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5llx01 | How are my headphones playing a "ghost station"? | Engineering | explainlikeimfive | {
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"A nearby AM radio station is being picked up and rectified by the TV. A simple AM receiver can be made with a junction of two dissimilar metals or a metal needle point on a crystal. I suspect the electronics in the TV are performing the rectification and the headphone cable is the antenna.",
"I have a couple of my own theories. 1) the audio from another input on the TV is leaking onto the audio jack channel. 2) the cable is acting as an antenna and picking up a radio station (but what is the receiver?) 3) I'm acting as an antenna and picking up a radio station (how would my headphones pick that up, and where's the receiver?)",
"Pirate radio yyarrr! This is actually normal and happens with low quality speakers. Essentially the wire in your headphones are not shielded well so they are acting as an antenna. They are able to pick up a certain AM frequency because of this. I actually was able to once get legitimate pirate music (literally yo-ho ho and a bottle of rum type music) once from some old crappy speakers I had would wake me up at night.",
"Somewhere in the headphone circuit there's a cheap half-bridge rectifier. The headphone extension is also unshielded, allowing it to act as an antenna. The AM radio signal is its own power. If the guilty circuit had used a **_FULL BRIDGE RECTIFIER_** ^^cough ^^cough ^^sorry or if the cord was properly shielded, you wouldn't pick up the station. Radio Shack used to sell (and may still sell) ferrite donuts called Chokes to snap over cables to eat parasitised RF signals. ------------- ^(**_FULL BRIDGE RECTIFIER_** ༠ཽ.༠ཽ)"
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5llzij | How do DSLR cameras work? | Engineering | explainlikeimfive | {
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"SLR as a term is pretty well defined - it stands for \"Single-Lens Reflex\". Forget digital for a moment - remember normal point and shoot film cameras? You'd have a small viewfinder at the top, which you'd look through. Well, the problem with those is that you're not quite seeing the same as the camera lens sees - a bit like looking through a gun sight. They'll be close, and at a certain distance it'll be the same, but you're ultimately looking through a different window. In addition, this also means you can't easily use adjustable lenses because you'd simply have to guess the focus and zoom. Well, SLR's solved that problem by having a mirror which moves. When you're not taking a photo the mirror is positioned so that the viewfinder is looking directly through the lens. In addition to being able to accurately compose the photo, this also means you can use adjustable lenses because you can physically see whether it's in focus or not. When you press the button, the mirror moves and exposes the film to exactly the same light you've been looking at. DSLR is simply the digital equivalent. The mirror is still there, but instead of film you have a digital sensor. You press the shutter, the mirror moves, and the sensor can now \"see\" through the lens. In day to day life, however, DSLR is somewhat synonymous with the idea of a higher quality camera. They generally come with additional features, better resolutions, better software and so on. But, strictly speaking, to be a DSLR they simply need that mirror system.",
"Slow mo guys did a good video on the internal mechanism URL_0",
"DSLR are the digital equivalent of SLR. Instead of a film sensor it uses a digital sensor ( a lot larger than other point and shoot camera). SLR or Single-Lens Reflex are a type of camera that use a shutter and a mirror. the shutter is highly configurable in its speed and opening time. the mirror is there to divert the image from the film/sensor to the view-sight. The shutter enable to configure the amount of light going to the sensor to produce the picture. Basically, when you press the button on a DSLR , 3 things are happening. First , the mirror gets out of the way. secondly, the shutter is opening. Third, the sensor capture the light coming in from the lens, then a processor take this information and save it to a memory card in a file that can be easily open and edited in a photo editor program."
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5lpqkx | Why is it so hard to completely prevent clipping of 3D models in video games? | To be clear, I know nothing about programming or 3D graphics. Naively, I would think you could just give objects some property by which they cannot pass through each other. Yet I see some degree of clipping in almost every big studio 3D game. Why is this so hard to fix? | Engineering | explainlikeimfive | {
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"It comes down to hitboxes. These are imaginary cubes drawn around \"things\" in games. The more detailed the hitboxes are, the more computations need to be done to determine if things collide. Lets say you have a minecraft dude. His hitboxes are simple because he's already a few cubes. Its easy to do the math to determine when one cube hits or intersects or runs into another cube. Or if I shoot your minecraft dude with a gun, all I have to do is aim within the imaginary hotbox cubes that surround your dude. Pretty simple. But as the 3d models of things (your Halo dude, that explody barrel, the monster) get more complex, the less ideal a few cube hitbox is going to be. no, you want the hitbox for your character to match the geometry of your character. If your Halo dude had a simple single hitbox cube, if you got a rocket anywhere in that imaginary cube it would count as a hit. But thats bullcrap because you totally jumped that rocket, it went _between_ your dude's legs. So now, to be more accurate the hitbox model that represents where your dude \"is\" has to be made up of a bunch of smaller geometric shapes. Maybe, the hitbox model of your dude is almost as complex as the visualization model of your dude. But as you add complexity to that model, all the math to calculate whether bullets, rockets, explody things collided or hit your dude, get a lot more complex. And complexity is fine, but there's only so much processing power available, given your game client and the server have to calculate not only whether your dude got hit by that grenade blast, but the other 63 dudes on the server. Its a similar thing to the calculations on how your dude is affected by the geometry of other things. Your guy is leaning up against a wall? If the collision/hitbox model of your guy was really detailed, and the geometry of your dude's model was programmed to do it, you could model individual limbs (nay, in some games with ragdoll physics, individual bones) and how they interact with a wall, a crate, riding that horse... but again, complexity and \"realism\" brings computations. So the guys who write game engines have to strike a balance between \"well maybe the wizard's flowing robes sometimes clip into the wall he's standing next to, but at least a 64 person battle has a decent frame rate\" vs. \"we have simulated character models down to individual chest hairs. But you can only get 2 frames per second.\"",
"Vfx student here. From what I know, In order to do that would essentially require creating everything as physics objects or create individual hit boxes for each element in the game. Not easy and can really place a burden on your computer. I am sure there is someone more experienced in this topic, but depending on how detailed the models or elements in the game are, it's just easier to allow clipping in a few of the elements rather than miss a release date or spend money trying to correct the problem. Hope that helps."
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5lqwjo | Whats the difference between torque and horsepower? | Engineering | explainlikeimfive | {
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"Torque is the real, measurable force applied by the wheels to the road. (It's generated by the engine, then multiplied by the gearbox, final drive, and wheels.) Because it's applied by a circular wheel, it's measured in a combined unit of weight and length - pound-feet or newton-meters. A torque of one newton-meter applied to the road is equivalent to the force exerted on the wheel's hub by a weight of one newton, suspended horizontally from a stick that's one meter long and attached to the hub at the other end. Horsepower is not a real measurable force - it is a mathematical construct that represents the engine's ability to accomplish work over time. The work is moving a certain weight (the car) across a certain distance over a certain time. You'll notice that compared to torque, time is now added. So if the weight of the car is the same, and the distance it's traveling is the same (let's say, a quarter mile), then to do the work over a shorter period of time - get there faster - you need to use up more horsepower. Because there is a direct mechanical relationship between the engine's revs and the wheel revs, and therefore the car's actual speed, horsepower is calculated as torque multiplied by revs, and divided by a specific coefficient to account for the difference in units. Note: this is about engine torque, measured at the crankshaft. The torque at the wheels is a much larger figure, multiplied by the gearbox, final drive, and wheel circumference. (A horsepower is around 745 watts, because James Watt calculated this as the power of a typical mining horse and used it for marketing, to show how many horses his engine could replace. In the standard system, one watt is the amount of work/energy that raises a weight of one newton to a height of one meter in one second.)",
"The super basic, non-mathematical answer: Torque is how much work you can do. Horsepower is how fast you can do that work. Think of a semi tractor-trailer next to a souped up Honda. Both engines could make the same number of horsepower, but the semi tractors engine makes a LOT more torque. The semi tractor can do a lot more work, but it takes longer to do it."
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5lr3kp | How do they build things in water? | Engineering | explainlikeimfive | {
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"There are numerous and various combinations of different construction methods depending on the structure required. Sometimes a coffer dam is built enable nearly dry construction, other times piles are drilled to reach bedrock, sometimes structures are built on land and moved to the water area for placement and sometimes boring machines are used to tunnel under the water. Like all engineering one solution never fits all."
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5lslxe | How is it that we put salt in ice cream machines to make the ice colder, but we also put salt on our sidewalks and streets to melt the ice? | Engineering | explainlikeimfive | {
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"Because you're not making the ice colder in the ice cream machine. In both cases your goal is to make liquid water colder, but the reasons for wanting colder liquid water are different. In the case of the ice cream maker, there's always at least a thin layer of liquid between the cream container and the solid ice, so colder liquid water means more heat transfers out of the ice cream and into the liquid water (so the ice cream freezes fast enough to freeze the air bubbles into the mix which is why ice cream has such great texture). In the case of the sidewalks, colder liquid water means more ice melts and flows off the sidewalk and melting continues at lower temperatures, reducing the slipping hazard.",
"TL;DR - Salt doesn't make ice colder. What you're going for in both cases is a state change - you want liquid water, not solid water (ice) - without having to compromise the temperature. Unless you have some continuous source of coolant (like my buddies at work that used to make iced cream with Liquid Nitrogen, lol) the ice you have is all the coolant you'll get, so you'll want to freeze the iced cream quickly before the elements warm the coolant (ice/water) beyond usefulness. In order to best transfer the heat away from the ingredients into the ice, you want the *highest possible surface area* of the spinning aluminum container to contact the coolant. Ice cubes aren't that great, crushed ice or party ice is better (smaller chunks), but ultimately liquid is best. You could use glycol or something, but the most available and safest liquid is water. If you want to get water cold enough to freeze the iced cream without freezing into a solid block itself, you have to add salt to lower the freezing point. Fun fact, ice rinks use a salt water (brine) which run through pipes in the concrete beneath the ice surface in order to maintain the temperature at around 19 degrees Fahrenheit. Salt does the same think to ice on sidewalks, except the motivation there is that you just don't want solid water (ice) around. Liquid water will flow away and reduce the hazard/obstacle.",
"These are both the same reason! It's a really good question. Salt makes the freezing point of water lower. That means when you throw it on ice, it tends to melt the ice. Even in the Ice Cream machine. What happens is the solid = > liquid process (melting) requires a small amount of energy (the heat of fusion) even if the temperature stays the same. In the sidewalk case, the large heat capacity of the sidewalk, driveway, Earth under the ice, ... gives up this heat without changing temperature. In the Ice Cream machine case, the ice is insulated from a large source of heat (by the ice cream machine's bucket). This means there is no good source of heat and the heat of fusion much come from the ice and the ice cream inside the can. The ice melts faster, even though it is driving the temperature down from the melting poinf of plain ice to the melting point of ice in salt water.",
"Salt lowers the freezing point of water. In the case of the streets, it means that the water will remain liquid at lower temperatures. In the case of the ice cream, it makes the ice slurry colder without freezing solid.",
"Salt lowers the melting point of water. As a result of this, some of it melts. Something people don't often consider about the act of melting ice is that it takes energy. To change ice at 0C into water at 0C, you need to add about 333Kj/Kg of water, which is quite a bit. This energy has to come from somewhere, and since everywhere is cold, somewhere has to get colder. This means both the water that's formed and the remaining ice cool off to make up for the difference in energy, and because converting a kilo of ice to water takes about the same amount of energy as heating that water from 0C to 80C, the temperature drop is quite steep for a given amount of water formed. This is also why the salted ice cube challenge is stupid. You're pressing ~-20C water up against your skin, frostbite is fast at that temperature with that much thermal conductivity.",
"There is a lot of bad info here. Liquid/solid is irrelevant, but what is relevant is that phase change from solid to liquid is endothermic, meaning it requires energy to occur. When you salt the ice, the phase change from ice to water robs the cream of its energy, making it colder and, hopefully, triggering a phase change in the unsalted water in the ice cream mix, from liquid to solid. So as the salt melts the ice, the transfer of energy causes the custard to freeze. If you had an outer bowl and an inner bowl, put ice into the inner bowl and poured molten metal into the outer bowl, you would expect the water to boil as energy goes from the cooling metal and into the ice. As the metal hardens, the ice melts and may evaporate. This is easy to grasp and is the exact same concept but instead of a phase change that is exothermic (molten metal loses energy as it cools and hardens) you have a phase change that is endothermic (salt melting ice from solid to liquid). The process simply works in reverse. Does that make sense?",
"There are a few factors to it, but some of them are material, temperature difference, and surface area. Thermal energy is always trying to balance out. If something has been in a room for a long time, it is going to be about the same temperature as the air and surface it is sitting on. Metal, however, feels colder than wood, even if both the metal and wood are the same temperature. This is because different materials transfer thermal energy at different rates and THAT is what you feel when you touch things, not the actual temperature. Metal is more conductive of heat, so you lose more heat from your hand to metal than from hand to wood. Water it's self isn't too great, which is why it take so long for it to boil, but the one thing it has over ice is surface area. The larger the surface area of a material, the more of that material is able to directly transfer energy from a heat source into it's self, so while ice may be colder, water can conform to the surface of whatever it is in contact to, due to it being a fluid, and is able to take heat from the soon to be ice cream faster than ice, despite ice having a larger difference in temperature than water compared to the ice cream. Ideally, you would want a liquid as cold as ice so that it can conform to the surface of the ice cream AND transfer the heat better, because the third factor here, temperature difference, matters quite a bit too. With a larger difference in temperature between two materials, you get a larger transfer of energy between them. salty water is nifty because salty water remains liquid when it is colder than pure water, so it fits this niche pretty easily. It is plentiful, not harmful to the environment, and cheap, so there is little to no trouble in using it to cool your ice cream down. For sidewalks, you want to help the ice melt, and since salty water becomes liquid at lower temperatures, the salty water on the surface helps make the ice under it turn to salty water and thus melt. ___ TL;DR: water can hold tons of heat, but sucks at transferring heat, but colder water sucks less at transfer. Ice sucks more because it has pockets of air, both at the interface, and within it, and that sucks at holding heat. Salty water allows water to not be ice at colder temperatures, which means it is even colder than cold water, and has no pesky air in the way.",
"This reminded me of a time a few years back, I asked my 13 yo son to go salt the sidewalk. Walked out to see what was taking him so long...uhm...he was using the kitchen salt shaker. I about peed my pants laughing so hard. Even funnier because he's a smart kid. Was a scholar athlete and is now a Corpsman. I still tease him about it.",
"The goal of adding salt to ice in both cases is the same, to melt freshwater ice. The melting point of saltwater is lower than freshwater. By adding salt the ice melts. On the sidewalk, the slippery is gone. In the ice cream maker, the bucket is insulated so the heat energy required to melt the ice must come from the ice cream container which freezes the cream. The rotating container has a stationary dasher in it that keeps the cream from getting frozen solid on the sides and leaving liquid in the middle.",
"The salt melts the ice in the outer layer of the ice cream machine. This sucks heat out of the inner layer, letting your ice cream freeze faster. Speaking from personal experience, you do NOT want the salt in the actual ice cream",
"As long as the ice isn't too cold, salt does 2 things to ice at the same time: 1. Solid turns to liquid (ice melts). 2. The water absorbs heat from its surroundings as it melts. On the sidewalk or road, the ice melts, or at least the hard ice gets softer and can be physically removed. If it melts completely, the resulting water flows to lower ground, or is carried off on a tire or a shoe, or it eventually evaporates in the dry winter air, or it re-freezes if the weather gets cold enough. In the ice cream maker, the ice melts, pulling heat from whatever it is touching (the metal can with ice cream mix inside it). The resulting salt-water flows out the hole in the side of the ice cream maker and kills your grass. But it is replaced with more ice (which is as cold as the freezer). Salt is introduced to this new ice causing it to melt and pull even more heat from the can and its ice cream mix, rinse, repeat. Eventually, enough heat is pulled from the ice cream mix inside the mixer to cause it to freeze into ice cream. Without the salt, the ice would have a hard time pulling enough heat from the ice cream mix fast enough to freeze the mix in any reasonable amount of time (or with a reasonable amount of ice)."
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5lt1xt | How does oil lubricate an engine without combusting or contaminating the fuel? | Engineering | explainlikeimfive | {
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"The fuel is sprayed into the cylinders, where it mixes with air, is compressed, combusted and then evacuated out. Engine oil is not put directly into the cylinders. It gets pumped and directed to just about all of the other internal components though. What separates the inside of the cylinder from the rest of the inside of the engine, is a set of piston rings. And actually, a tiny bit of the engine oil gets in between the piston rings and the walls of the cylinders and lubricates that movement. As I understand it, a tiny bit of the oil does get caught up with the combustion of the fuel. An engine has an oil consumption rate. So even if you don't have any leaks, you eventually do have to add oil. It's usually pretty low and most people simply get to an oil change interval before actually having to add oil. But some (likely older) engines can go though oil much faster and will need to be topped up regularly.",
"The oil and fuel are in two different areas and sealed off from each other by gaskets. And it doesn't ignite because it's ignition point is far higher than any temperature the engine achieves during normal operation.",
"Not the answer, but incidentally two stroke engines actually use fuel mixes with oil. URL_0",
"Piston rings act as a seal. They are precision machined to a thousandth of an inch. The rings actually dip into the oil sump to lubricate. Older engines \"burn oil\" due to wear on the rings."
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5ltyjy | Software Testing - Test Cases | Engineering | explainlikeimfive | {
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"**Test Case** A series of steps to test an application, typically a task a user will perform. Also called a test scenario. When it represents user actions, it can be called a business process. Example: Booking a flight. **Test Run** The results of executing a test case. This includes every detail associated with it, include what system you used, what version of the software, what data, and the results of each step. Example: When trying to book a flight from Cleveland to Spokane on 2/1/17, steps 1-10 gave the expected results, step 11 failed with a No Flights Available message (see attached screenshot). Test was run on the TEST4 environment, verion 0.0.1.31a. **Test Suite** A group of related test cases used to validate a specific set of functionally. Example: Bangor was added a new flight destination form Cleveland. The test cases Search Flights, Book Flight, Review Booking, Change Booking, and Cancel Booking are part of the test suite needed to validate this change. Edit Account Information and View Frequent Flyer Status are not."
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5m14x1 | How are some car radios capable of spelling out song titles and artist names when tuning into some FM stations? | Engineering | explainlikeimfive | {
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"Radio stations do a lot of clever work to fit more information in the audio stream then just the audio. Originally an FM station were just a simple mono audio signal. However they found out that the signal quality were good enough to deliver audio signals at much higher frequency then the humans can hear. So they composed the difference between the left and right audio channels and turned the pitch up higher then humans can hear and sent it out on the FM band. A stereo FM receiver were then able to split the audio signal based on pitch and turn the pitch down to its original pitch to then make stereo sound. Later on someone figured out that there were still a lot of unused signals above human hearing so they added a digital signal to a high pitch frequency so it can display the name of the radio station, what song is played and even codes for traffic information where it is supported. So the name of the song title is just part of a high pitch audio signals on the FM signal."
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5m5s09 | Why is it so hard to reverse-engineer something? Shouldn't it be simple to just copy the parts exactly? | Engineering | explainlikeimfive | {
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"No. Let's say you try and reverse engineer an iPhone. You need to know what each component is made of, this is NOT easy at all and requires some fairly high level analytical skills. You also need to know how each component talks to each other. An iPhone isn't just the solid stuff, and then OS installed; there is firmware that controls how say the capacitance from the screen is delivered to other bits of circuitry. There is software that controls the battery. Another example would be say a grain mill! You could build something that looks the same easily; a stone with an axel and then another stone on a pivot that can roll along in a circle. But if you don't know how to use it (the software) it's useless. With modern stuff the material becomes a big factor!! Touch screens are made of very special materials for one. Military hardware? Can also be very exotic composites, it's not just steel etc.",
"Everyone is using House as an example, but what about a cake? You can analyze a cake and determine it's made of starch and sugars, but could you really reverse-engineer that to come up with a list of raw ingredients AND a recipe to recreate the cake? Even if I gave you the exact list of ingredients, but no directions for mixing them (quantity and order) or baking it, what good would that do you?",
"Manufacturing engineer, here. It depends a lot on the complexity of the object and if there are critical parameters or tolerances. Reverse-engineering a simple table with square legs is easy. Now think of a nice table with a pattern lathe-turned into the legs and a stain. It may be difficult to determine the wood under the stain and the stain color. It will also take much longer to figure out the lathe tooling setup to replicate the legs. If the replica isn't exact, it could still be a nice table. When you consider mechanical and electronic items, the process is more difficult for a number of reasons. Electronic components are exponentially more complicated. If you can identify all the pieces, you still have to arrange them precisely. Imagine trying to copy a complete road map of Texas with a pencil and protractor - no tracing. If you manage to build the thing correctly, you still need to develop firmware and software so that it runs as closely as possible to what you are trying to reverse-engineer.",
"a real life example is that you can take a look at a house. it has some walls, roof, windows. pretty simple easy to understand concepts. now you are in charge of building your own house, and you know what a house is made up of. now, how do you make a rebar? what is rebar made out of? steel? great! how do we create steel? it's easy to copy simple things with simple materials, but it's extremely difficult to copy advanced things manufactured with complicated manufacturing processes.",
"yes. but you dont know the properties of all the parts involved. Or the reason they have that property. For example when the soviets tried to copy the american b29 bomber from b29's that had to land in russia, because they didn't know the purpose of all the parts, they [went as far as integrating the bullet holes]( URL_0 ), the planes had suffered into their copys. Without extensive testing, that sometimes includes the destruction of parts, you realy cant get all the material properties right. Add to that, that sometimes you just dont have the technology to replicate the original and reverse engineering can become very dificult.",
"Everyone here is talking about the manufacture of something, and they are explaining why copying things isn't easy...but that isn't reverse engineering. That's just trying to duplicate something. Copying stuff is easy. If you look at a piece of electronic equipment, a good chunk of the chips and processors are off the shelf. You can go and buy them and slap them all together and there you go. But that isn't reverse engineering, that's just assembling something. If company x builds a cool thing, and company y can't figure out how they did it on their own, company y then needs to buy the thing from company x and do a complete analysis of it. Reverse engineering isn't about copying something. So company y brings in the engineers to look at every single component and wire, and then write up the full specs based on what they see in the hardware. Going back to everyone's house analogy, it's basically looking at a house and then drawing up blueprints. It's not nearly as complicated as figuring out how to manufacture steel, but it isn't easy. It's time consuming and tedious. This is what reverse engineering is. Looking at a product, and then figuring out exact specifications for it. After you get your full list of specifications, you hand that off to another completely clean and brand new team to actually design something based on those specifications created from the original product from company x. Now company y has a product similar to company x, but they have plausible deniability that they copied anything.",
"Say you have 20. Did you make it by adding 5+5+5+5, or multiplying 4 x 5, or subtracting 10 from 30?",
"Just having a part's measurements does not give you the information about the manufacturing techniques involved, which have a huge effect on the part's performance. Furthermore, operating the resultant product requires a decent understanding of how it works. Blind replication won't just get you nowhere, it's not as simple as you'd like to think.",
"Ask me to make a lightbulb from scratch? I know enough of how to smelt and refine ores, blow glass, etc. that I could do it in under 3 months if you dropped me in the middle of the woods with the food/shelter to keep me and my project safe. Hell, with half a year I could make a power source to light it up as well, might need all of one community college course or two days in a library beforehand to fill in a few blanks. I'd almost consider doing it for a few grand at the end before remembering I could make more at minimum wage in that timeframe. Now, hand me a bulb, any bulb, and tell me to make that exact one? Hah. Fuck that. And you wanna know why? Specifics, my dear! I could be on Franklin's heels in a quarter of a year because I spend too much time on Wikipedia and lack a legitimately worthwhile outlet for my curiosity, and I'm reading about something that can be done successfully with fairly modest margins of error before it fails to work. I can almost ballpark a working plan to make everything I need from the stone hatchet and hammer to the turbine wheel powered by a creekbed or steam (or hell, hamster wheel using improvised woodland critters!) on the fly. Such is the power of decades of complacent fact-collecting paired with an overactive imagination that likes to ground itself firmly in \"bullshit that just might fucking work!\" But tell me to make that lightbulb. Any one fucking lightbulb. And let me do it in the city, with a project budget of a few grand? I will firmly tell you to go fuck yourself in your round hole with a square peg, and that's only because I don't know a wittier way to tell you to do it with the star-shaped peg. Because I can't be fucked to figure out what filament your bulb uses, if it's filled with x gas, normal air, a vacuum, etc. I don't wanna fuck with making the screw-in base. I don't wanna spend the time being a good enough glass blower to make the bulb the perfect shape, let alone figure out what kinda sand and additional minerals and whateverthefuck goes into it. And I don't want to fucking stamp the goddamn ink on the bulb, or lettering into the base. TL;DR Franken-fucking together a functional science experiment is easy because your target outcome has Texas-sized borders. Counterfeiting has pinhole-sized borders, so it's harder even if you're just making saltwater taffy.",
"It's easy to mix yellow and blue to get green. It's hard to get blue and yellow FROM green.",
"It is actually really really hard and expensive. Part of what makes companies rich are knowing how to making things cheaply. Anyone can make an iPhone. The trick is making it for $500 instead of $5 million. So even if you managed to figure out all the parts, you still don't know Apple's secrets of making an iPhone.",
"Say you've got a cup of coffee. We know that was made from coffee beans and hot water, but how would you find that out if you didn't know? You can't get coffee beans back out of coffee. You can analyze the coffee with some expensive equipment and find out what chemicals are in it, but you can't find out where they came from. Now let's consider an electronic device. It probably has some IC chips in it. You can't just take them apart and figure out how they work. It would be extremely expensive to analyze them on a microscopic level and figure out how to make an identical chip. All you can realistically do is measure the inputs and outputs and try to figure out how they're related. So, you're limited by what you can actually observe and measure. It's often impossible or impractical to determine exactly how something was manufactured. Parts are not always simple discrete pieces that can be measured on their own.",
"Lets think about a metal part you need to rebuild because its broken but you have no exact design for it. Now you go for an 3D scanner, scan the bad boy and create a mold for your new component. Then you pour in the metal and give it time to cool down. You wrap the component out of his mold, but it will be smaller than the part which broke down. That because metal shrink when it cools down. To merge out this problem, quite much engineering work has to be done and even then the piece wouldnt be like the broken one.",
"To carry the house analogy further, how do you know what gauge (thickness) wire to use for the electrical outlets, or how the plumbing is laid out. These things are buried inside the walls and invisible to you unless you start knocking down walls. There are many things like this in a house that you cannot see, and thus cannot replicate precisely. And it may not just be items you cannot see, but how they were made. When looking at a product you are only seeing the final result; how it ended up that way may not be obvious. Take christmas tree tinsel for example. Seeing the final result in the box tells you very little about how they are able to package it so cleanly. And it is actually very difficult to do; companies try hard to keep the exact method a secret. In both cases what we are really talking about is information. Some of the information needed to copy an object may be hidden or may not exist in the object at all. The big trick with reverse-engineering is being able to infer what you cannot see from what you can see. A more modern example: Some programmable computer chips come with fuses that can be blown after being programmed. This prevents any changes and prevents anyone from reading the program back out. One way reverse-engineering folks get around this is with a special machine that can shave off epoxy covering of a chip and expose the raw circuits inside the chip. Then they proceed to poke the chip with several very sharp sticks (probes) to learn how it was programmed."
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5m6m8a | on my Honda, there's an "eco" button that's supposed to help me save gas. Why wouldn't they just make that a permanent feature on the car instead of a button? | Engineering | explainlikeimfive | {
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"Because Eco-mode gives up a lot of power and throttle response in exchange for (slightly) better fuel economy. I have a Honda Pilot, and Eco-mode is very frustrating and even somewhat dangerous in many situations such as merging, going up hills, or passing. You punch the accelerator and... not much happens. I would not want this as the default setting on that car. I only ever use Eco-mode when cruising down long stretches of highway.",
"Sometimes people want more acceleration. Eco mode makes you accelerate slower and the engine outputs less power.",
"\"Econ\" reduces acceleration as well as A/C strength (to a small degree). There is also Sport mode in the models like the Civic (I have the 2016 Touring model), which increases throttle response and makes acceleration quicker, as well as simulates a higher gear (engine braking).",
"Everything has a cost. You don't just use less gas because you pushed a button and get the same performance as before. If you want more power, you need to give up speed, if you want speed, you sacrifice power. Eco mode usually turns off some cylinders from being used turning a V8 or V6 into a V4 engine. If you are burning less fuel, you are getting less power. More than enough to drive but acceleration will be slower and even top speed, though still beyond the speed limit."
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5ma4n5 | ; Why does traffic construction, (like an intersection), seem to take so much longer than other construction projects of equivalent size (like a medium sized building)? There seems to be huge stretches of time where little to know progress is made. What's going on? | Engineering | explainlikeimfive | {
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"1. Utilities in the work area need to be located by hand excavation (that's the law) 2. Utility relocation, protection, and support can be tedious and time consuming. Gas, steam, and electric are dangerous to relocate, therefore every precaution is taken. Telecom relocation is time consuming due to copper and fiber splicing. Water may only be able to be taken out of service at certain times. Sewer is typically fairly deep and time consuming to shore up trenches. 3. Materials cannot often be brought in and stock piled due to space restrictions. Depending on where you're working, they might not allow you to store any materials on site. This means everything has to be brought in when it's needed, even the excavation equipment might need to be removed and delivered daily. 4. Truck loads of material brought in (fill, concrete, pipe) have to be ordered and picked up or scheduled for delivery. Example: you order a concrete truck and it sits in a traffic jam, it gets there late. If it's been spinning in the drum too long, it's no longer any good and the load is rejected. Now you wait for another load to come. 5. Work permits typically stipulate the times you can work. I've gotten permits where we could only work 10am - 2pm, Monday - Thursday or 8am - 6pm Weekends only. Subtract at least an hour of productivity from that for opening up the job site and cleaning up. 6. Unforeseen circumstances cause a lot of delay (inadequate design on the engineer's part, poor planning on the contractor's part, utilities not known about until the tooth of a machine bucket ripped through it.) This is not to say that some of this doesn't happen in building construction, it does, but their job sites are usually less constrained than road work. Source: Civil Engineer, worked construction in NYC for 10 years.",
"Just for starters: There's a ton of ancient and delicate infrastructure under any urban street and there aren't great records of what-all is down there (and you can't see it until you've put a backhoe through it.) Some of that stuff is natural gas lines -measure thrice, cut once. If you built your medium-sized building underground you would be comparing apples to apples.",
"There's also the matter of money and resources. Most streets and roads are publicly funded whereas most buildings are private, with additional dollars associated to completing it on time and on budget. There's more money to be made in the commercial sector and a larger pool of subcontractors to choose from, unlike in municipal projects where you can only choose workers that have already been certified to work for the state/county. It's also a different skill-set. My brother who was a roofer for hotels could switch to residential without much trouble. But the electricians/ plumbers who work on municipal projects usually have much more training. Many times if you see the same orange cones up for a long period of time its because they're waiting on someone specialized enough to do the work or certify the work was done correctly. Source: friends and family who work private sector construction. Please correct any misstatements on the public side.",
"/u/Dennaldo has the most comprehensive answer, but didn't touch on crew scheduling -- maybe it wasn't an issue in NYC! You or your prime contractor may or may not have all the various crews that a project needs, available at the drop of a hat -- many construction projects are scheduled a year in advance. The sewer-pipe crew, for example, might be multitasking several road projects at once, since each of them doesn't need a full-time sewer crew. But, they may be working on project 17 on the other side of town for a couple more days when your project is ready for them again. So, everybody shifts to something else for a while. The worst thing to have happen is to have a crew show up on their scheduled-weeks-in-advance day, and **you're not ready** -- your project has been delayed by weather, or a previous task isn't quite ready yet. So, to keep that crew busy, they get sent (out of order, so to speak) to a different project, and YOU WAIT. To accomodate this, your project scheduler may allocate a week for three days worth of work now and then, so that a previous crew can lose a day without impacting the rest of the project. That's another reason why it may look like nothing is happening -- scheduled slack that turned out not to be needed."
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5mafez | Why did the automotive world move from 0-60 times to 0-62 times for cars? | Saw it on Grand Tour & thought it was interesting. | Engineering | explainlikeimfive | {
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"Nothing changed. Countries that measure speeds in KPH have always done 0-100KPH, and 100KPH is ~62MPH",
"100kph = 62mph. The specs of the car were in metric and the person/entity converted it for easier understanding in the American market.",
"Because 62 m/h = 100 km/h. The rest of the world outside the US generally uses the (much more sane) metric system, so any show that has an audience of non-US viewers would use that"
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5mdfgs | Why has Tesla's work on 'Free Energy' never been fully explored or completed in the modern day? | Surely by now someone or some company with the funds and resources would have taken on this task as it would revolutionize society put fossil fuels to bed? Is it due to the money being made by fossil fuels? or is there more to it? | Engineering | explainlikeimfive | {
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"Tesla never tried to produce \"free energy\". He wanted to realize wireless power transfer - but that still would have required a power source to run the system. The reason nobody ever put money on his idea was not just the risk of people tapping into it, but also that it's wasteful. Wireless energy transfer over big distance is inevitably going to cause losses, whereas conventional systems with power lines (to which his work contributed a great deal) can achieve great efficiency over long distances. The entire concept of free energy is not pursued by power companies because it's simply not possible. The preservation of energy, along with the laws of thermodynamics, are not something that is easily challenged, simply because they are supported by a lot of hard evidence. This of course doesn't stop a bunch of people from trying, but no physicist or engineer worth their salt will take them serious.",
"We don't use it for the very same reason that with don't use the Philosopher's stone for gold production, or the Fountain of Eternal Youth for healthcare. It's a myth, it's not real.",
"The biggest problem is most likely that this free ubiquitous energy doesn't exist. If it would exist, corporations would use and resell it."
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5merxj | How do our sanitary systems filter out the waste and unwanted objects that we flush, such as pencils or chewing gum, to produce clean water? | Engineering | explainlikeimfive | {
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"Typically they don't turn waste water into clean drinking water. In most places, the water is cleaned until it's safe enough to dump back into a nearby waterway, like a river, where it can be washed out to sea. Some places truly recycle water, but it's a lot more expensive and energy intensive. Regardless, the process to clean water involves running it through a series of filters, each removing smaller and smaller debris, before chemically treating the water to kill off anything left living in it. You can Google pictures of this filtration process, but it isn't pretty.",
"why are you flushing pencils down the damn toilet?"
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5mfq9i | How does the lever that reduces glare in your rearview mirror work? | Engineering | explainlikeimfive | {
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"The mirror glass is a wedge shaped prism. Normally, you use the rear which is silvered like a regular mirror. When you flip the lever, the glass tilts so that the front of the glass is reflecting the high beams to your eyes. It is not as reflective as the back, so they are dimmed."
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5mjong | What is the difference between an EM-drive and a microwave? | Engineering | explainlikeimfive | {
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"The basic element in both is a magnetron, or a different kind of of microwave source, but, instead of aiming them at food, they > are directed into a metallic, fully enclosed conically tapered high Q resonant microwave cavity. Which is a sealed enclosure in the shape of a truncated cone. *Supposedly*, the smaller flat section on one end produces less force than the bigger section, hence ~~magic~~ thrust.",
"The difference is the shape of the cavity. A microwave oven has a rectangular cavity while the EM drive is a weird cone shape. People think that making an asymmetric cavity will allow it to generate thrust. That's of course false, because [momentum is conserved regardless of the shape of the cavity]( URL_0 )."
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5ml2oi | Why do cars have an air setting for legs/defrost but not face/defrost? | Engineering | explainlikeimfive | {
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"Heat and defrost in a car are often related but different. In my car, there is one control for the vents that happens to also turn on the AC for the defrost settings. The defrost settings are either windshield or windshield plus feet. The purpose of turning on the AC is to dehumidify the air, removing fog from the windshield. In both cases, defrost implies hot air hitting the windshield. The windshield/foot setting is a compromise, as neither will be getting as much air as they would if it were exclusive. Because the air hitting the windshield quickly moves toward the vicinity of your head, it's good enough for the purpose of getting warm air to your face. You may need to turn up the fan speed to feel it. If you don't need to defog the windshield, you can of course just turn on the front vents. It's not necessary to have the AC going in this case, though in some conditions, you may want to and can turn the AC on manually. I vaguely recall some cars from decades ago that assumed the occupants couldn't handle separate settings for temperature and position, so always turned on the heat for foot and defrost and never turned it on for face. I've never purchased a car that dumbed down, and never will."
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5mli22 | One Way Mirrors | One way mirrors seem like a really common concept, seen in things such as classrooms, experiments, or even sunglasses. So how do they work? | Engineering | explainlikeimfive | {
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"They are actually transparent two-way mirrors. However, because there is a lot of light on the one side and little to no light on the other - note how the detective behind the glass are always in a dark room? - there is a lot of reflection on the brightly-lit side and little to none on the other, so all one side sees is reflection of itself while the other can see through the mirror."
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5mn8vd | Why do you need a NASA lens to record candle lit scenes on film, yet the human eye is as small as a mobile phone camera and can see low lit scenes just fine? | Engineering | explainlikeimfive | {
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"Our brain is incredibly powerful and can 'compute' the dynamic range and the white balance of everything we see. Even the the most expensive sensors on the best cameras available today can't recreate the wide dynamic range our eyes do for us, at least not without combining multiple images. Example. When driving through a tunnel as you approach the end your eyes see fantastic detail in the tunnel around you, AND in the bright outside the tunnel in front of you. Now try taking a photo of that (passenger!!) and see that you either get detail in the tunnel and super overexposed outside, or detail outside and underexposed inside. One day cameras may reach this level but not for a long while.",
"You're thinking of the f0.7 lenses made in the 1960s and used both by NASA and Stanley Kubrick. He wanted to shoot motion pictures (35mm colour film) by candle light and, at that time, film sensitivity required such a fast lens to produce the required quality. Today, both film and digital sensors would be able to do the same job with f1.0 or even f1.4 lenses, which are commonly available. Professional DSLR lenses have f1.4 as a very common prime (non-zoom) aperture and f1.2 is also available. Today, pros use these more for their very narrow depth of field more than for their bright images, i.e., they want everything except the subject to be very out of focus and blurry. You can find lenses with f numbers at and under 1.0 but they are expensive specialist items. For example, there's an [f0.85]( URL_0 ) for $2000 which is only half a stop slower than the f0.7 NASA special from the 1960s. Modern digital cameras will happily shoot stills and videos with standard zoom lenses in candle light. The problem is that the images will be incredibly noisy unless you use long exposures that are impossible for moving subjects or for videos. The quality would be unsuitable for movie or TV production work. The human eye is actually not too different. Yes, you can see by candle light, but your colour perception is missing or very muted and there is the equivalent of noise present. The human eye has a maximum aperture around f2.1, over three stops (eight times) slower (dimmer) than f0.7.",
"A rod cell in your eye can resolve a *single* photon. This can also be done with technology, but it requires relatively huge photo-multiplier tubes which are found in scientific apparatus and not consumer or professional cameras. The signal from the rod cells needs to be about 5 photons to be strong enough to reach the brain and be registered though, but 5 photons is still FAR better than a cheap CCD can do (I include $100k+ professional cameras in \"cheap\". \"expensive\" is the types of detectors used in multi- hundred million dollar particle accelerators that are the size of a cathedral - they can also detect single photons) (This is also helped by the insane dynamic range a human eye can achieve as the brain scales the output of individual photo receptors as needed, where a modern camera scales the output of all photo receptors together) There's a lot of crap here that either doesn't answer you or is just plain wrong."
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5moxde | Why are semis that carry liquid cylindrical, and not rectangular? | I was riding my bike down the road and semi carrying gasoline went by, and I thought, "why not make a rectangular container, shouldn't it hold more liquid?". Knowing I don't know anything about that stuff, can someone explain to me why we don't use rectangular semis for liquid transport? | Engineering | explainlikeimfive | {
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"Curved structures are mechanically stronger at storing contents under pressure. The pressure is pushing evenly of all sides of a curved surface, so they are less likely to burst. If you have lines or corners there is uneven distribution of load on the interior of vessel. More info can be found here: URL_0",
"* cylinders are stronger than rectangles...liquid loads tend to be heavier and can slosh, putting more strain on the trailer than solid loads * a filled tank of most liquids is already operating at near the maximum load limit, there is little advantage to providing extra space * the shape makes it easier to drain",
"Also, most tankers have multiple baffles or compartments in them. The weight transfer from thousands of gallons of liquid sloshing around, can easily overcome braking force and. An also causing roll overs on turns",
"Think of it in this way: Most materials are a lot stronger when you pull them and not bend them. Just think of a piece of paper. It can handle a lot of force when you pull it, but it will have literally no resistance for bending it. With metal it is exactly the same, only that metal itself is a lot stronger. When you weld metal together as a tube, it is a clever design, so when you put pressure inside the tube, the tube will try to expand. But to expand, its circumference would have to get bigger. And this means that the force caused by the pressure was converted into \"pulling-force\" circular around the circumference. With a rectangular container this wouldn't work. On the edges, the pressure will try to bend up the edges and usually the container will fail/rip open. But just imagine the rectangular container to be of a very bendable material, like rubber. Now apply pressure inside. As the pressure increases, the rectangular container will deform and end up circular. Because this is the most officiant form."
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5mqzvn | Why do boy bikes typically have a bar across the top whereas girl bikes do not? | And that carries over from kids' bikes to bikes for adults. Just seems to me that, if anything, given human anatomy it would be reversed. Edit to add: Thank you all for pointing out that women/girls traditionally wore skirts in which that bar would present a problem. So, I guess two better questions would be: 1. Why is it still common? 2. Why do male bikes have that bar at all? | Engineering | explainlikeimfive | {
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"Women used to wear long dresses to used to have to have to \"step through\" the frame in order to preserve their modesty. Males on the other hand could just pop their leg over the top. The tradition has just been maintained on most commercial bikes.",
"It's a carry-over from the days when girls and women only work dresses or skirts-and-blouse outfits. The bar on a \"men's\" bike would make riding one in a dress quite awkward.",
"I thought this was a holdover from olden times, when girls' bikes had to accommodate for dresses.",
"Because girls traditionally wear skirts and dresses which get pushed up by the bar on boys bikes. In Scotland boys bikes also have the low crossbar because of the tradition of wearing kilts.",
"As for 2, it's because of physics. Both men and women's bikes have the bar, which is necessary to form a truss in the central bike structure which is far, far stronger than just a single pipe. The only difference is the women's bar connects much lower than the men's, which structurally makes it weaker. This is due to a combination of men being physically heavier and that stereotypically men do more mountain biking/crazy outdoor stunts which would require the stronger frame. Where or not that's really true, men's bikes are actually the better design from a strength standpoint, and the altered frame on women's bikes is a concession due to the whole skirt thing and it's stuck around for marketing purposes.",
"Women used to wear dresses/skirts. They still do, but they used to too. The design of the front half of a bike is referred to as the \"front triangle\" (the portion of the frame from the forks to the seatpost). Triangles are the strongest shape in nature because forced is added/displaced equally on all three sides. The step-through frame, generally regarded as a \"woman's\" bike was to allow a woman to get onto the bike while wearing a dress/skirt (they are different things). The ability to use a bicycle was hugely liberating for women when first introduced. While the step-through allowed women (and those with hip issues) the ability to get on a bike, structurally the frame is not as strong as the triangle (where the top tube is much higher). There was the [Penny in Yo Pants initiative]( URL_0 ), demonstrating a trick using pocket change to allow women in skirts to ride bicycles. There isn't really anything in cycling that is \"gender specific\". Men and womens seats now have options that have no center channel. Beyond that, it's just a matter of frame size - cranks, gears, wheels, handlebars (incl. tape) is a lot of personal preference and bike fit.",
"I used to rent bikes. Low step are still good now particularly for people with hip or leg issues. I had an elder man renting specifically request the low step option for this reason. Also good for people who might lose their balance swinging a leg around, and of course, riding in compromising clothing. WSD options (low step) typically have a shorter distance from person to handle bars. This smaller space was built intentionally with women and their shorter wing span in mind. Personally I like having the bar there, and I do happen to have a longer wing span, so I typically take the male option of bikes."
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5mr6ba | What does the small hole near the top of sinks do? | Engineering | explainlikeimfive | {
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"It is there as an overflow. So if you forgot the plug in and the water open, the water should drain through there instead of overflowing the sink and onto the floors. The hole connects directly to the down drain pipe.",
"Additional to what is already said, it's there so you can have air flow into the pipe when you empty the sink.",
"They sell attachments that fit in there so your parents can monitor whether you brushed your teeth, and you'll never notice. Have you ever wondered how we just know?"
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5mro64 | Thermal Cameras | Engineering | explainlikeimfive | {
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"All objects emit infrared light. The amount is proportional to the temperature. There are a few types of cameras. The newest, most popular ones use an array of tiny thermometers called [microbolometers.]( URL_0 ). Each bolometer is one pixel. Their resistance changes with temperature. It is measured for each pixel and converted to a false color display. An interesting quirk is that they aren't good at measuring temperature accurately, so a shutter is periodically activated so they can calibrate the temperature to the temperature of the shutter blade which is in turn measured by a nearby conventional temperature sensor. All the pixels are then calibrated against that temperature.",
"The electromagnetic spectrum is large, the visible part is small. Just next to the visible part is a region called infra-red that is emitted by warm objects. Thermal cameras are sensitive to more of the spectrum than human eyes, allowing them to see the heat in objects."
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5mrub1 | why dont 18-wheelers (lorries) have automatic transmissions? | Engineering | explainlikeimfive | {
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"text": [
"Dude, They do have [auto's]( URL_1 ). And [video]( URL_0 )"
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"https://www.youtube.com/watch?v=8D6yzAvWFZc",
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5mtbex | What are the little black dots/lines for on the edges of car windshields? | Engineering | explainlikeimfive | {
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"Little 1in. Lines on either side of the windshield about 4in from the top indicate the bottom of legal tint area. Little dots called frits are used to create rough surface for proper bonding to take place during installation of the windshield. They are also used to help prevent being blinded without losing complete vision, working as a factory sun visor. Edit: Corrected a mistake brought to my attention by u/BlueRockStar.",
"The dots are acting as grit, to better make adhesive stick, instead of sliding around, since it is on glass. As for the lines, those are usually the heating elements for the defrost, and one may also be your antenna.",
"The black rim around the windshield is to hide whats underneath. The adhesive under the glass that bonds it to the metal of the car would not be attractive.",
"It is to help protect the adhesive from the UV rays that would break it down. Plus also hides it, as it wouldn't look attractive if you could see the bead of adhesive, the wavy pattern and possible air gaps from the outside.",
"The dots and lines are made of varying conductive materials so that defrost heat is retained and distributed by the glass better."
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5mx87x | What are the benefits that zero-G environments provide to science or manufacturing? | Engineering | explainlikeimfive | {
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"At the moment its mainly for science. Not much commercial activity in space yet, outside of communication and observation satellites. The main things that benefit from zero G are things to do with crystal formation, like alloys. Say you have a big pot of molten metal alloy. As it solidifies, some alloys form tiny crystals called dendrites. The way these dendrites overlap and intertwine determines the properties of the resulting alloy. In gravity dendrites are subjected to all kinds of convection currents, density fluctuations etc. As such, they grow in very irregular shapes and break before they grow too large. Therefore it is very hard to make an alloy that lives up to its theoretical properties. In space all these flows and currents are drastically reduced, or eliminated entirely. As such you get a much better alloy. Same thing for many other things relating to crystal formation. Zero G allows for bigger, purer crystals. If we look a few decades into the future, there are many things that could benefit from a space environment (provided launch costs go down, or we use materials readily available in space). Zero-G means you don't need to worry about support. This allows for much more versatile manufacturing methods. For example, right now silicium wafers used for semiconductor manufacturing are 300mm in diameter. Any bigger than that and the wafer flexes too much. In space the wafer won't flex due to gravity, as such you could conceivably have wafers tens of meters in diameter. Space is also a fantastic vacuum, which would really benefit semiconductor manufacture. Another cool thing about space is that liquid droplets will quickly form perfect spheres thanks to surface tension. This is pretty useful for several industrial processes. Zero G also allows you to mix normally unmixable gasses/liquids. Oil and water don't mix on earth, because the oil floats on top of water. In space they'll form a great emulsion for long periods of time. This allows for chemistry that's difficult or impossible on earth. Space is also a great place for dangerous processes. If some industrial accident leaks thousands of tonnes of neurotoxics into the environment its a terrible disaster on earth. In space nobody would give a shit, outside of lost profit. All in all, space manufacture would be pretty useful. But only if launch costs come waaaaay down, or we start exploiting asteroids and set up a nearly independent industry in space.",
"Also Space Veggies! URL_0 A lot more research on this is needed certainly but the potential is there."
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5my5dn | If coaxial is good enough to get the signal inside, why do we use all kinds of other connections (HDMI, Ethernet etc...) | Had some new services installed in my home recently and realized that they used coaxial cable for every service (TV, phone, Internet). I remember coaxial always being used for the TV, but it used to be a cable that just went straight into the TV. Then it changed to a cable going in a box that then hooked up to the TV. Now its the same but the box connects via HDMI instead of coaxial. Internet same thing, coaxial runs into the modem and then uses ethernet cables after that. Phone has its own modem which also then uses regular phone like jacks and connectors. But if Coaxial is what is importing all these signals into the house in the first place, why not standardized everything to run through coaxial inside the house as well? | Engineering | explainlikeimfive | {
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"The coaxial signal is very high frequency analog. It takes significant electronics to decode it and encode an outgoing signal. The box that does this is called a modem (MOdulator-DEModulator). If you add that electronics to every thing, it would significantly increase the cost, over a digital system like HDMI. High frequency analog signals are also subject to cosite interference when you have more than one of them inside a box, so things would need lots of metal boxes to put the components in. Net result, it would cost a lot more.",
"Because coax is essentially carrying radio signals, and anything working over it includes a full radio transceiver. Essentially it's much more similar to using wifi cards. You could replace your Ethernet connection with wifi cards connected via coax instead of antennas, it would probably work, but it's much more expensive than Ethernet, and significantly slower. It's a similar issue with HDMI, a current HDMI cable can be powered by a $25 raspberry pi zero (so whatever HDMI needs is less than that), but HDMI handles 48Gbps of data, much much more than your $100 cable modem is capable of. While a cable modem using current tech can be made to push 48Gbps over coax, it would really require 100 times the hardware to generate the right signals, making it a $10k modem, and you need one on each end of the cable.",
"Because each of those things have specific standards (physical and electrical) that were developed independently - many of them prior to the introduction of consumer Internet services from cable TV companies. Phones, for example, have used the same cabling, modular connectors, and signalling for 40+ years. Could you run phones directly over coax? Sure, but what would the benefit be compared to the expense of abandoning millions of existing phones. Years ago, we used to run Ethernet over coaxial cable. However, coax tends to be bulky and hard to work with, and the devices used to propagate the signal introduce multiple failure points to the network. So, networking switched over to twisted pair cable in the late 80s/early 90s. TP wiring is easier to work with and is less expensive than coax. HDMI was developed in the early 2000s, to provide higher quality digital AV between devices. It's no coincidence that HDMI came on the heals of wider adoption of DVD, and was developed around the same time as Blu-Ray. Each of the standards is optimized for its specific function and, after the cable comes into your home, the signals the cable company sends must be converted, by your modem, into the type that can be used by the connected device.",
"Another piece of insight here. From what I remember from college. The coaxial cable is essentially lossless. It can be run for miles and miles without signal degradation. You can't do that with ethernet. For simplicity sake, essentially you can't run Cat5e more than 100 meters (~300+ feet) at a time without a repeater to regenerate the signal and send it out again. Cat6 is the same at 1000base-T but it's more often used for 10GBase-T, or 10 gigabit per second rate, which means its maximum distance is about 55 meters. HDMI is the same story, topping out at 50 feet before signal degradation. [Here's a decent source]( URL_1 ) Notice the RG-59 Coax doesn't show a max length. IIRC from college, that's thanks to shielding and most importantly, impedance matching. [Wikipedia sources for support]( URL_0 ) Especially the \"matched load\" section there where it says \"for all l.\" If you tried to do the same thing that Coax is used for by using ethernet cables, it would cost you a fortune in repeaters alone. You can't do everything with Coax either. It has limits on splits. It's better for getting signal between 2 points, but not well suited for your network backbone like ethernet. There are pros and cons to all types of cables and their usefulness depends on application needs."
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5mybqm | What is the purpose of this structure in a dam? | This picture was taken in Portugal (Paradela's Dam). URL_0 What function have those structures? | Engineering | explainlikeimfive | {
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"Looks like an overflow emergency drain. In the event the level behind the dam gets too high, this structure, which is connected by pipe to a sluice way, allows water to drain without letting the dam be topped, which can be damaging to the dam structure. The smaller one I'm guessing is an air vent for that system.",
"Morning glory spillway. NOt necessarily for emergencies. Just gets water from one side to the other at a set elevation."
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5mygir | How does my car know if it is icy outside? | My car can tell me the outside temperature AND whether or not it is icy. What sensors does a car use to determine if ice is possible? Does it detect moisture and compare it with temperature? | Engineering | explainlikeimfive | {
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"If it's a Ford Focus III, than I'm sorry to tell you it's just a yellow light if it's +3 Celsius and a red light if it's 0 or below. Nothing more sophisticated than that. And it just so happens that at these temperatures, ice can occur.",
"to my knowledge, its completely dependent on temperature. typically triggered at 36 or 37 degrees to be safe. Though its possible, that if your car has a modem or satellite data link (like onstar or xm), it could be getting a real time weather alert instead."
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5n0ww6 | In the winter, when we 'heat up' our cars, what is going on mechanically that is actually better for the car than driving it immediately? | I've always had this perception that the internal machinery would sheer and wear more or break under stress in cold temps, is that basically correct? | Engineering | explainlikeimfive | {
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"In theory you want the metal parts to heat evenly before stress is placed on them. Cold things are generally more brittle which means they would crack instead of bending. In reality modern cars don't need any time to warm up. Modern materials and engineering techniques are designed to work in a wider range of temperatures.",
"Nothing - Modern engines are computer controlled and only need enough time for the oil to redistribute for \"heating up\". However, most people driving today were taught by someone who learned to drive in a carburated vehicle, that needed time to heat up so the fuel/air ratio would be closer to ideal and the metals wouldn't be under as much stress."
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5n0xbp | How has the steering wheel/accelerator gone basically unchanged throughout the automobile's history while most everything else in a car has been updated or changed? | Is our current method of steering really the most efficient way to do it or is it just a case of wanting to keep the familiar? | Engineering | explainlikeimfive | {
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"The alternatives like joysticks or trackpads have several problems: they make it too easy to make sudden sharp turns that would cause the car to skid. They require power steering and have no way to work if the power fails. They also don't make it easy to give physical feedback to their driver. I can't think of anything better than a wheel. You can turn it many times to get to full lock which makes it great for manoeuvring and parking. It won't accidentally get turned too much while the car is moving at speed. It's easy to keep it turned to the same degree - you just hold it in place where as a joystick is more work.",
"It is NOT the singular design. Early automobiles had many different control designs. Ford model T has 3 foot pedals: brake, reverse and clutch. And 2 hand levers: ebrake/mode lever and gear selector. The throttle is a hand lever on the steering column",
"I'd say the steering wheel actually has changed a lot. Think of all of the technology now present in a steering wheel- first it connects to a power steering system that assists you in turning the vehicle, rather than using brute strength. Next, think of all the buttons for things such as cruise control, and media center control. Finally, the steering wheel is now part of the safety design of a car, with an airbag inside to protect you in the event of a collision.",
"On the contrary, steering wheels have been endlessly tweaked and redesigned. The shape, auxiliary controls, angle, displays, etc have all been changed -- the only constant is that it's a \"thing you turn\". For example, here's a gif of how Formula 1 steering wheels have evolved over the decades: [F1wheels]( URL_0 )",
"Lots of early cars didn't have accelerator pedals like cars do today; many ran at a fixed acceleration (ie, ON), and you used gears to change your speed (roughly; 1= 5mph, 2 =12mph, 3=20mph, etc). Early Citroens ran like this, as did the Model T, and probably many others until the variable accelerator became standard."
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5n32fp | Why do rocket launch pads appear to have "holes" that lead the smoke/exhaust out through a side? | Wouldn't there be more thrust generated if the rocket launch pad was a flat surface? | Engineering | explainlikeimfive | {
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"I know what you're talking about, and while it seems like it would make sense, thrust doesn't require nor benefit from a backstop. Not to mention the reflected blast, sound waves, and chemical soup pouring out the ass end of a rocket could do real damage to the rocket itself if it didn't have somewhere to go."
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5n5ec0 | How can an autonomous (self driving) car work in adverse weather conditions? (Snow, ice, etc) | So I get how these cars can work on nice dry/wet pavement, but how can they work on ice or snow? How can it sense the ridge of death slush when changing lanes on the freeway? Knows it needs more potential stopping distance from sliding in snow? Not slide off on a turn, or see through some fog? Everyone says they're coming sooner than we think! (Only if you live in a southern state, perhaps). | Engineering | explainlikeimfive | {
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"They can't right now. That's why they're primarily being tested in southern states. It's a seldom publicized but openly admitted limitation of the technology. When the roads are obscured the systems are unable to determine where lanes are or even roads in general do when they cannot detect those things they cannot be engaged. The makers openly admit that snow ice and even heavy rain prove a significant obstacle that they're working to get around. As far as I'm aware all systems on the market today will disengage themselves in these conditions as a safety precaution, or prevent you from engaging them in the first place.",
"The same way you do. It can pretty easily determine the weather and road conditions. In fact, it would probably drive *better* than you in such circumstances since it will be aware of such driving conditions while many drivers just drive the same way they normally do (including going way too fast for the conditions). It also would have faster reaction times and better reaction choices to various rapid changes in situation, such as when hitting a particularly slippery part of roadway."
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5n6gxe | How 3D movies went from using blue/red cellophane glasses to just "sunglasses"? | Growing up in the 90's, I remember seeing 3D movies at museums and public attractions with that square, one blue, one red cellophane glasses with all the colors being bit funky. Now we use glasses without any coloration. How did this change happen? Did we discover new way to make 3D films? | Engineering | explainlikeimfive | {
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"The key idea of any 3d is to project 2 images on to the screen, and have each eye register only one of them. With red/blue, you would show one image in only blue color, and another image in only red color, using different shades of red. If you looked at the entirely-red-shades image through lens that was color red, you would see just, well, red. But if you saw it through blue lens, you would see all the different shades. Likewise for blue. Thus, you get(with wonky colors) 2 different images, one for each eye, which then could be used to do 3d. Modern tech however uses polarization, that is, the direction light is sorta \"waving\" at. Light is a wave, and it has direction, orthogonal to the direction it's going, where it's \"waving\" at. Typically white light does this waving thing in all sorts of directions, and it's a mess, but there are filters which can block all but certain orientation of this waving. Having one image transmitted only using light that's of certain orientation, and then have lenses of your glasses selectively block these orientations allows again you to transmit only one of the two images to both eyes. I don't know how expensive this new polarization technique is, but I can tell you that you can do pretty good job with this red/blue lens thing with very cheap materials, video device you use to show your red/blue 3d film has absolutely no special requirements, and it's pretty cheap to make appropriate glasses, so that probably explains why people historically did use this red/blue 3d thing despite color problems.",
"Polarized light is the secret. To your eye, polarized light looks like normal light. Normal light has waves, right? Normally, these waves kinda bounce every which way. But with a filter, you can ensure the waves only go one way, for example vertical. So what the 3D projector does is show two images, one composed of vertically poliarized light, one of horizontally polarized light, on top of each other. One glasses lens filters the one polarization, and the other filters the other polarization. So each eye now sees a different image. [Here's a handy lil diagram]( URL_0 ). For the other lens, the opposite would be true, the horizontal light would get past the filter but the vertical would not."
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5n9lbp | How are big items loaded in to a submarine. | I was wondering how does a submarine get loaded. Say if a fridge needs to be replaced how do they get it in and out. Does it just go in to the top hatch or is it be loaded a different way. | Engineering | explainlikeimfive | {
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"The normal accesses to the boat are removable, making a much larger hole for loading items in or out. Anything larger than those openings require cutting and welding the hull.",
"This is my favorite question I've seen all day... Reddit's curiosity never ceases to amaze me. They plan those things before they finish the sub. They could also probably dismantle the fridge and put it back together inside the sub. Or just specially-designed things that can be taken apart.",
"There are special tube ports for loading the torpedoes. The refrigerator components can be assembled inside. Submarines have changed over the years. The limit on mission is often the food. Large tin cans were stacked on the floor. Sailors walked on them until they were consumed. After everything was loaded potatoes were stored in one of the access hatches. If they went bad the smell was awful. Showers were very limited. The generator rooms were hot. There was a reason they were called pig boats. Nuclear submarines have a lot of power. So they can desalinate a lot of water. Much better duty.",
"I would think it depends on what that big item is and where it is installed in the submarine. Replacing the nuclear reactor would require some serious reconstruction. A fridge on a sub is likely a custom fridge assembled from modular components that fit through a hatch."
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5nb4fq | Why has my town installed dual traffic lights at a busy roundabout, I thought the point of a roundabout was to keep traffic flowing and replace traffic lights. | Engineering | explainlikeimfive | {
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"Roundabouts work very well when the traffic on both roads is approximately equal. Vehicles turning off one street create gaps in the traffic to let vehicles from the side street on, allowing an even use of the intersection. But if one road dominates with only through traffic, then side street traffic has no opportunity to get onto the roundabout. So occasionally they need to put stoplights on the through street, to allow cross-street traffic onto the roundabout and clear.",
"I don't know where you are, but in the UK, roundabouts often have traffic lights. Traffic lights on their own can cause a queue of people waiting to turn right (that's in the UK where we drive on the left - if you drive on the right in your country then there'll be a queue of people waiting to turn left instead), as well as traffic being forced to stop at a red light. Roundabouts on their own get around these problems. Traffic turning right (in the UK - left if you drive on the right hand side of the road) can enter the roundabout at the same time as everyone else and keep moving, and you only have to stop if there's someone on the roundabout that has right of way. But roundabouts on their own bring their own set of problems. At a busy junction, traffic on the roundabout has priority, which can make it difficult for traffic to enter the junction, and result in queues on all of the entrances to the roundabout. And if you're entering from a quiet entrance (where not many people exit) then it can be long wait for a gap when the roundabout is busy. Traffic lights at roundabouts attempt to solve all of these problems. They're often only active during peak hours, because the problems with roundabouts don't occur when it's quiet. But during peak hours, they can give some priority to joining traffic (but never so much that there's gridlock on the roundabout itself - it's important that traffic on the roundabout be given more priority), and they can also create breaks in the traffic so that it's possible to join from quiet entrances."
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5nbcqm | What a civil engineer does | My boyfriend's an engineer but every time I try to ask him what his job entails he gives me a super convoluted answer that I can't follow. So someone please, explain like I'm five. | Engineering | explainlikeimfive | {
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"How unlike a civil engineer to give a super convoluted answer to a simple question. /s. Seriously - I asked a civil engineer once how they like their coffee and they gave me a 20 page report. :-P The reason your boyfriend gives a convoluted answer though is because what he does is actually an extremely complicated job. The very short answer though is that they build stuff. Stuff like roads, bridges, tunnels, buildings, etc, etc, etc But it's not the actual building that they do (construction crews do that) - they more do work kind of like an architect but more complex - their job is to make sure that what is being built will fit into the environment it is being built in and will be suitable for the purpose it is being built in. Or (quite often) making sure that something that has already been built continues to be fit for it's purpose or can be repaired so that it once again becomes fit for it's purpose. For example: A civil engineer building a road will make sure it will be able to be built for the environment it is in (i.e. it won't crack or subside), that it will be able to handle the amount of traffic it will need, that the construction crew will actually be able to build it, etc, etc. And all of this with a budget about half of what he actually needs.",
"Civil engineers work on systems where the sum of the forces equals zero, i.e. there is *no* net acceleration. For example roads, bridges, dams. Mechanical engineers work on systems where the sum of the forces does not equal zero, i.e. there *is* a net acceleration in some direction. For example cars, trains, turbines, and all the moving subcomponents that make those systems work. Put more simply: civil engineers work on systems/structures that remain stationary (and need to resist outside forces and remain stationary). mechanical engineers work on things that move"
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5ncjzx | Where does excess power generated by solar panels go? | Say there's a house, completely off grid and self-produces 100% of its electricity. Now suppose with the use of solar panels it generates twice as much energy than it uses. Where does the excess power go? if it's not being used I understand with the use of solar storage solutions this isn't as relevant but yet again what happens when said storage solutions become full? | Engineering | explainlikeimfive | {
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"text": [
"I work in a building which is completely off the grid and is not connected to mains electricity lines. We have a row of twelve solar panels on the side of the building which generate electricity by absorbing the Sun's rays. The building's electrical appliances and lights don't use much electricity, so the panels can sometimes generate more electricity than is needed. In a room of the building, conneceted to the solar panels, are four large batteries. These batteries are similar to those you would find in a car but are larger and can store more electricity. The excess electricity not used by the building is pushed into and stored in these batteries. This means we can access that supply of electricity when the Sun is not in the sky or on cloudy days. In the event that the batteries were full and we weren't using any electricity, the solar panels system would stop generating electricity until it was needed again.",
"Solar panels will act as a heater if the power is not used. Similar to how an engine that is not connected to anything will just make heat and noise. The electricity will just be heating up the wires and the panels themselves.",
"It doesn't generate power that it doesn't use. Sunlight displaces electrons in the solar panel. If those electrons can't go anywhere then as each electron is moved there are fewer electrons left behind to move. Meanwhile the abundance of displaced electrons makes moving more electrons more-and-more difficult. Soon the sunlight is not moving any electrons at all. This is the same reason that batteries don't discharge (as fast) when the device they are in is turned off. It's also why your car battery might be _able_ to push \"500 cold-cranking amps\" but it is not normally moving anywhere near that much current. So the sunlight is a mechanical force. And \"voltage\" is \"electromotive force\" (that's the technical name for voltage). If nothing is using that voltage... if no \"current\" is being drawn... then the forces of electricity and sunlight reach equilibrium and the cells do _nothing_. So if your building has the _potential_ to generate twice as much power as it uses... it still only _actually_ generates as much power as it uses, and the extra potential is just meaningless. What normally happens in such a design is that you add batteries to store some energy for darker times, or you hook up to the grid and generate 100% of your potential, use half, and sell the other half to the grid. In other terms, I can reasonably lift fifty pounds, but I rarely lift more than ten. It's improper to ask \"what happened to the other forty pounds\" because they don't exist. That forty pounds didn't \"go anywhere\". It was never there at all. Same for the capacity of the panels to generate XXX current. If you only use the lessor YY current, then that's all that's generated. Same for your house on the grid. The grid _could_ supply enough power to melt your entire house in bright electric arcs. But since you never ask it for that kind of power it never happens. (And we have circuit breakers and fuses that prevent that request being filled if you should have something break and so ask for that kind of power.) So that's why turning off appliances and lights \"saves power\" by eliminating the place where such power might go, and so eliminating its actual production. TL;DR :: Electricity, when it piles up has \"back-pressure\" because that's how \"electrical charge\" works. That back-pressure slows or stops the generation of electricity in solar panels so that only as much as you use can actually be generated."
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5nfgnl | Why does gas you get in the US have so much lower octane numers than in germany? | Engineering | explainlikeimfive | {
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"Your octane numbers and our octane numbers don't mean the same thing. From an engineering perspective the octane number is actually a kind of hilariously arbitrary number that basically boils down a bunch of different fuel qualities, that all both individually *and* collectively control a fuel's likelihood to knock, all into a single number, and because of that the precise testing for octane numbers changes depending on the body doing the regulation. So it would be entirely possible for two utterly identical batches of fuel to get different octane ratings when tested by different countries. However, our fuels are also slightly different, as Europe is going to have a slightly different set of additives than we get in the US, but that doesn't really account for most of the difference; the differing standards do.",
"It's not. US and Canada uses RON(Research Octane Number)to measure octane while most of the world uses AKI(Anti-Knock Index). 87RON is the same as 90AKI for a reference point.",
"There are different ways of rating octane. The fuel is the same. From Wikipedia: Research Octane Number (RON) The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane. Motor Octane Number (MON) Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.[citation needed] Anti-Knock Index (AKI) or (R+M)/2 In most countries, including Australia, New Zealand and all of those in Europe,[citation needed] the \"headline\" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2). It may also sometimes be called the Posted Octane Number (PON). Difference between RON, MON, and AKI Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity,[4] and is not typically published for those countries that use the Anti-Knock Index labelling system. See the table in the following section for a comparison. Observed Road Octane Number (RdON) Another type of octane rating, called Observed Road Octane Number (RdON), is derived from testing gasolines in real world multi-cylinder engines, normally at wide open throttle. It was developed in the 1920s and is still reliable today. The original testing was done in cars on the road but as technology developed the testing was moved to chassis dynamometers with environmental controls to improve consistency.[5]",
"In the US octane is calculated two different ways and then averaged over those calculations (IE (rating1 + rating 2)/2). What this does is show a \"lower\" octane rating for US gas in general compared to EU countries because in Europe they only calculate octane once (no /2). As for WHY we don't make more other octane levels rather than the \"standard\" 87/89/91 is because of cost. Not long ago I could go to *some* gas stations and fill up with 95 octane (Sunoco for example 20 years ago) if I so chose, but those days are long gone because no cars sold in the US require that much octane and nobody wants to spend extra money filling up with more octane than is required. You CAN however go buy cans of octane boost if you choose at pretty much any auto store which advertise up to 101 octane per tank.",
"Octane primarily deals with the ignition pressure of the fuel. Lower octane fuel will self ignite (without a spark) at lower pressure than higher octane fuel. Cars with engines that operate with high compression ratios (mostly turbo charged and otherwise high performance engines) need higher octane fuel so that the gas doesn't pre-ignite and screw up engine timing/efficiency/performance. Because if it pre-ignites the fuel in the cylinder, not all of the gas will burn off, so the exhaust mix is screwed up, which makes the sensors angry, and you use more fuel than you should, and you lose some output power. As someone who has almost exclusively had German cars, and a former employee of a Volkswagen/Audi/Porsche dealer, I can tell you that there are very few German cars produced in the last 25 years or so that don't require high octane fuel, because of high compression. So this is a factor, as well."
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5ni6x0 | How does a firearm with a three round burst know when to stop after its third round? | Engineering | explainlikeimfive | {
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"There are a lot of moving parts to explain, and it is difficult through text, but essentially when you pull the trigger a 6 notch cam wheel doesn't allow the trigger to reengage and stop the bolt until the cam wheel has rotated half way around. The reason that it is 6 notches and only rotates half way around is because there are four shallow notches and two deep notches in that wheel. In this order. Deep, shallow, shallow, deep, shallow shallow. When the trigger is resting in the deep notches it doesn't allow the bolt to engage, however when pulled it engages the bolt, firing a round, then the wheel rotates to a shallow notch which does not prevent the bolt from engaging and thus fires the second round, then the wheel rotates to the next shallow notch which again does not prevent the bolt from engaging and thus fires the third round, the wheel then again rotates but this time to the next deep notch which allows the trigger to prevent the bolt from engaging a fourth time. So each three round burst rotates that cam wheel half way around, bringing it to the next deep notch which brings the bolt to rest. There are more moving parts but this is a basic explanation. Anything further would require illustration. Note that this is pretty much the most basic version, generally referred to as the Eugene Stoner. There are many variations as well, some are much much more complicated, especially if the weapon has a fully automatic option as well.",
"I know just links are against the rule, but this guy made a video with animated graphics of the inside mechanisms so you can watch how it works! URL_0"
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5niiln | How is 'memory foam' (I.E. memory foam mattress, pillow) made? | Engineering | explainlikeimfive | {
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"This is actually more of a chemistry related topic, but essentially foams in pillows/mattresses are created from polyurethane foams. Two major chemicals are used in the polyurethane production and other chemicals are used to adjust the rate of reaction to tweak the final product. The first chemical is some form of isocyanate, if we're talking mattresses then this is a semi-rigid foam and probably uses Toluene Diisocyanate (TDI) in the reaction. The second major chemical is referred to as a \"Polyol\" (essentially this means that it has multiple OH (alcohol) groups on the molecule, meaning that there is a high variance in the type of molecule you can use). A catalyst (typically nitrogen based) is used to initiate a polymerization reaction between the isocyanate group and the alcohol groups. The reaction releases CO2 as a bi-product which produces bubbles and causes the rising of the foam. The presence of the CO2 throughout the foam is what causes the formation of the pores in the foam. The reaction continues until it is finished and cross linking can occur between the polymer chains to increase the rigidity. Like I said, other chemicals come into play such as surfactants, catalysts,etc. which will determine the overall foam product's rigidity, porosity,etc. This is a fairly difficult process to perfect and is actually considered one of the most difficult branches of chemistry. -Source: Worked in a polyurethane foam manufacturing company"
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5nkloa | What would happen if I put a burning matchstick in the petrol tank of a bike/car? | Engineering | explainlikeimfive | {
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"Most likely, nothing. The inside of the tank is full of gasoline fumes, sure, but that's mostly what's in there. There's not enough oxygen inside the tank to support a quick flash, much less a full-on explosion. Now, if the tank was completely empty of liquid and only had fumes in there and there had been time for some regular outside air to mix in, then you might get something. The proper stoichiometric ratio for gasoline to detonate is about 15 parts air to 1 part fuel, so you need a *lot* of air in the tank to get a proper boom.",
"Generally nothing. The same thing holds true for cigarettes. They do no burn hot enough to ignite most things. Hollywood just loves to shoot scenes with flame and exploding vehicles."
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5np5xn | Argument that oil bi products used to make and maintain wind turbines makes them just as environmentally problematic as oil. | Engineering | explainlikeimfive | {
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"It's called a \"Life Cycle Analysis\", which means understanding and calculating the amount of energy and costs associated with producing components, shipping them, maintaining them, and then eventually disposing or recycling them. It's a way to measure the true cost. It's a similar argument that says a Honda Civic has less of a life cycle impact than a Hybrid."
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5np80n | How Medieval/Ancient large kitchens worked? | Engineering | explainlikeimfive | {
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"Well, before the invention of the wheel, you didn't really have civilization, and so no armies. You had maybe warbands. Before the steam engine - there were still mechanical advantage devices. Gearing and waterwheels go back to Ancient Greece at least, and you could tie some mules to a harness and have them walk around in a circle, driving the main wheel. Mills used water or wind power. And yes, a gigantic amount of manpower. For every soldier in an expeditionary force, there were several people doing the background work. But yeah, in those days the scale of war was severely limited by logistics. You've heard \"an army marches on its stomach\", and it was a lot more literal back then. Many of the great campaigns of history were not amazing because of the strategic abilities of the commanders, or the tactical superiority of the troops and their equipment - that played a part, but people would learn from each other's successes - but from the logistical abilities of the army to get food to the front lines. The Romans conquered the known world not because their troops were unbeatable - they certainly suffered defeats in individual battles - but because they built roads, had engineers, and could deliver food, water, construct a functional camp every night. The Mongols conquered the known world not because their troops were unbeatable - they were tactically dominant on the plains, but not in bogs or mountain passes - but because every warrior carried his entire kit on his horse and could forage for himself, so they were not dependent on vulnerable supply trains. Napoleon was defeated in Russia not because the Russians had superior generals (they had a few very good ones, sure) and not because the Russian troops were especially tough (they were fighting on home turf, sure), but because the Russians burned everything in Napoleon's path on the way in, and again on the way out. Hunger and disease always killed a lot more people than combat."
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5ny7ep | Why do we need so many different types of screw heads? Straight, Phillips, Torx, Square, Hexagon, etc... couldn't we settle on just a few? | Engineering | explainlikeimfive | {
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"They weren't all introduced at the same time, and therefore have to compete with each-other for market share. Originally there was only flat-head, this is because you can make a flat-head screw and driver very easily. Before there were different types of screws, they called the driver a \"Turnscrew\" Then somebody thought to themselves \"If there were two slots, like an X then the Turnscrew would be a bit harder to make but wouldn't slide out of the screw all the time. (this guys name was probably Phillips, not actually sure though) This idea worked quite well and so there were now two standards. They both co-exist because X is definitely better to work with, but the slot is always going to be cheaper and easier to make. Eventually a third person decided that the way that Phillips pops out if you apply too much torque is sub-optimal, so they came up with Robertson (Square type) This system managed to catch on quite well, but not become very widespread. This type is a little more expensive to make the screws than Phillips, but a little cheaper to make the drivers too. Now we have three competing standards. All of which have their strengths and weaknesses. All of which are able to take a viable slice of the market and compete with each-other. The other standards you've mentioned all came into the market in a similar manner, but I'm telling the story of the big three types because it's way simpler to explain the concept that way.",
"The simplest screw head, the flat head, allows your tool to slide out at the slightest misalignment. Phillips heads solved that problem, but introduced another: the screws strip easily when the driver cams out due to excessive torque. Newer designs have different balances of torque protection, size, manufacturing ease, etc. You also have a bit of this going on: URL_0",
"There's a lot of reasons, and many other answers have hit the high points. In general, \"sophisticated machinery\" means \"it's more expensive to make.\" * \"Flathead\" screws were created first because they're the easiest to make and didn't require sophisticated machinery. * \"Phillips head\" screws were created later because it takes more sophisticated machining to create them. They're easier to screw in than flat heads, but can be subject to \"stripping\" that makes reuse impossible. * They are, by design, subject to a problem called \"cam-out\", that means the screwdriver might slip and stop applying force. In good Phillips screws, this stops you from over-tightening the screws. In cheap Phillips screws, this makes it impossible to properly tighten them without stripping. * \"Robertson\" screws were created to deal with the stripping problems of Phillips heads, but take more sophisticated machinery to create. * Torx and Hex screws are alternate ways to try and address the problems with Phillips heads, and also require sophisticated machinery. (I think it's possible Torx was trademarked * Robertson, Torx, and Hex are more resistant to \"cam-out\". That means you're less likely to strip them, but you can also over-tighten them without a more sophisticated screwdriver designed to prevent over-tightening. * A few other head types exist and are called \"security bits\". The goal here is either to make a screw few people will have a screwdriver to turn, or in some cases make it very difficult to unscrew the screw without causing damage. These are for applications like public restroom stalls, where you don't want vandals to unscrew your screws. Common security bits have tri-wing, square, and triangular heads, but many tighten-only screws have drivers that look sort of like bottle openers. So the reasons so many heads exist are: * Some screws are really cheap to make, and the cheapest possible solution will always exist even if it's very bad. * Some screws were designed to be easier to use than the cheaper ones, but are more expensive and have varying problems with over-tightening or stripping. * Some screws are designed in the hopes that you don't have a screwdriver for them, so you don't mess with them. That's sort of why a lot of car mechanisms use different screws on one part. The manufacturer is trying to make it so the average person with a cheap toolset won't be able to properly disassemble and reassemble the mechanisms. But the licensed, \"qualified\" mechanic's shop will have all of the necessary tools. Don't ask me why they tend to replace all of the screws with inferior, half-broken ones. That probably has to do with the \"cheaper\" reason.",
"Different tools for different jobs. A standard screw is simplest and works will with hand tools. A Phillips screw is good with a machine driver, because it is less likely to slip. A Torx screw is less likely to slip than a Phillips, so it is better when a screw has to be really tight, but it is harder to align initially. A hex screw is good when you are selling assemble yourself furniture and way to provide a single cheap tool that can do all the work.",
"The older ones are simpler to make the screw and the tool. As machining methods have improved we've been able to design more complex screws/drivers to overcome the flaws in the old designs. The old designs are still used because they are very inexpensive to make and there are no licensing fees associated with the design. Edit:[ Informative Wiki article]( URL_0 ) listing types, uses and history"
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5o10mp | how do touch lamps actually work? | Engineering | explainlikeimfive | {
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"There's a tiny amount of electricity running through the lamp. When something touches the lamp, a little of that electricity flows into it, changing the current. Different materials cause different changes to the current. Human skin contact causes a pretty predictable change, so if the lamp detects a change that matches human skin, it toggles on/off.",
"Your body is a mediocre capacitor. However, a circuit can charge the outside of the lamp and detect the small current into your body when yu touch the lamp. You leave charged up, but not as much as a winter carpet spark, and the light turns on."
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5o32nk | How are rocket stages relit? What goes into the relighting process? | Is there a chemical? Or does it just... light up and continue? | Engineering | explainlikeimfive | {
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"SpaceX to ignite and reignite its Merlin engines uses an hypergolic mixture of triethylaluminum and triethylborane (TEA-TEB), which is what produces the green flash moments before the engine(s) are lit. Hypergolic means that the two substances react with each other nearly instantaneusly without any other input producing a flame that in turn will ignite the propellent and start the engine."
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5o3px5 | Why do screws/bolts/nuts get loose and have to be tightened, in the first place? | It happens so often, you have a mechanical problem because a bolt holding two things together has become loose, letting something wiggle around. But how do they become loose? It doesn't ever seem there's any pressure on the join in the direction that would cause a screw to turn, but they're always farther down the threads than you left them. | Engineering | explainlikeimfive | {
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"It can be caused by many different things. It has to do with motion of course. I have a wooden chair I use all the time. It squeaks and twists and after about 6 months a screw will fall out and I'll tighten them all up. It's just wear and tear really. Even on industrial machines rattling or a motor vibration will over time but very slowly push the screws out."
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5o5gob | can someone explain the lifecycle of a skyscraper (how long are they designed to remain structurally sound, what factors affect their longevity, etc.)? | Engineering | explainlikeimfive | {
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"Outside of Las Vegas they are expected to last hundreds of years. Keep in mind most buildings if properly maintained will will last until something catastrophic happens to it or maintanence stops and they decay and become unsafe.",
"Structural Engineer here. The design life of a structure is determined in coordination with the person building it. Whilst having a building that can survive any wind or earthquake event imaginable would be ideal, the trade off is increased construction cost, so normally people go for the minimum allowed, unless the building is needed post disaster. In my country, we typically design for what we call a fifty year design life. For typically buildings, (not hospitals or other important buildings) a fifty year design life relates to a 1/2500 annual probability that a large wind or earthquake event would occur. The longer the design life, the opportunity for a large event becomes more likely, so the structure needs to be come stronger as a result. So in terms of actual structural performance, the structure can survive indefinitely (with maintaince), until the large scale event occurs. The second issue affecting the longevity of a structure is corrosion. Steel obviously rusts over time, so left unintended over time steel will corrode, and eventually break. This can be prolonged with regular maintenance (i.e. Painting or other protective coatings), but eventually the steel will corrode and fail (spectacularly). You can continually swap out rusted steel for new steel, but at some point this gets more expensive than its worth. Happy to talk further if you have follow up questions."
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5oilam | How is Geometric Stiffness different to Young's Modulus? | Engineering | explainlikeimfive | {
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"The basic difference is that Young's Modulus \"E\" is a material property, and the geometric stiffness \"k\" depends on the geometry of the situation as well as the Young's modulus of the material. Specifically, k = E * A/L, where A is the cross-sectional area and L is the length of the specimen. This relationship makes sense physically: if you think of the resistance of a spring to being pulled, a thicker or shorter spring will be more stiff. A spring of the same dimensions will be more stiff when made out of steel than out of rubber because E of steel is much larger than E of rubber."
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5ok7ls | What is an NP-Complete problem? | Engineering | explainlikeimfive | {
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"Some computational problems are known to be \"easy\" to *verify answers for*, for a very technical definition of \"easy\". We call this the problem class NP. NP-hard is a related class of problems with the property that any problem in NP can be translated into an instance of an NP-hard problem using an \"easy\" algorithm. This means NP-hard problems are *at least as \"hard\" to solve* as *the hardest problems in NP*. After all, since the translation is \"easy\", we can solve any NP problem by translating it and then solving the NP-hard problem instead. NP-complete is yet a third class of problems, but it's simply the intersection of NP and NP-hard. That is, it's the NP-hard problems that are themselves \"easy\" to verify answers to and are therefore in NP themselves."
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5opmg8 | How do laser scanners at checkouts work? And how are the scanners by the door set off by unscanned items if they can't see the barcodes? | (I chose the 'Engineering' flair for this question because 'Magic' wasn't listed as an option) | Engineering | explainlikeimfive | {
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"Theft detectors at the door are set off by magnets, not barcodes. Usually expensive items have some sort of theft prevention device that consists of a large magnet that can only be removed at the registers; if you don't buy it, it's not removed, and sets the alarm off.",
"So it seems no one actually answered both questions. The scanners are just cameras that look at a bar code and take the pattern of the white lines and converts them into a number that the computer can find in a database to match to a product. The different spacing and thicknesses change the value. The alarms at the door are scanning for rfid tags. They send out a radio signal that the rfid tags respond too. When the tags receive the signal they use it to power up a weak response signal that the alarms scan for. The magnets they swipe the tags over just wipe out the rfid tags."
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5oqw4i | If man has only drilled as deep as 12 km into the Earths crust, then how do we know of all the layers that define the Earths core? | Engineering | explainlikeimfive | {
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"text": [
"Earthquakes. You know how light bends when it passes from one medium (say, air) to another (water, for example)? Shockwaves do something similar. When there's an earthquake, the shockwaves are detected [in many parts of the world]( URL_0 ). By measuring them carefully, scientists can figure out the path they took and what kind of materials they passed through, allowing them over time to build up a fair model of what's inside the planet. Add to that a lot of other observations, like the existence of a magnetic field, and some basic scientific rules about how different materials behave at different pressures and temperatures, and scientists can make some pretty good guesses as to what the internal structure must be.",
"Geophysics! - The mathematically based study of various physical properties of the Earth. This is then elaborated on with mechanical and chemical lab experiments, and data fed into numerical models to get the best picture of what's down there. In fact, we've had some idea that the Earth's centre had some crazy dense stuff for a long time - Newton's maths of gravity can give us the mass of the Earth. Divide this by the volume and you get the average density of the Earth, which is well outside the range of rock densities seen at the Earth's surface. Even the deep rocks occasionally belched up by volcanoes or exposed in certain places were not dense enough to account for the average density, so it was long hypothesised that a much denser core existed. Fast forward to the second half of the 20th Century and we started to use seismic waves to get an idea of our Earth's structure. This has been the most fruitful method - specifically, timing how long the waves take to travel through various parts of the Earth reveal changes in density (some sharp, some graded), as different materials have different physical properties and so change the speed of wave propagation. The fact some waves do not travel through part of the Earth at all indicates that it is molten - this is the outer core. Shear waves cannot propagate through this liquid outer core as they move via deformation of the medium, and liquids have no rigidity to deform. The global network of seismometers used to detect all this is also used to detect nuclear tests. This network and the computing power used to process data from them has advanced sufficiently to allow a sub-field known as seismic tomography - in which cross sectional images of the Earth's implied density and temperature (which also affects wave speeds) can be produced at a higher resolution than other seismic wave studies, giving a three dimensional view of structures such as rising plumes through the mantle if the cross sections are stacked. The actual composition of the Earth's layers has been determined by observing how various materials behave when subjected to high pressure and temperature experiments in the lab. The graded changes in density occur due to elements getting squished together with increasing pressure in the Earth to form different minerals the deeper you go (but made up of the same elements). The sharp changes in density occur due to a change in the elements that make up that particular layer. Iron fits the bill for the Earth's core as it has to be a metal (to produce the magnetic field), and it also stands up to predictrd density at the relevant temps and pressures. Iron also fits in a cosmic sense - there is a lot of it in the universe due to it being the end result of fusion in stars, and our solar system is no exception - we have iron based meteorites assumed to be fragments of proto-planetary cores from the early solar system."
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5ou410 | How does my cars steering wheel always re centre itself after making a turn? | Engineering | explainlikeimfive | {
"a_id": [
"dcma7e7"
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"text": [
"If you look at a motorcycle front wheel it is aligned at an angle relative to the handle bars. Such an alignment makes the wheels want to center themselves. The same thing is done with car wheels."
],
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3
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5owy9a | Why does SpaceX land their rocket on a barge on the ocean? | Why not land on flat, stable land? | Engineering | explainlikeimfive | {
"a_id": [
"dcmni12",
"dcmqir2",
"dcmrdyg"
],
"text": [
"Because landing on land limits the places you can take off from and the direction you can point your rocket. I believe the first successful test of the rockets did have them go on land, but the goal is to let the rockets take off in the most efficient places to put their payloads into orbit. If that means taking off over the ocean, then they need to have a landing spot on the ocean.",
"It primarily has to do with fuel. To get back to land, the first stage must burn more fuel to do an about face. This is fuel it doesn't have to spare if it needs to get the satellite to geostationary (a higher) orbit. Therefore it is easier to just 'keep going' in a parabola shape and land in the ocean. For low earth orbit, like ISS resupply missions, it has enough fuel to do that extra burn and return to land.",
"Your launchpad is in Florida, and your launching eastward. There happens to be a big ocean eastward of Cape Canaveral. Nowhere for you to land on. If you flew all the way back to the launchpad, that means you have to carry more fuel. If you just turn and execute a burn to eliminate forward momentum, that gets you to drop straight down and land on a barge in middle of ocean."
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5oxfe9 | Technical debt | what is this? A lot of my engineers at work talk/complain about it but I don't really understand the concept | Engineering | explainlikeimfive | {
"a_id": [
"dcmwtov",
"dcmri4c"
],
"text": [
"Technical debt is the software engineering buzzword for taking shortcuts that come back to bite you later. Now, maybe you *had* to take a shortcut to launch your thing on time, or maybe you're just a lazy POS. In my experience in software, it's a 50/50 mix. Here are some possible types of technical debt (not an exhaustive list): * Lack of tests. This is important for projects with large teams because the original author of some code isn't necessarily going to be there to review changes from other team members. The reason this is debt is because future well-intentioned changes could cause a regression in behavior, which will waste significantly more time with rolling back builds, finding culprit changelists, rolling back code (or fixing forward, not recommended 99% of the time), finding the bug, and rolling forward. * Poor encapsulation. Encapsulation is the idea that a chunk of code should be mostly self-contained, with anything not self-contained being established and documented. Think of it like an electrical system in a house: External influences are well documented (different plug types), the main logic lives in one spot (breaker box). However, let's now imagine that, because it was easier to do at the time and it saved construction time (somehow), the only way to reset your breaker box is to flush your toilet. This would be an example of poor encapsulation. (Now let's say you had to replace your toilet, and... oh no, you have to completely unwind your electrical system to be able to get at the toilet. Looks like a weekend project just became a 2 week project.) * Hacks. A hack is a form of a shortcut taken because it's trivially easy to do, even if not a great idea. [Here is an example of a hack outside of software.]( URL_0 ) This could be a fairly well-contained hack (like say calling a function that hits your server infinitely until it works instead of backing off if you detect an outage, since you just have to delete that one chunk of code and rewrite it), or it could be systemic (\"If I just give the whole application access to these bytes, it will be way easier to set them from all over the application,\" now you have to rewrite your whole application to fix it). Hacks are incredibly insidious in code, and often lead to more hacks. If a hack is fixed right away, then the cost of the hack was the time spent adding the hack plus the time spent doing it right. Often times, laziness or downward pressure from leadership results in people adding more hacks to work around existing hacks. If you wait long enough for more code to depend on the hack, now you have to spend the time to redo everything around it right, in addition to the spent doing the original thing right. I've seen many projects at my place of employment slowly die due to accruing technical debt. As it grows, your ability to get work done in a timely manner shrinks, until you're spending 3 months getting something done that should have taken a week at most.",
"It's a common agile software term. When you start making part of a program before other parts, you do work (spend $) and you get a part of the software. Let's say it's 1/2 of the software. Later on, when you're figuring out the next chunk of software, you notice that 10% of the code you already made has to be redone. This \"technical debt\" of 5% of your project is a debt you took on (perhaps without intending to) when you implemented the first half of the code."
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5oy2ek | How does tap water get to your house? | Engineering | explainlikeimfive | {
"a_id": [
"dcmxo3w"
],
"text": [
"Basically, you have the water lines in the streets. These are large, high-pressure pipes, carrying fresh water. So, when a new house is built, the company who laid those pipes adds a new, smaller pipe to your house. That water is distributed over many small lines inside your house. Now, there is different systems. Either A) the pressure is sufficient to reach all endpoints(taps, shower etc.) Or B) you have a Pump underground that adds pressure to it. This one is the more common one. Now, to have equal pressure between all taps and floors, generally there are systems in place to keep the pressure on the same level in the house. Though, for showers you have more pressure, usually resulting in a higher flow rate. I hope this helped."
],
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3
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5oyqrp | Why [in the US] is electricity run by private corporations? | Engineering | explainlikeimfive | {
"a_id": [
"dcn48pr",
"dcn5anu"
],
"text": [
"Lots of states allow for a company to own what is essentially a monopoly on a utility in exchange for the government having tight reins on the prices that the utility can charge. The advantage to having a private company running the utility is that they have more incentive than the government to run efficiently. If the management of a utility can cut costs by 5%, the company gets extra profit to invest in new business, and the management personally gets more money. If a government body cut costs by 5%, then that money goes to the government and the organization typically doesn't see any of it. There's less incentive to fire people who do poor work or find new ways to save the customer money because there is no extra profit to be made. It's worth mentioning that utility companies typically don't have a lot of margin. They're often considered \"old lady\" stocks because, although they reliably make a return on investment and seldom crash, they're almost never going to see the growth that a non-utility stock can. As a result, the long-term return on investment tends to be a bit low.",
"Let's say you and your school buddies want a new swing set for the playground. But even if all of you saved every penny of your milk money, you'd never be able to afford one. So instead, you go to the swingset guy and say \"if you build is a swingset, we'll pay you out of our milk money to use it.\" Well the swingset guy doesn't think this is a very good deal. After all, if you can't afford to build one yourself, he's not going to make his money back for a very long time. So you make a deal, he'll build the swingset, but no one else is allowed to build any playground equipment until he has made back all of his money. Well now that's not a very good deal for you. With no other playground equipment, he can charge whatever he likes for access to the swings. So you make the deal, he can only charge a fair price, that you and your friends agree on, and he can have control over all the playground equipment. That's how the utilities were built."
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5p0bag | Explain how electrical grounding works. | I've studied physics upto a high-school level, so this is what I know: * Current only flows in closed loops (Kirchhoff's loop law). * High current kills humans. From general safety tips, I know: * If the human is in contact with the Earth (like if he's barefoot on a concrete floor) ... * If a human then accidentally touches a live wire (like in a malfunctioning iron) ... * Then high current will kill the human (entering the Earth / ground). Further: * *Earthing* makes the iron contact the Earth through a wire. * If a malfunction happens, current will harmlessly flow through the earth wire, saving the human. However, I have to ask: **Why does current even flow into the ground?** The current should want the shortest route back into the circuit, and back to the power plant. A detour through the earth itself seems like the longest possible route (resistance-wise, of course). Could someone please draw a circuit diagram to explain how earthing works? [I've attempted this]( URL_0 ). I've reduced the human, iron, and Earth to resistors. The power plant is a resistance-free AC voltage source. All power cables are assumed to be resistance-free. To me, the concept of shocks/earthing only works if: * The AC voltage source is deliberately connected to Earth. * The resistance of the earth is very small (similar to that of an iron or human, in the Ω to MΩ range). | Engineering | explainlikeimfive | {
"a_id": [
"dcnfupd"
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"text": [
"The concept of \"current only flows in closed loops\" is just wrong, when taken out of the concept of circuits. The reason we can say this is because the way current *actually* works in that you get a buildup of electrons. If you just have a battery with a wire attached to one end, the electrons push out to the end of the wire, but then have nowhere to go, and all the electrons behind them get backed up like a traffic jam. If you connect that wire to the other end of the battery, then the electrons can move forever, since always moving \"forward\" will be possible in a loop. Grounding stuff breaks this \"rule\" because of what an electron ground is. Electrical grounds are basically giant empty spaces where electrons can funnel in. They *can* move in because there is effectively always space for them, whereas on something like a thin copper wire they run out of room really really quickly."
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5p0uwu | 911 planes. If the two planes that hit the twin towers did not go through either buildings. How come the plane that hit the pentagon went through 3 structures (6 concrete walls? | Engineering | explainlikeimfive | {
"a_id": [
"dcnjh90",
"dcnqah1"
],
"text": [
"Steel is stronger than concrete. And the plane had more velocity due to flying at a downwards angle. Extra line Extra line Extraline",
"Civil engineering student here, skyscrapers have far stronger supports than low-level buildings like the pentagon, concrete crumbles under non-compressive stress (ie a wrecking ball or plane going through the wall), steel is stiffer and greatly deforms before breaking."
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5p36iz | Is an electric shock safer to withstand while wearing shoes, standing on solid ground - or safer if standing knee deep in the water/river? | Not sure how it works. But in other words is it safer to let the current flow past (standing in the river), or resist it through e.g. rubber sole shoes? | Engineering | explainlikeimfive | {
"a_id": [
"dco2knu"
],
"text": [
"The former is better if we are talking about limiting the current going to ground through you in a situation like touching a live wire with only one hand. If you are actually well insulated from ground no current will flow and you won't get shocked; lineman servicing power lines can touch wires at many kV because they take all the precautions to remain insulated from ground and obviouly avoid touching at the same time the neutral conductor (which is also normally referenced to ground). If however you touch a live wire with one hand and offer a path to neutral/ground with the other it doen't really matter where you are standing or what you are wearing because the current path will be from hand to hand through your torso. EDIT: Thanks /u/whitcwa"
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5p6p49 | why does the tech industry advance so much faster than most other industries? | I feel like every 2 years our technology is almost transformed. 10 years ago I would never imagined the technologies today (Alexa, Surface Pro whatnot) yet most other industries has not experienced this rapid of a growth. For example, in the medical industry, we are still using the same antibiotics we did 20 years ago. Why is this? | Engineering | explainlikeimfive | {
"a_id": [
"dcov4vj"
],
"text": [
"The fastest innovations in tech are in the area of computers and software. The reason innovation happens so fast in that space is that the cost to building and trying out an idea is so small. If you think of an idea, you can try it out and build it right away. Compare that to something like medicine, where it takes years to figure out if a drug is working or not - or mechanical engineering, where it might take weeks or months to physically construct a device or machine to test out an idea. In software, you can think of something, program it, and try it out immediately. That leads to rapid iteration and much faster development cycles."
],
"score": [
5
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5pa02a | How are/were bridges built over large bodies of water, both now and before modern technologies? | Engineering | explainlikeimfive | {
"a_id": [
"dcpo99q"
],
"text": [
"That depends entirely on the type of bridge. Three famous bridges under construction. [Sydney Harbour Bridge]( URL_0 ) [Golden Gate Bridge]( URL_1 ) [Millau Viaduct]( URL_2 ) Over water or not, build the supporting structure first ('cos that's the strong bit) then build the road."
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"http://images.mentalfloss.com/sites/default/files/styles/insert_main_wide_image/public/2698614.jpg",
"https://upload.wikimedia.org/wikipedia/commons/d/d8/Millau_Viaduct_construction_south.jpg"
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5pc0dj | When ships get 'sold for scrap', how exactly are they broken up into spare parts? | Engineering | explainlikeimfive | {
"a_id": [
"dcq00es"
],
"text": [
"I once saw a very disturbing documentary about a place in India where they send these massive hulks, and virtual slave labor is breaking them down, I think they have to use welders to break them apart."
],
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3
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5pkmm7 | What happens if you put the wrong fuel in your car? Why is it so bad for the car? | Engineering | explainlikeimfive | {
"a_id": [
"dcruqac",
"dcrx1bg"
],
"text": [
"wrong fuel? like diesel? wouldnt burn, I imagine it would pool in the cylinder, eventually freezing up, maybe damage something. wrong octane? too high of octane, no big deal, just wasted money. too low, some cars will adjust their programming to compensate. those that dont will detonate the fuel before the piston hits the top so the explosion is literally trying to turn the engine backwards. Thats not great (wont destroy it immedietly, but puts extra wear on things)",
"Diesel in a gas car isn't so bad. Gasoline engines can't burn diesel, so the engine will simply stop running. You'll have to get your fuel system flushed of the diesel but there won't be any damage. Gas in a diesel engine, on the other hand, can cause significant damage. The gasoline will detonate early and damage the engine."
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5pl2qe | Why do piston driven airplanes still use leaded fuel instead of using unleaded fuel like all modern automotive engines? | Engineering | explainlikeimfive | {
"a_id": [
"dcrymrz"
],
"text": [
"Here's a pretty good article about it. Basically, until an affordable and proven alternative is developed, they'll keep on using it in piston-driven aircraft. URL_0"
],
"score": [
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"text_urls": [
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|
5pm1ir | If horsepower is calculated from torque (and RPM), then why do some engines have more horsepower than torque while some other engines have less horsepower than torque? | (Note: I'm referring to peak horsepower and torque here. You know, the numbers all car manufacturers advertise.) | Engineering | explainlikeimfive | {
"a_id": [
"dcs87va"
],
"text": [
"The formula for calculating horsepower is HP = Torque x RPM / 5,252. That means at 5,252 RPM, horsepower = torque as measured in lb-ft. However, the amount of torque being produced will be different at different engine speeds. If an engine makes the most torque at a high RPM (i.e. a motorcycle engine,) the resulting peak horsepower calculation will be high. If the engine makes the most torque at a low RPM (i.e. a semi truck engine,) the peak horsepower will be much lower than the peak torque."
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3
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5pux9z | Why do heaters vent air from the ceiling and not from the floor? | Engineering | explainlikeimfive | {
"a_id": [
"dcu23wu"
],
"text": [
"I'm not an architect or civil engineer, but I have lived in many places and in my experience home ventilation systems are more related to the climate of the area that the building is in. For example, all the new constructions I saw in North Dakota had vents in the floor; whereas in Phoenix, where I currently live, most new homes have the vents in the ceiling. In North Dakota, the AC will almost never be used, however heating is used 8-9 months out of the year. Since hot air rises, you want the vents in the floor. In Phoenix, the heat is never used, but AC is running about 6-7 months of the year. Since cold air sinks, you want the vents in the ceiling. Also, as the other person said, the architecture also comes into play. I doubt you will ever see floor mounted vents in a basement or industrial building. This is because the foundation is going to be several feet of solid concrete. And good luck running ducting through that. When you look up in an industrial building, like a supermarket or office tower, you are not actually seeing the ceiling. There is many feet above the false ceiling you see that is used for ducting and wiring. In these applications, venting from the ceiling is a matter of practicality. You could conceivably run ducting down through the wall and vent at the bottom of the wall, but that would be an unnecessary cost and no sane building owner would pay for that."
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5pwpox | Why do flight attendants request that airplane windows be open for landing? What effect does it have on anything? | Engineering | explainlikeimfive | {
"a_id": [
"dcue0j8",
"dcue3xv",
"dcuf38n"
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"text": [
"There are several potential reasons: * It provides a way for emergency responders to see into the plane in the event of a crash. * It provides additional light (useful if there is heavy smoke) for the flight attendants to more easily ensure no one is left in a row during an evacuation. * It provides occupants of the plane a way to see outside and have more information to judge the conditions outside an exit door which may not have a large window.",
"It allows you to see out the windows so you can follow what happens. If there is a crash you might see it outside the windows before the pilots have a chance to warn you, you might also see if you crash in the water or on land and take on your life jacket. When you have crashed you can see what the condition outside is before you evacuate. Is there fire, water or jet fuel on one of the sides so you should avoid opening the doors. Is the fire department already outside so you should let them handle the fire before you evacuate. When you evacuate what conditions can you expect outside the plane. And lastly the rescue workers can see though the windows if there are people or fire inside and direct their efforts accordingly. They might for instance have the tools to break though the hull of the aircraft and spray the inside with foam but this can be dangerous for the people on the ground and inside so you do not want to do this unless there is a fire and people trapped inside. And you want to extinguish the fire and not waste time and foam on areas where the fire have not spread to.",
"Same reason my grandmother insists I wear tennis shoes when I fly. Helps with a crash situation about 1%."
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5pyieh | Why hasn't the Flint, MI water issue been fixed? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"To really understand the answer to that, you have to understand what went wrong in the first place. The city, decades ago, used cheaper lead piping for much of the city's water supply. That in and of itself *sounds* terrible but is actually not so bad: the lead doesn't corrode into the water easily, and the pipes were treated to prevent that. It's something that *could* be a problem if mishandled but is not necessarily a problem by itself. The mishandling came when the city council opted to get water from the local Flint River instead of being supplied by Lake Huron via Detroit like they were. The water in Flint River was significantly more acidic and had naturally occurring chemicals that corrode piping. Again, sounds terrible but as long as you don't have lead piping, it's not a big deal. Except, of course, Flint *does* use a lot of lead piping. This could have been avoided anyway if the water had been treated properly to prevent the corrosion, but it was not. That corrosion is what caused the huge spike in lead found in the water. The pipes lost their protective coating and began corroding, which dumped all the corroded lead directly into the water. *There is no fixing that*. Flint had long since switched back to getting their water through Detroit, but the damage was done. Once the pipes started corroding, you can't go back and fix it. It's like getting a scratch in the paint in your car and the metal starts rusting, and the rust starts seeping under undamaged paint and causing it to flake off, which causes more rust. Except your car is underground and you don't know where it is. Fixing the pipes means replacing the pipes, and for the most part, *no one knows where the pipes are*. They have a general area, sure, but the plans for exactly where the pipes were laid were made decades ago and a lot of them were lost or never updated with new construction. No one is sure which pipes are made of lead and need to be replaced and which aren't. That means tearing through roads, sidewalks, and property to dig up (and probably damaging) a lot of perfectly good piping to find and replace all the bad lead pipes that have to get fixed. [It's going to be expensive]( URL_1 ), [maybe exorbitantly expensive]( URL_0 ). Flint was never a rich town to begin with. That's what caused this crisis in the first place: the city council trying to save money on water. After the crisis, the people who could afford to leave have almost certainly all left, leaving mostly people who *can't* afford to leave. Think about what that means: they don't have enough money to leave the place where their drinking water is literally poisoning them. The city simply doesn't have the money to fix it. And it's not like their neighbor Detroit is doing well enough to give them money - and it wouldn't be a loan, Flint can't afford to pay back a loan anymore than they can afford to pay for it themselves.",
"There is no quick or easy fix for it unfortunately. The incorrectly treated water created a corrosion problem in the pipes of the city, causing them all to leach lead into the water system. Without a top to bottom overhaul of the entire cities water lines, the problem can't be fixed. That will take approximately a decade, and will cost millions if not billions of dollars.",
"The damage was already done when they let the corrosive water into the system. That stripped away protection preventing lead from leaching into the water from old piping systems. They did switch back to Detroit water almost as soon as the issue was noticed, but that doesn't replace the protective mineral layer around the pipes. To fix it \"tomorrow\" would be to spend a billion dollars pulling out and replacing literally every pipe within the city water system. You need to pay a team of engineers to redesign the pipes to modern standards, purchase the actual pipe, pay a crew to install it, and also pay homeowners for destroying their front/backyards. This project will take years. The only other alternative is to simply keep running water through the system to allow the mineral layer to build back up. Eventually the old pipes will be OK, and lead levels will go below EPA levels. This process will also take years. Unfortunately, Flint isn't exactly a booming industrial town as it was a few decades ago. Their electorate voted for a city administration that promised to cut costs no matter what, which included switching water supplies. Yes, this was a fantastically bad call, as they saved more money by not paying for engineering studies that would have said as much. They also ignored their city water engineers who said it was a bad call. Those officials are being punished in due course. While we'll all feel super bad for them, it's tough to justify kicking out a billion dollars on their water system instead of 50 new schools literally anywhere else. They'd stand a better chance at getting credit to move out of Flint and relocate, as that would cost the taxpayers millions instead of billions."
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"http://www.usatoday.com/story/news/nation-now/2016/03/05/flint-water-crisis-could-cost-us-300-billion/81359834/",
"http://www.freep.com/story/news/local/michigan/flint-water-crisis/2016/05/27/flint-lead-lines-water-crisis/85032096/"
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5pyswe | Do I really need an oil change every 3000 miles? | Engineering | explainlikeimfive | {
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"Mechanics would love your business every 3k miles. [It's such a myth there's a dedicated Wikipedia page for it.]( URL_0 ) Refer to your owners manual for guidelines. I recommend that if you drive regularly (you commute 5 days a week), get your oil tested. Google an oil testing or analysis lab, some of them will give you your first kit free. They'll tell you a whole lot about how your engine is operating, and if it's time to get your oil changed. Use that as a guideline for your use case. I know that some cars combined with synthetics don't get an oil change for 10k to 15k miles. The rule of thumb now days is closer to 7k miles, even with petroleum oil."
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5q0wzm | How, if at all, are traffic lights coordinated within a proximal geographic area? | For instance does one light's timer take into account another one down the block or is each intersection its own individual node operating independently? | Engineering | explainlikeimfive | {
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"Sometimes traffic lights may be interconnected with other traffic lights and communicate with a control that helps ease traffic. Other times they operate by themselves some even use gears kind of like a clock to predict when to change. Most modern lights are digital though. URL_0 Edit: I found this information for you on Wikipedia. Midtown in Motion - New York City's adaptive traffic control system that employs multiple technologies. Cameras, microwave motion sensors and radio-frequency identification (RFID) E-ZPass tag readers are used as inputs as a mean to for monitoring traffic flow. The data is fed through the government-dedicated broadband wireless infrastructure to the traffic management center to be used in adaptive traffic control of the traffic lights.[29] Source : URL_2 URL_1"
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5q1g7t | How does an AA gun or a flak gun work? | In movies where air battles or bombings occur there are typically anti air guns shooting up at the planes. The rounds from the guns appear to explode around the same height as the plane with the occasional one hitting a plane. What determines when the flak round will explode, what causes the round to explode, etc. | Engineering | explainlikeimfive | {
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"Early models of flak shells had what /u/_YourPariah_ had. You figured out the altitude of the aircraft, then adjusted the timer on the shell to explode at the appropriate height. During the Second World War, the US and UK developed the Proximity Fuse, which worked like u/fofwalker says. Those shells detected an aircraft nearby and exploded. The new fuse was so secret, it was forbidden to use them on the continent for fear the Germans would get their hands on them. URL_0",
"I believe there's a timer in the rounds. Since you know how fast the round travels, it's pretty easy to calculate X number of seconds equals y number of feet in the air.",
"I'm no expert but I always thought that they had little radar devices inside of the rounds that would explode into shrapnel when near an airplane.",
"*I'm assuming you're talking about large calibre flak (such as the 8.8cm) and not lower calibre anti-aircraft guns that work the same as normal guns.* Flak shells in WW2 had 2 types of fuses, either a timed fuse or a barometric fuse. The timed fuse is pretty self explanatory and detonates when the timer expired. The barometric fuse on the other hand detonated when a certain (set) altitude was reached.",
"Timed fuzes, mostly. They generally knew what altitude the planes they were shooting at were flying, and how long it took for their rounds to reach that altitude, so they set a timer. The Allies also had proximity fuzes. They were essentially tiny radars that would detonate the shell when it got close. Very important to the war effort, almost on par with the atomic bomb.",
"The shells they are firing up at the planes have an adjustable fuse that can be set before firing to explode at different altitudes. The idea is to saturate the area around the planes with shrapnel and hope it hits the airmen, or something vital in the plane. Hitting a moving target with a purely ballistic trajectory is incredibly hard and timed explosions help even the odds."
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5q3kmd | How do bladeless fans like those made by Dyson work? | Engineering | explainlikeimfive | {
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"They have blades, they're just in the base. The impeller works like a conventional fan, and forces the air to the discharge ring where it is discharged to the room. (Specifically the impeller is a centrifugal or mixed-flow fan, judging by the image, not a generally accepted as \"standard\" axial propeller fan) URL_0 Now what it's doing at the ring is where the \"science\" is, because by discharging the air at a high velocity, it creates a low-pressure area at the discharge that induces room air into the discharge jet, effectively increasing the total airflow volume experienced by the user.",
"Dyson bladeless fans should really be called no visible fans. They have a fan, it's in the base of the device, not in the ring like a traditional fan. The fan in the \"bladeless\" fan pressurizes the air in the plenum that makes the rest of the base and the ring. The air is then shot out of a small crack in the ring. In theory the shape of the ring is like an aircraft wing, and creates a low pressure zone which draws in more air from behind the ring. Which is why they market it as an air-multiplier fan. URL_0"
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5q4ivg | Why are radiators often located beneath window shelves? | Seems to me like more heat would escape the room when the source is located in the least insolated part of the room, which furthermore has less mass to retain the heat than a wall. Or is my science incorrect? Please explain | Engineering | explainlikeimfive | {
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"you are almost right - it is usually the coldest spot in your room. But that also means, that this is the part of the room that is the hardest to heat. If you'd put the radiator at the other end of the room you'd have a very warm and cozy part of the room and the freezing part of the room right next to the windows. And to get the cold corner to a nice temperature you'd have to make the warm part of the room even warmer. Putting the radiator at the window leads to a more evenly distributed warmth in a room.",
"There are many reasons why. As said already, it helps with the heat distribution of the room by creating a warm buffer near the window to help minimize heat loss. This pocket of warm air insulates the rest of the room from drafts coming from the outside. It also helps decrease the amount of condensation on the window by keeping it warm enough to not reach the dew point. Space is also something to consider. Normally the area below a window is unused space so it makes sense to place the radiator there rather than take up space on another wall."
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5q5buo | will the imminent arrival of mass produced lab grown meat change the vegan perspective of meat eating. | Engineering | explainlikeimfive | {
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"This is such a common question over on the vegan subreddit they made it the first thing on their FAQ, and conducted a poll. The answer is that most vegans say they wouldn't eat it, as they're already used to and happy with their meatless diets. However, most *vegetarians* say they'd consider eating it, and both groups consider it a very positive step in reducing animal cruelty and are big proponents of it becoming cheap and viable as a meal option.",
"As a rule, serious vegans don't eat food that was produced by animals, even if they ae (largely) unharmed - no milk or cheese, some don't wear wool, eggs are out. For them, animal exploitation is the line they draw. So how will that apply to lab meat? Hard to say. It does come from a cell line extracted from an animal, so some will be opposed to it. Others will consider a one-time, painless extraction to be a small price to pay for potentially tons of cruelty - free, death-free food. We'll have to see.",
"Depends on the vegan. Some don't eat mean for moral reasons, some for health reasons, and some because their don't like it. You also have psychological factors. If you spent most of your life swearing how much you love your sprouts and you don't miss meat at all, you might feel the need to stick to your guns."
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5q85ch | Why is it when the hot water knob in the shower is turned, even a fraction of an inch, does the temperature change so drastically? | Engineering | explainlikeimfive | {
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"Depends on how much cold water is running at the same time. If your shower doesn't push a lot of water than a fraction of an inch turn would correspond to a huge increase in hot water compared to cold water. If your shower pushes a lot of water than it wont be so much. Hot water should be 55-60 deg C (~140F) and cold water is about 10C (50F). So already you're using a lot of hot to counteract the cold, and for a comfy temperature it's probably a 50-50 or so mix, if you skew that to 60-40 or 70-30 the temperature goes up significantly."
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5qc48k | How effective was the Great Wall of China at keeping Mongolians out of China? | Engineering | explainlikeimfive | {
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"The wall served two main purposes: stopping raids and providing warning of attacks. It wasn't really meant to hold back a large invading army. It was pretty easy for nomads to raid Chinese farming villages in the north with just a few men. The wall was someone effective in deterring that because it's hard to destroy a wall with a very small force and it only takes a couple people on a wall to fight you off. When it came to large invasions, the wall's main purpose was to provide warning and maybe slow invaders. In fact, the wall has signal towers all along it so that a warning could be sent to wherever it needed to go. The wall was too big to man with a large, permanent force that could repel an invading army, but an invading army would still either have to spend time getting through the wall or around the wall. While they were doing that, the warning signal would be making its way to the capital and/or army. [This]( URL_0 ) thread from /r/askhistorians goes into some pretty good detail.",
"I've been to the Wall and the story they give is that the smoke signals from the towers were the best defense, as mentioned earlier. Interestingly many locals will tell you that it was also built to deter evil spirits coming in from Mongolia as spirits naturally move upwards and so building a wall across the mountain tops would help to block that bad energy from entering China.",
"The original wall wasn't built to keep the Mongolians out - they wouldn't be united until 1200AD by Ghengis Khan. It was built mainly around 200BC to keep the XiongNu out. The XiongNu were Asiatic Huns and consisted of small tribes of nomadic peoples. Not too much is known about them because they didn't leave much archaeological evidence and it was very early in China's history, so Chinese historical accounts weren't too reliable. The Great Wall is actually relatively close to Beijing - about 100km away (the part designed to protect Beijing and vicinity). From the Great Wall, you can see the skyscrapers of Beijing on an unpolluted day, and you could probably see signal fires on the Great Wall before modern light pollution and tall buildings got in the way.",
"My totally uninformed opinion is that the Mongolians were know to be horse riding invaders. Horses would be difficult to get over the wall, so it would work pretty well at repelling them in large numbers. A ladder could get individuals over it, but if you're used to fighting on a horse you'll be at a disadvantage without your horse...",
"You will probably get a better answer at /r/askhistorians. In fact, you should try searching there to see if it's been asked already."
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5qcdct | Is it feasible to build a wall like the US president is suggesting along the Mexican border? | Engineering | explainlikeimfive | {
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"Consider 'building' a wall to be three parts: 1) building walls and gates in major populated areas. This part would be straightforward. It would cost money and take time, but nothing about it is revolutionary. We even have some fences/walls up already that could be used as templates. 2) building walls and gates in 'unpopulated' areas. These include large farmland, sparse grazing areas, national park/forest land, and otherwise inaccessible areas. This would be the most expensive part of the construction effort. A wall that makes sense to build in a dense city will take a massive logistics effort and cost to build in the middle of nowhere. Concrete mixers, roads, power, camps for workers, would all need to be build along the construction zone. While possible, it would be a monumental effort. We have some current surveillance efforts in these areas, but it's mostly a 'when we can get to it' level of effort. 3) continued maintenance. If it does end up getting built, the wall will leave a large bill to future presidents and society for upkeep and guards. One of the main reasons the Great Wall of China was eventually abandoned wasn't the construction cost, but the cost of keeping thousands of troops in the middle of (literally) nowhere to defend the entire stretch. Supplies, transportation, entertainment would all need to be provided to guards on those stretches. As soon as society decides that the cost of maintenance is too expensive, the wall will almost immediately be compromised.",
"Feasible, yes. Useful, hardly. & nbsp; * A large percentage of illegal immigrants exist due to overstaying their Visas. * Tunnels. * Unless you build it high enough, it can be flown over while still being under the radar. * A lot of illegal immigrants simply fly in on commercial flights. Some get caught, some don't. * The Gulf of Mexico exists. * The Pacific Ocean exists. & nbsp; A wall is more of a physical manifestation of Trump's foreign policy than actually being useful for keeping out illegal immigrants. It will create some jobs both short and long term...jobs that will likely be undertaken by immigrants, like most construction/maintenance/border patrol work.",
"Feasible and possible, yes. We could even do it without manufacturing capacity or power equipment. For example, see China. For a more modern example, see Cold War Berlin. The real question is...will it actually accomplish anything other than costing a f*ton of money and making Trump feel a little more masculine? Spoiler alert: almost certainly not.",
"It's entirely possible to build it; it's just a wall. The question is inherently about whether or not it's worth it, particularly considering most illegal immigrants will bypass it entirely by coming into the country through legal means and then simply not leaving.",
"A concrete wall and a concrete road are almost the same thing, with a 90˚ rotation. There are thousands of miles of roads in the Southwest US. Making concrete panels is easy, drilling foundation holes and filling them with concrete is easy, pouring posts on the foundations is easy, slotting the panels in between the posts is easy. The US has many hundreds of miles of sound control wall beside the road that's been made with this process. It will take money, and time, and concrete, and machines. There are some rugged places where it will take some engineering, but that's a starter project for new civil engineering grads. The Rio Grande river has to pass through the wall, and it's very large in that area. This will not be an easy place to build a wall. Serious engineering is required, but not Hoover Dam engineering. The \"will it be worth the money\" question isn't an engineering question.",
"Feasible? Sure. There are approximately 2000 miles of border and currently approximately 700 miles of \"wall\". What's another 1300 miles with enough resources to pay for and do the work?",
"One thing that also needs to be considered is animal habitats and migrations. Animals don't pay attention to national borders so putting up a wall will restrict their movement a lot. I don't know if Trump will care (probably not given his actions regarding the EPA) but if the wall were to be built, figuring out how to make sure animals aren't badly affected would certainly add to the complexity.",
"We aren't talking about a suspension bridge or a very tall tower or something difficult. We're talking about a wall. Walls are very easy to build. It does not need to be a specialized design. It just needs to be a wall that cannot be climbed. Like the peace barriers in Northern Ireland, or the West Bank wall in Israel, or the walls around prisons all around the world. It will be expensive, because it's a lot of wall. But it's not a complex technical structure.",
"There was a great post earlier today by a structural engineer that estimated it would need 3x the concrete used to build the Hoover Dam, and 6x the steel required to build an aircraft carrier. Not to mention the labor and overhead costs to build something that is by and large in the middle of the dessert."
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5qfli9 | Why aren't cars more fuel efficient? | The small Japanese family cars of the 1970s were pulling 30-40 miles per gallon on carbureted, naturally-aspirated engines that had to be throttled to produce any performance. Yet today, with direct injected, turbocharged, electronically managed engines, fuel efficiency remains pretty similar. What gives? | Engineering | explainlikeimfive | {
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"Things I learned during my Mechanical Engineering degree: * **Competing Factors**: Fuel efficiency isn't necessarily correlated with other positive attributes, like safety, cost, reliability, emissions, and engine characteristics. Designing a vehicle requires compromises between these factors. * **Emissions Standards**: Fuel emission standards need to be pretty universal. For example, Los Angeles is affected a lot more by high emissions than Denver, so car manufacturers abide by policies that lower emissions universally for the sake of L.A., even if it reduces fuel efficiency. It's an intertwining of politics and economics. For those who might be confused as to why fuel efficiency isn't always correlated to emissions: depending on several factors, an engine can emit different levels of various particulates, some of which are really damaging to the environment and public health."
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5qhjgy | How do missiles like iron dome chase their target? | Engineering | explainlikeimfive | {
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"Missiles have four common methods of tracking Active: Missile has an onboard radar and uses it to track the target after launch (more advanced aircraft missiles and surface to air missiles have these) Semi active: Missile has an onboard radar and is receiving information from the ground radar as it's signal is bouncing off the target Semi active ground guidance: missile and radar both track the target, ground station makes final decision on what and where the target it Passive: IR and TV missiles track heat and changes/differences therein to find the target However, that was all extra stuff lol. I think the Iron Dome uses proportional navigation. Like the previous comment, it triangulates where the ground is, where it is, and were the the target is going to be and makes adjustments every few seconds. Since missiles don't react to threats (how would it see them) this is an effective counter missile guidance method.",
"Unlike in anime, sci fi, and action movies, missiles do not \"chase\" their targets. They use sensors and math to predict the path of their target, and go to the point where their path intercepts the target path. They are also generally designed that when they get to the intercept point and explode, that they do not have to make a direct hit. What they do is throw enough shrapnel to destroy anything within a certain radius of the warhead."
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5qjhip | How are we able to shift from reverse to drive in a car while slowly moving backwards without damaging the shifter/gearbox or without the axels locking up? | Engineering | explainlikeimfive | {
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"Synchromesh dog collars. It's a little part inside the transmission that resists you pushing the gears together when they are not aligned. The feedback lets you snap the gear into place without damage. In an automatic transmission, there's also a torque converter serving the role of the clutch in a regular transmission. TL;DR: Because it's engineered to work that way.",
"Both the clutch disk (in a manual) and torque converter (auto) allow slippage between the engine shaft and the wheels as part of normal operation. The clutch is easiest to visualize, think of two flat plates pressed together, each with sandpaper on them. Whenever you are starting to move the engine plate is spinning but the one connected to the wheels is not. As they are pressed closer together (by letting up on the clutch pedal), the spinning one rubs against the other one until it is also spinning and now you are driving forward. When you are backing up and then going forward, the only difference is they are initially spinning in opposite directions but the friction will cause the disc to slow, stop, and then spin in the other direction. The torque converter serves a similar purpose int he automatic gearbox."
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5qlbmb | Why does the inside of the microwave not feel hot or even warm after use? | Engineering | explainlikeimfive | {
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"The walls of a microwave oven are designed to reflect the microwaves, rather than absorb them. Since air doesn't absorb much microwave energy, the only object inside the microwave absorbing appreciable amounts of energy is the food - as expected!",
"Because microwaves don't use heat to cook. They use radio waves which cause water and fat (and a few other things) to get hot. That does not generate enough heat to make the microwave itself all that hot from the very short amount of time food is in there."
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5qlrd8 | What is the purpose of drywall? Why is it used rather than wood? Why does there have to be such a big space between walls? | Engineering | explainlikeimfive | {
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"Drywall engineer here! (yes we exist) Many of the answers in the thread are correct, but one of the big reasons everyone is missing is the fire rating of drywall. Drywall is made of gypsum, a hydrated form of calcium sulfate. When the gypsum is exposed to heat, the crystalline water begins to calcine off. This reaction consumes a TON of energy, and prevents fire from spreading across the sheet for considerable time. You can aim a flamethrower at one side of a typical 1/2\" sheet of drywall, and the opposite side of the sheet won't rise above 220F for about 30 mins. Hopefully the fire department has arrived by then. Feel free to ask more questions, I find pleasure in explaining this kind of stuff! Edit-to kill some misconceptions, I work in capital projects engineering for a drywall manufacturer. \"Drywall engineer\" doesn't exist, and would be way too general of a field!",
"Wood houses are built using wood skeletal frames, the \"bones\" of these houses are studs. They provide sufficient structural support to keep the building standing and intact for decades, even centuries. You dont need to build housed out of solid wood, as it would just be unnecessarily expensive. Drywall replaced [lath and plaster]( URL_0 ). lath are thin wood planks that would be nailed to the studs in ceilings and interior walls. They don't provide structural support, they just create a flat surface between the studs, which would then be plastered. This was a multistep process that took several days to complete a room. Drywall, on the other hand, prefabricates the walls, ready to install. Just nail the sheet to the wall and you're basically done. Experienced drywallers can do i ln a day what lath and plaster-ers could do in a week, while offering a comparable result. This dramatically cut down construction time, required less labor, and thus saved money, so it was widely adopted.",
"drywall is cheap, versatile, easy to work with, consistent and fire resistant. The space between walls in the interior is used for sound proofing, and running services like electricity, plumbing, drainage and heating.",
"All of the other comments are fine but I need to add that a major reason is it used more than wood is that drywall is extremely flame resistant compared to wood.",
"I live in the UK. The majority of our houses are not made using drywall/frames. Mostly from a durability point of view and our climate being very damp also. We use concrete/mix foundations with brick construction for exterior and interior walls. Some new builds have drywall put in for minor separating walls but these don't get used without joists usually because of the weights involved in brick built houses. My understanding of American style drywall construction is the gaps between the sides are a form of insulation by trapping air in the space. It's also useful for hiding wiring/pipes etc and means it can be repaired easier without having to replace both sides. Wood isn't used for the walls from an expense point of view. They could use cheap fibre board but it's not durable.",
"Everyone seems to be ignoring your other questions. Walls have a surprising amount of stuff in them. Ductwork, wiring, plumbing, and insulation. If you made walls thinner it can be difficult to run all of this stuff. Also if you used less wood inside the wall it would be more flexible and wobbly. Some walls are actually framed thicker to accommodate for larger pipes. The wall behind a toilet is typically framed with 2x6s rather than 2x4s because the main plumbing stack is very large.",
"As a fellow engineer, your first line and my first line reminds me of a joke......how do you know if the person you are talking to is an engineer? Don't worry, they will tell you.",
"Buildings began as solid wall construction using logs or stone to as the structure, and a bonding agent to fill the gaps and add structure. But solid walls require a lot of heavy material and they don't insulate temperature or sound well, and it takes a tremendous effort. Also, every house was constructed individually so logs were hand shaped on site, and stone was assembled based on the available materials. When the hollow wall came into practice, precut (milled) lumber could be used as the 'bones' of a home dramatically reducing the work time, weight, and variations due to materials. With just the bones in place, the walls needed to be covered. For a long time, small, rough thin boards were used (lathe) to cover the walls, then a layer of plaster was applied to make it smooth, attractive, and air tight. But cutting/buying thousands of boards, nailing them up, and artfully spreading plaster is time (and money) consuming. Using large, premade sheets to cover the walls would make installation easier and cheaper. When drywall offered all of these benefits, it became to predominant material. However, other materials have come & gone with trends.... real wood (knotty pine is in my house), manufactured (fake) wood paneling, etc. Thoguh I didn't mention it above, the advent of electricity, indoor plumbing, and insulation all contributed to the development of these materials & styles. Likewise the scale that was needed to serve the growing population.",
"Dry is cheaper than wood by far. The space between the outside wall is used for insulation and vapour barrier.",
"I find it interesting that we in the Nordic countries have pretty much the same tradition of building single family homes as in the US (and Canada?), but our friends farther down in Europe (Denmark and south) prefer stone. I guess it is mostly relying on tradition, sparsely populated countries with lots of forest had easy access to, and the tradition of using, lumber. Also, it wood might be better suited when the winters are long and cold. Out homes evolved from log houses with external wood panel and interior clay/paint to studded frame(?) with interior cladding with either lath+drywall or OSB+drywall or drywall+drywall. Single drywall sucks. Outer wall have room for 30cm insulation (one feet for the metrically challenged). To remove problems with condensation in the wall, a plastic foil is needed behind the drywall on the inside.",
"Everyone else has answered about the drywall, but as for why is there such a big space between walls, that's so there's plenty of room to run hot/cold water, water drainage, electricity, cable, phone, AC ductwork, and finally leaving plenty of room for future additions/modifications.",
"Drywall is far cheaper than wood and it is far easier to repair should it become damaged. As to the space between walls that is there for sound proofing, the running of pipes, insulation, the running of electricity, the running of cable, the running of phone lines, the running of internet.",
"Additionally, wood moves. It expands, it contracts, it warps, it twists, it bends. Imagine that over a large flat surface. Plus, drywall is much easier to finish. Many people want nice smooth surfaces. The stud space is there for mechanicals, but mostly for a space in which to insulate. A higher r-value needs more space as it's the air pockets between fibers that creates the insulated value. You can't take an r-11 batt and just squish it down to fit a smaller void... it doesn't work like that. Here in the northern US, you are seeing more homes constructed with 2x6 and occasionally even 2x8 walls (over traditional 2x4 construction) in order to accommodate thicker insulation and higher r-values.",
"Is drywall the same as plaster board? (The standard stuff our interior walls are made of in the uk.)",
"old homes in the usa used board and batten construction. this was a thin wall made form 1x 12 boards with a thin strip to cover the gap between the boards. it is more expensive and flamable plus no insulation is provided other than the r value of the wood. edit: batten",
"I just wanted to answer the thickness part. Making the wall thicker increases the strength of the wall and makes the wooden studs more effective thus reducing the amount of wood required. If the wooden studs were rotated to look like this: \"- - - -\" it would make the wall thinner, but the wall would be more tempted to bend from the weight above it. Since the studs are placed like this \"| | | |\" it makes the wall thicker but stronger. Try taking a plastic ruler, it's easy to bend the flat side, but won't bend in the other direction. Now stand the ruler up and push down on the top part. See how it bows out in the middle and bends? Now imagine making a wall with multiple rulers in the two setups mentioned, you'll see the latter one is stronger."
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5qnlrs | Pipeline regulations | I understand oil spills are detrimental to our environment but so is transferring oil by truck. Are the oil companies not doing enough to ensure the pipelines are strong enough or cutting corners in some other way? Are other countries successful with pipelines? It seems like better regulations/ punishment would be the solution. Why isn't that talked about more? | Engineering | explainlikeimfive | {
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"Depends on the country and the regulator, which also depends on where the pipeline is going to, and whether it's onshore or subsea. Here in Australia, you're required to develop a Pipeline Management Plan (PMP) that covers all aspects of the pipeline, e.g.: - Route planning. - Soil erosion and subsidence. - Thermal effects. - Construction (material selection, welding methodology, installation, compression and transmission, integrity verification). - Maintenance (corrosion control, inspection, non-destructive testing). - And, at the end, decommissioning and environmental reconstruction. As for are they doing enough, well, in most cases yes. The majority of pipeline discharges are unrelated to the pipeline itself. Most common is people drive into them, or drag marine anchors over them, or they get dislodged or damaged during severe weathers. Hell, in Nigeria, the locals come in and cut holes in them to steal buckets of oil out of the pipeline, and in more cases than not it blows them the hell up. BP's Alaska pipeline spill was a direct result of cost-cutting. They scaled back on their maintenance program (especially pigging - where you run essentially a drone down the pipe and check corrosion and wall thickness), the pipe corroded and pissed crude oil out of the ground."
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5qqu3n | How did the spaceships Challanger and Columbia fail? | I know obviously two very different scenarios but what went wrong with these two? | Engineering | explainlikeimfive | {
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"For the Challenger disaster the right solid rocket booster had an o-ring that was not designed to fly in conditions as cold as they were that day. It could withstand down to 4 °C but ambient temperatures were -2.2 to -1.7 °C. Ultimately the failure of the o-ring destroyed the craft. For the Columbia disaster a piece of foam insulation broke off the external tank and struck the left wing of the shuttle. This meter-long piece of foam broke off when the craft was traveling at about 2,600 kph and likely caused a 15-25 cm hole in the wing. Upon reentry into the atmosphere this gap in the shielding allowed hot gasses to enter the wing and destroy the craft."
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5qqyl0 | What is the point of this USB adapter? | URL_0 | Engineering | explainlikeimfive | {
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"Maybe if you have a USB that won't quite fit into the plug for one reason or another? I've had it happen where a cord is bulky at the connection and my USB area is crowded, I guess if you want to ensure a tight fit this might come in handy as a small extender."
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5qrbr3 | How do they install plumbing, internet and electricity in old structures and homes that are centuries or millennia old? | Engineering | explainlikeimfive | {
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"I can only speak for plumbing on this issue. First, the contractor or plumber will go to the DPW and request a permit for the job. Next, you need to have your plan in order. A big job requires detailed plans including being up to code. This is the big problem with old houses. It can require lots of renovation to bring old buildings up to code. After you have your plans set up, someone from the DPW will meet you at the property and review the building and your plans. If approved, you do it. Basically, plumbing needs to be the same in any building, new or old. This requires tapping into the main water line, running pipe, branching it off to various rooms and fixtures, installing toilets, fixtures, etc. When you're finished, you get another inspection. The big difference between new and old plumbing is the lead issue. The word 'plumbing' comes from the Latin word for 'lead'. I forgot what the Latin word is... Anyway, current plumbing codes require no lead whatsoever. Old plumbing had lead in the pipes, the solder, and the fixtures. No good.",
"We are currently in the process of renovating our 1865 farm house. The structure is made of limestone rocks held together with mortar. There was no insulation in the walls. It's much like building a whole new house... on the skeleton",
"Sometimes for electric they will surface mount everything if the wall space is inaccessible or nonexistent. This means you would see all the pipe and boxes, similar to [this]( URL_0 ). They can surface mount plumbing and internet cable the same way. It's not pretty, but if you can't access the walls it's sometimes the only option.",
"Typically- any truly old buildings would be covered by a type of preservation law. Depending on the country, there might be codes to which a house is renovated. For example- in America, private property trumps all, unless the deed includes an easement- meaning the legal documents for the property include rules about what changes can happen. Also in America, some concessions are made that allow historic buildings to not follow all modern codes, provided there is no effect on public safety. This is why house museums often are not ADA accessible, even though it typically is mandatory for public buildings. This allows the house to have small corridors and no ramps- as those additions would greatly alter the property. So long story short- When dealing with historic properties, it is always important to know what laws apply to the renovation. It is always expected that plumbing, wiring, etc. MUST be updated. Therefore a contractor can receive permission to move forward with these updates.then these updates occur as they would with any renovation, doing what must happen to assure safety and such, demo-ing as little as possible. But for updates that are not \"necessary\" - like heated bathroom floors for example, depending on where you are- often times the government will request/demand that these changes not be made to preserve the historic quality of the house. Source: my degree from an American graduate school of historic preservation"
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5r5ja9 | How do transistors work and be the size of a atom? | I don't really understand how transistors work. I read they are like doors, if they are how is that any different then a switch? How can transistors be so small and still function, I read we can make single atom transistors and even subatomic transistors. Bonus question: I could be wrong but it seems the vacuum tube turned into the transistor. Are they wired and function the same way but a transistor is just smaller. Like moving from wires to PCB or entirely different. | Engineering | explainlikeimfive | {
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"The operation of a vacuum tube is a lot like a Field Effect Transistor (FET), but the actual mechanism of operation is a bit different. And the construction is very different. Transistors are \"solid state\"...there's no vacuum (or moving parts). So transistors are much more reliable and \"shrinkable\". One of the great things about transistors was that people figured out how to manufacture a bunch of them at the same time in a circuit configuration (an \"Integrated Circuit\", or IC). Then they figured out to make the whole circuit smaller, and smaller, and smaller. This is what enabled the microelectronics revolution over the last 50 years. Sometimes people describe transistors as little switches, but this is not quite accurate. They are actually little amplifiers, but we *use* them like little switches in digital electronics. (In analog electronics, we use them like little amplifiers, which is what they are.) In a FET, there are 3 connections. How much current passes between the Source and Drain connections is controlled by the voltage put on the Gate connection. (There's actually a 4th connection, but we can neglect it for this description.) So you can amplify a small signal by putting it on the Gate and letting it control a large current between the Source and Drain. In digital logic, you either put a very little voltage on the Gate, or a lot. So the SD current is either very little, or a lot. In this way, the transistor acts like a switch, except the switch isn't controlled by anything mechanical, it is controlled by the Gate voltage. The smallest transistor I've ever hear of is a [quantum dot]( URL_0 ), or perhaps a [single-electron transistor]( URL_1 ). These are still in their infancy, and I don't understand them enough to describe them. They don't really work like the ubiquitous FET that are in so many things today. In today's FETs, some of the materials are down to one atomic layer *thick*. But the whole transistor is still larger than an atom."
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5r6f6j | Why are cars designed so the fuel tank is easily accessible from the outside, but to refill the windshield washer fluid requires lifting the hood? | Engineering | explainlikeimfive | {
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"Because you fill the tank regularly. Most people can go months without having to refill the washer fluid. It is topped off during oil changes and most people probably never have to fill it themselves.",
"People need to refill their gas often multiple times a week. People need to refill their windshield wiper fluid yearly. Engineers want to protect your property however easy access to gas is a priority. To consolidate this dilemma many vehicles only allow access to the gas tank via an interior unlock latch.",
"You need to refill the fuel tank a lot more often. The fuel tank is often located some distance away from the engine, so it wouldn't make sense for the opening to be inside the hood."
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5r6ksb | How does a moon pool work (wet porch) | It's basically a boat with a hatch at the bottom to access the water. Ex. URL_0 My guess would be the air is trapped like an upside down cup in water. But...that would mean that the water pressure and air pressure would be the same, right? This raises my question, wouldn't this lead to decompression "the bends"? I assume it wouldn't take long either, scuba diving at 100ft would be 20 minutes. fyi, i know theres already a post on this, however they didn't address this. Thanks! | Engineering | explainlikeimfive | {
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"Yes, air pressure would be the same as water pressure. The bends happens when you reduce pressure too quickly, which is why it is also called decompression sickness. As long as the diver didn't come out of the wet porch and then immediately reduce the pressure to 1 atmosphere, they would be fine."
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5r6myd | why do you need a GFCI receptacle in wet places when it provides the same function as a circuit breaker? | The magnetic part of a circuit breaker should trip when there's a short circuit. I fail to see how this is any different *in effect* than a "ground fault". Is it just the matter of it taking a few microseconds longer to react than a GFCI, or what? | Engineering | explainlikeimfive | {
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"A circuit breaker trips when too much current is detected. Here \"too much\" is on the order of 15 *amps*. By the time the breaker trips it's far too late for the person being shocked. GCFI trips if the current imbalance exceeds a *much* lower value, around 0.006 amp.",
"A circuit breaker only shuts off if excess current is drawn through it. In most cases a short circuit between the hot and neutral will cause excess current to flow causing the breaker to trip. If there is a short between the hot and ground, again it should cause the breaker to trip. However if there is a short between the hot and some other ground path outside of the circuit, it might not cause excess current to flow. This could still be incredibly dangerous because you can be seriously injured or killed from as little as 0.05A Most home circuits in the US are 15A. So as you can plainly see, the circuit breaker will do nothing to help in this case. The Ground Fault Circuit Interrupter on the other hand compares the current flowing through the hot to the current returning on the neutral. If the two are not the same, then some current must be leaking out of the circuit somewhere else and that is clearly a dangerous fault condition.",
"A circuit breaker will trip on a fault current equal to the rated value in 10 or 15 minutes. An overload twice that would trip in a few seconds. A person will fry badly in that time. A GCFI trips in a few hundredths of a second. That's fast enough to prevent injury."
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73jg2i | In movies, how to they get the glass in windows/windshields to break as if a bullet went through it? | Engineering | explainlikeimfive | {
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"Other folks already mentioned the squib. However, as a separate fun fact, normal glass found in houses, drinking cups, etc is made from super heated sand (over 3000F). As you know is super sturdy, hurts like hell if you break it, etc. You can compete this same process with sugar instead of sand. The sugar glass is far far more brittle and doesn't shard as badly. However, when filmed (combine with added sound effects) appears like sand glass. So it's far easier and safer to punch, be near when a \"bullet\" punctures it, etc",
"A tiny pyrotechnic device called a [squib]( URL_0 ) . It's color coordinated so it doesn't show in the scene, and then triggered off-camera when the gun fires."
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73js4h | What was to keep a telegraph message from going past its intended destination? How was a message not received by another machine 10 miles further down or the "leap frog" paradox prevented? | Engineering | explainlikeimfive | {
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"I just want to point out that that's not what a paradox is.",
"Machine A only sends to Machine B. If you want C to get the message then B will need to relay it manually, then C to D. Alternatively some networks like rail lines would act like a party call so *everyone* gets the message all at once. You would need to use call signs to indicate which station the message was intended for, and of course only one person could be transmitting at a time.",
"Central switching stations There weren't that many telegraphs around, generally one per town, maybe a few in a big city. The first thing you telegraph would be a request for connection to the message destination and someone in the central switching station would unplug you from the main board and plug you into your destination so you can send your message to your destination. Telephones used this same system and ended up running on the same wires as telegraphs. Modern telephones use an automated switch board, but it is still wires running from every end point to central locations that connect you to your destination."
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73la9e | How does the Hubble Space Telescope take pictures with no star trails? | Wouldn't the increased speed of it orbiting Earth further reduce the exposure time than if taking a picture here on Earth? | Engineering | explainlikeimfive | {
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"it tracks the stars and moves to compensate for their drift, as do plenty of telescopes and cameras here on earth",
"First, remember that just because it's orbiting the Earth doesn't mean it's spinning. It's entirely possible for it to stay pointed in the same direction, even as it moves around the Earth. Second, the stars are very, very far away. You know how when you're riding in a car, nearby trees go by quickly, but distant mountains go by much more slowly? Well, the stars are so far away, that even at the speed Hubble moves, they still look pretty much stationary."
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73qc72 | What is the difference between the various semi-automatic gun mechanisms? | I know roughly how they work (the expanding gas is used to push the slide or bolt back) but I have no idea the difference between short vs long blow back, blow forward, direct vs indirect impingement, recoil, etc. I can't find great visual differences, and the Wikipedia articles are pretty technical and assume that I know more about the internals than I do. | Engineering | explainlikeimfive | {
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"The most simple form is straight blowback Straight blowback works by having an unlocked bolt behind the round in the chamber. when the gun is fired the gas pressure exerts a force on the bolt and it is forced away from the chamber. As it moves rearwards the empty case is pulled out. When the bolt reaches the rear of it's travel it moves forward again using the force stored in the recoil spring. On the way forwards it strips a new round from the magazine and pushes it into the chamber ready to fire again. The main disadvantage of blowback firearms is that the only thing keeping the bolt in battery (against the chamber) is the inertia of the bolt. In order to be safe the case needs to be supported in the chamber until the pressure in the chamber has dropped (after the bullet has left the barrel). As the power of the round being fired increases the mass of the bolt must increase. Delayed blowback is similar in operation except there will be some mechanism that will increase the inertia of the bolt without adding mass. For example the roller delayed blowback system used in the HK MP5 sub machinegun and G3 rifle or the lever delayed system used in the FAMAS rifle. The mechanism generally works by having a two part bolt having some method of forcing one half to move faster than the bolt face thus giving the bolt assembly more inertia than a one piece bolt of the same mass. Blow forward is the opposite of blowback. The bolt is in a fixed position and the drag of the bullet travelling through the barrel pulls the barrel forwards off the empty case. As the barrel reaches the end of it's forward travel the empty case is ejected and the barrel returns under spring pressure. As it travels back it collects a new round and chambers it. This method of operation is extremely rare and was only used in a few firearms Recoil operation means that when the gun is fired the bolt and barrel both move backwards together. This gives the bullet more time to leave the barrel than a blowback design. There are two main types of recoil operation: short recoil and long recoil. Short recoil operation means that the barrel and bolt are locked together when in battery and only travel a short distance before the barrel unlocks from the bolt. After this happens the barrel stops and the bolt continues. The empty case is ejected and the bolt returns forward collecting a new round and chambering it. The bolt gets to the barrel and moves it forward into the locked position ready to fire again. Most semi-auto pistols use a short recoil action with a browning tilting barrel design which works by locking the barrel into the slide via locking lugs above the chamber. As the barrel moves rearward it drops down which disconnects it from the slide. For example see the 1911. Other short recoil systems include the toggle locked (luger pistol) and rotating barrel (gsh18, beretta px4). Long recoil operation means that when the gun is fired both the bolt and barrel travel all the way to the end of travel. At this point the bolt stays at the rear and the barrel returns to the forward position. When the barrel slides off the empty case which is held by the bolt the case is ejected and the bolt then moves forward collecting a new round and chambering it. An example of this is the Browning A5 shotgun. Gas operated firearms use tap some gas from a port in the barrel and use it to operate the gun. Gas operated firearms can be put into 2 categories: direct impingement and piston operated. Direct impingement firearms work by blowing gas directly at the bolt carrier which then moves rearward unlocking the bolt and ejects a round. For example the AG m/42 rifle. An alternative is the system used in the AR10 and AR15 rifle which is where gas is tapped off the barrel and directed into the bolt carrier via the gas key. Once inside the carrier it expands in the space behind the bolt (which has a gas piston and rings at the rear) causing the bolt carrier to move rearward and unlock the bolt and then carry it the the rear. If memory serves this system was originally called an \"expanding gas system\" but is usually called direct impingement now. Gas piston systems work by directing gas from the barrel and using it to push a piston which moves the bolt carrier to operate the firearm. There are two types: short stroke and long stroke systems. Short stroke is where the piston only travels a short distance just enough to give the bolt carrier a kick which sets it into motion. Examples of this are the HK G36 rifle, FN SCAR rifle and the Steyr Aug Rifle. Long stroke is where the piston is attatched to the bolt carrier and travels all the way to the rear and all the way forward again. For example the AK47 rifle and M1 Garand rifle. Two different ways that the bolt can unlock are by tilting or rotating. All the rifles I mentioned previously as examples of gas piston systems all have rotating bolts. Examples of tilting bolts are the VZ58 rifle and the FN FAL. Other actions exist too, I forget the name but there is a gun that used a combination blow forward/blow back action. Also check out the Mateba auto revolver."
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73ubkd | Why do a lot of bridges only have short barriers on the sides vs. tall ones? | Engineering | explainlikeimfive | {
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"Walls only need to be a little higher than the vehicle's center of gravity. Steel in the walls will stretch and deflect the vehicle back to the road. The only way it would roll over the top is if the center of gravity somehow gets above the top of the wall AND still has sufficient momentum to carry it over. This is really unlikely. To have barriers go all the way up introduces a host of other problems. The first of which is the significant weight of the wall itself, which now has to be carried by the bridge structure. Then lets say someone smacks into the wall really good. They'll hit the bottom bit, cracking it like a tree. What happens when the top bit starts falling down towards the roadway? Also, every time this happens you'll need to fix the entire wall section, which is more expensive the higher it is. Take a look at bridge and roadway barriers as you drive around town now. They're all designed to break in key spots and NOT break in others. Most barriers will snap off at the base pretty easily, but the barrier itself is a continuous steel strip. The broken bases will slow your vehicle down but not stop it immediately. The steel strip will stretch and not break, stretching until your vehicle comes to a stop. Engineers do the math on how much stretching the barrier can tolerate, and make sure you can't stretch into another lane or over the side of the bridge. If you're going to die on a car wreck over a a bridge, it's going to take some significant effort."
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73ulas | what the benefit of using a buffer? | I'm reviewing some python code here and I'm wondering, what's the deal with a buffer size? Why is this convention useful? For reference this is the code: def main(): buffersize = 50000 infile = open('olives.jpg', 'rb') outfile = open('newfile.jpg', 'wb') buffer = infile.read(buffersize) while len(buffer): outfile.write(buffer) print('.', end='') print('Done') | Engineering | explainlikeimfive | {
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"It's to reduce the number of system calls you perform. Every time you call \"write\" it invokes the OS to actually write to the file. This takes a lot longer than a normal method invocation, so instead of calling \"write\" 1000000 times to write a byte each time, you can call it 20 times and write 50000 bytes each time. If you're wondering why you can't just read and write the whole file at once, you can - so long as you have enough RAM available to store the whole contents of the file in memory. If you're working with very large files you may not be able to fit it all in RAM and/or you don't want your program to use more memory than it needs to.",
"Imagine you're trying to move a bunch of bricks from one place to another. It would require significantly fewer trips (HDD writes) with a decently sized wheelbarrow (buffer) than with what you could carry by yourself."
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73ys5p | What filters out rainwater in car engines? | Engineering | explainlikeimfive | {
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"text": [
"An engine is waterproof generally, except for some small air vents and possibly the place where you add oil/transmission fluid, etc. All those places are on the upper side of the engine and protected from rain by the hood and the front grille of the vehicle.",
"Cars have air filters that filter out dust to prevent engine damages. Also, the air intake is usually constructed in a way that the air has to flow upwards at some point so water/dust is seperated by gravity. The water remaining in the air is just the moisture and it actually does no harm to the engine."
],
"score": [
6,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
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