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jdfxxf | why do washing machines keep themselves closed for approx. 5 minutes after the washing program ended? | Engineering | explainlikeimfive | {
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"Because they have to make sure all the water is drained out before you can open it and it spills out"
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jdhp4g | After a product prototype receives investment or crowdfunding, how do the founders proceed with mass manufacturing? | Engineering | explainlikeimfive | {
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"Once I have a working prototype in my hands (either one I've made or one I've been given from an outside developer), I go through a Manufacturing Release process to turn this bespoke device into something my company can produce in quantity. A large portion of this process is engineering review, which sometimes catches errors in the design, but mostly involves design changes to reduce the number and complexity of parts, make the machined parts simpler, and make the assembly process faster. Any machined parts need to be defined with fabrication drawings, which not only describes the shape of the parts, but the acceptable variations (design tolerances) in the finished part. Most of this falls under the \"Design for Manufacturability/DFM\" concept. Once the design is complete, we produce a bill of materials (BOM) - a list of all the things you need to make the product. We also create subassemblies - groupings of parts that a worker might assemble at one workstation and then move to another workstation - and those too get part numbers. Every part we buy as-is gets a part number and spec sheet, along with the manufacturer, preferred vendor(s), and their part numbers. Every part we have machined gets a part number and fabrication drawing. All of this goes into our electronic inventory system, so each part number ties to an unambiguous definition of what the part is and/or how to create one. By having all this documented and signed off by engineers, our buyers have all the information they need to purchase items or order fabrication runs when an order to make the product is approved. Our inventory specialists get to time purchases carefully, managing vendors and cost and leadtimes, making sure that the assemblers get the parts they need when they need them. While that's going on, we produce assembly drawings and procedures, to teach people who have never seen the product before how to assemble it. We have our technical writers prepare internal and external documentation. Assembly manuals, service manuals, user manuals. In reality, all these processes are happening at once, because we want our fabricators to give us feedback that might improve the fabricated parts, and we want our assemblers and service technicians to give us feedback that might improve their workflow, and we want our purchasing department to guide us to preferred vendors. Once all that is done (or, more realistically, *while* all that is being done) we produce a pilot build. We order maybe 10 units, our buyer goes out and purchases enough stuff to make 10 plus some extra for waste, and our assemblers try to build to our documentation. We may find additional weaknesses here - maybe a bolt is badly located and hard to get to, or we need to add additional jigs, test procedures, etc. These issues are reviewed and changes are made as needed. Finally, if the pilot build wasn't a complete disaster, we signoff on the first production run. These products might still have some inconsistencies and flaws, but good quality control should prevent defective units from leaving the building. Changes from this point on are full-on design revisions, and a process of continuous improvement will go on for the life of the product."
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jdk409 | what is the “ground” in a battery powered circuit? | What is the ground for devices like phones or laptops?Do all devices have a ground? Thank you :) | Engineering | explainlikeimfive | {
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"\"ground\" is an arbitrary reference, we normally use the ground as in the literal ground for this. Volts is a relative measurement not an absolute one. A good ELI5 for this would be: I have 5 apples is a absolute measurement. I don't sometimes has 6 apples depending on how you look at it. I always have 5. My car is going 20 miles per hour is a relative measurement. 20 miles per hour compared to what? I probably mean the ground but may be not. Their is no absolute reference for speed. The earth is springing around it's axis and orbiting the sun. The sun is orbiting the center of the galaxy, and the galaxy is in motion compared to other galaxies. If we use Andromeda as our reference point I am moving at over 1,000,000 miles per hour right now while I type this. ELI5 Volts measures how charged somethings electrons are compared to something else. What is the something else? We normally call that something else ground, and just like your car we normally compare to the earth. So a AA battery is charged 1.5 volts higher than the literal ground. We use literal ground for 3 reasons. First it's normally very available. It's very easy to get something into contact with the earth. Second It's a very consistent measurement. Just like the speed of the concrete road under your car is normally quite stable. So too is the electrical charge of earth. As such a AA will show as 1.5 volts above ground at my house, at your house, and at any place you want to measure. The third is it is very hard to get something charged to a lower level then ground. If you some how get bellow literal grounds charge then the ground its self will start to push electrical current into the system. So in a every day sense literal ground is the lowest level electrical charge. If are not comparing to literal ground we will normally indicate this by saying what reference we are using as \"ground.\" for example if I am using a AA battery as ground then a \"9 volt\" battery will have a charge of 7.5 volts relative to the AA. For any sort of work to happen, i.e. for the electrical circuit to do stuff, their must be a charge imbalance. i.e. electrical charge must be able to go from a high level to a lower level. What ever the lowest level the charge reaches is normally referred to as \"ground.\""
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jdooxf | How do we know what caused a rocket to explode when it’s been torn into a thousand pieces? | When a launch fails, you sometimes hear that it was caused by a single loose rivet in a specific part of the rocket. How is it possible to know this when it’s remnants are laying in the bottom of the ocean? | Engineering | explainlikeimfive | {
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"The remnants are mercilessly hunted. The results are combined with sensor readouts from all over the vessel, and there is usually video footage. Also, every single rivet is documented, and the reason for its presence is known, as well as the systems it is a part of and the possible interactions with other systems. It is therefore often possible to identify the root cause of a failure by working back from what is known.",
"all those rockets are returning data every second of their launch. So, we can use that data to understand what was going on inside the rocket and what its automated systems were doing.",
"Just like a plane is equipped with flight data recorders and cockpit voice recorders (black boxes), a rocket is kitted out with thousands of sensors. That data is sent as a telemetry stream to ground tracking stations. By analyzing the telemetry, they can tell where and when the first malfunction started. Microphones track the groans and strains of metals being stressed in a launch. Based on the time of arrival of the same sound at different microphones, they can triangulate where a sound originates - even the ping of a fracturing rivet."
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jdpuka | Why can’t airplanes fly above a certain height/elevation? | Engineering | explainlikeimfive | {
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"There is gravity which pulls aircraft down and the lift is the force opposing the gravity which keeps aircraft airbone. The lift is generated by airflow around the wing and it depends on speed, air density and parametres of the wing, and angle of attack but let's assume we try the best. You can not change the wing, it is part of the aircraft. Air density just drops, nothing you can do about it. So the lift you are able to produce is just dropping with increasing altitude. At certain point you reach the maximum and you can not climb more. Increase speed could be a solution but you do not have unlimited power and wing does not work properly over certain speeds so you can not accelerate forever. And it is more complicated, engine does not have to work so well in high altitudes (piston engines), construction limits. For airliners there is limit to maintain pressure in cabin because there is limit for differential pressure, safety of passengers which will not allow you legally to fly higher. For big aircraft like airliners you could find yourself in a trap called coffin corner. If you fly too slow the lift is not enough, if you fly faster the wing will not work anyway because the speed is too high.",
"Aircraft fly using a difference in air pressure between the upper surface and lower surface of the wing. The lower surface is flat while the upper surface is curved. The different shapes give rise to slightly different air pressures, so that the air below the wing exerts more pressure than the air above. This pushes the wing up, generating lift. For this process to happen, you need a certain baseline air pressure. The highest air pressure is at sea level, and pressure gradually decreases the higher you go. For example, most people who climb Everest need supplemental oxygen tanks because the air up there is so thin (low pressure) that just regular breathing doesn't provide enough oxygen to sustain life. The higher planes fly, the less air pressure there is, so there is a certain altitude at which there is simply not enough pressure to generate the lift needed to keep the plane in the air."
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jdqdb1 | One way mirrors. | How. Just how is a mirror transparent one way but opaque on the other side? | Engineering | explainlikeimfive | {
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"It's all dependent on how much light is in each room. What a one-way mirror does is that it reflects some light, while letting some other light through. This is true for both sides. In the room where you want the mirror to be reflective, you make it as bright as possible, so that the light from that room dominates. For the room you want to look from, you darken it, so that the light coming from the bright room dominates.",
"They're not actually mirrors, just tinted glass and they let through only a part of the light : it's the same for cars tinted windows, you can see outside because there is a lot of light, but nobody can see from the outside because the inside of the car is too dark for light to go though the glass. You can see through from the brighter side and if both sides are dark you can't see anything from both sides. Edit : typo"
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jdzn34 | why does the water temperature in the shower suddenly change when someone flushes the toilet? | Engineering | explainlikeimfive | {
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"It really depends in your system. In most places, you have pumps that builds up pressure (one for hot, one for cold), then a bunch of pipes, then the \"consumers\" (shower, faucets, etc.). The moment someone flushes and the toilet starts to refill, the demand of cold water increases drastically. The cold-water pump cant keep up, pressure in the cold-pipe drops, and less cold water comes out of your shower. The hot-water line is unaffected, because its hooked to a separate pump (and the toilet only draws cold water). If you have a gravity-fed system, the pressure in ths tank stays constant, but the throughput of your pipes still limits supply (at a given pressure, you van only force so much water through a pipe). TLDR: Hot and cold water comes in separate pipes. Toilet uses all cold water - > only hot water left for shower."
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je2z4w | It's 2020, why haven't shatterproof screens on phones become mainstream yet? | Engineering | explainlikeimfive | {
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"In short, any material that we know of that is pretty shatter resistant is either also susceptible to scratches, or doesn't work well as a touchscreen. The hard part is finding a translucent material that is transparent enough to use as a screen, durable enough to resist cracking/shattering, and works if used as a touchscreen. A lot of improvements have been made, but we haven't come up with a perfect solution yet.",
"Because materials science isn't easy. To get a perfect touchscreen experience, a perfect viewing experience, good thermal performance, good signal permeability, resistance to degradation, slim enough, and have it made cheap enough it must be the way that it is. So they make them that way and let the user choose which features to sacrifice for a tougher screen if any. You can sacrifice the slimness and thermal performance to put a protective cage around phone that will protect the screen from flat surface impacts. You can sacrifice touchscreen experience, sometimes viewing experience, and potentially add a pricey maintenance item to get a nice point impact resistant screen cover. I'm sure a better way exists or can be invented. Despite the income losses from screen replacements, any company would be chomping at the bit to be able to advertise a phone with a screen that simply cannot break."
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je4bze | In luxury high end cars such as a Mercedes or BMW, when you decline your seat backwards why does the head rest go up automatically? What is the logic behind this? | Engineering | explainlikeimfive | {
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"Because you're longer when you're laying back than when you're sitting up? They figure the only time someone would recline the seats all the way back would be to rest, since its not the most efficient or safe driving position. So, they adjust the headrests to allow you to lay comfortably"
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jeb4qc | Why are there no see-through toasters yet? | Engineering | explainlikeimfive | {
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"You mean like a toaster oven? It was invented before the pop-up toaster.",
"I have a see-through toaster. It was $40 on Amazon: URL_0 .",
"They exist they just usually are expensive or impractical. A toaster oven technically is see through. Making a see through toaster can be a challenge because using a metal grids or glass would be dangerous because it would get too hot.",
"The better question would be why aren't there see through toasters anymore. The first toasters were nothing more than a heater coil and a basket to hold the bread. Everything was out in the open. You could touch the bread, coil, everything. If you do a google image search for antique toasters you will find plenty of see through toasters. Some modern toasters have included glass windows as well.",
"There kinda are with toaster but ovens, but for like normal side by side ones I would assume it is largely cost, the side by side are really cheaply made thanks to it basically being a simple sheet metal only assembly sheet metal is super cheap to stamp and screw together, for a glass one it would require high temp glass, not hard to find but more expensive, it would need at least 2 panes of this per side, then those need to be secured together with an air gap to insulate people touching the outside, and you can't simply screw to glass so you then need bolts which are a more expensive and slower to assemble fastener, but on top of all that you still would not get a good view of the face of the toast because of the heating elements running in front of each face of the toast. I think it's basically way more expensive for little benefit."
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jebsnl | Why do some types of glass have a dark green tone on its borders? | Engineering | explainlikeimfive | {
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"Low iron glass will avoid this affect. Can make the glass softer without it though. Aquarium hobbyist can really get into the topic where folks pay premium for truly clear glass."
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jedww1 | What is 4 wheel drive / all wheel drive | Engineering | explainlikeimfive | {
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"There are different types of drive systems in cars. There are FWD cars where the power from the engine goes to the front wheels, RWD where the power goes to the rear wheels. Similarly, we have 4 wheel drive and all wheel drive cars. People tend to use the terms interchangably but, there is a bit of a difference between the two. As their names suggest, the power goes to all 4 wheels of the car in both the systems. But, all wheel drive cars tend to be (usually) full time all wheel drive, i.e., the power goes to all the wheels all the time. This system is usually used in rally cars, small cross-over cars and normal sedans. This system provides better traction and handling around corners and is useful for driving in light snow, dirt tracks, etc. On the other hand, 4wd system is usually found in off-road trucks and suvs. In these vehicles, usually a transfer case is present. This allows the driver to choose between 2 wheel drive mode and 4 wheel drive(high and low) mode. So, in these vehicles, the 4wd mode is only chosen in offroad situations. While simply driving on road, 2wd mode is chosen (as it is healthier for the transmission). A simple way to look at it is that 4wd is for serious offroading while, awd is for better handling around a twisty road and some minor offroading like driving rally or snow driving. & #x200B; I remember seeing a video which explained it pretty well and probably better than I did. I will try and see if I can find it & #x200B; Edit: there, found the video : [ URL_0 ]( URL_0 )"
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jeel13 | Since there's no pressure in space and spacesuits have air in them, how come spacesuits don't expand out like a balloon? How are astronaut able to articulate their joints? | Engineering | explainlikeimfive | {
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"The major joints have an accordion-like structure to them; they're called *constant-volume* joints. When you bend them, one side collapses as much as the opposite side expands, and because of that the pressure doesn't help or hinder your movement. As you were probably thinking, if a suit had tube-like limbs, it would go rigid and moving in it would be an exhausting pain in the ass. Page 2-15, second paragraph, of this talks about the Apollo joint design, and on 2-16 they show what the suits looked like under the fabric covering. Presumably they've only gotten better since then. URL_0",
"They’re made of strong reinforced material to keep the pressure and air where it should be. And they’re made to be as flexible as can be, but that’s not saying much"
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jeevl1 | Why do ketchup bottles suck so much? | Engineering | explainlikeimfive | {
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"There actually is a mysterious property with ketchup that makes this problem worse in squeeze bottles! Ketchup is a special type of material called a Bingham fluid. This is a fluid that doesn't flow until it's pushed with a certain amount of force, like a door that has to be knocked open. & #x200B; Regular fluids, like water, will flow some amount under any force, and the stronger the force the faster the flow. Ketchup stays stuck like a solid until the critical force is reached, after which it flows annoying well.",
"Pretty sure it has to do with the separating of the ketchup. Before they made the squeeze bottles this way you'd typically get a squirt of separated liquid out if the bottle first. \\*Some-friggin-how\\* the newer design stops this but also causes a sort of \"critical mass\" squirt. Having experienced the weird ass pre-ketchup liquid I can say that I definitely prefer the new style."
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jenk9h | what is that loud clapping sound that large lights produce when turned on? | Like you know those rows of lights start turning on one after the other with a loud clapping sound, what is that? | Engineering | explainlikeimfive | {
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"Probably contactors (large relays), as typical switches can't handle the current. Though industrial switches have quite the clunk too.",
"On TV and in the moves, it's mostly sound effects. With commercial and industrial lighting, large numbers of lights are controlled by relays. Those relays do click, but quietly. I dropped a pen on the desk just now from 4 inches. That noise is about equal to the loudest relays where I work, a 4 million sf facility with office, storage and manufacturing. It is possible that very old relay cabinet's may produce a much loudr sound due to the size of contactors. Very old electrical equipment was made in the US with little concern about size or material usage. Due to old equipment being overbuilt, it's not hard to find equipment over 100 years old still in use."
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jerxsl | why'd the shuttle leave a trail of billowing smoke during launch but other rockets don't? | Engineering | explainlikeimfive | {
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"The trail was from the Solid Rocket Boosters strapped to its side. The fuel for these had a lot of ingredients that left smoke trails (ammonium perchlorate as the oxidizer and aluminum powder in the fuel). The main engine on the Shuttle itself was a Hydrogen-Oxygen engine, so it actually just produced water when it burned. Most other rockets operate with liquid oxygen and some fuel (kerosene or Hydrogen are the most common) that typically doesn't produce much more than C02 and water as byproducts. You can actually see that after the boosters separate from the orbiter (and the shuttle engine is still on), the orbiter itself doesn't leave a smoke trail.",
"[Solid Rocket Boosters]( URL_0 ). The [shuttle's main engines]( URL_2 ), like a lot of other liquid fueled engines burned liquid oxygen and liquid hydrogen, resulting in water as the exhaust. The solid rocket boosters, however, burned primarily ammonium percolate and aluminum, along with quite a few other components, resulting in a [much more complex exhaus]( URL_1 )t, including some compounds that convert to hydrochloric acid. The hydrochloric acid causes water in the air to condense and thus creates the visible \"smoke.\""
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"https://en.wikipedia.org/wiki/RS-25"
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jeuo3z | What is the difference between 4wd (four wheel drive), all wheel drive (AWD), and saying a vehicle is a 4x4? | Engineering | explainlikeimfive | {
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"There is not an industry standard for these terms, but most simply put: AWD systems will power all wheels all the time. 4WD systems are two wheel drive until the 4WD is manually engaged for off-roading or bad weather. 4x4 is the same as 4WD. *Note that this is not strictly true all the time, and those terms were created by marketers, not the engineers designing the systems.",
"AWD is on all the time. 4WD is not. Also, AWD let’s each tire rotate at different speeds while 4WD typically locks the front and rear tires together. AWD is better for driving on the road while 4WD is better off-road, in general."
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jf0n2f | How do traffic lights know when to change colors, and what color to change to? | Do they have sensors? Is it a timer? How does the time of day affect it? I think about it often when I drive, because I've noticed the changes are different at night. | Engineering | explainlikeimfive | {
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"Sensors and timers. The time of day matters inasmuch as the timers can have different settings at different times of day. Keep in mind that, unless you're in a big city (and even then it's suspect), traffic lights are not generally connected to each other. The timers and sensor settings can be set individually so they can \"work together\" to a certain degree, but they don't \"talk\" to each other. 1st Street doesn't care what happens on 2nd Street.",
"Their cycle is set on a timer. The timing of each light is set based on how heavy traffic tends to be on a particular route. It's why you may wait at red for 2 minutes at one intersection, but 1 at another. The timers can also be set to change to a different cycle depending on the time of day. You may notice traffic lights cycle at a different pace at night than during the day."
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jfgax2 | How has asphalt not been replaced as the standard for roads in decades? | Engineering | explainlikeimfive | {
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"It’s a decently economic product whose long term performance is well known, is widely available, isn’t under patent, provides decent grip, decent durability, can be patch repaired, and isn’t too noisy to drive on. As you note - concrete is another product. This generally is more expensive but has a longer service life, so lifecycle costs are comparable, but it’s a lot noisier to drive on, which is generally a negative.",
"Asphalt is a waste product of the petroleum refining process. That means that even if there was no demand for asphalt as a road paving material there would still be the same amount of asphalt being produced every year. That means that oil refineries would either have to find something else to do with it or pay for it to be put in a dump somewhere. There is literally nothing else that its suitable for and no one wants to pay to dispose of it. This means that the only real option that oil refineries have is to just drop the price until its so cheap that it outcompetes every other possible road paving material.",
"Others have spoken to the economics, but actually - mechanically it is a pretty great road surface. It's plastic enough that it can deal with expansion and contraction as the temperature changes during the day far better than more rigid materials like concrete (which often have to have expansion gaps between sections, leading to a very noisy and bumpy ride). It's excellent at dealing with water run off, provides very good traction, is recyclable, and can be easily patch repaired. There aren't many materials that can compete with it in terms of performance - the fact it's economically so viable is simply an added bonus.",
"You're also making the mistake of assuming that there is only one kind of asphalt. There are hundreds (Or more) of variations of asphalt. Different ingredients, different applications, different qualities. There are constantly new variations being developed.",
"Pavement engineer and researcher here. As other answers note, it is cheap and widely available, with just one other product (concrete) that acts as a minor competitor. For reference, over 95% of roads in the US are made of asphalt, so concrete is not much of a competitor except in some niche applications (such as interstates with high truck traffic, where concrete roads can have a cheaper *life cycle cost*). However, it's not true that there has been no innovation, in fact there has been quite a lot of innovation. Well over 90% of all asphalt in the US is recycled either back into roads or as a roofing material, and in countries like India and Singapore, plastic (from grocery bags, for example) is blended in as well. Even the type of asphalt is different - back when the first asphalt roads were built, it was little more than plain crude oil being mixed in with aggregates (\"rocks\"). Today, it comes first as the byproduct of fractional distillation, and then undergoes more processing to achieve certain desirable properties, called a Performance Grade (PG). Just changing asphalt from one PG grade to another can be a multi-million dollar investment. And that's just the asphalt itself, there has been a lot of innovation in other additives that go into it. As an example, asphalt typically has to be heated to a high temperature (about 200C) to be blended with aggregates, which consumes a lot of energy. Today, something called a Warm Mix Additive (WMA) can be added to reduce that temperature to 150-180C, which saves fuel and hence CO2 emissions. WMAs are not something you can make from a kid's chemistry set - they're engineered materials, often nanomaterials, which interact with asphalt at a molecular level. I can personally name 10 people who have a PhD just in innovative asphalt additives, and the total number all over the world would easily be in the tens of thousands if not more. Another example is something called \"smart rollers\" - rollers being those big cylindrical wheels that are used to compact asphalt roads once they are laid out. It used to be that they just applied the same, heavy weight to the entire road for a certain number of passes. Today, there is widely-used technology wherein the roller can sense the level of compaction (think density) of a small patch of pavement and automatically change the load applied, so that the road overall has a more uniform level of compaction, which at least theoretically ensures better overall performance because you don't end up with some weak spots. Finally, I'll make one point on innovation in civil infrastructure in general, which is what I think the question was focusing on - it is slow. We are not Big Tech, our industry does not embrace innovation quickly. The reason is that these projects are huge in terms of time and investment, need a lot of experience to get right, have a deep effect on the public, and are often publicly-funded. Tried, tested, and reliable solutions are often preferred over new and speculative techniques and/or materials. Innovations are adopted slowly - a mile of road here, a test bed there. Some contractors pick it up, they tell their friends, who may try it some time in the next 5 years. If it's really path-breaking, it will eventually be used widely, as some innovations have. But if the benefits are incremental, then the industry would prefer to stick to old solutions that they are more comfortable with. Civil engineering is really old - often described as the oldest field of engineering going back to the very first civilizations in Egypt, Mesopotamia, India, etc. - and with that age comes inertia. Story of life.",
"It’s cheaper than dirt and easy to recycle. The asphalt-eater tears up the old road surface and grinds it back down, then they heat the tar up and re-pour it. You don’t need a lot of new materials and you don’t need to haul away much old material. This “mill and fill” resurfacing is cheap and effective for roads that don’t expect to carry huge loads of heavy traffic. Asphalt is prone to creeping and buckling since it’s not entirely solid, so you’ll see concrete used for high-traffic areas and bridges.",
"This video does a great job explaining some ways asphalt pavement is good and weaknesses. That channel has lots of related videos as well if you're interested in learning more. URL_0",
"In addition to others, you can even pour other waste products into asphalt to improve its qualities. \"Glassphalt\" has ground-up glass in the asphalt.",
"There is a lot of good answers but I also wants to add the fact that asphalt makes it easy to dig up the road and repair a broken pipe or wire and then patch it up in no time. Concrete would be harder to open and requires more work/time to make it nice and flat again.",
"Another consideration to be mindful of is construction and repair time. Concrete must cure for days before being opened to traffic. This is acceptable for new construction, but to close an existing road for weeks while the asphalt road is removed and replaced with concrete would likely cause a traffic nightmare. Even repairing concrete roadways requires over 48 hours over weekends to complete. But mainly it's the cost, usually its reserved for heavy vehicle locstions where they stop and turn which causes severe rutting on asphalt.",
"There also *has* been some (relatively) recent innovation in finding new road materials. They just all involve improving asphalt and asphalt manufacturing processes, rather than coming up with something entirely new. Look up warm mix asphalt if you feel like boring yourself to sleep by reading scientific papers comparing road surface materials.",
"The US uses asphalt everywhere because it's the cheapest available decent quality product. US has a fair bit of oil and petroleum production, of which bitumen (needed to make asphalt) is a side product. This isn't the same everywhere in the world. In New Zealand we don't produce any oil locally, it's all imported at high cost. Asphalt has a lot of weight, so importing it doesn't make much sense. Our highways are mostly just tar and gravel. On a hot day the tar melts and you can pull chunks of it out. It's a lot different than asphalt and I actually prefer it to driving on asphalt. The rough texture creates a lot of grip. URL_0",
"There is a lot of innovation behind how to pour asphalt and recycle it. Because of all the other reasons listed, innovating other materials and processes have been the go to for chemical and paving companies. Google special treated base or cement treated base. I know because my dad works for a paving company and previously worked in an asphalt lab. I built a few road myself one miserable summer.",
"Truck driver here. Asphalt is quieter, smoother and may have better fuel mileage. Concrete wears tires at greater rate. Asphalt can't take the abuse from a 3000 lbs car at 70 mph, it'll crumble in a short time. Add 80,000 lbs of truck at 70 mph. The asphalt will fail. I think mostly because the road bed under concrete is much more built up and reinforced than asphalt is. Notice when asphalt is repaired or used as a patch in concrete, it continually fails. I'm not an expert, but I pretend to be one on the internet. The previous message is not intended to treat, cure or prevent any diseases. Message was distributed by weight, not volume. Contents may settle on shipping.",
"There's plenty of sound opinions in here, I just wanted to chime in about concrete. The reason concrete isn't widely used is because it needs to be reinforced with rebar to be used as a wearing surface for roads. Asphalt is pliable and somewhat plastic, so when heavy trucks drive over it, it sort of bends and moves as it's stressed in different areas. This has it's own repercussions on the base course, but the asphalt itself will retain it's structure for the most part. Concrete on the other hand is extremely rigid and brittle, so when heavy loads are applied it has the tendency to break. That's why steel reinforcement is used in conjunction with scoring joints to allow some panels to move relative to each other, but each panel (since it's got essentially steel cages throughout each panel) will remain rigid and will resist breakage. Concrete isn't terribly uncommon in road ways, but it's a very hefty investment relative to asphalt. It's generally used over bridges, and intersections/junctions that get a lot of use. The balance there being 1) let's use cheap asphalt that we're going to have to replace every 5-10 years or 2) expensive ass reinforced concrete that will hopefully last 20. It's also pretty easy to replace small segments of asphalt, but concrete is a little more difficult due to the reinforcement. Signed, a civil engineer currently inspecting two major road replacement projects.",
"Asphalt is simply cheap, and easy to repair. Any other option is only one, or the other, or neither. We can make asphalt by the ton, but things like concrete are harder to do.",
"You speak as if there has been no innovation in asphaltic or bitumen-bound surfacing in the last 50 years when in reality it's come a long way. There are at least 3 basic types of bitumen macadam. These are asphalt concrete, stone mastic asphalt, and hot rolled asphalt. AC is cheapest and most commonly used with good structural strength. SMA is used on some high volume roads and can be made as porous asphalt. HRA is, in the UK at least, the most common surface course for major roads but it is the most expensive and requires serious skill and care to lay properly. Each has dozens of subtypes and each subtype has a bunch of different suppliers with bespoke mixes of aggregate, sand, binder and additives. Hence when surfacing a road there are lots of choices to be made to achieve best performance based on the expected life, types and volume of traffic, location, weather and so on. We're now using clever things like polymer modified binder to allow easier laying with better service life. There are also innovations in quality control and testing plus new options in prolonging the service life of older surfaces, like retexturing, surface dressing, micro asphalt, and high friction slurry surfacing. It's a constantly moving industry and there is always development."
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jfgipr | How come in old houses all the bedrooms are upstairs? | Engineering | explainlikeimfive | {
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"*is confused in British*.. is it not standard to have bedrooms upstairs in most houses where there is an upstairs? For me personally it's what I want because monkey brain feel safe in tree lol",
"Two primary reasons: - Since entertaining in your home was much more common, it made sense to have the communal entertaining rooms (living room, dining room, etc.) on the first floor and keep private rooms (like your bedroom or dressing room) on the second floor. This way, guests wouldn't wander into private areas, and guest wouldn't have to go up and down the stairs. - Heat flow. Heat would rise to the bedrooms during the day, and keep them warm(er) during the night when the fires burnt out.",
"It's warmer, because hot air rises. In old houses, the upstairs rooms were sometimes not even heated, there were just registers to allow warm air to float up. It's safer. You have time to wake up and get ready if you hear someone breaking in. You can see farther out the window. Animals are less likely to enter. It's quieter. No one walking over you. Put the kids to bed and keep doing whatever.",
"Where do you live? It's still common in North America for new houses to be built with the bedrooms upstairs. Can you show me an example of this modern house you're talking about with main floor bedrooms?",
"Because it's a nice way to organize your home: - Bedrooms are meant for sleeping and not for common use, so they are located in the least accesible place. Kitchen and living room are most accesible for the opposite reason. - Privacy: Having guests in the common areas not crossing into \"private\" bedrooms is easier if there is a physical separation with stairs. - Flats and apartments also follow this... bedrooms are usually at the end of the hallway. Not that sure if this is only an \"old\" house thing because many new houses are like that.",
"Upstairs is considered private family space, while downstairs is more public entertaining space. And heat rises, so residual heat from day would warm the upstairs for the night. You see more 2-story homes in colder climates (think about development patterns) because they have full basements instead of slab foundations, and the added cost of a bigger basement/foundation and bigger ceiling to insulate vs. adding a 2nd floor reducing foundation footprint and roof size relative to square footage.",
"Really just depends on the style of house. But it is still extremely common for new builds to have bedrooms upstairs.",
"The \"central heating\" was one wood or charcoal stove,mostly used for cooking.Open vents to upper floors provided heat by rising hot air.",
"I have a 1938 house. I have 3 beds and a bath upstairs and 2 beds and a bath downstairs. Half bath in unfinished basement. My parents house is 1946. 2beds, 2bath upstairs and 1 bed, 1 bath downstairs. Brother has ~1940 house. 2 bed, 1 bath downstairs. 1 bed, 1 bath upstairs. Brother two has ~2000 house. 4 bed, 2 bath upstairs, half bath downstairs. Bath hookup in unfinished basement. Sister has a ~1950 house but it's one story, 5 bed, 2 bath.",
"Everyone in this thread is breaking the #1 rule of this sub where you’re only supposed to give an answer if you really really know lmao Everyone’s just fucking guessing and reasoning which is fine but not what this sub is about"
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jfmed8 | how do winter tires work? | Engineering | explainlikeimfive | {
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"They provide better traction in winter weather for multiple reasons: - Normal tyre rubber hardens in the cold, reducing its ability to grip. Winter tyre rubber is designed to stay soft at cold temperatures - Winter tyres contain studs, small metal pieces that just out that lets the wheel claw at the road for grip. - They also have much deeper grooves in them than normal tyres. Think of the difference between a pair of dress shoes, and hiking boots. Deeper treads let the car claw and grab for more traction.",
"They tend to have a lot more grooves in them. This means less total rubber in contact with the road and a less stiff tyre overall which isn't so good in dry Co ditions. But it allows stand water to escape which prevents aquaplaning in very wet conditions, which is when the tyre kind of floats on puddled water on the road and loses most of its grip, so definitely something worth avoiding! Depending on the design the grooves can also be sized/shaped to collect snow in colder climates which actually improves grip on snow. They can also be made of softer compounds, which in lower temperatures behave similar to hard compounds in warmer temperatures. Another way to look at this is how bad summer tyres could be in winter. Your cold tyre could become too hard to bite into the tarmac on a dry day. You could aquaplane or just lose grip on a wet day. And you would simply lose loads of grip on a snowy day."
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jfo6v5 | How do temples on top of mountains or cities built in the side of cliffs get their building materials to these remote locations? | It can’t all be carried by hand, can it? | Engineering | explainlikeimfive | {
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"Short answer, yep, labor. Enough humans, with enough time, and enough motivation (money, religious conviction, slavery, etc) can move an almost unimaginable amount of material. Of course we've harnessed beasts of burden, but when it boils down to it, 100s-10,000s of people, with enough time, can build amazing things. Think about it, a dude can carry a 50lb block, 10 dudes can wrangle a 500lb block, etc etc.",
"Assuming you're talking ones that have been there for hundreds of years...Sometimes they use horses, mules etc and can probably set up some winch and pully set ups in some cases. But basically, yes, all by hand.",
"Yup. People are actually quite able to move lots of stuff. And sometimes miles, etc. For instance, around me we have a lot of old mining history. The big long cables used to make tram lines was hauled up by mule strings. Each animal would carry a loop or two of cable and then it would go to the next mule for a couple loops, etc until there was a long string of miles all carrying the same long piece of cable."
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jgbf5t | Can someone explain what lock up on a torque converter is? And why do diesel truck enthusiasts add switches to make their torque converter a lock up on demand? | Engineering | explainlikeimfive | {
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"There's a problem with internal combustion engines, which is that they aren't efficient at all speeds. That's why cars have different gears - so that you can change the speed of the car and keep the engine more or less at the most efficient RPM for the engine. The other problem is that ICEs can't *stop*. If the wheels stop turning, the engine does not want to stop turning. That will either damage something or stall the engine, or both. The solution for manual cars is a clutch, which is made of several disks with coatings to increase friction between them. One side of the clutch is attached to the motor and the other side is (ultimately) attached to your drive wheels. When the clutch is engaged, the high friction forces the disks to turn together so that the wheels turn with the engine. You can disengage the clutch with a pedal so that when you stop, the motor can keep going and the wheels can be stopped, and nothing breaks. You can partially engage the clutch to send power to the wheels when there is a mismatch between the speed of the wheels and the speed of the engine until the friction forces the two to match rotation speeds, which is also important when changing gears. Cool, but what about automatic transmissions? Instead of a clutch, automatics use a *torque converter*. The torque converter is a round housing with fan blades and full of a very viscous fluid. One \"fan\" is connected to the engine and the other is connected to the wheels. Instead of friction, the torque converter uses the viscosity of the fluid to transfer power. The fan attached to the engine forces the liquid to spin, creating a vortex of fluid inside the torque converter. This drives the fan attached to the wheels so that it spins with the vortex, too. The engineering of the torque converter is a bit more complex, but that's the short version. Like a disengaged clutch, the fan on the engine side is free to rotate regardless of what the wheels are doing since there's no direct connection. When the brakes are engaged, the friction from the brake pads holds the wheels, which stops the fan on that side of the torque converter from spinning. Once the brakes are released and the wheels are free to spin the vortex of fluid can cause the wheel side fan to start spinning, transferring power to the wheels. Both the wheels and the motor are free to spin at different rates until the viscosity of the fluid causes them to match. Good for stopping, also good for when the transmission is changing gears. The downside of the torque converter is that because nothing is ever 100% efficient at transferring power, the engine will *always* be spinning just slightly faster than the wheels. There will always be some amount of friction and loss of power. A switch disabling the torque converter creates a direct connection from the engine to the wheels, which transfers the power from the engine with much greater efficiency. It's also important when you're towing something large with a truck, since the friction of the wheels with a heavy load may overcome the viscosity of the fluid in the torque converter. The engine turns and turns, but it simply can't overcome the weight of the load and the wheels side fan won't turn nearly as fast as it should. With a direct connection the engine is better able to drive the wheels regardless of the load. The downside is, of course, that it creates additional wear on your engine, your drive train, and your tires since there is still some loss of energy even if it's a smaller loss. Those parts all what to turn at *slightly* different rates which puts strain on all of them and the parts connecting them - which is exactly what the torque converter exists to minimize."
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jggrk0 | I accidentally put my car in reverse while it is still moving forward, and it made a terrifying noise. What happened in engine/gearbox? Does this result in permanent damage? | Engineering | explainlikeimfive | {
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"So, Automotive Engineer here. A gearbox connects the engine to the wheels, via some sort of clutch (something that makes the wheels gather speed progressively and not instantly. When not giving a car example, think of slowly pushing a fidget spinner and start pushing it faster and faster until you can't make it spin any faster. Same with a clutch. It starts spinning the wheels little by little until they get to the same speed, be it an automatic or a manual trans) and the transmission. So the order is: Engine - Clutch - Transmission - Wheels Now, the engine creates a rotary motion near the clutch, but you CANNOT make it spin the other way around. A transmission takes this rotation and multiplies it/reduces it, but when engaging reverse it makes the wheels spin the other way, as such the transmission itself revolves the other way, the engine keeps it's regular old rotation direction. Now, what happens when you take that fidget spinner and try to spin it the other way when it already spins? It stops and vibrates (probably). That's your transmission. You are basically telling your transmission to spin the other way instantly. A car has a lot more weight than your hand, and it's much more violent than the fidget spinner example. As such, that judder is violent and you hear that grinding noise. If the wheels don't spin then the transition is seamless. The noise more precisely comes from the gears (cogs, wheels with teeth on the edge of them, whatever). When you are driving forward, all the gears inside turn the same way, but when engaging reverse, one is forced to turn the other way around so the wheels can turn the other way around. As such you are connecting 2 gears with different motions into one another, and telling one of them to stop and turn the same way. If the wheels are staying still and engaging reverse, the shock is minimal and it is normal. When the wheels are turning forward at a decent speed and you want to reverse on the spot, the shock is large and you will probably break your transmission. If you are barely crawling forward but engage reverse you will hear the grinding noise and feel the shock but not nearly as bad. If you do it once in forever due to not paying attention, nothing will happen, but if you keep doing it you will mess up your transmission. So, when you want to reverse, always come to a complete stop and engage reverse, because you cannot control it any other way.",
"How did you manage that? Most cars (manual and automatic) built in the last several decades have mechanical blocks preventing you from placing the transmission in reverse while the vehicle is moving forward. Your clutch is the most likely part to receive damage from doing this, and if it's damaged, it's definitely permanent."
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jgmcm0 | why do bikes for men have that top tube in the frame? | I understand why it would be easier for women not to have that high bar in the bike frame as it would not work with long skirts and dresses. But as the... area, so to say, is quite sensitive for men, why does their bike frame have a top tube? | Engineering | explainlikeimfive | {
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"A well fit men's bike should never really get in the way of their balls when standing over it. Stunt bikes tend to be very short, and mountain bikes need to be as strong as possible, which a top bar is. BMX bikes actually are made with a slanted top bar, specifically to avoid \"racking\" your nuts. The lower top bar (or missing top bar) was put in place mostly for women's fashion. Originally it allowed biking while wearing a dress. Later, tight pants. The low bar allows mounting without having to lift your leg really high. This actually makes women's bikes really popular with older women, who are (at a younger age than men) more likely to have hip mobility issues. The downside of a lower (or missing) top bar is that you lose a lot of the strength a traditional top bar adds to the bike. You're left with either a less resilient bike, a heavier bike, or a much more expensive build. When women still had to wear dresses, they were also expected to ride in a much more reserved manner, so the weaker frame wouldn't have been as much of an issue. You can still find modern bikes made with this lower or missing top bar, but if you look at top of the line women's road or mountain bikes, you'll find they look very much like a men's bikes. Giant's women's road bikes actually have a slight nod to the dropped top bar, with a slightly downward slanting top bar - which is more aesthetic than functional. Most of the changes have to do with the parts on the bike (special saddles, smaller gap between handle and brake or handle and shifters, and the frame usually accounts for a shorter torso. Generally, more ergonomic choices (though some cosmentic) and less... well sexist. For a casual bike to ride around town, where weight doesn't matter, a dropped or non existent top tube is going to be easier to get on and off, and more easily set to a variety of riders. In fact, many bike share companies choose this set up for that reason. However, once something is labeled as \"women's\" it is really hard to convince men to get over that trend en masse.",
"The top tube provides a lot of rigidity and strength to the bicycle frame. It's possible to design frames that are stiff and strong enough to use without one, or with a much lower top tube, but it requires much stronger structure at the down tube and seat tube joint in particular and that means more weight and/or costlier materials. And in the long run, the frame will be subject to more flexing and have a shorter lifetime. These disadvantages are fine if you literally can't ride a bicycle with a top tube, because a bike is still superior to walking in many ways even if it's heavier than it could be, but if you're interested in better performance and you can accommodate the top tube, it's a much better design.",
"To be honest, the Western world gets this wrong. A bike without an upper frame tube is known as a \"step through\" , not specifically designed for females. Much handier for delivery riders, shorter riders, and riders that frequently dismount for various reasons, and yes, anyone wearing a dress. When's the last time you saw someone wearing a dress on a bike?",
"I belelieve that the crossbar was there for strength? But then they had stronger materials so they could build bikes without those. So they started making \"dress friendly\" bikes for women. And the crossbar bikes stayed for men. But i dont believe there is another reason.",
"ELI5: A high top tube would be difficult for a woman to mount without flashing everybody everything under their skirt/dress. Therefore, bikes with high top tubes were USUALLY used by men, and the opposite for women. (Because men wore pants and had no such problem.) However, that classification is entirely baseless. A woman can ride a \"man's\" bike and visa versa. Back in the day, were was nothing really separating the two. In modern times, since mostly everybody wears shorts/pants, anybody can ride any type of bike they want. That said, the \"high top tube\" version of a bike is MUCH stronger than the \"step through\" design, so the \"high top tube/men's\" version of bikes are the \"best\" version, in terms of strength/weight. THAT SAID!!!!.... Bike manufacturers have caught onto this \"trend\" and tend to produce bikes that fit typical male bodies in the \"men's, high top tube\" style and bikes that fit women in the \"low top tube/step through\" style. Men and women are differently shaped if you think about the average man and woman body. Men tend to have longer legs and shorter torsos (but also longer arms), and the opposite is true for women. Therefore bike manufacturers tend to make \"women's\" bikes that are shorter (to the ground) but longer (lengthwise) and \"men's\" bikes that are higher from the ground but a bit shorter (lenghwise.) (This isn't entirely true because there are more factors to consider, but you get the idea of customizing bikes for each gender.) Of course, this is all scaled to the height of the person, and since men tend to be taller than women men's bikes are, in general, simply larger than women's bikes. (In reality women's bikes are SHORTER (lengthwise) than men's bikes because while their torso may be longer than a man's, their arms are shorter.)"
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jgn9ks | What is the origin of the "double-click" to open computer programs? | I've always wondered from a programming/computer science perspective why a double click became the standard procedure for opening up desktop items. | Engineering | explainlikeimfive | {
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"Mice originally only had one button, so you needed a way to distinguish between selecting something and actually opening or running it. Thus, click and double-click. It was invented by Bill Atkinson in the early 80s.",
"It was something introduced into widespread use by Apple when they first started using mouse and windows GUI type interfaces and later copied by Microsoft. (Apple didn't actually invent the whole mouse and windows and gui stuff they copied it from Douglas Engelbart at xerox. In his obituaries he was in some version credited with having invented the double click, but I could find no good sources to confirm this). At that time the mice used by apple only had a single button and single click and double click were ways to differentiate \"select\" vs \"execute\". Microsoft copied that for Windows even though they quickly standardized to two button mice and today have mice with scroll-wheels and more buttons than that. Since web browser follow a link by single clicking it and today many applications have wandered onto the web and desktop GUIs have become more touch screen friendly the use of double click has fallen a bit by the wayside, but it is still around.",
"Its accidentally click protection to avoid opening programs that you dont want to open. Its far less annoying having to click twice on something you want to open than having to wait a moment for an unwanted program to open so that you can close it."
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jgsszs | what type of math is used to make telescopes? | Engineering | explainlikeimfive | {
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"All maths associated with optics, so things like trigonometry and reflection. Making a telescope requires extreme precision, and a very good understanding of how lenses affect light. Any mistake you make literally gets magnified by the telescope. If we're talking about advanced telescopes astronomers use to make measurements today literally every type of math is involved. Everything from field equations to Pythagoras' theorem to the economics of running such a massive operation and everything in between. Even orbital mechanics are important if we're including space telescopes like the Hubble telescope."
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jgy8et | How do my car knows that the wheels loose grip and need to activate ABS? | Engineering | explainlikeimfive | {
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"It's constantly checking the speed of all four wheels. If one or two of the wheels are not spinning as quickly as the other ones while you're on the brake, it knows that those wheels are skidding.",
"Wheel speed sensors determine how fast the wheels are turning as opposed to how fast they are expected to turning. If too fast, brakes are applied. If the wheel isn’t spinning as fast as it should, brakes are released or more power is provided.",
"Within the hub of each wheel is a speed sensor. The ecu (the car computer) then compares each of these readings to each other to determine if a wheel rotates slower than the other wheels. If so, the ecu will change the hydraulic pressure being applied to that wheel to reduce the braking for applied to it to prevent locking. The car can also get a speed reading from the gearbox or differential for comparison. As an added answer, the same applies for stability control. If the driven wheels rotate faster than the non-driven wheels the ecu will reduce power."
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jhepka | What is the clutch in a car? | Engineering | explainlikeimfive | {
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"Simply explained it is two discs that press against eachother. One disc is conencted to the engine and the other is connected to the gearbox. When the discs are pressed together they can transfer the rotation from the engine to the gearbox. When the discs are separated (when you press the pedal) you can change gear in the gearbox.",
"The clutch is a component in the transmission that connects and disconnects the engine from the drive shaft. In a manual transmission, the driver controls the clutch with the *clutch pedal;* in an automatic transmission, the car's internal computer handles it."
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jhttw1 | Video game engines | Engineering | explainlikeimfive | {
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"It’s like the framework for a game. A template you could say, so everyone doesn’t have to start from scratch. Frostbite is still used because it’s EA’s proprietary engine and they force all their developers to use it, even if it doesn’t necessarily suit their purposes. That’s one difficulty BioWare ran into with Anthem. If they are updating an engine, they are likely adding new features or fixing bugs. Some engines do certain things better than others. I have no specific things I could list, but there are reasons Unreal and Unity work so well. Frostbite on the other hand, apparently lacks support for an over-the-shoulder 3rd person camera, which is sort of fundamental with a game like Anthem. They had to work around it.",
"Imagine you have to create a text document. The engine would be the software you choose to create the document. You can choose between microsoft word, notepad, wordpad, libre office etc... Different softwares for different needs. You can create one yourself or pay a company to use their engine. When devs are updating an engine, they are either fixing bugs or adding features such as raytracing in order to be up to date with current industry standards and expectations.",
"Like others already said, game engines are simply frameworks. To elaborate - a (modern day) game engine already has a system for memory management so you don't have to build one from scratch, already has a system for physics so you don't have to build one from scratch, already has a graphical rendering system, already has an animation system, already has a compartmentalization system for assigning certain scripts to certain entities, already has a game compilation system, already has a system for audio, a system for game controls, etc. In other words - you either use a pre-built game engine and build a game, or you build a game from scratch and spend a huge chunk of effort and time building a worse and less widely applicable game engine (all the systems which actually allow you to build the game) before being able to build the game. Either way, your game needs infrastructure.",
"Video games are made of several key pieces: pictures, sounds, maps, game mechanics, and software. The engine is the software. Computer programmers save time by re-using things they have already made. This is called a code library. You put a bunch of code libraries together, and you get an engine. Now here is the trick; code libraries made in 2012 would be obsolete today, if they were not updated. But programmers usually update code libraries, so there probably is a recent version of it. So when someone says “Unreal engine,” that’s more of a general term. It’s like saying you own a Chevy. That’s not specific. What kind of Chevy is it? What is the year and model? Also, good ideas never go out of style. So lots of code is re-used for decades."
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jhvmah | How do does radio signal keep on travelling in space? Shouldn't it just fade away. | Engineering | explainlikeimfive | {
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"There’s very little to impede an electromagnetic wave in the vacuum of space, but what *does* cause some “fade” is the [Inverse Square Law]( URL_0 ). Basically, no matter how focused you make a signal, the beam will spread out, and as it does, the original power is spread out over that whole surface area. You can demonstrate this with a laser pointer. If you shine it on the wall in front of you, it’ll be a tightly organized dot. But shine it down the street and the dot will be several inches across. *Disclaimer* if you want to experiment, be careful where you shine a laser pointer, certainly not towards any kind of aircraft.",
"Yes, it fades. Whether you can detect that or not really depends on if you have the equipment to detect it at that level",
"What is there to fade it? On earth the atmosphere interferes, so the waves don't reach very far, but in space there's nothing. That's not to say there's no fading. The source can only emit a given amount of radiation. This intensity lowers the farther you go. For an analogy, imagine a huge [bicycle wheel]( URL_0 ) with spokes. At the centre, the spokes might occupy all the directions, but at a distance, the spokes only occupy certain areas of the edge. That \"frequency of spokes per length of edge of wheel\" is analogous to \"the intensity of waves per unit area\". Nowhere is the middles the spokes change.",
"It's because it travels through electromagnetic waves that permeates the universe, it's not like sound waves that need a physical interaction to travel from one place to another. But, you are on the right track, because on larger distances other electromagnetic sources interfere with the original signal and they tend to \"wash up\" instead of keeping the initial properties of the signal",
"Waves can be detected in one of a few ways; they either/or * interact with existing particles in their environment. Sound is an example, requiring some sort of medium (in most cases, air/water) to continue. * are a result of outputting particles at specific intesities (amplitudes) or intervals (frequencies). Light, for instance, is the particle itself. Because the particles exist as their own medium, they can travel through space, and because space has relatively low amounts of other particles, they can travel without interference for the most part.",
"Astronomer here, there is a signal from the early part of the universe (13 billion years ago) called the cosmic microwave background. If you were around even a billion years after the signal/imprint was formed, you would see it as more likely the cosmic x-ray or cosmic gamma-ray background. But due to the expansion and accelerated expansion of the universe, the light has redshifted so much it's wavelength is now in the microwave bands (which is effectively a radio signal). Light fades via redshifting, aka the wavelength increasing in size as the universe itself increases in size. This is why the most distant stars look redder to us than the closest stars. And stars/any light moving towards us look bluer.",
"Radio and light waves are technically the same, and they behave identically on the science level, the only difference is that we can actually see one. Radio waves just pass though most objects, unlike light, those waves just see the world made out only glass This allows us to do experiments using something *we can understand by observing it.* If you have a light bulb, you can see it emitting light, and it is clearly visible. If you stand 10 meter away, you can probably still see it, but as you walk further away, it gets more and more dim compared to the surroundings. This is just like radio waves. To compensate, we could use a bigger light bulb, that pumps more watts into the air, and we see it from further, [we clearly see a light house from a distance]( URL_1 ), but not a small AAA battery powered torch. There is a standard for this called \"signal to noise ratio\", which basically tells us how bright the wanted light is from what we want to see. Eventually, going brighter and brighter doesn't work, you cannot put a 1MW nuclear reactor on a small space ship. Other things are used. See it like putting a reflector behind the light bulb, to shine more light into the wanted direction, this allows a bigger distance. An extreme example of this is a laser. Compared to your light bulb, a laser light seems weak, [but over long distances]( URL_0 ), it suddenly becomes the brightest light source We could also increase the receiver size, which allows us to better isolate the noise from the signal. We use big receivers to receive the signals from the Voyager space probes. **TLDR**: The signal fades away, but we have ways to pick it up by increasing transmit power, or better receivers"
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jhvv2c | Coasting (Holding down clutch or staying in neutral) in Car and Bike . What exactly happens inside the engine/transmission? Does it damage the car in any way? | Yes, i know riding the clutch (resting foot on clutch) is bad and damages the car. But what about fully pressing down the clutch or staying in neutral while the car is going? I asked several car enthusiasts (not engineer/mechanics), and they have different opinions. Some said it doesnt do anything to the car itself, just kinda dangerous because we have less control and reaction time (which i agree), some said it will damage the transmission over long period. Will you care to explain just what happens inside so we can decide the best answer for my question? Is fuel consumption better than simply releasing the gas? (Is there any difference between car and bikes?) | Engineering | explainlikeimfive | {
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"You know how a clutch works? Its essentially two plates with high friction, which can be separated or brought in contact. They couple and decouple the engine from the rest of the drivetrain. This is important so that the engine can still rotate when the car is standing still. & #x200B; When hard components move against each other, abrasion happens. Abrasion is when parts scrape against each other, loosing small particles. This is the main cause of damage to your clutch. The clutch transmits a moment by friction. The maximum of the friction force depends on the 'normal force' - aka how hard the plates are pressed together. & #x200B; If the clutch pedal is fully pressed, the plates of the clutch are separated. There is no power transmitted and no contact - > no abrasion. Thats whats called \"coasting\", and its not damaging (but probably wont safe any fuel in most cars). If the clutch pedal is released, the plates move into contact and are pressed together with some force. The force transmitted between them forces them to move at the same speed, after a short period of acceleration.During this short period, the plates move against each other and abrasion happens (thats unavoidable), but once they move at the same speed everything is fine. Problems occur when the clutch pedal is slightly pressed, so the plates are in contact, but the force between them is not high enough to ensure they are rotating at the same speed. Then they are in contact, but there is still relative movement between them and abrasion happens. Note that this is still acceptable in some situations - e.g. when accelerating from a stop, when fine-controlling your speed to park, or particularly when starting uphill; you just want to minimize it as far as possible. & #x200B; Does this happens whenever your foot is on the clutch? Depends on the construction and state of your car - the clutch pedal MIGHT have a small dead zone before the clutch actually engages (or before the force gets small enough to allow the plates to slip), in which case it wouldnt do damage. Anyway, i wouldnt speculate on that and just go with the best practice of not riding the clutch.",
"For a manual transmission, it is almost always a complete non-issue. The layshaft is usually at least partially submerged in oil and the transmission is lubricated by splash action just like a differential is. One gear goes down and gets oil on it, contacts the gear above it and boom since it already has oil on it there's no problem. The disconnect happens between the engine and the transmission, but the axle is still spinning the gears and the gears are still dipping down in the oil. In an automatic it depends on the particulars of the design. However there seems to be a misunderstanding that the torque converter is the pump, or that the neutral/park position in an automatic disconnects the torque converter from the entire transmission. Since an automatic *absolutely requires* oil pressure as its clutch packs are driven hydraulically, if it were in neutral or park there would be zero pressure to actually be able to shift into drive or reverse. To this end, a common design is to put the oil pump right at the input of the transmission and *before* the point where neutral disconnects engine from wheels, so technically as long as the engine is running the transmission will be receiving continuous lubrication. However on an older car the engine might default to its idle speed in neutral, which may not be spinning the pump fast enough for adequate librocation. A modern car with electronic throttle control may or may not adjust idle to compensate for that and make neutral safe for the transmission when coasting."
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jijxpz | Can someone explain volts, watts and amps please? My interested is sparked! | Guys n gals, Can someone please explain the role of amps, volts, ohms and watts in either basic electrical and non electrical terms? Many thanks! | Engineering | explainlikeimfive | {
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"Water is a really good analogy. Instead of a wire carrying electricity, imagine a pipe carrying water. Amps is how much water is flowing through the pipe. Volts is the water pressure. Ohms is how much water pressure is lost going through a pipe. Watts is how much energy the water stream has at the end of the pipe.",
"These units are used to describe electricity and energy. Let us start with watts. Wattage is a flow of energy over time. Higher wattage means more energy faster. A small fire has less wattage than a big fire, but depending on how long they each burn, the small fire could release more energy overall. We call this 'speed of energy' power. Watts measure power, in the same way that meters measure distance. There are other measures of power, like horsepower, but watts are by far the best for use with electricity. Now, electricity is the flow of electrons. Electrons move from 'higher pressure' to 'lower pressure'. As they move, they do work - they can heat up a wire or spin a fan. Thus, each individual electron releases a tiny bit of energy as it moves through a device. The energy released by each individual electron is known as 'potential' and we measure it using volts. A 9-volt battery releases exactly nine electron-volt of energy for every electron that moves through it. If you have the same number of volts, but move twice as many electrons, you get twice as much energy. Hopefully, you can tell what we're missing: How many electrons are moving? I mean, everything with voltage has relied on individual electrons, but almost no devices work off of individual electrons. This leads us to current, measured in amps. This tells us how many electrons move every second. One amp is about 6241000000000000000 electrons moving every second. This means that the power (watts) of an electrical flow is equal to its potential (volts) times its current (amps)."
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jin2a0 | why in NYC do their sewer systems emit steam? | Engineering | explainlikeimfive | {
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"That's not the sewer, that's the steam system. It's used for heating buildings. [ URL_0 ]( URL_1 )",
"They don't. When you see steam coming from the ground, what you're observing is the steam power system under the streets of New York heating condensation in the air. URL_0"
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jix7ez | How can Voltage be negative? | Engineering | explainlikeimfive | {
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"Voltage is a relative measurement. You have voltage between two points and never voltage in a single point alone. Which of the two points you select as your zero referance is arbitrary.",
"Voktage is the potential difference between 2 points. Imagine a jump rope. If the reference point is your hands, the height of the rope is positive at the top and negative at the bottom of the cycle.",
"Essentially what gnonthgol said. A nice analogy is water flowing in pipes. Imagine the water as the electrons. The flow of water is the electric flow. Voltage in that analogy would be elevation. Water flows from the higher altitudes to the lower ones due to gravity, and electrons flow from the regions of high voltage to the low voltage due to electrostatic forces. Just as we just declared sea level to be zero altitude, we just declare one point in an electrical system to have zero voltage. Its for convenience and has no real meaning - water doeant care if its sitting at 10m or 20m, it only cares whether the pipe is going up or down."
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jj3hum | - Machine Learning | Is machine learning and AI code written by a human that then goes on to write its own code without any additional human interaction? | Engineering | explainlikeimfive | {
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"[This]( URL_0 ) should answer most of your questions. While I feel that constantly suggesting CGP Grey videos on ELI5 might be missing the point of this subreddit, the problem is that they seem to have been intentionally *made* to answer many of the questions here.",
"ML doesn't so much write new code as it learns which inputs matter for making decisions. The ability to do this is written in the code, and the machine makes adjustments to its decision making based on new information. So, lets say I program a machine to identify pictures of dogs. I give it the ability to analyze a picture (I code this) and tell it 15 attributes that make something a dog - ears, nose, tail, etc. (I code this too). I then feed it a bunch of pictures. It analyses the picture based on those 15 attributes and when it hits a threshold of 'certainty' is shows me the picture and says, \"I think this is a dog - am I right?\" You tell it yes or no. Do this a few thousand time. Each time it gets input - yes or no - it changes the weighting of each of those 15 attributes. Originally, they all may have been weighted equally, but after a few thousand trials the machine will 'learn' that ears produce a lot of false positives, so it will weight ears less in the algorithm that determines whether or not it thinks it is a dog. Likewise, it may learn that a certain combination of nose/tail/eyes is _always_ right, so it will weight that combination much more heavily. Very complex ML algorithms may even allow for new parameters to be factored in; maybe you didn't tell it to look at tongues, but if it notices that tongues are a good indicator it will start factoring that data in too."
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jj4e7p | How do the build the lighthouses in the ocean when there is always the risk of storms and huge wave force to knock the partial building down.(example Brittany lighthouse/la jument) | Engineering | explainlikeimfive | {
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"With great difficulty! Lighthouses are built on rocks that are exposed at low tide, so it's possible to dig into the rock and build the lowest parts of the lighthouse for a few hours each day. The stones that are used for the base of lighthouses are really large, so they are very heavy and difficult for the sea to wash them away. Most importantly, the stones are also shaped a bit like jigsaw pieces, so that one stone 'locks' into another. This makes the unfinished lighthouse quite strong: but they do get damaged while they are being built and often have to be repaired before they are finished. Once they are finished, the shape of the lighthouse helps keep them safe: lighthouses are wider and have thicker walls at the bottom, getting thinner at the top, just like a tree trunk. This makes them extremely strong and resistant to the waves, just as trees resist the wind.",
"I haven't watched this one, but here is an old doc series in engineering where they discuss it URL_0"
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jjg0q6 | What exactly happens when a thunderstorm causes a power outage? How does that happen? | Engineering | explainlikeimfive | {
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"It is often something cutting a power line. For example, lightning strikes a tree and the tree falls on a power line, breaking the connection. Now the power can’t get to your house because the line is down. Once the power company fixes the line, you get power back.",
"Lightning or wind could break a tree causing it to fall on power lines. Lightning could also strike and break the power lines or the transformer directly. There's also the possibility that the lightning rod isn't properly insulated, meaning all that electricity going down causes it to affect the electricity in other parts of the house, causing the circuit breaker to trip."
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jjvnsa | Lighthouses in the middle of rough body of water, how were they built? | [this post]( URL_0 ) got me thinking. How was this possible? Especially back in the 1800 or early 1900’s. | Engineering | explainlikeimfive | {
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"You either divert the water using a temporary dam (in the case of a river, usually) or you create a bulwark style dam by dropping prefabricated walls into a square and then pumping the water out. Also, you wait for calmer seas if you have to build in a place that tends to get choppy like the lighthouse you linked to. Once the water calms down/is diverted, you build up your foundation on whatever bedrock or outcrop you have available. Then you just keep waiting for calm seas to continue building. Some lighthouses have taken decades to complete because of this."
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jk031n | how do “transformers” explode? | I live in New Orleans and am sitting through Hurricane Zeta with no electricity at the moment. I’ve heard about a half dozen transformers explode in the last hour or so. I took electrical engineering an age ago, so I know how a capacitor can explode, but how do the “transformers” on the telephone poles explode? Are they not transformers? ELI5 and ELI-a-freshman-in-college appreciated. | Engineering | explainlikeimfive | {
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"The transformers you see up on telephone poles have oil inside of them. When something fails or causes a surge of electricity large enough the result is combustion of the oil."
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jk5hz7 | How did fuel injected engines work before we would have had computers to control them? | how did an engine without a carburetor exist as early as the 1950s when modern fuel injected engines can’t really function without being computer controlled? And why would we still use carburetors for so long after fuel injection already existed? | Engineering | explainlikeimfive | {
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"Modern fuel injection engines use the computer to fine-tune the fuel air mix, generally to maximize fuel efficiency but they have power curves built into them and all sorts of tweaks. That's not necessary for fuel injection to work, though. It can just open the injector for a set period of a revolution and call it good. Older injection models worked like that just fine, using analog sensors on the cam and crank shafts to monitor timing. Later versions could even take into account the throttle position with a simple relationship rather than an actual computer calculation. Modern technology could do that as well, but they're not set up to. You can't adjust the injection timing well that way, and it's just all around inferior to the modern EFI setups in terms of both power and efficiency. As to continuing to use carburetors: They're cheap, simple, and could dump a metric fuckton of fuel if you had a big motor you were trying to feed at WOT. early injection systems could be a bit quirky, and it could be problematic to get them to deliver the right amount of fuel across a wide RPM band, particularly in larger, thirstier engines. You also got intake injection systems that served as a sort of in-between, with one or two injectors sitting where an older carburetor would to get good atomization, but without the complexity of an injector per cylinder setup.",
"Carburetors use intake air to pick up fuel via the venturi effect. The fuel/air mixture then passes through the intake manifold, the intake valves, and into the cylinders. The carburetor is built into the throttle body. The throttle plate controls airflow through the carburetor; the carburetor controls the volume of fuel going into the airstream. Modern fuel injection is usually \"direct injection\". Fuel pumps feed pressurized fuel to the injector; the injector opens to spray fuel directly into the cylinder, but only during the intake stroke. There is another, earlier type of fuel injection: Throttle Body Injection. The carburetor components are stripped from the throttle body, and replaced with a single injector. Like with the carburetor, the fuel/air is mixed in the throttle body, and passes through the intake manifold. The control of throttle-body injection is much simpler than direct injection, because they don't need to be timed to the intake stroke of each cylinder. The benefit is electronic control of the fuel mixture. A simple computer can gather data from a number of sensors to determine how much fuel to spray.",
"Modern fuel injection is rather complex just because we try and maximize fuel efficiency, the power produced, reduce emissions. That requires a lot of sensors and computational ability Prior to the opec fuel crisis of the 70s, nobody cared about that. Gas was cheap, a few miles to the gallon was normal. A carburetor was simple and inexpensive so it worked for most applications. It wasn't really until the changes in culture, laws and fuel price that people actually cared about fuel efficient cars and manufacturers made them. Injectors can be as simple as squirt on timing pulse"
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jkaalo | why does having different diameter wheels/tires on the same axle damage a differential? | I've seen the Jam Handy differential video multiple times. I understand what a differential does and why it is needed. What I don't get is why it can damage the differential to have even a small difference in diameter of the wheels. Like running a mostly worn tire and a brand new one. This seems especially bad with AWD vehicles, if your tires are moderately worn and one gets damaged, it is recommended you replace all 4 to prevent damaging the differentials. & #x200B; EDIT: Thanks for the replies, the answer seems pretty straight forward. It's just more wear. In my mind I didn't really see the difference, since things are constantly moving in a differential, even during "normal" driving. Seems like I was slightly oversimplifying how they work. | Engineering | explainlikeimfive | {
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"This applies mainly to limited slip differentials, which are meant to limit slip caused by two wheels rotating at different speeds (such as during a loss of traction) by bleeding off the excess rotational energy as friction heat. That's fine in limited durations but it's not designed for that continuously. Long term, it causes damage to the differential by overheating its gears and lubricant."
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jkc3ck | Why are V formation engines (V6/8/12) considered better than having the cylinders in a different formation, such as in a straight 6. Bonus points if you can explain why more cylinders is better. | Engineering | explainlikeimfive | {
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"What it really boils down to is packaging and materials. V-configuration engines are easier to package and fit into an area than an inline configuration, as well as using less material since things like cooling pathways, cam set-ups, intake/exhaust manifolds etc. can utilize the same space on the inside of the V. For the whole more cylinders = better argument, that is not necessarily true. The old adage \"no replacement for displacement\" is being disrupted by hybridization, downsizing & turbocharging, and advanced controls & technologies. One real benefit of more cylinders though is that, for instance, V6 vs V8, it is easier to balance vibration from the engine felt by the passengers for each bank of cylinders to have an even number of cylinders, a V6 has 3 on each bank and results in two cylinders moving up while the other is moving down, while a V8 has two and two. If the engine were opposed (boxer) configuration, it would be able to mitigate vibration even better, but again, boxer uses more material and space. & #x200B; Source: Graduating with M.S. in Automotive Engineering in December"
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jkhslj | Why isn't there just one type of screwdriver head? | Engineering | explainlikeimfive | {
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"text": [
"They all have different pros and cons. Straight: super cheap & easy to build, doesn't require anything fancier than a knife you don't like, terrible to use Philips/Pozidrive: \"cams out\" (stops driving) at a relatively predictable torque. This was great for automated assembly machinery back when torque-limiters weren't practical. But it's crazy easy to strip and very sensitive to using the wrong bit size. Requires dedicated & sized bits. Roberts (square): Difficult to strip, excellent in high torque applications, requires a relatively large head to get enough torque due to the low contact angles. Requires dedicated bits but not super-sensitive to size. Hard to cam out. Allen (hex): Difficult to strip, even lower contact angle than square so bigger heads, super cheap tool (hex stock is cheap) but very sensitive to size. Almost the only one that works well off-angle if you have a ball-hex drivers. Doesn't cam out at all. Torx (star): Almost impossible to strip, excellent in high torque, can get away with a smaller head due to high contact angles. Requires relatively difficult to build dedicated bits that must be exactly the right size. Hard to cam out. Triwing/pentalobe/security-torx: Designed to be hard to find the drivers so that people can't mess with your stuff. Either great or terrible, depending on your point of view. In application, similar to philips (triwing) or torx (everything else).",
"There is a difference in how had they are to make and the functionality. The simple slot that is just a straight cut was the first type because you can just cut them in the screw with a saw so very simple to make. A major drawback is that they do not help in centering the screwdriver. The design based on a cross starts to emerge in 1930 as away so the crew driver center itself. It was important because pneumatic tools started to emerge and they were used in factories. The was harder to make the simple cut slot. There are many of those design types in part because they were intended and companies made their own designs so they did not need to pay license fees. There have also been changes in the designs so you can apply more torque. Allen keys that is more generally called hex socket and is also from the 1930s. They have the advantage you do not need to apply and downward force when you use them. problems that the head will be larger for most of them. They are problematic in flat head screws as you need a very small variant so it can handle less force than a cross design. Today there is star-based designs like Torx where you do not need to press down the tool hard and they can handle higher force than hex. I think that Torx and similar are the superior design. If you even have used them and Philips for the same task as in wood screws the Torx are a lot simple to use and seldom came out. I suspect that they are a bit harder to make than cross-based designs so cost a bit more and that is why they are not used everywhere. Or it is just what people are used to so old designs stay in usage. There are one other types of consideration in some application and that is how they look. So in furniture etc that might be the primary consideration. If it has vintage look a slot drive looks better than any other types. In other cases, hex is more discrete than cross or Torx."
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jl0n3t | why are sauna's always build with wood? | I wondered about this, it must have more to it than just the aesthetics, right? | Engineering | explainlikeimfive | {
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"text": [
"A couple reasons. The big one is that wood is unlikely to get hot enough to burn you. A sauna can be quite hot, and stone or metal walls/benches would be very uncomfortable to touch at that temperature. The wood also absorbs some moisture and slowly releases it along with resins and other natural chemicals that smell very nice and make for a relaxing atmosphere."
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6
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jlhmq5 | Why can you flush toilet paper in some countries and can’t flush it in other countries? | Engineering | explainlikeimfive | {
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"text": [
"Fun thing happened to me in India. I pooped in a public toilet that was basically a bombed out hole with no door. I used toilet paper. As I was leaving the next guy grabbed me a started yelling. I had to take the used toilet paper out before they would let me leave. I ended up using two old plastic bottles to get it out. It was scary, embarrassing, and disgusting all at once.",
"Some counties sewege pipes can't handle toilet paper, and are only big or sturdy enough for poop."
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12,
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jljvwc | How do gun ranges stop the bullets from going any further? Do they ever have to replace the walls? | Engineering | explainlikeimfive | {
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"text": [
"The backstop of an indoor gun range is usually comprised of a dense, soft material somewhat like mulch that absorbs the kinetic energy of incoming projectiles and slows them to a stop. It does need to be replaced on a set frequency as it fills up. The captured bullets may be sold to a smelter and recycled into new ammunition. At an outdoor range, the backstop may just be a big pile of earth. All you need is something heavy and dense that will absorb that energy."
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5
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jlwgdy | At what point does a bowl become a bucket? | Engineering | explainlikeimfive | {
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"text": [
"Buckets don't have a tapered or rounded bottom - it's just a cylinder. They also usually have a swivel handle. I think either of those traits would qualify as a bucket. The height of a bucket is also usually greater than the diameter, while the opposite is usually true for bowls."
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7
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jm09mr | How do they put high rise cranes up? | Engineering | explainlikeimfive | {
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"gas5lmy"
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"text": [
"They build themselves. The initial crane is built generally with the help of a mobile crane on wheels. The crane has a little cage built around the tower that has hydraulic devices to push itself up, and it can push itself up along with the crane top. The cage first lifts the top crane itself, disconnecting it from the tower. New sections of crane tower can be lifted by the crane itself and inserted into this cage. Then it just rides up even more on this new segment to go higher."
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6
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jmlpbk | How can modern aircraft fly on just one engine if the other one fails? Shouldn't the torque produced by the functioning engine make the aircraft yaw? | Engineering | explainlikeimfive | {
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"\"Shouldn't the torque produced by the functioning engine make the aircraft yaw\" It does, in fact one of checklist items to do if an engine fails is to trim the rudder by an angle that the aircraft flies straight",
"The yaw can be compensated with the rudder as the plane moves forward. You couldn't probably take off with it, but definetely keep it flying straight. This isn't ideal, but anything that keeps the plane flying in a case of emergency is okay, I guess.",
"You're correct. We refer to this as asymmetric thrust. We compensate for this by using the rudder. Multi-engine aircraft are designed with this exact scenario (loss of one engine) in mind. For this reason, engine placement is a key part of aircraft design. Manufacturers want to place the engines as far out on the wing as possible to reduce cabin noise, but the engineers want to keep the engines as close to the body of the plane as possible to minimize the possible asymmetric thrust during an engine failure. So this leads to finding a happy medium. The engines aren't right up against the body of the plane, but they're not out at the wings tips either. So, when an engine fails, we deflect the rudder in the opposite direction of the failed engine. That is to say if the left engine fails, we deflect the rudder to the right. This deflection allows the plane to continue flying in a straight line. Even with this rudder deflection we can still control the plane fully in all directions. Of course we won't be able to go as fast, but that's not a major concern. As long as the plane is kept above a minimum speed then it will fly just fine. A modern airliner can (depending on weight) easily maintain somewhere between 20,000-30,000ft and 200-300 knots of airspeed on one engine. So essentially an engine failure in cruise or in descent is a non-issue for an airliner. During the take off though, that's not the case. This is the worst time for an engine failure to occur (low altitude and low airspeed and high thrust setting). This is the reason that pilots practice this manoeuvre over and over again until it becomes muscle memory. The procedure if an engine fails during the take off is essentially to keep the plane flying straight (using the rudder) and fly a certain speed (we call this speed V2). This speed is the most efficient speed that we can climb at with one engine. The plane will keep climbing (even on just the one engine) and then when we get to a safe altitude (typically 1000ft) we'll lower the nose and pick up some speed and keep climbing away.",
"The yaw and roll can be countered by adjusting the ailerons and rudder. It would cause some drag and wouldn't make for a great flight, but one engine will be enough to at least keep you flying level in most planes."
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jne2d6 | why and how do Nintendo switch cartridges taste bad? | Engineering | explainlikeimfive | {
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"gb0s6yl",
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"text": [
"The cartridges are very small, to the point where they present a choking hazard if accidentally (or intentionally) swallowed. To deter people from placing cartridges in their mouths, the cartridges are coated with denatonium benzoate (Bitrex), a **very** bitter compound. The idea is that they would taste so horrible that anyone who accidentally tastes one would be immediately repulsed by it. Of course, Reddit being Reddit, users started posting memes about how horrible the cartridges taste, leading to a few users intentionally licking cartridges out of curiosity.",
"Nintendo adds some nasty tasting chemicals into the plastic because little children have a tendency to stick anything they can in their mouths. Making the games taste bad helps keep children from swallowing the games and choking."
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jnpu8w | How do apartments and hotels calculate how many elevators they need in a building? | With hundreds of residents in one building moving all over the place and sometimes with only 4 elevators, it somehow doesn’t create too much backlog with the people wanting to go on the elevator. How do the planners figure out they need this many elevators, and how do they predict the activity of the residents to determine the amount before the building is even being built? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Everything in a building is code based. This in particular falls upon the architect to determine maximum and expected capacity of the building. Once this is determined, then they use the code to give them an answer to the number of elevators."
],
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5
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jnus0x | Why do weightlifters wear a belt on their waist? | Engineering | explainlikeimfive | {
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"When you lift something heavy, you have to brace your core to protect your spine and stay tight. Imagine flexing the ab muscles and much as possible, as if you were anticipating someone punching you in the stomach. Now, you need to do this regardless of whether or not you wear a belt, but what a belt gives you is something to brace against. The most simple way I've seen it explained is this: Imagine you can squat 500lb. This means you can generate around 500lb of force, right? But if you tried to squat an empty bar, you wouldn't be able to put 500lb of force into it because you'd have nothing to push against. The belt gives your core something to push/brace against.",
"The reason weightlifters SHOULD wear a weight belt is to give them a proper external cue to increase intraabdominal pressure as they push their abdomen hard against the belt. This, plus performing the valsava maneuver increases the stiffness of the core stabilizers for heavy lifts, ideally squats and deadlifts. A TON of lifters use belts improperly though or use belts for unnecessary reasons, such as wearing it the entire session which potentially weakens the core.",
"Gonna take a swing at summarizing what we have here - the belt helps stabilize your core muscles so you don’t accidentally hurt yourself while picking up something heavy."
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jofkos | What exactly makes a clock 'tick', as in make the sound? | Most (all?) clocks have some sort of pendulum built in, either a proper one, a balance wheel or an 'electronic' one (quartz crystal). However, regardless of those differences all the clocks/watches I own tick once a second. What makes that sound? Also, is it a mechanical necessity (like in light switches, see e.g. [this video by Technology Connections]( URL_0 )) or could we do without and it is a design choice by now (people just expect clocks to tick)? | Engineering | explainlikeimfive | {
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"So mechanical watches are controlled by a coiled spring, there area series is gears and oscillating escape movements..the ticking sound is the teeth hitting the gears on the escape wheel It's hard to explain text, so this 1949 video would help you visualize it URL_0 In quartz watches they sometimes simulate it by activating the motor once a second, and sometimes you can hear the gear and motor activate.",
"It's mostly the large second hand snapping into place. I removed the second hand from a particularly loud watch and it made it nearly silent. The volume of the sound comes from the resonance of the watch/clock body as well as the mechanical interactions when the second ticks over. For mechanical watches, they tick multiple times per second, ex 8x per second, and you're hearing the escapement/balance wheel tick back and forth as well as the second hand. Not all clocks tick, some use a sweeping second hand that beats too fast to hear the little clicks as it moves. Also digital watches of course don't tick. Basically the way a quartz watch/clock works is that a chip counts the beats a quartz oscillator makes, and when it gets to a certain number, it tells a small electromagnet to move the second hand. That movement is the tick. It's definitely not necessary, I have 2 watches that you need to put right up to your ear in a silent room to hear."
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jol3yq | why are the spacesuits are still as bulky as when human went to space for the very first time? Although we’ve came along way with technology and materials. | Engineering | explainlikeimfive | {
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"They are still in an extreme environment. Radiation, instant 400ish degree temperature swings, and obviously vacuum. The life support systems alone to handle that need to be very reliable and redundant. That's inevitably bulky. The suit has to be as flexible as possible to allow the astronaut to work, but it also has to be relatively rigid, otherwise it would just be a balloon. Flight suits have gotten smaller, but from a mission and funding perspective, there hasn't be a giant incentive to produce a completely new generation of suit. They're being studied/tested now, but until there's an actual mission that requires their increased capabilities, they aren't the highest priority.",
"Coming a long way with materials is great, but at some point you're just playing with physics The big bulky EVA suits have to do several things 1. Have an oxygen supply so the astronaut can breath 2. Have an active cooling system so the astronaut doesn't cook from their own body heat 3. Be insulated to the astronaut doesn't promptly roast in the sunlight 4. Be puncture resistant so the breathing air doesn't escape The insulation and the cooling are the two bulkiest ones. You think of space as being cold but that's because space doesn't have much stuff in it which also makes it a terrible heat sink. You're generating about 100W of heat and passing it off to the air, but in space you're generating 100W of heat and have no where to really get rid of it except slowly through radiation. The space suit has water cooling in it to help pull heat from the astronaut and keep them from overheating from their own body heat. The sun is also obscenely bright, and with no atmosphere to reduce the intensity the astronaut get hit with about 1000 W of light over the area of their when they're in the sunlight and its important to keep that heat from getting into the meatbag and limited cooling system inside which can't deal with a 10x increase in heat. It doesn't matter how fancy your fabrics are, you still need thickness to provide insulation, and bulk on the back to provide the cooling",
"Although new space suits appear as bulky as the ones we had for Apollo, they are actually vastly superior: easier to get in and out of, easier to maintain, more flexible. (I am talking about the Artemis suites here, not the ones on the ISS currently). A space suit is like a space ship. It needs to be pressurized, thermally controlled, and allows for joint movement. These constraints make it very difficult to build a slick sci fi suit.",
"Fascinating note: the first suits were sewn by the Playtex Corporation (yes, the bra people), because they were the only people who could consistently stitch the suits to the standards demanded by NASA. Worth reading about. 1/32nd of an inch, through multiple layers of different fabrics and rubber, and each stitch was counted to make sure that the right number of stitches appeared on each seam.",
"If you’re referring to the EVA suit used on the ISS, it was originally designed in the ‘70s and first used in 1981. While there have been upgrades since then, you are still basing this off of something that is almost 40 years old and has been in use since the space shuttle first launched. The periodic upgrades have all needed to be compatible with the other pieces that were already in use, so it’s a slow process to improve."
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jor9y8 | How are transistors and other electronic components able to be made so thin? | Engineering | explainlikeimfive | {
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"gb9url9"
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"text": [
"by using a process called lithography. Silicon wafers are put in a liquid that's reactive to light and a map of the transistors is drawn on a transparent film; light is shown through the film and where the light hits the silicon wafer is etched; the shaded areas remain untouched. The solution is then washed away leaving you with a silicon wafer that can be cut up and put into chips."
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josgwu | how have they brought air inside the International Space Station? In liquid form? | Engineering | explainlikeimfive | {
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"gb9zusk"
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"text": [
"> In liquid form? In a way, yeah. Usually in the form of water, which is safe to transport, doesn't have to be pressurized and you only have to vent the excess hydrogen."
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4
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jp0jdf | What does cocking a pistol actually do? | ELI5: Like when guys in movies push the thing on the back of the gun down, what does that do? They always do it to signal that they’re about to shoot whoever they’re pointing at, but their pistol fires just fine without doing that. So what does it actually do? Also, why don’t rifles have those? | Engineering | explainlikeimfive | {
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"In early firearms the gun wouldn't fire without the hammer being cocked back. This is referred to as \"single action\" in that the only action pulling the trigger does is releasing the hammer. In more modern firearms it will make for an easier trigger pull. Since these are \"double action\" firearms where pulling the trigger both cocks and releases the hammer. So cocking the hammer manually removes the force needed for the that part of the action.",
"They’re cocking the hammer. How a bullet works is on the back end of the bullet in the brass case there’s a little firing cap, that cap explodes when hit and lights the gun powder. The hammer that they’re cocking back is what will fall down and hit the firing cap hard enough to set it off. Pulling that hammer means all that’s left to do is pull the trigger, as pulling the trigger is what will release the hammer and let it fall.",
"It depends on the type of revolver. Some revolvers require you to cock the hammer before each shot manually. Many shooters do it anyway as it makes the trigger pull smoother and less jerky than if they have to rotate the cylinder, pull back the hammer, And release it with a single trigger pull. Most rifles don’t have a hammer, but a firing pin instead. Same basic idea: it hits the primer on the cartridge but it’s like a spring loaded needle inside the bolt of the rifle."
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jp1zx0 | Fountain jets height | The way the line fountains are designed, is that there is one long big pipe that runs down the middle of the fountain. There are holes drilled into the pipe. From these holes goes a jet of water straight up. Now, how do all the jets pushing water to about the same height? I heard that in fountains of Vienna there is a simple design solution, but I am unable to find anything about it. The obvious thing that comes to mind would be to have a really big pipe (to neglect this effect of drag) or that the pipe is narrower towards the end to account for drag. But both seem to me quite impractical... I hope the question is clear. | Engineering | explainlikeimfive | {
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"text": [
"I think that the pipe is the same size all the way but the size of the nozzles (the holes as you call them) is adjusted to take account of the decreased pressure the further along the pipe run it is."
],
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jp4z9z | Why are GFI's more sensitve to water that a breaker? | I am being told by someone who worked in electrical that he doesnt know why, but GFI's are more sensitive to water. Thinkin like an engineer, I can't figure out why two devices which are designed to do the same thing (shut down electron flow if too many pass by per second) can behave differently? I understand that a GFI is just another breaker to protect us, which makes sense, but how can it be more sensitive to water? | Engineering | explainlikeimfive | {
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"text": [
"A breaker measures the total current going down the hot wire, if it exceeds a threshold (15A or 20A in the US) for a little while then it'll trip. Breakers are good at dealing with surprise dead shorts which draw a huge amount of current and moderate shorts which will lead to wires heating up and burning in a wall. GFIs have a circuit in them that measures the difference in the current going down the hot wire and coming back on the neutral wire. In a normal device they should be perfectly matched as there isn't anywhere else for the electrons to go so the GFI is set to trip if more than 5 mA gets misplaced. If you were to drop your hair drier in the tub with you then some of the current will flow through you and the water to get to the grounded drain pipe. If only 5 A flows through the water then a standard breaker will never trip, you're below fire hazard levels of current so it doesn't care. The GFI will trip because those 5 A are going out on Hot and *not* returning on Neutral so it cuts the power quickly. It only takes about 50 mA of well placed current to kill you so a 15 A or 20 A breaker really does nothing to prevent you from getting electrocuted, while a GFI is explicitly built to protect against it",
"A breaker is meant to shut the circuit down if there's too much current going through them, so as to not overheat and start a fire. A GFI is meant to shut the circuit down if there's current going out but not coming back in, so as not to electrocute someone. It's not that it's sensitive to water specifically, it's just that water is one of the things that causes that to happen."
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jp7989 | Why is it easier to drive round a corner in a lower gear, even at the same speed? | Engineering | explainlikeimfive | {
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"text": [
"Engines have different performances at different rotation speeds, with your typical family car generally performing at its best somewhere in the 2500 to 4000 revolutions per minute (petrol/gasoline engine). This is the most responsive range, where you have good control over engine speed with just a little extra gas, or just easing up slightly. If the revs are too low, it's hard to accelerate, and if they are too high, the engine becomes noisy, can cause damage, and you can't speed up without changing gear. For a given speed, the higher the gear, the lower the revs. So, at 15mph, 1st gear might be 5500 revs, 2nd maybe 4000 Revs, 3rd 2500, 4th 1500, and 5th borderline stalling. So if you are taking a corner at 15mph, 2nd or maybe 3rd is where the engine will be in the sweet spot. Of course, if it is a high speed 50mph corner, 2nd would break your engine, 3rd would be struggling and noisy, 4th and 5th would be better suited. So, it isn't always easier to drive round a corner in a low gear, it's easier to drive round in the most suitable gear."
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jq3g5z | Why can’t airplanes get into space? | Engineering | explainlikeimfive | {
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"Airplanes require airflow to generate lift under the wings. After the air thins to a certain point, the plane can't go any higher",
"Planes are held aloft by the lift generated from air flowing over the wings. If you go high enough there isn't enough air to create the necessary lift, and so you come down.",
"Engines require oxygen and the wings require air passing over them to provide lift, in addition height isn't the problem for orbit it is velocity, rockets don't go straight up, they just take off vertically shortly after lift off they then lean over and have a lot of horizontal movement URL_0",
"Planes don't carry their own supply of an oxidizer to burn fuel against, since the atmosphere provides oxygen for the engines. They are also designed to propel themselves laterally with engines, using lift generated from the wings to lift the aircraft.",
"Rockets don't go straight up, they go slightly diagonal at first and then when the air thins out they start going perpendicular to try and fall past the Earth aka get into orbit. The ISS and satellites are really just falling, but they are going so far sideways they keep missing the ground/Earth. The air is what keeps airplanes aloft and air is needed for engines to work. At a certain point there becomes too little air for lift and to burn fuel. Ignore where this image came from (a flat earth site), but this is the [flight path a rocket takes to get into space]( URL_0 ) They normally fly East because it is easier to follow Earth's rotation and it gives them a speed boost to get to orbital speed.",
"Airplanes, by definition, require air to work. They generate lift from the motion of air passing over their wings. Propellers and jet engines also need air to generate forward thrust, for more or less the same reason. There is no air in space. An airplane could get you quite high, but it cannot take you into space any more than a submarine can travel above the surface of the ocean. It's not actually that hard to get to the edge of space. The space program uses rockets not so much for the going-up part, but because to get into orbit (or to leave the Earth entirely) you need to go sideways really really fast.",
"If you replaced all the jet fuel with rocket and fuel and oxidizer... it still wouldn’t work. To get into space, you have to be going *really* fast, sideways, about 7.5 km/s fast. To get that fast you need a ton of fuel, rockets carry roughly 10kg worth of fuel just to get 1kg worth of payload into space. In order to make getting into space more efficient, rockets drop their expended fuel tanks and engines. Planes can’t really do this and the extra weight of all the control flaps and whatnot means you’d need large wings to be able to lift this weight. Bigger wings means greater drag which also means you’ll need more fuel, but wait! That’s more weight which means bigger wings, more fuel.... you get the picture. Spaceplanes are really, really hard, even harder than rockets."
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jq7oel | Why are F1 tracks made from Asphalt , but concrete roads are preferred on civilian roads ? | Engineering | explainlikeimfive | {
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"Most roads are asphalt, there are some exceptions like high load highways in some places in the US, etc. But by far the vast majority of \"Civilian roads\" are asphalt. They're far less expensive to lay, far quicker, to lay. They are quicker to relay and basically recyclable...",
"Tldr is concrete is cheaper but has a lot of drawbacks. It cracks easier for example so it won't stay intact as long as asphalt. And F1 tracks probably have very specialized requirements for their roads. Another thing is that asphalt can have varying properties depending on the actual blend. Look up practical engineering on YouTube they have a great video on that topic."
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jqaai2 | What exactly is game engine and why do games show what engine they are using? | Engineering | explainlikeimfive | {
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"Game engines are basically just code libraries that deal with the complex aspects of games, most commonly used for 3-D games. The mathematics and code to manage and process 3D games is VERY complex, especially when it comes to the rendering of such games. So developers adopt the old \"why re-invent the wheel\" method, and just use an existing engine someone has made and tested before. As for why developers advertise, I can only speculate, but it is likely because the engine you choose directly has an impact on the physics and visuals of a game (reflections, lighting engine, ect). It's why (among other economic reasons) triple A games tend not to use Unity. Does this make sense?"
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jqbldx | How long Are huge buildings like the Empire State Building predicted to last, will there come a time when it will need to be demolished? | Engineering | explainlikeimfive | {
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"There was an article in smithsonian magazine years back that talked about how long various structures would last. It was basicly indefinitely as long as they were maintained, it went on the logic of how long if we just up and left them. As I recall, the empire state and twin towers(article was pre destruction) would stand for around 50 years to a century untill sea water seepage rotted out the foundation steel when the pumps stopped, and they would be toppled in the next big hurricane. I remeber the St Louis arch would be about the same time period before being taken out by tornados. The longest lasting would probably be hoover damn or norad. Neither of which would be functional, but they wod last thousands of years as recognizable",
"It depends on maintenance. If well maintained, they could last indefinitely. However, there will likely come a time when the required maintenance is too expensive and/or technically too difficult and the building will be demolished. If humans die out, [this YT video]( URL_0 ) speculates on how long various buildings will last.",
"Buildings have a design life to them. Somewhere between 100-150 years is typical. It is currently one of the challenges facing the field of structural engineering"
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jqj8sw | How did they get the international space station in space? How do they keep it from crashing down into earth? | Engineering | explainlikeimfive | {
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"They took it up in sections and put it together up there. Most of the speed it needs to maintain its orbit was imparted by the rockets that put it there, but it does also reboost itself periodically to maintain the orbit.",
"The got it up there in pieces, and assembled it in space. It doesn't crash down because it is in orbit. Basically it is traveling so fast horizontally, that even though it is technically falling towards earth, it misses completely, and continously whips around the planet. Constantly falling. Constantly missing.",
"Orbit is literally falling over the horizon. Gravity is pulling it down, but it’s going so fast it keeps missing the earth. That being said, there is still a little atmosphere at it’s orbit that it slows it down, so it muct occasionally reboosted.",
"Others have noted how it was assembled in space, pieces were brought up by the space shuttle and bolted together. It is in orbit, where there is so little air that it only slows down an infinitesimal amount due to drag (one of the two main reasons that you can't throw a ball or something for forever), and it also going fast enough that by the time it has dropped to ground level, the earth has curved away from it, so it has missed the earth (the other reason you can't throw a ball for forever, you tend to hit the ground after a bit). It is worth noting, however, that it does have to get boosted from time to time, because it does slow down some, and if it slows too much then it will actually hit the ground. From what I've heard, they use whatever rocket happens to be visiting to give it a little push from time to time. They also have to maneuver sometimes to avoid debris. Eventually they're going to give up on this task and it will slow down enough that it starts to fall lower and lower towards the ground. The lower it goes the thicker the air will be, slowing it down even faster until it eventually has a fairly traumatic period of breaking apart and burning up due to the immense friction it will experience in the thicker air. Some large parts may actually hit the Earth, but the goal is to hit the Pacific ocean somewhere so it doesn't kill anyone.",
"43 flight took parts up for assembly, 36 of the flights were the US Space Shuttle,4 Russian flights (2 Soyuz-U, 2 Proton-K) and 3 Falcon 9 flights for NASA",
"Side answer that I hope will get accepted. Look into the game kerbal space program. Its a space flight simulator game that you manage your own space center sending green little aliens called \"kerbals\" to explore their solar system. It has a steep learning curve but it will teach you all about space exploration, space station building and orbital and flight mechanics."
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jqp33h | Why is Da Vinci considered a genius? | Engineering | explainlikeimfive | {
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"text": [
"He was a polymath that did work in several fields that was years beyond his time. He designed incredible early versions of both the army tank and the helicopter. Every inventor stands on the shoulders of those that came before him. Davinci worked with the best info available in his time and came very close to some really amazing concepts. If he had the advantages of modern technology and materials available to him, he could have done some absolutely incredible stuff."
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jqtohm | why some towers like Taipei 101 have a tuned mass damper because they're in an earthquake-prone area, but other skyscrapers don't use mass dampers like in Japan, a country that's also in an earthquake-prone area? Are there more ways to protect buildings from earthquakes? | Engineering | explainlikeimfive | {
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"Height has a lot to do with it. Mass dampers aren't the only way to protect a building from earthquakes, but they're very effective at protecting extremely tall structures. Taipei 101 is over 500m tall. The tallest building in the whole of Japan is only 300m tall. So there just isn't any need for a mass damper when more traditional structural methods work fine. Some structures in Japan *do* have mass dampers though, such as the [Akashi Kaiky bridge]( URL_0 ) (currently the world's longest suspension bridge) and the [Tokyo Skytree]( URL_1 ), which is the tallest *structure* (not building) in Japan.",
"You know how clock pendulums swing at a particular frequency? Well buildings are a bit like upside-down pendulums and they also sway at a particular frequency, called the resonant frequency. If this is close to the frequency of the vibrations from the earthquake then the building will sway more and more until it collapses. What tuned mass dampers do is shift the building’s resonant frequency higher, away from the earthquake frequency. Shorter, wider or stiffer buildings will already have a higher resonant frequency so may not need a tuned mass damper. It is also possible to put normal dampers into a building structure (a prominent example from a slightly different field is the Millenium Bridge in London). I wouldn’t be surprised if many skyscrapers have tuned mass dampers that are hidden in service areas and not widely known about."
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jqzjue | How do the scissors know which hand I’m using, and why do they care? | Engineering | explainlikeimfive | {
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"When you close your hand naturally with a pair of scissors, your hand is pushing the ends of the two blades together because of the position of the pivot point. If you have the scissors in the wrong hand, then your are pushing the blades apart naturally. That is why right handed scissors do not work well in the left hand and vise versa. If you compare left handed scissors to right handed scissors, you will see the two blades are on opposite sides of the pivot point for each pair.",
"Two reasons. With right-handed scissors, the top blade is on the right-hand side. Naturally you have the scissors in your right hand and the paper in your left hand. The paper rests upon the bottom blade and is secured on both sides of the bottom blade (on the left side by your hand and on the right side by the top blade). This creates a clean, straight cut. If you switch hands, you now have the top blade and your right hand both on the right side of the paper, and nothing securing the left side of the paper. When you cut, the left side of the paper is likely to bend up (since nothing is holding it down), creating uneven cuts and perhaps not even cutting at all, just folding the paper in between the blades. Second, when doing fine, detailed cutting, having the top blade on the same side as your hand allows you to see what it is you are cutting. If the top blade is on the opposite side of your hand, then it can obscure paper, including any guide lines you are using to determine where to cut.",
"You hands are actually pushing the blades together or apart while squeezing the scissors, and using them with the incorrect hand pushes the blades subtly apart as you close them, which is just enough for paper to get caught between them instead of getting cut by them. The correct hand pushes the blades together as they close, so they cut."
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jr8pm6 | Why are boat propellers on the back and plane propellers on the front? | This is obviously based on the assumption that the principle is the same for both craft. If that is true then what is the benefit of their respective locations? I understand that based on their current designs why it may be “convenient” but it seems like a “pushing” vs “pulling” debate would result in a universal trait/answer for both craft. | Engineering | explainlikeimfive | {
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"There are planes with pusher props on their backs. On water vehicles I'd assume you'd prefer the turning instability caused by having the thrust center at the back This is also why combat jets use vectored rear propulsion, apart from the obvious aero benefits."
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jrg3a7 | Why do you need a large speaker to play good bass sounds but a small mic can record bass sounds just fine? | Engineering | explainlikeimfive | {
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"text": [
"Think about it like this: Deeper noises require a lot more air to be moved. A small speaker struggles to move a lot of air, but a lot of air has no trouble moving a small microphone. This way of looking at it also leads us to predict that high-pitched sounds are more difficult for large microphones to detect, which is accurate. At least, in terms of the actual detecting component of the microphone."
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jrgjqi | Why does a clock sound like "tick tock" and not "tick tick" or "tock tock"? | Engineering | explainlikeimfive | {
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"When it comes to mechanical clocks like grandfather clocks, the sound might be different depending on which way the pendulum swings. If you are referring to a normal hang-on-the-wall analogue clock then you are having auditory hallucinations. Clocks like that always make one pretty much identical sound every time it \"ticks\", and the words \"tick tock\" are just a made up onomatopoeia which we use to describe the sound. The reason it's tick tock instead of tock tick or something along those lines has to do with the conventions of English language showing a specific preference of vowel order in certain situations."
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jrh5yb | What is the use of gyroscope in airplanes? What is the concept behind it? | Engineering | explainlikeimfive | {
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"Gyroscopes have an internal spinning disk, which will always remain level, no matter the orientation of the housing. Therefore are used as a reference line for measuring the pitch and roll of the aircraft.",
"The gyroscope tells you if you’re flying straight and level without the need of outside visual references. Go flying on a moonless, cloudless night or in some clouds and you’ll lose orientation in a hurry especially if you get caught in clear air turbulence or something like that.",
"Gyroscopes are used several critical flight instruments that give the pilot information on their direction of travel and orientation. One of the most critical instruments we use is the [Attitude Indicator]( URL_0 ), which tells the pilot where the plane is relative to the horizon (pointing up, pointing down, banking lef or right, upside down?) by using the deflection of the gyro. This is critical because a pilot loses all external references when flying in clouds, or above them at night. When the brain is denied visual data, it will try and guess based on the unreliable data your inner ear is reporting. This has killed a lot of pilots, and so we receive a huge amount of training on how to recognize and resist these spatial illusions. A gyroscope is also used in the [Heading Indicator]( URL_1 ) which tells the pilot which heading the airplane is flying based on deflection of the gyroscope. The overall concept behind it is that a gyro resists deflection from its balance point, so you can use the deflection to indicate a direction or rotation."
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jrjl3i | Why do some parts of the road sound different when you drive on them? | Engineering | explainlikeimfive | {
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"text": [
"I assume because different surfaces will have a variety of textures and densities that make the tyres vibrate at particular frequencies."
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jrrr9k | How is it that A/C units are so large, yet a refrigerator that can make things much cooler, is so much smaller? | Title | Engineering | explainlikeimfive | {
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"Refrigerators only have to cool a small very well insulated box. AC units have to cool a much larger area that usually isn't nearly as well insulated (leaky windows and doors, sunlight coming in, etc).",
"a \"large\" fridge is around 27 cu ft. An average sized bedroom is 1600 cu ft. An average 3 BR house might be 20,000 cu ft.",
"It’s all about tonnage. A refrigerator for the most part is a closed space 95% of the time. Therefore it only has to remove the heat from around 6 cubic feet of space. An air conditioner on the other hand has to attempt to remove heat from around 18,000 cubic feet, assuming 1800sq ft and 10ft avg ceiling height. That’s a significant difference in size. The air handler in an AC unit is meant to blow vast amounts of air over a coil that is roughly the same size as the coil in a refrigerator, only much higher velocity, without icing up."
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jrvl1r | What method is used to determine the direction that airport runways face? | Engineering | explainlikeimfive | {
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"Local wind direction Planes don't like taking off or landing with strong cross breezes so the main runway will generally be parallel to the prevailing wind, or as close as they can get given the plot they have. Taking off and landing into the wind also lets the plane use a lot less runway and clears traffic faster. Bigger airports will generally have perpendicular runways, you can see that [Newark has two main ones that run roughly north/south and a smaller east/west runway]( URL_0 ). Having parallel primary runways is nice because one can be used for takeoffs while the other is for landings or extra takeoffs if needed. You can't do this much with runways that cross as there's a much greater risk of collisions and jetwash",
"All other factors being equal, the predominant wind directions are used to determine runway direction. But that doesn't work perfectly everywhere, because some airports have not been able to expand their property to the amount needed to put in a runway in the preferred direction. So sometimes they put in a slightly longer runway in a different direction. Earlier aircraft were more sensitive to the wind direction, so early airports were built with different runways in different directions. More modern aircraft are not as sensitive, so for safety and efficiency the modern practice is to build multiple parallel runways in the predominant wind direction instead."
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jrwe7y | How Do Optimizers and Activation Functions Work In Neural Networking? | I'm currently trying to learn about machine/deep learning and with neural networks I'm finding myself confused. I'm currently using tensorflow and in the tutorial I'm programming a network to decipher somewhat tricky to see numbers between 0-9. I know that the activation function is a function that when executed on a neuron, passes its output to the next neuron and that the function is a result of an equation involving input, weight and bias. I know that optimizers are algorithms used to reduce losses in order to increase learning rate. Where I am stuck is how come the functions and algorithms improve accuracy when I could be using them incomplete different scenarios e.g I may use the adam optimizer for my network when trying to decipher what numbers are displayed but I can also use it for facial recognition projects right? How can the adam optimizer or any optimizer of sorts and activation functions improve the networks capabilites. Surely one optimizer and function can't be universally used right? I apologise if I am being ignorant, I'm new to this. | Engineering | explainlikeimfive | {
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"You've asked about two different topics, so let's take them one at a time. The first is activation functions and the second is optimizers. ******** Activation functions exist to allow neural networks to use simple linear transformations for the bulk of their heavy lifting without making the final result just be a linear transformation. To break that apart, imagine you're given a data set of points in a 2D plane. Some are red and some are blue. Your task is to come up with a model that predicts whether a new point you've never seen before is red or blue. What you could do is just draw a line through the plane and declare that every point on one side of the line is predicted to be red and every point on the other side is predicted to be blue. In other words, you take a point (X, Y) and compute A\\*X + B\\*Y + C and see if that value is positive or negative (selecting A, B, and C to define the line you want; the format of this equation allows it to be easily generalized to more dimensions). This works OK for data where a line matches the data nicely, but most data doesn't. To deal with more complex data you make three neurons, each computing a linear transformation like that. You put in (X, Y) and it compute A\\*X + B\\*Y + C = N (neuron 1), D\\*X + E\\*Y + F = M (neuron 2), and G\\*N + H\\*M + I = output (neuron 3, which takes neurons 1 and 2 as inputs). This *feels* like it ought to be more representative. However, if you go through all the algebra you find that output is just G\\*(A\\*X + B\\*Y + C) + H\\(*D\\*X + E\\*Y + F ) + I, or multiplying everything out we have (GA + HD) X + (GB + HE) Y + (GC + HF + I). This is the same exact linear transformation we had to begin with! We did a lot more work of combining three neurons together, but the end result can't do any better than drawing a line through the plane and calling everything on one side of that line red and the other side blue. That same problem exists no matter how many layers of linear neurons you use. The algebra gets messy and you quickly run out of letters, but the same problem will be there as long as each layer only performs a linear transformation. The problem also exists with higher dimensional data. If the input was a point in 3D space then the initial neuron would be something like A\\*X + B\\*Y + C\\*Z + D. If the input was a set of 1000+ values, each representing the pixel intensity at a certain point, then you'd have 1000+ weights (the A, B, C, ...) for each neuron. To get away from this problem of everything devolving to a single linear transformation you have to introduce nonlinearity somewhere. That's the activation function's job, and the only hard requirement that activation functions have (though really they also need to be differentiable for training to have a chance). Some networks go for extremely simple activation functions, like the ReLU that simply equals its input for positive values and equals zero for negative values. Others prefer to try to keep the output range in check using something like a sigmoid function. A common thought process behind activation function design is that a neuron may be conceptualized as \"firing\" or as \"inactive,\" where the value of that neuron tells us which mode it's in. This thought process argues that a neuron that's \"firing\" ought to pass a strong signal to the next layer, proportional to the strength with which it's firing, while inactive neurons shouldn't affect the output at all. This allows some neurons to not participate when they're not needed, letting the signal from activated neurons come through clearly without being drowned out in the noise. The same activation functions are seen in many network designs because the need for nonlinearity is universal in neural networks--if a problem can be solved by a linear solution then it didn't need a neural network in the first place! There's still plenty of research (and a lot of trial and error) on activation functions so there's no clear best option, but activation functions effective in one field are often effective in another, too, since they solve the same problem in both fields. ******** The question on optimizations comes down to how one finds the proper weights for a network. As mentioned in the previous section, one may have a neuron that takes in 1000+ inputs, multiplies each one by a weight, and adds that all together to represent the output. In order to come up with an effective neural network you need to figure out what each of those weights should be. That's something that can be done by hand for networks of a few inputs and weights, but generally it's much too complicated for humans to grasp. This is where training comes in. During the training process the neural network is provided with an input. It processes that input like it would any input and produces an output. That output is then checked to see if it's \"good\" (where \"good\" could mean \"agrees with human labels for the data\" or something else, depending on the application). When the output is good the weights are left alone, but when the output is bad the training process computes how each weight should be tweaked to make the output better (this requires taking a *lot* of partial derivatives, and is why having analytic derivatives is so important to neural networks). That process only gives relative magnitudes of adjustments--if your neuron is A\\*X + B\\*Y + C\\*Z + D then it could determine you want to change A by +3, B by -2, C by +1 and D by -1, but that doesn't mean you just add 3 to A, subtract 2 from B, and so on. Perhaps you choose to add 0.03 to A, subtract 0.02 from B, and so on. More generally, when you get the signal from one single training example you don't want to take drastic steps in the network's weights, nor do you want to take too small of steps. To see why, imagine one is trying to get to the top of a mountain and the only tool at your disposal is one that tells you the slope where you currently stand. If you measure the slope and move 1 mm in the direction of that slope then you'll quickly reach the top of the pebble you're measuring, but you'll never get to the top of the mountain. If you go 100 miles then you'll skip over entire mountains at a time. Optimization processes seek to find effective ways to take the gradient information from a single training example and slowly work towards the \"top of the mountain\" (i.e. the best set of weights). This is a process that all neural networks must undergo, hence its applicability to networks designed for a wide range of tasks."
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jrys71 | Why do some portable fans have their highest rotation setting closest to the OFF setting? Wouldn’t it make sense for it to gradually get faster as you switch the knob? | Engineering | explainlikeimfive | {
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"A fan takes a lot of energy to start spinning, but very little to keep spinning once it's already in motion. If the lowest setting came first, it would have a very difficult time spinning up, let alone getting to speed. By having the highest setting first, it lets the fan start up and then gradually come down to speed.",
"Adding on to what other people said, It should be noted many modern motors don't require as strong of a current to get started, and the dial is a legacy feature. Here's a great video by Technology Connections on the topic: URL_0",
"In engineering it's called jerk. It's like velocity and acceleration. I think it's the derivitive of acceleration. The high setting jerks the fan in motion as you go from off to hi to low.",
"It has to do with the power of the motor and the weight it has to overcome. If you unplug a fan at a low setting and then plug it in while still at the low setting it can actually be bad for the motor.",
"A motor that isn't spinning is basically a short circuit. Only once spinning does it provide an opposition to the electrical current and stop drawing so much. As you can imagine a dead short is not good. Things get hot, things break, things set on fire. The best way to start a fan is full power, to minimize this period and avoid any chance of the fan being jammed with not enough torque to get it moving. One it's spinning it is easier to keep moving, and doesn't draw enough current to overheat anything. That said, really large motors do the opposite. They start with intentionally reduced power and voltage. They have more than enough torque to start, but upon starting they can mechanically shock things (water hammer from a pump breaking a pipe) and drastically drop the voltage for other device (lights flicker, computers error).",
"URL_0 There is a video on this, enjoy. Technology Connections video."
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jrzws3 | Why does feedback make that annoying high pitched sound? | Hello! Tried to google this to no avail, so I'm hoping y'all can help me out here. I understand how feedback occurs: mic is hearing itself, too close to speakers, etc. What I cannot find information one is why that would create the worst sound in the world rather than an echo chamber? Why that sound? HOW does that sound come to be when the audio input itself is literally any other sound? Please eli5 because I'm still working my way through college and haven't done an advanced science courses yet. Science is something I love but haven't had as much exposure to as I'd like. Thank you in advance! | Engineering | explainlikeimfive | {
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"Microphones 'hear' certain frequencies better than others. If you start out with broad spectrum noise that contains all sorts of frequencies, the microphone will hear a particular frequency louder than the others that are present, so the signal that goes to the speaker will contain more of that frequency. Now when the sound coming from the speaker reaches the microphone, the mic's preferred frequency is already louder than the others, and again the microphone will pick it up better than the others. If this is allowed to continue for a number of cycles, that frequency is going to dominate. In practice amplifiers and speakers also have certain frequency ranges where they work better, and the dominant feedback frequency is basically going to be the peak that you get when you add the frequency response curves of the mic, amp and speaker on top of each other. It's not always the same frequency because different PA systems are going to differ, but it's most likely going to be in the mid-range."
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js0gsq | What exactly determines how fast a car can go from 0 to 100 km/h? Is it a combination of horsepower, torque and weight? Does RWD or FWD have an impact on it? | Engineering | explainlikeimfive | {
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"Torque and horsepower both are important, torque more so. RWD/FWD don't matter in and of themselves. Its the traction they can provide. RWD tends to give more traction as the weight of the vehicle settles on the back under acceleration. However, all wheel drive can allow even more as there is more surface area to distribute the force for acceleration. Electric vehicles have an advantage as they provide full torque and power right from the start while combustion engines have a power curve that rises and falls through their rpm range. Edit - Left out weight. Weight also matters. F = M\\*A. The less mass the less force is needed for the same acceleration. So keep the same force, but drop the mass and you get increased acceleration."
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jsdc4a | Why are there momentary blips in local power for a whole town? | Sometimes my whole local area has a power outage lasting only a few seconds. Not enough to cause much real annoyance. But enough to reset everything from my PC to the clock in the cooker. How does this happen and why are there sometimes a few within a short period but no other issues for years at a time? | Engineering | explainlikeimfive | {
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"Quick outages are usually caused by brief shorts like a falling tree branch hitting a power line. They are rectified just a second or two later by something called an auto-recloser which senses these shorts, monitors the line for clearance, and restores power without need for a crew to come out."
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jsov5d | Explain why modern aviation is safe. | Engineering | explainlikeimfive | {
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"> The annual risk of being killed in a plane crash for the average American is about 1 in 11 million. On that basis, the risk looks pretty small. Compare that, for example, to the annual risk of being killed in a motor vehicle crash for the average American, which is about 1 in 5,000. URL_0 .",
"Very smart men and women spend their entire lives designing and building these planes. Then very smart men and women spend their entire lives inspecting and making rules to make certain these planes are in tip top shape and safe to use. Then very smart men and women spend their entire lives training to fly these planes and making sure everyone gets where they are going safely. (Non ELI5. Air travel is safer because it’s not dependent on a new 16 year old driver who is on their phone controlling a half ton SUV at 75mph. It relies on countless people who dedicate their careers to engineering, regulation and training. Just don’t fly on something like N Korea Air, Aeroflot, or Spirit. Jk on spirit, but seriously though. Don’t.)",
"Avionics engineer here, I could give some insight into this, and maybe give you a good reason why air travel is so much safer than driving for example. There's less shit to hit in the air. Thanks for your time! If you have any questions, just reply to my comment. I will ignore them to the best of my ability.",
"Turbulence is chaotic motion of air. It can feel quite unpleasant (although I personally actually enjoy it). It exists in pockets, and causes jostling of the aircraft, but doesn't really hurt anything. At least, besides your leg if you spill hot coffee on yourself due to the jostling. One of the nice things about air travel is that you can't really hit anything. Even if you managed to get into extreme turbulence, shaking the plane violently every which way, you still wouldn't hit anything, so besides being mighty startled you wouldn't be injured or killed. The wings could break, if you chopped them off or something. Bending is not a sign that things are about to break - a well-engineered structure can withstand many times the force it takes to visibly bend before it breaks. In fact, all things bend a bit when they are pushed on. Plane wings tend to be stronger than the passengers - the force on the plane would have to be tremendous (and far above anything they actually experience) for them to break. Commercial airlines are very well-regulated, well-designed, and controlled by trained experts. There are also, again, just not any things in the sky to hit. Without hitting anything, it's pretty hard to hurt the passengers."
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jsyltp | why is it harder to push a shopping cart or dolly over a bump than it is to pull it over? | Engineering | explainlikeimfive | {
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"since the handle is below your shoulders, you are actually pushing the cart forwards AND down, but when you pull it, you are pulling it back AND up! therefore the upwards force makes it a bit easier to pull over a bump."
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jt17uy | What's the realworld difference between rear wheel and front wheel drive? | Engineering | explainlikeimfive | {
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"Which wheels propel the car? The rear wheel drive car propels from behind it's center of mass, which provides more rotational agility since you steer with the other wheels. Front wheel drive propels from in front of the center of mass, which provides more stability when the un-powered wheels might slip.",
"There is not much of a difference until you accelerate so much that the tyres start loosing traction. This might easily happen in rain, on gravel or on ice. When you start to lose traction on a set of wheels they stop guiding your car. In general the front tyres makes it so youcan turn and the rear tyres makes it so you can go straight. This means that if you accelerate too hard in a front wheel drive car you end up going straight in corners which is called under steer. Doing the same thing in a rear wheel drive car will cause the car to turn more then you command it to which is called over steer.",
"One additional aspect: The Center of Mass of most cars is pretty far to the front (because thats where the engine is usually placed). Meaning that with FWD, there is a lit more weight and thus traction on the driving wheels. Shouldnt make much difference in most situations, but RWD gets stuck in snow and the like easier because of that.",
"Oh man there are a lot. It has an effect on taking curves - FWD understeer while RWD oversteers. It has an effect on traction - RWD gives you better traction when drag racing and when towing... because the weight of the car/truck is shifted to the back. FWD is generally better traction for small cars and normal driving where the majority of the weight is in the front. It has an effect on cost and weight - FWD is cheaper and lighter while RWD has to have a long drive shaft and a rear differential. Driving feel and stability is noticeable too... if you start to accelerate and lose traction in FWD it's usually not too bad and easy to correct, while in a RWD it can be pretty easy to fishtail and lose control."
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jt4ht6 | Why do some airliners make a loud high pitched whine, while others make a dull roar? | Engineering | explainlikeimfive | {
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"Rolls Royce engines vs GE engines?? No expert, just my personal observation. RR engines have the 'growl' while GE engines spin up into a whine.",
"There are a couple of things to consider when answering your question. First, where are you observing (listening to) the airliner? Are we talking on the plane, on the tarmac, taking off/landing, on the ground when the plane is flying overhead? Second, what planes are we talking about? You mention airliners but there are of course different sized aircraft. If you can provide more detail I can definitely help!",
"Different engines have different designs. One of the biggest variations in design is the “bypass ratio”. Turbofan engines can create thrust through a combination of expelling hot gas out the back of the engine or by using the power of the engine to turn large fans at the front of the engine (much like a propeller). Low bypass engines rely more on the jet exhaust to generate thrust. This means the main noise producing core of the engine has to be larger than a comparative high bypass, this makes the engine louder. The engine also has to throw mass out the back end at a higher rate, so the engine turns faster and this gives it the higher pitch. High bypass engines are the opposite. They run at lower speeds and with smaller combustion cores, so they’re quieter and much more fuel efficient. They growl more than whine."
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jt78qx | Why is the F-117 designated as a fighter when it's only been used as a bomber? | Engineering | explainlikeimfive | {
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"The alternatives, like the F/A-18, are equally confusing. The plane isn't really a \"bomber\" in the B-52 sense of the term either. It's a highly maneuverable plane, and skillful maneuvering is required to avoid being shot down. Air Force pilots are trained in two pipelines: fighter and airlift. The fighter pilots learn about highly maneuverable planes, and how not to lose control of them. Airlift pilots learn about the control of much larger multi-engine planes, more like the airplanes we fly from airport to airport in. These two training pipelines also influence the nomenclature of the planes these aviators fly. The fighter pilots fly planes with F or A nomenclature, and the airlift pilots fly planes with the B or C or K nomenclature."
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jt84u4 | why is it that switching off an electronic device and switching it back on solves most of the problems we face with it? | Engineering | explainlikeimfive | {
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"Most of the time it’s because it clears the RAM. Programs that are running are stored in RAM, and after the device has been on for a long time sometimes the RAM fills up with garbage because not everything is perfect. In the old days it was even worse because most programmers had to deal with the RAM their programs used manually. Some devices, usually low powered or mission-critical ones, are still programmed manually. These days it’s mostly automatic, and operating systems are better at spotting problems. But it’s not perfect, so restarting can help.",
"You can think of any device as having a variety of 'states' - different configurations it can operate in. Some of those states in any complex device are going to be non-functional ones. Most of the time when you expire a cataclysmic error - one that stops your device from working - it's a consequence of being in one of those states. On electronic devices, power cycling resets the state to the initial state. That doesn't make it a universal panacea. There are ways to preserve state over a power cycle (fixed storage, for example). If you delete the O/S on your smartphone, power cycling isn't going to help you."
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jtaplr | How does a Car's axle handle the weight of the car? | In my mind the car's axle (at least the back one since those wheels don't pivot) is just a rod from one tire to the other that spins and therefore spins the tire. Since the car is only supported by the 4 tires and the car is only connected to the tires via the axle then the axle must be 1. Rotating and 2. Holding the weight of the car. So how do you hold up thousands of pounds of weight while spinning without being destroyed by all of the friction? And if the answer is lubricant then why does that lubricant not need to be changed out over time? Thank You! | Engineering | explainlikeimfive | {
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"The axle tube, which is not rotating, is providing support also. But the real answer is lubrication for the friction part obviously, but more to the point the bearings. The sphere is a strong shape and ball bearings take full advantage of it, though steel-on-steel while rolling along each other is very low friction to begin with (an advantage for steel rails on train tracks). Roller/needle bearings, while not spheres, are still circles in reference to the way the weight is going and circles are also a strong shape (notice all the use of arches in very old stone architecture). Some modern axles come with a claim that it is \"lifetime fluid,\" and this claim depends on how well it is sealed from the outside elements and the parts inside being well-machined and well-mated. Others still have a recommendation of changing every X miles. This of course is looking at solid tube axles like on a heavy duty truck. A ton of vehicles these days sport independent suspension. In this case only the part of the axle going through the hub and connecting to the wheel supports any real weight -- after which point the weight is carried by the suspension assembly that connects the hub to the car."
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jtar3t | Why do you need both hardenable steel and mild steel for a good knife? | Bingeing Forged in Fire and wondering why it’s so (seemingly) important to have mild steel at all. Wouldn’t a hardenable (i.e., won’t bend, roll, crack) steel alone just yield a stronger blade - assuming you can get a grinder gritty enough to create the edge profile? | Engineering | explainlikeimfive | {
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"You want really hard steel for the cutting edge so it will maintain the sharpness and not dent easily on hard materials but you want the rest of the blade to be milder so it has some give to it and doesn't shatter or snap when put under stress. You want it to be able to bend a bit.",
"I'm not too knowledgeable, but having too hard of a substance will make it brittle(it's shatter into pieces, develop microfracture) literally like just a really hard stone knife, having too mild will make it's edge go off, causes bending.",
"I'm unsure of how they're making anything as I haven't watched the show in a while, but there's a blade making style called San Mai where a hard steel is sandwiched between two softer layers. This gives the blade some flex to prevent the blade snapping or breaking, while still having a very hard and durable cutting edge at the core. Of course, someone who knows what they're doing can temper a blade differentialy to achieve the same effect - hard edge, soft spine."
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jtgg4n | Why are commonly used batteries round while car batteries are square? | Engineering | explainlikeimfive | {
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"Ease of manufacture. A regular battery is a few layers of different materials forming concentric cylinders, within the battery. Like, if you cut it in half, it would have layers like a jawbreaker. For small batteries that need a long life, this is a quick easy way to make them. Car batteries, specifically lead-acid car batteries, are made up of a stack of lead plates. This, plus a square (well, rectangular prism) shape maximizes the surface area of the cathodes/anodes for the given space. Unlike regular batteries that are meant to slowly discharge over a long period of time, car batteries are meant to quickly discharge (but only by a volt or two) over a few seconds while allowing the car to draw hundreds of amps during those few seconds. After that, the alternator provides most of the car's electrical needs. & #x200B; Also, the commonly used batteries you're referring to, even the ones that are square, like a 9v or 12v (lantern battery), if you open them, you'll typically find round batteries within them. It's easier, faster and cheaper to make round batteries and arrange them to a square form factor than it is to make actual square batteries. & #x200B; Also, of note, 'square' batteries, made up of plates, are much more likely to have problems if if they're damaged. A round battery, if it gets dented isn't likely to be a big deal. A square battery (think, li-on batteries you'd see in a phone or the kind that come in 'pouches') are made up of very thin plates. A dent in the side of one of those has a real chance of creating a short between two plates which can mean anything from a non-working battery to a very real fire hazard.",
"Another reason batteries are different shapes is to reduce the chance of damaging electronics by using the wrong voltage."
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jtn5pp | How does a rotary engine like that found in a Mazda RX-7 work? | Engineering | explainlikeimfive | {
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"As the rotor revolves inside the chamber, the volume available for the fuel+air mixture changes. This compresses it and after the spark the gas expansion drives the rotor forward. [Here]( URL_0 ) is an interesting Wankel animation.",
"They work on the same principle of suck, squeeze, bang, blow as any other combustion engine. But instead of a piston going up and down inside a cylinder, requiring four strokes to complete the cycle, you have a triangular piston rotating inside an elliptical bore. As the piston rotates its faces will create an airtight seal with the walls of the bore creating a chamber of varying size. When the face is towards the long axis of the bore the volume will be large and when the face is towards the short axis the volume will be small. This means that through a full revolution each chamber will go through all four phases required for combustion in only one revolution. And since a triangle have three faces there are three chambers as opposed to the single chamber of a piston engine. This means that you have essentially increased the volume of the engine six times compared to a traditional piston engine. There are still other factors involved so rotary engines is not mean rotary engines are far superior to piston engines. But there are certain things that make them better for racing."
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jtpp6n | How do submarines work? | How can they change their vertical position? | Engineering | explainlikeimfive | {
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"Submarines have large tanks inside them that they can fill with water or air. More air = up. More water = down. If they balance them out just right, then the submarine stays put without rising or sinking.",
"When the Sub is on the surface big areas at the front and back of the ship are filled with air. Fill those with water and you sink, to come back up fast use compressed air to blow the water out(submarines keep alot of compressed air). Underwater if you are driving forward, you can use the Submarine's bow, fairwater and stern planes like \"Wings\" to \"Fly\" through the water to where you want to be. There is a person on the submarine that works with the guys controling the planes to pump water off and on with big pumps to help get to which depth you want without going too shallow or too deep.",
"They adjust the balance of the mix of air and water in their ballast tanks so that most of the time they are at neutral buoyancy (neither sinking nor rising) at the depth they want to be. Then they adjust the speed and angle of the dive planes to ascend or descend in a controlled way (water flow over the planes has an effect similar to airflow over an aircraft's control surfaces). The ballast tanks are adjusted slightly to maintain neutral buoyancy and level trim. In an emergency situation, they can flood the ballast tanks for a quicker crash dive or blow them empty for a quicker emergency surface. There can be some risks with that, especially if their compressed air is depleted or they surface underneath something. In the unhappy event that they get stuck in the mud on the seafloor, the method of getting back up again is (or at least used to be) for the crew to run back and forth from one end of the ship to the other and jump to try to rock it loose."
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ju0mbt | Say I had a car with a 3L V8 engine (idk if that’s a real engine) what does that mean? Also what’s the difference between Torque and Horse Power? | Engineering | explainlikeimfive | {
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"Let's break it down into 4 parts? 1. Engine: the V8 part 2. Displacment: the 3L part 3. Horsepower 4. Torque ENGINE The main part of the engine consists of certain 'cylindrical' parts which is funnily called as cylinders itself. The way these cylinders are arranged gives the letter of the engine. If they are arranged in a straight line, they are called inline engine (I or L), if they are arranged in shape of a V, then it's called a V engine. We also have W engines where 2 V shaped engines are arranged together. The number after that shows the number of cylinders. So, a V8 engine means an engine with 8 cylinders arranged in form of a V-shape. DISPLACEMENT There are certain rods that move in the above mentioned cylinders called pistons. As the engine starts working, these pistons move up and down in the cylinders. The total volume covered by these pistons is pretty much the displacement of the engine. So if the car is a V8, then one piston would cover around 0.375L or 375 cubic centimetres or 22.8 cubic inches. Hence 8 times 0.375 L gives 3L of displacement. The displacment is pretty much responsible for the power of the engine. More the displacement, more the power. HORSEPOWER & TORQUE Horsepower (HP) and torque are measures of powers of an engine. Though they are sometimes used in place of each other, they are not really the same. Torque usually refers to the power that the engine can give while the car isn't moving. For example, a truck needs a whole lot of power to get it started from rest because of the heavy weight it has. Hence, truck engines are usually high torque engines. Horsepower is related to this torque and also how fast the engine is running (how fast the pistons move up and down). Racing cars generally need high horsepower to maintain high speeds. So more the torque, the faster you are off the starting line. More the horsepower, the faster you can sustain in the track. In short, a car with high horsepower and low torque would feel slow in the beginning but will gain more power the faster you go. A car with high torque and less horsepower would feel like it's faster in the beginning but may feel sluggish as you go faster until you shift gears. This is my first answer on Reddit. I don't know if this is how you can explain to a 5 year old. Sorry if I made any mistakes. I hope I was able to clear out some stuffs?"
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jua6sr | How did the military manage to get trenches built during WW1 | During World War I/II both the UK and Germany spent time building trenches as a base, to hide. Why did the opposition allow for the trench to be built. I should imagine it took years to get them to a reasonably sufficient state, why did the opposition not destroy this and prevent supplies? | Engineering | explainlikeimfive | {
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"Trenches were mainly a WW1 thing and the earliest trenches are just a hole you can lay down in, the trenches grew and improved over the 4 years of the war. If I give you a shovel and a couple hours and tell you to dig a hole you can squat in to avoid being shot you'll manage to dig that hole. If I give that same order to 10,000 dudes with shoves standing in a line then you have a basic shallow trench in an afternoon. If I give you all night you'll have a trench you can stand in and little passages to get out of it. If I give you a week you'll have expanded your trench network so it connects to every nice French bistro and wine cellar you've found so far, and now you have a very elaborate trench network! The start of trench warfare was the Battle of the Marne when the Germans stopped their retreat from France and dug a trench to protect them from the forces they knew were following them. They were able to setup machine guns and get a deep enough trench to protect them while giving them good lines of fire at the attacker. This led to the Race to the Sea where both sides started rapidly digging trenches northward trying to get around the other sides but neither managed. There was no good way to destroy an entrenched position early in WW1. Planes weren't an option, biplanes were limited and really only carried bombs that you can physically pick up (~25kg) which is pitiful compared to WW2 developments with 1000kg and even 5000kg bombs. Tanks didn't exist yet so that's right out. Artillery could work, but HE shells just dig holes when they hit the dirt so they predig bunker slots and don't do much else. Mines were actually one of the more popular options, you dig a tunnel under the enemy trench line and set off a 200-500 kg bomb underneath it and cause it to collapse, but the other side is doing it to you too. The only effective way to stop the enemy from building more trenches was to take the trenches with your foot soldiers which is why so much of WW1 is digging trenches and then massed charges across no man's land with horrific casualties. It actually was one of the more effective options",
"They started digging in towards the beginning of the war, and the nature of conflict didn't change much throughout the war. Wars and battles before that had been about movement, so they certainly didn't expect to be in trenches for so long, nor to have such a network. They were dug by hand, as and where needed, and as quickly as possible - the trenches didn't take years to dig. Many weren't in a good state at all, with flooding a common problem, as well as damage to latrines and the walls collapsing to reveal the dead who had fallen in no man's land. Some trenches were little more than ditches to crawl through. Both sides let the digging happen because the were doing it too - they weren't going to fall back and surrender ground, but nor could they advance, so they dug down for protection and a war of mostly attrition started. There were trenches all over Europe, so it wasn't just the UK and Germany who did this. There is an example of trenches being built very deliberately that I can think of: the Germans built a fortified line of trenches behind the front line and then retreated to it because it was better organised and defended. The firepower was different then too. Both sides would shell each other, which damaged trenches and supply lines as well as killed and maimed, but it was harder to see what was going on without air observation (aviation was in its infancy, and was used to gather intel before they started aerial battles and dropping bombs). Trenches offered protection from gunfire, so once there was enough cover it became harder to actively stop them digging without going over, which would expose the attackers completely. To minimise damage done by shells falling in trenches, trenches zigzagged (like: |—|_|—), meaning the blast could only go so far before being absorbed, with the earth offering protection to those who weren't too close to where the shell fell.",
"The trenches weren’t dug by heavy equipment, they were painstakingly dug out by soldiers tunneling sideways and staying below the sightlines of machine guns and artillery. The opposition would stop it if they could, but that would require exposing themselves to the other side’s artillery and machine guns. The longer you’re unable to stop the trench construction, to more fortified the rear lines become. By 1917 the trench lines had become elaborate subterranean fortresses, all dug and reinforced by hand.",
"Militaries have been using units originally called saps to engineer and build trenches. The sappers would start the trench out of reach from enemy fire and they wouldn't build very far in a straight line before zig zagging the trench. From within the trench they could put up big guns to keep enemies away and then continue digging towards the enemy. The U.S. Army still trains Sapper's to this day. They are demolitions experts used to clear the way for the units they support."
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jub5ox | Why are cars painted? Wouldn't another material be just as cost effective, still protect the surface and not chip with the mildest impact? | Engineering | explainlikeimfive | {
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"> Wouldn't another material be just as cost effective, still protect the surface and not chip with the mildest impact? The paint *is* a colored protective coating. I'm unsure as to what you mean by \"another material\" - what did you have in mind?",
"Paint is a fairly broad term for a wide variety of protective surface coatings. Most surface coatings fall into this category. The few that don't tend to be extremely brittle and flake significantly worse than paints tend to. Anodizing, for instance, works for phones, but cars tend to be made of plastic or thin metal, both of which flex a fair amount during regular use and any such coating would quickly shatter and flake away.",
"Originally cars were painted to preserve whatever materials they were made of, commonly steel. Bare steel when exposed to the elements will start rusting quickly. As for using other materials, lets say aluminum. Aluminum will not rust, but will corrode due to oxidation, and look poorly after some time exposed to the elements. Lets say you are also thinking of plastic that is strong enough for impact, the plastic can come a certain color, but to make an entire car of shiny plastic would cost extra, so its better to paint the exterior surface. The paint in all cases protects the underlying material. The plastic from UV ray degradation, the steel form rusting, and the aluminum from corrosion. It makes the all the materials last longer, and look better."
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juqt8a | Why do sister ships exist? | Taking the example of the Titanic, and it's sister ships the Olympic and Britannic, why do these exist? Wouldn't it be too intensive an investment to make just one of them, let alone three? | Engineering | explainlikeimfive | {
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"Basically designing a ship is expensive once you have the basic plan for a ship you can make multiple copies cheaper than a one off.",
"Because they planned on using all of the ships at the same time. It's like asking why Delta has more than one airplane. With multiple, you can carry more passengers, travel to different locations, and make more money.",
"Well, it is really difficult to design something that big, so it is only natural that they’ll use the same schematics to build multiple ships, there is no reason why they souldn’t"
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juz2lv | please: Why do European countries heat homes with radiators and US homes use air ventilation systems? | Engineering | explainlikeimfive | {
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"I think it's because houses in Europe are much much older than America. You'll see radiators in houses in the east coast of the U.S. because that's where England first colonized and it's older, but just about everywhere else started building houses after the idea of ventilation systems was introduced.",
"Two major reasons. Houses in Europe tend to be older or at least have an older building style. So it may just be habit and easy availability if it’s put into newer houses. But possibly the larger reason is that most modern US houses have air conditioning units that will need to use vents. If the vents are already there, it’s easy to just have a combo AC/heat unit that uses vents instead of two separate systems. And for the northerners that don’t need AC, well, the rest of the US market uses vents, so it’s the cheaper method. Most of Europe is a little colder than the US, so AC is far less common.",
"I don't disagree with other answers but I just watch my cousins build a house in Germany. I don't know that you could _phyiscally_ add forced air. The house has concrete floor and some kind of a concrete block is used for walls. Even things like wiring were cut into grooves in the wall or poured into a thin layer of concrete on the floor. I tend to thing that building methods play some role in it.",
"Forced-air systems are the way to go if you want your system to be able to both heat and cool. Plus, in the right climates, they can be paired with heat pumps, which can be extremely energy-efficient. The downside to all that is mechanical complexity. They have— literally— a lot of moving parts, plus logic boards, refrigerant lines, and all that jazz, which add to both the upfront cost and ongoing maintenance. Radiators are much simpler (though actually pretty tricky to install correctly in the first place), but they can only heat, not cool, and there's a physics limit to how energy-efficient they can be. You see them in older buildings, because, well, they're old tech."
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jvb7ps | How can dry lubricants like graphite work better than liquids? Wouldn't they just cause more friction or wear? | Wikipedia article on the subject was a little too technical, getting into layered molecular structure and non-lamellar structures and such. Hoping this sub can make sense of it. | Engineering | explainlikeimfive | {
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"Powdered graphite is essentially sand made of graphite. You wouldn't use sand as a lubricant, so what gives? Sand is made of silicon in a very stable crystal configuration. Graphite is carbon in a layered, unstable configuration. Putting diamond powder into a mechanism would be worse than sand, so it's not the carbon. Graphite is softer than almost any metal, Even paper can abrade it, that's how pencils work. Graphite powder works by forcing graphite into all the little cracks and flaws in the metal surface. The graphite is so soft that it wears until the surfaces match exactly, and can slide freely.",
"The blanket statement \"they work better\" is misleading and doesn't help understand the differences in this case. Lubrication can be thought of as doing two different functions, the first is reducing friction, the second is protecting from rusting. If I rub two things back and forth with a dry lube, an oil, or a grease, they're going to behave and accomplish those goals differently and in different proportions. Graphite penetrates the surface \"pores\" of your materials and helps even them out so there's less 'grit' to grab and then it just stays there until it's wiped out of those pores. Oils and greases do something similar, but also film over the whole surface so even less contact occurs, and prevent oxidation. Different tools for different jobs. They wear off/escape differently, attract dirt and grime differently and are significantly different to clean off when it's time. It's actually an ongoing drama in the gun world over oil vs grease, or if letting carbon accumulate on certain bearing surfaces is ok, since the carbon fouling left over from gunfire is extremely similar to graphite dust. (Grease at the way imo.)",
"Put a dab of oil on a glass surface and a dab of graphite also, cover them with lint from the dryer screen, now blow the lint off the glass. Oily substances attract dirt.",
"Two sheets of graphite have very little holding them together, and because of how the atoms are oriented, little friction occurs between them once they get moving. So imagine having two very smooth surfaces sliding over each other.",
"Adding to others on why graphite works, because it is dry, it it suitable for applications where you don't want an oily product carrier to get gummed up. Locks can use dry graphite or in a spray or liquid carrier that evaporates. Same with gun mechanisms."
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jvmfh4 | Why is riding the clutch in a car bad, but on a dirtbike it is highly recommended? | Engineering | explainlikeimfive | {
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"Different types of clutches. A car has a single plate dry clutch. It’s simple, light, durable, but doesn’t tolerate a lot of heat. A bike typically has a multiplate wet clutch. That means the clutch plates live in an oil bath, and can shed heat super easily. You can slip the clutch in a bike all day long. Now, this isn’t universal. There are some cars with multiplate clutches and some bikes with dry clutches, but in both cases those are usually specialized race instances.",
"You don't really ride the clutch on a dirt bike, you want to keep it covered at all times so you're ready to use it. Most cars use a hydraulic clutch and dirt bikes use a cable operated clutch. With a hydraulic clutch comparatively little pressure is required to disengage the clutch relative to it's clamping force, so just the weight of your foot on the pedal can cause it to disengage slightly causing unnecessary clutch slip. Your hand resting on the clutch lever of a dirt bike is not enough pressure to disengage the clutch. They're also vehicles used in very different situations. On a dirt bike on a track you're using the clutch more often than you do driving a car to the store.",
"Motorcycles often have wet clutches, which are surrounded in engine oil, helping keep their temperature from getting as high as when you slip the clutch for an extended period on a dry clutch. Also, a motorcycle engine produces much less torque and the weight is much lower so even though the clutch is smaller, the surface area is subjected to smaller forces"
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jvuycj | How can you have the same water flow from the tap, no matter which part of the city you live? Shouldn't the people living close to the pumping station experience a lot stronger water stream? | Engineering | explainlikeimfive | {
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"Municipal grids are set up to supply water between about 50-80psi, and a lot of engineering goes into designing the layout and placement of things like supply lines and booster stations. Pressure reducing valves are also employed to reduce incoming pressure in areas where it's too high. So basically the municipal grid is designed so that everybody gets more or less the same water pressure no matter where they are in relation to the source.",
"Water pressure doesn't come from the pumping station. Pumping stations are used to fill water towers, and gravity is then used to provide a constant water pressure to everyone. This has the added benefit of being able to run the pumping stations at a constant rate instead of trying to vary it to keep up with fluctuating demand. As long as you can, *on average*, fill the water tower faster than it drains, then you're fine.",
"Pressure regulators. Water in your tap doesn’t come from a single line attached to the pump/gravity feed. It is “distributed” into multiple systems that regulate pressure across their own service areas. Otherwise people on 50th floor of a skyscraper would have a dribble while people on ground floors would have fountains coming out of their taps.",
"You are right, it does. But people who live closer to the pumping station or towers will have pressure regulators. Look outside your house near the main shutoff valve, there should be a pressure regulator there where you can adjust the pressure it allows through. Careful though, increased pressure can lead to consequences from popping hoses and even leaks in welds in your walls"
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Subsets and Splits