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9jr0k5 | Why not use single edged blades? | Hi! So internet doesn't provide much support in this question-as we all know most of blades are sharpened on both sides with similar angles-but why not simply use an one sided edge?It would cut the same and would be much better and easier to sharpen-something like a cutting triangle. | Engineering | explainlikeimfive | {
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"I think you mean [chisel grind]( URL_0 ) where one side of the blade is flat. It works well, but has the disadvantage that the knife may push toward one side while cutting, and the cutting location is off center which requires some learning.",
"A knife sharpened on both sides of the edge will cut straight, because it's symmetrical. A knife sharpened on only one side--and they do exist, for special purposes--would constantly want to cut in a curve if you were pushing it through something semi-soft like a block of cheese. This isn't an issue for a blade that's only used to cut shavings off the surface of something (like the wood chisel that this shape is named after), but with a general-purpose knife, you could end up cutting anything, so it's worth the extra effort to sharpen it with a symmetrical edge.",
"I have several woodworking tools, the chisels and plane blades are sharpened one side only, I have a small knife also sharpened one side. I use it as a marking knife and it is one side flat so it can follow a template closely. It is Japanese."
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9jvcmp | In the CIV games, only certain boats could travel away from the coast. In real life what determines if a boat is able to safely travel across e.g. straits/seas/oceans? | Engineering | explainlikeimfive | {
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"A number of factors: - size of boat to carry enough food and other supplies, including extras in case something gets broken or lost, or the trip is longer than expected - unless you're talking about speedboats driven by large motors with hydroplaning hulls, the speed depends on the length of the boat. - Is it large and well-protected enough to deal with storms and heavy seas? - if a motor boat, is there enough fuel? (Most get poor gas mileage). If it's a sail boat, can it fly enough sails, good enough sails, to make good headway with the available wind? If a rowboat, will the crew have enough stamina? - if the trip is longer than a day you need multiple people so that some of them can always be awake, without driving everyone nuts from either sleep deprivation or being cooped up in a cramped boat.",
"There are quite a lot of factors that affect the seaworthiness of vessels and their ability to sail away from the coast. In the case of a trireme, they're built with a fairly shallow draft. That means they are not very stable in rough seas. (However they are very good in shallow water.) Generally they're not likely to be built to withstand rough seas. Ideally they'd be in a sheltered harbour or drawn up on a beach if the weather turned bad. Triremes also require a substantial crew of rowers compared to their size. This means they can't stay at sea for too long without running out of supplies - most importantly water. Triremes tended to stop frequently to resupply. There were cargo vessels, of course, which were rounder and fatter, but even these had similar problems. I don't think they were any better in rough seas. However there's another crucial issue that isn't related to ship design. Think about the civilisation tech tree. What is it that lets you progress from triremes to caravels, ships that can cross oceans? It's not a new shipbuilding technique. It's (usually) *astronomy*. In other words, it's *navigation*. It's all very well having a ship that can sail the high seas, but who's going to do that if they can't find their way to where they're going, or back again? Even up to the 15th/16th centuries, ships sailing the Mediterranean didn't like leaving sight of land in case they were lost. And that's a pretty small sea. If you want to travel long distances out of sight of land, the ability to figure out where you are and what direction you're heading in is crucial.",
"In addition to what others have said, it should be kept in mind that the important part of you question is the word safely. There isn't really a lower limit when it comes to technology and crossing the ocean. There is always a chance that you might make it, just not always a big chance. Thor Heyerdahl famously demonstrated that per-columbian American's could have traveled to the Polynesian Islands despite having close to no technology in the area of ship building. He build a raft using material and tools available to them and used it to successfully sail across the ocean. Of course he had modern technology as a backup in case of trouble and he had modern knowledge telling him where he was going and how to get there, but those were not limitations of the raft itself. It is not so much if your boat is capable of sailing the oceans, but if you are crazy enough to risk it. For most of history most sea-fearing people were not crazy enough to take stupid risks. They kept to the shores and in familiar territory when possible. If ships were optimized for littoral waters instead of the open sea, than that was not so much a limitation of shipbuilding but also ships being built for the purpose people were going to use it for."
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abgzei | Why is german engineering considered legendary? | Engineering | explainlikeimfive | {
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"This reputation, in part, can be seen as an offshoot of the German arms industry dominance in tree 1800/1900s when they basically armed every other nation on a continent (China, Africa, most of South America, etc) with high quality firearms, typically better than anything locally produced. Even today many of those firearms are still well-regarded and many nations still use German firearms (Mauser, H & K, DWM, etc). Their vehicles also saw a similar high grade of over-engineering or percieved such from WW2 where a lot of German vehicle companies began experimenting and having to engineer for use all over the world."
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abhnoq | How did people go about installing electricity/wiring in old buildings which were not designed with this intention in mind? | I’m on my first episode of Grand Hotel and this question just popped into my head. Considering a lot of older buildings, even say those built in the 1800s, were not constructed to support electrical installations— how did people *make lightbulbs work*? | Engineering | explainlikeimfive | {
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"First they installed tube and knob lines in the rafters of the attic / roof which depended wholly on the style of the structure. Then lines were fed down either by running over walls, through hollow plaster and lathe walls or through the disconnected pipes that previously used to supply town gas. When the wire was in place they soldered in a a light bulb socket of whatever regional design before the Edison socket became standard was common in that region and the other end were directly soldered into the tube and knob lines. They then connect the tube and knob lines into the power lines in town or if in a country house a personal generator. A lot of early light fixtures, sconces, were re-purposed gas lights.",
"Its called Chasing, you cut into the plaster or stone/brick work, deep enough to fit a plastic/metal conduit or just the insulated wire. Then plaster back over it. This can be done with a hammer and chisel or specialist tools. If its a listed building sometimes we can not cut into the stone work, instead fix the wire/conduit to the wall then plaster over it. All old stone buildings have about 2 or 3 inch thick plaster render on most internal walls. Plenty of room to fit a wire in and cover back over.",
"Easiest way is to have a good drywaller come behind you and do patch work Cut out strips of drywall to route the wires through walls and ceilings. If you are lucky and there is an unfinished basement and attic, its not to bad to fish walls without damaging drywall to bad, but its still kind of miserable",
"Well we can do anything after the fact. Electrical isn't required to make a building stand up and it isn't going to make it fall down by adding it. Having said that, working in any house older than 1960 is a pain in the ass and I either quote a price I can't refuse or just flat out turn it down. Old houses suck."
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abk5on | For humidifiers, why is the refill hole always on the bottom of the tank? | Engineering | explainlikeimfive | {
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"Because you're looking at bottom fill humidifier.. if you look for a top fill humidifier, it fills from the top"
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ablx6q | Can someone explain to me dB levels of antennas and what is good or bad? | I work in the cell phone industry and often hear enginerds talk about how this or that antenna is at minus 20dB or whatever. What does this mean? is that good or bad? and how does this relate to a noise floor. What is a noise floor? Thanks in advance. | Engineering | explainlikeimfive | {
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"dB by itself is a relative measurement. When someone says “that antenna has 10dB of gain” that means it has 10dB of gain as compared to another antenna, usually a plain dipole or a theoretical isotropic radiator. When you get gain out of antenna, it’s always a trade off between gain and directivity. A 0db gain antenna receives equally in all directions. A 24dB parabolic dish can’t hear well from either side or the back. You may see other terms like “dBm” which is dB as referenced to 1 milliwatt. You’ll see that a lot in the wifi world. The access points output power level measurements are usually in dBm and the received signal level is the same. So if you see your access point reporting a signal level of -95dBm, that means the signal is 95dB lower than 1 milliwatt. Or “that signal was 30dB over the noise floor” which is another relative measurement.",
"A noise floor is the point at which the electrical noise is bigger than the signal.. Let's say you're in a loud bar. The noise floor is however loud the bar is, let's make up some imaginary metering system and say that the bar is 20 Emus loud. So if you want to talk to your buddy, you're going to have to be at least 21 Emus loud or he won't be able to hear you. But... If you were 21 Emus loud at one foot away from yourself, you know how sound isn't as loud the further away you get right? So if your buddy is at the other side of the bar, your signal may only be 12 Emus loud by the time it reaches him. 12 is significantly less than 20 so your message gets lost in the loud bar. So you're going to have to be loud enough so by the time it gets to him, it'll be say 25 Emus loud so it stands out from the background noise of the bar. The same in electronics. There's electrical noise everywhere; cosmic microwave radiation, electromagnetic hum caused by power lines, broadcasters on a nearby frequency, etc. So the noise floor is all that added together, and your devices have to be able to be \"loud enough\" to each other to overcome that noise so it can be picked out by the receiver. This is also where the term signal-to-noise ratio comes in which is how much louder the signal is compared to the noise."
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abne1m | Why do the pipes under sinks have two 180 degree turns? | Why can’t the water flow straight down and what is the importance of these turns? | Engineering | explainlikeimfive | {
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"They are called traps and always full of water to prevent sewer gasses from coming up through the drain.",
"It's called a P-trap, and it exists to keep a bit of water blocking the pipe (a water lock) so you don't get all the smells from the sewer going directly up your drains.",
"Primary reason is sewer gasses as others mentioned. Secondary: catch anything that may go down the drain, like a wedding ring, so that it is recoverable. Some [p-traps have screw off bottoms]( URL_0 ) for this reason"
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abohpn | How do car intakes keep rain from getting in when driving in the rain? | Engineering | explainlikeimfive | {
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"Well, the primary way is that the intake is usually under the hood where it's out of the rain. But, even for ram air intakes there isn't usually that much water in the air. The little air that is there usually splatters on the back of the ducting. Ultimately, there is a filter on the air intake that doesn't let water in."
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abot7i | Is it possible to transmit electricity using one single wire instead of two? | If it is, what are the implications/disadvantages of such system? | Engineering | explainlikeimfive | {
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"Yes. Such a system is known as [single-wire earth return]( URL_0 ). As the name says, rather than using a second wire to complete the circuit, it connects both ends to the ground and transports the electricity that way. It's been used extensively for rural electrification. The benefits are self evident, in that it requires half or a third as much wire (and very cheap wire (often ordinary steel, as opposed to more expensive aluminum used in other systems) can be used due to the low current), pole capacity, maintenance on above, etc. Downsides are that transmission capacity is somewhat lower than multi-wire systems, voltage regulation is somewhat problematic without fancier equipment, and grounding can be somewhat problematic in some places (e.g. areas with permafrost or very dry soils).",
"If the destination has access to ground (literally, the earth), you can send power with one wire.",
"Yes, and no. There are systems that seem to use a single wire, but they use the ground as a return path. Effectively, the Earth becomes the second wire. Electricity always requires a circuit.",
"With alternating current you only really need one wire as long as the other wire goes to ground. With direct current you have to finish the circuit back to the power supply. The power coming from the grid to your house is just a single line",
"Let's pretend you have an air tank with a pump and a valve. If you pump extra air into the tank, then open the valve - air rushes out into the room. If you pump air OUT of the tank then open the valve, air rushes in from the room. If the air in the tank is the same pressure as the air outside... air doesn't really flow at all, even with the valve wide open. Electricity flows the same way - if part of a system has more electrons than the rest... they start 'pushing' to try to get from the high pressure area to the low pressure area. If you reverse the 'pressure (voltage)' they go the other direction. But there always has to be a high pressure area and a low pressure area for flow to happen. In a two wire system, one wire is the high pressure area, and the other serves as the low. But, just like we can use the air in the room to be either the high pressure or low pressure side of the flow with our air tank and pump, we can use the electrons in the earth to be the high or low voltage side of a circuit. So electricity always has to have somewhere to GO if you want it to flow, but you don't always have to run two wires to make that happen."
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abpbpn | How does wattage affect transmitters and receivers? | Saw a post about New Horizons transmitting data through space with a 15-watt transmitter and the main reason we are able to get this data is actually due to the receivers on Earth being massive. So: 1. How does having a high watt receiver allow us to get data from extremely long distances? 2. What happens if the roles were reversed? Massive watt transmitter to a small watt reciever? 3. Do receivers get more interference the more the wattage is increased? | Engineering | explainlikeimfive | {
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"It's not that the receivers are high wattage. It is that they are *physically* huge, and very sensitive. Being large allows them to capture more signal. In a transmission/reception, the key thing is \"signal to noise ratio\". As long as you have good SNR, you can amplify the signal and get data.",
"Your question is at the heart of a big field of study called [communication theory]( URL_3 ). Some key ideas from this field: First, no receiver is perfect: it will receive signal power from the transmitter, but it will pick up \"noise\". This could be random static from deep space, but noise is also created by the electronics in the receiver itself. Second, the [Shannon-Hartley theorem]( URL_1 ) says that the data rate depends on the ratio of signal power to noise power picked up by the receiver (signal-to-noise ratio). This works for any form of communication including the human ear: it gets harder to understand what someone is saying if the room is noisy, but you can compensate for that by speaking slower or louder. So, there are three ways to communicate faster: 1) Increase the power of the transmitter. 2) Make it so a larger fraction of the transmitter's power is actually received. 3) Decrease the noise level of the receiver. Regarding point 2, we get into [antenna design]( URL_2 ). Radio waves spread out as they travel, so the farther the transmitter is, the less power will be received. Making the receiving antenna bigger in diameter will obviously collect more of this power. Surprisingly, making the *transmitting* antenna bigger helps just as well: a big antenna can focus the signal more tightly than a small one. An interesting fact about antenna design is that it's symmetric: if 1% of the signal is received when antenna A transmits to B, then 1% of the signal will be received when B transmits to A. Okay, so here's our final list of things that will let us communicate with a spacecraft faster: 1) More powerful transmitter 2) Physically bigger transmitting antenna 2) Shorter distance (can't change this sadly) 2) Physically bigger receiving antenna 3) Lower-noise receiver Note that the *power* used by the receiver doesn't matter, only its noise level. New Horizons has the most powerful transmitter, and the biggest antenna that we could fit on it. 15 watts doesn't sound like much, but the entire spacecraft runs on 200 watts total and the transmitter isn't 100% efficient. Its 2-meter antenna isn't all that big either, but it's got to fit inside the rocket. We compensate for these limitations on the ground side. We use [FREAKING HUGE]( URL_0 ) 70-meter receiving antennas on the ground, and super high-tech low noise receivers. And even so, the signal-to-noise ratio is so small we can only receive data at about 1000 bits per second. But what happens when we want to *send* data to New Horizons? Unfortunately the super high-tech low-noise receivers are way too big to put on a spacecraft. So we compensate by sending out a *lot* more power when we transmit from the ground ... about 20,000 watts. New Horizons can't hear very well or talk very loudly, so on Earth we compensate by listening very carefully and shouting as loud as we can. So, to sum up by answering your questions: > How does having a high watt receiver allow us to get data from extremely long distances? It's not the power of the receiver that matters, it's how low-noise its electronics are. The power of our ground antennas matters, though, for transmitting *to* New Horizons. > What happens if the roles were reversed? Massive watt transmitter to a small watt reciever? Only transmitter power matters, but communication is symmetric in terms of antenna size. You can compensate for a small transmitter with a big receiver, and using a bigger antenna helps both sending and receiving equally."
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abqa07 | Why do exterior doors of houses always open inwards? | They are made so that they are easily kicked in with only the lock and handle keeping it secure where as if you were to try and kick it out it’s nearly impossible due to the way the frame is made. Also they need space inside for opening whereas if were to open outwards there wouldn’t ever be obstacles in the way. | Engineering | explainlikeimfive | {
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"I assume so people don’t just pop off your hinges and remove the door?",
"Most front entry doors in our area swing inward, and the justification for it used to be that outswing doors are unsafe because their hinge pins are exposed outside, where they are easily popped out by a burglar to get into the house. But that argument doesn’t fly anymore. Most prehung entry door manufacturers now install special security hinges on their outswing doors that have non-removable pins. You must open the door and unscrew one side of each hinge to remove the door. Another type of security pin is only removable when then door is open. So outswing exterior doors have become more acceptable. But there are pros and cons for both types of door swing. OUTSWING DOORS PRO More resistant to high wind and driving rain in a storm. The Insurance Institute for Business and Home Safety (IBHS) recommends outswing exterior doors as more hurricane resistant because “positive pressures actually push them more tightly against the door seals, which helps reduce water intrusion, and because it is much easier to achieve impact resistance from an outward swinging door.” Most exterior doors installed in South Florida’s high-velocity hurricane wind zone are outswing for this reason. Not easily forced open from the exterior. CON Not practical in cold regions, where a heavy snowfall could prevent opening the door. Not what most people are used to. INSWING DOORS PRO The customary swing for a front door. Enables installation of a storm or screen door. CON Easier for a burglar to force the door open with a blunt impact. Conversely, this also makes it faster for fire/emergency services to knock the door down when necessary. Less weather resistant than an outswing door. Exterior doors for commercial buildings always swing outward, with just a few allowed exceptions, because the door must open in the direction of the flow of people exiting the building in an emergency. You will likely have your choice of which way to swing your residential front door, but we recommend checking with the county or municipal building department for any special local restrictions before making your decision. The available floor or landing area for the door swing is another consideration.",
"Also: snow. Door opens out when you get 2+ feet of the heavy wet snow. . . . . . and your climbing out a window to shovel yourself out. Likewise, jamming a wedge under the swings-to side locks it. I’d rather be able to use a wedge to lock others out, than to be locked in. I mean think of how scarily effective reversing the swing on doors would allow arson-as-a-murder-method to be.",
"It's so you don't hit the guest that is knocking on your door when you go to open it. Fun fact: In public you'll find that most exterior doors open to the outside in order to prevent stampeding during emergencies.",
"Don't forget storm doors. Hard to put on a storm door when your main door opens outward.",
"If they were made to open outward, that would put the hinges on the outside of the house. That would make it easier to remove the door and gain access to the house in a quieter manner, which would be unsafe. It would also mean someone inside the house couldn't barricade the door closed."
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abqjfv | What's the difference between negative terminal and ground? | Engineering | explainlikeimfive | {
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"Nope, all the same. The negative terminal connects to the chassis essentially turning every connected metal part of it into a negative connection.",
"For most vehicles, negative is usually directly connected to the chassis, which is supposed to be treated as ground. But *some* vehicles exist where *positive* is ground (connected to the chassis), and negative therefore has a voltage less than zero.",
"Based on your wuestions it sounds like we are specifically talking about automobile wiring. Ground is literally a connection to the earth. Burried outside your house is a long metal bar stuck down into the ground connected to the ground busbar in your breaker panel. This allows any current that \"escapes\" via shorting or some other means to travel directly back to earth as a safety. In a car there is the tires that have been purposly made tk be conductive. The \"negative terminal\" in the car is just all the metal frame and body components acting like a big wire going straight back to the negative battery terminal to complete the circuit. This simplifies wiring by allowing you to attach the negative wire from any electrical component to the nearest frame or body instead of a seperate wire all the way back to the battery. It also keeps all of the metal car pieces \"bonded\" and helps reduce the chance of electrical arcing and causing a fire."
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abt80h | Why are cruise ships not registered out of the port they leave from? Why are most the North American ships registered to Nassau, The Bahamas? | (If I flair this wrong please correct me) | Engineering | explainlikeimfive | {
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"Because when ships are at sea they follow the laws of the country of registration, so most cruise ships will register in countries with lax workers right laws to save money",
"Most ships are registered under \"Flags of Convenience\". Because they travel internationally, they are free to register in any country that will take them. They operate under the laws of that country and they usually register in one that has little regulation and low fees. They may rarely if ever visit their home port. URL_0",
"Most countries allow foreign ships access to their ports. For example a Norwegian ship is allowed to ferry cargo between China and the US. And this have created a market for countries to make registering ships with them cheapest. If it costs $10M to register a ship in the US and Panama offers to register the ship with them for $5M then the owners would much rather register the ship in Panama. They still have access to the same ports at the same rates no matter where they are registered."
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abu8og | Why does flushing the toilet regulate the temperature of the shower (as seen in movies) | I've never experienced this myself, even though I have tried my hardest. :) | Engineering | explainlikeimfive | {
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"Toilet only gets cold water in, if you are using the shower with both cold and hot water, suddenly the supply of cold is reduced so the temperature mix is changed (more hot).",
"So no one has answered why you have never experienced it. There are a couple of reasons all coming from the fact that people USED to get burned from a toilet flush. Low flow toilets and shower heads mean that a sudden change in water draw from another source doesn't rob the shower of the cold pressure. Higher overall pressure from the water supply and input pressure regulators mean that when a pressure drop would have occurred on the cold line it is compensated. If you really want to see this happen in person go to an older house (maybe a cheap Air BNB) and try turning on the cold on a faucet and flush the toilet. If the flow reduces while the toilet tank refills then you have the perfect plumbing for 2nd degree burns in the shower.",
"The shower head mixes hot and cold water from two seperate pipes. When you flush the toilet, it uses cold water, dropping the pressure of the cold pipe in the shower, which in turn makes the water in the shower head hotter for a few seconds",
"Your shower water is a mixture of hot and cold water, with you setting the temperature you like by using the knobs to determine how much of the water is hot and how much is cold. Your hot water is generally stored in a tank. Cold water comes into the tank and then it's heated. Cold water, on the other hand, comes in cold through the pipes coming into your home. The amount of water your pipes can deliver is the same constantly. It may not be enough to provide cold water to both the toilet and the shower at the same time. Without enough cold water, the shower water becomes mostly hot water or all hot water for a few seconds until the toilet is done filling."
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abxg4n | When 4G came out it wasn't true 4G, it was 4G HSPA then 4G LTE. Now I'm seeing comercials for 5Ge. What do all of these things mean and will we have real 5G wireless soon? | Engineering | explainlikeimfive | {
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"5Ge is AT & T marketing for the latest release of LTE Advanced called LTE Advanced Pro or sometimes Gigabit LTE. It is essentially a backport of some 5G technologies that are compatible with the LTE Advanced hardware to provide a transitional network. This allows for a faster network without requiring complete replacement of the radios. Real 5G has been launched in some test markets, but as of now there is no benefits to it for mobile phones. Right now there are very few mobile phones that have 5G radio. 5G radios right now are typically on a separate chip which means they decrease the battery life. Don't look for real 5G to be widely available until 2020. Real 5G requires a hardware upgrade on the towers and phones. 2019 will start to see 5G showing up in more phones but carrier coverage will likely still be somewhat limited to larger markets. You can get 5G in some markets for fixed wireless services. These are the mobile companies attempt at the home internet market.",
"Well to answer the last part, no, true 5G won't come too soon. 5G can't be simply installed on a tower. It doesn't have the range to blanket an entire city. They have to install on rooftops in cities for the time being. And it has issues penetrating walls like 4G can. I've seen estimates that service extends as low as 500m from the transmission site. So they have to spread transmitters all over like a net. [Here's an article on the '5Ge' distinction.]( URL_0 ) It's essentially 4G+. Edit: a word. Also like to point out that I should have said that while there are some ‘true 5G’ coverage areas, they’re few and far between for the moment, and last I saw there were like 2 or 3 available phones that could take advantage of it, besides some router devices. That iPhone or Android you have on you now can’t take advantage of it. What is almost certainly rolling out first to most places is apparently ‘5Ge,’ which is just really enhanced 4G. It’s a bit like if Ferrari took a Nissan and through in some engine enhancements and then marketed it as a Ferrari. It’s not really a Ferrari, it’s an enhanced Nissan.",
"I understand your confusion, as cellphone makers will not exactly lie, but not tell the truth either about what 4G means. There are several current ways to implement a wireless radio based network, and to be honest its a MESS of standards. ripped right from wikipedia to show how convoluted this aspect of networking has become: \" LTE is commonly marketed as **4G LTE & Advance 4G**, but it does not meet the technical criteria of a [4G]( URL_9 ) wireless service, as specified in the 3GPP Release 8 and 9 document series for [LTE Advanced]( URL_12 ). LTE is also commonly known as 3.95G. The requirements were originally set forth by the [ITU-R]( URL_10 ) organization in the [IMT Advanced]( URL_0 ) specification. However, due to marketing pressures and the significant advancements that [WiMAX]( URL_13 ), [Evolved High Speed Packet Access]( URL_4 ) and LTE bring to the original 3G technologies, [ITU]( URL_1 ) later decided that LTE together with the aforementioned technologies can be called 4G technologies.[\\[3\\]]( URL_3 #cite_note-3) The LTE Advanced standard formally satisfies the [ITU-R]( URL_10 ) requirements to be considered [IMT-Advanced]( URL_6 ).[\\[4\\]]( URL_3 #cite_note-4) To differentiate LTE Advanced and [WiMAX-Advanced]( URL_2 ) from current 4G technologies, ITU has defined them as \"True 4G\".[\\[5\\]]( URL_3 #cite_note-5)[\\[6\\]]( URL_3 #cite_note-6) \" [ URL_8 ]( URL_3 ) So, LTE advanced \\*IS\\* a 4G (fourth generation) networking system....except that.. its not TRULY? ~~If you want to get super gritty with it all, I believe IEEE~~ **~~802.16~~** ~~2-2016 is the current documentation that I would trust.~~ Its all just a mess..",
"Until 5G, the G meant generation. 1st, 2nd, 3rd generation -- the 4th generation had two competing technologies, LTE seems to have de facto won, but it took too long for the technology to win a singular 4G naming convention. 5G is also the 5th generation wireless telecom technology, but some clever engineer also though to double the operating frequency from 2.4 to 4.8 GHz to make it approximately 5GHz as well. (5G wifi is called 5G because it operates at this frequency, but is wifi, not 5th generation wireless) And since range of a signal is less at higher frequency, as others have stated. It requires more infrastructure to operate, and thus will take time and investment to propagate through the world.",
"Dave Lee explains the difference of 5G and what we have now, I'll leave a [link]( URL_0 ) to the video.",
"*n*g stands for “nth generation”; 4g HSPA (high speed packet access) was a 3g technology to faster than regular 3g, it used faster packet switching. LTE: “long-term evolution” the standard agreed by all carriers that will remain in place long-term. LTE will be the fallback for 5g. Standards take a long time to evolve and as a standard, need to be stable at some point. 5G e “evolution”: a particular evolution of 4th generation tech, most certainly not yet a standard 5g connection. Carriers have yet to prove 5g outside of smaller experiments. The standard has been mostly written so carriers and hardware are planning for it. Phones and carriers are using this as BS marketing. there is no 5g yet even though there working on it. There’s still several issues with 5g tech. 5g e is just marketing."
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ac4ytr | These new Ultimate Thule photos have me wondering about New Horizons.. | Engineering | explainlikeimfive | {
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"1. Radio waves, just like every spacecraft ever. The exact same radio waves we use here on Earth. 2. Yes, but asteroid belts in real life are nothing like in science fiction. There's no clutter. Asteroids are so far apart that the odds of any impact are so low, trajectory planners don't even bother to factor that in. 3. New Horizons used only 1 gravity-assist at Jupiter to send it to Pluto. It did not approach any other planets. 4. It's powered by something called a radioisotope thermoelectric generator. Basically it uses the decay heat of chunks of plutonium to generate power, because, as you correctly surmised, solar power is totally impractical that far out. 5. Yes, but it's going really fast and there's very little fuel left, so it's mostly just going where it's going. There's not enough fuel left to alter it's trajectory enough to visit any other objects, so they'll most likely keep what's left for attitude control. Again, control is with radio waves, but it's not in real time. At it's present distance, it takes any signal from Earth over 6 hours to reach it (and the same amount of time for any signal from it to reach Earth). 6. Yep. It's very cold, although not *that* cold that's it's close to absolute zero. We rigorously test all spacecraft and spacecraft systems for what we expect them to encounter during their lifetimes, including things like temperature and radiation."
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ac58sv | If things in orbit in space are moving extremely fast, how do they counter random space debris hitting things like the ISS? | Wouldn't even the smallest rock do insane damage travelling at those speeds? | Engineering | explainlikeimfive | {
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"They do their best to keep track of every single piece of debris. NASA is currently tracking over 19,000 near Earth objects. There is a real danger of an object hitting the ISS or a satellite. Objects have hit the ISS before, and holes and cracks have been made and patched. However, satellites are less sturdy and if one is destroyed it would likely cause a chain reaction of destruction. This is seen as almost inevitable in the future, and NASA as well as other space programs are trying to come up with clean up programs.",
"/u/cieluv pointed out pretty well that NASA tracks debris and that prevention isn't perfect. It's also worth noting that the volume of space is *very* large, even in earth orbit, compared to the number of objects in it. Often one of the best defenses against collisions in space is simply that they are not especially likely to occur. Space is huge, most space junk is not. We're dealing with an area larger than the surface of the entire earth."
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acd0hy | The point of Volts, Amps, Ohms, etc... | Now before you say how **"*****I've seen these posts so many times...*****"** I'll say I've seen the good ol' water explanation which helps with understanding what they are. what I'm wondering now is how do I *actually* use this information. For instance, why does **X** need **Y** Amps and **Z** Volts and what happens when you increase one of them and a followup question is how can ***I*** use this information Thanks in advance | Engineering | explainlikeimfive | {
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"Amps, ohms, and volts are all related to each other through the equation V = IR. r stands for resistance (measured in ohms), I stands for current (amps) and v for voltage (volts). If you increase voltage, your resistance or current must decrease proportionally to match, and so on for any other changes within a circuit. If you have a higher current, you need a larger diameter wire than an equivalent circuit with a lower current and higher resistance/voltage. Generally you probably won't care about this stuff directly affecting you unless like, you're traveling to a different country that has outlets with different voltage outputs than where you live (you would need to find the proper adapter or new charger cables for your items), or if you're trying to replace a power cable for a laptop or anything else with a mini transformer in it. Different pieces of equipment have different needs when it comes to these variables. Xray equipment needs high voltage transformers between the power company and the xray machine, for instance, but a regular TV or household appliance does just fine plugged into a normal outlet. You need to know what your equipment requires as far as power/electricity in order to make sure you don't irreparably damage it or the circuitry within your house/company/whatever.",
"I used this information lots of times during my time in Film School. Back then we shot with tungsten 650w and 1000w bulbs in ordinary houses with wall sockets. It was very easy to put too many lights on one breaker and trip it. The lights are listed in watts but the fuses and breakers are Amps, so you need to figure out how many amps each light draws budget your power. The same rules apply for all household power. 1000w / 115 V = 8.7 Amps.",
"> why does X need Y Amps and Z Volts Usually, you don't \"need\" a certain number of volts if you're designing a device. You *assume* a power supply of a particular voltage will be available to you, and you go from there. If you're designing something to be plugged into a wall socket in the US, you assume you'll have 110 V for a power supply. If you're designing something portable, maybe you assume you'll have 1.5 V or 3 V, standard voltages for everyday batteries. & #x200B; Then you design a circuit with that voltage as your starting point. The elements in your circuit will have a certain inherent electrical resistance to them. People often recite Ohm's Law as V=IR, but it's more accurate to say that I=V/R. Both equations are mathematically identical, but the cause and effect relationship is better portrayed in the second one. You start with your power supply voltage *V*, the elements and arrangement of your circuit determines the resistance *R*, and the current *I* that flows through is just a result of those two features. Your device will try to pull in as many electrons as it can to get the current up to what's predicted by the expression V/R. & #x200B; Things start melting down and blowing up when the designer doesn't notice that the circuit is going to pull in more current than the device can handle, or when a home user has plugged in the 17th device to the one wall outlet, not realizing that the resistance of the circuit drops every time he adds a new device (See *Resistances in parallel circuits*), which means more and more current flowing through that one circuit.",
"Volts is energy per charge - it's like an electric pressure. Just as water will flow from on top of a hill to the bottom of a hill, electrons will flow from high voltage to low voltage. It is energy per charge, so the amount of voltage is like the height of the hill with water flowing on it - a taller hill means water will flow faster. Amps is a measure of current, just like water current. Amps is literally just a measure of how many electrons pass a certain point in a wire. If you could shrink down to microscopic size and count the electrons that pass (per second), you would be measuring amps. So let that take us to power (watts). Volts tells you the energy each charge makes, and amps tells you how many charges flow by - so if you multiply these, you get the total energy that pass per second, or watts. Ohms is a bit more abstract and is defined in terms of amps and volts. Ohms is a measure of resistance - as current flows through a metal, some of those electrons bump into atoms making them slow down, lose energy, and the metal generally has some resistance to the flow of electricity. One ohm of resistance is the amount of resistance such that one volt of energy per charge only has enough pressure to push through one amp of current. More ohms means more resistance means the current goes down. So what is all of this used for? These are just the basics of every electrical appliance in existence. Aside from a simple light bulb, most electrical devices have tons of little things inside of them resisting the flow of charge and directing the flow of charge."
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acim2d | Why do zippo lighters stay lit? | Normal lighters go out after you stop pressing the release button. | Engineering | explainlikeimfive | {
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"A \"normal\" lighter is full of compressed butane. When you hold down the button, it lets a stream of flammable gas out of the lighter & that burns. A Zippo is more like a candle or oil lamp. There's a wick soaked in flammable fuel that will burn as long as there's fuel & oxygen to make it work.",
"Zippo lighters suck. You've got a compartment filled with liquid fuel. And a string that dips down into that liquid fuel. the string sucks the fuel up into it, just like if you dipped the edge of a paper towel into water. the water crawls up. its because of \"capillary action\". So the string is soaked with liquid fuel. its soaked all the time. When lite the fuel starts burning. And the string sucks up more fuel constantly. Zippo lighter fluid also evaporates. So even with the lid closed fuel is constantly escaping. You have to refuel them ever week or so even if you aren't using them. Bic lighters have a little mechanism that opens and closes a valve to allow fuel to be released. They are much better because the fuel is trapped inside. Zippo lighters were invented first. we associate them with World war 2 and cool old-school people."
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ackye4 | Why is there sand stored inside the base of some seats on a train? | Engineering | explainlikeimfive | {
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"Sand is spread on the track when the train needs extra traction. Under the seats along the sides of the carriage is just a convenient place to store the sand."
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acyqy9 | How do passenger train drivers ( for example Metra trains in IL) know which route to take to go from A to B everyday and who tells them this everyday, which track to use? | Engineering | explainlikeimfive | {
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"Train drivers also have to be taught the routes before they're allowed to drive over them themselves. Here in the UK we need to know every speed, junction, station, braking point, gradient, curvature of the line, controlling signal, sidings, tunnel, potential trespassing sites, potential contamination sites and probably some more that I've forgotten. So if I'm booked to drive a specific route, I know exactly where I'm supposed to be at a specific time and I'll know which junction signals to look for on approach.",
"Please flair this topic under the engineering category.",
"Train drivers don't decide to take this route or another, the dispatcher decide for them by setting the Switchs and signals in the correct way.m"
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ad2rso | How are sewers made? | Engineering | explainlikeimfive | {
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"On all the major construction builds I've been a part of all the underground services go in first then everything else on top.",
"I interned one summer many years ago at the NYC Dept of Environmental Protection’s Sewer Analysis group. I can confirm that the sewers generally run down the middle of the street. For installation and repair, the street is closed and gets torn up. The oldest sewers in the city only date back to the mid-nineteenth century, so it makes sense that the streets are used to route services. It’d be wasteful to tear up buildings to lay new services."
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adave0 | How does putting your foot on the car accelerator make the car move | Engineering | explainlikeimfive | {
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"Opens the throttle valve on the engine allowing more air/fuel mixture to flow in and be combusted. Historically your accelerator pedal was mechanically coupled to the throttle, these days it's mostly done electrically with a sensor on the pedal and an electric motor to move the throttle valve",
"Because no one's covered it, diesels don't have throttle bodies, so they either: A) Have the accelerator pedal attached to an injection pump (in mechanically injected models) which would just control flow/pressure B) Have the accelerator pedal attached to a sensor, and the ECU would not only control flow/pressure, but would also control injection timing"
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adfrkd | gyroscopic precession and why 2 blades on a wind turbine don’t work | Engineering | explainlikeimfive | {
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"Two bladed turbines work, and they do exist. In general, increasing the number of blades gives diminishing returns, meaning that increasing the number of blades reduces the amount of power you get from each blade. However, longer blades increase the cost. It just turns out that for large wind turbines, making them with three blades is more cost effective than a two bladed design with longer blades or a four bladed turbine with shorter blades. & #x200B; Gyroscopic precession is the effect that you get when you're moving a spinning object around, like a fidget spinner. Basically, the object wants to keep spinning in the direction that it's spinning, and if you force it to spin in another orientation instead, it's going to try to get back into its original orientation. & #x200B; & #x200B;"
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aditn2 | Why do computers make quite a bit of sound while phones seem to be completely silent? | Engineering | explainlikeimfive | {
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"Mostly because computers generate far more heat than a phone and so they needs fans to dissipate that heat. They generate more heat because they are more powerful.",
"PCs have fans in them to keep them cool. They often also have mechanical hard disks with moving parts. PCs need this cooling because they are considerably more powerful than phones (assuming you are comparing ones from around the same time), so they produce more heat. Having fans in a phone wouldn't be very practical, so the components are designed so that they shouldn't get too hot without them. That means they can't be as powerful as PC components. Mechanical hard disks have the advantage that you get a lot of storage space for your money. But again, they are too big for phones so phones have solid state storage (i.e. purely electronic with no moving parts). That's why phones have much less storage than a typical PC.",
"Computers have the benefit of not being moved and so having access to wall power. This greater energy access is able to be employed to make desktop computers more powerful but also generate more heat, motivating the use of fans to shed that heat faster. Mobile devices lack the power and assurance of ventilation to do this so they use less powerful, more efficient methods of computation. Desktop computers also are designed not to be moved during operation so they can employ things like moving disk mechanisms that are less expensive than solid state storage but don't react well to sudden physical shock. They also produce more noise than solid state storage which mobile devices use for its resistance to physical impact."
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adlu4y | Why do almost all products that require batteries, have them inserted in different directions? | Engineering | explainlikeimfive | {
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"Because effectively all batteries are implemented in *series* rather than in *parallel*. Having the batteries face different directions allows for the most efficient path for positive to negative, in *series* connection. Edit: effectively all batteries that are installed in opposite directions as described. I realized that my response implied that nearly all batteries are ever applied in series, which is incorrect."
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adv486 | How can one gun be more powerful than another that uses the same ammunition? | Engineering | explainlikeimfive | {
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"If they use identical ammunition then the most likely way that one weapon is more powerful is because it has a longer barrel. When the bullet is fired the gases from the powder expand behind the bullet and push it down the barrel. The longer the bullet is in the barrel, the more time the gases have to push against the bullet and it will come out going faster. So, a rifle will shoot the same bullet faster than a handgun. But, many weapons use the same caliber ammunition but have drastically different cartridges behind that bullet. For example a 5.56mm NATO cartridge has the same caliber as a .22 but much more powder behind it.",
"There's a difference between having the same caliber & using the same ammunition. A .22LR and a .223 Remington are basically the same caliber (diameter of the bullet) but the .223 has a much larger bullet and much more powder behind it. Other than that, the only thing I can really think of would be barrel length. The longer the barrel of a weapon is, the more time the expanding gasses of the gunpowder have to accelerate the bullet, making it faster & giving it more energy. For example, the original M-16 with a 20\" barrel would have a muzzle velocity of 3,150ft/s while the short-barrel M4 carbine, basically the same weapon with a 14.5\" barrel only has a muzzle velocity of 2,970ft/s. That's 1.84 kilojoules of kinetic energy v. 1.64 KJ - about 10% less for the short-barrel version.",
"others of same caliber isnt same as others with same ammunition. Two bullets can be of same caliber, but different firepower. Caliber refers only to the physical size, not its other characteristics. More gunpowder, less gunpowder, etc. There's also stuff like rifling etc.",
"Barrel length is also a factor - a longer barrel allows for a longer acceleration time (to some point, if a barrel is too long, the bullet will lose more energy from friction). For rifled barrels, rifling type can also affect bullets by giving them better or worse stabilization, so they will lose different amounts of energy after leaving the barrel. And ammnition also can be different - it is not just the bullet, but also the amount and type of proppelant in the cartridge can be different. A sturdier gun can use ammunition with more propellant, thus generating more force, even though the caliber and bullet stay the same."
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ae7sam | How is heat produced as a byproduct in electronic systems? | Engineering | explainlikeimfive | {
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"Usually it is from electrical resistance, which can be thought of as electrical friction. Moving electrons around creates waste heat in the wires. Certain materials are easier to move electrons through (conductors) and other materials are relatively difficult (resistors)."
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aegr5a | What makes electric things vibrate? eg. phones, tablets etc. | Engineering | explainlikeimfive | {
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"Generally vibration is created by a small motor with a weighted attachment that spins at high speeds. Think of what happens when you spin a pair of scissors by the handle on your finger. If the scissors are closed they glide smoothly through the air without much up and down movement. Now open the scissors and do the same thing. It's much harder to recreate that same smooth fluid spin and you have to actively move your hand and finger to compensate for the added weight. The motors in electronics do this same thing, but they are in a purposely constricted space and don't have the auto calibration that your hand/wrist/finger do to smooth out that spin.",
"Either a motor with half a circle on the end. As the half circle spins it makes the motor vibrate. Or a material called a piezoelectric crystal is used which will vibrate when electricity passes through it.",
"Usually a little motor that spins something around really fast to create vibration. If you look in the handles of the clear video game controllers from the late 90s and early 00s you can see the mechanism working. It's pretty rad"
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aei44m | How do the engineers make sure that the rotation in a piston engine would be in the desired direction? (clockwise or counterclockwise) | A simple slider crank mechanism can turn the crank both clockwise and counterclockwise. How is it ensured that it is always in the right direction? | Engineering | explainlikeimfive | {
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"A typical engine is started with a starter motor. As long as the starter motor turns the right way the engine will turn the right way. Momentum will keep the engine going the same way. Some engines are started manually in which case there is often a directional clutch. This both prevents someone from turning the engine the wrong way and also prevents the crank or pulley to move as the engine starts up. Engines which does not have such directional clutches are designed to be started by engineers who knows the correct startup procedure. & #x200B; It is possible for engines to get turned backwards. Most engine designs will not sustain power in the reverse direction but will not take damage from it. So they will slow down to a halt. There are designs that will be able to run in reverse. This is an issue with for example older industrial diesel engines. If you choke the engine and then fixes the issue in the last stroke of the engine it might turn backwards and continue to run in reverse. The immediate danger is that the gears are now the wrong way so reverse gear will make you go forward and forward gear will make you go backwards. This sudden change can often cause crashes. However the issue is also that the intake and exhaust will be reversed. So the engine will pull in air from the exhaust that contains sot and dust particles and spew hot exhaust out the intake manifold where it may damage components like the air filter. The plumbing may also contain one way valves that is now blocking the flow of air and can further damage components. & #x200B; In addition to diesel engines it is also possible to get two stroke gas engines to run in reverse. However these will still send the gasses the correct directions. Some two stroke gas engines are actually designed to be reversible. This can for example eliminate reverse gear on some equipment.",
"Starter motor does a pretty good job of encouraging the engine to spin in the desired direction. Then angular momentum does the rest."
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aelhnq | why do modern elevators in tall buildings slow down when it’s windy? | I work in One World Trade and take a super fast-moving elevator 60+ floors up every day. A bunch of us in the office have noticed anecdotally that the elevator slows down a lot on windy days. Does anyone know the reason/physics of why this would be the case? | Engineering | explainlikeimfive | {
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"On a windy day the building will slowly sway back and forth. This motion puts more stress on the elevator cable. So, they slow down the elevator to keep the strain on the cable within limits. If it's really bad they might even shut down the elevator. You can read more here: URL_0"
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aemojo | What are the differences between making a 90 minute movie versus three 30 minute TV show episodes, production wise? | Engineering | explainlikeimfive | {
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"when you make three 30 minutes shows you expect there to be a delay between when people watch each episode. Often times (before Netflix) this was because the episodes were created one at a time, and released when they were done. Often releasing one episode per week. If there is a delay you story telling needs to account for that. You cannot expect your audience to remember minor details from something they watched 7 days ago. But you CAN expect your audience to remember things that they say 60 minutes ago.",
"Depends on the show. There are 2 types of TV shows - multi camera and single camera. Multi-cam are the traditional sitcoms like Friends or Big Bang Theory. They're shot on a stage with a set of the main location. They shoot using a 3 camera setup where the actors act out a scene and the director uses 1 of the three cameras at a time to capture the scene. They shoot usually 2 days per week. They shoot the show in script order in front of a live (usually paid) audience. Production lasts for 22 episodes a season or most of the year except for some hiatus time toward the end of the year. Production usually starts in the winter around February. & #x200B; Single cam is similar to a movie in that they shoot out of order. Meaning if a scene takes place at the beach early in the script and then another scene in the script takes place on that same beach later in the script, the production would shoot both scenes one the same day. It doesn't make sense to go back to the same location again to shoot the new scene. Single cam shows use one camera to capture the scene, so if two characters are speaking, the director will shoot closeups of one actor, then re-do the scene with closeups of the other actor. Same in movies where there is a single camera. Versus a multi-cam show, single cam shows will use different locations more often and not be constrained to one set. Single cam shows will shoot one episode at a time, but will be in production 5 or more days a week. Reason they don't shoot multiple scenes of different episodes at once is because there are usually several directors on a season and they are only contracted for a certain amount of time. Same with extras and guest stars on shows - you want to minimize the time they are on set for budgetary reasons. Sometimes they will shoot parts of different episodes at the same time if a location is difficult to get. Production starts in February usually, but could be later since most now are only 8 episode seasons. & #x200B; Movies are like single cam show, but shoot mostly for about 8 weeks. The thing here is to minimize the amount of time main actors are on set. If a main actor can only be on set for 6 weeks, great since you can pay them less and are more likely to secure their commitment to the project since it's only 10 weeks or so of work including rehearsals. & #x200B; In all of these, the main issue is the release schedule. How are the production faring in light of the network or studios' timelines for release.",
"Tv shows usually have a different director for each episode. So a director can film an episode one week, and then next week start post production (editing, effects, etc) while another director starts shooting the next episode. That way the cast and crew is kept busy every week."
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aen9k2 | Do internal combustion engines use more fuel at more RPMs? Or they use more fuel when the throttle is more wide open? | Engineering | explainlikeimfive | {
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"14.7 air to 1 part fuel. The more you press on the accelerator the more your throttle bottle opens to allow more air in, thus more fuel. The more air and fuel the stronger the combustion this faster the RPM."
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aexcw1 | What is the importance of washers used during assembly of furniture, etc? | Engineering | explainlikeimfive | {
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"It spreads the load so your screw doesn't damage the wood. It can also be used to stream out the load in weaker areas so it doesn't tear through."
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af6emp | when a flashlight is about to die, it becomes very dim. Why don’t phones do that same thing? | Engineering | explainlikeimfive | {
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"My dearest five year old, Great observation! That dimming is a voltage drop. And, as it turns out, yes the batteries in phones (and laptops) do have a similar voltage drop. Now, those batteries are usually more advanced than a headlamp's. But what really does the trick is the power supply! Internal mechanisms make the voltage constant for sensitive equipment. That dimming of the light, for a computer could be a real bad thing. So, the manufacturers do some clever things to make the voltage smooth."
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afdjkv | does a television set displaying an all black screen absorb more light from other sources than a television screen displaying an all white screen? | Engineering | explainlikeimfive | {
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"No. How much light the screen is producing doesn't really alter its reflectance as far as I am aware. It will likely impact how much you will subjectively notice though, as the light coming from the screen will overpower reflected light from elsewhere."
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afflb4 | Why do NFL coaches and personnel have headsets with cords? | With all the advancements in Bluetooth and other technology why are there still cords running up and down the sidelines? | Engineering | explainlikeimfive | {
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"There is a lot of electrical noise in a stadium. A large stadium has 80,000 seats. That’s a lot of users who are competing for the 2.4GHz band that Bluetooth uses. Even if they use the UHF and VHF band they are still limited on channels. The support crew, television crew, security, vendors etc using wireless products are still competing for the available frequencies. It becomes a very congested electrical magnetic environment.",
"basically, there were alot of issues in prior years with wireless headsets going out in cold and rain. so it's simply just a case of wired things being more reliable albeit arduous",
"Because cheating. Wireless signals, aside from technical problems, can be intercepted by other folks and used to cheat the game."
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afhm4e | Hexagons are the most efficient shape for stacking adjacent to each other while not wasting space. So why are lots of batteries cylindrical? | Also, wouldn’t electric cars and home battery storage, etc. increase its energy density if they could be packed with no gaps? | Engineering | explainlikeimfive | {
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"The contents of the cylinder are essentially a long flat sheet of thin materials, all rolled up into a round log shape. To get the same contents into a hexagonal shape, you would need some sort of former in the center of the cell, which is wasted space. So you either waste it inside the cell, or outside the cell. The cylinder is cheaper, and faster to make, and then you have plenty of room in the wasted space around the outside for things like cooling passages.",
"I don’t know if it’s relevant in the case of batteries, but in general, corners are structural weak points and can allow deformities to form in the seams. Hence why windows in boats are circular.",
"They would be a lot harder to manufacture. It's pretty easy to cut stuff into circles, roll into cylinders. Also, hexagonal batteries would be very prone to damage at the edges, and you generally avoid damaged batteries.",
"Sorry, how is a triangle not more efficient than a hexagon?"
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afj75r | Thrust bearings and axial load | Currently I am in a first year mechanical engineering degree. We are covering bearings. I understand most of the bearings and there uses. Could someone explain to me how a thrust bearing works and what an axial load. Most explanations online don't make sense to me. | Engineering | explainlikeimfive | {
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"Axial is parallel while a radial load is perpendicular. Your typical ball bearings are radial. When you start getting forces from different directions, it tears up the radial ones fast so you use the thrust bearings. They are shaped differently and and handle side pressure by design",
"Thrust bearings are typically ball-type, split-race bearings designed to assist the transfer of axial loads between components. They can handle radial as well as axial loading, whereas a roller bearing is designed to contain radial forces and reacts poorly to axial loads. Example: A turbo-prop engine with a mechanically coupled compressor and turbine would use roller bearing(s) to contain the push-me/pull-you forces acting between the two sections (axial load) while the roller bearings fore and aft of the ball bearing would handle the radial loads."
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afqxsh | What happens to all the trash in landfills? And plastic wastes? | I know this question has probably been asked many times before, but I am still quite baffled as to how are we dealing with all the trash that's being produced on a daily basis. How are we not running out of land for landfills? And for trash made out of materials that don't disintegrate easily (such as certain types of plastics) how do we deal with them? And reports like this [ URL_0 ]( URL_0 ) make me feel that we are not doing it properly. & #x200B; | Engineering | explainlikeimfive | {
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"Landfills are just a hole in the ground that we throw trash into, then cover in dirt. Sometimes groundwater can leach through the landfill and pick up particulates from it, especially older landfills. Now we use a layer of compacted clay or even a plastic liner to stop groundwater from passing through it.",
"Hey! A topic I know something about! Yep. Landfills are big holes that we fill with trash. Nothing more to it. They are packed really tight both to reduce volume and to reduce biodegredation. The organic fraction of the landfill breaks down over time which causes the release of methane and other greenhouse gases (bad) and which also causes collapses and subsidence (also bad.) Otherwise, the contents don't really go anywhere. As such, landfills (typically old quarries, mines, etc) are a non-renewable resource and when they're full, they're full. If your city doesn't have more holes in the ground it then has an expensive problem. Fun fact: most recycling programs aren't driven by altruisim. They're driven by the economics of limited landfill space in big cities. Most recycling is about \"landfill redirection,\" not because putting trash in landfill is inherently bad, but because once the landfills are full, the cost of disposing of the residual waste (i.e. non recyclables) is very high. Another fun fact: some landfills are constructed like Lego blocks. The waste is baled in big plastic cubes and packed nearly in the landfill then covered over. The idea is that in the future, it will be cheaper or economical to recover that waste and recycle it in a future landfill mining operation! Source: supply the waste industry with recycling machines.",
"When we fill up a landfill, the garbage is covered with dirt and left to decompose over the course of a few months, for biodegradable stuff like food, a few years, for more resilient stuff like wood, or even thousands of years, for non-biodegradable stuff like metal or plastic. For stuff in the latter category, the only real way for them to be broken down is through chemical attack. This is why it takes so long. As far as waste disposal goes, landfills are kindof a middle ground of environmental impact. It's generally not as bad as dumping it all into a river, but plastics and metals should be recycled, and bad management can lead to contaminated groundwater. Most of the microplastic (plastic particle) contamination comes from countries that are not handling their garbage properly, or at all. While no country is innocent, many less developed countries are just dumping their trash into nearby rivers, as they lack the infrastructure to deal with it properly. As for land use, there is a staggering amount of land on this planet, we won't run out anytime soon."
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afwg1g | What is shift factor and load when referring to generators | Engineering | explainlikeimfive | {
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"Shift Factor is a pretty obscure electrical power term. When a change in generator output occurs, the change in current measured at the junction to the power grid, called the flowgate, isn't exactly the same. It's a function of transmission dynamics and distances. Shift factor is the ratio of flowgate change to generator change. Load is generally the amount of power needed to operate the device powered by the generator, though there are more esoteric definitions for obscure cases."
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ag1aiy | How important is choosing the right voltage in chargers? Would a slight .5 change have any noticable effects? | Engineering | explainlikeimfive | {
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"Basically, it depends a lot on what you're charging. Most \"chargers\" these days aren't really chargers, they are just constant-voltage power supplies. The actual charger is built into the phone or other device. If it's anything involving USB, the voltage usually needs to be pretty close to 5 volts, within several hundredths of a volt. 0.5v would probably be too much, though it likely would still *work*. The USB specification is very complicated, with different volts and currents and signalling to decide how much to use -- it's like a whole book just for power supply. Most 12 volt power supplies are a lot more forgiving -- \"9 to 15\" or even \"10 to 30\" is sometimes the range -- but not always. I doubt that there are many well-designed devices that you would kill by using only half a volt too much on 12 volts, or that wouldn't work with only 11.5. When directly charging batteries, the voltage matters quite a bit -- and in some cases, like when charging lithium batteries, you can't just connect it up to a voltage or you'll probably cause an explosion."
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ag8c6f | How do multiple programmers work on a game/project together? Do they each work on completely different parts or do they have to communicate on what they've been doing and what needs to be done? | Engineering | explainlikeimfive | {
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"Planning, documenting code, and compartmentalizing tasks. Or, in lots of cases, it's just total chaos.",
"There is a lot of communication. It's fairly common to have daily updates about what everyone is doing. On a big project there's no way for everyone to know exactly what everyone else is doing, but you might know broadly what each sub-team is working on. Developers use \"source control\" software. What that means is there is a server with a \"master\" or \"main\" version of the code, and each individual submits their work to that, and it tells you if someone else has made changes to the same file so you can merge the changes. This also allows \"branching\" where you can make a copy of the code for a specific group of people to work on without interfering with what anyone else is doing. Then they can merge that back into the main version when they have finished the work they are doing.",
"I’m actually in this situation! 1. A project manager controls what we do (what issues we should work on, who works on what, time to spend on any issue, etc.). He makes sure we don’t waste time chasing weird stuff and we don’t both do the same thing. 2. We have a workflow system that tracks issues and who is working on what. Basically, each to-do is listed separately and we can assign it to someone. When that person makes changes in response, others can comment on them, and there’s a do work - > peer review - > project manager review flow. 3. We also have a version control system. There’s a master base of high-quality, stable code. When we want to change stuff, we make a branch, which is like a working copy. We then do work on the branch and when done, submit the changes for the review process mentioned above. If everything is okay, it gets merged (combined) into that master base. 4. We have regular meetings that set the direction until the next meeting. This helps to keep our development process focused.",
"In a corporate environment, we have a few different systems involved such as: \\- Agile/SCRUM, basically how the team is organised, including stuff like updates on work done/to do etc. This also includes all the individuals in a team since naturally authority over development goes to the Team Lead (or Scrum Master, usually these two do the same thing) whilst ownership of features and determination of priority is the domain of the Product Owner. Which depending on the company could either be an external person paying your company for the work, or a senior (CTO etc) designated that role based on having gathered the requirements in the first place. \\- VCS (Version Control Systems), these track code from the beginning commit (i.e. creation of the repository. With repository being essentially just a specific location for a project)) all the way through any commits that have reached the remote repository (i.e. the web hosted one that a company pays for, as opposed to a local repository which exists just on your computer). These allow you to see what branches exist, when they were made, what changes were made, who they were made by etc. \\- Issue Tracking. Usually take the form of some ticketing system that allows you to specify: which project, what the issue is, current status, who is to work on it, priority level, story points etc. The priority of a ticket essentially determines when it gets done. If there's a lot of coding to do for a low priority issue, you can pretty much guarantee it's going to the backlog for a long time. \\- CI (Continuous Integration). This means that code can quickly become part of the whole system and therefore available to other developers with little effort. In essence it is essentially a pipeline between your code and the finished product. This is relatively newer, so a lot of companies are behind on this aspect. & #x200B; Just because these systems are in place doesn't mean it always works. For example you can \"break the build\" and become the laughing stock until the next person who does it. There are also merge conflicts, which occur like so: \\- A branch called \"master\" exists for some code \\- You make a branch from this code, called \"Branch1\" here \\- Another developer branches from the same code, called \"Branch2\" here \\- You make changes to Branch1 \\- You Pull Request your code to the master branch, and it gets merged \\- The other developer makes changes in Branch2 that were in the same areas as your code in Branch 1 (not the same code, although it doesn't matter either way) \\- They pull request their code into the master branch, now they have a merge conflict to resolve."
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ag9bre | Common-Mode Voltage and EMI | New to Hardware, Help Getting Started on Understanding Spec Currently looking to use a CAN transceiver to build some tech for my car. One thing I noticed while reading the datasheet was "Differential receiver with wide common-mode range for high ElectroMagnetic Immunity". I've tried looking up what exactly this means but no luck. I was hoping someone could answer: 1. What exactly is common-mode range? Doesn't this have to do with differential amplifiers? 2. Hoe does common-mode range affect EMI? | Engineering | explainlikeimfive | {
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"As other answers say, noise from the environment around the circuitry (and especially around the wiring that's connected to the circuit's differential inputs) can induce voltage (and current) in the input. One of the reasons the wires that carry the differential input signal are twisted together (often called a \"twisted pair\" of wires) is so they both occupy the same physical space and the source of the noise will induce the noise signals equally in both wires. Since the noise signals are induced into both wires equally, the signal is common (identical) in both wires. This is where the term \"common mode\" comes from. The noise is being induced into the wires in a mode that's common to both wires, so it's called a \"common mode\" signal. The real signal you want to receive through the wires is different on each wire, so it's a \"differential mode\" signal. The receiving circuitry is designed to amplify the differential signal that's on the wires and cancel out the common signal that's on the wires. Going back to my first sentence above, both types of signals can cause the voltage on the input of the circuit to rise and fall. The differential signal will make the voltage go positive on one wire while it goes negative on the other wire, and vice versa. A common signal (created by the noisy environment) will make the voltage go positive on both wires together, and go negative on both wires together. 1. The term \"common-mode **range**\" refers to how wide a positive/negative voltage swing the circuit can handle when both wires are at the same voltage. I.e., when something induces the same voltage in both wires, how much can that voltage be? Up to +24 volts and -24 volts? +/-48 volts? More? The range of voltage that the circuit can handle in common-mode can be different than the range the circuit can handle when the wires' voltages are different (differential mode). 2. Common-mode signals are usually induced into the inputs by EMI (electro-magnetic interference). The range comes into play with respect to how strong the EMI is in the environment, therefore how strong a voltage it will induce into your circuit's inputs. If your chip can't handle the range, it will cause trouble for registering the desired differential signal, and in extreme cases, harm the chip."
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agdg8s | How do they build the lighthouses and other buildings from those photos where giant waves are constantly crashing into them? | I know in rivers and such you can build temporary dams, but how are these ocean constructions possible?! | Engineering | explainlikeimfive | {
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"They build them at another time of year, when the seas are calmer. The photos are taken at the very highest wave times.",
"Carefully, one piece at the time when the season was good. To start with, the photos you see with these huge waves are extremes, there are a lot more peaceful days also. If you consider the Rock Bell Lighthouse, that is a lighthouse on a 20 hours a day submerged rock in the North Sea. It took them four years to build it. They had to build their own shed on poles there first otherwise they would have commute from and to their boat at 1.5 km away from the rock by boat. They had to bring all the stones by boat to there, all pre-cut. Have a read up on URL_0 to find out what kind of madness this lighthouse constructoin was, the constraints they had to work in were idiotic. Later in a documentary on the industrial wonders of the world this lighthouse was included."
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agfb8n | Why do electric guitar pickups need to be soldered? Why isn't there a universal socket or something? | Why haven't guitar and pickup manufacturers agreed upon some kind of plug in and play system for pickups? Soldering seems so old fashioned and tedious. | Engineering | explainlikeimfive | {
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"Because plugs can get loose or corrode over time and lower the signal integrity. Also a pickup is not really intended to be switched as often to really make a plug necessary",
"It’s probably just not worth developing one. Also space and reliability, you don’t want it coming loose during a gig!",
"Signal integrity tends to degrade at every temporary connection. Even a good connection has some losses since the contact area will be so small. Remember, this is an analog signal, not a constantly-refreshing digital signal. Proper soldering creates a joint so good that it's as if it isn't even there. Maybe a plug-n-play device would catch on with lower-end gear, but never in the pro or semi-pro market. As an aside, you should invest in a little temperature-controlled soldering station. I recommend Hakko or Weller. You might become a convert if you have the right equipment."
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aggly6 | why aren’t 2x4’s actually 2 inches by 4 inches? | When looking at lumber sizes, nothing is the actual size they claim, i.e. 2x4’s, 2x6’s, etc. Why s this? | Engineering | explainlikeimfive | {
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"Timber used to be exactly as it was called. So a 2x4 was actually 2x4 inches. Now they are made to be more uniform and are milled and sanded down. So their actual size is closer to 1 1/2 by 3 1/2. Source: URL_0",
"Adding to what others have said: Old style wood used to be closer to the actual dimensions, but even then the sizes varied by a fair bit. If you ever get the chance to measure joists in an old house you’ll quickly find they’re all different widths and depths - maybe +/- 1/4” wide and a little more variation in depth. The move to the “nominal” sizes came from a few sources. 1. When wood dries it shrinks. The exact amount it shrinks is dependent on how wet it was before it was dried and what the grain is doing at any particular point. So you could cut a bunch of 2x4s (actual) but then you have to dry them before use and they’ll all end up slightly different sizes in a somewhat unpredictable way, and maybe not even consistently along the length. You could try drying the wood first before cutting it but that takes a LONG time. So they cut, dry and then finish it. The 1/2” reduction in each dimension for a 2x4 is generally plenty to accommodate this process so the final pieces are all equal. Deeper sections actually have slightly more drift from the noted size due to more shrinkage due to more depth. 2. This brings us to consistently. When walls and ceilings were finished in plaster it wasn’t that big a deal if a piece was a bit deeper than the adjacent one. The plasterer comes by with thin wood pieces (called lath) and nails them to each member - they’re flexible enough to work around diffferences in depth of adjacent pieces, then they layer the plaster on - during this they can make the plaster a bit ticker where required to even out irregular floor or wall pieces so you get a flat surface in the end. Today we use drywall (or similar) which comes in large sheets. If your wall pieces are all different thickness it’s going to look like crap because you’ll see the small bulges and indents in the wall where they drywall follows the wood profiles. So there’s a very tight tolerance for thickness that is a bit more stringent than there used to be. Note: this only really applies to framing lumber. Manufactured wood products (laminated veneer lumber, parallel strand lumber, etc) are the actual dimensions given - because they’re made under more controlled circumstances and don’t have shrinkage to deal with. They are also used in more specialized and engineered applications. Hardwood is different too as it is generally sold by the exact dimension (more or less) - this is because it’s normally used for furniture or other applications where it’s going to be put through a substantial amount of cutting, machining and other processing by the buyer so small differences in thickness and/or depth in the rough cut wood aren’t really an issue.",
"The lumber is rough cut and then planed to its final dimension. For smaller dimensioned lumber, a tolerance of 1/4\" is needed on each face to ensure that a uniform, straight board can be cut from the rough cut (which is the true dimension). For larger dimension lumber the required tolerance is larger; hence 2x8's are actually 7 1/4, etc.",
"Nowadays timber is milled and planed to ensure it looks a little more finished, thus it's a little smaller than 2' by 4'.",
"The milling process to my understanding. The original cut is 2x4, but after planning & sanding, the measure isn't a true 2x4, 3x10, etc.",
"Lumber shrinks when dried. In the old days, there was no definitive size standards and people would get lumber by ordering it from the mill at various cuts, and 2 x 4 would often get cut at 2 x 4 but wind up smaller after it had dried. Some regions would cut larger, others smaller. If you _really_ want to know more, here's a 59 page pdf detailing the history of lumber sizing, provided by the forest service. It's got _all_ you could ever imagine wanting to know about the history of it. URL_0"
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agol9z | Cern just proposed a new particle collider that is a 100km loop...Considering all variables, ground expansion/contraction etc., how do they keep everything level and in its necessary position over such large distances? | Engineering | explainlikeimfive | {
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"text": [
"The tunnel will be larger than the actual accelerator device, and then they can adjust the position of the accelerator with things like shims and such to fine tune the path. Then it is just a matter of carefully measuring shorter distances with extreme accuracy, such as using lasers within the tunnel to measure distances and angles between reference points.",
"It doesn't need to be absolutely perfectly aligned for the sake of the beam. There are many steering and focusing magnets that guide the particles to where they need to be. Here's a plot of relative momentum change in the LHC during a period of running: URL_0 The wave pattern is due to tidal forces on the Earth's crust. The tunnel is big enough that this measurably affects the accelerator! The noise from 12:00 onwards is an earthquake in New Zealand."
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agoq9c | Why does old electronics produce a high ptched noice when turned on? | Plenty of old, and new electronics produce high pitched noices when turned on, is it the electrons somehow doing it, or are there small sparks in the circuits? Best example of this is probably old TVs. | Engineering | explainlikeimfive | {
"a_id": [
"ee7rf9j"
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"text": [
"The specific component is called the \"flyback transformer\". The whine is mentioned in this section: [ URL_0 ]( URL_1 ) More specifically, the high frequency alternating magnetic field makes the transformer core vibrate at whatever frequency is being made. Depending on the initial quality of the transformer, and how well it has aged (the varnish they coat everything in breaks down after a while) you'll get a louder or quieter unit. The same thing happens with normal 60hz (household current) transformers too, it's just a much lower note, because of the 60hz cycle. Again, as the varnish breaks down over the years, you will get a louder and louder note. For the big ones, people will even sometimes have them re-coated for just that reason."
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ah38ir | How do zippers work? | Engineering | explainlikeimfive | {
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"text": [
"The zip is made from two lengths of plastic “teeth” and an interlocker which is the bit you slide up and down. Thats the zip. Th zip itself is shaped sort of like a “Y” on the inside. This means that when you pull the zip up, the “Y” tapering into a single point causes the interlocking teeth of the zip to do just that, interlock. When you pull the zip down, the “Y” is backwards, causing the interlocked teeth to split and open the zip."
],
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16
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ahasrd | Why is it that the front wheels of a semi-trailer have rims that extend further out than the tyre but the rear wheels have rims that are recessed? | Engineering | explainlikeimfive | {
"a_id": [
"eeczdns",
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"text": [
"The rims are shaped like a bowl. There is only one wheel/tyre at the front so the \"bottom\" of the bowl is showing but there are two tyres/wheels stuck together at the back so they put one wheel back to back with the other so the nuts and bolts that attached the wheels to the axel are passing through the shortest distance giving the strongest grip. The outside wheel is showing the \"inside\" of the bowl because of this arrangement. ( 1 Front Wheel )( 2 Back Wheels () A silly way to attach 2 back wheelsthat no one uses because you would need really long bolts and they would break under pressure because physics be that way.",
"They are all the same shaped rim. When you double up tires you want to join them all at the same connection point. So the back wheels are doubled up with inner rim pointing out and the outer rim pointing inward so that both tires can make a strong connection to the axle at just one point. There may possibly be gains to having different style rims for the different types of connections but that is outweighed by the need to carry multiple spares."
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ahhjxw | Why do front wheel cars handle better on ice and snow than rear wheel? | Engineering | explainlikeimfive | {
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"text": [
"Put a pen flat on a table. First, drag it along by its tip. Then, push it in the game direction from the back. Which of the above resulted in a more stable path? Obviously the first. Same thing with a car. With FWD, the front wheels are dragging the rest of the vehicle behind it, resulting in a more stable trajectory. With RWD, the rear wheels are pushing the rest of the vehicle in front of it, which isn't stable in limited traction scenarios.",
"They only accelerate better because the weight of the engine on the drive wheels. They don't stop or turn any better than rwd.",
"There are 2 main reasons. First, most cars have more weight over the front axle than the rear. FWD cars usually have ~60% of the weight over the front, while RWD cars usually have only ~40-50% of the weight over the rear wheels. Second, if your drive tires start spinning, it's relatively easy to handle in a FWD car. You just let off the gas a bit, and maybe turn in more. In a RWD car, you need to ease off the throttle, but not too much, and turn in the opposite direction. It takes more skill. That said, modern cars with stability control can pretty much negate this issue."
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aho0qp | How does the ISS not run out of oxygen? | Engineering | explainlikeimfive | {
"a_id": [
"eegbelx"
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"text": [
"Electrolysis of water (H2O) is the main method to generate oxygen aboard the ISS. Water is split into oxygen (O2) and hydrogen (H2). The oxygen is vented into the breathable cabin air system, known as the Oxygen Generation System, while the explosive hydrogen is vented externally."
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ahpqy9 | Why do Tesla’s Battery Farms take up so much land area? Wouldn’t it be more economical to stack them vertically? | Engineering | explainlikeimfive | {
"a_id": [
"eegumfr",
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"text": [
"If you want to build a single story building the walls only need to be strong enough to carry the weight of the roof. And the roof tends to be quite light weight. However if you want to build a two story building the walls and columns in the first floor needs to be able to support the floor and all the machinery and people on the second floor above it. This weighs a lot more then just the roof so the walls are much more expensive to build and they take up more space. So it is common for structures to be built as low as practically possible to reduce construction costs. And as the factories you refer to are located in the middle of nowhere there is no shortage of land to use so there is no reason to spend money on a taller building.",
"I thought they put the large battery farms in the middle of nowhere in places where land is generally cheap. Stacking can probably come with its own challenges and expensives. I guess I figure this is like asking why all housing isn't built as highrises. I could be completely wrong about the locations of these battery farms though."
],
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ahtih2 | How do some dryers automatically sense when your clothes are dry? | Engineering | explainlikeimfive | {
"a_id": [
"eehyigu"
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"text": [
"They measure the humidity of the exhaust air. When it's not moister than the input air, the clothes are dry."
],
"score": [
11
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ahx3rq | How is information retained in solid-state memory devices after power is turned off? | Engineering | explainlikeimfive | {
"a_id": [
"eeiz4wk"
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"text": [
"Think of an SSD as a bank of millions of switches. When the switch is on, it encodes a 1, when it's off, it encodes a 0. That's how the drive encodes data. When the power is off, the 'switches' simply stay in position, so the data is saved."
],
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ai08zl | How the authorities find leakage in the long distance urban natural gas pipes? are they safe? | Engineering | explainlikeimfive | {
"a_id": [
"eek9qsb"
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"text": [
"Natural gas is expensive, and you don't want to loose any of it. The owner of the pipeline has a financial incentive to ensure that there are no leaks. There are of course regulations anyway, but there are a lot of controls done by the owner of the pipeline too. First. The gas contains some moisture. Not that much, but still enough that if there is a leak it'll immediately start to soak the insulation around the pipe. In the insulation, there are metal wires. As a precaution. Those metal wires are then constantly monitored with an electrical current. If the wires all of a sudden are connected, it's a pretty obvious sign that the insulation is soaked. And that suggests a leak. (it can also be someone who has been near the pipe while digging for something else entirely, who has damaged the plastic around the insulation. if that happens, rain water will start to leak in and cause the same effect.) If you make sure to go out and find the suggested leak within a day or two, you'll probably be able to fix it long before it gets real dangerous. Second. The pipeline is highly pressurised. Some 80 bar or so is not that uncommon. It's a pretty noisy burst once it leaks for real. To ensure that there are no leaks, the pressure is constantly monitored. If the pressure abruptly goes down, there is a leak somewhere. The monitoring equipment will be able to tell which section of the pipeline that is leaking, and shuts valves surrounding that section, so that the loss is at the very least only what is in that section. Third. The gas contains a trace gas. Or sometimes several of them. Often something that smells like rotten eggs. The whole idea is that everyone who comes near a leak will feel nauseous and report the foul smell. Instead of being choked to death on the odour-less natural gas. Combined, this is what makes the pipeline safe. Bonus info: an old colleague of mine used to work with distributed heating. They often shared utility rooms with the natural gas distribution. Whenever they went into one of those rooms, they had to wear a portable gas alarm. A gadget that sounds if you encounter too much gas and need to get out. He said that not even when the trace gas was so dominant in the room that you threw up from it, did the alarms sound. That trace gas is potent, even in very, very small doses."
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ai11rv | What's the difference between detonating a bomb and destroying one? | Police in a nearby city pulled a car over and the driver had multiple outstanding warrants, so they searched his car. They found a bomb and took it away to be destroyed in an empty field. If they don't set it off, how is it destroyed? Do they just take it apart piece by piece? & #x200B; I tried looking through ELI5 and Google, and couldn't find anything except the destruction caused by nuclear weapons. :/ | Engineering | explainlikeimfive | {
"a_id": [
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"Some bombs can be blasted apart with a small explosion that won't set off the bigger explosion. For example, C4 is very stable and takes a blasting cap to set off. There has to be the right combination of both heat and kinetic energy to set off a block of C4. To get rid of a bunch of C4, you can hit it with a powerful blast of water that will (hopefully) tear apart the block of explosive without actually setting it off. You can also (hopefully) blast away the cap so that if it goes off, it's away from the bulk of the high explosive and (hopefully) won't set off much, if any. If there's a complicated trigger on the explosive, depending on how the explosive is detonated, you can put a shaped charge on the trigger and (hopefully) blow up the trigger without setting off the bomb itself. If you have a weak, slow reaction in the bomb, you can even strap a powerful enough explosive that literally blows the bomb apart faster than it can explode."
],
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ai6fgs | Why do high end luxury watches such as Rolex have such a strong connection to diving? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Prior to dive computers being reliable and accessibly priced having a very reliable timekeeping device was a must-have for diving. It's important to time dives out properly to avoid problems like decompression sickness.",
"Rolex invented one of the first mass market water resistant watches. It was called the Rolex Oyster. They advertised it by having a professional swimmer wear it while attempting to swim the English channel. So right off the bat, people distinguished Rolex as a sports watch as opposed to a classical dress watch. Scuba diving requires people to keep accurate time to know how long they've been underwater, how much air they have left, etc. Right around when Scuba was invented, a few different companies including Rolex released dive watches that could dive as deep as humans could using the new technology. Around this time, famous divers started showing up in TV shows and movies. Jacques Cousteau would wear dive watches. In a memorable scene in a James Bond movie, Bond swam up to a party and unzipped his suit to reveal a fancy dinner jacket and bowtie underneath. He used to wear a Rolex dive watch as well. Rolex, in particular, sponsors diving expeditions because they know it's good marketing. For example, they sponsored James Cameron's record setting dive into the Mariana Trench. He wore a Rolex watch, and they created a special edition watch to commemorate his dive. Dive watches are incredibly popular today, even if the wearer doesn't dive. Many of the most popular brands including Rolex, Omega, Seiko, etc. are best known for their dive watches.",
"Only a few of them actually do. Rolex is the most prominent one since their submariner line was used in diving, especially the now incredibly valuable Comex dials. Blancpain also has a stronger tradition with their 50 Fathoms, which was actually used by the French Navy in the 50's. Omega has a history with the Ploprof being used back in the 70's also by Comex. Ulysse Nardin has a strong maritime tradition, having made actual marine chronometers back in the days. Aside from that, the really high end watches like Vacheron Constantin, Patek Philippe etc. don't have much connection with diving, if they even have any dive watches at all. Now a days, a dive watch is just another line of watches that a lot of companies make, much like how many automakers have made SUVs. Brands like Audemars Piguet or Jaeger LeCoultre have a diver line, they are just a 'style' along with their other models. In fact most major watch brands have several major watch lines: 1. Chronographs 2. Dive watches 3. Plain watches 4. Complicated watches Many of which can be a mixture of types, like dive watches with chronograph functions. So sure you could use a US$400k watch like a Richard Mille 025 or 028 for diving much as you could drive a Bentley Bentayga off road, but odds are you won't."
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ai8auq | How does tubing along the top of a wall prevent the use of ladders to get over it? | Engineering | explainlikeimfive | {
"a_id": [
"eelvxve"
],
"text": [
"I dont exactly know what your talking about do you have a photo of a reference of this ?"
],
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ai9gik | How do automatic doors work? | Engineering | explainlikeimfive | {
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"eem1lr2"
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"text": [
"I'm going to assume you mean how an automatic door knows someone/thing is there for it to open. First off, it can depend on the door in question and specifically what sensor it uses. Most automatic doors have fairly cheap sensors, effectively they are just passive infrared and it goes off whenever it detects any notable difference in temperatures of whats in front of it (ie, you and the surrounding air). Deviant Ollam, a physical security penetration tester, [explains these sensors in this lecture]( URL_0 ) as well as how to bypass them."
],
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3
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"https://youtu.be/rnmcRTnTNC8?t=675"
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aidbfb | Dry-firing a bow is bad because with no arrow the "energy" has nowhere to go. Mathematically it makes perfect sense but what is physically happening to the materials to cause this? | Engineering | explainlikeimfive | {
"a_id": [
"eemvvhr"
],
"text": [
"The Energy goes someplace, it's just not the right place. The bow designer designs the bow to put the energy into the arrow. With no arrow, the energy goes into the string. This moves the string too fast and too far. Then it \"rings\" back and forth too many times. All these excess motions eventually allow the energy that should have gone into the arrow to go into heat in the air around the bow. The downside is that the excess motion causes excess wear."
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aidguy | Do you need to ‘warm up’ your car before driving in cold weather? | Engineering | explainlikeimfive | {
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"text": [
"The only reason I \"warm up\" my new vehicle is for the defroster to thaw out the windows and to give the butt and steering wheel heaters a chance to get going. Older vehicles need it more to circulate the fluids and get the oil up to operating temperature.",
"99 cars out of 100, no. starting it and getting yourself ready to drive will be enough to prevent damage. if its -20f and it takes longer to start, and it sounds weirder than usual, let it sit until it sounds normal. old cars won't matter unless you're putting in a heavier oil to prevent oil leakage. i'm counting the days until i get a new car and am putting 20w50 in it in the meanwhile. i do have to let it sit right now at -5f or it'll stall when i move it.",
"Mechanic here. No, its slightly better for the engine to not warm it up. Engines take the most wear and tear on cold starts and the quicker it gets up to temp the better. That does not mean hop in and drive it like you stole it to warm it up. You want to drive it nice and easy until its warmed up. Now when I say \"slightly better\" i mean the difference between getting 500k vs 550k out of an engine. So if you want to warm it up before you get in it, go ahead. The difference isnt big enough to worry about, so dont feel bad if you just hop in and go."
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aippxv | How do those bank tube things work at the drive thru | Engineering | explainlikeimfive | {
"a_id": [
"eepjeip"
],
"text": [
"The tube is connected to a large fan that collects air from the tube. The capsule creates a reasonably air tight seal within the tube. When that happens, air pressure outside the tube pushes the capsule through the tube. This step is very similar to air pressure pushing your drink through your straw when you suck on the exposed end of the straw. When the capsule reaches the end, it's stopped or dropped out of the tube allowing the customer or teller to interact with the contents. For tubes that go two directions, there's a door that changes which way the fan draws air allowing the capsule to be moved in both directions."
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aiptys | If my furnace has an exhaust but no air intake from the outside air.. doesnt that suffocate? | Sure, there are some cracks in anyhouse.. but all winter the heater has an exhaust for gas and some air but theres no air intake. wouldnt that eventually bring the oxygen levels low? lets say if you only opened the door to your house a couple times a day.. im sure air quality is way better in homes with air intake to the furnace. | Engineering | explainlikeimfive | {
"a_id": [
"eepuwil"
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"text": [
"There should be some sort of fresh air supply to the room if it is what’s considered a “confined space”. Your heater needs 50 cubic feet of air per 1000 BTUs. This is a significant amount of space. If it doesn’t meet that guideline then your basement is a confined space. As an example, an average Natural gas fired furnace is around 100,000 BTUs. The room that it is in would need to be 25’ X 25’ X 8’. Anything less than that is a confined space and would require a fresh air source to follow the National Fuel Gas Code."
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aiz2mq | Why do I have to warm up my car during cold weather? | Engineering | explainlikeimfive | {
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"eeripyr"
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"text": [
"Cars have motors. Motors are made of metal. Metal grows a little bit when hot and shrinks a little bit when cold. Small explosions happen in the engine to make the engine move which moves the car. Explosions inside the motor warm up the metal. So when the car is driving the motor gets hot. The engine is designed to run while it is hot, the parts are made to fit together better when they are warm, while the car is driving. Before the motor warms up at the start of the journey, the parts of the motor don’t fit together as perfectly, so the motor does not work as well, the parts rub on each other more and wear out faster.",
"From what I know this is outdated info since most vehicles nowadays don’t have a carburetor and use fuel injection instead. Please correct me/add on.",
"Metal expands when it gets warm. If you have a carburetor (mostly pre 80s vehicles) then it's a good idea to warm it up before driving. Inside the carburetor is an hourglass shape which helps to cool and condense the air going into the engine. If the air outside is already cool and condensed, it can cause the fuel lines or jets in the carburetor to freeze. If you don't have a carburetor, you don't necessarily have to, but it's still not a bad idea to let the engine idle for a minute for two reasons. One, you want the engine to build oil pressure before driving (this only takes about 30 secs). Never start your car and immediately start driving, give the oil pump time to get oil throughout the engine to decrease wear over time. Secondly, the pistons are oval shaped when cold, so letting them heat up and expand into the round shape of the cylinder gives optimal performance and prevents wear and tear.",
"Unless it's a really, really old car, you don't. And I mean old. Like, 1950s or 1960s. Actually having to warm up a car isn't a thing anymore. Sort of like the 3000 mile oil change. Simply unnecessary anymore. Fire it up, wait maybe 10 or 15 seconds, then go. The best way to warm up the car is to drive it."
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aj909g | What exactly went wrong on Apollo 13 and how was so many things missed? | I just watched the Ron Howard film, and I have to say it was one of the best films I’ve ever watched. But it left some unanswered questions in my mind, like how did this miss all those errors? As well, if they used the same rocket as the successful Apollo 11 and 12, what was the difference with 13? How was everything missed? | Engineering | explainlikeimfive | {
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"text": [
"Basically it was a design flaw, an assembly error, and a testing error: a chain of events that led to near disaster. Each thing on it's own wasn't enough to cause the explosion, but the unlikely chain of all 3. The genesis of it started in 1965, before the first Apollo spacecraft was even built. The spacecraft was originally designed with a power system to operate on 28 volts, but during the design process, this was raised to 65 volts to match the power supply of the launch tower. One of the subcontractors who built the oxygen tanks didn't change this, and continued to manufacture oxygen tanks meant to operate on 28 volts. A few years later, in 1968, the spacecraft that was to be Apollo 13 was being assembled, and the oxygen tank was dropped, bending the vent pipe. It was determines the tank was still ok to use because there was no visible damage, so it was installed anyway. Later, during a test, the tank was filled with liquid oxygen as usual, but when it came time to empty it, it wouldn't drain, because unbeknownst to anyone, that pipe was bent. Instead, they decided to simply turn on the heater (the heater was used to turn the liquid oxygen in the tank to gaseous oxygen for use as needed) to let the oxygen vent off as gas overnight. Now here's where the wrong voltage comes into play. The thermostat attached to the heater inside the tank was supposed to cycle the heater on and off so it didn't get too hot, but the 65 volt power supply was too high for 28 volt circuitry in the tank and it blew out the thermostat. This meant the heater stayed on all night instead of cycling on and off, and as a result, it got so hot inside the tank that it burned off the teflon insulation on the wires. The next day when everyone came in, all they saw was that the tank was empty as expected. Now it's April 13th, 1970. The spacecraft is 2 days into it's 3 day journey to the moon, and everything is going as planned. Mission control asks command module pilot Jack Swigert to stir the tanks. There's a fan inside the tanks that stirs the liquid oxygen to get more accurate quantity readings. So Swigert, flips the switch to stir the tanks. The electricity flows through the exposed wires inside a tank filled with oxygen and arcs, igniting some of the charred remains of the teflon insulation (fire + concentrated oxygen = bad). This caused the tank to explode. The explosion slammed close the valves feeding the fuel cells (the fuel cells generated power), tore holes in the other oxygen tank, and blew off one entire side of the service module, also damaging their main antenna and the main engine. Sorry for the long answer. The only difference on 13 was the dropped tank. That triggers the chain of events that leads to the explosion, It could have happened on any. previous flight, but it didn't.",
"In a nutshell, the oxygen tank that produced the explosion on the service module was damaged when it was accidentally dropped during a testing procedure. The damage was internal, and thus went unnoticed. Other Apollo rockets didn't have the same problem because their O2 tanks were never damaged."
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aj9dxu | Whats the difference between winter tires, regular tires, and all-season tires? | My car’s tires are all-season and have worn out. It’s time to replace them, and I’m trying to figure out if i should switch over to winter tires (as we’re in the winter time and the heavier snow falls have yet to come), or to continue purchasing all-season tires to use year round. | Engineering | explainlikeimfive | {
"a_id": [
"eetqzlz",
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"text": [
"I can answer the practical differences, someone else will most likely be more eloquent with the chemistry. The rubber is different, to help driving \"feel\" the same in different conditons. Ever put a twizzler or gummy bear in the freezer? They react the same way rubber does to cold - it becomes hard, brittle and wont deform as well (deforming in this context is actually a good thing for when you want something to grip a surface). This means they wont hold onto the road (or whatever else) as well. For the others, a lot is also based on how the tires are cut (tread pattern). Its all a balancing act to maxmize traction and tread wear (how long the tire lasts), minimize unnecessary rolling resistance, noise, vibration and harshness. There is also a lot that goes into tires rated for different activities that take these differences to the extreme. Think racing slicks vs drag radials vs mudding tires vs sand tires... Etc etc.",
"A huge part of what makes the grip good is about the rubber mixture. The softer it is, the better the grip is. And, at the same time, the softer it is, the faster it wears down. Just like everything else, the rubber goes hard by itself in cold weather. So to achieve the best grip with the least wear, the rubber mixture differs between the seasons. If you use winter tires in the summer, they'll wear out faster. If you use summer tires in the winter, it's easier for a small sharpish-rock to cause damage you need to fix. Summer tires have tread that is kind of silent, and helps remove water from underneath the tire. So that you don't always loose control of your car just because you found a poodle of water. Winter tires have \"canals\" that push mod out from underneath the tyre, to somewhat improve grip. And a tread that comes in groups, so that the tire is - at least in theory - able to push through the mod and get a good grip down on the pavement. It's also treaded in groups in a way that makes it possible to \"dig-push\" a grip in snow rather than just rely on friction right from above. All those extra patterns makes the tyre a lot more noisy, so they are not there on summer tyres because the noise is a comfort factor. Winter tyres also often have spikes, that improve the grip on ice. The spikes too are a noisy thing, and they cause a lot of extra wear on the road, so they are generally speaking not allowed unless you definitely need them. All-weather tyres are some kind of middle ground. They don't have spikes. The tread is *mostly* summer oriented, but they also have some thought given to how to handle mod. And the rubber is not exactly summer and not really winter either."
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ajevod | Would switching batteries from parallel to series make a toy race car (for example) go faster? | Engineering | explainlikeimfive | {
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"It would go faster but for a shorter time as there would be less capacity at that higher voltage. All this presumes the motor can take the voltage and it's not regulated to the lower voltage. In most small toys, there would not be such regulation. Years ago I started taking those 2.4vdc hand screwdrivers and running them on 12vdc motor cycle batteries. They had tremendous torque and speed. I got them at garage sales with dead batteries so it was cheap enough to experiment. I abused them driving screws and bolts and never burned any up. Of course, those Johnson motors were more robust than the common toy. I say, if you can afford it, go ahead and experiment with it. Do it safely on a protective surface to begin with.",
"Think about it as a water analogy. You have two pumps (batteries). Each produces 10 lbs/square inch of pressure, and pumps 10 gallons/minute. If you want to increase the volume you're pumping, you put them beside each other, run two hoses from your water source, one separately to each pump, and two separate outflow hoses - now you're pumping twice as much water (20 gallons/minute), and your pumps are in parallel. & #x200B; However, if what you want is to increase the pressure, you put your pumps in line. One line in to pump #1, and the pump produces, say 10 lbs/square inch of pressure. You run the outflow from that into pump #2 - the water comes in at 10 lbs/square inch, the second pump boosts it another 10 lbs/square inch, and it comes out at 20 lbs/square inch - twice the pressure you have with only one pump. Your total throughput is the same as with one pump though. That's your pumps in series. & #x200B; In the case of your batteries, pressure is \"voltage\". Putting your batteries in series (nose to tail) produces twice the voltage, which (depending somewhat on your motor type) makes your little race car go faster."
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ajg1wv | what does the bag that doesn’t inflate on airplane oxygen masks actually do? | “Oxygen is flowing even if the plastic bag does not inflate”....why have a bag there in the first place, then? What’s its role? | Engineering | explainlikeimfive | {
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"It’s called a non-rebreather reservoir mask. In hospitals it’s also called a trauma mask. It comprises of a mask and a bag attached. There is a series of one way valves between the mask and bag and also on the side of the mask (which are really only flaps of flimsy plastic). Oxygen flows from the source, into the bag, and then up into the mask. Ideally, before use you should occlude the valve between the mask and bag in order to fill the bag with oxygen (the reservoir). Then you should attach the bag tightly to your face to minimise any gaps between your face and the mask. When you then inhale, the valves on the sides of the mask close and the valve between the bag and mask opens. Thus you inhale a high concentration of oxygen from the bag. When you exhale, the opposite happens. The valve between the mask and bag closes and the valves on the side of the mask open. Thus you exhale out of the sides of the mask, and not into the bag (thus you do not rebreathe the same gas in and out of the bag over and over, hence the name non-rebreather). While you are exhaling, the bag is refilling with oxygen from the wall. With a full bag of oxygen and a tight seal they say you can get up to 85% oxygen in every breath. If you do not inflate the bag, you are only getting what’s coming out from the source. I’ve no idea what the oxygen flow rate is on a plane but in a hospital this is about 15L per minute. This sounds like a lot but when you consider that an average breath in an emergency might be easily 1-2 L, inhaled over half a second, you can see that the peak inspiratory flow rate is about 120-240L per minute. The oxygen source is not delivering the oxygen fast enough to provide this breath as pure oxygen. What happens is that you entrain air through the gap between your face and the mask. During cabin decompression this air will have very little oxygen, and you will probably become hypoxic and pass out pretty quickly unless a rapid descent is made in order to repressurise the cabin. Long story short, you really should inflate the bag with oxygen first in order for the mask to work, but it’s far too complicated for the average person to learn how to do this in an emergency. In reality it’s a token effort which might be enough to keep you alive but unconscious until a descent is made.",
"The tube releases oxygen whether you are breathing or not. The bag is to collect some oxygen if you aren't currently inhaling, rather than simply going to waste spilling out around your face. Since you'll probably be breathing rather rapidly (out of terror or what not) it isn't likely to collect enough to inflate, but they don't want you to see that, think you aren't getting oxygen, rip off the mask, and need rescue.",
"It's just an additional reservoir for air. You should be able to inflate by pressing on the one way valve you would normally breathe from"
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ajj8dt | Unleaded gasoline | Why is it that almost all (USA) gas stations say unleaded gasoline? I know that in the old days cars needed leaded to run. Now cars are better, what happened?, More specifically what technology improvements for cars made leaded gas obsolete? (Other than electric cars) It seems since every gas station sells unleaded gasoline does anywhere still sell leaded gasoline? What still uses leaded gasoline? Why add lead to the gasoline in the first place? Obviously there are health risk associated with lead poisoning, how toxic are the gas fumes from both leaded and unleaded? | Engineering | explainlikeimfive | {
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"Tetraethyl lead was added to gas to allow for higher compression which increased engine power and fuel economy. In the late 70s and early 80s most countries began phasing out the use of lead additives in gasoline in favor of other octane boosters because of the serious health effects of leaded gas emissions Leaded gas is still sold for some specialty appications, and for use in some aviation engines.",
"> Why add lead to the gasoline in the first place? Tetraethyl lead was used to make fuel more resistant to detonation (also known as \"knocking\" or \"pinging\"), which is the air/gas in the engine cylinder exploding before it is supposed to. It also lucubrated the valve seats, preventing them from wearing out. > More specifically what technology improvements for cars made leaded gas obsolete? (Other than electric cars) Technology didn't really make lead obsolete. The health problems associated with lead exposure lead to its removal and technology was forced to catch up. Specifically, harder alloys were used for valve seats, more advanced refining practices reduced the need for octane boosters, and other octane boosters, such as MTBE (which was then later replaced by ethanol), were developed. > What still uses leaded gasoline? Basically the only thing that uses leaded gasoline now is small aircraft. Most aircraft that run on aviation gasoline use a fuel called 100LL, which means \"100 octane, low lead\" (which as the name says, contains less lead than older formulations like 100/130). Efforts are underway to phase it out, though they're moving slowly. NASCAR also used leaded fuel until 2008, at which point they switched to an unleaded fuel.",
"URL_1 If you want more fun info, this episode of Cosmos explains a lot as well :). Basically, [this dude]( URL_0 ) discovered that lead was being spread everywhere via industrial sources, including cars, and started campaigning to remove lead from gas.",
"In the 70s and 80s, emissions requirements were strengthened sufficiently to effectively require new cars to be equipped with catalytic converters, which remove nitrogen oxides and the products of incomplete combustion from exhaust fumes. Catalytic converters are incompatible with leaded gasoline because the lead particles would coat the surface of the catalytic converter and render it useless. As a result, new cars required the use of unleaded gasoline. So in an indirect way, regulations on smog causing emissions also resulted in the reduction of lead emissions, though this was not the original intent. (Unleaded gasoline was banned later, but only after it had fallen out of common use.)",
"Both answers are mostly correct. Tetra ethyl lead was added to gasoline as a cheap, easy way to raise its ignition point a little. This allowed engines to run at higher compression without “knocking”- starting to burn before the end of the compression stroke. (This is very bad for the engine and will ruin it eventually). The higher compression allowed engines to make more power with less fuel. It had the added benefit of making the fuel more slippery and reducing wear. It was known early on how VERY toxic the TEL was. The workers who produced it suffered serious neurological damage until safeguards were introduced. It was suspected that the TEL released into the air by cars was poisoning people, albeit more slowly. Oil companies denied it, and spent a lot of money preventing any regulation of TEL. Eventually, thanks to the work of the scientist profiled in that Cosmos episode, it was proven that the whole world is covered in TEL and that it remains toxic for many years. Leaded gasoline was mostly banned in the US in the 1970s and lead levels in the soil and water have been slowly decreasing. It is still too high to safely grow food in urban areas almost 50 years later- people with backyard gardens in cities often build raised beds and fill them with soil from the country. Advances in engine and fuel chemistry technology allow high compression without TEL. It is still used in some parts of the world.",
"Epa emission requirements We're the cause. In order to run unleaded gas engine manufactures had to put harder valve seats in their cylinder heads do to the lack of lubrication caused by the new fuel.",
"Gasoline is a bit too explosive to work well in internal combustion engines so they need to add something to make it a little less explodey. Tetraethyllead was found to be the *cheapest* additive that would do the job. The health risks were known all along so, when nonlead based additives and better engine technology finally converged to become cost comparable, TEL was phased out fairly quickly. An additive is still needed but better control over engine timing and pressure also helps to mitigate the conditions that lead to pre-ignition. The fumes were, by today's standards, very toxic. I believe there was about 2g of lead in every gallon of gas and it was, of course, vaporized making for a very efficient delivery system. Heavy metals like lead are accumulated in the body so any exposure was cumulative. Another interesting effect of lead is that an early symptom of lead poisoning is violent and anti-social behavior."
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ajk7s1 | I’ve often wondered how much astronauts had to endure during a launch of a Saturn V, does the movie “First Man” actually portray how much astronauts went through at launch? With that much vibration, why didn’t it destroy instruments? Would you take the ride? | Engineering | explainlikeimfive | {
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"[Here's that actual g-force profile of the Apollo 11 Launch]( URL_0 ). You can see that it peakeded just shy of 4Gs at Stage I shutdown, 150 seconds into the flight. Then it drops considerably, never going above 1.75 Gs for the remainder of launch, which lasted just shy of 12 minutes in total. 4Gs is uncomfortable but tolerable, especially for the short period of time they experienced it, and the fact that they trained to handle it. As for the vibrations, astronauts have described the first 1-2 minutes as being very uncomfortable, but the vibrations diminished significantly after the launch vehicle went supersonic and cleared the densest part of the atmosphere. So essentially, the first few minutes were uncomfortable but tolerable, and the remaining roughly 10 minutes wasn't that bad. As for the instruments, every single component on the spacecraft was designed, built, and tested to withstand the forces and vibrations involved during launch.",
"Because everything was designed for it. And yes, I would take the ride."
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ajnp8h | the difference between a computer's BIOS and Hardware Abstraction Layer. | I could be completely off here but just based off of the wikipedia pages it seems like they're both there to provide the computer with access to hardware, with the BIOS having additional functionality during the boot up process. | Engineering | explainlikeimfive | {
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"The BIOS operates at a level below the operating system. When you turn on the computer, there's no OS loaded, so the PC needs to load the OS from disk. But in theory it can't do that, because, until the OS has loaded, the computer doesn't know how to read from the disk. Catch 22! So the PC loads the code from the BIOS chip, which then loads the OS from disk, and the OS takes over. The BIOS isn't really used after that. The HAL is part of the operating system. It only comes into effect once the OS has loaded. & #x200B; So yes, they're both ways of providing the computer with access to hardware, but in different ways and at different times.",
"BIOS is the lowest level software that's pre installed on the motherboard. The BIOS checks that all the hardware is dandy and then boots up the OS. At this point the OS takes control of the hardware. Different hardware use different instructions in order to directly control devices in the computer. Because OS's need to run on a variety of machines, they contain a HAL which basically translates higher-level commands from the OS into specific instructions for the hardware it is running on."
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ajnss7 | How the engines in twin-engine cars work together? | Engineering | explainlikeimfive | {
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"I mean, they would only theoretically need to share a crankshaft. The crankshaft is basically what the pistons \"push\" against to rotate the flywheel that connects to the transmission. A V8 engine is sometimes thought of as simply 2 inline 4 cylinder engines sharing a crankshaft. Volkswagen once designed a W16 Engine that was basically 2 V8s that shared a crankshaft. You can just use the same principle for more engines. Its not really thought of as using multiple engines basically, just more pistons.",
"What do you mean by twin-engine? Gas-Gas, Gas-Electric, Electric-Electric or something else entirely?"
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ajyaw7 | so how do all the clocks synced to phones/computers know what time it is? Like which one is in charge? | Engineering | explainlikeimfive | {
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"They're synced with either a server or cell phone tower which uses network time coordination protocols that gets synced with coordinated universal time. Coordinated universal time is determined by international atomic time which is the average output of 400 atomic clocks.",
"in the US, the National Institute of Standards and Technology ([ URL_1 ]( URL_0 )) , part of the Department of Commerce, is responsible for operating the atomic clocks that track the \"official\" US time."
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ak18s3 | why is it that when disarming a bomb, that you dont just cut all the wires at once? | If you cut all the wires then it would not only take away the powersource but it would render it useless, atleast thats what seems would happen | Engineering | explainlikeimfive | {
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"Edit: here's a link with some good answers URL_0",
"Because if you could then movies with bombs in them would be pretty anti climactic. In real life bombs tend to be much simpler and easier to defuse (assuming they even work to begin with)."
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ak53ht | How are our water pipes pressurized? | Engineering | explainlikeimfive | {
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"Many cities have water towers that use the force of gravity to pressurize your water, so when you use it, it is essentially pushed by gravity to your faucet or wherever.",
"Gravity. Towns with hills will pump water up to a storage tank and let gravity do the rest. Towns with no hills... that’s where water towers come in.",
"There’s several ways. 1) Water from a high reservoir is piped to a low place. Gravity does the work 2) The water is pumped from a low place to a high place like a reservoir or water tower. Then gravity does the rest of the work 3) Pumps without a reservoir or tower",
"There are a couple of different ways depending on your geography. The easiest way to keep the water pressurized is to have a water reservoir on a hill so that the water gets pressurized on the way down from the hill. The issue then is how do you get the water up the hill if there is no water on the hill. And for this there is pumps which can pump water from sources further down and up the hill to refill the reservoir. Depending on how much water is being used the water level in the reservoir might become lower but the pumps will be able to refill it over time when people are not using as much water. But the pumps can not turn on and off fast enough to match the load exactly. But there can be other issues, what if you do not have a hill to place your reservoir on. Then you just place a tank on top of a tall building or tower. This is why you often see big water tanks on top of building and as free standing water towers in towns. But then what if you can not build tall structures to mount your tanks on. It is possible to have a pressure tank in the system which is filled with air. Unlike water air will compress when pressurized. So as the pumps add water to the pipes the pressure increases causing the air in the tank to compress letting water into the pressure tank. When the demand for water is higher then the pumps can supply the compressed air will push the water out of the tank. This is a more expensive system but is an option where an elevated water tank is not desired."
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ak5ilb | why bigger trucks use diesel and most cars use normal gasoline? | Engineering | explainlikeimfive | {
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"Diesel engines are more fuel efficient, which is important with heavy trucks. Most cars are gasoline powered because gasoline engines are cheaper to make, lighter, more powerful for their size, and emit less of certain types of pollutants.",
"The traditional view was that diesel engines were efficient and provided lots of torque (good for towing loads), but were slightly harder to drive (a narrower power band meaning you need to be more specific with great choice), and were rougher in sound and performances. In a truck the downsides of gearing and sound are not as big considerations, and the better efficiency and torque are particularly beneficial. In a car however, the torque and efficiency are not as critical in general use, while the ease of use and the sound and feel of an engine become more notable issues with a more fickle car buying public. A lot has changed as diesel engines have been developed however, with modern engines being pretty comparable to a petrol engine - while they are pretty rare in the US, they are pretty common in Europe and other areas (though there are currently some concerns regarding the different emissions).",
"Nobody yet has mentioned regulation. If you go to Europe, diesel cars are common. They are much less common in the US. Diesel tax is 6 cents higher than unleaded gas on a federal level. That likely has a pretty small impact, but the diesel tax in Europe is often lower than the US. Diesel engines are also more expensive. When gas is 2.00 a gallon, spending more on an engine to improve fuel economy isn't deemed important for a lot of consumers. If gas was 5.00 a gallon, like it is in Europe, spending the extra money on diesel to get better fuel economy makes more sense. US also has stricter emission regulations compared to Europe. This results in even more expensive engines. I also think diesel is less profitable for auto manufacturers, so if demand isn't there, they are not going to go out of their way to try to create the demand. So if you wanted to see more diesel cars, the solution is quite easy. Lower emission regulations, (to be the same as Europe), and increase gas taxes, to be the same as Europe. You would see a rise in diesel car sales very quickly. I'm not saying we should do that, but it is one of the main reasons why diesel cars are not popular in the US.",
"Diesel has about 15% more energy per volume, so that means fewer fill ups with the same sized tank."
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ak8c6f | What are the pros to nuclear energy? Is the storage of waste still a problem? What roadblocks are stopping it from being viable? | Engineering | explainlikeimfive | {
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"It isn't. Storage *is* a consideration, but the problems caused by nuclear waste are infinitesimal compared to those caused by fossil fuel power. To answer the title question, nuclear is already viable. The biggest roadblocks are political. That said, I'd prefer molten thorium fluoride reactors, or ideally fusion, over conventional fission but even fission is better than coal or oil."
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akbwf7 | how does a wankel rotary engine work? And how does but the power onto the wheels ? | Engineering | explainlikeimfive | {
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"To answer the first half of your question. The rotary engine takes the normal suck, squeeze, bang, blow, of the your traditional reciprocating engine, but gets rid of the lost energy by having no pistons and no up and down movement. Instead they created a housing shape called an epitrochoid, which looks like a chunky figure 8 and a rotor which most car guys refer to as the dorito. This is a triangle with rounded edges. The rotor is rotated on an offset (this allows it not to spin in a circle, but instead the rotor spins in the exact shape as the funky figure 8). Inside this housing it sucks in the air and fuel, squeezes the air fuel mixture, combusts the mixture once compressed using 2 spark plugs per cycle, and exhausts the spent mixture out of an exhaust port (which gives some amazing braps). Your typical wankle engine has 2 rotors, but people like mad mike and rob dahm have made more popular to the world using 3 and 4 rotor engines. These engines rev higher since they have less rotational mass, and make power very quickly. They do however have some flaws. The Dorito must ensure that at the tips of the triangle seal incredibly well. These seals are called apex seals. They use oil from your motor to ensure a solid seal. So every 2 fuel fill ups it is recommended to top up your oil. The other “downside” is that they really don’t make that much torque. Typically also these engines have lower longevity due to the maintenance required on the engines and specialized nature. To answer the other half of your question. From the block back it is the same as every other engine. The rotors spin a crankshaft called the output shaft with lobes mounted eccentrically (offset so the Doritos can spin inside the chunky figure 8) and that connect to a flywheel which then connects to the transmission like any normal car. How stuff works has a good write up on it if you want more Information. TL;DR : Doritos spin inside a chunky figure 8, magic happens which leads to amazing braps, and joy ensues once you don’t blow your apex seals."
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akckew | Why are Diesel engines better than gas in some situations? As in why are most big trucks diesel, but very few cars (at least in the US)? Is it a power thing? Efficiency? | Engineering | explainlikeimfive | {
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"Diesel engines have better fuel economy and higher torque (think of it as pulling power) than equivalent petrol engines which makes them more suited vehicles which will be traveling long distances and carrying/towing heavy loads."
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akcz6p | Why don’t cheap car companies design cars that look like, for example, a Ferrari or a Lamborghini? does it cost more money to simply make the car body good looking? | Engineering | explainlikeimfive | {
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"When you're driving a 1.4 litre, four cylinder family car, would you rather it looked like a supercharged V10 mid-engined hypercar - or would you rather it was designed to maximise luggage/passenger space and represent more accurately the kind of car it is? What would be the point in having a car with supercar styling that took 10 seconds to hit 60mph? Never mind that you assume that the styling of these cars is particularly popular, I don't think they're quite as popular as you might imagine.",
"Yes, it does cost more to manufacture a body that has complex curves. It takes more time to design, build, and fit the panels.",
"Several issues here. First, car designs are protected by copyright and design patents: if you tried to build a car with the same shape as a Ferrari, Ferrari would sue you. But you could design your own car with a supercar shape but without the fancy engine and suspension. This *would* cost more, those complex body angles and low-slung frame are tricky to design and build. But the bigger factor is that nobody would buy it. To look like a sports car, it'll need to be a two-seater with very low ground clearance and no cargo space. Those are all big drawbacks for someone with only $25,000 to spend on a car who needs to use it as a practical daily car to carry their family and groceries around. There have been some attempts to make a super-sporty looking car for cheap. Probably the most famous is the Chevy Corvette. Especially in its '60s and '70s versions, it had a streamlined racing-style body, a big engine, and none of the handling and suspension features that would be found on a high-end sports car of the day. It was never exactly cheap, but it's always been a hell of a lot cheaper than a Ferrari."
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akge2b | Why do scientists research commonly known stuff? | Just read about how research shows that stretching slightly reduces muscle soreness ( URL_0 ). It's been known in society for a long time before this that stretching reduces soreness, so who is paying scientists to research it and other things similar? What's the benefit to those paying? | Engineering | explainlikeimfive | {
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"Actually if you read the article it does next to nothing. It reduces soreness by between half a point and one point on a 100 point scale. So if you normally get soreness of 41/100 after going for a run, you could stretch and change that to 40.5, or maybe to 40. So essentially the time spent stretching is not worth the reward. You wouldn't notice the difference in those scores. Your comment is exactly why we need to research commonly held beliefs, they may seem obvious but are often wrong. In addition, it's impossible to give someone placebo stretches in a research study, so there's a very high likelihood placebo accounts for that 0.5 to 1 point change that the article is reporting.",
"You've just beautifully illustrated why scientists research commonly \"known\" stuff: just because something is commonly thought to be true because it sounds intuitive or it's \"common knowledge\" doesn't necessarily mean that it's correct. And in this case, it turns out that it isn't correct: > The evidence from randomised studies suggests that muscle stretching, whether conducted before, after, or before and after exercise, does not produce clinically important reductions in delayed‐onset muscle soreness in healthy adults.",
"It's worth finding out why and how something works, because once you know the mechanism behind it, you can use it more effectively, refine it so it works even better, and apply the same techniques to other purposes. We've long known, for example, that tea of beech bark soothes pain and fever. Figuring out the active components in the bark has given us convenient and highly effective tablets of aspirin.",
"I think one of the more important points of science is never to assume anything. Everything has to be proven with evidence. So it wouldn't matter how common the knowledge is, it still has to be proven using the scientific method to be used in science. Also, in doing this they will find a LOT more information than just the common knowledge it's self. They'll have an exact quantified basis for that knowledge, as well as discover exactly WHY and exactly HOW it's the case not just the common knowledge THAT it's the case.",
"The fact that an apple falls from a tree naturally and it hits the ground has been well known to humanity for hundreds of thousands of years. It took someone asking why an object falls towards the ground to enable a dramatically more detailed understanding of our universe. Everyone has known forever that light helps us see things. It took someone asking “but what is light, actually?” to give us basically all the technology we have today. It’s about why. And as others have pointed out, verifying our common sense which is often wrong.",
"Lots of common knowledge (*especially* about the human body) is wrong and/or baseless Like the whole 8 cups of water a day thing",
"In addition to what everyone else is saying, well known/established studies are still replicated to ensure that they’re actually true and not due to sketchy stats etc. Source: the lab I work in does replication studies for that exact reason.",
"Because scientific testing can point to WHY something is true, or uncover little-known wrinkles. It also separates placebo effect (something feels different because you expect it to) from actual effect. Also, common \"knowledge\" often comes from old folk tales, religion, logical fallacies, and the like. If you heard them just a few times, you'd laugh them off. It's only because they've become ingrained in popular imagination that you believe them.",
"Also just to add to the good points others have already made, researching/doing studies on things that are \"known\" is an important part of the scientific method. One study saying stretching does or does not reduce soreness does not really carry much weight BUT a hundred studies carried out by different researchers following correct methods all showing similar statistically significant results would be a much greater indicator of what the facts are. Reproducibility of results is key. 🤓",
"You should check out the structure of scientific revolutions by Thomas Kuhn if you're interested in why we investigate common knowledge. Academia can get stuck in paradigms based on axioms that we regard as self-evident, but may not be the most accurate representation of the world. At one point it was common knowledge that the sun was the center of the universe until scientific progress proved otherwise and the paradigm shifted. Another example would be euclidean geometry presented in the elements, which was used as common knowledge for over a millennia until riemann came along with his geometry that altered the axioms set forth by Euclid so that they better represented the world.",
"The point of research and science is to take something we take for granted and do everything we can to prove it wrong. If we fail at proving it wrong, it's likely true. It's not fact that it's true, but it's very likely is. This will raise a few questions while we do this: Why is it true? Cue further research ad infinitum. As Albert Einstein said: \"As our circle of knowledge expands, so does the circumference of darkness surrounding it.\" The more one studies something, the more questions arise. And speaking of Einstein, there's constant attempts to find caveats to the general theory of relativity. While we do know it kind of breaks down at a quantum scale already, we still do research at the cosmic scale, trying to find evidence that it's wrong so that we can make an improved theory.",
"I heard a joke that might shed some light on trusting common knowledge. A woman was teaching her daughter to cook a ham and the first thing she did was cut off both ends. Her daughter asked why and she said she didn’t know, that’s just how her mother taught her. So she asked her mother, who said the same thing. So she asked her grandmother. Her grandmother said her roasting pan was too small for a whole ham so she had to cut the ends off so it would fit. Common knowledge is not always right or fully understood. Researchers want to understand things fully. They want to know the mechanisms and the limits. In the case of stretching, it used to be the case that coaches would recommend hyper extension stretches. Some high school and college athletes ended up needing joint replacements later in life because of it. As for who pays for it and where the value is, that’s a different question. This sort of research is usually done in university. Most of the hands on work is done by graduate students and undergraduates. Whatever the results or the practical applications may be, the act of doing the research in a rigorous and meticulous way serves as a great training tool for the students. Those students may not go on to study this topic for the rest of their lives, but the skills of scientific inquiry can be applied to lots of things. Often when professors are writing grant applications one of the questions is about training of students. The granting agency wants to know how many students of different types will be impacted by the grant."
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akhklt | Why some IPhone chargers are charging my phone slower than others ? | For me an IPhone charger is just a metallic wire connecting my phone to the power outlet. So why some of those (mostly the cheaper ones) are charging my phone slower than official Apple ones ? | Engineering | explainlikeimfive | {
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"I have two chargers on my desk, one which says 12W and one which says 10W. The 12W charges my phone faster. The more power they are able to provide, the faster the charging will go. Have a look for the power values of the two chargers."
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akjgqe | Why are airlines specific about the weight of bags when the passengers weight vary so much? | Engineering | explainlikeimfive | {
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"Passengers don't usually need to be carried around by baggage handlers. Lifting heavy items is an occupational hazard. There are rules about how much weight a person can lift regularly on the job. Generally lifting over 50 pounds regularly is going to need special equipment or a \"two man lift\".",
"The baggage limit has to do with the people who actually lift your bags in the terminal. It's for their safety so they don't have to lift 100+ lb bags and risk injury. This is the ONLY reason.",
"In addition to what others have said. People have to pick up the bags to load/unload the plane. Personnel injuries are more likely with heavier bags.",
"Passengers weight fluctuation is accounted for because they can't unpack 20 pounds of fat. They have a hard limit on bags to a) get more money and b) you can always throw away some clothes",
"As a society we are in favor of accommodating people's physical differences. Even though it costs a bit more to fly a 100kg person than a 50kg person, we charge them the same. But people have complete control over the weight of what they choose to pack — it's not a hereditary or medical condition. (edit: typo)"
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akmdul | Why are petrol engines so quiet compared to diesel ones. Aren't they based on mini-explosions inside the engine? | Engineering | explainlikeimfive | {
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"The difference is that diesel engines work at a much higher pressure than gasoline ones: A regular gasoline engine compresses the air at a roughly 10:1 ratio, meaning that 1000 cc of air are compressed to just 100 cc of air before ignition. A diesel engine meanwhile compresses the air at a ~20:1 ratio, so the same 1000 cc of air are compressed to just 50 cc before ignition. This increased pressure leads to a louder explosion. On top of that, bus and truck diesel engines are often much bigger than gasoline engines, running at a low RPM with more displacement since that's more efficient."
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ako7xj | Why most military jets went from Center Stick to Side Stick? | Engineering | explainlikeimfive | {
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"The center stick was designed originally to let the pilot exert more force, before the aircraft was fly-by-wire (no special amount of force needed).",
"It was one of the big advantages of going from fly by physical link to the control surfaces to using fly by wire. Far less faffing about setting up the control runs (Rigging) and saves a lot of weight. Modern sidesticks also have force feedback now to represent the forces on the control surfacesthat would have been felt by the pilot if there was a physical control run.",
"There's a wide range of reasons, most of which have to do with pilot ergonomics. In a center stick configuration, the pilot has to sit in an upright position which is not the best for tolerating high-g maneuvers or longer flights. By moving the stick to the side, the pilot can sit in a more natural, reclined position. With the pilot reclined, the cockpit doesn't have to be as tall, which gives engineers room to move other components around into a configuration that might be better for aerodynamics or a lower radar return.",
"Haven’t seen it mentioned yet, but the actual REASON they moved the stick has to do with human factors. Primarily things like being able to see screens better without the stick in the way, being able to pee easier, and a big one is it keeps their legs from getting tangled up if they have to eject.",
"One other issue is interference with the G suits. From the Blue Angels FAQ; \" Additionally, G-suits would detrimentally impact flight safety.The Boeing F/A-18's control stick is mounted between the pilot's legs. The Blue Angels have a spring tensioned with 40 pounds of pressure installed on the control stick that gives the pilot a \"false feel.\" This allows the pilot minimal room for un-commanded movement. The pilots rest their right arms on their thighs for support and stability while flying. Therefore, inflating and deflating air bladders in a G-suit would interrupt this support and stability, causing un-commanded aircraft movement. \" URL_0 Side sticks don't have that issue.",
"Not sure what planes you're talking about as I'm not sure what all the planes are. But I do know that fighters need side stick because in high g maneuvers you can't hold a center stick, you need something to hold you arms, so fighters have a side stick that let you use it while using the armrest.",
"Follow up question: Why haven't we switched to side joystick for cars??? You'd get rid of the steering wheel, all of the pedals - and it'd work for left or right hands easily... Plus - awesome power slide."
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akrn7h | Why do zippers work only when grabbed by the dangling part? | Engineering | explainlikeimfive | {
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"text": [
"There's a little catch in there to stop the zipper from opening of its own accord. If you look closely you might be able to see it"
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al2d46 | How do iron lungs work? | Engineering | explainlikeimfive | {
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"text": [
"Iron lungs were used on people who did not have the ability to breathe on their own. The lungs rely on sets of muscles to expand and shrink the lungs in order to pump air inn and out of them. It would be quite hard to install artificial muscles or something so they did the next best thing. They changed the air pressure around the body of the patient but not around his head so that the lung would expand and contract.",
"Artificially inhale and exhale for you. Usually by using negative and positive pressure. Lock your body in vacuum, and your lungs begin to fill up (because negative pressure means they are \"pulled\" outwards, so they expand, and take air in). Pump pressure inside, and your lungs go down, exhaling air. EDIT: There's apparently more than one version of Iron Lungs. Here: URL_0"
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aljr8c | Why are triangles the strongest shape? | Engineering | explainlikeimfive | {
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"text": [
"Triangles are only strongest shape in certain applications. For example, a circle is stronger when containing pressure from the inside. Hence why most pressure vessels are cylinders."
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alnjg3 | In a big city like Chicago how are the drainage and sewer systems maintained during winters, when temperatures drop to like -20 and everything just freezes instantly? | Engineering | explainlikeimfive | {
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"There's this thing known as a \"frost line\". It's the depth that the ground will freeze to, given a prolonged temperature. Cities know how cold it can get, and bury their sewage lines well below the frost line. This ensures that they don't freeze, even in extremely cold winters.",
"While the frost line is important for pressurized water main, most sewers are actually hot in winter. Most of the sewage comes from your house, where the water is well above the freezing temperatures when it get to the underground pipes. The combined heat from every waste in every house the pipe is connected to will keep everything warm, combined with the fact the pipes themselves are buried underground, with the ground itself acting as insulation. That’s why in very cold temperatures you can see steam coming out of manhole covers. Drainage can freeze has it’s doesn’t typically contains any household wastes. Here the frost line is a bit more important, but not critical since there’s no pressure. It’s not as critical as water pipes, which can burst if they freeze because of the pressure. Source : Civil engineer in Montreal. EDIT: As someone else pointed out, the fact the water is constantly moving in sewers helps a lot. Pressure pipe, like the water line from the street to your house, can freeze in extreme cold if you’re not using it. That’s why it is recommended to leave a tap running if you’re worried about your water service to freeze.",
"First of all everything does not freeze instantly. Larger moving bodies of water takes a good while to freeze. And secondly it is under ground below the frost line. This is normal in all cold countries. In super cold places permafrost can cause other solutions."
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alovn5 | G-Suits | How do g-suits prevent the body from g-forces despite they can't prevent the acceleration if the body? | Engineering | explainlikeimfive | {
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"They don't prevent you from experiencing g-force. You can still go into G-LOC in such a suit. They just make it easier to resist the effects. For example, they compress your legs so that blood can't all pool in your lower extremities and make you black out as easily.",
"They don't make the body experience fewer G-forces, they instead make the body more tolerate to G-forces Under positive G forces, your blood will move down and pool in your legs, this can result in you blacking out. G-suits squeeze your legs to prevent the blood from pooling there and can bring your G tolerance up from 5-7 Gs to 7-9 Gs which for a fighter pilot means they can make tighter turns for longer than the enemy and could save their life."
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alsc47 | How does an extension cord overheat? | I am hearing that it is extremely dangerous to plug space heaters into extension cords. I googled it and people say that the extension cord can overheat and start a fire. So my question is: how is having an extension cord any different than the wires in the wall? Do they have different materials? Do the wires melt the insulation? | Engineering | explainlikeimfive | {
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"text": [
"When electricity moves it creates heat. The more electricity is being moved, the more heat is made. The smaller the thickness of the cord, or the longer the cord, the more heat it creates. If a smaller cord that is also long (like an extension cord) is used to power something that needs a lot of electricity (the space heater), the heat from electricity moving can be so much that it melts the cord and catches fire. ELI4: If you running and the road is empty and wide, its easy. If you're running and there's a lot of people, but the road is wide its harder but doable. If you're running but there's a lot of people and the road is narrow, you might bump into people or get jostled. If you're running but there's a lot of people, the road is narrow, and the race is really long, someone will likely trip, fall, and cause everyone to fall with them.",
"It comes down to the wire size of the extension cord and the wattage of the heater. The bigger the number of the wire size the smaller the actual circumference of the wire. Smaller wire can't handle larger loads (watts) so when you try to run high loads through small wires you can over heat the cables and melt insulation and start a fire. Safest thing to do is always buy bigger extension cords for heaters, minimum #14, I'd recommend a #12."
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dbuvty | How a wooden barrel stays watertight | I would have amused the round shape would make the joints between the pieces of wood weak, let water escape. Is their some form of lining or insulation(?) to stop the contents from leaking out. | Engineering | explainlikeimfive | {
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"text": [
"The planks (called staves) are wedged at high tension against each other & bound by the steel bands - as the liquid in the barrel soaks & impregnates the wood staves they swell and press against each other forming a water tight seal The staves have to be carefully sized when assembling the barrel to make sure they fit tightly together Here's a video that demonstrates how they are made: URL_0",
"It’s the metal rings around it. Moisture makes wood expand, the rings hold it together, so water makes it even more dense as a barrier.",
"Whiskey barrels are made with White oak (Quercus alba) due to the lack of open pores (these pores are filled with tyloses which plug the pores providing an air tight seal called a tight cooperage). These pores are located on the end grain (cross section of the tree) and allow water to travel up the tree. If a barrel is not required to be airtight (slack cooperage) then you can use Red oak (Quercus rubra) which does not have tyloses to plug its pores. The staves are slightly cupped and fit tightly together to provide a seal along the sides of the staves. Tight cooperage was sometimes sealed with glue or pitch then burned to provide an even more of a seal."
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dbvqjm | Why don’t cars have external airbags? | Engineering | explainlikeimfive | {
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"text": [
"They cost a lot of money. But there are some manufacturers looking at adding an airbag to the hood in case the car hits a pedestrian.",
"They already exist but are not widely used. Companies like Volvo and jaguar have toyed with or even implemented these ideas for pedestrian safety. It's just very costly to have an airbag system for pedestrians. It would be more expensive to have it wrapped around the whole car for any sort of collision. So unless you're comfortable paying 40k for a base model corolla, it's unlikely we would see external airbags anytime soon"
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dc19h0 | why can't clothes dryer send the static to ground? | Lots of static electricity is created when drying your clothes. Why can't the dryer send the static to ground? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It does. The problem is that clothes don't give up their static easily. The dryer has to touch the part of the clothes where the static builds up in order to discharge it. Touching every square inch of shirt is difficult.",
"If an ion emitter is placed in the inlet air stream it releases positive and negative ions (oscillates, some of them neutralize eachother, but most make it to the clothes), they neutralize the static build up wherever it is occurring on the materials. It is a very low cost bit of electronics - used widely in the manufacturing of sensitive electronics to prevent damage during handling. It decreases dry time by allowing for more free movement of the garments. I don't know of any production dryers currently utilizing this technical solution.",
"Because static electricity is a connection from some charges to other charges. If one 'charges' are in ground, then a static electric discharge still exists from charges in clothes to charges now in ground. Static is eliminated when both charges are somehow connected. One of many techniques is an ion generator. Then no current (a static discharge) happens because those charges are already discharged.",
"The problem is that clothes don't conduct electricity. If something conductive, like a piece of metal, gets charged up you simply need to connect it to ground at one point. But when something which doesn't conduct electricity gets charged up, connecting one point to ground only discharges that point. Then the only solutions are increasing conductivity via putting something on it or high humidity, or connecting ever spot on the thing to ground."
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dc3ebj | Why do trains make a low pitch noise when they start accelerating and why is there a linear progression of pitch to speed | Engineering | explainlikeimfive | {
"a_id": [
"f25q2g2"
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"text": [
"I assume you mean modern high speed train, refer to **Electromagnetically excited acoustic noise.** faster speed = faster rotation of motor = faster and more frequent vibration, same with a string instrument, a low frequency would produce a lower pitch, whereas a high frequency produces a high pitch."
],
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dc5d6d | How’s does an automatic transmission know when to press the clutch? | Engineering | explainlikeimfive | {
"a_id": [
"f266b0e"
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"text": [
"An automatic transmission doesn't have a clutch. Instead it uses something called a [torque converter]( URL_0 ). If a picture is worth a thousand words then a video has to be worth ten thousand. On that note, [here's an old-timey video]( URL_1 ) showing how torque converters work."
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dc6lwm | if elevators get stuck why don’t they fall all the way down because they’re not working right? Is there a chance for that to happen? | Engineering | explainlikeimfive | {
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"theres counter weights n such and tons of safety stuff, cause obviously thatd be a huge problem",
"Mainly due to engineered fail-safes. Fail-safe doesn't mean it won't fail; when it fails it'll fail safely. In this case the engineers made it so that the brakes are normally engaged and you have to do something to get it moving. The more dangerous something is, the more redundant fail-safes are implemented",
"I usually find this guy entertaining: [Fact Fiend discusses the invention of the safety elevator]( URL_0 ).",
"As a rule the motor needs power to move it up and down using the cable. As per a previous comment, counter weights are used to make the elevator weight neutral so it uses less power. In the event of a cable failure, it has throw out breaks that grab onto the guide rails that are spring loaded and once activated need intervention to release.",
"Any elevator is required to have multiple safety measures in place for exactly this scenario. Quite often it is the safety mechanisms that causes the elevator to get stuck in the first place as they falsely engage. In order for the elevator to fall you need to sever all the cables used to lift it as these cables are attached to counterweight that balances the weight of the elevator car preventing it from falling down. But then if the cables are severed there are several breaks in the car itself which will stop the car from moving unless you pull at the main cables. But even then there are other breaks which detect if the car is going to fast and will engage to stop the car if it moves faster then the motor is rated for. Lastly there is a shock absorber in the bottom of the shaft so that if the elevator car were to fall down it would stop at a survivable rate when it hits the bottom of the shaft."
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dcat7o | What physically happens if you downshift into a lower gear at a high speed in a car? | I’m trying to picture it in my head. Is the clutch moving too fast for the engine? Or is the engine moving too fast for the clutch? Since the clutch and engine rotate at the same speed it baffles me. Same thing when you rev the engine really high at a low speed and you upshift , the RPM drops pretty hard, why? | Engineering | explainlikeimfive | {
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"Think of it with a 10 speed bike. If you are already at a high speed, and you switch to a higher gear (the kind of gear you'd use to climb a hill) your feet a pedaling like a maniac, but the wheels are already moving way faster than that gear is calibrated to move, and without any resistance in the pedals you throw out your knee. Kind of the same thing with a car, if the vehicle is already at a higher speed, and you shift to a lower gear, in order for the vehicle to be at equilibrium, the engine RPM has to drastically increase to match. Shift TOO low a gear and the RPM goes too high (redlines) and you can blow something."
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