flow. One thing to understand about merging is that sometimes it's caused by construction (adding irony to the I-4 project). Another is lack of oversight. Sometimes - and I'll use Altomonte Springs as an example (fellow Orlandians relate) - a highway is built, and is not imagined to expect a surge in traffic in the near future. With Altomonte, there is an exit with a major intersection (St. Rd. 436) that funnels an endless amount of cars. With people traveling from Lake Mary, DeBary, Sanford, etc, and all the thru-traffic being added with a never ending funneling of cars, a bottleneck occurs quickly. So adding more lanes does not help. [Adam Conover explains this well in his show]( URL_3 ) (Can't find a clip of the show unfortunately). & nbsp; The way to fix this would be to funnel traffic in a proper pattern with the **right number of lanes**. [Here is an example]( URL_8 ) (sorry for simplicity) that I made showing how traffic could be fixed. Similar to a **HOV lane**, but instead it's designed for *thru-traffic*. This is traffic that is either trying to go through most - if not all - of an entire city whether the commute is on the opposite side of town, or the driver is on a road-trip. This allows minimal stopping for people exiting. Now, the second half is the *exiting bypass*, and this allows people who need to - let's say - get off between Exit's 83-86 near downtown, people don't have to stop for people merging. The goal is to funnel people into as few lanes as possible. If you've ever seen a river, as long as water doesn't get squeezed into a small funnel-shape, then it will flow smoothly no matter how wide. If people don't merge, this stops a lot of accidents and \"*Snakes*\" in the road if you will. & nbsp; The next is **bypass** ability. Even with my idea, there will be back-up without sufficient bypasses for people who are not driving *straight through* the city. Let's say you're trying to get from Deltona to Titusville. Titusville is located Southeast of Deltona, so instead of driving through a city, and then *merging* into lanes to go east, it's easier to go the *hypotenuse* route, which is usually a *loop*. Thing is here in Florida, we have nothing but [freaking tolls!]( URL_6 ) Everything in yellow are bottleneck roads with traffic lights and businesses. The only *free* way through is down I-4. This adds to the stress. Believe me, [Atlanta]( URL_2 ), [New York]( URL_5 ), and [Los Angeles]( URL_0 ) are no picnic either. This asks a major question, how efficient are bypasses? Well, they too need to change design, because they can become worse than the main interstate through the city; Atlanta how I hear you calling. & nbsp; **Back roads** are key to alleviating traffic. In Kansas City, the highways have a tendency to backup quite horribly. But they clear in thirty to sixty minutes, while *so* many cities (Orlando) can have it last for almost three hours. The reason is the ability for people to get off when they need to. KC has a grid system as do many cities. It's not a gorgeous design, but it is most effective. People can get off the interstate early and hit a road that goes straight for dozens of miles, and on top of that, many neighborhoods have thru-roads. This is the complete opposite in Orlando. Only downtown has a grid. There are no guarantees that a road will continue in a straight manner for very long. Neighborhoods have *no freaking thru-roads*. This is mostly because of lakes. There's a ton of them around here. But with that, the city needs to find a way to go around and alleviate traffic. One bizarre manner looks like [this]( URL_7 ). We have a dozen or so of these bridges everywhere. Missouri is working on making highways more efficient and was the first state to implement [Diverging diamond interchanges]( URL_1 ) in Springfield, and almost every bridge they construct now over an interstate is of this design, and it eliminates left turns onto the interstate in intersections that don't have space for *cloverleaf* designs. It has proved to be very quick, efficient, and effective. & nbsp; The final thing to note is **spacing between cars**. When a bottleneck occurs and people brake, it causes others to do the same creating a \"*Snake*\" effect. I think [CGP Grey]( URL_4 ) explains it best in his video about how people need to maintain distance away from a car. Great story, once I was driving down I-4 to one of the theme parks, and of course there was a bottleneck. I decided to keep my car going slow, and I maintained 15 mph while the cars in front would go like 35 mph and then slam their brakes into a full ten second stop. But, that gave me room to maneuver while they waited and then started up again. What's better, is that the person behind me did the same thing and maintained a good two-hundred foot or so gap between our cars. And on top of that, no one saw the gap around my car and decided to zoom into the gap. In essence, **This other driver and I ended a freaking Orlando, FL bottleneck!** Regardless, the solution to traffic is long and complex, and this post only hits the tip of the iceberg. The contents of this post are a combination of my opinions, observations, and content I gathered from other media platforms. Take them as you will. If you got this far, you are either magical, or a reader who skips to the end. Either way, thanks. **EDIT:** grammar and stuff",
"I'm not an engineer but I play one at work. Traffic jams are caused by one thing and one thing only: people slowing down. Adding more lanes does not actually reduce traffic jams because there are always \"pinch points\". That famous building next to the road? We can't tear it down to make more lanes so no matter how many lanes you build before you reach the building you are funneling people into fewer lanes to get around the famous building, which causes them to slow down. Picture a stop light. Everyone in line is stopped when the light turns green. What happens next? The first guy in line starts to go, and then a few second later the second guy goes, the a few seconds later the third guy goes. We now have lost capacity on the roadway because the guys later in line didn't start going at the same time as the first guy. depending on the number of cars at the light this could impact that travel lanes a mile behind the light as the further back you are from the light the later you start to accelerate.",
"They have done math before to calculate traffic. They found out that a car cutting off a semi can make traffic up to 2 miles behind it come to a dead stop. URL_0",
"I'm surprised no one's mentioned it yet, but sometimes adding lanes will increase traffic. If you merge on the highway on the right side and want/need to get over to the far left, the more lanes you cross, the longer it will take you, which also ties in to the second point: The number one cause for both traffic and accidents is *incompetent driving*. For an overly simplified example say you have x ppl in 1 lane spaced evenly apart. The 1st guy touches his breaks for no reason (happens outrageously often), the distance between him and the 2nd guy shrinks. 2nd guy touches the breaks but a little harder, to let the distance get back to what it used to be. 3rd guy does the same. Eventually 1 guy and everybody behind him come to a complete stop. This obsession with touching the pedals, breaking and accelerating over and over again will cause frequent total stops, aka rush hour traffic. I get really triggered when people with nothing in front of them, going exactly the speed limit, tap their fucking breaks for literally no reason. > _ <"
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6dfffa | How do streets without traffic lights work? How do people not constantly get into wrecks? | Edit: I didn't specify enough, but I actually meant the huge streets where there are about fifty cars just swerving around each other without any organization. | Engineering | explainlikeimfive | {
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"There is a town in Holland, Drachten, where they REMOVED all traffic lights and traffic signs. The city planners thought that people would be a lot more careful if they didn't know what car or bike or pedestrian was going to come from where and whether it would stop or not. And they were right! Cars started driving way slower, stopped making assumptions, looked in all directions more carefully, gave way to pedestrians and bicyclists a lot more and the accidents in the town went down. by A LOT! URL_0 URL_1",
"Because there are rules you have to follow even if there aren't any traffic lights. Give way to the people coming from the right. Stop at a stop sign. It's not that hard. You don't need traffic lights, they just expedite traffic on big roads.",
"When lights go out you treat it like a 4 way stop Edit: if other assholes don't know how to handle this round robin way of intersecting, you go when you feel it is safe, if that fails, when it doubt, throttle out my friend."
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6djti7 | How does tire tread work? Wouldn't that reduce the area of contacting surface between the tires and flat ground, thus less friction and more dangerous? | Engineering | explainlikeimfive | {
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"Completely smooth tyres (slicks) work really well in dry conditions. If you have water on the road surface, then a slick tyre can end up with a layer of water between the tyre and the road, something known as aquaplaning. This causes problems with braking and steering, and so is clearly not a good thing. Tyre treads are designed to move water away from the area, thus allowing rubber to contact the road instead of sitting on a film of water.",
"Slick tires with no treads would work well enough on dry surfaces, but on wet road, water would become trapped between the tire and the ground, causing the tire to lose traction. Treads solve the problem by providing channels the water can be pushed into, allowing the rubber of the tire to keep better contact with the road.",
"You're right. There is a reason why the tires of F1 cars are completely bare/smooth (slick tires). It helps them to grip the road better than regular grooved tires, especially when turning at 150km/h. However, this only works when the asphalt is bone dry. In wet conditions, slick tires become completely useless because of a process called aquaplaning, in which water gets between the flat surface of the tire and the ground beneath it. This causes the tire to lose traction as it loses contact with the ground and the car will begin to lose control. Slick tires aren't allowed for common road vehicles as they aren't safe in wet weather conditions at all. Tire treads in grooved tires act as channels for water to pass through the tire whilst allowing for as much contact with the ground as possible, preventing aquaplaning from occurring. The slight grip loss from having tire treads is negligible as compared to the increased safety in wet weather conditions, or any condition in which there is liquid. It would be far easier and far safer to increase the tire width by a centimeter or two to compensate for the small loss in grip."
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6dnesx | What really happens when everyone in a building flushes their toilets at the exact same time? | Engineering | explainlikeimfive | {
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"We did this at our High School back a lonnnngggg time ago. After a few unsuccessful attempts due to lack of timing we initiated \"Operation Royal Flush Phase IV\". At the bell all toilets were to be flushed, all taps turned on at the sinks. All tolled there were probably two or three hundred fixtures. At the bell we all did our thing...I was in the B-200 wing Men's washroom... Flush.......a slow gurgle.....the water down the trap . a low rumble.....then.....you could feel it coming.......every toilet and sink literally exploded with regurgitated liquid.....hitting the fan......omg nothing so grand had ever been seen before it was a total success. Even more so as they had to close the school for a week to get it back in shape....",
"Two things will happen. 1. Water supply pressure will drop. If you have a high building, water could flow back to lower sinks by gravity. 2. An air bubble will be trapped inside the sewer lines. Between the flush of floor 1 and the flushes of floors above. This air bubble wants to get out of the way. The air will take the easiest route, which could result in your toilet \"exploding\" or pushing all water back trough the sifon. The sifon is the j shape that prevents smells from leaving the sewer. We used to have this problem with our toilet on heavy rain. All the water would storm its way down the sewer pipes. And since we were at the lower part of town, the air pushed away by the water would let our toilet \"explode\" the sifon contents on the ceiling. An extra vent was placed in the streets to be the easiest path for the air. It has not happened since then.",
"If it's a modern building and there are no obstructions in the waste line, the toilets will all flush normally. The water service is sized to supply every fixture at the same time. The waste lines are as well. Edit - Apparently that isn't true for a skyscraper though, I never built one of those.",
"Alright, So, I was doing my Fire Inspector training and I was able to test this at a newly built NFL stadium about 4 years ago. We called it the \"Super bowl.\" We recruited local Girl and Boy Scout organizations, schools, and had volunteers sign up to flush all the toilets in the stadium at exactly the same time. The purpose of this was to test the plumbing and simulating \"half-time\" when most attendees go to the restroom. As the local fire department we were assessing the stadiums ability to handle that much pressure loss. The reasoning is the sprinkler systems require a certain amount of pressure and we wanted to simulate the worst case scenario: Fire during half-time when everyone is busy flushing shit, literally. Tldr; Fire department I was at did this at a NFL stadium being constructed. We had volunteers flush all the toilets as a stress test, called it the \"Super bowl.\" Nothing exploded. Edit: Inclusion. Edit 2: System we inspected was getting its water supply from a small body of water nearby. Our fire department was ensuring that this eco-friendly water system was capable of handling a heavy workload (bunch of flushing at same time) and still maintain enough pressure for fire sprinklers while being stressed.",
"Obviously the answer is \"the waste lines will revolt, backup from the pressure and spray your entire bathroom and kitchen with liquid shit.\"",
"This very test is done at large stadium venues before they open to the public. The Don and Mike radio show did a stunt at Jack Kent Cook stadium (now FedEx Field) where participants would poop in the toilets first.",
"Iirc they had to do this in a South American city. Due to water rationing the waste wasn't getting discharged properly, causing a severe blockage.",
"There was an episode of Ahh Real Monsters about this exact thing. During Superbowl everyone shits and flushes at the same time and the monsters in the sewers use the sudden rush of water to do an annual race on."
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6dplux | What is the purpose of hackathons and why are these marathon learning sessions not as popular in other professions? | Hackathons are hosted by institutions or corporations to get many students to learn and practice coding all night or all day long. Is it there to benefit the companies or is it like a free learning experience and workshop for everyone? It seems unusual that few other professions have hackathons, as there aren't "mathathons" where kids practice doing math problems all day | Engineering | explainlikeimfive | {
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"Programming, for anyone who's never tried it, is a very focus-intensive activity, and can be not strenuous at all. These things make marathon learning very useful, as new information can easily be picked up and utilized. (That is to say, you could learn how to use a function and then be able to use that function proficiently in mere seconds.) Compare that to math, which is hard to understand intuitively at most levels. Learning new math tricks takes time, so marathon learning is not a generally good idea in math. Or compare that to history, which must be learned sequentially and intensively for a student to create generate something worth reading. Or compare that to pottery, which is not a high-focus field and thus is not suitable for long sessions in which students may become bored. Many companies will use hackathons to get programmers or students to learn how to use a specific language, API, hardware, etc. Sometimes, hackathons are just \"hey, go work with other people and make something cool.\""
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6dpt0s | Does cambering your car wheels actually have any benefit? | I understand that the extreme camber that is the new fad probably doesn't do anything beneficial and most likely is counter productive. But is there a reason to camber your wheels more that required to keep them flat on the road? | Engineering | explainlikeimfive | {
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"A tiny amount of negative camber helps during high speed turns where all the weight transfers to the outside wheels and the tyres deform by a degree or two. F1 cars typically run with 1, maybe 2 degrees of negative camber to keep the tyre wear from cornering more even (and hence last as long as possible before needing a pitstop). If you're not driving in a way that involves tons of lateral G-force then it's not worth it.",
"While negative camber (leaning the top of the tire in towards the car) is beneficial for cornering, it can be overdone. If it's to far negative like in stanced vehicles, it becomes worse than having no camber at all. If you have a 6 inch wide tire that only touches the pavement on the inside 2 to 3 inches, it would be the same as having a 2 to 3 inch wide tire with no camber. People stance their vehicles to look good, not perform good."
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6dumq9 | How is the pattern on a key chosen? And how are they all different so that two keys cannot open the same door? | Engineering | explainlikeimfive | {
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"In mass produced locks, there might be, say, five pins in the lock. A key will open that lock if each pin is at the right height when it rests on the key, and the key is turned. For each of the pins, a manufacturer will have a set number of lengths that they make. They are numbered 1 to 6 or 1 to 7 for common locks. These are called bitting numbers, with 1 being a short pin and a shallow cut in the key, and 6 or 7 being the longest pin they make and the deepest cut in the key. To make a lock, then, they pick a sequence of numbers like 34125, put pins of those lengths in the lock, and dial that number into a machine that cuts a key with the right depths in the right places. The convention is that the number is read left to right, and the first number (3 in the example) is closest to the part of the key you hold when using it. Now, they can't choose just any number. If you had 34**16**5 you might not be able to get the key in the lock because the slope between the 6 and the 1 is so steep. Nor could you have 3**61**25. The key would go in just fine, but it might never come out. So, how do they choose these so that keys don't open multiple locks? They don't. They just make enough that it's somewhat unlikely that the key to your house is~~n't~~ the same as your nextdoor neighbor's. It helps that there are different shapes to the keyways, that is, the wiggly shape of the hole the key goes into. A key might not even go in to a lock it wasn't made for. Here comes the bad news: it's cheaper to make identical locks and identical keys. Many manufactures do. Have you ever seen those little beige cash boxes with a black handle? The ones you've seen probably all have the same key. Electrical panels in a business with a little lock on them so that kids and bored customers don't fiddle with them? Same key as the cash boxes. Locks tend to be a really good psychological deterrent to the average Joe, but terrible at ~~supping~~ stopping someone who is reasonably determined to get past them. EDIT: double negative, oops. EDIT2: I have got to stop posting from my phone. Supping? Seriously, autocorrect?",
"A lock is made up of pins. Each needs to be lifted a certain height to allow the lock to open. Now let's say that height is set to a digit so there are 10 unique possible heights. You multiply the number of pins by the possible heights to get the different possible combinations of locks that can be made. Which answers your last question: they aren't all different. The key to your front door will probably open some other door. But if there different enough, the chances of finding a matching door are slim to none. There are easier ways to get through a locked door than trying every potential key.",
"Related question: How do locksmiths make 'Master Keys' so one key that can open say, a dozen locks, but also create a dozen keys that can only open one of those locks?"
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6dvc75 | How is rocket fuel pumped into the combustion chamber of a rocket engine? | The pressure in the combustion chamber is pushing out all exhaust gasses which make the rocket go up. So I assume the fuel has to be pushed into the combustion chamber even harder, so how is it done and how are the exhaust gasses prevent from entering the fuel tanks? | Engineering | explainlikeimfive | {
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"Your assumption is correct, and the various ways that propellant is supplied under pressure to a liquid-fuelled rocket are referred to as the different \"cycles\". Probably the simplest one is a pressure-fed rocket. With this cycle you have the propellant tanks pressurized to a higher pressure than the combustion chamber, by filling the empty space in the tank with a gas like helium, that itself comes from an even higher pressure tank. This works fine for small or low pressure rockets, but with larger rockets or high pressures, the propellant tanks have to be so strong that they become impractically heavy. Then you have the \"expander\" cycle, which uses a pump to pressurize the propellants. If one of your propellants is something like hydrogen, that boils at a convenient temperature, you tap off some of the liquid propellant coming out of the pump, use it to cool parts of the engine that need cooling anyway, which boils the propellant. You now have a supply of warm, high-pressure gas that you can use to run the pump and then just dump into an exhaust pipe afterwards. If that doesn't give you enough pump power, you can move up to a \"gas generator\" cycle. With this cycle you tap off some fuel and some oxidizer from the pump and burn them in a separate combustion chamber. This gives you a supply of very hot gas with a lot more energy in it than the expander cycle, so you can use it to run a much higher pressure pump. The exhaust is again dumped overboard or through an exhaust manifold in the rocket nozzle. Then you have the really complicated \"staged combustion\" engines, which are like the gas generator cycle except the propellants are not burned completely and are injected into the main combustion chamber of the engine. These can also supply a lot of pump power and you don't lose as much performance, as the exhaust from the pump still goes through the whole engine and provides some thrust rather than being \"wasted\". In case you're wondering how much power it takes to run the propellant pump for a large rocket engine: the pump for the F-1 engine used on the Saturn V rocket's first stage uses the gas generator cycle and produces about 55,000 horsepower of pump power.",
"There's a [turbo pump]( URL_0 ). That's a fuel pump which is driven by a turbine, which itself runs on rocket fuel and oxidizer. Another way to do it is to pressurize the fuel tanks using compressed gas, so that the fuel is pushed into the combustion chamber by pressure. This makes the fuel tanks quite heavy though."
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6dwx5n | What part of a jet engines make them so loud? | Engineering | explainlikeimfive | {
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"There are three places where significant sound is produced. The first is inside, anywhere you have blades. This is especially true of the compressor (first part of the engine) and the turbine (last part of the engine) where there are blades on the rotating part of the engine that go past stationary blades. Every time one blade goes past another you get a tiny pressure wave (i.e. sound). There are hundreds of blades and the rotating part is spinning incredibly fast, so this leads to a fairly loud, very high pitched sound. The \"whine\" of a jet engine is coming from here. The next is from the burning of fuel. In a car engine fuel is aggressively exploded at one point in the stroke, while in a jet engine the fuel is burned in a continuous process. This means that you don't get individual loud explosions to muffle, but it's still a source of white noise. The biggest source of noise, though, is when the very fast moving air comes out the back of the engine and has to mix with the slow moving air. Engines for commercial jets are designed to minimize the difference in air speeds. One way of doing this, which has the added benefit of making the engine more efficient, is to hook up an additional fan onto the same shaft as the compressor and turbine. This fan is used to create a stream of moderately fast air. The very fast air can mix with the moderately fast air, then that can mix with the slow air that didn't go through the engine at all. This more gradual mixing makes a commercial jet much quieter than an equally powerful engine on, for example, a fighter jet. This process of putting a big fan on the front of the engine makes a \"turbofan,\" which is what almost all jets are these days (contrast with a \"turbojet\" which has no fan). Passenger jets and cargo planes use a big fan, passing more air through the fan (and around the compressor and turbine) than goes through the core. This is because they prefer fuel efficiency and low noise. Fighter jets also use a fan, but they pass a higher percentage of the air through the core of the engine, since they prefer a higher power-to-weight ratio and a smaller size. Fighters also sometimes dump a bunch more fuel into the air after it's gone through (or around) the core. There's still plenty of oxygen left in this air, so this allows them to (inefficiently) create more thrust. This is an afterburner and it is incredibly loud since it increases the speed of the exhaust, reduces the amount of slow mixing that is allowed to occur, and it performs combustion right at the end of the engine where any noise generated is free to propagate outside of the aircraft. Anyone who's heard a fighter turn on their afterburners while at low altitude can attest that it is *incredibly* loud, which really shows just how much has gone into making passenger jets quieter than they could be."
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6dy50o | What happens when a parachute doesn't open correctly? | I just read a story of a navy seal dying of a parachute accident. Aren't all parachutes designed the same? Is there no procedure in place to ensure every chute is safe to use? What are the factors in play that could change the way a chute opens? I don't know. I'm just surprised to see people at such a high caliber of expertise still have these problems. | Engineering | explainlikeimfive | {
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"> Aren't all parachutes designed the same? No, there are many designs. > Is there no procedure in place to ensure every chute is safe to use? There is. The process is performed by humans who can make mistakes, and equipment can still fail regardless. > What are the factors in play that could change the way a chute opens? Bunches. Incorrect folding, damaged or worn cables, position of the diver when opening, the list goes on. > I'm just surprised to see people at such a high caliber of expertise still have these problems. No experts are so good that they are flawless, and no process so good that nothing can ever go wrong.",
"Parachutes have to be packed and prepped ahead of time. If this isnt done correctly then it can cause accidents like this. Parachutes also suffer from wear and tear over time and so can snap or have other issues. Finally it could be user error. As much as theyre elite soldiers they can still make mistakes. Maybe he didnt use it correctly or some other issue happened during the jump.",
"Designs vary, as with many things. You do however have to repack your chute before every deployment, a small mistake there could leave you plummeting to the ground with a chute that won't release."
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6dzfe7 | Why electronics require such specific voltages as 3.3v, 5v or 12v? | Is it just plain standardization? Why such numbers were chosen? How come we never see a household device requiring like 10v? | Engineering | explainlikeimfive | {
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"Two different things: Common batteries come in a multitude of 1.5 volt because a single cell of a alkaline battery provides 1.5 volts when full. This voltage does not change if the battery becomes bigger or smaller, that only changes the duration it can provide this 1.5 volt. The other, 3.3v, 5v and 12 volt (and you are missing -12 volt) are standardized voltage levels in electronics (and thus computers) and then specially transistors and all inherited technologies like digital chips: Digital chips (IC's, integrated circuits) specially the TTL series have an \"low\" or 0 level at between 0.0 and 0.8 volts and a \"high\" or 1 level between 2 and 5 volts. So the maximum voltage you need there is 5 volts. Bingo, there is your 5. -12 and +12 volt are (where?) the voltages used for communications, but early logic used +12 because of noise / interference. You needed a huge difference between a 0 and a 1. With the TTL logic later on this wasn't needed so much anymore and you could go back to 5 volts. Now 3.3 volt: It's part of making chips faster without melting. If you double the number of transistors on the same area and double the frequency, you will need four times the power consumption. That's a lot of heat. If you decrease the voltage for that chip, you will reduce the power consumption and the metal lines on your chip won't melt.",
"It is standardization, but not necessarily by any organization. The reasons for the specific numbers are rather hard to pin down, but it makes sense that engineers settled on a few voltages as the most common. Early transistors worked best in the range of 12V, and that was the same as car batteries. Lots of parts like light bulbs, motors or relays are made to work at specific voltages, so there was a lot of incentive to settle on a few voltages. You don't see 10V often because it is so close to 12V that most engineers would just design for 12V instead. For a long time 5V was the main standard for digital circuits. This was probably due to the introduction of 7400 series TTL (transistor-transistor logic) ICs in the early '60s. Later CMOS parts (which are still widely used) were made to be compatible. The 3.3 and lower voltages are now often used because high speed circuits can switch faster with lower voltages."
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6dzoxk | how would you connect to the internet if a government severed all connections similar to what happened in Egypt during the Arab spring | Engineering | explainlikeimfive | {
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"Presuming we're part of the secret resistance trapped in a tyrannical dictatorship, I'd recommend the following: 1. Satellite phone. These are essentially cellphones that you can attach to portable antennas for direction communications with satellites. They're expensive compared to standard cellphones and your bandwidth will be limited. But they're portable and relatively easy to conceal. 2. Shortwave radio. This uses terrestrial radio signals that can stretch beyond the boundaries of any nation. It's not very portable, but it's relatively concealable: the antenna needs to be (somewhat) exposed but it's relatively low-profile. You can also communicate while sitting in your secret underground bunker (unlike a satellite phone). However, the nefarious secret police can also track your signal if they're so inclined. To get around this, you could mount the radio in a vehicle but you'd quickly run into serious signal processing issues as shortwave isn't the best medium for digital data signals in the first place. 3. Two-way satellite. The consumer satellite service you're thinking of actually uses ground stations (which have been seized by the government). What you need is the big (meters in diameter) satellite dishes used for direct communication with the satellites. These are *very* noticeable, since they're fixed emplacements that require line-of-sight to the sky. So the government probably has a good idea where to send their soldiers to shut down communications. However, the most likely path is simple human frailty: *someone* has access to those telecommunications links and that someone is susceptible to bribery/coercion.",
"This is not unique to Egypt during the Arab spring. Almost all countries involved in the Arab spring tried to shut down the protests by cutting Internet services. And a lot of other countries are doing the same. Some are helped by American companies like Cisco to make firewalls to filter out traffic. If there is a filter in place then you might be able to circumvent it using TOR. The public relays is usually blocked but the TOR project is distributing information on hidden relays to affected areas. If Internet is completely cut off then there is a chance that the phone networks is still working in which case you can use old fashioned modems to call international lines and connect to the Internet. There is a number of modem centrals that is still operating free of charge to anyone who connect. Another option is to use satellite based Internet solutions. Satellites cover a larger area then a single country and can be used in neighboring countries with little problems. For example the satellites covering Italy is very popular in Libya. When it becomes very hard to connect to the Internet then people also set up hand to hand messaging services. We see these types of services in almost every country with a limit on Internet access. You can use a computer very effectively using thumb drives and removable hard drives to carry the communication although real time services is out of the question."
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6eagm1 | Why is there a gap between the toilet seat and bowl? | Engineering | explainlikeimfive | {
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"text": [
"Prevent liquid (pee) from getting trapped in between, which leads to bacteria and mold growth. By having a gap, it can evaporate away."
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6eeutc | If you're searching for a used car of a certain type and you keep seeing the same year and model everywhere, does that mean that model year sucked? | Engineering | explainlikeimfive | {
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"Not necessarily. There may have been a particularly good financing deal available that year, or it was just a very popular model. For older cars, finding a good number still in circulation can actually be good news. That suggests that the car didn't have any major mechanical problems that killed them all off.",
"No. Leasing is popular. The car is owned by the dealer, people basically rent it for a year, and then sign a new lease after a year for a newer model car. The dealer sells the car as used. Lots of cars of a particular year, typically last year's model or the year before, tends to pour out onto the market."
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6efag7 | Why does the exhaust from classic cars/hot rods, boats, and other vehicles with gasoline combustion engines have disctint smells detectable from a greater distance than other vehicles? | Yesterday I was driving with the windows down and noticed a distinct smell - it was the car show about a quarter mile away hosted by a local diner. This made me realize that exhaust from classic cars/hot rods has a distinct and easily identifiable smell; boats/marinas are similar in that the smell of boat exhaust is also unique and discernible from other exhausts. Being that they all use gasoline, why is it that exhaust from classic cars and boats have smells unique to any other gasoline-fueled vehicles? | Engineering | explainlikeimfive | {
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"Because these lack a 3-way catalyst and do not run at stoichiometric air fuel ratio. The smell is related to unburned hydrocarbons and nitrogen dioxides.",
"I had an interesting conversation with my daughter (ER doctor, NYC) recently. Apparently the exhaust of newer cars is not as lethal as older autos when used for a suicide attempt. Nowadays people who enclose themselves in the garage with a running car are more apt to turn up at the ER with brain damage (instead of the morgue) if discovered in time, and the timeline for death is greatly extended, so discovery is more likely. Plus the exhaust is likely to make them nauseous, so they abandon the attempt instead of falling asleep. I wonder if there is anything in the medical or engineering literature about this."
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6egwt1 | What is the difference between a Straight and Flat V8? | I do not understand the difference between the two. All i know is that the straight 8 is becoming one of the past, and that v8 & supercharged engines are becoming more common in 'muscle' cars. Such as; the new 2017 Dodge Challenger SRT Hellcat, and a little older Shelby models. | Engineering | explainlikeimfive | {
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"Straight 8 has 8 cylinders in a single row like this from above ○ ○ ○ ○ ○ ○ ○ ○ V8 has 2 rows of 4 cylinders arranged in a V shape when looked from the end like this from above: ○ ○ ○ ○ ○ ○ ○ ○"
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6em9y1 | Why is it easier for the US to intercept short- and mid-range missiles than it is to intercept long-range missiles? | Engineering | explainlikeimfive | {
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"Long range missiles ([ICBM]( URL_0 )), fly at very high altitudes and very high speeds. They use sub-orbital trajectories to reach their targets, meaning that they begin by going mostly up, and then perform most of their flight outside of the atmosphere. When they come down they travel at almost orbital speeds (close to 8km/s) making them close to impossible to intercept on their descent. [edit] formatting.",
"Long range missiles travel very very fast and come in pretty much from orbit. They are traveling about 7km/s A medium range missile is about 4km/s A short range missile is about 2 km/s So you need to hit something going very fast and you don't have a lot of time to aim at it once it comes down from space.",
"As others have pointed out the speeds and distances involved are very significant, but there is a bit of a deeper question about why those numbers are so significant. Imagine we are defending against a short range missile fired from an airplane. The missile is armed with a conventional explosive warhead and needs to get within a few yards of its target to do its job. Because of that it needs a guidance package that is intelligently guiding it in. This gives it a lot of accuracy but it opens it up to being spoofed. Heat flares, chaff, concentrated energy bursts, can all be used to confuse or blind this system and if you pull that off the missile is toast. You can also try to shoot these things down. The CIWS system looks like R2D2 sporting a big erection. Basically you tie a very, very, big gun that fires an insanely high number of bullets (75 bullets every second) with a radar system and just spray bullets in the direction of the incoming missile. You might miss 1,000 times before you get a hit, but the fucking gun fires so fast it doesn't matter. However intermediate range missiles started becoming more of a thing. The problem with these things is that because they go MUCH faster than short range missiles, and because they are MUCH bigger even if you do shoot them and they disintegrate in the air, if they get anywhere near the target they are aiming for when this happens there momentum will carry them into the target and they will still do murderous damage. So you need to destroy them further out. That means you need a missile that is going to fly out 10, 20, 30 km from your ship or base and intercept them. This sounds hard, and it fucking well is. But you have three HUGE advantages. First if you try to shoot them down from the target, or from something relatively close to the path of the target (i.e. they are aimed at an aircraft carrier and one of its support shits is the anti-missile ship). all you have to do is get your interceptor to fly straight towards the incoming missile and then... explode early. If your intercentor is just a huge bomb filled with ball bearings or other fragmentation and it explodes a half second away from the missile to be intercepted you will have this nice big clowd of debris traveling very quickly towards the missile to be intercepted, while it travels very quickly towards this debris. The speeds actually help you. Keep in mind though, its still fucking hard to do this and impressive as hell that it can ever be done. For an ICBM your interceptor isn't at the target, it isn't even on the same trajectory. There is no cheating and you need a body to body contact for your kill for a lot of reasons. So its a quantum leap up in terms of difficulty."
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6emzdo | What happens if everyone in a city flushes their toilets at the same time? | Engineering | explainlikeimfive | {
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"I've done work in shit plants. You can absolutely tell when everybody in an area goes to the bathroom at the same time. There's peak hours where the waste coming in is so much worse then other times. At the plant I was at, it was 7-8am and lunch where things got noticeably bad."
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6en447 | How do bricks work? | Are they structural to making buildings stay up? Or just an attractive exterior? Are there different types? How tall can a brick building be before the bottom bricks break under the weight of the bricks above them? | Engineering | explainlikeimfive | {
"a_id": [
"dibht6q",
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"text": [
"They used to be structural but today most cases they are more for the thermal mass and the style. Most buildings are wood/steel/concrete structurally today with the brick layer is only an outer layer that provide: - Mass to help control temperature - Protection from the elements - Style You can identify that a brick wall is of this type because all the bricks will be lengthwise (\"wide\") across the entire wall (usually). In older buildings they do have a structural function. In these cases a brick wall isn't just one layer of bricks but several layers stacked and interlocked together. You can identify these because every few bricks in height you will see a row of \"thin\" bricks. These are bricks layed inward so that the outer layer will interlock with the next layer of bricks. The total height they can support is based partly on the thickness of the wall (something like a height of no more then 20 times the walls width at the base), though it's fairly rare to see a building of this type taller then 10 stories as it becomes increasingly more complicated to make a brick building taller without another supporting structure.",
"We stopped making buildings out of brick or mostly brick a long time ago so I doubt they'd be structural in anything remotely modern, but they can absolutely be structural and there are plenty of buildings made entirely of brick. These days they're just for decoration, and yes there are many different types of bricks. I Googled largest/tallest brick buildings and it looks like they can be about [this big]( URL_0 ) without being supported by steel, so not particularly tall"
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6eo4ax | How do ball bearings work? | I've been playing with a fidget spinner and just can't understand why the ball bearings are keeping it spinning for so long | Engineering | explainlikeimfive | {
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"dibpbrv"
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"text": [
"The inner races (the two metal rings) that sandwich the balls in there have grooves on the inside so that each ball only touches each side in one or two places (depends if it's vertical or not). They keep it spinning because it greatly reduces friction. Nothing is sliding against one another, and the entire spinner is touching the bearings in just a few little places, and where it does, it's smooth metal balls rolling on a smooth metal track."
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6eo77q | What are the major roadblocks to 'industrializing' spider silk? | It seems to be the Holy grail of textile sciences, so why haven't we been able to create an agriculture around it like silk worm silk or synthesize it in a lab? | Engineering | explainlikeimfive | {
"a_id": [
"dibwpgj",
"dibq935"
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"text": [
"Unfortunately, spiders themselves cannot be used to create any decent amount of thread. For one thing, they are cannibalistic and like to eat each other when placed in close quarters. Also, the orb weaving spiders (the ones that create the strongest type of fiber) can create 7 different types of silk and only really one of them is useful as far as strength properties go, so you have to literally [incapacitate a spider and manually draw the silk]( URL_6 ) to get the correct fiber from them. And, even if you do that, you would need [over a million spiders]( URL_5 ) to create anything useful as around 30,000 of them are needed to create a single gram of spider silk. Not really scalable. Now, that being said, artificial and transgenic spider silks are being created and industrialized as we speak. There are many companies and universities that are developing it and are on the cusp of commercialization using various vectors to achieve spider silk production via genetic editing of various organisms. These vectors can produce 2 things directly: spider silk protein powder and spider silk threads. Each has advantages and disadvantages. The spider silk protein powder is created by genetically altered bacteria, yeast, and goats that produce the proteins in their milk. The goats are inefficient, producing only about 2 grams of protein powder per liter of milk. Also, the goats take a long time to breed, so expanding production with this method is very slow going. The bacteria is more efficient, but the preferred bacteria, E.coli, can't store very long gene sequences, so need to be truncated to produce slightly inferior proteins and need to grow in a vat to make enough protein to be usable. The yeast method is the best protein method as it uses yeasts like *Pichia pastoris* that are able to store and transfer longer gene segments efficiently and accurately. The yeast also will reproduce much more efficiently with much cheaper “fuel” (mainly sugar water) to create much higher quality proteins than the bacteria method. Both the bacteria and yeast method have a very short gestation time, so any gene “tweaks” can be done to vary the properties of the proteins for custom applications. After they get the protein powder, they can then mix it with other substances to change their properties, turn it into a foam or film, or spin it into a fiber. Unfortunately, the mechanical spinning techniques such as wet spinning and electrospinning are still lacking and cannot spin fibers strong enough to measure up to natural dragline spider silks, but they are still being developed and I think it is only a matter of time before this issue is overcame. The spider silk fibers can be directly created by genetically altering silkworms. These silkworms get various strains of spider DNA injected into them and they can naturally spin different types of fibers. This method allows them to create much stronger fibers than the protein method, but it takes a longer gestation time and a lot of mulberry and space to expand production. Also, since you are directly producing the fibers with this method, it would be more costly if you wanted to create foams or films that can be made with the protein method. Now for the major companies creating the silks: **[Bolt Threads]( URL_7 )** is a San Francisco based company using transgenic yeast to create proteins that they spin into fibers for textiles. They have already released a limited production of [spider silk ties]( URL_13 ) and are working with Patagonia to create more textiles from their silks down the road. **[Spiber]( URL_10 )** Is a Japan based company that uses bacteria to make their protein powder that they plan to use in [automobiles]( URL_2 ) and spin into textiles. They are working with Goldwin, the main producer for The North Face Japan, to create jacked called the [Moon Parka]( URL_4 ) that should hopefully be out this winter. **[Kraig Biocraft Laboratories]( URL_11 )** is a Michigan based company that uses transgenic silkworms to create spider silk threads directly. They are currently fulfilling a [contract with the army to create bulletproof material]( URL_9 ) at small scale and are hoping to open a [large scale sericulture facility in Vietnam]( URL_1 ) in the near future to start mass production of their fibers for use in textiles. **[AMSilk]( URL_8 )** is a German based company that uses transgenic E.coli to produce protein that currently is being used in [cosmetics]( URL_3 ) and can be used in [medical applications]( URL_12 ). They are also working with Adidas to produce a [spider silk sneaker]( URL_0 ) that should be out in the near future. These four companies are the ones that I feel are the furthest along, but there are many more that are out there that I can go into detail about as well. I do try to keep up to date with what is going on in the spider silk field and keep /r/SpiderSilk updated with the latest news and events, so if you are interested in keeping up with this new, revolutionary technology, check it out.",
"Have you not heard of Spider Goats? URL_0 Here's the Wikipedia entry for the sort of father's of this business: URL_1 So. It's on the way. Some secret DARPA-equipped soldiers are probably wearing it right now. The main roadblock was simply that spiders don't produce enough of it under natural circumstances,and require a fair amount of space per individual to produce."
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"https://www.wired.com/2016/11/compost-adidas-spider-silk-shoe/",
"http://ipaquangnam.gov.vn/eng/tin-tuc-chi-tiet/lanh-dao-ubnd-tinh-tiep-va-lam-viec-voi-lanh-dao-cong-ty-kraig-biocraft-laboratories-hoa-ky.html",
"http://newatlas.com/lexus-paris-2016-concepts/45466/",
"http://www.cosmeticsdesign-europe.com/Business-Financial/AMSilk-and-Rahn-enter-European-distribution-deal-for-silk-biopolymers",
"http://www.spoon-tamago.com/2015/10/20/moon-parka-outerwear-made-from-synthetic-spider-silk/",
"https://www.wired.com/2009/09/spider-silk/",
"https://www.youtube.com/watch?v=aLSGBQUA8l0",
"https://boltthreads.com",
"https://www.amsilk.com/home/",
"http://www.foxnews.com/tech/2016/07/19/us-army-eyes-dragon-silk-for-bullet-proof-vests.html",
"https://www.spiber.jp/en",
"http://www.kraiglabs.com/",
"http://www.news-medical.net/news/20140129/AMSilk-completes-preclinical-testing-of-proprietary-silicone-breast-implant-coating.aspx",
"https://www.forbes.com/sites/rachelarthur/2017/03/10/bolt-threads-is-launching-its-first-bioengineered-spider-silk-product-at-sxsw-a-necktie/#bca5baf4d13f"
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"https://en.m.wikipedia.org/wiki/BioSteel"
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6er6r6 | What is plastic made from? | How far back would you have to go before you found a natural resource? | Engineering | explainlikeimfive | {
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"dicdyir"
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"text": [
"Plastic is a relatively broad term, but it is used to describe organic polymers, meaning very very very long chains of mostly carbon, generally surrounded by hydrogen. Plastic is made through refinement of petroleum byproducts, meaning it comes from oil."
],
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6evrt2 | Why can't you put AA batteries in series, grab some wires and charge your average phone? | For example, GreatScott!, made a video on how to charge your phone with AA batteries, however, he made a complicated circuit to get the job done. Isn't it as simple as giving the device sufficient current at a regulated voltage? *New to electronics | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It used to be that easy, and on some phones it still is. However, now some phones require some sort of signal on the USB bus to indicate how much current the charger can supply and won't activate the charging circuit until those signals are seen. Or you can get even more into it like Apple devices and they won't charge (or they'll at least bitch loudly) unless they see the Made For iPhone/iPad authentication chip in the charging circuit. The signal on the USB lines can be as simple as shorting the two data lines and just having +5VDC and GND or it can be as complex as having a chip in the charger that can negotiate on the USB data bus and say \"Hey, I need power, can you give it to me?\""
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6ewhqt | how can TOR, or other proxy tools, provide anonymity, when all the traffic, howsoever directed, goes from our computer to the internet via the ISP? | Engineering | explainlikeimfive | {
"a_id": [
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"didknpm"
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"text": [
"Lets say that Adam wants to send a letter to Zack. The only way to do this is to give it to Larry to deliver. The problem is that he doesn't trust Larry not to read the letter, so what does he do? Well, he establishes a code between himself and Zack, encodes the letter and sends it. Now Larry can deliver the letter but can't read it. That is the basis of encryption. The problem there is that while Larry can't read the letter, he still knows the letter is being mailed to Zach. We can fix this by sending the letter to Carol first. We set up a new code with Carol and send her a letter that says (in code), \"Send this letter to Zach\". Now Larry can deliver the letter without knowing the contents _and_ without knowing the recipient. Now, what happens if we don't fully trust Carol either? Well, we can get _another_ person involved - Dan. We set up the same system - we send a coded letter to Carol that says, \"Send this letter to Dan\". Dan gets the letter, decodes it and reads, \"Send this letter to Zach.\" Now _no one_ in the entire chain knows the full story; Larry knows the sender, Dan knows the recipient, and Carol only knows the intermediaries. In this example, you are Adam, the website you want to go to is Zach, Larry is your ISP and Carol/Dan are Tor nodes. Your ISP knows you are connecting to a Tor node but has no idea what data you are sending nor who you are sending it to. Each of the intermediary Tor nodes knows the previous node, but not the origin or destination. The final node knows the destination, but nothing before the node that send the request. Since no individual node knows all the information, you are protected from any individual finding out the whole story - the only way for any given person to learn who the sender and recipient were is to get _every_ node to agree to give up the data and put the pieces together - something that is near impossible to do given the number of Tor nodes out there and their commitment to privacy.",
"Your traffic is encrypted on your device, goes to the proxy server, is unencrypted, the server makes the request, the inwards traffic is then encrypted again and decrypted when it gets back to your device. So your traffic, when it goes to and from your ISP, is encrypted. All they can see is the encrypted data, which is useless."
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6f00vd | A first-of-its-kind plane is built, how exactly do they test such a vehicle before its first flight and why does it take an additional two years? | [Stratolaunch]( URL_0 ) Read title; why does it take two years and how do they test it? I know it's a lot of safety procedures and make sure it's safe, but how do they test its ability to fly without actually flying it? Surely, it's not as simple as putting it into a wind tunnel, or is it? | Engineering | explainlikeimfive | {
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"Actually a lot of it will be wind tunnel testing (size doesn't necessarily matter as long as its aerodynamically the same). But going from there it's handling and control characteristics testing in combination with EP procedure development. That's why there are a metric shit ton of ground runs and taxi tests then high speed taxi tests. Additionally, since it's a first and likely only if it's kind, they have to start hunting for the 'oh crap' factors that will seem obvious later, but are lost in the wash now. Combine that with FAA/International flight standards and approval processes, I'd say 2 years is pretty optimistic depending on how they've been front-loading their paperwork. In any case the dual-fuselage design has always been just an insane design to me, and this aircraft is a beast and a half. Hope to get to watch her slip the surly in person one day."
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6f17d0 | How does a trains wheels actually stay attached when the train is moving or changing track? | I've been using trains a little more frequently lately and I've always been interested in the engineering side of machinery but when I look at the small bit of metal that holds the train to the track it amazes me how it stays attached. It amazes me even more when I hear it change tracks because in my head all the train is doing is sliding onto the new track and falling into place with the hopes that it doesn't de-rail. Obviously people that are way smarter than me know what they're doing with this stuff but I would love to know just how they got to this. | Engineering | explainlikeimfive | {
"a_id": [
"dielklu"
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"text": [
"When trains \"change tracks\" it is the track that changes first. The train just follows the changed track. The track has to align properly or the wheels won't continue along the rail. Like [here]( URL_0 ) Train wheels are kind of like big spools. They have edges that go below the surface of the track so they don't fall off it. [Often only on one side]( URL_1 ) which is enough."
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"https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTpq6b554LeKV-b_-cAW2oBkVIJLQ8Y8Vn0CFSdnDtd3D7PjbFk"
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6f6z3d | Why do we place offshore Wind Turbines in places with strong water currents? Surely more power could be generated by the water turbines given that water is roughly 816 times more dense than air? | Recently in Victoria, Australia, they announced plans to build a bunch of offshore wind turbines. This location has strong winds but also has strong water currents. I can appreciate that wind might move faster than the water currents, but the water carries with it much more mass and hence the kinetic energy of the water would be much greater. So, usually you'd try to tap into the source with the greatest energy. Right?? I feel like I must be missing something, like there's concern about the water turbines hitting dolphins or schools of fish. | Engineering | explainlikeimfive | {
"a_id": [
"difwwal",
"difxqql"
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"text": [
"Ocean water doesn't flow terribly fast, so to get enough efficiency out of a water turbine you'll need to place them in the ideal spots and also need some heavy duty mechanics to get the most out of the larger forces. Also since water is more dense, turbulence and flow are a bigger concern so you need to be creative, like putting large cylindrical shrouds around them. All this makes them expensive, on top of having to be installed underwater. Still, as manufacturing techniques and technology advance we will definitely see large scale tidal stream generators, they are already being tested.",
"Building turbines to work in air is fairly straightforward. Building turbines underwater factors in a bunch of new problems- you need to waterproof things, you need to prevent corrosion, it's a lot harder to perform repairs, it's harder to install, and you also need to put the cables to collect the power underwater as well, repeating all of the above problems. The turbines are also under greater strain and suffer more friction from water than air."
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6f7cf8 | Why do toilets in America get blocked so often. | So I'm from Australia and Ive always wondered about this and a TIFU thread got me thinking about it again. But I often see in tv or other Amercian media toilets getting clogged and I can never work out why. I've never heard of or experienced it in 20 years is that because our (Australia compared to America) sewer systems are better or is there another reason? | Engineering | explainlikeimfive | {
"a_id": [
"difyq79",
"dig2o5n"
],
"text": [
"Old buildings and old sewage systems is the primary cause. You also will sometimes have cases where someone did not do something up to code.",
"Government regulations limited the amount of water that toilets could use. Until manufacturers figured out how to make them work well with less water this was such a problem you had people from border cities like Detroit going to Canada to get toilets that could flush a load down with a single flush without clogging."
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6f9p9l | How are police lights and other flashing lights made, so that they do not trigger seizures in epileptic people? | Engineering | explainlikeimfive | {
"a_id": [
"digikte",
"digpbz4"
],
"text": [
"They aren't. The lights can, and do, trigger seizures. Typically however if a person is that prone to seizures they don't often have a license or drive frequently.",
"Despite popular opinion only a small percentage of epileptic seizures gets triggered by flashing lights. Most cases of epilepsy are actually not photosensitive."
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6fd3p9 | most ships have electricity onboard. Do they have grounding cables? Where does the electricity go? | Engineering | explainlikeimfive | {
"a_id": [
"dihchyd",
"dih9rur"
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"text": [
"The concept of ground on a ship (or generically, marine use) is somewhat more complex than on land. First, the concept of *ground* is simply a common reference for zero volts. In the simple sense, it does not matter how this is established. In practice, especially on a marine vessel there are several things to consider. First, most large ships have both AC and DC circuits. All the DC circuits should have pos/neg directly connected, and never use a ground shared by AC. With AC, you will have a ground bus (a large wire) that all the AC gear must be bonded (connected) to. Again, the idea is to get everything to a common zero-volt reference. No need to actually get them to a real \"ground\" like on land. There is also a \"lightning plate\" that is used on some ships to connect tall masts too..this plate is mounted under the boat...in the water. In some cases (esp. military) there are a lot of radios and RF gear on board, so those will be grounded in a separate circuit on their own. This keeps things like engine and lighting noise out of the radio.",
"Such boats either have a generator or batteries (for smaller ones). In either case it all works in a closed loop contained within the ship. There are no grounding cables much the same way there aren't any in cars or airplanes that have power outlets on board."
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6fhhiy | Why are most American college dormitories built with cinderblock interior walls? | Engineering | explainlikeimfive | {
"a_id": [
"dii6tpd"
],
"text": [
"Because the school wants to spend as little money possible building and maintaining the premises. Doing so helps guarantee profit from offering living quarters in the first place. You can't jump off a pong table and fall through a drywall when the walls are made of cinder, or punch through cement in the middle of a fight. Easy to clean, and stands up to a lot of abuse."
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6fivug | Ugly power lines, poles, transformer cylinders and other mess of stuff cloud my neighborhood. But my well-off parents' neighborhood has not a single wire in site. How? | Engineering | explainlikeimfive | {
"a_id": [
"diiira5",
"diiimt7",
"diilpqb"
],
"text": [
"All those things can be run underground, but it can cost up to 10 times more than overhead systems. This cost means that they tend to only be put underground in regions where people are willing to pay that price, ie wealthy neighborhoods.",
"The power is ran underground which is quite a bit more expensive to do. Each house will have some sort of power box near it housing the concealed transformer connecting it to the underground grid.",
"Lots of comments about the price which is true. One other factor I want to mention is age. Is your neighborhood older than your parents' neighborhood? Many older communities are serviced by overhead electrical utilities. Buried powerlines and padmount transformers all the way to the end-user are a relatively 'new' thing. You may be asking why they don't convert, and the answer to that question is difficulty and cost (which share a lot in common). Negotiating all the other buried utilities such as natural gas, sewer, water, etc can be very time consuming and expensive. It is generally not a very good return on investment for established neighborhoods."
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6foiku | How our major cities would get electricity without using coal to boil the water at nearly every electricity plant? | I am having an argument with one of my coal miner uncles and he says that the primary source of electricity is obtained by burning coal to boil water that power nearly 95% of all power plants in the world. I suppose we need a lot of coal right now. What arguments can I counter him with and is he just plain wrong? | Engineering | explainlikeimfive | {
"a_id": [
"dijr1xd",
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"dijqx32",
"dijqvsx"
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"text": [
"I don't think he's correct. According to [this]( URL_2 ), globally only 40% of our power is coal. [In the united states, stats are similar]( URL_1 ). As much as I don't want to rag on the guy, his future as a coal miner is not looking great. Coal usage is going down, and next up in line for stuff we can burn is oil and natural gas. The mining process for these is different (definitely doesn't require the big worker crews, much more pipelines and engineers). Wikipedia [also has a nice chart]( URL_0 ) near the bottom of the page on what renewables we're using for our power needs. Hydroelectric USED to be an enormous portion of it, but that has other problems (like there's only so many rivers we can dam) that prevent it from growing. Onshore wind has been the US's largest growth for power production, and while it's only recently become viable, rooftop solar setups are a tiny chunk but growing.",
"Well, you could show them [this page]( URL_0 ) which has an unsourced, undated claim from the fucking WORLD COAL ASSOCIATION that says that coal only provides about 41% of global electricity. Seems like if anyone was going to exaggerate the amount, it'd be them, and even they only put it at not quite half. Coal definitely is and has been important to generating electricity, and I wouldn't be shocked that it is and will be the plurality electricity source for a while since it's so good at it and so cheap. But it's nothing close to 95%.",
"Coal is still a major global source of electricity, but it's not anywhere near 95% of the power generated: URL_1 I suppose he's right if you live in Mongolia. China is around 80% on that chart, and the United States is around 40%. However, that chart is only from 2011, and things have changed a lot since then. As of 2016, the US is down to 30% electricity production from coal. URL_0",
"I don't know the exact numbers, but 95% coal worldwide sounds really unlikely. Natural gas, petroleum, biomass, burning waste, solar towers, solar photovoltaic nuclear fission, wind power, hydroelectric, wave power, and geothermal are all ways to generate electricity without coal. Many of the above use similar technology as coal but have a different source of heat to boil the water. Others find different ways to move the water over the turbines. Others still turn the turbines without boiling water. And others still produce electricity without turbines."
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6fqo3l | Why do so many bathrooms have their light switches outside of the room? | Seems like it would be more useful to have the switch IN the room you are in... why is this? | Engineering | explainlikeimfive | {
"a_id": [
"dik8smg"
],
"text": [
"Bathrooms have water pipes in them, and it's safer to keep switches and outlets away from water unless they (switches and outlets) are waterproof."
],
"score": [
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6fqrdz | why do some ATM's hold on to your card for the whole transaction, and some give it back right away? | Engineering | explainlikeimfive | {
"a_id": [
"dikbodu",
"dik9r9l"
],
"text": [
"ATMs run by banks hold on to the card throughout the transactions, so that, if they determine that the transaction is fraudulent - too many wrong pin entries, for instance - they can retain the card to protect their cardholders. ATMs run by others don't do this.",
"Chip enabled ones need access to the ship throughout the transaction. Magstripe ones don;t need the card once they have the data off it. Magstripe ones only keep the card so they can choose not to give it back if it's stolen, though that function is rare today."
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6fryoa | How do % grades work for hills? | I'm completely baffled by hill grades, and it's embarrassing! A few key points: * What is a 100% grade? Is that a 45-degree angle or a 90-degree angle? * Why does a 5-10% grade seem so intense? They have warning signs for trucks on 5% grades, but that doesn't seem like much! * I really start to confuse myself when I try to calculate the grade of a hill I'm walking/biking/running on. Let's say I'm walking on a 3-4-5km-sided triangle, where my hill is the 5km hypotenuse and the rise is 3km. That means I'm walking at a 30-degree angle, right? What percent grade is that (is it as crazy-high as I think it is?)? Is the grade calculated based on the fact that *I walk* 5 km and go up 3km, or is it based on the imaginary base of the triangle so I'm going up 3km over the course of 4km along that line? Help me I'm burying myself in a logic puzzle. | Engineering | explainlikeimfive | {
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"It's rise in incline divided by run So, imagine a hill that increases 1 foot in height for every twenty horizontal feet, you would have a 5% grade. 1/20 = .05 = 5% For a 100% grade, it would be one foot increase in height for one foot in length. 1/1 = 1.00 = 100% How to figure out what degree of an angle that it would require a little bit of trigonometry.",
"A 100% grade is a 45-degree angle. The amount you rise is 100% of the amount you move horizontally. URL_1 URL_0",
"100% is 45° angle. The percentage is the value of the tangent x 100. It works like this: 100 m horizontal and 100 m rise is 100/100 = 1 = 100% 100 m horizontal and 50 m rise is 50/100 = 0.5 = 50% The hypotenuse doesn't play a role. For a 4x4 car a 100% incline hill is almost unclimbable. In your 3-4-5km-sided triangle, you walk 5 km (the hypotenuse). The incline is calculated 3 (rise)/4 (horizontal) = 75%."
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6ft3h8 | How do motorcycle/bike sidecars work? | Why does it go straight instead of just turning around itself or veering a certain direction by default? | Engineering | explainlikeimfive | {
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"text": [
"A sidecar basically makes a bike into a trike. Wherever the front wheel points is the direction that the whole vehicle will track. Turning radius is increased with a sidecar fitted."
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6fw2j8 | How does turning a shower knob more or less regulate the temperature of the water? | Engineering | explainlikeimfive | {
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"text": [
"Depends on the shower type. If it is one that heats cold water. Then it varies the amount of heating applied to the water. If it mixes hot and cold water together then it varies the ratio of hot to cold."
],
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6fyhfp | How can a 9V battery power a 40,000V stun gun? | As seen in this YouTube video: URL_0 Is he over exaggerating or is 40k the real number? | Engineering | explainlikeimfive | {
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"Power = volts × amps. A transformer can keep roughly the same power while changing the ratio of volts to amps. E.g 9V×0.5A = 40,000V×0.000113A A transformer works with two coils of wire around iron. The ratio of turns around each coil is the ratio of transformation. I made something like this as a kid. I got very fine wire from a car and wound thousands of loops round a nail using the reel from a fishing rod.",
"There's a type of circuit called a voltage doubler or multiplier utilized for D.C. spark generation. It's basically some capacitors, a transformer, and some diodes. It steps the voltage up to super high levels capable of generating a spark like in a taser. Electroboom has a good demonstration and write up URL_0"
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6g2dc1 | How does a cars fuel gauge work so that it doesn't change when the car goes up and down hills or around sharp turns? | Engineering | explainlikeimfive | {
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"The sensor signal is averaged over long time. Unless youre wildly accelerating or turning for endured 30 seconds or more, you won't see much of a difference.",
"Not all of them do that. My first car was a 1980 Mustang, and going up hills my low fuel light would come on, and going down hills it would go back off.",
"I've had cars where they do change when going up/down steep hills... Used to bug me. At the time, I thought the best way to fix would be to have sensors on all sides and take the average. Not sure if they actually do that tho."
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6g2uqi | Why are USB, HDMI, etc. connections not designed so there is no 'right way up' | I have a hard time believing it would be that cost prohibitive. | Engineering | explainlikeimfive | {
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"The newest iteration of the USB standard, [USB-C]( URL_0 ), *is* reversible as far as having no “upside-down.” I can't speak on the others, but the new USB plug is designed to be durable and robust.",
"It's easier to fit the wires in there with loose tolerances for placement if they only go in one-way. However, due to improved manufacturing techniques, current generation plugs (USB-C, Lightning, etc.) ARE designed to go either way up. The older-generation plugs were even worse: they had a live-line pin using the old DIN connectors -- but different hardware used the same connector for different purposes, with a different pin being live.",
"It *used* to be cost-prohibitive. Not so much anymore. The original USB was standardized in 1996, back when manufacturing techniques were not nearly as advanced as they are now. The desire to keep the standard strong and ubiquitous throughout the market is what kept the connector the same for years upon years. That was one of the biggest benefits, you could plug any USB standard into any USB port and it would work. As time went by, and as devices got smaller, the need for a new connector came about which is what prompted Mini-USB and Micro-USB. While this addressed the size concern, it was still limited by the manufacturing techniques. Now that \"we have the technology\" we are seeing more and more connectors moving towards the reversible connection standard. But it is a slow progress because so many devices out there only support the older standard that companies are hesitant to adopt the new standard.",
"Complexity. For nearly all standards. Every single pin is defined for a single purpose. Even reversible connectors have pins labeled in a certain order. So when you plug in a non reversible cable into a non reversible socket. Pin 1 on plug always matched pin 1 on socket. Now imagine you have 6 pins. Three on top three on bottom. 1-3 on top 4-6 on bottom. Now sometimes you get pin 1 connecting to pin 4 so you need to be able to detect that inversion and then reroute the internals to accommodate. This increases cost and design complexity. And frankly until now it hasn't been a big issue.",
"As far as the USB goes there is a little crease on the bottom I always look for. That has saved countless seconds of frustration."
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6g6i7j | How are transistors (and others small computer parts) made if they are so small? | Engineering | explainlikeimfive | {
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"You ever see an old movie or slideshow projector? Shine a light through a tiny picture then through a lens and it projects this massive image on the screen from a tiny picture. Turns out we can do that in reverse. Shine a light through a big picture and lens and we can project a tiny image on a tiny screen. Scientist have found stuff that breaks apart when certain kinds of light gets shined on it. So the manufactures coat a tiny chip with the stuff, then make a big picture with the circuits they want, they then shine the special light through and break apart the stuff so it forms the circuit they want, just very tiny. This is called photolithography.",
"I can't ELI on this but it's done by having UV light chemically react with the substrate and thus etching the transistors in a silicon layer. Since you're using light you can now use a lens to shrink this down to those tiny sizes. This is the very basics of it, pretty clever stuff."
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6g6kui | How does my call from the United States reach Australia? | When I call Australia from the United States, how does my call reach Sydney? It's such a long distance away. Is it all underground cable in the ocean? Because placing a call to Australia, I hear no delay between me the receiving party. How does this all work? Thanks guys. | Engineering | explainlikeimfive | {
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"The vast majority of international calls travel through fiber optic cables running from one continent to another at the bottom of the ocean.",
"Here is an interactive map of all the cables and there connection points: URL_0 Also here is a diagram of a cable : URL_1",
"Careful. I once knew a guy who had to pay nine hundred dollarydoos for a collect call to Australia"
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6g84es | Why hasn't the hydrogen engine taken over the combustible engine market? | In middle school I was in a science fair and the kid across from me had a hydrogen engine prototype. He explained that it's a combustible engine that basically runs on water. So why haven't they taken over the market and afaik why haven't we made a way for it to run on salt water? | Engineering | explainlikeimfive | {
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"Hrm... okay, so lots of problems here. 1. Hydrogen engines do not run on water. They burn (oxidize) hydrogen in order to produce energy. Although the hydrogen can be extracted from water via electrolysis, most hydrogen is manufactured by breaking apart methane from natural gas. Even if the hydrogen burned came purely from electrolysis, you still need to provide energy to the electrolysis reaction in order to make that hydrogen. Said energy would come from power plants, coal, gas, nuclear, solar, whatever. 2. hydrogen is a gas at room temperature and atmospheric pressure. It is also invisible, undetectable to any human sense, and highly explosive. These all make it less than ideal for a fuel source. hydrogen needs to be liquified or highly compressed in order to have the energy density to drive a car more than a few miles. Now consider what would happen if two such cars were to collide. A canister of pressurized and highly explosive fluid is not what you want to have in your car in such a situation. The extra material that would be required to contain and protect the hydrogen would make a car much heavier than the plastic/sheet metal gas tanks in standard automobiles. And heavier = less efficient. 3. Those issues aside, hydrogen makes an appealing fuel because of its high efficiency. The combustion reaction of hydrogen and oxygen produces a lot of energy without requiring much to sustain itself. And since it doesn't produce CO2, it's appealing as a \"green\" technology (though it does produce NO2 and I think NO3 due to the nitrogen in the air, and those are both greenhouse gasses as well). The problem then comes down to efficiency. As I said, most commercial hydrogen is made from natural gas, because the amount of energy required to break down that gas compared to the energy that the released hydrogen produces is rather good (I recall reading somewhere that it's about 80-90% efficient? Don't have a source for that though). Generating hydrogen through electrolysis is much less efficient, somewhere in the 10-20% range. Using natural gas doesn't really help the environment. The carbon output shifts to the hydrogen processing facility, and you're spending more energy than just burning the natural gas in the car itself. Using electrolyzed hydrogen helps the environment only so long as the source of your electricity is much, much cleaner than the car (because you're spending so much more energy to liberate that hydrogen), but it's a massive spike in demand to the electrical grid. It's possible that hydrogen could replace gasoline in automobiles, but for now the cons outweigh the pros. Not to mention there's the logistical nightmare of installing new facilities in every gas station in the world to store and distribute hydrogen. Electric cars perform many similar functions, but have many fewer drawbacks, which is why they've been pursued more vehemently.",
"> He explained that it's a combustible engine that basically runs on water Oh boy, it's this scam again. You can't run an engine on water, and the fact that it hasn't taken over the market should be the first clue. So in theory, you pass an electric current through water to break it into hydrogen and oxygen, burn those gases and get energy back. But functionally, you will **always** get back less energy then you put in to split the water in the first place. It's a thermodynamic certainty that you'll always be running at a loss. Now, hydrogen isn't a terrible fuel for combustion in and of itself, but pure hydrogen is exceedingly rare entirely *because* it's so good for combustion; it reacts very easily. Thus, you have to provide energy to split the water up and regain that hydrogen. Worse, burning hydrogen in an air-breathing engine isn't actually emission-free, because air contains nitrogen gas. At high temperatures (which hydrogen is very good at producing when combusted), oxygen and nitrogen react to for oxides of nitrogen (collectively, NOx), which are the emissions that VW recently got in trouble over.",
"Hydrogen engines don't run on water, they run on hydrogen gas. Hydrogen can be sourced from water, but it's extremely energy intensive to separate water into hydrogen and oxygen. Hydrogen is also difficult and dangerous to store in significant quantities (see: the Hindenburg disaster)"
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6gabt3 | Why are subway costs so high in the U.S. compared to the many other nations that have subway systems? | Engineering | explainlikeimfive | {
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"We don't really have a clear answer. Lots of theories but no concrete reasons. It's probably a mix of the following though: 1. Private property rights are stronger so it costs more to acquire land and getting caught up in a lawsuit is more likely. 2. Budgets for project planning is pretty ad hoc and its not unheard of for a project to be ready to go and then get cut at the midnight hour. You can later bring the project back but you need extra money to get things going again. 3. Several layers of government make it hard to figure out who is actually responsible for what. Also the state might have all their money together but needs to wait on the federal government and vice-versa. 4. Bad project planning possibly from an overall lack of expertise when it comes to managing a subway project (fewer subways overall, fewer opportunities to learn what works and what doesn't in building one). 5. Labor rules that enforce workforce requirements that may not be strictly necessary (comparisons in Europe found less people operating the same equipment used here)."
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6gcnpn | Why do different explosive materials make different sounds when they explode? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"explosives explode at different velocities. some explosives explode slower than the speed of sound, while others are much faster. the higher the explosive, the faster the explosion, the \"sharper\" the sound."
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6gddxn | Are power banks like batteries, in that they are made of multiple cells (like a 9V is really 6 x 1.5V) or no? | I've got several - 2600 mAh, 4000, 10,000, etc. Are they smaller units 'stacked' together inside or are they just one big unit? | Engineering | explainlikeimfive | {
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"I'm not an electrical engineer (IANAEE) but nobody else has really answered your question so let me tell you what I know. (Or think I know) Different materials combined naturally make a specific current. For instance Alkaline batteries make 1.5 volts per cell. One AA battery is one cell. You can put two of these cells in series (end to end like in a mag flashlight) to make 3 volts. An alkaline 9 volt is 6 small cells in series. Etc. Other materials such as lithium ion batteries make 3.6 volts per cell. Put two cells together to make 7.2v, 3 in series to make 10.8, etc. Use a regulator on those three cells to restrict the voltage to 9 volts down from 10.8 and you have a nine volt battery. So to answer your question, yes, a 9 volt battery is generally more than one cell in series. But how many cells to reach your desired voltage depends on the materials of the battery. Oh, and mAh is the capacity. One AA alkaline battery and one AAA alkaline battery will both have the same volts but the AA is bigger so it has more mah and will last longer. You increase capacity by connecting batteries in parallel, not series. This is accomplished by not putting them end to end but rather connecting all positives to one another and all negatives to one another."
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6geaar | What's the reason for nuclear plant smoke stacks having a concave shape? | Engineering | explainlikeimfive | {
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"Airflow. The cool air is pulled from vents around the base and it rises after it is heated. The shape allows expansion at the top, perpetuating the draw at the bottom.",
"They're not smoke stacks - nuclear plants don't produce any smoke. They're cooling towers.",
"The shape of the towers creates a natural chimney effect that allows for a lot of cooling without needing fans. If you don't have the big cooling tower shape, then your towers need tons of fans to do the same cooling. These towers are to cool the water used in the condenser to turn the plant steam back into liquid. Only about 1/3rd of us nuclear plants use them. More fossil/coal plants use them than nuclear. The plant can either draw 600,000 gallons per minute from a lake or river to cool its condenser (and return much hotter water back to the lake/river), or they can build cooling towers that don't return any hot water to the lake/river and only require water to make up for evaporation in the towers."
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6gfa2h | How does having the engine in the back of a car change how it drives? | I was wondering whether changing where engine is in the car changes how it drives. | Engineering | explainlikeimfive | {
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"Engines are extremely heavy. Moving all that weight from one end of the car to another is going to affect how the car handles.",
"engines weigh alot. typically 500 pounds ball park. put a 500 pound weight on a lever about 15 feet long and you can see how that would affect weight transfer"
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6ggv3u | What about the architecture of a GPU makes it useful for executing AI processes? | I hope I've articulated this question correctly. I would like to understand why something originally intended for rendering images is apparently very useful for AI. FWIW I once read and found reasonably understandable a Schaum's Outline on CPU architecture, but have no similar basic grasp of GPU architecture. | Engineering | explainlikeimfive | {
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"CPUs are designed to work on successive tasks, they have just a few identical cores that each perform a task. They're good for complicated mathematics with dependent answers GPUs are designed to work on parallel tasks that are generally simpler. They need to do the same math for each pixel and the result of one pixel doesn't depend on the next. A CPU would be very good at for (i=1,i < 1000,i++) B[i]=A[i]+B[i-1] You can't calculate B[2] without first having the answer for B[1], there's no way to calculate more than one value for B at a time A GPU would be very good at for (i=1,i < 1000,i++) B[i]=13*A[i] It would distribute the load across all of its cores and work towards solving all of the Bs at the same time. Your CPU only has a few cores so it'll work on solving B[1]-B[8] in one round, then solve B[9]-B[16] in the next and so on. AI processes are generally simple math but require lots and lots of rounds and data points. A GPU can calculate the updates for all the nodes at once so every couple clock cycles you launch into a new round, while a CPU can only calculate a couple nodes at once and must progress through them. It handles each math step faster, but can't do as many in parallel so it takes far longer"
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6ghd9p | How close can a speakers sound same as the hearing the instrument naturally? | I mean, how do we evaluate how clear a voice is? Is there a unit for it? And are there speakers so clear you can't even differentiate if the instrument was playing right in front of you or not? | Engineering | explainlikeimfive | {
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"There are speakers that can be put behind a curtain, and an orchestra put next on them, and most people wouldn't hear the difference. These setups cost as much as houses. There are speakers so precise they overdo it, giving away that they are speakers. There are several ways to measure a speaker's quality but there's only one that matters: listening to it. Speakers are like glasses, they sound different for everyone so only you know what you'll like. Short answer: yes, but it's not cheap",
"There isn't really a unit of measure for accuracy. The closest measure we have is THD or total harmonic distortion. The less harmonic distortion in an amplifier and speaker, the more natural the sound will appear. For instance high THD in bass frequencies sounds boomy or bloated like a loud car stereo. High THD in treble frequencies sounds like an old radio turned up too loud or a megaphone. There are different aspects of amplifier and speaker design that can affect realism including dynamic range, noise, distortion, and frequency response. To produce an accurate sound it needs to clearly record the original performance, amplify it, and play it back without taking anything away or adding anything that wasn't in the original. For instance noise would be adding something to it. A recording that didn't cover the full spectrum of human hearing would be taking something away. Amplifiers are of different classes such as A, AB, D, etc. Class A is the closest to perfect reproduction but is very inefficient and creates a lot of heat. AB is pretty close but much more efficient. The differences are in the way the amplifier circuit takes a low level audio wave form and makes it louder. Speakers will usually use crossover networks to send different frequencies in a recording to speakers optimized for those sounds such as bass to a woofer, mid range to a smaller speaker, and treble to a tweeter. How well built the crossover is will affect the clarity of the sound as well as the tonal balance of bass to mids, to treble. The quality of the speaker and how stiff it is, how powerful the magnet is, the size of the voice coil, and it's dynamic resistance to the amplifier signal all affect the quality of sound and how loudly the speaker can play back a signal without distortion. In general a speaker cone needs to be very stiff. There is a type of problem on moving surfaces like a speaker cone called modal breakup. If you imagine the speaker as a flat piece of paper, ideally it should move up and down without bending the paper. But at certain frequencies, the paper will bend in different shapes like ripples on a pond. These cause distortion and color the sound. Speakers tend to be designed so the frequency at which this modal breakup occurs, is higher in frequency than the speaker will be played back at. For instance a woofer with a modal breakup at 100hz is fine if the crossover only sends it audio that is below 80hz. The frequency at which this happens changes with the stiffness of the speaker, the material it's made with, and the support structure and speaker size. To fully explore your question would require a 200 page book but these are some of the things to consider. The pursuit of realistic audio is generally the elimination of distortion and noise at every path in the signal from the original recording, through the recording medium like CD or Vinyl, through it's amplification, and it's playback from a speaker or headphone. A flat frequency response where the bass, midrange, and treble are in balance with each other, and how loud or silent a speaker can play back is in the same range of loudness as the original instrument. For instance drum sounds that when played back are as loud as a real drum, vocals that when played back are as loud as a singer in your room, etc."
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6ghzad | Why do some vehicles (certain busses, semi trucks, etc) have completely flat front ends? Isn't this the last aerodynamic shape possible without getting concave? | Engineering | explainlikeimfive | {
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"A lot of vehicles prioritize length and internal volume over aerodynamics. A bus operator for example wants to be able to fit the maximum number of people in his buses, while still staying under the total allowable length for a bus.",
"There's a lot of different answers here. I can't exactly link this, but way back in grad school, I was part of a group working on the math part of a larger problem in fluid dynamics (air is a type of fluid), that was very roughly similar to a flat box moving through a compressible fluid. TL;DR: the air in front of the truck smooshes up and creates a relatively high(er) pressure zone that very loosely approximates an [albacore hull]( URL_0 ), which is pretty efficient in moving through air/water/fluid. To start - this wasn't my model/project or anything, but a few people in class with me helped out figuring out the math involved. Moving on - using the idea of a box moving through a compressible fluid as a frame our model spit out something like this (hugely simplified): imagine the flat cab of the truck moving at 50mph down the highway. The air immediately in front of the cab slows dramatically and compresses as it encounters the windshield/grill, before it turns ~90 degrees and scoots across the front of the windshield and off to the side of the truck. This creates a relatively higher pressure 'bubble' immediately in front of the truck. This little 'bubble' of air in front of the cab forces the air that comes next (as its driving down the road) to move off to the side and deflect at an angle, much more efficiently. If you were to picture it, imagine that flat-front cab having an invisible bubble/dome (made of higher pressure/compressed air) over the flat front which helps it move through the air easier. To be clear, its not the **most** efficient shape possible (that would be more conical), I'm saying that its far more efficient/aerodynamic than you might guess. Plus it has the visibility/volume benefits that other people are mentioning.",
"There are some weird answers in here... Having a semi-flat front isn't the worst actually, you can look at a box fish for example. Second these vehicles aren't meant to move very fast, so drag doesn't play a big role...but what about transport trucks on the freeway going 70 mph? Well they're usually pulling something that's going to kill any aerodynamics, sure they could be made more aerodynamic, but the priority goes towards the engine compartment and design, and the flat front helps feed air into the engine for combustion and the radiator for cooling.",
"It's mostly about maximizing usable space. For buses, an engine in the back takes up less space than in the front (because it can take up the entire vertical space) and you don't have to run the drive shaft as far to power the rear wheels. So for city buses this allows you to have low floors, which improves handicap accessibility (no stairs) and for long-distance buses it allows more cargo space underneath. Semi-trucks like this are more common in Europe because Europe has regulations governing the total length of trucks, so a shorter cab allows a longer trailer. Limits in the US are generally only based on the trailer length.",
"Flat cabs or cab over engine busses also increase visibility in the front. When you have a long nose of the vehicle sticking out in front on nearly the same plane as the windshield there are lots of blind spots. People get on and off the bus and cross the street in front of the bus, thus creating a high likelihood of getting run over if they are in a blind spot. That's why slot of school busses have the arm that extends out the front so people walk out in front far enough to be visible.",
"Very large vehicles have a lot of inertia, so air drag does not have as much of a practical effect at street speeds as it would on normal automobiles. City buses in particular spend so much time slowing down, stopping, and speeding up again that their average speed is low and thus air drag is not much of a factor. Only at much higher speeds - such as those achieved by a maglev train - would a very massive vehicle with a lot of inertia need to be designed aerodynamically. This is why the relatively slow trains in the US look like this: URL_0 While the Shinkansen bullet trains in Japan look like this: URL_1 Aerodynamic needs change with both mass and speed. Lower mass or higher speed = you have to take air drag more into account."
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6gjate | Why is "jumping a car battery" enough to make the battery work again indefinitely, if it was a dead battery? | Engineering | explainlikeimfive | {
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"Your battery normally doesn't die because the alternator charges it. When a car isn't running, the engine obviously isn't either. to start the engine, the battery is used. once the engine starts the alternator charges the battery back up and you are ready for the next time you need to start your car. when someone jumps your car, they give you enough energy to start your engine but then your engine charges the battery back up to full!",
"Car batteries are rechargeable. When you start your car the battery produces enough electricity for the spark plugs to start everything running then a part called the alternator sends electricity to the battery. If the battery is empty it can't make the spark plugs spark and the car won't start. A jump start provides enough power to get things going and then the alternator takes over.",
"When the engine is running, it drives the alternator, which constantly charges the battery up. When the engine is turned off, the alternator is no longer turning, so the battery is not being charged. This is why you can drive forever with your lights, air-con/heater, radio, iPod, etc connected without draining the power in the battery. But if you leave these accessories on when you've turned the engine off, the battery begins to run flat. Most of the time, a flat battery is not really \"dead\", it's just temporarily drained (e.g. because you've left your lights on without the engine running). Jumping the battery provides enough power to turn the engine over, and once the engine is running, the alternator will charge the battery back up again. This is why you're supposed to leave the engine running for a period of time after jumping a battery."
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6glv7d | How do water towers work? How has technology not progressed to make them obsolete? | Engineering | explainlikeimfive | {
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"It's almost the perfect system. You are only dependant on gravity to make it work. No electricity no problem. Gravity has your back. If you have an extended power outage you only have to get external power to the pump at the tower to make sure everyone has water. As bad as hurricanes, snowstorms, etc are if would be an order of magnitude worse if you did not have clean water. Basically let physics do its thing. If the Fukushima nuclear plant had used gravity instead of electricity as an emergency cooling backup then no one would probably know what Fukushima was.",
"A kids TV program here in the UK was going to film a water tower being demolished . They filmed all of the setup stage where the long-derelict tower just outside town was refilled with water then had a big drum of explosives lowered into it Those things are reinforced concrete and it takes a huge bang to blow it apart, so having the water in there spreads the pressure evenly to avoid shrapnel taking out everything for miles around. By the time it was all done the light had faded so they left it to blow it up in the morning. When they came back the tower was gone. Some time in the night the weight of water had been too much for it and it had collapsed completely. Nobody lived close enough to hear it go. Some poor sod had to dig through tons of collapsed concrete to extract the big drum of explosives too.",
"It's not so much that the towers supply water pressure as that they keep it the same all the time, and also ensure adequate supply around the clock. A residential suburb might see a quarter of all water consumption between 7 and 8 am, when everyone is showering and flushing at the same time. For small suburbs using water from wells, storing a sufficient supply means they don’t need big pumps to handle peak demand all at once. Big cities have much less of a supply problem, and demand is balanced by industrial users and spread out through the day. In addition, modern pumping systems can regulate pressure pretty well for a large number of users, without needing a gravity standpipe.",
"Water towers are used to establish the water pressure of your town's system. If you lived in a hilly area, then a big water tank towards the top of one of those hills would serve the same purpose. The tower establishes the pressure in the system by gravity - which is why they're tall. As an added bonus, if the power goes out you've still got a supply of water for at lest some time. URL_0",
"Technology ? It is such an effective and simple system...",
"Water towers are like capacitors in electronics. They store energy and can smooth fluctuations in supply and demand. The more you fill them, the higher the pressure (or voltage) they deliver. There will be a use for elevated reservoirs and capacitors for quite some time."
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6gmlcb | How does the ATM count and verify cash inserted in envelopes? | Money is placed in an envelope and then inserted into the ATM. You also type in how much money you are depositing but presumably the machine also verifies and counts the cash that is going in. How do machines count cash in envelopes? | Engineering | explainlikeimfive | {
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"> How do machines count cash in envelopes? They don't. They record the transaction and when the drop box is transferred to a bank later on the bank employees manually count and verify the amount of money was correct.",
"If it's all in an envelope, the machine doesn't verify it. It just trusts you. However, when the deposit is audited & verified later and there's only a $20 bill in there versus $2000, you're going to be in deep shit for fraud. Most cash-accepting ATMs these days don't do envelope deposits anymore. Cash is fed into the machine where it can electronically count it and deposit it accordingly. Checks are scanned and handled electronically, but the the ATM may still ask you to input or verify the amount of the check. This is another case of \"if you like to the ATM, you're on the hook for fraud\". Sure, if you accidentally enter $470 instead of $450, I doubt the bank will go after you (they'll just eventually debit the extra $20). But if you deposit a $20 check and say it's $2000, expect a knock on your door from the local police department."
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6gnn7t | why do pens dry out if you leave the cap off even though most caps have holes in the top? | Engineering | explainlikeimfive | {
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"**TL;DR:** Air, humidity, and heat circulation levels. Air has two ways of drying out stuff. The first is through simple \"Brownian Motion\" - the effect where absolutely still air has individual particles (molecules) that move around and when they hit some water, knock some loose and evaporate them. This doesn't work very well at all when the air is already humid (filled with water). The second is through general motion, like if a breeze or wind is blowing and pushing ALL SORTS of molecules past, say, a pen's nib. This really affects stuff if the air is warm, and it really steals a lot of water or light oils from something like inks, soaps, or gels, particularly if the air isn't already packed with moisture. Putting a pen's nib in a cap with tiny airholes pretty much stops all breezes and causes the small bit of space around the pen's point to stay full of water already... so more of the pen's ink won't dry up and crust everything all up when you try and write with the pen the next time. There's just not enough air circulation to really dry the pen out.",
"The other thing to note is that many pen caps—particularly for felt-tip pens that *are* at risk of drying out, because of the type of ink they contain—have two sections, one inside the other. The inner section is usually fairly small, and is designed to form an air-tight seal around the tip of the pen to stop it from drying out. The outer section is much larger, so it's easier to grip. Holes are usually moulded through this larger section, so that if the pen cap gets caught in a child's windpipe, air can still pass through it, supposedly reducing choking risk. These holes go around the inner section, so they don't affect the ability of the inner section to seal the pen."
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6gsm46 | why is it now code to install outlets upside down? | Engineering | explainlikeimfive | {
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"If a conductive object falls accidentally across the main two prongs of a \"right side up\" (😮) plug that isn't completely flush against the outlet, it will close the circuit. If it's your finger you get shocked. If it's metal there could be a spark. If there's a spark there could be a fire. Building codes are designed to prevent things like accidental fires. By installing the outlet \"upside-down\", you put the ground prong on top of any plug that has one. The ground prong can't create a spark all by itself, so it's safer to touch accidentally.",
"I don't think they have to be that way, but it's not required by or against code. I have seen it done in a way that was handy, where electricians flip them if they're tied to a wall switch. It becomes an easy visual cue that the outlet is associated with a switch rather than live all the time.",
"As far as my experience with outlets. It's not really union practice or code. I have been a union member for 5 years now with local 716. It really boils down to whats pre-existing, what the blueprints call for, and/or AHJ (authority having jurisdiction)."
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6guoh9 | Why can't diesel electric trains go faster much faster than 130 mph? | The fastest diesel-electric train tops out at around 140 mph and trains that routinely travel faster than 140 are all electric. Is this a mechanical limitation or a practical one? Could a diesel-electrical solve the speed problem by having a larger engine or multiple units? Could a petrol-electric or a gas-turbine engine propel a locomotive faster than 140 mph? | Engineering | explainlikeimfive | {
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"Diesel engines used for trains are very efficient, but they are very heavy. This is perfect for freight trains, which need a lot of weight on the locomotive in order to generate enough traction to pull the heavy train. High speed trains however are generally lightweight, so they don't need as much traction. But in order to accelerate quickly and reach a high speed, they need a lot more engine power than a freight train does. By making the engine lightweight, they can therefore reduce the amount of power needed to accelerate and maintain speed. So instead of a heavy diesel engine, they would need to use one closer to a car engine, which is less efficient. The French actually planned to make their TGV with a gas turbine, which would be very expensive to run with today's oil prices. It's also worth pointing out that the tracks that are used by high speed trains in Europe and Asia are almost completely electrified anyway, so it's by far the cheapest option. Even freight trains often use electric locomotives in Europe.",
"Speeds above about 125 mph start to require exponentially more power. Since diesel-electric trains carry 100% of their power generation on board, they become very heavy above this speed range, and it's just much more efficient to use offboard generators (electric trains)."
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6gvjnp | What are septic tanks and what are they used for,more improtantly why do only America have them? | I'm from the Uk so I've never heard of anyone having them over here. | Engineering | explainlikeimfive | {
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"A septic tank is a waste solution for buildings that are not connected to a municipal sewer system. It's a big underground tank that's connected to your toilet and you fill it up with shit. Then microbes break down the shit and toilet paper. Eventually you need to have your septic tank pumped. They are very common in houses in rural areas. People in the UK definitely have them. More people in the UK live in city centers like London than in the countryside but people in the middle of nowhere Scotland definitely have septic tanks.",
"Septic tanks do exist in the UK. A septic tank is basically a private sewage treatment system for places not connected to municipal sewers. It's a big tank connected to the sewage line on one side, and a \"leach field\" on the other. Sewage goes into the tank, where it is broken down by enzymes and microbes, before it is fed into the leach field where the soil absorbs the now decontaminated waste.",
"They evidently must exist in the UK, as here's a government page talking about them: URL_0",
"Septic tanks are large containers in the ground that hold bodily waste after its flushed down the toilet. They are mostly used in the country,since there isnt a citywide sewage system out there. Someone will probably come along that can elaborate in greater detail,but thats the basic concept as I understand it(or they can post before I do and in an easier explanation)"
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6gwh9u | What is the purpose of the holes in sink across from the faucet? | Engineering | explainlikeimfive | {
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"They're another drain to prevent your sink from overflowing, if your main drain gets clogged up or is closed, and your faucet is open."
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6gxuuh | Are roundabouts more efficient in cost, speed, and safety than traffic lights? | I am talking specifically in 4 way roundabouts with medium to high traffic | Engineering | explainlikeimfive | {
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"There is a detailed analysis [here]( URL_0 ) In summary: *Safety* Roundabouts are safer than traditional stop sign or signal-controlled intersections. Roundabouts reduced injury crashes by 75 percent at intersections where stop signs or signals were previously used for traffic control, according to a study by the Insurance Institute for Highway Safety (IIHS). This includes a 90% reduction in fatalities. *Speed* Roundabouts move traffic through an intersection more quickly, and with less congestion on approaching roads. Roundabouts promote a continuous flow of traffic since traffic is not required to stop – only yield – so the intersection can handle more traffic in the same amount of time. Studies by the IIHS of intersections in three states, including Washington, found that roundabouts contributed to an 89 percent reduction in delays and 56 percent reduction in vehicle stops. The only case where this occasionally fails is where the **difference** between peak flow and normal is very high. In this case traffic lights are used to assist the flow at the highest peak. In the UK this is known as a \"gyratory\" *Cost* Where long-term costs are considered, roundabouts eliminate hardware, maintenance and electrical costs associated with traffic signals a saving of between $5,000 and $10,000 per year. One caveat I would make is that understanding how roundabouts work must be part of the driver learning process as it is in the UK. In those cases where roundabouts are rare and drivers not trained to use them there can be problems with drivers making unnecessary stops and not merging with the flow correctly.",
"Roundabouts can work well but they do depend on a few things. If the traffic is very busy indeed, they will lock up, and it depends on people being courteous when using them. Stupidly busy times, lights are better, otherwise roundabouts work better. In the UK they get around this problem in some places by having roundabouts that have traffic lights on them, but the traffic lights only kick in at peak times.",
"Safer, yes, because everybody is, more or less, travelling in the same direction. As for capacity, it depends. There is a lot of science done on it, so depending on the amount of traffic on the connecting roads, different solutions are best. In order, from least traffic to most: * Uncontrolled intersection * Intersection with right of way (assuming the traffic is assymetrical) * Traffic lights * Roundabout * Plane separated intersection In other words, if there is very little traffic, there is no capacity gain, likewise if there is too much traffic, which can cause a roundabout to \"lock up\"."
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6gz0dk | Why are we supposed to open the window shutters during landing and take-off on an airplane? | Engineering | explainlikeimfive | {
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"In the event of a crash there might not be any electrical lights inside and it might become very dark. Also when the shutters are open passengers inside the airplane can look outside to orient themselves and decide the best way to evacuate. And emergency crew on the outside is also able to look inside the aircraft to see if there are any smoke or fire inside the cabin and more effectively direct their attention to where it is needed.",
"So that in case of an emergency, you can assess outside conditions if you need to evacuate. No one wants to open the emergency hatch to find a roaring inferno of fire outside. Same applies to emergency services looking in."
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6h2cvd | Why does by bike tire need an inner tube, but car tires don't? | Engineering | explainlikeimfive | {
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"Spoked tires require a tube. Can't seal air in a rim full of holes for the spokes to go through. Same goes for motorcycle tires I had on my bike.",
"Car tires did require innertubes in the past, but improvements in manufacturing of both tires and rims have made those needs obsolete. Car tires are steel belted, massively improving their inherent strength; bicycle tires are not.",
"Tubeless tires requires the lip of the tire to have a stiff steel wire. This presses the rim and secures a seal. Tubed tires don't have this so easier to mount and dismount. This means they're cheaper to mold as well as cheaper to install."
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6h2l81 | Is it possible to use dirty water for flushing toilets rather than fresh water? What would be the complications in initiating such a task? | Engineering | explainlikeimfive | {
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"It is possible, but only worth doing when you really need to save water. Systems that do this are commonly referred to as grey water systems. They gather the runoff from sinks, showers etc and pass it through a basic filter, at which point the water is called gray water. Gray water is then used for flushing toilets or other tasks where cleanliness is only a minor issue. Such a system can be expensive to set up, and does have filtration requirements, the water still needs to be clean enough that flushing the toilet doesn't leave a bunch of gunk in it. The only place I have heard such a system be used are antarctic research stations, where conserving liquid water is quite important.",
"Yes you could, the problem is that you would need to have a whole new water system to bring that water to your house and that would be so costly that no city would do that. Another option would be for the building to recuperate the rain water and use that for thing like flushing toilets. But that increase the building price.",
"The city I lived in was in a severe water shortage. When showering, I would wash my crack then put a 5 gallon bucket over the drain and continued my wash. After a normal shower, the bucket was near full. When done, the grey water could be used to flush the toilet or water the flowers, and would be used up in short order. This works if you have normal adult strength and can move 50 pounds of water around.",
"It is possible to use so called 'grey water' to flush toilts or do other various things that doesn't necessarily need potable water, like watering your lawn for instance. There are some houses set up to capture grey water for use, but its not the norm. It'd be an extra expense when building a house and may or may not be a selling feature for a future buyer.",
"Using grey water has its problems. If you leave grey water for long, it builds bacteria and makes a stink. It also makes a bio film that sticks to surfaces. Now imagine that bathroom that doesn't get used everyday. Someone uses the toilet and flushes the tank. Then they wash their hands and drain goes into the toilet tank. It sits there for a few days or a week before the next person comes to use the toilet. If you've ever left the dirty dishes in a sink for days, that's how it'll turn out."
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6h32he | How come airlines no longer require electronics to be powered down during takeoff, even though there are many more electronic devices in operation today than there were 20 years ago? Was there ever a legitimate reason to power down electronics? If so, what changed? | Engineering | explainlikeimfive | {
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"There are a lot of misconceptions every time this subject is brought up. EMI, Electromagnetic Interference, is a serious consideration in aircraft design and operation, and has been for decades. I highly recommend this NASA report from 1995, [PDF here]( URL_0 ), which details several incidents, aviation and otherwise. Probably one of the most famous is the series of five UH-60 Blackhawk helicopters that crashed between 1981 to 1987. The accidents were a mystery for some time, but it was later confirmed that they were caused by signals from radio tower which caused the stabilator to go to a full down position, which put the helicopter in a dive. These accidents earned the UH-60 the nickname \"lawn dart\" at the time. IIRC in the 1990s it was quite common for the crew to instruct passengers to turn off all electronic devices for take off and landing. This is because it was not uncommon for devices to cause things like radio static or in severe cases minor interference with navigation. To be clear, I'm not sure that consumer grade electronics ever posed a deadly threat to commercial aircraft. However, EMI shielding and testing was not nearly as thorough back then as it is now. Part of the reason for that is small electronic devices were not ubiquitous back then. Asking people to simply turn off an electronic device during take off and landing (critical phases of flight for navigation and radio communication) was not a big deal to people back then. It was easier for the FAA to just require that they be turned off, than to require extensive (and expensive) testing. Additionally, I'm not aware of any credible sources which say that the reasoning was that passengers would pay more attention in the event of an emergency. It was certainly my personal experience that back then passengers stuck their noses in magazines and books as much as they do their cell phones and laptops now. If that was ever an official reason it was almost certainly not very effective. **The FAA's decision a few years ago to officially allow electronic devices at all phases of flight was, as far as I can tell, for two reasons: better understanding of the risks because of increased testing, and the fact that we all knew people were doing it anyway.**",
"The TL;DR is that the FAA used to have rules forbidding non-approved devices. They loosened these because they realized it was dumb. Interfering with the planes electronics? Sure, its possible. But RF interference isn't a thing due to FCC certification, and it would have to be an *extremely* noisy device to cause slight interference with gauges. My wife has made phone calls when we've been up flying general aviation, and have had no issues aside from the occasional \"GSM Buzz\" in the headset - same as you'd get with speakers and a GSM phone. Shielding? Nope, not really. Most of the electronics nowadays are digital (which helps), and shielded wires... but no more shielded than the cable you use to charge your phone. And they're not \"hardened\" by any means (unless we're talking military, which is a separate point entirely). The GA stuff I fly personally? Lol... and zero issues with a 1975 airplane (and probably 1990s electronics...) Network congestion on the ground? Likely not - you're more likely to just lose signal and get kicked by the cell system, and not the FAAs problem. Remember, the FAA makes rules for *airplanes* not *cell phones*. Source: Avionics Test Engineer and pilot.",
"Lots of good responses here, and for the most part bang on. I've been involved with the testing and certification of aircraft at my airlinel to allow the use of onboard portable electronic devices, and in some cases onboard transmitting portable electronic devices. In the industry, these are known by the acronym PED or TPED. The rules vary from country to country, but in Canada, before an airline can allow the use of PED or TPED during critical phases of flight, they have to demonstrate that they will not interfere with the onboard aircraft systems. This is commonly accomplished by blasting large amounts of RF inside the aircraft, in various locations throughout the cabin, of varrying frequency and transmitting power. I'll admit, I'm not an engineer, so the details of this test are a little lost on me. Anyway, while the RF storm is being conducted inside the aircraft, we need to test all of the aircraft systems and every possible combination of RF interference. This is done by actually powering up the aircraft, all electrical systems and all the engines. To test our aircraft took two 12 hour days of sitting in the airplane with the engines running and not going anywhere. At the end of the day, I was quite surprised with the results. Our aircraft passed most of the tests, but failed a couple as well. The RF radiation was causing the door proximity (PROX) sensors to fail on the forward cargo door, causing warnings in the cockpit that the door was open, when in actuality it was not. As you can imagine, this wouldn't be a good thing to happen in flight. Long story short, after completion of this testing we can use non-transmitting PEDs in all phases of flight, and we can use Wi-Fi in non critical phases plof flight, but it's the cellphone frequencies that caused our issues so we are not allowed to have cellphones active on cell networks during any phases of flight ( from cabin door close at the start to cabin door open at the end.) Modern aircraft are built with this in mind, and all of this testing is normally completed by the manufacturer during the design and development phases. For older aircraft, this process that I outlined above needs to be completed.",
"I've been told by a friend that is a pilot that the reason for the power down during take off and landing is that those are the most dangerous times when on an aircraft. Therefore, they are hoping that people won't be distracted by their electronics, or god-forbid, create numerous hard plastic and metal projectiles to fly through the cabin in an accident. The last time I flew we still had to power down during take-off and landing.",
"If there was ever any real danger there's no way they'd even let you have them on the plane. Plane crash prevention based on the honor system?? I don't think so...",
"Airline pilot and flight instructor here. The laws (regulations) still forbid the pilot(s) from using unapproved electronics during typical flight and on specific types of instrument approaches (CATII AND III). As for consumer grade electronics, they would interfere with the instruments back when the regulations were written. Here's the \"ELI5\" part: pilots used to navigate with very sensitive electronics called automated direction finders (ADFs). These were essential very sensitive devices that operated on AM radio waves and would tell you the difference in angular deflection between the nose of the aircraft and where the radio beacon was. These radio stations known as Non-Directional Beacons (NDBs) were effectively AM radio stations that broadcasted specific morse code identifiers that would let you know that you had the correct station. The ADF however, was sensitive enough that a handheld radio or other strong electromagnetic fields generated by any decent sized and poorly shielded electronics in the cockpit could deflect the bearing pointer on the ADF and cause loss of navigation fidelity in the instrument. In fact, whenever an aircraft would fly near lightning (within 30nm of a cell and honestly far too often) the ADF would deflect to point directly at the lightning strike (which emits all radio wavelengths simultaneously). So the rules were created to prevent erroneous readings from causing airplanes to navigate poorly and geneally into each other or the planet.",
"Ironically, I have a degree in computer engineering with a specialty in radio signals, but I'm not going to weigh in on that aspect of the issue because I don't know enough about avionics to pretend to be an expert. However, there's an important concept in capital-R Risk (the practice of identifying and mitigating risk for corporations) which essentially boils down to \"if the cost of an incident is incredibly high and the cost of mitigation is incredibly low, you pretty much have to do the mitigation.\" It costs the airlines almost nothing to enforce the \"turn off your electronics\" rule on each flight. The flight attendants don't make more money for enforcing it, and passengers don't have the option to change to another airline because all airlines enforce it. Thus, cost is approximately zero. However, one crash in which the airline is found to be at fault - a fairly likely scenario if the crash was caused by some avionics fault induced by a heretofore unknown mechanism of electromagnetic interference from a personal device - could cost the airline hundreds and hundreds of millions of dollars. Thus, you find yourself in a situation where the rate of risk is impossible to measure (we don't know of specific ways that avionics could fail, so we can say low but not precisely how low) but the cost of an incident is definitely extremely, extremely high, and the cost to mitigate the risk is extremely low, approaching zero. Airlines are going to take that deal. Maximum ELI5 answer/TL;DR: If you could eliminate a small risk of suddenly dying by scratching your cheek once a day, you'd scratch your cheek once a day.",
"This was based on the fact lots of navigation radios needs 118-132 MHz clear. Very basic (old) instruments were unable to tell if a signal was interference or legit navigational aids. Back in the day the \"transistor radio\" revolutionized personal audio and the FM transistor radio was even better. So people had these on planes and thought it was much better than the movie, and it was 20 years before cassette tapes. Even eight tracks were 10 years out! Simply put FM radios work using a small local transmitter that \"mixes\" with the incoming signal. This way the incoming signal is converted to 21.4 MHz and a fixed tuned crystal converts that 21.4 MHz signal to audio. Lets say you're listing to 103.1 MHz on the FM band. Your FM radio will be making a signal at 124.5 MHz and \"mixing\" it with the antenna input. This will make 124.5-103.1 and output 21.4 MHz. The problem is it radiates the 124.5 MHz frequency too. In expensive radios they would filter and shield this to make it a non-issue. However in cheap radios, they would radiate this signal. Since 124.5 MHz is in the aircraft band, that would override anything from the ground and interfere with navigation. This is why the electronics ban started. Later on the FCC would make it illegal to use the a radio that generated 124.5 MHz, but that was years after it was banned. Cellular phones were lumped in with this starting in the 90's as the early ones were very high power and could radiate in the radar frequency ranges (1030/1090 MHz). A modern cellular phone will not work in an airplane and is much lower power.",
"When mobile devices started gaining prevalence, airline operators weren't certain the device signals wouldn't interfere with radio signals and other systems on the plane, which could interfere with the plane's operation. Since then, planes have been built with better electromagnetic shielding on their electronics, so those fears haven't really panned out. However, another concern might be that the attempt to connect to cell towers on the ground while traveling several hundred miles per hour - hopping between towers every few seconds - might cause some network congestion on the ground. Regardless, since those regulations were put in place, device makers started introducing \"airplane mode\" features that shut off all device radios. That being prevalent today, airlines now tell passengers either to turn off devices *or* to put them in airplane mode.",
"Aside from the other reasons I've seen here, there's another I've been told. The vast majority of airline crashes happen in the first and last 15 minutes of a flight, aka take off and landing. If a crash were to happen, the entire cabin would rapidly shake and everything would be flying around. They tell people to turn off and put away electronics because that is a lot of stuff flying around and injuring people. Contrary to popular belief, most plane crashes are not fatal, they are more like rough emergency landings. Everything needs to be secure so the cabin doesn't have 100 cell phones flying around hitting people in the face.",
"long answer, yes there was a legitimate reason. the first transistor radio's (1950's, 1960's) were extremely \"noisy\" RF radiation was emitted from the device at much higher levels and did interfere with the instruments in the aircraft. As the FAA is a Gov't institution it moves extremely slow. the Personal Electronic Device(PED) rules were put in place in the 1960's. FAR 91.19 basically putting the prevention and monitoring of EMI on the airline operators. (its easier to tell you not to use it than screen each device for compliance). during the rise of the PC and laptops 1980's this regulation was revised( 20 year gap in regulation change) and again pretty much once each subsequent decade currently FAR 91.21. the change has been twofold One the PED's use less power and emit less RF radiation than older devices. and two aircraft electronics have been required to have more shielding against EMI then previous generations of aircraft. not by the FAA but by the airline operators via requirements sent to the aircraft manufacturers and their vendors. The FAA puts the onus of ensuring that PED's don't interfere with safe operation of the aircraft on the airline operators. Currently all restrictions on PED use inflight are at the discretion of the airline operators. Source: EMI technician; Avionics test technician.",
"TPED testing and more strict qualification testing for critical systems, i.e. Level C and above. Levels are assigned based upon safety impacts based on identified failure modes ranging from No Safety Effect to Catastrophic. Level C represents that there is a failuremodes that may introduce a Major safety impacts, such as significantly higher crew workload (i.e. something fails and it reduces safety margins as pilots need to mitigate it while flying the plane). You can look at the FAA rgl library and see past incidents where transmitting devices were impacting critical systems such as Communication, Surveillance and Navigation radio systems or flickering display units in the flight deck. A prominent one that happened was on Boeing 737s and specific Honeywell display units which would turn off from WiFi and Cellular signals. This forced Boeing to replace all those DUs on new and flying aircrafts, not a cheap nor quick task by any stretch, we're talking millions upon millions of dollars if not more. (Am avionics engineer, deal with this kind of certification a lot. In summary, we build critical systems that are more resilient to external emissions.) If you wanted to get really in-depth with it I would suggest the RTCA documents DO-297 and DO-307. For qualification testing Section 20 in DO-160 has your susceptibility requirements. There's two types of coupling identified in aviation, Backdoor Coupling, i.e. like a device causing interference with an Display Unit and causing it to flickering, or introducing interference on the cabling. The other is Front Door Coupling and primarily applies to radio systems that have interference being introduced on their intended receive frequencies. I.e. say my ILS Glideslope is 335MHz and something transmits on this frequency. ILS is an instrument landing system primarily used for low visibility landing, i.e. CAT II and above. We generally have to assume that if there's not enough pathloss to the antenna to prevent coupling of an interference on the same frequency this may cause the ILS system to mislead and go off target and mislead the pilot or autopilot. This is Catastrophic as you will rely upon those systems in low visibility landing situations. It's another thing to 'jam' the system as this will notify the pilot of the failure and they can correct it through their procedures, resulting in a Major hazard. The notification failuremodes however to warn the pilot of a failure is Catastrophic, however. For part 25 aircrafts, such as your normal commercial airliner, AC 25.1309 provides in Appendix 2 I think a list of example failure modes and their hazard effects (called a Functional Hazard Analysis or Assessment -- FHA). The FAA PED ARC report is also another great resource that really summarizes backdoor and front door coupling hazards.",
"Non 18 paragraph answer: they used to not know what cell phones, laptops, etc would do to planes electronics so they went with better safe than sorry. Now they know they won't interfere so they let you use them.",
"Technically, there was probably no reason to power them down. However, there was speculation that it could potentially interfere with the aircrafts electronics or navigation equipment. Better safe than sorry. We in the airline industry are terribly sorry for the super inconvenient shutting off of your phone, we know this is a close call on if it's worse to shut off your phone for a few minutes or to have everyone on the flight die.",
"I remember watching a documentary called \"Journeys with George \" about the 2000 election. In that movie, the press plane had a mechanical issue and they moved the governor (bush), and the entire press to a new plane immediately and every single reporter and election staff were on mobile phones for most of the takeoff and landing. There was secret service, all sorts of people. From that moment forward, I never used airplane mode ever again, and I flew weekly for ten of those sixteen years.",
"This video should clear things up for you guys. URL_0",
"Interference, allegedly. However, the Mythbusters crew were unable to cause any interference using a **wide** variety of cellphones (new and old), and a slew of different airplane systems. URL_0",
"Sadly this is not true all around the world. I recently endured a 20~ hour journey on China Southern where for some unknown reason mobile phone use is banned throughout flights, even listening to music on flight mode etc.",
"The FAA specifically allowed it. That's literally the only reason, not complex or anything like some of the people here are trying to make it out to be. URL_0 2013. Before that time, yes, you still had to turn off electronics during takeoff",
"Air traffic controller. For obvious reasons we can't have devices on or in our work spaces! However, I do know the old analog cellular phones could sometimes leak (locally) and we would hear like a Morse code rapid ping on our frequencies. Maybe since everything is now digital in nature it doesn't interfere with the old com systems anymore?",
"My mentor in university was an airline engineer. He told me that consumer grade electronics have never been a problem. If they actually were, turning them off would not be on the honor system. The real reason according to him was due to cell phones connecting to different towers across different states and the constant connections caused problems for early cell phone carriers.",
"Whenever the answer is a long and complicated one, filled with mumbo jumbo and requires lots of details to try to make it fit...its BS We used cell phones and all sorts of other electronic devices including walkie-talkies during takeoffs and landings during my Secret Service days 1989-1995 and those were old planes... The truth is airlines want an excuse for pilot error and to mitigate their own legal responsibilities, end of story.",
"It had to do with fears that a cell phone could somehow interest with the planes electronics or radio communication, and in the case of an accident would help to reduce the number of small hard things flying around the cabin. Ultimately they have realized that cell phones aren't nearly powerful enough to interfere. And in an accident the cell phones become a non issue neways (in a hard enough crash to where they would be dangerous, the people are dead anyways).",
"News to me... In Europe they still require you to at least switch on flight mode during take off and landing. I once spend an afternoon reading a collection of airline staff reports on the subject: (Only very few) pilots reported noise on their radio headset during landing and take off. It was assumed that this noise was caused by passenger devices constantly trying to connect with antennas on the ground, searching for service. For example, one pilot who experienced noise after passengers were asked to switch off devices had his cabin crew go through the plane to check manually whether all devices were shut down. They found one device still running, they switched it off, and reportedly the problem was now solved. No research or tests have been able to replicate these problems though.",
"So why is airplane mode a thing or at least why is it called that?",
"I'll try to keep it real short. & nbsp; Basically it was known that it was possible that electronics could create interference, nothing ever happened with regards to interference, so they lightened the restrictions.",
"If there was a legit need for them to be off they wouldn't let you still keep them and just take your word for it because it can do the same thing whether it is in your bag or in your hands actively.",
"Also, not unrelated, there was an American Airlines windshear crash that happened right around the time cellphones became commonplace. Just so happened we didn't understand a lot about windshear during that time, and while the investigation went on - they questioned whether or not it had to do with cell phones. Immediately changed the rules to disallow them. In typical FAA fashion, it took this long to come back around.",
"I asked a friends dad who flew dash 8's in the 80's-90's and he said that with the old analog phones and older planes that weren't shielded as well it would cause the navigation systems to go screwy. nothing major that they didnt know how to deal with, but it was annoying and if other systems failed potentially a problem. Newer planes have all the wiring shielded and modern cell phones use way lower power than the old ones.",
"There was a legitimate reason originally: some electronics produced large electromagnetic interference fields (a form of radiation) that could interfere with the communications and controls of a passenger plane. It was too difficult to educate flight attendants adequately to have them making the judgment calls item by item on what to allow, so the rule was a blanket \"no devices\". Subsequently, aircraft manufacturers have \"hardened\" most of the critical elements of newer aircraft. The term \"harden\" in this case means to make electrical systems resistant to electromagnetic radiation. There are still holdouts, and the industry is rightfully very conservative about what they allow.",
"ok the reason for aircraft to request power down of electronics were due to during that era of the 1st gen mobile phone are using the similar frequencies of what the clockpit is using for their transmitters. since everything were analog signalling back then, cross talk happens. this causes interference to the signal and can cause disaster. well if you work in the aircraft industries, you will know that to change a certain SOP (standard operating procedures) is a heck of problem because there are so many steps to do, so many files to re-document, so many approval to make, so many debunking to prove and proposing of a better/proven solution etc. for that (generally laziness in updating the rules and that much of time wasted just to update it) is the reason why till 2016 it is STILL a requirement to power down the electronics during takeoff and landing. so now, someone/some group actually read into that and did the updating hence this powering down is no longer needed. the science behind this is that, since now all devices are running on Octagonal signal(digitized), signal cannot be interfere in this manner. just imagine, phones is running on an example frequency, 2.1ghz, if it is like the older days where by technology is still running on a single plane (frequency plane), then there will be full of collision and interference. but now, since it is digitized, it is running on not just the frequency plane (FDMA), it is also running on time plane (TDMA) and also on coding plane (CDMA). so it means that to really interfere a signal, you need the precise frequency at the correct hop of time at the correct position of phase. this is why the current radio doesn't interfere with airplane take off or landing. there are more to this but this is suffice. i work in telco and i'm a radio expert. my best friend fly commercial airline, he is an expert in airplane stuff and was a geek to that. i asked this question many many years before while i studied radio and realised your question and have asked him.",
"I always thought that it was just so that you listen to the safety demonstration or the pilots instructions.",
"Why do service stations not allow use of mobile phones near bowsers, yet allow me to use my radio key to lock the car?",
"Literally just watched a YouTube video about it today. I'm new to the sub, so I'm not sure if this is allowed (pls let me know) URL_0",
"We still have to power everything down in China, and can't have phones on at any point, even in airplane mode. Of course, most people do their best to ignore the rules.",
"I bet there is a group of terrorists who have dressed and acted under the guise of being a techie and has been trying for years to take down planes by carrying as many electronics as possible!",
"I was once told my cell phone could cause Electromagnetic interference to aircraft systems, I replied how about the 1000's of phones within a mile of this aircraft why wouldn't they interfere with the plane as well. My point was that phones do not affect plane electronics.",
"Related slightly, as in a practice that continues where it may not need to. Isn't it true that mobile phones can be used at a gas station and it's actually static from car to human that causes spontaneous fires? Sane people, please don't test this theory, you may just blow up. Candidates for the Darwin award, you just carry on.",
"In the past many electronic devices had analog signals and noisy power supplies. Analog signals are high powered and operate over a broad range of frequencies. Newer, digital electronics can operate at much lower power levels and operate at specific frequencies that can be tuned out of aircraft sensor systems. Add to that, many aircraft systems are digital now and resist interference better than analog system.",
"Only interference I've ever seen in the flight deck is if a cell phone is left off of airplane mode, and begins searching for service, you can hear a static in the headset. It's much like putting a blackberry beside an old computer speaker and can hear that pulsing static sound. Phone has to be relatively close to the headset cord to cause this. Not a huge issue these days though more just an annoyance.",
"Some airline companies such as Air China still forbid the use of cell phones at all phases of flight. I was used to keeping it on since I'm from Canada and we never require airplane mode, but I was approached by one of the flight attendants who sternly told me to turn my phone off even though my phone was in airplane mode and I was watching an offline video. Get with the times Air China..."
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6h4u8m | Why did the Titanic's watertight compartments not have a watertight top? | Every now and then I nerd out on engineering disasters. This week I got into the Titanic's sinking. I see that one of the prominent reasons it sank so fast is the "transverse bulkheads", walls that helped form its watertight compartments, were not watertight at the top and the "top" was not very far above the waterline. It seems to me incredibly stupid to call a compartment "watertight" if you know one side of it isn't watertight. But I also know when things look this stupid to me, I'm missing some vital piece of information that is key to making sense of the situation. My only guess is if the compartments were watertight on all six sides of the imaginary cube, the risk that air being compressed by incoming water could compromise the seal would increase? Why didn't they think sealing the top of the compartments was a good idea, if that isn't it? | Engineering | explainlikeimfive | {
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"Expense, and the fact that it would have been seen as a needless expense and probably gotten in the way. Even as designed, if they hadn't hit the iceberg in such a way as to tear the whole side open, they probably would have been fine and the bulkheads would have been sufficient.",
"They didn't need to be watertight at the top, as long as the top would sit above the waterline when that compartment was flooded. Remember, water will only rise to the waterline, no higher. As long as the ship was buoyant enough to remain afloat with the weight of water in that compartment, and would not sink low enough for that water to flood over the watertight section into other sections, the buoyancy wouldn't be compromised. It's the same principle as an ordinary canoe. The top isn't watertight, yet the boat floats, because the water cannot rise above the edges of the canoe to flood the interior. The reason the Titanic sank so fast isn't because the compartments weren't watertight at the top, but because *so many* compartments were flooded by the massive gash (possibly also because the crew was slow to seal them, but I'd have to look that up to verify)."
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6h4wgi | When X hires someone from Y to design something (e.g. CPU or GPU chips), how does the hired person do the job? | For example, Google recently hired a chipmaker from Apple. How does the person do the job without infringing on technology from Apple? Does he need to create a new design from scratch? | Engineering | explainlikeimfive | {
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"No modern CPU or GPU is designed by a single person. There are fairly large teams with different areas of specialization. You start with the architects, who come up with the overall plan for how the chip is put together and how the various blocks interact. Then you have teams designing blocks. Then circuit design teams to implement the block designs. Then various layout people to hand optimize what the automated tools create. And various other special functions. So when someone comes in and joins an existing team, they are usually working within a framework that's already started. They simply have to avoid putting forth ideas that they know are infringing. That's not a trivial thing, since it is virtually impossible to design a complex chip without infringing on *someone's* IP. You simply have to avoid the most recent, whiz-bang inventions or the critical ones that might incite another company to actually pursue litigation. Since everyone infringes on everyone else, most companies want to avoid lawsuits because they are an expensive, time-consuming mess that only makes lawyers rich. So if you don't infringe on anything too important it kinds of slides by. Usually."
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6h53i7 | How are traffic light timings determined? | Engineering | explainlikeimfive | {
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"It depends. Many lights have induction sensors. So they generally have one direction (the main street) be green, unless the sensors detect that there are cars in the other direction. Then they go through the cycle to let the other cars through. In many places (especially heavy urban areas) the lights are timed. There is bad timing that does nothing, other than going between directions every x seconds, and there is timing that attempts to allow traffic to flow in one direction down a main arterial without stopping. That may be why you can go down a road and never hit a red light, if you drive around the speed limit. And there is a large branch of civil engineering that is dedicated to figuring out optimal light timing and traffic. Personally, I much prefer environmental and don't love the traffic engineers. But...they can do some good things with traffic engineering."
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