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8oga1o | How do alternating temperatures in showers work when you rotate the valve/handle? | Engineering | explainlikeimfive | {
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"There is a hot water line and a cold water line. You adjust the amount that each line is using by turning the handles in the shower. They both are fed into a central line that exits the shower nozzle. Happy showering!"
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8ok3l0 | Why are bridges made of concrete while the adjacent roads are made of asphalt? | Engineering | explainlikeimfive | {
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"Concrete is durable and has a long \"life\" so they're great for holding the bridge up. Asphalt is cheaper to make and sets faster when building a road. It's also recyclable and gives better traction for the wheels during rain and snow. Asphalt is also easier to fix (the lines you can see over road cracks or filled potholes). If concrete gets a crack or pothole the whole slab has to be replaced. Source: URL_0",
"Asphalt is very weak and its main purpose is just to make a solid smooth driving surface. This is why on blacktop roads you see all those black squiggly lines, this is because the asphalt is cracking and separating because its weak. Even asphalt roads are typically sitting on top of at least 6\" of concrete to stabilize it. Now concrete is used for structural purposes and is very strong so it can with stand all of the weight and force that comes with bridges. Also if you ever see a bridge being built it is made up with more steel than concrete. All of the concrete pillars, beams and even the driving surface has more steel than concrete in it. TLDR: Asphalt is weak and cannot be used as a structural component while concrete combined with steel can hold an enormous amount of weight. Source: worked asphalt gor a couple years and also have built several roads out of concrete and I have inspected few bridges."
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8oocrd | Why do some phones have 2 cameras on the back? | Ive noticed in the iphone x and stuff like that but why 2 I don't get it | Engineering | explainlikeimfive | {
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"Much like your very own eyes, which you use to perceive depth (3D), the two lenses add a plethora of additional capabilities to the camera. Try closing one of your eyes while trying to pick something up in front of you, or catch an incoming ball and you will notice a slight difficulty in doing that. Whilst your vision looks clear, crisp and beautiful with one eye closed, you notice that some capabilities are lost. This works the same way for the iPhone X. Using both lenses, you can take more accurate portrait mode photos, this setup helps tremendously in differentiating you, the subject, from everything else around you; successfully blurring the background. It also adds the ability for you to zoom in slightly without losing quality (optical zoom). There are also benefits to be gained when using the camera to display artificial objects in the real world, more accurately placing digital objects in the real world by reading your surroundings more efficiently and accurately."
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8ooels | how does heat in the ISS not build up if there is no medium? | So on the ISS there is a constant influx of energy be it food or electricity from solar panels. All of this energy ends up being dissipated as heat. Now on earth this heat can be released into the atmosphere. We can use the air to transfer heat away but in space there is no medium for heat exchange. How do we get rid of that extra heat? | Engineering | explainlikeimfive | {
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"There are 3 ways to transfer heat. Conduction, convection, and radiation. Conduction and convection require a medium, but radiation does not, so that's how all heat is transferred in space, like the heat we get from the sun. The ISS has several large radiator panels that it uses to radiate excess heat into space. You can see them in [this]( URL_0 ) image. They are the 2 large sets of white panels pointing towards the bottom of the image and the 3 smaller ones pointing towards the top. They're connected to an ammonia coolant loop that picks up heat from the station and dumps it into the radiators.",
"The heat from the space station is radiated away into space from its outer surface. All bodies that are above absolute zero temperature emit radiation and the wavelength depends on the temperature. For commonly “warm/hot” bodies the resulting radiation is low frequency infrared light, also known as “heat radiation”. Your body emits that too all the time. That’s why you can be seen against a colder background by a thermal imaging camera."
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8oqi7q | how do touchscreens work? | Engineering | explainlikeimfive | {
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"Imabgien a fishing net with many lines running vertically and horizontally. When a large fish hits the net it bends slightly to accommodate the fish. If you have sensors on each rope that makes the fishing net, you can figure out where the fish hit and how heavy it is. Touchscreens use the same idea but they use electrical signals instead of ropes. When you press down, your fingers actually have some tiny effect on the electric field which is measured to figure out where you tapped and how hard."
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8otrjk | When an electrician is initially wiring a house with 120VAC, how do they determine which leg is neutral and which one is line? | Engineering | explainlikeimfive | {
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"The electric company hooks up the meter and there is a spot for the neutral, and two line (hot) legs (typical, USA). The electrician runs his cable from the meter to the breaker box, and just matches the hot legs and neutral, grounding the neutral bus at the panels as well."
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8owzwm | How on earth do parking garages underneath skyscrapers support themselves? | Just started a new job. The building I work in is 18 stories high. I park directly underneath it in an underground parking garage that is 4 stories below the ground. Every time I get out my car I am praying the dang building doesn’t collapse on me. How on earth does a hollow parking garage support a skyscraper?? Edit: This building is located in the United States. | Engineering | explainlikeimfive | {
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"A typical compressive strength of concrete is something like 5,000 psi. That means a square column 1\" x 1\" can support 5000 pounds force. A round column 36\" in diameter can support about five **million** pounds force, and if you look around your parkade, you will likely see several such columns holding up the building. Don't worry, unless you live in China.",
"The building's structure includes the underground parkade. Think of the parkade as the first few floors of the building. It just so happens that the architect decided that the car floors should go underground, and the people floors should start at ground level. Structurally, the floors are identical.",
"18 stories isn’t actually that high for a skyscraper. You will note that your parking garage has giant pillars spread throughout it. Those support beams (plus ones you can’t see) are what holds up the building. They are designed to a pretty absurd safety factor, if you live in a nation where they actually inspect things then you are more than good."
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8p0yg9 | Can a restaurant emptying its fryer grease traps down the drain cause the sewer to back up, Or is it only other types of grease that do this? | Engineering | explainlikeimfive | {
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"Any type of grease or fat going down the drain can cause fatbergs to form and clog the sewer. That is why it is illegal for them to do that. They have to dispose of their used oil in a very controlled manner.",
"Of course, that's why they don't do this. Health inspectors typically want to see effective grease management. Many of these systems are passive grease recovery devices, and there is a market for used grease."
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8p2g6s | How does my seatbelt know to lock on jerky motions, but not when pulled out slowly? | Engineering | explainlikeimfive | {
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"A centrifugal clutch (I think that's the term). When the belt is pulled, it unroll from a spool. If the spool spins too fast (because jerky motion), a mechanism is pushed outwards and locks it.",
"There's actually two mechanisms. One uses centrifugal clutch that engages when the spool spins at a certain speed. And one is a pendulum mechanism that engages when there is a sudden change in motion. URL_0"
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8pdgqt | Underwater welding, how does it work? | Engineering | explainlikeimfive | {
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"> Wouldn't the electricity take a less resistant path through the water and maybe through the guys doing the welding? Potentially it could, but the welding is performed in such a way that the path of least resistance is between the welding stick and the object being welded. That is another factor which protects the diver: The welding is performed using a stick which is coated in flux that vaporizes, forming a protective layer of bubbles that insulates the arc from the surrounding water."
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8pkz3x | Why does the Thompson SMG have a higher muzzle velocity than M1911? | Today i found out that Thompson have a slightly higher muzzle velocity than M1911 pistol in Wikipedia. Why is this the case even though both of them use the same type of catridges? | Engineering | explainlikeimfive | {
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"barrel length. once a round exits the barrel it's no longer being pushed by the pressure of the explosion of powder. If you increase the time (read: length) that the bullet is pushed the more velocity is imparted onto it by that force.",
"The Thompson has a longer barrel which gives the exhaust gasses from the cartridge a greater period of time to push on the bullet and accelerate it. [When a pistol is fired there is still a lot of energy in the gas behind the bullet]( URL_0 ) but there isn't enough barrel to let it keep pushing as much as it can."
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8pykj6 | How does the oldest satellites manage to communicate accurately back to earth despite limitations of technology at the time of construction? | Engineering | explainlikeimfive | {
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"> Why does even the most powerful consumer and commercial electronics consume so much electricity to deliver wireless and satellite signals How much power do you think your consumer devices are using to transmit power? Your Wifi router and phone are using less than 1 watt of power to communicate and they're transmitting in all directions. 1 watt isn't much power at all Voyager is using 22W and a directional antenna to communicate back to big 70 meter antennas on Earth that can hear really really *really* faint signals. They also blast megawatts of signals back towards voyager so that it can hear us on its much smaller antenna > yet dated satellites can transmit through millions upon millions of miles of space debris and electromagnetic fluctuations? Between Earth and Voyager there's basically nothing once you're outside the atmosphere. Space is really big and really empty."
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8pz2sv | How does the water table work? I just did deep enough and then there's water? Why aren't deep caves flooded then? | Engineering | explainlikeimfive | {
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"> I just did deep enough and then there's water? basically. if you had a cup of water, and added sand until the top was dry, you would have a water table. you can do this near the beach. dig down a bit and the sand is wet. the earth is a bit more complicated, though. for instance, certain materials can form a barrier to water. clay is quite famous for it. a layer of clay can trap the water and keep it lower than it normally would be, or elevate it so its closer to the surface than you would expect because the water can't slip through. solid rock can also keep water out, and the water in the ground will go around it. > Why aren't deep caves flooded then? most of them are. the ones that aren't are the exception, and mines spend huge amounts of resources keeping water out. most caves are formed by water. a small fissure in rock has water flow through it for millions of years and it slowly erodes it, opening the fissure wider and lower as gravity pulls it down."
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8pzlza | How do pressure sensors on weight scales perceive how much weight is on it? | Engineering | explainlikeimfive | {
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"Might not be true for all of them, but the scale I work with on a daily basis has a flat sheet of metal resting on top of it that you place the items to be weighed on top of. Underneath the sheet is a large grid of balls that are kept up by a spring system. The more an object weighs, the more it will push down on the plate and the further down the balls will sink. Then sensors convert the depth the balls have sunk to into a unit of measurement that is displayed on the screen. The one I work with displays grams, kilograms, and pounds. To make sure it remains accurate at the beginning of my shift I make sure nothing is on the cover plate and zero out the scale by pressing one of the buttons on the front face of it. After the display reads zero, I add a 1 kilogram weight to it and make sure the scale reads exactly 1 kg. If it is off for any reason, just remove the weight and repeat the zeroing our process until it is correct."
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8pzrob | How does an x-ray (i.e. airport security) of a laptop not affect any of the transistors in the memory (HDD, SSD, RAM, Cache)? | Aren't stronger electromagnetic waves (like gamma radiation or x-rays) particularly disruptive to electronic devices? If so How do they overcome that problem? | Engineering | explainlikeimfive | {
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"Here’s the thing, X-rays can harm your laptop. They don’t necessarily need to harm the transistors but they can affect other parts of the hard drive or the laptop which can ruin the device It mainly depends on the sort of material that you use. Yes, gamma and x-rays are powerful but they also have limits. They can’t go through every metal. Laptops aren’t made of just one metal, they’re a combination of many different ones. So in other words, some metals in the laptop will be vulnerable to the X-rays while others won’t. Transistors in particular are made of silicon. Silicon is capable of absorbing X-rays and isn’t vulnerable to them. Which is why it won’t affect that part of the memory in the very least. Overall, I strongly suggest being careful when it comes to “X-rays and electronics”. Hope this helps.",
"I did a little research and found out that airport scanners seem to use lower doses of radiation compared to e.g. scanners used to scan packages: > Avoid U.S. Postal Service radiation scanning of mailed packages. According to the CompactFlash Association, X-ray scanners at airports will not damage CompactFlash cards but radiation scanning by the U.S. Postal Service may damage them. 1 Because of this warning by the CompactFlash Association regarding mail irradiation by the U.S. Postal Service, it may be preferable to use a commercial service such as FedEx, UPS or other private carrier as an alternative to mailing Flash storage devices by U.S. mail. ([source]( URL_0 )) I guess this is because at airports they are allowed to open luggage if they can't properly identify an object whereas opening up letters or packages is a bigger deal legally. Note that you are exposed to all kinds of radiation all the time because it's occurring naturally, so any storage device has to handle low doses of radiation to function properly."
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8q2riu | What is the purpose of this wall outlet? | Engineering | explainlikeimfive | {
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"Is it a connector for cable television service? Cable television wall plates are typically a single \"F\" type RF connector on a plate by themself, or sometimes on the same plate with a phone jack. (/Short comment)",
"Does it look like this? URL_0 If so, that's for coaxial cable, which could be used for feeding data to a TV (from a satellite or cable service, for example) or it could be used for a computer network in some cases. The TV use is probably more likely.",
"You'd attach a coaxial cable to that, and then plug the other end into your TV or cable box (or perhaps into your ISP's modem/router). On the back side of that \"outlet\" is a cable that runs to an antennae or satellite dish or to your ISP/cableTV."
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8q3xop | Why is copper piping traditionally used in plumbing since it's very conductive? Wouldn't it mean more heat is lost as hot water is transported? | Engineering | explainlikeimfive | {
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"It is more durable than clay, less likely to corrode than iron, and less toxic than lead which were the other options at the time of use. In modernity PVC pipes are more common.",
"It’s ductile, at the time it was an inexpensive, less toxic option to lead piping. It’s fairly easy to work with.",
"Copper is nice because its easy to form into pipes, strong enough to hold the water, doesn't produce harmful stuff when wet(rust), and is easy to seal joints(soldering). The fact that is conductive is kinda a downside but really not a critical characteristic because if you're pulling hot water through it quick enough it'll still be plenty hot when it reaches the faucet and if you really have a problem they make pipe insulation which also keeps you from touching the pipes. Copper was a pretty good solution for the last hundred years or so. Copper piping is becoming less common these days in favor of PEX or other plastic pipes which are bendy so its super easy to get places, doesn't require soldering, and isn't made of copper which is far more expensive than it used to be."
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8q6aia | How do adhesive factories (super glue, caulking, etc...) prevent their machines from seizing up with dried glue during production? | Engineering | explainlikeimfive | {
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"When the glue is running in the pipes it's usually not exposed to air and it spends very little time in the tube so it can't clog up. These factories might be running the filling machines 24/7 or when the machine is turned off, they run a solvent through the pipes to clean the left-over glue.",
"Well, how does glue in a tube keep from drying up? It's just not exposed to air, water, or other reactants that would cause the glue to harden.",
"Yay! I've actually worked with manufacturing superglue as an operator of the machine. The industrial machine that makes it is pretty big with a lot of tubes. One morning when we came to work the machine malfunctioned due to it BEING SUPERGLUED TO ITSELF! The glue in the tubing was usually heated to a very high temperatures during downtime to avoid this from happening, this would lessen its adhesive properties. My coworker had forgot to turn the heat on while ending his shift. The machine was down for several weeks and they had to bring in a speciaI team from the other side of europe using some very nasty chemicals in order to unclog it. I found it ironic how million dollars worth of machinery designed to make superglue managed to.. superglue itself. This was the running gag for a while. The management did not find it remotely funny, lol.",
"I didn’t work with glue or caulking but I was a machine operator at a sex toy factory so we worked with the silicone or rubber material (still don’t know what it is.) It came in buckets, texture was similar to sand or mud. The sand materiel made “harder” toys and the mud material made more “jelly like” toys. The machines were set at certain temperatures to melt the material and molds would be filled. We would mix the material with the “rejects” as well so no material was wasted. But to answer your question, last 30 minutes of work we would turn off the machines and have to basically unclog the machine by poking it with a metal stick or else it would dry up and get clogged up. Here’s 2 vids of the actual factory I use to work at URL_1 URL_0 Edit: should’ve mention that it was very important that the material was still hot before unclogging cause once it dried up it was a pain to unclog. The next morning we would just start the machine, set it at a high temperature, feed it and let it run for a bit to get rid of any dried excess material that was there the day before. Willing to bet money they do this with glue as well.",
"In order for a resin to cure you generally need air, light, or another chemical. In an adhesives plant there is a fair bit of engineering built into keeping these things away from the resin. Also they use an absurd amount of solvent.",
"Former Quality person at a glue factory. In all cases, the polyurethane glue we made was kept in an inert atmosphere (nitrogen, argon) to prevent moisture cure within the reactor system. Additionally, the material is formulated to reach a particular viscosity/free isocyanate content that targets the customer specifications. Typical solvent used was ethyl acetate, which doubled as a raw material/cleaner in solvent-based product. Typically, the ethyl acetate was heated to reflux which increased it’s cleaning ability. When material cured, pipes were washed in n-methyl pyrrolidone at a relatively high temperature. There were times of incorrect chemical addition, which resulted in a solid reactor. That called for a clean-up crew to cut material out with high pressure water, and usually resulted in some disciplinary action for the operator.",
"Similarly, I work in a polyethylene plant and the product is very hot which prevents it from solidifying, but at least once every few years the temperature of the product will dip enough that the plastic will solidify, forcing them to shut down the unit and cut thousands of pounds of plastic out of 60’ tall, 12’ diameter reactors using chain saws.",
"I work as an operator at a phenolic resin facility, where several of our mineral-resins just love to caulk & clog the pipes. I cant speak for other processes & products, but our method to avoid entirely massive headaches is to do as following: a, Keep the reactor-interior in a sub 0.3x atmospheric pressure environment. - This makes sure that oxidization that can set off caulking won't occur. b, We regulate the temperature carefully. Too hot and the resin starts charring into what looks like very very brittle, miscolored glass. Too cold and it solidifies/coagulates (depends on type of product). Between 50-200°c is the general safe-zone. After almost every batch we alternate between running boiling water, methanol, sodium hydroxide, sulphuric acid and even 16 bar of air (16x atmospheric pressure) through the reactor & all affected piping. This usually helps. If you have any more questions about chemical industries I'd be happy to help!",
"Nothing is exposed to air. Normally, pipes run through the ceilings from the compounding rooms where the product is pumped into the production machines. Also, the machines go through a preventive maintenance schedule that can happen as frequently as they need as determined by pilot runs. Source: Am Quality Process Engineer",
"I used to work in an industrial epoxy factory (pretty much made bondo and specialized versions for watercraft and aerospace also). We had a very acidic solution that I can’t remember the name of that we would clean the machines with when they needed cleaned out at the end of the day or when switching from one type or color to another. It was kind of a pain because of the size of the machines but the acid wash made it so it wasn’t to hard to get all the dried epoxy that was left over.",
"When you get the Elmer’s glue for arts and crafts that glue doesn’t dry up, when it does it’s usually only the tip that’s exposed to the air. When you break that tip off the bottle of glue works again. With mass production of these adhesives steps are taken so that air and heat won’t dry the glue up.",
"A little bit different of an answer here. I work at a company that manufactures label adhesives. We use [gravure coating]( URL_0 ) to apply the adhesive. At 20 seconds you'll see a tray filled with an orange adhesive. The [gravure roller]) URL_1 ) (which is an engraved roller) picks up a lot of ink/adhesive from the ink fountain. It uses the doctor blade (basically a large razor blade) to scrape the excess ink off the roller. When the substrate is rolled between the gravure roller and the impression cylinder is when the adhesive is transferred. This type of adhesive needs to go through an oven to cure. So at room temperature we are pretty safe from any adhesive drying/clogging issues.",
"Factory worker here! The glue nozzle tips are kept hot. The one on our case erecting equipment is kept at around 250 degrees or so. The hose that transports the glue and the glue pot is also kept around the same temperature. It is transfered by a pump in the glue pot. Air \"shoots\" the glue into the designated area by means of an automated pneumatic valve, which is triggered by a infrared \"photo eye.\" The photo eye is triggered by the non-erected case. After the glue has escaped the hot temperatures, it dries extremely quick, within 3 seconds or so. Viola! Glue stays hot the entire time is the answer you're looking for.",
"Industrial Maintenance Tech here. A lot of cleaning and breaking the machine down for maintenance. We don't deal with super glue, but we do have a potting machine. Even though it requires two compounds to cure, it still clogs the solenoids and switches up badly and has to be broken down regularly for cleaning.",
"Glue jockey here. There are a few ways that we keep things from getting seized up at my plant. In the reactors where the chemicals and powders are mixed, as well as the next process that filters the glue, and finally the storage tanks, there are agitators that are constantly turning to keep everything in motion. Any time after a batch is moved, all the lines and tanks are flushed with hot water. As mentioned before, most everything is air tight, so the glue usually doesn't have time to dry before the next batch comes through. And yes, we do run 24/7 operations. Periodically, the reactors and tanks are cleaned with a chemical solvent. There are times when the tanks and lines get so caked up, though, that lines have to be broke apart or a person actually has to get in the tank and remove the blockage. Hope this helps!",
"So I worked maintenance at a corrugated cardboard factory. We used a tons of adhesive daily. It was kept warm and wet, the operators added water to it and it was stored in tanks that constantly mixed it. They would clean the equipment daily in theory to keep it from drying and hardening.",
"Sorry for any formatting issues, on mobile. My time to shine. Adhesives all harden differently. Most with exposure to air, some by cooling and others moisture. In the type that is done by cooling, the pipes and tanks are wrapped with what are called steam trace lines which are basically half inch lines with high pressure steam in them. Those are covered by an insulating clay then another insulating layer of fiberglass. The other two are either kept in an environment lacking oxygen and moisture. Most of your caulking takes a long time to set so it's not that big of an issue for some exposure to air. Source: have worked in industrial glue/caulk production facilities",
"Different glues adhere for different reasons. Superglue activates with moisture from the environment so if you can keep humidity away from it, it will stay fluid. (this is why it glues to your fingers before it glues to anything else) White glue adheres when it loses moisture so keeping it away from air should prevent it from clogging. Two part epoxy needs to combine to react. If you can deprive the glue from it's adhering reaction you're golden."
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8q6gb5 | Why are missile-launched nuclear bombs cone-shaped? | I notice that missile diagrams and animations nearly always show the nuke payload as being in a pointy, cone shape. Google image searches of MIRVs show the same, many pointy cones within a larger carrier that isn't itself cone shaped. Animations on the news of nukes re-entering the atmosphere invariably show them pointy end down, nose toward target. The bomb itself isn't cone shaped, right? So why is the bomb-carrying re-entry vehicle shaped like a dart, and why pointy-end first? Re-entry vehicles OTHER than bombs don't come in like that. Manned space flight capsules have a pointed end, but they come in blunt-end first. The Space Shuttle came in (mostly) belly and underwing first. Having a large heat shield protects the rest of the vehicle. Cone shaped with pointed end first subjects most of the body to re-entry heat. I imagine that the cone shape on a missile helps during launch, but why should the re-entry vehicle be shaped like that? | Engineering | explainlikeimfive | {
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"Manned space capsules come in blunt end first because they need to slow down by a lot. Nuclear warheads want to maintain their speed in order to strike their target faster",
"A long, uninterrupted cone is a very good shape for hypersonic flight. Since reentry vehicles are ballistic (no power, no guidance) they don't require control surfaces, communications antennas, or any other equipment that might require complex shapes. A simple cone shape means they'll fly fast and straight right where they're aimed. A reentry vehicle isn't terribly concerned about heat shielding, because it isn't carrying people, and it isn't slowing down. The weapon inside can get pretty darn hot and still function perfectly, and it's only spending a few seconds in atmosphere before it goes kaboom anyway.",
"As noted by another the blunt end of a manned space vehicle on re-entry was to assist is slowing the vehicle down and to reduce the stress on the human body during deceleration. The space shuttle likewise had its shape to slow it down and to allow for aerodynamic qualities during the landing phase. Also it was designed to be reusable such that the coating was primarily non-ablative like on an Apollo capsule. By having a larger surface area it could handle the heat easier. ICBM warheads are by design single use. They have no human occupants so they can tolerate higher g forces and temperatures during re-entry. By using an ablative pointed shape you provide sufficient protection to the warhead and allow for a rapid descent such that any last minute (really last second) ABM systems would have a narrow window of operation. Unfortunately the US has gone down the kinetic kill vehicle route that requires a physical hit to destroy a missile/warhead. The older Safeguard system used the Sprint missile system with low yield nukes to kill nukes by both physical destruction, neutron flux (emp) effects, and disruption of the flight profile. Thus they could still “miss” a direct hit but still kill the warhead at altitude. Still a nuclear detonation, but the cities were saved. URL_0",
"I actually recently saw a [US Air Force training film]( URL_0 ) that covered this. There are two big factors, really: * At supersonic speeds, the projectile creates a shockwave as it moves through the atmosphere. A streamlined, pointy, shape creates the shockwave close to itself, which also means that it has to deal with all the heat generated. A blunt projectile creates the shockwave in front of itself, so the highest heated area is actually the air *in front of* the projectile. * The steeper the re-entry angle, the more accurate the projectile is and the faster it decelerates. The total energy is the same, but the faster deceleration concentrates that energy over a shorter period of time, meaning it ends up at a higher temperature. This latter factor is more important for ballistic missiles. They can withstand the very high stress load of decelerating at a very steep angle, and the shorter period of time they spend being heated can be counteracted by coating the front with an ablative material that vaporizes taking the heat with it. Manned space craft, however, cannot decelerate as aggressively. So they use a less steep re-entry angle and a blunter shape to reduce the max temperature. (And a lot use ablative coatings as well.) Watch the video, though. It's both hilariously corney and very informative."
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8q7jji | why do champagne bottles have tops you can pop with your hands and wine bottles require a corkscrew? | Engineering | explainlikeimfive | {
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"Champagne is under very high pressure. That's why the corks are tapered as well; in order to hold them in.",
"Conventional wine is flat, sparking wine (champagne, prosecco, etc.) is not, and therefore, has a significant amount of pressure buildup. The flared single use champagne cork is necessary to keep that pressure in, while a traditional cork would simply shoot out of the bottle. An analogy would be water bottles vs soda bottles. You can't use the thinner plastic and shorter cap design on a soda bottle because the carbonation would cause it to burst."
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8q7wys | What makes certain cars so much more modifiable than other cars? | Engineering | explainlikeimfive | {
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"Some cars have a higher proportion of their parts that are interchangeable with other years, or even other models. That is, some cars have a lot of parts that are standard for all cars of that era and brand. That means modified aftermarket parts are much more available, because instead of producing a modified part for only maybe 100,000 cars, you're producing it for 1 million cars. The opposite effect would be things like high-end sports cars, in which every single piece is unique to that car, and that model year, so good luck finding niche modified parts or kits for it.",
"A mix of the engineering of a car, it's popularity for an application, and it's price (and probably other things as well). If a car is well engineered, or 'over engineered', then it will respond well to modifying in that it won't (or is less likely to) break down or blow up when it's modified. Example [Toyota Supra]( URL_2 ) and the [2JZ engine]( URL_0 ). If it's popular for an application (for example, drifting) then people will want to modify it for that. The aftermarket will respond to this by producing modifications. This makes it easier to modify that car due to the availability of parts. So the aftermarket produces more modifications because more people are modifying them. And so on. Example, [Nissan Silvia S13/S14/S15]( URL_3 ) and the [SR20 engine]( URL_4 ). If a car is cheap to purchase then it can allow people interested in modifying easy access to a car that can be modified. Example, [Honda Civic]( URL_1 ) and [Mazda MX\\-5]( URL_5 ) (also see the first point). A cheaply bought car can mean there is more money left to spend on modifications and there's likely to be a lot of these cars about so it's worthwhile the aftermarket producing products as they can sell a lot of them. The second and third point combine as well. Cheap and popular cars are generally more common so are more readily available to buy but also easier to come by second hand parts to keep them running."
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8q9rkw | Why do Diesel engines sound totally different from gas engines? | Engineering | explainlikeimfive | {
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"They ignite on compression alone which gives that knock sound, unlike a gas engine that uses spark plugs.",
"Ahoy, fellow redditor. Yer not alone in askin', and kind strangers have explained: 1. [ELI5: Why do diesel engines sound different compared to petrol engines? ]( URL_4 ) ^(_1 comment_) 1. [ELI5: Why do diesel engines sound so different from regular gasoline engines? ]( URL_1 ) ^(_4 comments_) 1. [ELI5: Why are diesel engines so much louder than normal car engines? ]( URL_0 ) ^(_19 comments_) 1. [ELI5: Why do diesel engines have that distinct rough rumble noise? ]( URL_2 ) ^(_9 comments_) 1. [ELI5: What gives a diesel engine it's unique sound? ]( URL_5 ) ^(_7 comments_) 1. [Why do gas trucks sound like 60s muscle cars and diesel trucks sound like tractor trailers? ]( URL_3 ) ^(_1 comment_)"
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"https://www.reddit.com/r/explainlikeimfive/comments/77h490/eli5_why_do_diesel_engines_have_that_distinct/",
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"https://www.reddit.com/r/explainlikeimfive/comments/50u8aa/eli5_why_do_diesel_engines_sound_different/",
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8qanv5 | If black absorbs the most light, why aren't solar panels black? Wouldn't that be the most efficient? | Engineering | explainlikeimfive | {
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"text": [
"Most solar panels I've seen are either a black or dark blue. What you must be referring to is the sun's reflection on the glass that you see. It's harder to see the black because the glass panel reflects soooo much light. Edit: after doing some reading the black panels tend to get too hot making them less efficient. Thats why they use a dark blue."
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8qc3hs | how does the Hubble space telescope pinpoint and capture images of objects while spinning around the earth? | Engineering | explainlikeimfive | {
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"text": [
"The things Hubble looks at are so far away that it's motion around the Earth - or the Earth's motion around the Sun for that matter - barely makes a difference. Any difference it does make can be adjusted for with digital processing.",
"Hubble uses its [Pointing Control System]( URL_0 ) to accurately aquire and lock on to a specific target while rotating around the Earth. Simply put, the System makes use of five types of sensors that basically measure Hubbles orientation in space and its acceleration. An actuator system is then used to react according to the sensors measurements. You can think of it like a giant [chicken head]( URL_1 ) in space."
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8qdijd | how do some screws/lids screw on so that they always finish tight facing the right way? | Whereas some finish in different places depending on where you started. | Engineering | explainlikeimfive | {
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"Threads for lids can be single start, or multi start. If it always finishes in the same place it’s a single start, meaning it has one set of threads. If it’s multi start, it can be put on in at least two, but sometimes three different locations, and will finish in one of three possible locations. It’s easy to look at the thread and see if it’s one spiral, or two or more spirals."
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8qfqoy | Since 99% of bridges are designed to be a straight span over a highway, why isn't there a "best" design that's represented everywhere? | Engineering | explainlikeimfive | {
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"text": [
"I don't know where you got that 99 & #37; figure from, but each bridge is a unique challenge that has to be designed for those conditions. They aren't cookie cutter designs that can be repeated. The distance, height, stability of the terrain, what type of traffic will travel over them AND HOW MUCH traffic are all contributing factors. That informs what kind of roadway materials, and how much to use. Staying just with land bridges, how high up are they? That will tell you if the support is an arch? What is it going over: Rock, grass, loose sediment? The Williamsburg Bridge supports foot, car, and rail. Then of course there's cost. If it's a really long distance, you will need a different type of bridge than if it's a 200 foot overpass. Is it one lane, two, four? You get the idea. Each design must be optimized for those conditions. But even a straight\\-over\\-land still faces these challenges."
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8qmf64 | Why do aircraft entertainment computers behave so slowly, in comparison to other electronics, like phones? | I am trying to understand what is the bottleneck that causes online entertainment systems to behave so slowly. Are they just using super low-end electronics, or is the software just extremely inefficient, or is it something else? | Engineering | explainlikeimfive | {
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"They are usually very old computers, because of the long delays in safety certification for equipment being installed into an airplane.",
"in-flight electronic systems have to be certified by the FAA. Before being installed or retrofitted in an airplane. You can develop new systems and then won't be available for an airliner customer to purchase for years pending FAA approval. Once approved and installed and delivered to customer, you're already talking about 5 year old hardware.",
"It's a shared system, that's your bottleneck. Newer systems, from panasonic at least, run from SSD's these days. It's actually pretty fast, but still hard to find. Most airlines still use the older and therefore slower systems.",
"They are just terminals, it's just one or two computers that run every entertainment terminal for the entire aircraft. Basically, they are just slightly intelligent screens, and it's a server that does almost all the work for everybody.",
"You have to take into consideration the age of the electronics. Im sure they are pushing 5-10 years of operation. Meaning they were submitted for approval even years earlier than that. If you fly on a 787 or the A350, those Entertainment systems are Grade A awesome!"
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8qpk24 | How do pillows that claim to cool your head work? | Engineering | explainlikeimfive | {
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"text": [
"Thermal conductivity. Essentially the pillow is at room temperature, but your head is typically ~20°F warmer. Heat, much like a gas, always tries to hit equilibrium (everything at the same temp.) As such. The pillow will absorb the heat from your head. Now here's where the claim comes in. Different materials will conduct the heat at different rates. If it's very slowly, it's an insulator, like your blanket or the stuff in your walls. If it's doing so quickly, it's a conductor, like the copper heat sink in your computer or coolant in your car. So, if the pillow manufacturer makes the pillow out of a material that is w better conductor than insulator, it will absorb the heat from your head faster, then radiate it throughout the pillow, and ultimately into the air or bed, or wherever it can go. The difference in temperature at that point is enough to make it feel \"cool\", even if it's only a few degrees different from a normal pillow.",
"Some of them work by using materials with high porosity and air flow channels that reduce the thermal insulation that is caused by the foam that most pillows are made of. That makes them do a better job of allowing your head to radiate heat and feel cooler. Some of them have gel layers that act as a great sink. The high thermal conductivity of the gel absorbs the heat from your head and then re-radiates that heat into the room. That effectively gives your head a larger surface area, causing it to cool more effectively."
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8qv2o8 | How does liquid soap, when put into a soap dispenser, turn into a foam? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The soap dispenser has a mechanism to mix air into it to make it form a foam. It doesn't just spontaneously foam up, the dispenser does it by design."
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8qvg94 | Is there an architectural advantage to “The Pentagon” building being shaped as a pentagon? Like does it provide more security, or is it simply for aesthetics? | Engineering | explainlikeimfive | {
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"text": [
"It's a fascinating story. The book Pentagon a History by Steve Vogel goes into it in detail. The idea was to build a building for the War department with a lot of square footage without exceeding the low building height limits of the District of Columbia. The original location was a rectangular space with one corner cut off by a river. They made plans for this location, essentially a building that completely covered the lot. Then they found that the ground wasn't strong enough to hold up the building. They moved locations, to the present site, and wanted to make up the time. Since the plans for the other site had: chunks of building that were straight, chunks of building that met at a 108˚, and chunks of a building that met at 90˚; they asked what shape could they make without redrawing those plans. It turns out you can make a regular pentagon shape that has more area inside than a square shape. Those are essentially the only shapes you can make without drawing plans for a different kind of corner. So, they reused the shapes to make the present building.",
"It would be cool if there was an amazing architectural advantage to the shape. The truth, as truth often is, is spectacularly boring and ordinary. The simple truth of the matter was that the land that the government purchased for the new military headquarters was [pentagonal in shape.]( URL_0 ) The building was designed to make the most use out of the land.",
"The original location was the [Arlington farms]( URL_0 ) that is like a uneven pentagon and size limitations for the building so it had the shape of a uneven pentagon. The Arlington farms is today a part of the Arlington National Cemetery. The location was changed and the size was not limited the same way but the same planes was used because it was during WWII and it was needed as soon as possible. The design had som limitation like 4 floors so not to block the view and steel used was limited and it had to be a quick build. If you look at [this image]( URL_1 ) you can see the if exactly in the original location."
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8r4hnq | Why is hot oil better for quenching steel than cold oil? | I heard once that hot oil cools the steel quicker than cold oil does, I would assume the opposite. | Engineering | explainlikeimfive | {
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"text": [
"You are correct in thinking it's the opposite. Oil cools the steel slower than water, and because of the slower cooling, the steel is less likely to develope fractures due to thermal shock.",
"Important to note that when steel is hot, it expands, which changes its \"grain structure\". Kinda like wood, a tight grain good(oak and other deciduous trees), loose large grain bad(pine and other conifers). When the metal is hot the grain structure is large, because the metal is expanded. If cooled too fast, not only can it shatter because the outside of a hot expanses core instantly becomes cold and small, but also the grain structure will not shrink properly and tightly, making the metal brittle. Therefore a slower cool down will allow all the grain to go back in its proper place nice and tight and strong. Note that it has been a while since my metallurgy class for welding, hopefully my details are still acurate.",
"If it’s cold oil, it could actually shatter the steel when you quench it. The temperature difference even with hot oil is extreme enough to make it cool down drastically"
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8r4n14 | How do fibre optic cables bend? | I've seen fibre-optic cables being bent and I know they're made of glass but I've found no explanation to how it can bend such tight radii without breaking. (I know it loses some of its fibre optic properties but still doesn't explain why it breaks) | Engineering | explainlikeimfive | {
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"text": [
"Same reason a piece of paper can flop around but a tree trunk can't. The thinner you draw a material, the less stress you concentrate on a bend radius. For a thick material to bend, the outside must expand while the inside compresses. Thicker cross sections require more intense expansion/compression to achieve the same radius. In optical fiber, the glass has been drawn to just a few hundred micrometers or less, dramatically reducing that stress. The bulk of the cable is polymer jacketing material to protect the glass.",
"Way more of an obvious answer than I thought, cheers guys.",
"regular glass is formed by crystallizing in and around a bunch of other substances. You wouldn't be able to tell just by looking at it but you can't pass signal through it as there's no structural integrity to pass that signal through. Fiber optics is essentially pure silica, it's heated and compressed and cooled while stranded (or drawn). The crystallization is more resilient, and orders of magnitudes smaller. that said, much of the fiber optic cables that are more bend friendly are actually plastic these days.",
"Glas is not completely stiff so you can bend it. The amount you can bend a object of a given material depend on it thickness because the thicker it is the more the edges need to be stretched or compressed. The glas part of a optical fiber for communication often has a 125 µm diameter that is 0.125mm the rest of the fiber is protective coating Glass wool that is a common insulation material that you likely have com in contact with is made out of glass. The fibers are foten 0.012 mm in diameter or 1/10 of a optical fiber. It is flexabe so i you touch it you understan tha glass can be benables"
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8rjvib | What's the purpose of sun/moon roofs in a vehicle? Is it functional or more of a 'we did it because we could' kind of thing? | Engineering | explainlikeimfive | {
"a_id": [
"e0rvdva"
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"text": [
"The sky is beautiful and the wind in your hair on a lovely warm summer day is fabulous. That's why people buy convertible cars. These roofs are cheaper and give you some of the same benefits."
],
"score": [
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8rk6cj | What gives one car better mpg than another? | Currently I drive a Prius and get 42ish MPG while other cars can get significantly different gas mileage. Apart from overall weight, and aerodynamics, how would one design a car with great gas mileage? | Engineering | explainlikeimfive | {
"a_id": [
"e0rxt6a"
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"text": [
"Engine style. If your Prius had a v8 engine it would use significantly more gas. Number of cylinders, displacement, supercharging, turbo charging, and tuning all have impacts on mpg for a car beyond size and style."
],
"score": [
3
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8rlemd | Why do automotive engines idle around the same rpm regardless of number of cylinder count? | I understand that rpm stands for revolutions per minute which is what prompts the question. My logic would dictate that that a four cylinder engine would take less time to make a full revolution than a six, eight, ten, etc. which would increase the amount of full revolutions per minute at a stable smooth idle over a larger cylinder count engine. I have owned many different cars over the years including four, six, eight and even one 10 cylinder pick-up truck and every vehicle I have owned seams to idle at around the same range. | Engineering | explainlikeimfive | {
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"text": [
"So the alternator can charge the battery. And you will have enough torque to move effectively."
],
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8rmxtx | How do powders stay dry when they’re dyed? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Some mixtures get color before they become powder. For example, powdered make-up is a mixture of different ingredients. It often starts as a liquid mixture, but dries into a powder form. So, the color is in the mix. Not all powders are white. Artificially colored sand is probably like colored sugar: it gets wet when you put liquid dye on it, but then you spread it out and allow it to dry. The pigment stays on the sugar/sand, while the water evaporates. That leaves you with tiny grains, each with a thin layer of color on the outside."
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8roszc | Why aren't ocean-faring boats covered to keep out the water? (pseudo-submarine) | Maybe just a shower thought, but im watching shows where boats are being pummeled by strong waves in storm and tipping over (nautical term?) and it seems like it would solve a few issues... | Engineering | explainlikeimfive | {
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"Like, container ships? Because they're loaded and unloaded from the top. In the port, a huge gantry rolls along over them, picks the containers up one by one, and deposits them on a shore vehicle. You couldn't do that if the ship had a roof. Cruise ships? They basically are already. The only stuff on the outside of those boats is outdoor spaces– lounge chairs, pools, etc– where it wouldn't be the same if it were indoors.",
"Because any covering on the boat would either: A) Act like a giant sail and slow the boat down, or tip it completely over, depending on how strong the wind is B) Get destroyed and blown away by the wind Or, if you’re asking why boats aren’t designed to lie mostly underwater: It would have to be heavier (to overcome the force of buoyancy and sink And the more surface area a boat has underwater, the more drag is has, which lowers speed and costs extra fuel"
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8rqalh | How come in the age of Voip and 4G and GSM, TV can have an HD quality of video but the journalists are still waiting for ages before an audio question reaches them? Why wouldn't they use skype? | Engineering | explainlikeimfive | {
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"text": [
"Most reporters in remote locations are going to be connected through a satellite uplink rather than 4G or a fiber line. It takes about 0.1 seconds for a signal to go from Earth to a communication satellite in geostationary orbit. This results in a minimum of a 0.4 second delay between the guy at the desk finishing his question and the answer from the field making it back. This is due to the speed of light and without a fiber link or a super duper high bandwidth 4g connection there is nothing they can do about it"
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8rxrxf | Why are there so many unexploded WW2 bombs? Why were these bombs so inefficient? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It isn't that the bombs were particularly prone to malfunction, it is just that there were **so many** bombs dropped in total. The Allied forces dropped 3.4 million tons of bombs between 1939 and 1945. London had more than a million kilograms of bombs dropped on it within 24 hours! With all those bombs something will go wrong eventually.",
"The war machines of the combatants were racing against the clock, so the goal was to deliver maximum destructive power *per unit time* - not to achieve maximum reliability. And sometimes the two metrics were at odds. If you could deliver 1000 bombs in a week with 97% reliability (hypothetical numbers), or 2,000 with 90% reliability, the latter would have been chosen because the first would mean 0.97 x 1000 = 970 explosions, while 0.90 x 2000 = 1,800 explosions. But the latter would mean 200 unexploded bombs while the former would mean only 30 unexploded bombs. Maximizing destructive power *per unit time* also meant lower reliability."
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8rz7kf | Why our camera lenses rounds, but photos are rectangle? | Engineering | explainlikeimfive | {
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"text": [
"Your photos are rectangular because the sensor is rectangular. The lens does produce an image circle inside the camera,but light is only recorded by the pixels on the rectangular sensor.",
"Round lenses are easier to produce while square frames most efficiently use film and produce more reasonable end products. We could have square lenses in theory but making them and minimizing distortion would be very difficult."
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8s0l65 | Are there situations in which a person has to manually write code in Binary (i.e. when a new CPU model comes out or if someone wanted to create a new CPU architecture)? | Engineering | explainlikeimfive | {
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"Writing in binary isn't needed because there are alphabetized commands that dirrctly map to the binary commands. These commands are called assembly language. Writing assembly is equiv to writing binary commands.",
"There used to be. Back in the dawn of time, or at least the dawn of programmable computers when people still hadn't agreed what a byte was, programs (and input for that matter) was written on punch cards. If there was a hole in the card that was a one, if not it was a zero (or sometimes it was the other way around). If you forgot to write down which order your cards were supposed to go in and dropped the box, you were screwed. These days, though, binary code is only ever used as a gimmick. Adding more transistors to a processor is all done by computers. Edit: oh and about updating assembly, it does happen occasionally, but for the most part it's set in stone - or rather set in silicon wafers. Each command in assembly corresponds to a physical set of transistors on your processor (more or less).",
"> If Intel adds 1 billion transistors to a new CPU model, does it \"just work\"out of the factory with the x86 instruction set, without any software adjustments? x86 is retro compatible: newer CPU can run older x86 binaries without problems. Intel (and AMD) adds extension to x86 with new processor releases, software has to be rewritten to use these new extensions. When a new CPU architecture is created, compilers for it are written and tested on other CPU (so software can be made for the new architecture out of the gate. The first CPUs were programmed by hand, in binary."
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8shxia | Why is a vehicle left in a low gear like first (or even reverse) without the brake applied less likely to roll or move than left in top gear? | Engineering | explainlikeimfive | {
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"If you're in first gear, to get the car moving at any sort of speed, the engine has to rev pretty high, right? If the engine is off, and the car is in gear, in first, that now means that in order to move the car, the drive-train would have to spin the engine very fast, which takes a lot more effort. For each turn of the car's wheels, the engine would have to turn many times. If it's in top gear, then the ratio of engine rotation to wheel rotation might only be 1 to 1. That means to get the wheels to turn once, the engine only has to turn over once, which takes a lot less effort.",
"In low gear the engine has the advantage. In high gear the rolling car has the advantage like leverage. This is mechanical advantage. In the same way it's much easier to open a door by pushing on the handle side as opposed to pushing near the hinge."
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8sko7y | How is it possible that all of the web-based applications on my phone indicate a weak connection, despite my WiFi indicator showing full bars? | Engineering | explainlikeimfive | {
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"text": [
"Your WiFi indicator is just how strong the signal is from your device to the router, and has nothing to do with Internet connection quality. Internet connection quality depends on the line going into and out of your house, how many people in the area may be draining the bandwidth, and any service issues that your ISP may be having at their distribution points.",
"You can be getting a good connection to your wireless router, but getting a poor connection from the router/modem to your ISP. Could be an actual issue, or simply too many other people also trying to use shared bandwidth."
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8slveu | why do they design highways so the on ramp of new traffic happens just before the off ramp? | Don’t know if this is the right place to ask this question but I just don’t understand why highways tend to be designed this way. Wouldn’t there be less chance of accidents if people trying to merge weren’t competing with people trying to get off? Wouldn’t there be less gridlock too? Is there a reason that I’m not seeing that makes this a better design than having the off ramp before the on ramp? | Engineering | explainlikeimfive | {
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"The cloverleaf, or partial cloverleaf, allows traffic to exit and enter without stopping, through traffic on both roads to maintain speed, and requires only one or two short bridges. The downside is the weaving of entering and exiting traffic becomes a major problem with increasing traffic volume, as you've obviously noticed. The typical alternative is a diamond intersection, which forces one road to have traffic lights (usually when a highway crosses a surface street), or expensive long bridges that allow exiting traffic to exit before entering traffic (stack interchange). So why is because they work at moderate traffic volume, and they're cheaper than a full stack interchange. But many cloverleaf interchanges are being upgraded, and they will likely disappear eventually.",
"OK, you are thinking about the [cloverleaf]( URL_0 ), which is the most common type of interchange for large roads. There are other types of interchanges where the incoming traffic does not compete with the traffic leaving, such as the stack interchange, cloverstack interchange, or the turbine interchange. You can read about these types of interchange on [this Wikipedia article.]( URL_1 ) Each type has advantages and disadvantages. In some types, you can maintain higher speeds. Others are safer. The greatest advantage of the cloverleaf is that it is inexpensive as only one or two bridges are required."
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8swa1k | why do wooden ships sink if wood is naturally buoyant in water? | Engineering | explainlikeimfive | {
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"text": [
"Wood is naturally buoyant when it's dry. Waterlogged wood will absolutely sink; hence, driftwood [in aquariums]( URL_0 ). Wooden ships of old were sealed with pitch or tar to keep water both from getting between the boards, but also to protect the wood from the water. Regardless, the wood still gets pretty heavy with water. The ship doesn't float because wood floats, but because you're displacing the water - exactly the way a metal ship floats. Initially, the ship is going to be weighed down by all the things that are significantly more dense than both wood and water, like cannonballs. Once underwater, the tar will slowly dissolve away, and the wood will rot and become waterlogged, and stay down. Still, you still usually get lots of wooden chunks of a ship that will float around until they either wash up on the beach or waterlog and sink. That debris is called *flotsam* - unintentional debris from a ship, usually from the ship being destroyed. (*Jetsam* is debris that was deliberately thrown off the ship, either as trash or to lighten a sinking ship.)",
"The ship only floats because it displaces more water than it weighs. Once water starts flooding in it no longer displaces enough water because it now weighs more. The individual boards might float but the ship as a whole cannot.",
"Because there is a lot to them besides wood. Sailing vessels have a weighted keel, for instance, that can weight thousands of pounds. Nails, rigging, cargo, copper plates to minimize fouling, fittings and brightwork of all kinds; it adds up."
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8syfb9 | what jewels are, and do in watches. Are they really jewels? If so what kind and what purpose do they serve? Do the number of jewels indicate the level of quality or value? | Engineering | explainlikeimfive | {
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"Yes, they are commonly rubies or sapphires. Very tiny ones. These crystals are so hard that they can turn a pointy bit against a piece of brass for a long time at very low friction without wearing out. This reduction of friction allows the watch to operate with less energy, so it doesn't need to be wound as often.",
"Inside a mechanical watch, you've got a bunch of very fine moving parts. When metal moves across metal, it tends to create friction and wear down unless you've got lubrication, bushings or bearings. The solution people have settled on for watches is to make [tiny bearings out of sapphire or ruby]( URL_0 ). In theory, more jewels means that the watch has more jewels at the proper places while fewer jewels means that they cut costs in a way that will reduce the accuracy/life of a watch. Obviously, none of this really matters much if you're dealing with a quartz watch - either mechanical or digital.."
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|
8t2ihg | Why do some toilets have those blue neon lights? | Engineering | explainlikeimfive | {
"a_id": [
"e145gs9"
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"text": [
"It's partly so that drug users can't find their veins to intravenously inject stuff in the privacy of a public toilet. Edit: Also the mice have mini raves when there's no one there."
],
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36
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8t38sm | In places where water is scarce, could a dehumidifier collect water from the air that would be potable? | It's been humid in my area for a couple days, and my house dehumidifier has been emptied a few times which got me wondering about the water quality in the tank. Is there enough water content in the air to pull liquid water out in places where people don't have enough water to drink? Also, how would the quality and pureness rate? If the machine was kept clean would the water be drinkable? | Engineering | explainlikeimfive | {
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"Yes. It's called an atmospheric water generator. The cost is that it uses a substantial amount of energy.",
"Theoretically yes, but areas that don't get much rain will also have proportionally dry air. So, you wouldn't get much water from the air. In addition, this would require refrigerating a heat exchanger which would require a steady supply of electricity which is also usually a problem in areas of the world with hardly any access to fresh water. Edit: spelling",
"*”According to the Environmental Protection Agency, stagnant condensate can harbor biological contaminants, including mold, mildew and algae, especially if the collection bucket isn't cleaned regularly. Moreover, the condensate can contain lead and other metal residues from the component parts of the dehumidifier. Unlike distilled water (see Nitty Gritty), dehumidifier water is never sterilized through boiling. In case you were still entertaining the thought, let me make it clear: do not drink the condensate! It is better to be thirsty than to be sick”* URL_0 I usually just pour mine into the garden.",
"The quality depends on the machine itself, the materials it's made of, etc. Strictly speaking, the condensation effect affects water directly. There's not \"need\" for it to collect other unwanted stuff from the air. In fact, you could filter the air to remove dust before using the dehumidifier, and end up with very pure water. The problem is that, where water is scarce, humidity is also low. This would require a ton of energy and yield little water in those cases. It won't work in a desert. Collecting dew, which is a natural version of what the dehumidifier does artificially, is mentioned as a survival technique if you're stranded on an island for example. Islands are a great example of where there may be humidity, but not drinkable water. I'm not sure how effective it is, but likely better than nothing. It just wouldn't be cost effective on a large scale, to provide water for a whole village for example.",
"To add a different take on this there are some places, I want to say in South America? That place nets on the sides of mountains which collect water from the clouds passing over the mountain. This allows them to collect water without the energy requirements of an active humidifier. However as you might guess if there aren’t any clouds there isn’t any water.",
"The short answer is yes, you can. There was an experimental bilboard but up in Brazil IIRC that does just that. Collects fresh water from moisture in the air. So why don't we have a bunch of Tatooine-style moisture farms feeding thirsty deserts? The long answer is that it's too energy intensive. There's really not a lot of difference between an AC and a dehumidifier. They both work the same way. You pass air over cold coils to remove heat and moisture. The compressors draw a lot of electricity, as anybody with an air conditioner will attest to when they get their summer hydro bill. It's not as big an issue in a place like Brazil, where their air is very humid. You'll get a lot of fresh water. But in an arid environment, you'd need an awful lot of those things to get enough usable water. Sure, you could build a bunch of solar panels to power them for essentially free, but those initial building costs are going to be very high. A cost that would make even wealthier countries shudder. It's the same reason why you don't see desalination of sea water used more often. It's cheaper and more efficient to just pipe or truck water in from far away sources.",
"The quality of water really depends on the dehumidifier itself, but in theory it could produce drinkable water. Though in regards to: > is there enough water content in the air to pull liquid water out in places where people don't have enough water to drink? No, not really. Let's say you have a temperature of 30°C and a humidity of 100%. We then have about 27g of water per kg of air. To get water out of air, we have to reduce the temperature, so that the air gets oversaturated. Let's say we cool by 10 degrees (=10K). We now have 14.5g per Kg of water. that means we have a Δ of 27-14.5 = 12.5g per Kg of water. The specific heat capacity of air is 1,005 kJ / (kg K). (lets simplify with 1kJ/kgK) So if you need 1l of water (=1kg), you would need: 1kg/12.5g = 1kg/0.0125= 80kg of air 1kJ/(kgK) * 80kg * Δ10K = 800kJ or 222,24Wh Then you would have to pump these 80kg of air through the dehumidifier. 1kg of air is 0.773 m³ or 773.455L, so 80 * 777.455L = 62196.4 L Let's say we have the goal of producing 1L of water every 4 hours. that means we have to pump 62196.4L/4h = 15549.1L/h That would add at least another 120Wh on our energy total. So, but that would all be possible, if energy was literally none of your concern. What I haven't mentioned yet, is that all of this is under the best possible circumstances. First of all I assume the theoretical 100% efficience when looking at the energy you might need for the dehumidifier itself. In reality, you would be happy if you got 50% efficiency, effectively doubling the energy consumption. Then I assume 100% humidity at 30°C. There's only one place on earth this is regulary the case, and this is a rainforest. In general you can assume that anywhere there's anything near 100% humidity, you don't have any issues with water. Then if the humidity drops below that, for example in a desert, where you would need water, you only get water out of the air, if you cool it below the point that air can hold that amount of water. In the mojave desert, humidty is about 10% to 30% at a temperature of 40°C. so 15.26 g/kg of water. You now have to reduce the amount that the air could physically hold below 15.26 g/kg. When cooling the air, first the humidity rises up until 100%. If the air is saturated it releases spare water: That would be at around 20°C ( 14.62 g/kg). Meaning you would have to cool the air by at least 20°C (from 40°C to 20°C) before you see any water. And at 20°C you would have a yield of 15.26g/kg-14.62 g/kg = 0.64g/kg, so basically nothing, you would have to pump 2000kg of air through the dehumidifier to get 1L, that's *1554910L of air*. Simply put: in places without water, the air also has no water. tldr.: it could be clean depending on the dehumidifier, but you couldn't generate a meaningfull amount of water with it."
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8t4s7e | Why Do Ceiling Fans Make Less Noise than Normal Fans? | Engineering | explainlikeimfive | {
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"text": [
"For one, ceiling fans are generally moving a lot slower which generates less noise. Turn a ceiling fan up to high and it will make more sound Also, since ceiling fans are intended to be a permanent fixture to a room, the better quality ones use larger better quality motors than \"normal fans\", which run with less sound. The shape of the blades can also affect how much noise they make"
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8t9lm7 | How can big swimming pools have underwater lamps without risking to electrocute people in the swimming pool? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The electricity doesn't go into the water to make light. It goes into a light source. The light source is then shielded from the water by thick glass so the electricity never reaches the water.",
"You can think of voltage as the shove electricity gets to push it down wires or through water or whatever. Water requires more of a shove to cross than copper wiring so as long as the lamps work on a low voltage they could be immersed in water and not electrocute anyone.",
"There can be a sealed bulb and low voltage. 12 volts will power a sealed bulb (similar to an old style car headlamp) and is completely waterproof. 12 volts won't shock anyone, and the path through the bulb is easier than the path through the water, so the water doesn't really affect it."
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8tf1ai | How do flooring companies make a floor surface that is LESS slippery when it gets food/liquid on it? | Engineering | explainlikeimfive | {
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"text": [
"Most of the time there's grooves to give way to more traction. Think of concrete in playgrounds, most of the time it has grooves in them to keep the kids from slipping if it gets wet. It adds extra traction"
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8ti2ej | Why do wine bottles have that huge indent at the bottom? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It’s called a punt, and I believe it has to do the the durability of the bottle in transport.",
"They're called 'punts' and are tradition at this point. Back in the era of glassblowing every bottle by hand, punts were the last section of the bottle to be formed."
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8tlhhq | How does the wheel on a pirate ship control the ship? | Engineering | explainlikeimfive | {
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"text": [
"There's a rudder on the rear-bottom of the ship. When the wheel is turned, so is the rudder, which changes the direction of the vessel."
],
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8tofiv | Why do boat steering wheels need so much more turning than car steering wheels? | Engineering | explainlikeimfive | {
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"text": [
"What you're talking about is Mechanical Advantage. Depends on the size and design of the rudder and steering gear. However the idea is that turning the rudder or propeller stem shouldn't require excessive effort on the wheel. This, regardless of the total force or torque on the rudder itself produced by water flowing around it. A fairly large rudder on a boat of 100 tons displacement is going to take a lot of force to turn over underway, so the wheel will have a fairly high gear ratio to give the helmsman easy control, and to prevent loss of control in high seas. In general boats don't need to turn quickly to avoid sudden obstacles because they don't tend to move quickly and there's usually plenty of room to manoeuvre. So having to turn the wheel a couple dozen times from extreme port to extreme starboard, isn't really a problem. Also makes it easier to trim the rudder slightly to maintain a straight course."
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8ttdvx | How is auto stop-start on modern cars more fuel efficient? Growing up I was always told that turning off and starting your car burned more gas than just idling. | Engineering | explainlikeimfive | {
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"text": [
"What you were told was wrong, leaving your car idling for as little as 10 seconds takes more gas than turning it off and back on. I was told the same thing, but it's wrong.",
"I would imagine this is just a myth, similar to how people believe it's more efficient to just leave a light bulb on than it is to turn it off and turn it back on (which isn't true). A quick search shows that it takes about 1/2 teaspoon of gas to start a car. Might take a little more or a little less depending on how cold/warm the car is. A car idling takes about 0.2-0.7 gallons per hour. Even the most efficient estimate that's 153.6 teaspoons per hour, 2.56 teaspoons per minute or about 12 seconds to run through 1/2 teaspoon of gas while idling.",
"Older cars up to the 80s sometime, they used carburetors and low pressure fuel pumps when ever you turn the engine off the carburetor had to meter out some fuel to restart the engine. New cars use high pressure injection to run the car when you shut it off and restart it the injectors spray a very small amount of fuel to start the engine. The difference is maybe a few cc's of gas and you probably would not notice it unless you were to keep very accurate records",
"This used to be somewhat true in older cars that used carburetors rather than modern fuel injection systems. The more prescient issue was that of starter motors not being as good as they are now, and those getting worn out prematurely. Even then, idling for more than a couple of minutes in a car that used a carburetor would use more fuel than it'd take to crank it back over. Nowadays, the difference in fuel between starting and running is absolutely tiny, and the tech on starter motors and the like is much better, so you'll save fuel by turning off the car at stop lights, hence auto stop-start"
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8u2m3q | What are those pallet looking things that people put over their hedges for? | Engineering | explainlikeimfive | {
"a_id": [
"e1c3ris"
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"text": [
"They keep frost from damaging the plants during the winter. They also protect against the wind. Evergreen plants like holly are the most vulnerable from wind and frost."
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8u6imx | Why is it dangerous to bathe during a lightning storm if the water pipes are already buried underground? | In the off chance that the lightning does manage to hit the pipes, doesn't being underground mean they are grounded? | Engineering | explainlikeimfive | {
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"text": [
"The pipes are grounded, but you are a really good conductor and closer to the ground.",
"The lightning strike will follow all possible paths in proportion to each path's resistance. You may be in a high resistance path, but some current will still flow your way, and it doesn't take much current to kill you. Also, some soils are actually quite resistive, so a metal pipe could become a good conductor.",
"I think this goes for houses that use an un-grounded water cistern/heater located in the attic. Houses that use plumbing that travel through the attic or near any un-grounded metal/electrical wiring etc are the houses that you shouldn't shower in during a lightning storm."
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8ughgq | How were rope bridges built over long distances? | I don't understand how people got ropes across big gaps in times where technology was not advanced enough for it to be obvious. Please help. | Engineering | explainlikeimfive | {
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"1 climb down the valley and across with a really long rope and pull it tight when you get to the other side. 2 attach a string to some kind of projectile and use it to pull a larger rope across.",
"Shoot an arrow attached to a thin rope. Tie thin rope to thicker ropes. Pull ropes across.",
"A man started by throwing a smallrope across the river. Then the othermen used this small rope to pull the larger ropes across. Large stones stand on each side of the canyon. ... The largest ropes formed the floor of the bridge."
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8ulrk5 | Why are many manholes placed right in the path of a car's tire on roads? | They are repaving the road by me, and they have the road surface milled down. All of the manholes and sewer grates are now sticking up really high and are super hazardous. Which made me realize how many manholes are placed directly where a car's tire would/should be (supposing they are staying within the marked lanes). I started actually taking notice and nearly all of the roads in my area (Southeast PA) have them in seemingly the worst location possible. Why is this? | Engineering | explainlikeimfive | {
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"I don't know for sure but I'd guess it's because the tunnel is under the road and the ladder down is on the side of the tunnel. Which more or less places the ladder under your tire, apparently."
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8umyvt | What is the actual sound you hear coming out of a car exhaust, is it the sound of pistons moving, fuel being burnt or something else? | Engineering | explainlikeimfive | {
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"It's essentially the sound of hot gas expanding out through the exhaust valves of the engine at very high speed, dozens to hundreds of times per second depending on the speed of the engine and the number of cylinders, with the frequency being decided by the engine speed due to some funky things about acoustics and how your ears perceive sounds.",
"n an [engine]( URL_0 ), pulses are created when an exhaust valve opens and a burst of high-pressure gas suddenly enters the exhaust system. The molecules in this gas collide with the lower-pressure molecules in the pipe, causing them to stack up on each other. They in turn stack up on the molecules a little further down the pipe, leaving an area of low pressure behind. In this way, the sound wave makes its way down the pipe much faster than the actual gases do.",
"I feel like the ELI5 version is something like this: Fuel goes in, spark happens, then controlled 'burn' or explosion. The sound of the 'explosion' echos inside the exhaust pipe. The more cylinders, the louder/deeper the noise (there's obviously more to it than that, but that's simplified). The pistons themselves don't make noise, unless something has gone VERY wrong. Had a discussion with a friend of mine about a topic similar to this. She asked me why small import cars sound higher pitched, and muscle cars made a low rumble. Hope this helped!"
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8uotue | Why is road salt stored in complex, geometric shaped buildings as opposed to a standard warehouse or shed type structure? | Engineering | explainlikeimfive | {
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"I'm making an educated guess that the conical/pyramidal buildings to which you refer give the greatest amount of interior volume for the cost and amount of materials used.",
"I have been inside hell (former port of minneapolis) which was a transfer station for salt being barged in. It was an absolutely massive dimly lit warehouse. Not all road salt is stored in those tent like structures but I think as mentioned previously it is a cost measure.",
"Because those building are not \"complex\", they are cheap. The roofs are basically a plastic tarp over a steel lattice. The geometric shape is what provides the greatest stability with the least amount of steel lattice, and the roofs are dome or cone shaped because A) it prevents snow from accumulating, and the construction would collapse under a heave snow load; and B) a pile of salt is also cone shaped so there's no advantage in having a rectangular building, whereas a in a normal warehouse you often want to have shelves up to the roof along the walls."
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8v420l | elevator logic | Eli5: I've always thought the programmed logic in buildings with multiple elevators seems inefficient. Recently the thought crossed my mind that the logic dictating how the elevators correlate to each other might be based more on power conservation than speed/efficiency. Or maybe it's just dumb programming ( for example, a building with three elevators could space one out towards the upper half of the building instead of always making the trip from the bottom, or one evatpr could automatically go wait at the parking garage during peak hours). Any elevator programmers on Reddit that can eli5? | Engineering | explainlikeimfive | {
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"The amount of energy used by an elevator isn't really enough to bother with optimizing around. What you need to be concerned about is making sure that *people actually get where they're going* without feeling fucked over (or trapped). Generally, this means that an elevator going up will keep going up until it's serviced all calls to go up & an elevator going down will keep going down. Stopping on every floor on the way to the lobby is annoying but moving back up a floor when you're already going down is *infuriating*. That generally works well enough for mid-sized buildings. Larger buildings will have more complex rules that may vary depending on time of day. An elevator car might be limited to a certain range of floors while other elevators will be an \"express\" from the ground floor to a mid-floor \"lobby\" where you transfer to other elevators. If you wanted to make a set of really complex rules, you *might* be more power efficient but you run the risk of trapping somebody in the middle for long periods of time if you're trying to optimize around any sort of average measurement.",
"Never worked on an elevator but had to program one as a project in university, so the reality may vary slightly. Elevators are programmed with energy efficiency in mind first. Only then comes time. On high enough buildings (30+ levels) elevators are indeed allocated only one specific range of levels. Also not all may go to the garage levels."
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8vc2ny | How was the SR 71 Blackbird able to capture and process 72 mile wide pictures with 1960s technology? | Engineering | explainlikeimfive | {
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"Film can be *extremely* high resolution since the resolving power is determined by the size of the grains of light-sensitive material within the film, and those grains can be ground extremely finely. For example Adox CMS 20, a high resolution film in a 25mm camera can potentially resolve at nearly 400 megapixels, although realistically when scanned would yield between 50 and 80 megapixel resolution. The SR-71 was equipped with an ITEK Panoramic \"Optical Bar\" camera. It contained film 5 inches wide and 10,000 feet long to yield output of roughly 4 gigapixels per image, taking photographs nearly horizon to horizon. When you are flying extremely high that means 72 miles per photograph (with the best resolving power being directly downward). Using film more than 40 times larger than the typical camera helps out a lot.",
"Three technology was pretty simple, but made to extremely precise requirements. First of all, the film was extremely wide and shot in a continuous format. Imagine how a photo scanner works. Kind of the same principle. Wide film = very high resolution. Now, add to that the fact that the optics (lenses) we're probably the best that could possibly be made at that time. Basically, everything was designed for a single purpose - get high resolution images from 20+ miles up. Considering the tech that was needed to fly at Mach 5+ at 120,000 ft, the camera tech was the easy part"
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8vhlrd | How can a bullet be traced back to the gun that fired it? | Engineering | explainlikeimfive | {
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"Well I think you’re asking about two different things. First off, the ballistics of it: each hun will leave a unique rifling pattern on the bullet as the bullet is fired from the barrel and spun. Rifling is small grooves on the bullet. Second, the bullet is often not destroyed on impact. Most are designed to stay in one piece. So by firing another bullet from a gun they think may be the murder weapon, they can compare the grooves. The other part is they can figure out trajectory by the pathway and angle that the bullet entered so they can figure out roughly where it was fired from."
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8viwsr | Why do US cities expand outward and not upward? | Engineering | explainlikeimfive | {
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"They expand upward when land is scarce or expensive, and they expand outward when the opposite is true. In most cases, it is the later. The US is _huge_ and available land is not a problem that we have to deal with. Most major cities have more than enough surrounding land to expand on to at a fraction of the cost of a skyscraper. There are a few exceptions, like New York where the value of being on Manhattan Island warrants the cost of upward expansion, but it just doesn't make financial sense for most cities.",
"I'd like to add that in addition to building out being easier and cheaper than up, some cities in the US have local ordinances forbidding buildings above a certain height. Boulder, CO is one such place, which restricts buildings to no taller than 55 feet. EDIT: Spelling",
"The replies so far are on point. But let me tell you a little story of my neighborhood. I live in an European city with around 2 Mio people. Rent costs kinda exploded in the past 15 years and apartments are hard to find. People are quite upset about that. Furthermore in my neighborhood there was this old, ugly building. It was built in the 70s for a discount furniture store that closed in the 90s. There was a gym in until like 2002 and since then it's empty. Next to it is a small 60s house, the ugliest thing you've ever seen, also empty. So the city decided to buy the land and build affordable housing there. Good thing, right? Houses in the neighborhood are around 8 stories, the proposed house is about 10 stories, same as the building that is to be demolished. Additionally there's a slim tower on top of that at the corner, that's anoiter 5 stories. This should create a bunch of affordable apartments, the architects chose a very subtle approach that's neither overly ugly nor overly showy or noticeable. That architect didn't try to compensate their personal issues nor were they trying to set themselves a landmark. So there was a neighborhood initative to prevent this building from being built because it's ugly (compared to an abandoned discount store building that has the charm of a rusting shipping container), because it takes away all the sun or just because it's new. Local newspapers picked up on this and discovered that the \"announced specs\" were off, the building is 10cm higher than the old one and their calculation from the door to the subway station was off about 2m. If you went to the article on the homepage of the newspaper or their Facebook page you could literally find dozens of people who were condemning any building with more than 3 stories and idealizing the suburbs and one-family-home as the only acceptable style of building. So often enough the reason not to expand upwards (as they do in Asia quite often) is because of morons who complain because of boredom and change itself. I've seen several buildings and plans not making it to construction because of citizen protests. It's ridiculous and stupid and my sole goal in life is to never become one of those people.",
"1. Land is much cheaper in much of the USA than in some other, more crowded countries. 2. When you build upward, you may annoy your neighbors. When you build outward, you don't create this same effect. 3. Often the builder doesn't have to pay much of the cost of roads, traffic jams, train lines, sewer systems, water delivery systems, and other costly infrastructure. The cost of the \"sprawl\" they create is not paid by them.",
"There are a few reasons that this has and continues to happen in the United States: 1. The value of land. The city of Phoenix, for example, has relatively cheap land compared to the city of New York. Thus, there is little motivation to construct tall buildings, which can cost much more (wood frame vs steel frame). 2. City and State zoning ordinances. Some cities have extremely relaxed zoning laws, allowing builders and developers to do as they please. A great example of this is the city of Houston, where zoning laws have been almost non-existent. This is referred to as urban sprawl. 3. Finally, and this is something I have not seen otherwise noted, a massive portion of the United States has been developed along side the automobile. This has allowed you to live 5 miles from the grocery store with no problem at all and you can see that trend with urban sprawl as a whole. This example makes a lot of sense when you apply it to older cities vs newer cities. Chicago and New York, for example, compared to San Diego and Seattle, which are sprawled geographically. Edit: changed my last sentence in response to u/fatherweebles",
"Here’s the explanation for my Canadian city, which I’ve been told is one of the most sprawling cities in the country: The fire code requires higher water main flow rates for higher density streets. Streets with only houses are built with the smallest possible water lines, for $$ reasons of course. So if you want to tear down a block of houses and build a block of apartment buildings, you also have to tear up the road on that street and install larger water pipes... ...but unless you picked juuuuust the right location, you’re going to discover that you have to also tear up and replace the next street over, because the water on your street comes from a street with a small water pipe... ...and then you look at the next street over and the next street over and you realize it will cost 5 million dollars extra to build your block of apartments, just because of the fire code. And then you realize that you’d actually make more profit from buying empty land on the edge of town and building McMansions, so you do that instead. Of course, it’s cultural too. In my city unfortunately, living in apartments is seriously frowned upon. The majority of society hates them. If people liked apartments, they’d sell for so much money that the extra $5mil cost of tearing up roads wouldn’t even be a problem, because those apartments would sell sell sell!",
"Many modern cities are increasingly growing upwards as well, but the simple physics of it is that even modest resources can create a ground level building. The higher you go, the more sophisticated the methods and the more intense the material requirements become. This means that outward is a more accessible proposition where your only major concerns are infrastructure, roads, power, water, etc. The actual buildings are much simpler.",
"Out is significantly easier. In order to expand up you pretty much need to tear up what's there and replace it all, including the roads and other infrastructure. Think of your average city block with just single family houses versus that same block with large apartment buildings. That's 100x or more the number of people that need power, water, and that'll be driving their cars. You need wider roads to accomodate, much larger water mains and sewage systems, and the surrounding businesses will even need to adapt to the much higher volume of customers. To expand out all they need to do is continue with the same general building style. The odd road might need to be adapted to have more lanes, or a new road might have to be put in, but those are minor in comparison.",
"Given the choice, most people would prefer to buy their own land and have their own house. As an area becomes more and more packed, and property near downtown gets more and more scarce, people build upwards and live in condos/apartments.",
"Cars. Cities on the east coast were built before the car, so they are more dense and walkable. Cities built after the car could be further away. Look up suburban sprawl.",
"There is a move towards vertical space. There's something called \"air rights\" which is the value of the space above a building. The air above the roof is so valuable they want to capitalize on it. In NYC, you have all these high-rises and then small 1 or 2 story structures. Developers see that as wasted space so they want to demolish smaller units and use that space for taller buildings. On the other hand, a lot of colleges have city ordinances that prevent tall buildings (esp in small communities) with a smaller footprint and prefer longer ones that aren't so high.",
"in addition to what others are saying, Americans also want to own homes more than people in other countries do. its part of the American Dream and many people couldnt fathom living in apartments their whole lives. That calls for outward expansion and creates suburbs",
"I see a lot of talk about regulations and stuff. One thing missing is cultural. In America, the idea of owning your own land is huge. It's a sign of success. You go out, get your career, get a house, a dog, a wife, a white picket fence, two cars and two and a half kids on a tree lined street with a side drive. Then you build a man cave in the basement to get away from it all, and build a deck to invite people over to watch you singe meat so they'll all be suitable impressed with your perfect life. Then after the party is over you go back to your man cave and cry over your credit card debt with a case of cheep beers before going upstairs to your already asleep wife. Wait. What was the question? Oh yeah. It's also because owning a home is culturally important in the USA.",
"It's a combination of zoning and land use restrictions (and space available). Same reason there are no skyscrapers on the coast of California.",
"Real engineering did a great video on this very topic: [ URL_1 ]( URL_0 )",
"Quality of life issues, for one: URL_0 URL_1",
"San Francisco has nowhere left to build but upward, and they refuse to do that. Rents then go up to the highest in the nation, even more than Manhattan. Then you have cities like Seattle that refuse to either expand upward or outward. The result is you then you get an out-of-control homeless problem.",
"We have the space to spread out here. And it's far easier to build many shorter buildings than it is to build a few very tall ones.",
"Chicago and New York both have more skyscrapers than the entire eu combined. Why are you asking about the us?",
"Because people don't want to live like rabbits in blocks of flats. Most people prefer to have a house with lawn and garden and some living space.",
"most things like these go the way of the least resistence. if its cheaper/more profitable to build outside the city, people will do. if its more profitable/better to build in the city, people will build in the city",
"Aside from the differences in land value and vertical construction costs that others have mentioned, in many cases, local governments subsidize the roads and parking areas. This means it is considerably cheaper to build out instead of up. This contributes to urban sprawl; it's inherently unsustainable also, so it eventually leads to urban decay. See URL_0",
"Depends on the city... Chicago expands upward, New York expands upward. In many cities, however, land is cheap and everybody has cars so density had been viewed as less necessary. There were also cultural aspects like whites wanting to flee minorities, the desire to have a patch of land, that caused people to move further our rather than build more densely in closer proximity to the city center.",
"Charleston, South Carolina did it because they have a law where no building is allowed to be higher than the church with the tallest steeples. Not even the parking garages. Since Charleston is on a peninsula, it gets to deal with not only massive flooding that increases each year, but also lack of available parking without the benefit of being New York. Religion is the reason why, in Charleston. Las Vegas did it because during the housing market crashes they were selling land and making empty housing developments, so that they could continue to take loans from the bank, etc, even going so far as to pay actors to act as \"cool neighbors\" when people came to open house days. Greed is the reason why, in Vegas.",
"To expand upward, you are putting more people per square foot. That's fine until you consider that people need to commute. That means, as you increase this density, you increase the commuter traffic. This forces the use of public transportation. But as places like Tokyo demonstrate, this has hard physical limitations. Once you reach the carrying capacity for your public transportation system, further growth within that immediate area is impossible, no matter what. Outward growth does not have (exactly) this problem, so long as you add more roads, and scale the residential and business areas somewhat evenly.",
"We, in the US, have a larger square footage to work with in comparison to cities in other countries. Take Romania for example. The apartment complexes have a lot of floors. The buildings have to move upward because there is not enough land to support the population. It’s a very small country by square mileage, as are many European countries. But they really don’t have much to work with when all of the real estate in the surrounding area is taken. Too many residents? Build it taller. I live in Texas, the state is enormous and the distance between two towns “out in the country” could be anywhere between 10 miles and 50 miles. You can travel for over twelve hours in a single direction and still be in the same state. The major roads seemingly last forever, and it is common for the speed limit to be 75 miles per hour, even on rural highways with two lanes per side. But the cities are also widely spread out. If you drive through the city in moderate traffic, it could take you nearly an hour to reach the opposite side, or longer. Dallas, Arlington, and Fort Worth are huge. Fort Worth is the 15th most populated US city as of last year, with Houston coming in at number 4, and Dallas at number 9. Fort Worth only has a handful of buildings over ten floors high. The tallest building is Burnett Plaza, which is 49 stories and under 600 ft tall. For size comparison, the Empire State Building in NYC is more than double that height. And this is nothing compared to places like Chicago, New York City, or Miami. They have much larger buildings and way more of them, and a large mass of land to build with. My point is, the US is a very big country and with a much smaller population in ratio to the available real estate.",
"Living in a large metro area in the US, I wish we could build upward and have all the space in between be efficient highway designs and free parking. That would be the dream",
"Cars. Before cars, people had to remain within walking distance for all their needs. So to keep people close but still have a growing population, you just build up. More modern cities however have been erected after the prevelance of automobiles, making it possible for suburban living.",
"A little late, but I'll add my explanation coming from the perspective of a traffic engineer. While cheap abundant land is a part of it. The bigger factor is the post ww2 decision that success meant owning your own home and owning a car. State and federal governments supported this by building lots of highways between cities and through undeveloped land (and through minority neiborhoods) this expansion of highways also led to the decline of American passenger rail. Then the suburbs were built, the federal government also helped fund these new towns by subsiding mortgages (but not subsiding Apartments except for the very poor). This meant that it often was more desirable and cheaper to move out of the inner city where you took the bus, streetcar or subway to work and move to a place where you had a plot of land and would drive to work. This started a cycle where people would move out farther and farther from the city, with a longer and longer commute and where they could afford those cheaper plots of land. This cycle is called \"drive till you qualify\". It also means that the metro areas for mid sized American cities can be the size of European or Asian cities with 5-10 times the population."
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8vk4sz | What tells a transistor to turn on/off? | If a transistor works by stopping electrons with voltage, what applies the voltage to the transistor? | Engineering | explainlikeimfive | {
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"Whatever you want! The voltage could come from a microphone or guitar pickup. These produce small voltages and low currents, so the switching effect can be used to make the audio signal louder, and eventually powerful enough to drive a speaker (usually with much more than 1 transistor used overall). As I implied in that explanation, the voltage can also come *from another transistor* or related circuitry. Another example is it could come from a computer (which is ultimately transistors but... let’s not worry about that) which can’t supply much voltage or current, just like the guitar pickup or microphone. This lets the low-powered computer control high-powered things like motors or lights. Now, *inside* computers the signals that drive transistors almost always come from other transistors. The ways they’re wired together are a bit tricky, but the basic idea is simple. Imagine voltage (signal) from 2 separate transistors is needed to activate another one. Either one doesn’t provide enough voltage. Whether the third one turns on tells you if *both* the drivers have been activated, and this forms the basis of logic operations like “if x and y are both true, do z”. If either or both of the first transistors can provide voltage to activate the third one, you can do logic like “if either x *or* y are both true, do z”"
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8vnvy2 | I give up. Exactly how do resistors work? | Yeah, I know there are formulas I can calculate with but I still don't get it. Here's an example: Running a laptop power supply, 15V, 2.5A, to power some chinesium LED strips. (I'm mainly doing LED projects and I know LEDs pull as many amps as they can and will burn out. I get that.) I put a 1 Ohm resistor on there and it's just about as bright and cool as ice. No resistor and it gets fairly hot. We good so far? I put a **5** Ohm resistor on an it barely powers the light. 22 Ohms and it's about the same, 47 is right out. How is this possible when resistors are measured in **thousands** of ohms? I pulled some from a tiny circuit board that (according to an online calculator) measure between 1 and hundreds of thousands of ohms. I am so lost. | Engineering | explainlikeimfive | {
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"I think your question is more how LEDs work since your changing the resistors and seeing the LED behavior change. Since the resistance is changing the amount of current is also (the formulas you mentioned). The more resistance the less current that gets to the LED. So your questions is why does the brightness of the LED change... less current going through it means less light to emit. The light source are the electrons in the current. So less electrons, the less light you see."
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8vr28x | Why Will it Take Months to Rescue the Thai Boys Trapped in a Cave? | Engineering | explainlikeimfive | {
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"Waters have risen since they entered the cave, as such they need to scuba dive out. The dive is so perilous in its flooded condition that only special rescue divers have traversed it so far. So you essentially need to train 11 year olds to dive and then line up specialist divers to accompany them. You could probably do one dive per day with one child once they are actually trained."
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8vse7q | How does the OpenBSD hyperthreading exploit work exactly sharing cores? | Please tell me if I'm correct in understanding this [Ars Technica Article]( URL_0 ). I'm not familiar at all with hardware architecture either AMD, Intel, and ARM. In fact I know nothing so assume the worst. One isolated core (y) is processing keys while leaking data in a shared x core. Someone writes code on z core to access a shared x core from z core to steal y cores data. How does one core(y) leak into x core in the first place? If I'm understanding this correctly it's something to do with hyperthreading which is... Huh? How does that work exactly? Is the hyperthreading forcing y into z shared core? Any processing on key algorithms is always isolated. Could this be solved in the OS level? | Engineering | explainlikeimfive | {
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"Hyperthreading is a hardware feature which virtually splits a physical core into 2 logical cores. This enhances processor usage because when one logical core currently waits for data from RAM or so, the physical core can just switch to the other logical core instead of waiting and doing nothing, which happens pretty often. For this to work some parts of the processor have to be duplicated, like registers, while other parts can be shared. One of the shared parts seems to be the TLB. Now the TLB is basically a cache to faster convert virtual addresses to physical addresses. Virtual addresses are used by the running program, while physical addresses are used by the RAM (basically). The OS can configure the virtual adresses so that each running program thinks it has it's own RAM. When the TLB does not have information about a virtual address it asks the OS what to do. That takes time, which is why this information is put into the TLB so that subsequent access to that virtual address can be resolved faster. Like every cache the TLB cannot keep information for all virtual addresses, so it kicks out an entry when a new entry shows up. The way it decides which entry is kicked out depends on implementation. Now if the encryption program and the attacker program run on the same physical core and on different logical cores, they both use the same TLB in turns. And because access to virtual addresses takes longer when the TLB does not have the information, the attacker program can detect which of its entries have been kicked out. Now with the knowledge about the implementation which entries are kicked out of the TLB, the attacker program knows which virtual addresses the encryption program could have accessed, and thereby can determine which part of the code of the encryption program has run recently. With that it *might* be able to determine parts of the key the encryption program uses or the message it encrypts. OpenBSD's solution simply is to not use hyperthreading. Other than that the OS could avoid to run any other process with the encryption program on the same physical core, but for this the encryption process would need to be marked specifically. Another solution, which is mentioned in the article, is to write the encryption program in such a way that knowing which way the process walked through the code does not share any information about the data it processes. Edit: I hope this is ELI5 enough, if not I can happily answer questions."
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8vue32 | Why is it not efficient to build mechanical batteries for grid-scale storage ? | I see tech posts about development of all kind of batteries, but not mechanical ones. It would seem that you could build a dam with 2 reservoirs where you pump up the water to store and you use it as a normal dam when the grid needs it. Or I've seen a light for places where there's no electricity, where you fill a bag with heavy stuff and lift it up to power it. On a very large scale with a lot of bags and very, very heavy objects, why would that not be a good way to store the solar and wind power and make it more consistent ? Edit: It exists ! This is awesome ! While checking all you guy's links, I also learned about the [flywheel]( URL_0 ), wich seems to be a more efficient, but shorter term energy storage solution. This makes me hope we don't end up in 50 years with the oceans full of lithium batteries, wondering ''How could we possibly guess that would be a problem ? '' Edit 2: I'm learning to compared these storage solutions between themselves in terms of : -The amount of energy they need to build the mechanical battery VS the amount of energy it will store in it's expected lifetime. -How little energy they lose while storing and releasing it. It's expressed as a %. The best flywheels claimed to be 90% efficient for example. ( It's justified by the impredictibility of solar and wind power, and the peaks of demand on the grid. ) Those are the main ones you will want in every system. Other factors, like maximum storage and how fast it can go from storing to releasing will depend on the needs of the grid. | Engineering | explainlikeimfive | {
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"It is, you just need hills. China does, it, anywhere that has a lot of hills does it. It just is not usually worth building a hill to put a reservoir on top of. The weight based one doesn't scale properly, and is a lot less safe, also the masses required are enormous, you might as well just build a hill for the reservoir.",
"> It would seem that you could build a dam with 2 reservoirs where you pump up the water to store and you use it as a normal dam when the grid needs it. It's called [pumped water storage]( URL_0 ) and we're already doing it.",
"I remember [seeing this video a few years ago]( URL_0 ), and it fascinated me. They basically fill some train cars with heavy things, and set them atop a hill. When they need power, they let the train cars go down the hill, and generators in the cars are then powered by gravity. How do they get up the hill again? Via electric motors, powered by the excess generating capacity of a wind farm. Anyway, I've always remembered that video and wondered why we don't see things like this in large scale today."
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8w4fxe | why do American style electrical outlets have holes in both prongs | Engineering | explainlikeimfive | {
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"\"Bumps\" inside the outlet fit into the holes and keep the plug in place so it can't be pulled out easily.",
"Fun fact: US plugs were originally meant for the \"nose\" (ground) to face up to make it harder for things to short across the terminals of the neutral and hot. We flipped them over because the \"face\" looked more pleasing but it also means they'll catch any thing on the terminals if the plug is even slightly out. Tinsel, for example, still catches houses on fire at an alarming rate, and these days it's just metalized plastic. The rest of the world wised up and not only codified their grounds high, but also insulate the back half of their live plug pins.",
"There's actually tiny little prongs inside the outlet that fit into those holes. They help hold the plug in.",
"I know 1 function of the holes on the plug (male) is for lockout/tag-out. The idea being if a appliance is broken you can put a tag on the plug stating it is defective and not to use it until it is repaired.",
"UK here... one thing I’ve wondered, what happens when/if you plug in the wrong way round? Doesn’t always seem to be any safety to stop destroying all your electrics constantly."
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8w76zo | How does underwater welding work? | Engineering | explainlikeimfive | {
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"text": [
"It can be done pretty much the same as dry land welding. There are some differences in method to make for a better weld, like isolating the area from the water, but thats not necessary. Mostly to keep it from cooling too fast and not being strong. This isnt a requirement though. I believe they may use a different type of welding rod also. Typically you would create a gas pocket around the weld to keep it from oxidoNg The general premise is the same as on land. Electricity makes it hot, stuff gets melted, cools into a solid piece. The same way the gas cloud on dry land keeps oxygen from oxidizing the work, the gas cloud keeps the water and oxygen from oxidizing the weld. Which would make for a shitty weld. Oxidation is a cancer to metal"
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8wa5zw | Why do LEDs have to be diodes? Also: Are there any components analogous to LEDs that can operate with any current direction? | Engineering | explainlikeimfive | {
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"Diodes work by having a junction that causes an electron to change energy levels like falling off a cliff. It can fall off the cliff easily but can't climb back up LEDs work by sizing this cliff so when the electron falls and loses energy it'll emit a photon of visible light The nature of this cliff keeps current from flowing both ways. There are other ways to generate light with electricity but they aren't quite as efficient and generally require energizing a gas and getting it to emit light To make a bi-directional LED you can just take two LEDs and face them in opposite directions (antiparallel) this way current alternates which one it is flowing through. Super cheap LED bulbs will often do this",
"Here I’m just answering the second question. Well we have light emitting capacitors, which are known as Electroluminescent wire, which require AC and light emitting resistors (though we call them incandescent light bulbs)",
"Well, LED stands for Light Emitting Diode :) But it's actually pretty easy to turn an LED into a device that allows current to go in either direction. Attach two regular diodes to either end of the LED, with all the directions lined up. Now you have 1 LED and 4 regular diodes and you've essentially turned it into a bigger LED with two inputs and two outputs. Current can now go into either of the input diodes and out of either of the output diodes but it cant go out of the input diodes or into the output diodes. ie you've forced current to go across the LED rather than skipping it and going across the input or output diodes. Now attach each input to one of the outputs. Now you have two leads coming off your Franken-LED. Each one has one diode going into the LED input and one coming from the LED output. So now if you put that device in-line with a circuit you can light up your LED by sending current through in either direction."
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8wa7wo | How does keg tapping work, and why is a favorable outcome expected when driving a stake into a pressurised container? | Engineering | explainlikeimfive | {
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"I can only give you an answer from a UK perspective as I know beer delivery can be slightly different to other countries in particular the US. There are two types of traditional beer container here, Kegs and Casks. A Keg is pressurised and absolutely under no circumstances should you try and hammer anything into one. These are the same as the Kegs that I associate with college frat parties in which you attach a metal tap into the top of it that has a special connector that locks in place and withstands the pressure in order to release the beer safely. A Cask on the other hand, while it does contain pressure it is only as a byproduct of the beer inside and not gas that is pumped in afterwards. With a Cask it is important to let it sit still for a long period to allow it to settle. Ideally 24 hours. This is known as Stillaging. The next step is to vent it by tapping a small wooden stake, known as a spile, into the top of it and allow the excess gas to escape. If you've allowed it to settle it should just vent gas and possibly a little beer but this will stop pretty quickly. The last step is to knock in a tap at the bottom in order to pour beer from/attach a beer line for your bar."
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8wbzj1 | Why do most rifles use rotating-bolt system instead of straight-bolt system? | I read that the purpose of rotating-bolt action is to lock the cartridge inside the gun chamber, but isn't the cartridge locked the moment when it's inserted into the chamber ? I am still confused about the locking mechanism, like what does it do to the whole cycle of the gun mechanism ? ***Additional question:*** Semi-auto rifles had been around way before World War II, and they are known for their advantages of having better rate of fire and mostly larger capacity than their bolt-action rivals. Then why weren't they as widely used as bolt-action rifles during World War II era ? **Thank you.** | Engineering | explainlikeimfive | {
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"The barrel is just a tube with a very particular shape. The cartridge can simply fall out if nothing holds it in. The bolt of a rifle is kind of like a key. By inserting and rotating, it locks. You can't rotate your house key 90 degrees in the lock and pull it back out again, and it's the same way with the rifle bolt given that the rifle is built of thicker, sturdier stuff. As others have stated regarding bolt action guns used in WWII despite the availability of semiautomatic weapons: bolt guns were cheaper to make and repair, accurate, already familiar to the troops, and already in use with the military. Many WWII military forces saw semiautomatics introduced during the war, even if the standard gun was still bolt-action.",
"The bullet only sets in the barrel without the locking bolt the casing would move back as the bullet moves forward. Think of having a cardboard box with a brick in it and explosive between them. If nothing is behind the lighter box the explosion will move it more than the heavier brick inside it. (box being the casing brick being the bullet) Bolt actions remained popular due to their reliability, fewer working parts to malfunction and no gas ports to clog. They were also more accurate back in the day.",
"the problem is the mechanism that keeps the bolt from moving backwards when the rifle fires. a linear bolt needs a mechanism that can \"tell\" the bolt when it's allowed to move and when it's not. while they're not terribly complicated, they're much more complicated than a rotating bolt and the advantage is minimal. to a military that wants thousands or millions, the additional cost quickly outweighs the benefit. for many private gun owners, the simplicity is the appeal. those who would buy more complex mechanisms can be enticed by semi-automatics. > Then why weren't they as widely used as bolt-action rifles during World War II era ? mostly, they were expensive. many nations lacked the resources to seriously capitalize on the new technology and were fighting with variations on their WW1 tech. russia was so starved for resources that they had to shift *away* from a semi automatic main battle rifle they had been planning (the SVT), and back to the mosin, which extends to even pre-WW1. they *still* regularly had fewer guns than troops also, the nations that fielded them often encountered problems. cheaply made ones were prone to fouling. italy shat out a number of weapons over the course of the war that are infamously bad. the US's garand and thompson are famous, for good reason, but were so horrifically expensive that the military was scrambling to find cheaper alternatives. all of which the troops *hated,* usually because they failed if dirt looked at them funny.",
"As far as your second question, bolt action rifles were easier to make and way more reliable. Automatic firing mechanisms have a tendency to jam",
"Because without the rotating bolt the chamber wouldn't be locked. The cartridge would only stay in the chamber by the force of the spring pushing the bolt which in turn pushes on the cartridge. The force of the spring is enough to keep cartridge in place but not for long enough when firing. If you fire without the lock the pressure would blow out back through the chamber which means no fast boolit. The lock is there to delay the blowback until pressures in the chamber are at a safe level. Same reason pistol-barrels tilt. You could delay the blowback with a much heavier spring but then it would be too heavy to repeat the whole process. You can also have a heavier bolt like older submachineguns had but with rifle-pressures it would be too heavy to be practical. ELI5: When the thing goes bang pressures go high. Spring is too weak to resist pressure for long enough. Rotating bolt helps spring fight back against pressures until they calm down."
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8weof4 | Structurally, how is a GPU different from a CPU? | On a transistor level, how does a GPUs structure make it better than a CPU at certain tasks and worse at others? Are there logic gates in a GPU? | Engineering | explainlikeimfive | {
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"Vast oversimplification, but you can think of a GPU like having thousands of weak cores while a CPU has a few powerful cores. When you're rasterizing graphics, each pixel is independent of each other--a GPU can calculate thousands of pixels at the same time. But not all processes are this stateless. Oftentimes you can't proceed without knowing a previous step. In fact, most tasks are like this, and that's why CPUs are still more important. Only some tasks are suited for mass parallelization."
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8wgb9q | Why are scuba regulators made of brass? | It seems that most scuba first-stage regulators are made out of chrome-plated brass. As a relatively soft and corrosion-susceptible metal, brass seems like far from the best option. Why is brass superior than, for instance, stainless steel? | Engineering | explainlikeimfive | {
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"Brass is much less suceptible to the kinds of corrosion caused by salt water. Over time, stainless hardware would become pitted and the seal would be compromised. Brass will simply patina on the surface and then stop corroding as quickly. Brass is also much more cost effective to mold/machine than steel for this purpose, with no real drawback in functionality, which is likely the main reason. There are nitrogen based stainless steels like H1and LC200N where the carbon in the manufacturing process is replaced entirely by nitrogen, making them effectively corrosion proof in salt water, but these are very expensive to use, and brass works just fine for the usage."
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8wi368 | What’s the difference between a decent tripod and a great one? | I currently have a Manfrotto 055xprob and it serves me rather nicely. It is light, enough for me to carry around for hiking and has very good stability. But then, I see tripods like a fully kitted Manfrotto 546b with wheels and all that is over $1100. Is there really enough of a difference to justify the price? | Engineering | explainlikeimfive | {
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"Biggest difference would likely be rigidity. As for whether it's worth the price, I can't tell you. If you're a billionaire and like taking long exposure photos in strong gusty winds, you might even want something beefier. If weight is important and you don't do long exposures or video, it's probably worse than the cheap one. It's like comparing a pickup to a semi. If the pickup suits your needs, a semi is going to be more trouble than it's worth."
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8wik0n | Why can't we drill 1m diameter hole above the location of taiwan kids trapped in a cave instead of diving to try and rescue them ? | Engineering | explainlikeimfive | {
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"text": [
"Experts are considering it... URL_0 PS - It’s in Thailand (tropical, touristie place) not Taiwan (political place where people from the old China live).",
"What if that cause the cave to collapse onto the kids trapping them or even killing them. Their safety is more important than getting them out hastily and risk getting them in harm’s way",
"Any idea why can't a scuba diver go down there with breathing gear and take the kids 1 by 1?"
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8wld56 | Why is the musical instrument the triangle triangular in shape? Would other shapes produce different sounds? | Engineering | explainlikeimfive | {
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"It’s would be easier to hit a straight edge cleanly, without sliding along the metal or bouncing and hitting another part of it. It would likely be easier to predict the ringing (resonant) frequency of the straight edges than a circle for example. It’s also way easier to make 2 bends in a metal rod to make sides of a known length, for a certain tone. To produce a circle I imagine you’d need to wrap it around a circular item and you’d need one of a different size for different sized circular instruments. I’m not sure how the timbre (character) of the sound would change but a circular instrument of a similar size would have a different pitch because it’s one long side instead of 3 distinct ones. But the biggest reason for a triangular shape is likely tradition, which originated with ease of making them."
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8wpfza | why must you open propane valves slowly? | Trying to get the bar b q grill going, my father always told me to open the propane valve slowly, like 1/4 turn then wait before opening it a full turn. If you open it quickly it doesn’t work. | Engineering | explainlikeimfive | {
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"Now that you're 5, it's time to tell you the truth: you can open it all at once. We just didn't want you monkeying with it when you were younger.",
"You don't need to do that. If all the burner valves are closed then you can just open it all the way, then open one burner valve and light it, then light the rest. If the burner valves are already open and you open the tank valve to quickly, the regulator will detect a possible leak and prevent the propane from coming out properly. To reset it you would need to shut off the tank and then disconnect the regulator from the tank for a few minutes before trying again. Please don't light your dad's BBQ if you are only five years old.",
"I always turn it to the left, as far as I can. Have i been doing it wrong all along? Lol.",
"There’s a regulator on it that shuts down the flow if you turn it on too fast. This prevents certain catastrophic failures that would otherwise result in fiery death.",
"the regulator, the thing that controls the pressure of the gas inside the grill, depends on the pressure inside the system, a spring, and a tiny plug that constricts the gas flow. if there is no pressure inside the grill (like when you first attach the tank) snapping open the valve too quickly can cause the plug to be pushed in and block the gas instead of just restricting it. it will then stay that way as long as the tank side remains pressurized. this is harmless, but obviously keeps you from using the gas until you close the tank and detach it so the regulator can depressurize. I suspect your father somewhat misunderstood his own solution, and slowing down enough to do the quarter turn was what actually did it. in a system as small as a grill (even an extravagant one), the process of coming up to pressure is extremely fast. most people don't, or even can't, open the cylinder valve fast enough to cause the regulator to lock up. it's more common with ball valves, which are intended to open quickly."
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8wumop | why do tornado/emergency sirens use that whining drone sound instead of a beeping or something similar? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The whining is created by what is basically a whistle driven by a powerful electric motor. It spins a cylinder with carefully positioned slots in them in order to create the resonant whistle and characteristic whine of the storm/air raid siren. The benefit here is that by adding a more powerful motor you can easily and reliably create an *enormously* loud sound which is easily recognizable through various background noise. By gradually changing in pitch it will hopefully not be overpowered by some nearby noise which is exactly the same pitch.",
"Car alarms make a lot of noise and are distinct. Do you pay attention when they go off? Nope. The air raid and disaster emergency sirens use a sound distinct to something bad happening that is nearly impossible to ignore or drown out and when you hear it, you immediately know to pay attention."
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8wx277 | Why do tray tables and seats have to be set back while planes are taking off and landing? | Genuinely curious as to why we have to put our tray tables up and put our seats forward on take off and landing. What purpose does doing it serve? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Imagine you sitting down in your seat. Seat belt unbuckled tray table down. The 100 tons of aircraft and cargo and passengers are all buckled in. The plane is landing. Now imagine a critical failure of the landing gear. Not exploding just collapsing a foot or so. The nose dives down the plane lurches forward. So does everything in the plane. Including you. That tray table has now broken your ribs or caused some internal bruising. It’s the same as holding something on your lap in a car accident. Where is the cute puppy or laptop gonna go. With the momentum of the vehicle. Stow your tray table. Put your items in the overhead. Turn off your phone or put it in airplane mode. There are reasons for all these things. Some are outdated. Most aren’t. The airlines would love to have you do whatever and not care. But liability lawsuits would cripple them."
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8wyre4 | How do pilots know ahead of time when turbulance is going to occur? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Meteorological information can be used to predict turbulence with reasonable precision. Also, aircraft will report when encountering turbulence and air traffic control will relay that to other aircraft in the area.",
"I think they can anticipate turbulence by looking at weather radar or radio messages from other aircraft that has been through it. Clear air turbulence, however, can strike at anytime because there isn't a way of knowing."
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8x5jem | How does a car tire work when there is no tube? | Engineering | explainlikeimfive | {
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"text": [
"The tire bead makes an air tight seal where the tire contacts the wheel. The tire bead is made of a strong braided steel cable loop that is covered in rubber. The rubber makes it air tight, the steel makes it strong enough to not blow off of the rim."
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8x6d67 | does it cause anyone any inconvenience if you don't wash your recycling thoroughly? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Yes. at some point someone has to sort through that stuff. If it's nasty and greasy or otherwise covered in other garbage and grime that makes their life suck a lot more. Then they'll have to wash it themselves. It's a common misconception that at stuff \"burns off\" and you can just throw it all in some magic recycling machine. A surprisingly small percentage of what people actually put in the recycling bin is even recyclable to begin with. Most municipalities don't get super picky about it because they know if they were people wouldn't bother width reycling at all but there's a reason China recently has flat out refused to accept recycling from the us anymore. It's because so few Americans are courteous enough to actually properly sort and clean thier recycling.",
"I used to work in a recycling depot as a temp worker. 99% of the people putting recycling in the blue bag didn't do a damn thing to clean off their recyclables. You are setting a good example even by making sure what you recycle isn't contaminated. Just be aware it takes a lot more peopple to follow that example to make a significant impact."
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8x9z09 | How do trains turn? | I get that they have cone shaped wheels, but I fail to see how that helps them turn on the track. | Engineering | explainlikeimfive | {
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"text": [
"Cone shaped wheels help trains stay on track when the track bends. The train is basically \"falling\" into the correct orientation. It is difficult to explain in text without picture so I hope [this video]( URL_0 ) explains it.",
"Cone shaped wheels essentially means you can choose how large diameter the wheel has depending on where on the cone your wheels touch the rail. If you have a small wheel and a large wheel connected to the same axis, you will turn in the direction of the small wheel, right? Now if the rail turns, to the left, and the train goes straight, the left wheel starts going off the rail inwards - meaning the smaller outer part of the cone is touching the rail instead of the center, and the right wheel start going off outwards - so the inner part with a larger diameter is now touching the rail. Left wheel smaller, right wheel bigger, so it will start turning to the left - in the same direction of the rail. This mechanism is self stabilising, whenever the train starts turning less than the rail, the wheel diameters will adapt accordingly so it starts turning more, and vice versa. Why does a small and a large wheel connected together turn? think of them as two parts of a single cone, a cone is just continuously smaller and smaller wheels, right? cones don't roll straight!"
],
"score": [
4,
3
],
"text_urls": [
[
"https://www.youtube.com/watch?v=UYbCZn-AAXs"
],
[]
]
} | [
"url"
] | [
"url"
] |
8x9z0f | How come the back windows of a car often don't go down all the way? | Engineering | explainlikeimfive | {
"a_id": [
"e21tjxu",
"e21tir0"
],
"text": [
"Because the way the back door is shaped to fit the rear wheel, dont give enough free room for the whole window to slide inside the door’s frame. There is just not enough room for it.",
"A window not rolling down a couple more inches isn't going to keep kids from hopping out. The reason these windows don't roll down all the way is because of automotive door design; the windows rolled down as far as they could before reaching the top of the wheel arch, and then they had to stop, because they simply had nowhere to go."
],
"score": [
9,
8
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8xfa0z | How jetfighter's defense systems know when they're beeing locked-on by other jet's attack unit (and then worn a pilot about it)? | Engineering | explainlikeimfive | {
"a_id": [
"e22v8gj"
],
"text": [
"There are a multitude of sensors that help alert pilots to incoming attacks, but the main one is the Radar Warning Receiver (RWR). The RWR is a set of antennas that detect the radio emissions of nearby radars. A computer then analyzes those emissions to determine whether the radar is pointed at the aircraft, and whether its emissions match the signature of known tracking/targeting radars. If the computer thinks the radar signal looks like a guidance beam for a missile or AAA piece it alerts the pilot(s) with an audible alarm and a message on their display."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8xo7ko | This may be a dumb question but how does a car/truck tire handle the weight from the vehicle and not pop? | Engineering | explainlikeimfive | {
"a_id": [
"e24duca",
"e259rxb"
],
"text": [
"They're simply really big. The larger the area you have touching the ground, the more weight you can have. Let's say you put three tons balancing on a needle. You're taking all those three tons, and concentrating them on one single spot, and that needle is gonna pierce right down through the asphalt. However, say you put three tons on a sled. The sled's large surface area helps to spread out the three tons, and you put it on the ground with no problem. Tires may not have as much area as a sled, but they still have quite a large contact area, enough to allow trucks and cars to drive effortlessly. This is also why tanks have tracks, by the way. America's main battle tank, the M1A2 Abrams, weighs 70 tons; the tracks are absolutely massive to help spread out those 70 tons.",
"In addition to what /u/SkyEyeMCCIX said, they're also thicker and made out of far stronger material than your average balloon. Engineers design things based on [stress]( URL_0 ). Whatever material you're working with has a *strength*, which is the max amount of stress it can withstand before breaking, bending, popping, snapping, or whatever. The stronger the force you apply to your part, the higher the stress. But if you make your part bigger/thicker/bulkier, you lower the stress. So if you're designing a tire for a certain pressure and it keeps popping, it means the stress is too high. So you either make the tire walls thicker (reduce the stress), or you use a stronger material that can handle that stress level, and then the tire won't pop."
],
"score": [
7,
3
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Stress_(mechanics\\)"
]
]
} | [
"url"
] | [
"url"
] |
|
8xru0z | I am learning basic electronic circuitry, what is the difference between Digital & Analog? | Engineering | explainlikeimfive | {
"a_id": [
"e254nj9",
"e254qry",
"e2556lh",
"e2553xq"
],
"text": [
"Digital signals have two states, on or off. Analog signals have a continual range of values between their minimum and maximum. A normal light switch is digital, a dimmer switch is analog.",
"Digital means that the signal is divided up into discrete states, while analog means that it can be any value. Think of digital like writing: there's only twenty six letters in the English alphabet. Even if someone's handwriting isn't perfect, you can usually tell what letter they intended to write so you can still read it- it doesn't matter that it doesn't look exactly like every other letter \"A\" ever written. Analog is more like a painting than letters- each tiny piece can carry a ton of meaning (that's why a picture is worth a thousand words) but the downside is that even a tiny bit of noise in the line can make you lose some of that meaning.",
"Analog control stick on your controller. Push a little bit, and your character walks slowly, push the stick hard all the way in one direction and they run. Digital is like a d-pad. There are the 4 directions, and you are either pressing a direction or moving, or not moving at all. No states in between on or off. If you can transpose this to circuitry you'll understand the concept. This is why Digital to analog converters are so cool, you can convert an analog signal to digital for use with IC and stuff, then decode it back at the end.",
"Think about a 5 volt circuit. Digital asks \"Is it on or off\" Analog asks \"What is the voltage, exactly? Is it 3? 3.8? 4?\" Analog technology is a record player. The groove moves a needle along a wavy track that represents the waveform of the music being played. The needle moves inside a coil, generating an analog voltage, the voltage changes in relation to how the needle moves and the amplifier feeds that analog signal into an analog speaker. Digital technology is more complicated. Think about a sine wave, analog signals are smooth waves but digital signals are only on or off. Digital signals take that analog value and turn it into bits. a 3-bit number can represent a digital number between 0 and 7. With this, we can break that sine wave up into steps, and each step is 1/8 of the total wave. It's a lot lower resolution. As far as arduino is concerned, analog are going to be your inputs from potentiometers (variable voltage) and your PWM outputs"
],
"score": [
13,
5,
4,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8xrwkh | Why do some electronics allow you to place multiple batteries in the same configuration while others require an alternating configuration? | For example, my TV remote I have to alternate them positive up then positive down, but my Amazon Fire remote can put both batteries positive up. | Engineering | explainlikeimfive | {
"a_id": [
"e255h3g"
],
"text": [
"URL_0 In a series circuit, the current through each of the components is the same, and the voltage across the circuit is the sum of the voltages across each component. In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component."
],
"score": [
12
],
"text_urls": [
[
"https://en.m.wikipedia.org/wiki/Series_and_parallel_circuits"
]
]
} | [
"url"
] | [
"url"
] |
8xu3cy | Why haven't they designed an emergency parachute for passenger jets? The military can air drop tanks, but I've never heard of a emergency parachute for an entire plane. | Engineering | explainlikeimfive | {
"a_id": [
"e25p43y",
"e25rrpa",
"e25p84y",
"e25p1dg"
],
"text": [
"Very very few passenger planes suffer failures at an altitude where a parachute could help. The vast majority of incidents occur during take off or landing Even in the event of an in air double engine failure you're probably still significantly better attempting to glide to an airport than making a poorly controlled landing in a parachute",
"There are whole plane parachutes for small, private airplanes. That is [Cirrus's]( URL_0 ) big thing. The technology doesn't scale to larger aircraft, they are too heavy and travel too fast for a parachute to be effective.",
"It would be impractical. You can't just shove a tank out of an airplane and hope for the best. It is an engineered controlled drop. When an airplane is in trouble, it can be spinning or oriented in a way that would cause the parachute to get tangled or not deploy facing the right way. Add that to the fact that manufacturing and installing one on every aircraft would be insanely expensive compared to the number of actual situations that one might even be needed.",
"It would be expensive and add a lot of weight. Most plane crashes take place near the ground too, so a giant parachute would be ineffective. But even when you're up in the air depending on the damage a parachute could very likely be useless."
],
"score": [
11,
6,
5,
4
],
"text_urls": [
[],
[
"https://cirrusaircraft.com/innovation/airframe-parachute/"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8xv0wz | high-pitched frequency noise I hear when my phone is plugged into aux and charging on car cigarette lighter. | Engineering | explainlikeimfive | {
"a_id": [
"e25yv0p"
],
"text": [
"It's called \"coil whine\". There's little metal coils and the electricity makes them vibrate real fast and they make a noise. In more expensive electronics, they stop them from making that noise by putting hot glue on the coils to hold them in place. The noise doesn't mean there's a problem. But it can be annoying."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8xw9rh | How do we keep super accurate time? | Even high-precision watches loose seconds per year. Yet several websites will show me the __exact__ time. How do we reliably measure what time it is without loosing seconds? Is there some ultra-accurate clock somewhere? If so, what clock do we use to check if the ultra-accurate clock is accurate? In the middle ages, there wasn't an exact correct time. So how did we decide what precise time it is in the first place? Having trouble rapping my head around this. | Engineering | explainlikeimfive | {
"a_id": [
"e268o3t"
],
"text": [
"The [official US time]( URL_0 ) is maintained by the [National Institute of Standards and Technology (NIST)]( URL_1 ) using ultra-accurate atomic clocks. The official SI definition of a second is the time that elapses during 9,192,631,770 cycles of the radiation produced by the transition between two levels of the cesium 133 atom. Atomic clocks are incredibly precise instruments that can measure those tiny fluctuations into atoms, and because those atoms are operating based on the fundamental laws of nature they are constant and unchanging. NIST also provides calibration services. If you need to know **exactly** how long a foot is, they're the guys to ask."
],
"score": [
14
],
"text_urls": [
[
"https://time.gov/",
"https://www.nist.gov/"
]
]
} | [
"url"
] | [
"url"
] |
8xzyxg | How does reprogramming car ECU increase performance so drastically, without touching any engine parts? | Engineering | explainlikeimfive | {
"a_id": [
"e26xzwi",
"e26z3bo"
],
"text": [
"It's for the longetivity of most mid-range cars. You can turn down performance to reduce stress on components to increase part life or turn up performance to have the exact opposite effect. Often times on leaned out or performance tunes there are several issues that become apparent over short distances like coolant And oil temp due to the added stress. Most of those things either can't or won't be monitored by your average driver.",
"Well manufacturers have to comply to certain emission specifications and want to have the car be reliable also so they put a very conservative tune in to accomplish this. While if you want to tune it yourself you can be a little less conservative by adjusting timing and changing boost controllers to add more power and make emissions harsher. Stock turbo cars are very very conservative I've found and its lot easier to get some easy power but upping the boost from sometimes factory like 6psi to 8 10 or even sometimes more depending on what the vehicle can \"safely\" handle"
],
"score": [
6,
6
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8y1ir6 | How do gasoline pumps automatically stop filling when your tank gets full? | Engineering | explainlikeimfive | {
"a_id": [
"e27bb41"
],
"text": [
"on the nozzle is a hole. the pump sucks the fumes of the gas trough it. when the tank is full it sucks gas in this hole and a mechanism cuts off the gas flow."
],
"score": [
73
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8yehst | why is it that sometimes some electric windmills are not spinning despite facing the same direction as windmills that are spinning? | Engineering | explainlikeimfive | {
"a_id": [
"e2a9z43",
"e2abyd2"
],
"text": [
"It takes a fair bit of oompf to get them going. Some have starter motors, but if the wind is just a bit slower for that one than others, it may not kick in. Also, they can have brakes put on so they're not spinning during maintenance.",
"It depends, there are a few cases where it wouldn't be spinning The wind could be too fast for that one so it put on the brakes to avoid damaging itself It could be undergoing regularly scheduled maintance and would be brought to a stop and locked in place for that It could be broken and awaiting repair. If anything goes wrong in the wind turbine it tries to just bring everything to a halt and wait for someone to come fix it. This minimizes the risk of damage to the wind turbine because you will have a much harder time breaking something that is locked in place than something that is spinning wildly."
],
"score": [
7,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8yjm05 | Why engineers use mechanics to produce linear motion in electric tools? | Recently I've been watching a lot of YouTube power tools reviews (with disassembly), and for example in reciprocating saws - where ONLY linear motion is required - it is done with a mechanism that converts electric motor's turning into strokes. Why is that so instead of using big, buffy electromagnets to produce push-pull motions? What's the advantage of converting rotary motion, or, rather, what are the disadvantages of using a single electromagnet? I can potentially withstand an ELI12 on that matter. Thanks in advance! | Engineering | explainlikeimfive | {
"a_id": [
"e2bcr12",
"e2bd1kg",
"e2bctte",
"e2bd76t"
],
"text": [
"Rotary motion is simpler and more efficient To make it go in and out you'd need a solenoid, circuitry to change the direction, and a big DC power supply because an AC solenoid won't do anything. It's not very efficient since you'll spend energy making it go forward, then bringing it to a stop, then making it go backwards, then bringing it to a stop. That's wasting half the energy. Rotary motion requires a bit of mechanical work but once designed it's just another metal hunk. The AC motor requires no supporting circuitry if you just want one speed. Most of the energy is used getting the rotating shaft up to speed and that keeps spinning so no energy is lost bringing it to a halt, just the light blade mechanism. The rotating mass also has a fair amount of inertia which will help the blade power through obstructions at the end of it's stroke because the obstruction would have to push enough to stop the rotation rather than just keep the stationary blade in place",
"To get more force out of an electric motor without changing the speed you can either use bigger coils and magnets, or you can spin a motor the same size and torque faster and use a gear reduction to get more torque. The second option is nearly always cheaper and lighter. A linear motor with enough force to run a saw would have to be very big and heavy, using a lot of copper and potentially expensive magnets. It may also put more vibration into the tool and user, because more mass is in reciprocating motion, and it's harder to offset that vibration with a counterweight.",
"It is much more efficient to convert rotary motion to reciprocal. A linear motor or solenoid would have to accellerate and decelerate the blade assembly 30 times per second. The rotary converter keeps a relatively large mass moving in the same rotary direction all the time and that acts as a flywheel. A solenoid usually has a shorter stroke than a reciprocating saw needs. A linear motor would require more complicated drive electronics. The only power tools I own that use linear motion in the motor are an engraver and a shaver. Both have very short strokes. My other shaver is rotary and is lighter, quieter, and does a better job.",
"A rotary motor to reciprocating mechanism is going to produce smoother motion, as it has built in flywheel effect, and the motion naturally slows at each reversal point because (most) such rotary-to-linear mechanisms produce sinusoidal-ish output. A linear motor without a lot of fancy (pronounced: expensive) control mechanisms would just slam the blade carriage back and forth like a double-ended pile driver."
],
"score": [
19,
5,
4,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
8yp2xn | Why do nuclear smoke or steam stacks have their specific iconic shape? | Engineering | explainlikeimfive | {
"a_id": [
"e2cn5om"
],
"text": [
"These sorts of cooling towers aren't exclusive to nuclear power plants, but the gist of the reason for the shape is > The hyperboloid shape aids in accelerating the upward convective air flow, improving cooling efficiency. Also, strength and fewer materials to build. Basically the shape has better flow due to hot gas physics than if it were a straight tube and is stronger and less expensive. Here's some further reading: URL_0 **Edit:** added more info"
],
"score": [
5
],
"text_urls": [
[
"https://en.wikipedia.org/wiki/Cooling_tower"
]
]
} | [
"url"
] | [
"url"
] |
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