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b83ygq | If water become a gas in a vacuum, wouldn't it be more efficient to build a steam engine inside a vacuum chamber ? | Engineering | explainlikeimfive | {
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"Yes. If something is making water boil, then there must be a flow of heat. You can build a heat engine that extracts useful work (e.g., to generate electricity) from that heat flow. Could this be possible in some way using a vacuum chamber to boil the water? Vacuum doesn't make water boil. Heat makes water boil. When water boils, the vapor carries heat away. If you suddenly expose an open container of water to vacuum, two things will happen: (1) the water will start to boil, and (2) the water will get colder as it boils. When the water gets cold enough---maybe cold enough to freeze solid---the boiling will stop. In order to continuously boil water, at any pressure, you must have a continuous supply of heat. So, what you didn't ask was, would pulling vacuum on the outlet of a steam turbine improve its efficiency? Well, here's the kicker: In large thermal power stations, that is what they actually do. The working fluid in a large thermal power stations is de-mineralized water that flows in a closed loop. There is nothing but water in the loop (i.e., no air), so at the cold end of the turbines, where the temperature may be as low as the temperature of the cooling water that they draw from a nearby river, the pressure can be much less than atmospheric---almost vacuum."
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b8hbnm | - How does a gun silencer manage to suppress a gunshot so well ? Why is it never actually completely silent either ? | Engineering | explainlikeimfive | {
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"The principle of operation of a firearm suppressor is that it provides a lot of room for the hot gases to expand inside the suppressor, before it exits the barrel. The more expansion the gas undergoes, the lower its velocity gets and the cooler it becomes. Both of these characteristics reduce the noise signature when the gases eventually do leave the barrel. It can't get completely silent because at some point, gases leave the barrel, and we can hear that. You can get pretty damn close, though, with low-pressure subsonic ammunition and a really big suppressor.",
"Smarter Every Day made a good video about this [on YouTube]( URL_0 )"
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b8k01b | - How does a step up / step down transformer work. | What is the best real world analogy to a transformer. | Engineering | explainlikeimfive | {
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"A gearbox. A small gear [in picture]( URL_0 ) pushing a big gear multiplies the speed 4x but at the cost of 1/4 the torque. Similar process with electromagnetic fields, and numbers of wires. You trade volts for amps, and vice versa",
"I’m guessing that you want to understand how it works, not what it does. This is a little beyond most 5 year olds but as simple as I can go. Electricity flowing in a wire makes a magnetic field. A magnetic field near a wire makes electricity. If you put 2 loops of wire near each other and put electricity in one, electricity comes out the other. If you use more or less loops of wire then you can change voltage (which is sort of like pressure) of the electricity."
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b8lvyr | How does a helicopter pilot bail out if he is going down? Clearly they can’t use an ejector | Engineering | explainlikeimfive | {
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"They don't. If a helicopter is going down, so are the crew and passengers. The pilot(s) need to do everything in their power to arrest speed prior to impact with the ground. Fortunately, unless the rotors are completely wrecked, there is usually a lot that the pilot can do to minimize the impact.",
"An ejection seat is perfectly possible on a helicopter. The [Russian KA-50]( URL_0 ) has an ejection seat. It works by blowing the rotors off before ejecting the pilot. Sikorsky has used a similar system in one of their experimental helicopters.",
"Helicopters can autorotate, which means they use the big propeller on top to slow themselves down and land somewhat safely. To do that, they switch the way the blades are facing so the air going by as they fall makes the blade rotate, then switch them back to make them lift the helicopter. Some military helicopters, though, do actually have an ejection seat. The same control that fires the ejector also fires explosive bolts that release the rotors, so they fly off before the pilot can hit them. (I learned that from an Apache pilot at an air show.) They try really hard not to use that system, but if they're too badly damaged to autorotate, it's better than just hitting the ground.",
"If I'm not mistaken some military helicopters do have the ability to block their rotors and use an ejector seat. Not sure if it's widespread or still in use. Other helicopters can autorotate (\"float\") down. Or crash.",
"It's essential to attempt to control the inevitable crash. The procedure is known as \"autorotation\" and basically the pilot tries to use the last bit of lift from the rotors to not die. There's some great videos on YouTube if you look up autorotation & training for it.",
"A heli pilot in my military unit said he'd rather land a helicopter deadstick than a fixed-wing plane any day, because helis just need a clear patch the size of the heli to land, and an airplane needs an unobstructed flat runway.",
"They don't. All passengers go down with the helicopter but the good news is that it's actually really safe to land a powerless helicopter as long as rotors are intact through auto rotation. It's akin to coasting to a stop in a car. Give it a Google it's the only thing I've ever seen that makes helicopters look safer than planes. My mom's a pilot she used to practice them all the time and send my dad videos pretending she was crashing. Also high risk helicopters like for the military (like a fighting helicopter not a transport helicopter) have very well engineered seats to mitigate the damage of falling out of the sky in an uncontrolled way as if you had a damaged tail rotor. Also there are some helicopters that eject rotor blades then the pilot but the vaaaaast majority do not. I think some sikorskys have it and some other military helicopters but it's not wide spread by any means.",
"Imagine a Fan and a Pin Wheel. A Fan spins its blades and blows air at you. You blow air at a Pin Wheel, and its blades spin. Both spin in the same direction, but one pushes air, and the other gets pushed by air. The reason this happens is the angle the blades are at. & #x200B; When a helicopter is going down the pilot can changes the angle of its blades so that by falling, it makes the helicopters blades spin faster and faster, building momentum (Pin wheel). However, if the blades go too fast, the momentum is too strong and they will break. So once the blades get enough momentum the pilot changes their angle (Fan mode), so the momentum is now pushing air, and providing lift for the helicopter. As the momentum run out, the blades are no longer lifting the helicopter so the pilot changes the angle of the blades again (back to pin wheel). The pilot does this again and again until they can land. Always being careful to never build too much momentum in the blades. & #x200B; By doing this a pilot can safely land a helicopter even with engine failure. AFAIK it may be safer than landing an airplane with complete engine failure."
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b8n7vk | How do fuel pumps know my tank is nearing full and cut off supply? | Engineering | explainlikeimfive | {
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"Inside the nozzle there is a small tube. When you are fueling, the tube is sucking in air as the fuel is being delivered. When your tank fills up, that tube sucks up fuel and creates a vacuum in that tube which releases the automatic shutoff valve."
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b8nln6 | why are the tips of the wings on an airplane curved up? | Why are the wing tips bent? Seems structurely less safe? How is it more aerodynamics? | Engineering | explainlikeimfive | {
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"There's a low pressure area on top of the wing, and a high pressure area bellow it. This is caused by the shape of the wing, and it's what allows an aircraft to fly. Because of this pressure difference, the air wants to flow from the bottom of the wing to the top, and at the wingtip it can do this. This leads to a loss of lift at the end of the wing, because the pressure can equalise. It also causes strong vortices called Wingtip vortices that are very hazardous to aircraft flying behind. Winglets/sharklets prevent/reduce this flow of air over the tips and thereby increase the lift provided by the wing",
"That curve at the end of each wing helps mitigate \"wingtip vortices\" which are exactly what you would imagine, a wind vortex originating at the tip of each wing and trail behind the aircraft. These vortices cause extra drag so the curved tip disrupts the vortex allowing for decreased drag"
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b8qt64 | Are current car tire and rims more efficient than their older counterparts? | I noticed that older vehicles had bigger tires and what seems like smaller rims but now the rims seem to be bigger in diameter and the tire much smaller/thinner. Are current tire/rim combinations more efficient? | Engineering | explainlikeimfive | {
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"Rims have gotten lighter and stronger while tire compounds have evolved to have better traction and longevity. The only reason rims are bigger is because of esthetics. The ride usually gets harsher and going beyond factory tire diameter will reduce performance. Also old cars had worse suspension so having more tire meant less abrupt shock"
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b8s3ur | Why stones are used on train tracks? | Engineering | explainlikeimfive | {
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"Essentially it's a really cheap suspension, drainage system and anti vegetation system. URL_0 It distributes the weight away from the narrow tracks to the surrounding ground. It also absorbs vibrations making it a form of suspension. It stabilizes the train and keeps it in place, also over time digs into the ground and stabilizes the entire track structure. It provides a effective way to drain out water so it doesn't pool up. As the trains move the rocks grind against each other effectively grinding down any plant matter that might form. If you dig into it's a really genius system. Technically much better then the asphalt roads we use.",
"I believe it is because during travel, a train will put tremendous weight on the tracks and there must be some \"give\" to the surface or else the train would fly off the tracks if it were rigid.."
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b8t3if | How do the saws that cut casts not cut skin? | Engineering | explainlikeimfive | {
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"Doctor uses shakey blade not spinny blade. Shakey blade has teeth to bite into hard cast, while it only moves the skin.",
"The \"blade\" vibrates and the more resistance an object it comes in contact with has, the more it digs in. So a cast is harder than skin, it cuts easier. Skin allows more pressure on it, so it doesn't cut as easy with this saw.",
"Resistance is key. Think like this, if you try to write on a bit of paper that is unsupported (floppy) you wont be able to, put some tension and you will be able to. Since the sawblade only vibrates, and does not spin, skin can withstand contact without being cut (its \"floppy\"). But the \"un-floppy cast offers a lot of resistance, and the blade can do its job. Worth noting, you can get friction burn from this though although rare as the nurse/dr doing the cutting has a rough idea of the depth to go."
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b8y06i | How do slow close toilet lids slow close? | Engineering | explainlikeimfive | {
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"Self-closing toilet seats are made with a slow-close hinge that uses a spring or tiny air cylinder. The hinge allows the seat to lower onto the bowl softly and silently. Slow-close seats lower themselves in a smooth, controlled motion as soon as you start to push it down"
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b9856a | Explain to my mom why she can’t put gas in her car while it’s running “because race car drivers do it”. | Engineering | explainlikeimfive | {
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"Well, there's no technical reason she can't. There's a small chance a running engine could cause a spark that ignites gasoline fumes, but the biggest reason for that rule is because distracted people do dumb things getting in and out of running cars, and cause accidents. It's just generally a good idea to turn the car off, because it eliminates the risk of problems like locking your keys in it, forgetting to put it in park, your kid/pet knocking it out of park, etc.",
"Because at the race track there are fire personal just off screen ready in case there is a fire.",
"There's no real reason she can't. That \"rule\" comes from back in the day when cars had the fuel cap behind the license plate, it was close enough to the exhaust the fumes could ignite. Obviously thats not the case anymore. At the same time, theres no real reason to leave it running."
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b98877 | What's the difference between a "2 stroke" engine and a "4 stroke"? | Engineering | explainlikeimfive | {
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"A 2 stroke engine does two strokes per cycle: * One stroke down to provide power as fuel is burnt * one stroke up to clear exhaust then it repeats A 4 stroke engine makes 4 strokes: * one stroke down to provide power * one stroke up to clear exhaust * one stroke down to draw in fresh fuel and air * one stroke up to compress the fuel and air then it repeats The second system requires a more complex engine, but because it draws and compresses the fuel air mixture and is better at removing exhaust it's more efficient. Further 4 stroke engines are lubricated by spraying oil in the cylinders, while 2 stroke engines are lubricated by mixing oil with fuel. Oil doesn't burn as well as fuel, so partially burned hydrocarbons are part of the exhaust.",
"In a 4-stroke engine each piston goes through a four \"stroke\" cycle. Intake (down), compression (up), power (down), and exhaust (up). In a 2-stroke engine exhaust and intake happen at the same time, at the bottom of the power stroke. So the piston only moves up to compress, and then down once each cycle. 2-stroke engines are simpler, lighter, and cheaper but also generally less efficient, dirtier, and develop less power at low RPM. Most lightweight 2-strokes also require that the fuel be mixed with oil to lubricate the engine."
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b9g8tn | How does Solar Energy production work? Exactly what are we harnessing from the sun? | Last year we got solar panels installed on our house, and I'm just curious how it all works. Thanks in advance. | Engineering | explainlikeimfive | {
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"It's something called the *photovoltaic effect,* where the energy from a photon of light gets absorbed by the atoms that make up the solar panel. This absorption energizes the electrons in the outer shell of the atom, making them jump up into a higher energy state, ejecting them from the atom and causing them to flow through the panel, creating an electric current.",
"This is a really good question, and the answer depends on what framework you're dealing with in your physics equations, but boils down to \"light\" in the simplest terms, or more specifically \"light energy\". But we don't instinctively think about light the same way we think about electricity or energy, when they're essentially two sides of the same coin. So let's talk about electromagnetic radiation, which is the broad term for what light is. Electromagnetic radiation is the term we use to talk about the movement of photons through space; photons being the fastest known things in our universe. They are massless, so they can travel at the speed of light without violating the laws of relativity, and we talk about them based on their energy level, which is essentially how fast they vibrate. We usually think about the visible light spectrum: ROYGBV (get out of here Indigo, you're not a real primary color), as what we can see. But we also know about infrared (what your TV remote uses) and ultraviolet (what gives you sun burn and skin cancer) radiations, that also come from the sun. These are all the same thing, essentially: photons vibrating at different frequencies. The sun's constantly going through nuclear fusion reactions that are throwing out all sorts of radiation due to the forming of subatomic bonds being a very energy-intensive process, and that excess energy throws off photons at different energy levels. The higher the energy level, the more dangerous it is to living things (since the frequency/energy level getting higher means that the photon can get through smaller spaces at a subatomic scale, and high-energy radiation breaking the bonds that hold our DNA's cell replication instruction together is essentially how most cancer starts). At the lower end of this spectrum, even lower than IR waves, we have radio and wi-fi carrier waves, and also microwaves (which, you'll remember, heats up food). And that's the thing to remember: All of these light sources will transfer heat (which is just another way of saying that they will transfer energy) when the protons hit something (the light doesn't shine *through* the wall of your house, so much like a person running into a wall, it doesn't have enough energy to break it, so it just heats up the surface a bit. If it was just one photon, we wouldn't notice, but it's trillions per second across every square inch of surface that the sun hits. If you put that wall close enough to the sun, it would melt or otherwise be obliterated by the amount of energy it is getting hit by, just like if you take enough people running into it or pushing it, it will eventually fall over or break down). Solar panels, then, are made specially to be put in the sun, and have the electrons in their materials knocked free by sunlight, which then generates an electrical current that we can harness. (The material used in the panels is made specifically to lose electrons this way, but unfortunately I don't really know *how* they do that.) Once the electrons start a current flow, it can then be put through wires and stored with batteries.",
"Solar cells are made of silicon mainly. Silicon is an atom with 4 electrons in its outer shell but if we put in aluminium (3 outer electrons) or phosphorous (5 outer electrons), they replace some of the silicon atoms in the crystal lattice of silicon. This replacement causes a lack of electrons (p-type) or excess of electrons (n-type) because of the difference in the electrons in the outer valence shell. The magic happens when both of these are done right next to each other in the same silicon wafer. At the junction, these excess electrons combine and form a little neutral region but because of a kind of positive charge on one side and a kind of negative charge on the other, an electric field sets up which pushes any electron that appear in the neutral region towards one end. Light is an electromagnetic field and carries some energy. For example, infrared is also an electromagnetic field and that is what gives us the sensation of heat near a hot source like fire. We can feel infrared transferring energy more easily because we easily absorb it unlike visible radiation like light. When sunlight falls on the solar cell on the neutral junction, the energy from the light cause some of the neutral atoms there to lose electrons, which as we saw above get pushed towards one end. This causes an actual imbalance of charge on the two ends but because of the internal electric field pushing electrons in one direction, the electrons from one end cannot go to the other to correct the imbalance. This is the electric potential we get as output from the cell as attaching a wire to the 2 ends let the electrons flow from one end to the other through the wire. This movement of electrons is current which our appliances need to work. As to your other question, the solar cells fail after a time because the dopants (like phosphorus and gallium mentioned above) diffuse through the silicon and get to the other side which destroys the little neutral junction and the whole effect it had ends. Diffusion ruins a lot of semiconductors devices like computer chips too because when we have a high concentration of something next to low concentration, which happens everywhere when there is a metal contact at the semiconductor, diffusion takes place and there is no real way to stop it.",
"For the real ELI5: Light has a lot of energy, called photons. When you shine it on certain materials, the material gets all excited and moves its own energy, called electrons. But why do those electrons move? Well, what happens is a photon travels through space reeeally reeeally fast. Like a million bajillion times faster than you or me can run! And when a photon hits an electron, it kind of knocks it out of place. Like if I pushed you really hard, you would go flying! And since the sun sends us a LOT of photons, they knock around a LOT of electrons! If we connect a wire from one end of the material to the other, the electrons that get knocked around will go through it like a straw. And if we put something on that wire like a light bulb, the electrons will move all the way through the wire and light up the light bulb. Then they’ll go back into the material because they like to be in there. It’s like if you wanted to ride your bike around the block, and you got tired going through that light bulb, you would want to go back home and sleep! That’s pretty much how solar panels work!"
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b9gqvo | Why seatbelts sometimes look up while driving and sometimes they’re loose | Lock* | Engineering | explainlikeimfive | {
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"Seatbelts are designed to lock up when they are suddenly and quickly moved, like in a car crash, to keep the driver/passenger in place.",
"Many seatbelts also have a feature where, if you pull them all the way out, then they will only be able to retract (basically locking the seat belt against you). Letting the seat belt roll back all the way resets this."
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b9ru9d | why do digital (especially mirrorless) cameras still need shutters? | I understand that for film cameras, the exposure is solely dependent on the time duration for which the film is exposed to light. However, why do digital cameras (especially mirrorless cameras) still need them? Can't they just keep capturing the signal from the entire sensor for the shutter speed, and process the signal afterwards? From what I understand, that is how electronic shutters work, right? What is the advantage of having the mechanical shutter? Furthermore, why is there still a click when an electronic shutter is triggered? | Engineering | explainlikeimfive | {
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"The click from an electronic shutter is completely artificial. It's just for the camera user to let them know they took a picture. It's because we all got used to physical shutters for decades, and people got used to the sound and what that sound means, so they added the sound in, even though the camera doesn't make the sound. You should be able to go into the settings on your digital camera or your phone, and turn on or off the sound of the shutter if you want."
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b9tmcr | Why, when making a phone call and using the loud speaker, the other person doesn't hear himself but only what I say? | Engineering | explainlikeimfive | {
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"The phone's electronics know what sound the speaker is putting out, so they electronically subtract this from what the microphone is receiving. URL_0"
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b9txf3 | Why the windows of airplane are oval shaped? | Engineering | explainlikeimfive | {
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"The inside of the plane is under pressure and you don't want the windows bursting out. Corners are the weakest part of such a seal, so rounding the windows eliminates the weak points.",
"Corners are weak points some early jets had square windows and the planes crashed due to metal fatigue at the corners, so the windows are rounded.",
"Both of the other commenters are on the right track. Pressure is better contained in round shapes. Forces on a fuselage as it negotiates climb, maneuvers, and descent need a certain amount of flex and stretch. Hard corners provided a (bad) point of concentration for such forces as they try to spread the load along the fuselage. For THE example on the topic, see the original DeHavilland Comet.",
"Sharp corners are bad for anything that has pressure (like the inside of an airplane); the pressure can push apart the corners and burst open the container. This is why all [pressure containers]( URL_0 ) are round / mostly round; this distributes the pressure evenly across the surface.",
"DeHavilland Comet - \"world's first commercial jet liner - problems started to emerge, with three Comets lost within twelve months, after suffering catastrophic in-flight break-ups. Two of these were found to be caused by structural failure resulting from [metal fatigue]( URL_0 ) in the [airframe]( URL_1 ), a phenomenon not fully understood at the time. The other one was due to overstressing of the airframe during flight through severe weather. The Comet was withdrawn from service and extensively tested. Design and construction flaws, including improper [riveting]( URL_2 ) and dangerous concentrations of [stress]( URL_3 ) around some of the square windows, were ultimately identified. \""
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b9udfz | Why can't somebody program a script to try every password combination and hack the whole world? | Would it be too many combinations? | Engineering | explainlikeimfive | {
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"Yes, way too many. Trying a password takes time. The more security oriented the service is, the longer it takes. If you add 2 seconds to the password check time, you make things a lot harder. Using the [XKCD standard password]( URL_0 ) \"correcthorsebatterystaple\" you've got 26^25 possible combinations of the 26 lower case letters at this length. That's 2.4 • 10^35 . At 2 seconds each try, that 5 • 10^35 seconds. That's 1.6 • 10^28 years (16,000,000,000,000,000,000,000,000,000) and the age of the universe is 13,000,000,000 years.",
"As others have mentioned, bruteforcing your way through every possible sequence would take a very, very, very long time to [HACK THE PLANET]( URL_1 ). On top of that, websites tend to use [two-factor authentication]( URL_0 ) to increase account security. That way, if one password gets hacked, you still have to verify the account with a separate device. The chance of someone being able to bruteforce *both* devices devices is astronomically low (as long as you aren't a big dummy and use the same password for everything)",
"A 4 character code with 72 different characters available for use (26 letters both upper and lower case, plus 10 numbers, plus 10 other special characters) will give 26,873,856 possibilities. That's 4 characters only, or 72 to the power of 4, and I guessed at the 10 special characters, I'll bet it's more. I don't have any passwords that are that short, nor do most platforms allow it. Even 5 characters takes it to almost two billion possibilities. At two billion possibilities and a rate of one try per second, it would take over 63 years to try them all.",
"Because there are a lot of possible passwords. Imagine you have a single letter password. Only a single letter, no upper case no numbers no symbols. How many possible passwords would that be? 26 obviously: a b c d e f g h i j k l m n o p q r s t u v w x y z You can easily try all of these in no time at all. What if you have a two letter password: aa ab ac ad ae ... ba bb bc bd be ... za zb zc zd ze ... zw zx zy zz if ypi write all of them out you will have 676 possible password. because each of the 26 possible first letter will have to be combine with each of the 26 possible second letter meaning you have 26 x 26 passwords (you can also write that as 26^2) What about 3 letters: aaa aab aac ... zzx zzy zzz Now you have 17576 possible password ( 26 x 26 x 26 = 26^3) for each letter you add you have to multiply the number of possible password by 26. If you have an 8 letter password you have 26^8 possible different passwords which is slightly less than 209 billion passwords. If you tried 1000 of these passwords per second it would take you 6 years and 7½ months. That sounds still doable. Of course in real life passwords don't just consist of only lower case letters. If you add upper case you go from 26 to 52 possible letters, this doubles the number of passwords per letter. an 8 letter password that used both upper case and lower case would have 256 as many possibilities as a lower case one and we would have to try for 17 centuries if we tried 1000 per second of them. If you add number you end up with 7 millennia of try9ing 1000 per second just for an 8 character password that may contain uppercase, lowercase and numbers. If you add 32 special characters like these: !\"#$% & '()*+,-./:; < = > ?@[\\]^_`{|}~ You would have 94 possible characters (26 lower case, 26 upper case, 10 number and 32 special characters). An 8 characters password would have 94^8 possible passwords. This is 6 quadrillion and would take 200 thousand years at 1000 characters per second. Now this is just 8 characters. For many this is the absolute minimum and many more need more characters. Each additional character would make it have 94 times more possibilities. At 10 characters we are talking 1.7 billion years. For comparison the sun will engulf the earth is less than 8 billion years so just 11 characters would be enough to not be able to guess all potential passwords even if you had literally all the time in the world and guessed 1000 passwords per second. At 13 characters you could try 1000 passwords per second until the last star in the universe has gone out and not reach the end. It would really take a long time to try all these combinations. It gets worse when you realize that 94 possible characters are a very conservative estimate. Most modern software will allow just about any character to be used in a password that people can type with their keyboard. This can be stuff like umlauts like äöü and accents áà etc but also every single Unicode character there is. If you feel so inclined you can have stuff like the Chinese character for fire or a crying emoji in your password if the software allows it. This would bring the total number of password to much much more ridiculous heights. Of course the fact that most software requires you to use some combination of at least one letter, number or special character slightly lowers the total amount of password to try, but only slightly. In theory there is also the wrinkle that in real life the password does not get compared to an actual stored password but a hash of that password. Depending on the implementation that total number of hashes can be lower than the total number of possible passwords. This might sound like it would save you some time and allow you to get the right password with fewer attempts, but a simple 128 bit has would still represent 2^128 different possibilities, which would still take more time than our galaxy has likely left even if you tried them all at an extremely fast rate. Of course writing a script to try all the combinations is relatively easy. You could probably do it as a one liner in most script languages. The trick is keeping the computer running after all the stars in the universe have gone out and the question wether protons will decay if you wait long enough starts answering itself.",
"Even a 4 number code has 10,000 combinations. Regular alphanumeric passwords would take too long to guess"
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ba0vw1 | - If im using a portable battery to charge my phone, what makes it charge my phone and not pull battery power from my phone to charge itself? | Engineering | explainlikeimfive | {
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"Because the battery pack has different connections for charging and discharging. One port is connected to the circuits to charge the battery, and the other is connected to a 5v supply created from the battery. Some phones can act as power banks when connected with an OTG cable, which is the one with a socket instead of a plug. These detect the OTG cable, which is wired differently, and change the way they work."
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ba1c5l | why do home thermostats have a "heat/ cool" switch? Why can't you simply set a range and have it automatically determine whether to use the AC or the Heater? | Engineering | explainlikeimfive | {
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"There are actually thermostats that have an 'auto' mode that does switch from heat to cool and vice versa. Typically, only higher end thermostats have this, though. This is because it takes more advanced temperature sensors to allow an 'auto' function to work. Say it's summer and you have the thermostat set to 'cool', and 78 degrees. The AC blows cool air into the house, but it might reduce the temperature to 77 degrees. This is typically intentional, to increase the time between the system turning off, then on again as the temperature rises from outside heat. In this case, if you were in an 'auto' mode, the furnace would kick in, which would not be desirable in the summer! Premium thermostats that do have an 'auto' switch for heat and cool have extra setpoints or criteria before allowing the system to shift modes. For example, some use the date to determine what month it is, to prevent the furnace from being used in the summer. Otherwise, it would be 'turn AC on if temperature hits 80F, and furnace if it hits 70F' or something like that."
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ba2ptz | Why do washing machines have their own concept of time? | Engineering | explainlikeimfive | {
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"There's several steps in the wash that have a variable length, mainly the spin cycles. The machine will try to balance the load in the drum by speeding up and slowing down. It then tests if the load is balanced by speeding up and sensing how much wobble there is. If there's too much it slows down and tries again. This can take anywhere from 1 to 5 minutes and for a long cycle happens 3 or 4 times.",
"Often the delay will be caused by an uneven load during a spin cycle. My machine is a front loader and if the load isn't balanced it will keep restarting the spin cycle until it balances. So the timer says 8 minutes remaining for as long as it takes to balance the load.",
"\"if everything goes well,this will be done in about 5 minutes. You loaded shoes and rocks into an old machine. This may take longer than 5.\"",
"Yeah those aren’t “timers” per se. The machine has a lot of sensors to tell the state of the load inside and it’s estimating how long is left. It’s the same as when a computer tells you that installation will finish in two minutes but actually takes 30.",
"The time remaining is dynamic and can change based on inputs from the machine's sensors. Mine often beeps to say it's done, but then won't unlock the door for another minute or so. Bitch, you weren't done! Beep a minute later.",
"There are 2 main causes; If the washer detects soap suds in the spin cycle it will go back to the rinse cycle. If the washer goes unbalanced while spinning, it'll add a bit of water, shake it around a bit to redistribute the load, then start the spin cycle over again. Source: I am an appliance repair technician",
"Check all the filters! Ours was really messing up the timing, and then months later broke down. Turned out there was another filter I didn’t know about that was completely clogged. Got that fixed and now it’s pretty much spot on in terms of time left.",
"Thought it was just me. Put on the washing machine and it says 1H remaining. I calculate that I can hang dry my laundry and leave 1H later at 1600h. At 1600h, it's still 12min remaing.... 😑",
"I think the machine also tests the exhaust water at the end (depending on the cycle mode) to check if it is properly rinsed/more or less dry. If not, then it might continue for a while longer.",
"Fuzzy logic control. The machine has an idea how long a process should take but it uses feedback to alter to cycle length to achieve it's target performance criteria. Example, you know a generic cup takes two minutes to wash. But if the cup is very dirty and after a minute you see it will needs to be scrubbed longer increasing the time needed. Alternatively a clean cup you see is clean after a very short time scrubbing and the time needed is less then a minute. In this example the feedback sensor is your eyes and target criteria is based on this feedback. In a washing machine this could be a turbidity sensor looking at how much \"dirt\" is suspended in the cleaning water."
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ba4fg9 | 240VAC between live and ground, but 0VAC between me and earth/live | If I probe my electrical outlet, there's 240VAC between live and earth, and 0VAC between me and earth. But there's also 0VAC between me and live. Does that mean I can grab the live wire and be completely safe if I don't close the circuit? | Engineering | explainlikeimfive | {
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"No, and don't try it. The meter has 10 million ohms resistance so when you measure between the live wire and you there is some current limiting. If you are completely isolated, then grabbing the live wire will still cause some current to flow due to capacitive coupling. And there may be leakage current which changes rapidly and without notice. It is true that a bird (or you) can sit (or hang) on a power line without being electrocuted, but in that case the bird or you are completely isolated from any ground."
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ba9g84 | Why does adding a "radius" or "fillet" reduce fatigue in certain metal joints? | Engineering | explainlikeimfive | {
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"Sharp edges are stress risers. Stress is defined as a force applied over an area. So if you apply a large force over a small area, you get high stresses. This idea of stress can be used to calculate when something will fail. When you get dramatic changes in geometry, you get large stresses. A sharp corner is a very dramatic change in geometry, so you will get a very high stress at that point. The higher the stress the sooner a part will fail due to fatigue. Fun fact: This is why many packages have serrated edges. It makes them easier to rip open.",
"Stress kinda flows like warer threw the material. So all the stress has to go suddenly around a sharp corner and therefore a stress peak emerges."
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baatpj | How come sometimes a pen will write perfectly fine on one part of the paper, But won't work at all on other parts of the paper? even when writing with the same angle and pressure? | Engineering | explainlikeimfive | {
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"The bad pen can stop working if you touched the paper with sweaty on greasy hands. The oil reduces the traction between the ball on the tip of the pen and the paper (it stops rotating as you move the pen, so the ink doesn't get out. The good pen doesn't have this problem because the tungsten ball is better and the ink is more liquid, not much, but enough to get out more easily. I am not the pen expert, this is just my 2 cents :) . EDIT Wow I didn't expected so many upvotes on this comment :D. I have never had so many points on anything I posted, my karma is doubled in the past 4 days lol #karmawhore",
"Greasy paper, usually. The oils in your skin or wherever else your paper may have been exposed to oil stops most pens dead in their tracks.",
"There is a small ball in the tip of most \"ballpoint\" pens. As you drag the pen across the paper the ball deposits the ink on paper from the part that is in contact. As you continue the ball rolls and the portion that deposited the ink rolls up inside where it comes in contact with the ink in the reservoir. Sometimes the ball gets stuck. Sometimes you move it in a way (small circles) that the depleted portion of the ball doesn't have a chance to get re-inked",
"I have noticed this using cheap paper, a long time ago I watched a documentary on paper making and apparently they add granite dust to the paper to make it more gritty so that the pen ball will roll over it rather than sliding. My guess is that there are places on the paper that did not get treated as evenly as others and that is what leads to the un even writing experience.",
"If you find this happening on a *clean* piece of paper, it is probably cheap paper. Cheap paper can have an uneven \"finish\" so that part of it will be \"matte\" and part of it is \"glossy\". Most pens are designed to write on \"matte\" paper.",
"it's because that part of paper has been greased by your filthy oily finger. text text text because if stupid bot text and more text text text",
"The pen relies on friction between the ball point and the paper to deposit ink on the papaer. Assuming as you point out that all parameters related to the pen haven't changed, then the most likely explanation is that the something has made the frictional properties of the paper to change and therefore the ballpoint can not properly deposit the ink on the paper.",
"This might not answer anything but a pen will write easier if you put a second piece of paper under the first piece of paper you're writing on.",
"It can also be caused by imperfections in the paper itself from the manufacturing process. Candy bar wrappers, sandwich bags and other contaminants from employees can get into the pulp and wreck havoc on the finished paper product. It’s not just pen defects or skin oils. Many paper mills ban vending machines for this reason and have lunch/break rooms located away from the manufacturing facility.",
"Either the ball in the ballpoint pen tip isn’t rotating due to an external coating (oil from hands and wrists) deposited on the paper before writing, or the paper isn’t gritty enough to cause the ball to roll.",
"The ball in a ball-point pen has to roll/rotate to put ink down. Some parts of the paper are different, and don't make the ball roll enough to make it write. This is usually because of how the paper is made. Try writing on wax paper that comes on the back of adhesive stickers with a ballpoint pen. It's infuriating."
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badyyp | Why is it so difficult to store renewable energy? | Engineering | explainlikeimfive | {
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"Because energy storage sucks. Anytime you convert energy from one kind to another there are losses. You can only convert so much energy at a time, the storage only works for a limited time versus something like a generator that keeps going if you add more fuel. Batteries - expensive, limited lifetime, take up room, typically are more efficient when discharged or charged slowly. Heat or extreme cold makes them less efficient. Not light. Pumped storage - requires land for pond or dam, hydroelectric turbine, water evaporates leading to losses, etc."
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bajgrg | What is a CVT in a car and why do a lot of people hate it? | Engineering | explainlikeimfive | {
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"You've probably seen a multiple speed bicycle with 5 or more gears on the rear wheel. If it were a CVT, it would look more like one cone, rather than distinct gears, where any spot on the cone can be use. So between 2 of the bikes physical gears, the CVT can great anywhere between the 2 gears. People hate them because they are soft shifting, especially when compared to a manual shifter. Beyond simple feel, the cars they are put in tend to be smaller cars and the shift points tuned to higher mileage over performance, although most have sport mode and manual shifting that is able to be enabled via the shifter or a button.",
"A CVT is a type of automatic transmission that, in it's purest form, does not have several \"gears\"; that is, first, second, third, fourth, overdrive, etc. (CVTs do have reverse, though.) & #x200B; A CVT avoids the need for \"gears\" by using two cones, facing in the opposite direction, with a V-shaped belt between them. By moving the cones, you change the ratio between the two cones, thereby changing the ratio of engine rotational speed to axle rotational speed. & #x200B; There are two primary reasons for having a CVT. First is to make best use of the engine's optimal performance range. Second is to provide a smoother experience by avoiding the need to shift \"gears\", either automatically or manually. CVTs are excellent in small cars with limited power, making up for the loss of power experienced by a traditional automatic transmission. They also help with fuel economy. CVTs also have far fewer moving parts which, in theory, mean less things to break. I don't know if that's proven to be true or not. & #x200B; Because of their design, driving a true CVT is an odd experience; however, many CVTs offered these days are not true CVTs. I say that because consumers complained so much about the new and odd behavior and \"feel\" of CVTs that auto manufacturers programmed the CVTs to act more like an automatic transmission; that is, they used software to create shift points, so the car feels as if it is shifting \"gears\", even though it actually isn't. & #x200B; Some people comment you lose the ability to perform engine braking with a CVT, and that's mostly true. Because of that, the cruise control doesn't hold speed well when going downhill...something I've noticed on my car. For me, it's not a big deal since I never engine brake anyway. & #x200B; I love manual transmissions, but they are a PITA in the city/traffic. For me, the CVT is a great choice for an automatic transmission...much preferred to the standard type of automatic."
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bajyzx | How does exhaust affect engine performance? | Engineering | explainlikeimfive | {
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"I'm guessing you mean how can changing the exhaust system on a car increase performance? When combustion happens in an engine, fuel and air is burnt in the combustion chamber, this causes an expansion which pushes the piston down. This is what generates the power in a normal car engine. However this combustion of course results in leftover gas, which is the exhaust gases which have to be pushed out of the chamber so that new air and fuel can be sucked in. The power generated from the expansion is however also used for pushing the gases out and sucking in more fuel and air. In short, the output power is the generated power minus the work the engine has to do, this includes pushing exhaust out. A sportier exhaust system has less flow restrictions than a stock one, more flow in the pipes makes pushing exhaust gases out easier and therefore subtracts less power from the expansion. More airflow in the exhaust can be achieved by having straighter, bigger pipes and no muffler for example. Sorry for the novel but I hope it was easy to understand"
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bal9k3 | Why do modern vehicles still use a dipstick to check the oil level instead of an automatic gauge? | Engineering | explainlikeimfive | {
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"Some do have an electronic gauge. But a dipstick is still best for numerous reasons: Physical dipsticks are crazy reliable! Unlike sensors, connectors and wiring which are all things that you dont want to fail on such a critical task. You can only use a dipstick while the engine is stopped which means if all your oil has drained out for some reason, you'll see that before starting the engine and have it make a horrible rattling noise to tell you it's dry. When you lift the bonnet to check your stick, you also subconsciously look around the engine bay and may notice something else. If you simply sit in the driver's seat and let the car do a check, anything could be happening under there.",
"A visual inspection of the oil condition is of great value. You can see if the oil looks dirty or if it's still relatively clean, and for instance, if your oil is frothy, you have antifreeze in your oil and have a serious problem.",
"Since the question is phrased 'vehicle'-let me add this. The Suzuki Burgman Motor Scooter does not use a dip stick or a sensor\\[save a 'low oil' light}. This machine uses a 'sight glass'. Which is to say, a circular window the size of a US quarter, with embossed lines to both edges, and marked \"F\" or \"E\". A whole world better than a dip stick, IMHO."
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basq0r | How do optical mice work, and why do they have to touch a surface for it to detect movement? | I was wondering whether it would be possible to use the system of an optical mouse, but not necessarily have to use it along a surface. I want the same functionality, but I want to be able to hover the device above the table, not necessarily touch it. This is for an application different from what mice are used for. | Engineering | explainlikeimfive | {
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"An optical mouse has a camera underneath it. The camera constantly takes pictures of the surface beneath it, compares that picture the one it took a fraction of a second before, and from that determines how the mouse has moved. This camera takes highly magnified images of the desk surface, and, because of this, has a very short focal depth. If you lift the mouse a tiny distance from the surface, the images are now hopelessly blurred, all the images look the same, and it can't detect the movement."
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bb1y4x | Do ships use ocean currents like airplanes use the jet stream to get around faster? Is there an equivalent ocean "jet stream"? | Engineering | explainlikeimfive | {
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"Absolutely! Off the easy coast of the United States is he Gulf Stream, it runs northish about 5 miles per hour. Northbound ships will stay in the Gulf Stream while southbound ships will avoid it.",
"Absolutely, nautical charts don't just plot landmasses, they plot tides, currents, depths etc. Back in the age of sail, it wasn't just currents but also prevalent winds. The trade winds, for instance, derived their name from the fact that they were seen as essential for long-distance voyages. Following the right trade wind was like a highway for sailing ships."
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bb889d | how do contact lenses work to help you see? | Engineering | explainlikeimfive | {
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"Normal sight is made possible partly because of the part of your eye called the lens. It is an oblong shaped piece of clear tissue that bends light. It is shaped in such a way that light entering from various angles is all bent so that they hit the same spot on the retina on the back of your eye. Eye sight problems can be caused when this lens is not shaped correctly, meaning light does not bend all the way, or bends too much. Artificial lenses, like contacts and glasses, fix this by bending the light as well, in such a way that when it hits the natural lens of your eye, it is able to bend it appropriately to hit your retina in the right spot to focus one the image."
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bbax1b | Why do high end sports cars have scissor doors? Is it just for aesthetics or is there a practical reason? | Engineering | explainlikeimfive | {
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"Typical high end sports car are much wider than regular car due to increased performance and the scissor door in high end sports car allow their owner to exit the vehicle easily even parked in between cars. By having the door opening up instead of traditionally outward, the owner would gain a lot more opening to get out of the car vs having to squeeze between the car and the door to not dent the other car.",
"One of the first modern cars to have doors that didn't open from the front or back was the Mercedes gullwing, and it had upwards-opening doors for structural reasons. A door represents a big hole in the structure, which means a weak point in the lower part of the chassis; high-performance cars generally want a stiff chassis that doesn't flex during cornering, so to reduce the impact of the door on that crucial structural part they moved the door up. Today, we've largely figured out ways around that so many modern supercars will have fairly traditional doors, but it's still a valid way to give yourself a little extra room to fit structural components so you see that the serious cars still have it."
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bbi5nt | why don’t toilet drains go straight down? Wouldn’t that make blockages less frequent? | Engineering | explainlikeimfive | {
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"If they did, sewer gases would also come straight up. The p trap is an intentional block using the toilet water to stop sewer gases from coming into your house.",
"Almost all drains, sink, shower, toilet have a p trap to keep a small plug of water to seal the drain and keep sewer gases which can smell had and have toxic gases as well from coming into the house. And you'll have a roof vent or ideally one vent for each branch of the sewer line to vent out sewer gases and to equalize the pressure in your sewer lines.",
"If drains went straight down, they would be directly connected to the sewer line, and all of the smells and dangerous gases could get directly into your house. Traps keep a water \"block\" between the sewer line and the house. Sinks, showers, tubs, and even washer drains all have traps. Until the 1940s, some houses were built with whole-house traps, a single trap outside the house that prevented gases from getting in and allowed the \"straight-down\" drains that you have asked about, but they have not been allowed by most building codes since then because they were difficult to maintain. The current P-traps or S-traps are better at creating a higher velocity of water thus somewhat cleaning themselves.",
"Ooh ooh I know this one! Funny thing about piping is that it always smells bad down there. ALWAYS! Also, contrary to what one might think, pipes are mostly empty, only carrying stuff when you flush or shower etc. So in order to prevent bad smells from coming back up, your toilet (and sink and shower) use a neat trick to block the nasty gases: that twisty loop. It creates an obstruction made from water that saves you from febreezing your house 24/7",
"Because first off it traps smelly gases from going back up the toilet, and second because toilets are actually flushed by water momentum. Once water starts flowing into the bowl quickly, it will completely empty due to the momentum of the water continuing to suck the rest of the water in the bowl down with it. Your toilet also pours a little extra water in the bowl to refill it and the trap as the tank fills up.",
"Aside from the sewer gases issue, any toilet not on a ground floor would have to have a pillar on the floor underneath for the shitter pipe rather than having the pipes in the walls, and this would rather quickly become a problem in apartment buildings. And have you never accidentally dropped a thing in the toilet? You wouldn't get it back! I've noticed different countries generally have different toilet depths / water levels in the toilet. In the UK the bowl is quite deep and the water level low, whereas the American toilets I used were mostly very shallow with tonnes of water in them.",
"I can just picture all the plumbers in this thread cracking their knuckles and getting ready to type.",
"It’s by design. Toilets and sinks use what’s called a P-trap to contain fumes from raw sewage pipes. It’s a very basic plumbing technique that’s been around for as long as plumbing. Basically, water sits at the bottom of a U shaped pipe so that air from sewage pipes can’t pass through the drain.",
"Technically, toilets (at least in the U.S.) are just really large porcelain p traps (s bends).",
"Sewers smell awful! Toilets and sinks have that bend so that the water prevents that smell from getting into your house.",
"\"Blockages\" I'm now remembering the story about the family with robust bowel movements who had a communal 'poop knife' that was not stored in the bathroom, because multiple bathrooms and only one 'poop knife'."
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bbijtw | Why do formula 1 racecars not have windshields? Doesn't that make it less aerodynamic to just have the driver exposed? | Engineering | explainlikeimfive | {
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"I believe it’s a safety thing - to make it easier to get out in a crash and they do crash a fair bit. It certainly would be more aero to have an enclosed cockpit.",
"actually they do have a windshield (although it's a tiny one) and it divert / deflect the wind away from the driver / cockpit area if you are refer to a fighter jet cockpit style windshield / canopy, few years back some testing has taken place for the purpose of improving safety but at the end F1 has adopted the \"Halo\" instead due to visibility issue F1 Driver Sebastian Vettel reported that he felt Dizzy after driving with windscreen equipped on his car"
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bbjisr | Why do Americans always talk about oil changes in their cars, while in the UK there is seemingly never any mention of it. | Engineering | explainlikeimfive | {
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"Most people here probably just get it done as part of the routine servicing and don't have to think of it separately. Do American cars get regular services by garages or dealers?",
"Couple of suggestions:: * Because all cars need to have a yearly MOT testing and * Because emissions and fuel economy can incur financial penalties (insurance, tax, congestion costs) \\- keeping an old car can be no longer economic so there are fewer clapped out old cars on the road. Newer cars don't need an oil change as often as old cars with dodgy engines. * Because in order to sell on your car for a good price you need to have a log book that shows its service history \\- people tend to have their car serviced regularly (yearly) An oil change is usually included in that process so there is no need for it to be done as a separate item. People are more likely to say \"my car needs a service\" than \"my car needs an oil change\".",
"I used to own a garage here in the UK, Almost all of my customers who didn't run classic cars would have the MOT and service done together (it saves money too) but it means it is all done in one go with no hassle, They would leave it with me in the morning and collect after work with a fresh MOT and a full service done. Most people here do few enough miles that the once a year oil change is perfectly fine, Indeed for many of my customers the oil change was early every year as they just didn't cover the mileage, I only recall a few cars needing oil changes more often and those were taxis that did airport runs and rep mobiles. So for many here it is simply a part of the annual routine and there really isn't much to talk about."
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bbl8gj | When do you use the different gears with an Automatic Transmission? | Engineering | explainlikeimfive | {
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"This article explains it pretty flawlessly if you have a few minutes URL_0 Essentially, if you have 4,3,2, and L, then your gearbox has 6 gears to choose from (not counting reverse). L (low range) will hold the gears much lower than they would be if in D(rive), allowing the engine to provide more torque, for towing or steep hills. Selecting 4, 3, or 2 will limit the maximum gear that the gearbox will go, but other than that it will behave as it would in D."
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bbp0vc | What causes the random patterns on a TV screen when it is broken, my guess is that pixels have a default pattern to display show that would be displayed | Engineering | explainlikeimfive | {
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"Depends on the type of screen, and the manner in which it's broken. You said \"pixels\", so we'll talk about LCD screen. LCDs are made of several layers with different functions. Here's a little rundown with points of failure: Glass layers protect your screen, but can crack and chip. They would then refract light differently and inconsistently - possibly obscuring anything below it. Minor damage won't be too bad. The polarizing layers are for ensuring that the light coming from the screen is the right \"polarity\". Through this layer you can see the coloured light from the liquid crystal layer - if this layer is damaged you may instead see the backlight or no light. The backlight is a bright white. There are two electrode layers, one in front and one behind the liquid crystal. These allow electricity to flow around the LC, which changes their orientation, which changes how light refracts through it. If these fail, the LC layer will become uncontrollable and cannot display images. The liquid crystal layer itself, as mentioned, is controlled by the electrodes around it. The name states that it can act like a liquid but has a crystalline structure. The alignment of these crystals is important for the colour that comes through - breaking it will cause patterns like you mentioned. There's no default pattern, just the way the crystals end up aligning themselves based on where and how they were damaged. Then in the back is a backlight. If that breaks it will likely not emit light, or it will flicker. Drop or hit an LCD screen and a bunch of layers will break. A broken screen looks the way it does because of a series of failures combined. I doubt you meant CRTs but here's a short summary of those. If the tube in question breaks it will stop shooting electrons at the phosphor. If the steering coils fail it may prevent sections of the screen from lighting up. If the phosphor gets damaged it will change how electrons light up the screen. If the glass breaks there will be refraction issues."
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bbqif7 | Why are ships always being scrubbed ? | I recently moved to a place with a great view over an industrial canal. I enjoy watching all the ships go by. But I'm mystified by the amount if scrubbing going on on these ships. These are all industrial ships carrying either containers, dry mounts like sand and such, heavy equipment to large for road transport etcetera. Almost always there is at least one person with a hose scrubbing parts of the ship, even when it is raining or freezing. Why is this ? Do ships really need to be continuously cleaned for some reason or are these people just really bored ? | Engineering | explainlikeimfive | {
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"Salt water is extremely corrosive, so ships need to be almost continuously cleaned and repainted to keep them from rusting away. You'll see it with all kinds of ocean-going vessel, including cruise ships and military craft.",
"Military ships have far more crew than what's needed to operate the ship. This is so that they have 1) spares to replace combat losses, and 2) people to perform damage control and emergency repairs during combat. However, that means that they ALSO have lots of sailors on board that don't have enough truly productive work to keep them occupied. It would be bad for \"good order and discipline\" to let the crew get lazy, so . . . busy work. Sailors don't strip and wax the floor because the floor needs new wax, they do it because sailors need to be kept busy. They don't get told to work on painting a corridor until they've used up all the paint because the corridor is badly in need of a new paint job. Source: Six years in the US Navy."
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bbr7jx | How exactly is the data (an image, a movie or a song) stored on a computer? | Any detailed explanations would be great. I know it has something to do with 1s and 0s but, please.. explain like I am 4. | Engineering | explainlikeimfive | {
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"There's several layers to it. But in essence it's still 1s and 0s. First, you have the physical layer. Depending if you're storing it on a hard drive or flash drive (like an USB or SSD) Hard drives literally have a disk inside with an arm that reads or writes data by checking the magnetic field of the surface of the disk. SSDs and Usb drives work differently because there's no physical way of seeing what those 1s and 0s are. Instead, they have transistors, wich are basically tiny tiny switches that you flip on (1) or off (0). **EDIT:** There's no holes on a hard drive. Those are on DVDs or CDS, wich have creases or bumps that a laser reads as data. After that, you can use bits (a one or zero) in groups (bytes) to form more complex lines of codes. A byte is just a group of bits. Another layer above that is how your computer \"reads\" the zeros and ones to know what those bits are meant to be. This is way more complex than this but basically your computer knows how some types of files are meant to look. So your pc already knows the basic structure of an mp3 before ever seeing one, it then recognizes the file and uses a specific tool to open it (iTunes for example). If you change the extension of the file from. Mp3 to whatever extension like mp4 or pdf or whatever, essentially nothing happens to the data bytes, but your pc won't know how to use it's tools to view the file."
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bbvv2s | Why are some buildings not rectangular? Their tops are L shaped | Why are some the top of buildings L shaped instead of rectangular? Ex: one half of the building is 40 stories, the other half of the building is 32 stories, or sometimes even as low as only 5 stories Wouldn't the real estate developers want to build a rectangular 40 story building to maximize rental real estate? | Engineering | explainlikeimfive | {
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"There can be regulation needs. Or simply aesthetic desire for more visibility (imagine all the buildings in a row arw 40 stories - they have good views front and back but nothing to the side. Make half the building 20 stories high and now three sides of the top half have good views - can charge more! There may not be the demand for as much floorspace as making it all 40 stories would provide. And building higher is expensive. All these and others will be considered"
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bbzomk | If you keep turning on and off a light/lamp it may "break" and not work anymore. How does this happen exactly? | Engineering | explainlikeimfive | {
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"Old lamps emit light by having electricity course through a very thin wire, heating it to extreme temperatures. This causes it to emit light. But heating/cooling it too much puts stress on it, and it can break. When it happens electricity can no longer circulate, and the lightbulb is broken.",
"incandescent and halogen (filament) bulbs have a high inrush current, because cold things have a lower resistance than hot things, so in the fraction of a second until the filament heats up, you'll have a higher current going through, which can stress it. AC causes filaments to vibrate because it's making a magnetic field across the filament coils that switches direction 60 times per second. Since there's a higher current when you're switching it on, the magnetic field is stronger (it's still weak of course, but the filament is pretty weak) so you have a filament that is moving a lot, which then gets heated up quickly and boom. Bulbs will almost always burn out when you switch them on, rather than during use. Also, DC bulbs last longer because the magnetic field doesn't switch back and forth. Also, next time you're in a theatre that hasn't moved entirely to LED fixtures and are still using halogen bulbs, look directly into the fixtures that aren't 'on', and you might see that there's a tiny glow. It's practice in some places to prewarm your bulbs so that if you have cues that require the lamps to go on quickly, it reduces the inrush, and makes it less likely to burn out when the lights are turned on."
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bc154c | Why do we use dogs instead of technology for smelling. They seem very unreliable. | Engineering | explainlikeimfive | {
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"A well trained dog is both incredibly reliable and an incredibly sensitive instrument for picking up odors. Depending on the breed, a dog's olfactory sensors (smell receptors) outnumber humans by 50 times, and the part of their brain dedicated to analyzing information from the olfactory sensors is 40 times larger than the comparable area in human brains. Robot/machine noses do exist, but they tend to be good for limited applications, and can get \"confused\" easily. For example, they generally must be tuned to pick up a specific molecule in a specific ambient concentration to have a positive read, and they can be overwhelmed by similar molecular compounds or otherwise produce false positives for any number of reasons. Current technology for many (most?) smell-based investigations are simply not as advanced as what a dog possesses naturally."
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bc4twt | What is the hole near the top of a Lollipop stick for? | Engineering | explainlikeimfive | {
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"So that some of the candy goes inside it and helps secure the candy to the stick. Otherwise they might separate too easily."
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bcccu8 | How do the SpaceX boosters stay upright when landing? | Engineering | explainlikeimfive | {
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"1) The rocket engines swivel so they can push sideways and keep the rocket straight. 2) There are [\"grid fins\"]( URL_0 ) at the top of the booster that can pivot to steer the rocket like an airplane's tail fins. 3) When the tanks are empty of fuel, most of the weight of the booster is in the engines, which are down at the bottom. So landing is still a tricky process, but the boosters are less tippy than they look.",
"There are grid fins and cold gas thrusters on the rocker that control the orientation of the rocker. The tocket engine are gimbaled so they can be swiveled side do side so you can control it that way to. When the engine is not on you have to remember that the rocket is mostly empty tanks and the heavy part is the engine on the bottom so it will as long narrow object with one heavy end fall with it pointing down. The problem to keep the direction when the engine is one is the same when you land as when you launch the rocket and it is done by gimbaling the engines. When it is on the ground it is stable because of the landing legs that is extended. All of this is done by the computers in the rocket.",
"Cheers to you all for taking the time to give such great answers for me. The sight of the boosters landing simultaneously is one of the most incredible things I've ever seen. Humans are capable of doing some pretty amazing things!"
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bciffc | Why is there height restrictions on amusement rides? | Pure and simple, is there science behind it? Is it a way of enforcing age restrictions without actually enforcing age restrictions? ELI5? | Engineering | explainlikeimfive | {
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"Tall person bang head on pole, small person slip out safety restraint. Both not ideal scenario.",
"It’s safety reasons. Restraints can’t fit all people due to the design. Source: I was a ride operator.",
"One of the main concerns when designing a ride is to make sure the people riding it go where you want them to go, which means keeping them riding as opposed to flying out of the vehicle. Usually this is done by applying some sort of lap bar or shoulder harness which keeps them in their seat, but this of course only works on people of a certain size and shape. If you want to press down on their shoulders and trap their torso in place, but the person's shoulders and torso aren't there, the person isn't going to stay put. Then when the ride flings around loops and curves some midget is going to be hurled halfway across the park to impact somewhere like a rotten watermelon. Another issue is that the ride is going to be passing by various objects, perhaps scenery or the supports of the ride structure itself. It wouldn't be a good thing if a rider is 9 feet tall and when the ride zips past a steel strut it takes off their head, showering the other passengers and surroundings in arterial spurts of blood. Insurance premiums go up, cleaning is a big chore, etc."
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bcklgq | How do hackers find the IPs of specific locations like power grids, nuclear facilities, etc? Are there other non-physical forms of "making contact and getting in" apart from an IP? | Engineering | explainlikeimfive | {
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"For a start, there's services like Shodan. ### Shodan Shodan is like Google, except rather than searching for webpages, you search for services running on specific ports which are exposed to the internet. On top of knowing almost every exposed port, it also does things like fingerprint the software behind those ports, which kind of server it's running, its version, if any known exploits work on it. If it's exposed to the internet, chances are Shodan and similar services know about it. Armed with a list of services you can now throw exploits at them, millions at once from hundreds of thousands of compromised computers all over the world in illegal botnets. The ones which succeed get reported back to a command and control server, and then that entry point is used to start scanning around inside, effectively trying to identify where the original server is, and what else it is connected to once inside the firewall. ### DNS scanning What about something a bit more available? Well most services are run on specific IPs that have a DNS name attached to them, to make things easier to work with. There are many services out there which help map which DNS name maps to which IP, and of course, because it's a DNS name you know they all tend to be connected. Here's Reddit for example - URL_0 Click \"more\" on observed subdomains and you can find hundreds of relevant IPs and services. ### Humans suck Alternatively, you target the weak link, this is almost always a human, and by and large humans are a bit dumb. You find the target that you want and then spear phish it. Find the email addresses of people working at the facility and then contact them through it, maybe try to get an immediate foothold by attaching a trojan (most people will open an infected PDF, office macro, or click a link if you send it to them, if you social engineer them well enough e.g. \" < plant manager name > . Please see the attached doc, it contains a report on staff performance and we need you to check it over. Signed, < Name of executive you found on their website > \"). Let's say you don't want to expose yourself by attaching an offensive payload, you can still use this technique to do recon, even a simple reply can potentially give valuable information, such as a series of IP addresses used when the person replied, that might help you narrow down your potential Shodan results from billions, to a few thousand. ### Feeling Around Either way, once you're inside, you're usually past the main defences, the perimeter firewall. It's then a case of moving about inside. Once you've got the ability to execute code inside the network you can then try and connect to other machines inside that network, and run exploits on them, even if they were not directly accessible to the internet. The goal is to move between servers and computers (this is called lateral movement) while trying to gain access to something that would allow you to reach more important computers (escalating movement), for example a technicians PC might not be crucial, but if they've got the admin password to the control system stored in password.txt, or if you can secretly install something like a keylogger, then it's is going to allow the attacker to access something potentially more damaging. ### Unlimittteddd Powarrrr What's more damaging? Well there's usually a handful of servers which are responsible for controlling all the other ones, these are often called domain controllers, or SCADA systems which control machinery. When the US/Israel wanted to shut down Iran's nuclear program, they hacked the SCADA system controlling their nuclear enrichment centrifuges by using software which would move between windows systems inside the refinery plants, until one of them was eventually connected to the heavily protected control system, at which point it took control. ### Opening the door, reaching back out Regardless of how an attacker gains a foothold, once they're on the inside, it's common do what's called a reverse shell, or reverse connection. The infected computer or device contacts another server on the outside, and waits for instructions. Outgoing traffic is usually much less restricted than incoming traffic, and offers a more reliable path through the firewall. ### Back to the original question So in general... the external IPs are not overly important. While they certainly can be used, targeted attacks at a specific location tend to try and find their way in using other methods. Other than that, it's just a case of throwing a few billion requests at things and seeing what sticks... then take your pick from the results. I think there was a defcon talk a few years back when they did a random IP scan of remote desktop.. and the first thing which came up was the monitoring screen of some kind of chemical plant. Found it! URL_1 Edit: Cleared up a bit of text, added headers, added the link."
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bcqokd | What is the purpose of a canard on an airplane? | A canard being that wing structure on an airplane's nose. | Engineering | explainlikeimfive | {
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"Canards can help with a variety of things 1. Extra lift - They're another wing at the front of the plane so they provide additional lift 2. Lower stress on the main wing - When you try to climb, the elevators on the tail push the tail down, this also puts a downward force on the rest of the plane that the main wings have to overcome to climb. 3. Better maneuverability - You can now raise the nose while lowering the tail and the additional control surface(turny bit) up front increases the overall maneuverability of the plane. 4. Stall prevention - You can make the canard have different dimensions than the main wing so that it stalls out at a different angle, this means you can pull a tighter turn than your main wing would normally allow 4. Looking cool! - Because they do",
"Canards reduce drag and increase efficiency. A traditional design (with the stabilizer on the tail) has the wing and the tail *opposing* each other. The wing is trying to lift the plane up at the center of gravity, but that also means the nose will want to pitch up. Without a stabilizer of some kind, the nose will simply pitch up until the plane stalls, and then your plane crashes. The tail applies a small force forcing the nose to pitch *down*. When these two forces are balanced, the plane stays level. But that means you have two forces opposing each other. The wing is trying to lift the nose, and the tail is trying to drop the nose. Since the tail is obviously connected to the rest of the plane, if it is applying a *down* force, the entire plane tries to go *down*. That means your wing has to lift *up* an equal amount to overcome this overall *down* force. Whenever you put a force on a plane in any direction other than forward, you must also increase drag as your flight surfaces push air in a direction. You're creating a down force, which increases drag *and* makes your plane want to go down, so your wings have to add a little *more* drag to keep your plane going up. With a canard design, the stabilizer is in front of the wings. The wings are generating lift at the rear of the plane, so the *rear* wants to go up instead of the nose - which will case the nose to drop. To counter this, the stabilizers are creating a slight *up* force on the nose of the plane. Both surfaces are making your plane go *up*, which is what you want your plane to do anyway! So instead of your wings have to do extra work to counter the stabilizing force, your wings have to do *less* work because the stabilizing force is also helping your plane go up. That's less drag, which means more efficiency. The downside is that your plane is less stable, especially if you have a plane with a puller-prop configuration (that is, a propeller on the front of the plane, pulling the plane forward). The air that moves through the prop is accelerated and washes over most of the plane behind it, which includes any control surfaces. That means at *zero* airspeed you can still have a little bit of control because the prop is moving air over your control surfaces, even if the plane isn't moving forward through the air. With a canard, the prop is probably in the back so there's no prop wash going over your stabilizer. If you are at low or zero air speed, you have zero control. Even if the prop is in front, the prop wash is \"dirty\" air and is too turbulent to \"stick\" to the control surfaces the way it should to give you control. Also consider a stall - that is when there isn't enough air flowing over the wing in the right way, so the flow separates from the wing and you lose lift. This happens if you're going too slow *or* if the angle-of-attack is too high - meaning, the wings are pointed too far up relative to the direction the plane is going. If you're in a stall, you want to pitch the nose of the plane down, lowering your angle of attack so that you can 1) reduce drag so that you can increase your airspeed, and 2) get air flowing properly over the wing if they were already pitched too far up. Fixing a stall usually means pointing your nose towards the ground and letting gravity speed you up. In a traditional plane, what happens if your wings stall? The wings normally want the nose *up*, so if the wings aren't working, the opposite happens and the nose comes *down* - exactly what you want to happen anyway. If you stall so badly that even the stabilizers on the tail stall and don't give you any control, the plane is still going to want to do what you want it to do. With a canard, the wings want the *rear* to go up. What happens when the wings stall on a plane with canards? The opposite happens, and the rear goes *down*, which means the nose goes *up* - that is the *opposite* of what we want to happen. That's increasing your angle of attack, which is putting your plane deeper into a stall, which is *very bad*. And the canard wings themselves at the front of the plane naturally want to generate lift, pulling the nose up *even more*. So with no input from the pilot, the plane is going to try very hard to put itself into a worse stall and become unrecoverable, which means your plane crashes. The more surface area your wings have, the harder it is to stall them. So if you have a canard design, big wings make your plane safer. Big wings also increase drag, which defeats the purpose of the canard design in the first place. TD;DR: Traditional designs have the stabilizers trying to pull the plane down to balance the up force of the wings. Canard designs are more efficient because your stabilizers and your wings are doing the same thing - lifting the plane up. But canards are less stable unless you reduce the efficiency, which defeats the purpose of the canard design."
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bcqtol | Why do wind turbines only have a few, thin blades and not many to catch more air? | I'm aware that more blades create more rotating mass which will eventually become a hindrance but why aren't fabric blades/sails used? Something like original windmills have. Surely this would catch much more air without adding significant weight. | Engineering | explainlikeimfive | {
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"You basically answered your own question. It's not as effective. Modern wind turbines don't work the way a sail works. The wind doesn't \"push\" the turbine. The \"sails\" are shaped and work like airplane wings. The wind blow \"at\" them and creates the same pressure difference. Additional note. Modern wind turbines have \"brakes\" built in because they are efficient enough that if you don't have the option of slowing them down, they will turn so fast, the force would cause them to fly apart.",
"There are a couple things getting in the way. First of all, long, thin wings are more efficient than short, fat wings. This has to do with vortices that are generated at the wingtips. The longer and pointier your wings are, the smaller those vortices are, which is better. So you want long, thin blades instead of short, fat ones. Sails were the shapes they were because of the limitations of the knowledge and materials at the time. The next problem is the turbulence of the air passing over the wing. The air coming off of the rear of the wing is messy and turbulent. That's not what you want for the best efficiency. What you want is smooth, undisturbed air. Since a windmill is rotating its \"wings\" around, if a wing is too close behind the one before it the disturbed air doesn't have time to settle or blow away. If you have more blades on your windmill, they'll be too close together and you'll lose the efficiency that you wanted from more blades, which defeats the purpose. *And* the whole thing will be heavier, which takes more wind to move it. So the most efficient set up is going to be to have long, thin, light blades that are far enough apart that the air is as calm as possible, which means fewer blades. The most efficient windmill would be a single, absurdly long blade with a counterweight, spinning absurdly quickly. That isn't realistic, so it's three long, thin blades."
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bcsneu | Why are there so many knobs and buttons in a plane cockpit? | I obviously don't understand the logistics of flying, in my mind you need steering, thrust, and landing gear, but that still leaves about 600 buttons unaccounted for. what is all that? | Engineering | explainlikeimfive | {
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"Here's the simple answer: To start a plane: involves either: ground power or APU power, various start switches, etc. The more engines, the more switches. To start a car: turn key and go. Lights on a plane: navigation, beacon, strobe, logo, landing, taxi, cockpit, instrument panel, MCP panel, etc Lights on a car: inside, and outside. Air pressure settings on a car: air conditioning, or windows. Air pressure settings on a plane: pneumatic valves, crossfeeds, bleed switches on APU, PACKS, etc. Navigation on a car: phone or dashboard interface Navigation on a plane: IRS, radar wx, VOR/DME, ILS, FMC data, ATC instruction. As you can see, the components of operation are the same as in, you need lights, you need air, you need navigation etc. On an aircraft, each aspect of flight must be redundant and isolated. Therefore, you have more switches. And processes are typically not automated. You can choose how many engines you want to start, in what order, and other parameters. There's also much more technical information that's displayed to the pilots such as temperatures of exhaust gas, rotational metrics on the engines, fuel pumps and fuel flows among others. Everything is its own thing in planes. Cars on the other hand, those are much less robust but simpler to operate.",
"There's a lot of circuit breakers there too. Kind of like circuits in your house, or fuses in your car. There's a lot of electronics in the air craft and a lot of fuses can be blown. They need to be easily accessible to be reset."
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bcuydz | How does regenerative braking work with hybrid cars? | Title says it all! I want to get a Hybrid car but I’m not sure how they work or if they’d work for my needs. Edit: I don’t drive all that much, admittedly. Max 24 miles a day here in good ol’ CA, but I drive a fair amount on the weekends. I don’t deal with too much traffic, however. | Engineering | explainlikeimfive | {
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"A hybrid car is an automobile which operates its wheels using electric motors and a battery, but instead of having as much battery storage as a fully electric car it instead trades battery capacity for a small gasoline or diesel engine. That engine can be run in its most efficient power band in order to generate electricity for use in the electric motor or to charge the battery, increasing efficiency of the automobile as a whole. Regenerative braking uses the energy of movement of the automobile to turn the electric motors on the wheels into electrical generators, capturing some of that energy back into battery power for use in the electric motors again. Capturing that energy puts drag on the wheels which slows the car, exactly what braking is supposed to do. As for if this \"works for your needs\" we can't really know with what you have told us."
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bcvnd2 | How do rocks (track ballast) able to support a train? | Wouldn't these large size gravel shift when load is on top? How do, essentially, rocks support a train on its rails & sleepers? | Engineering | explainlikeimfive | {
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"1) I assume the gravel is compressed when it is installed, e.g. with a heavy roller and/or a vibrating plate, so that if it's going to move down and fill a hole then it does that while it's being installed, not when a train is on it. 2) The rails and sleepers do a good job of spreading out the load. While a car only touches the ground in 4 small spots at the base of each tyre, with a train the load from the wheels is spread out first along the tracks by the rails, then across the tracks by the sleepers. 3) The rails and sleepers aren't moving. Driving cars along a gravel track will tend to dig out gravel from under the wheels as the wheels slip and push gravel out backwards; that doesn't happen with a railway track because the train wheels only touch the rail not the gravel. 4) The railway line does get maintenance occasionally; this will presumably include filling in any low spots in the ballast. There are special trains they run along the tracks to look for places where the rail has moved, so they can schedule maintenance.",
"They do shift, but only a small amount over a considerable amount of time. That's why every so often they have to do maintenance on the track. If you look at a typical shunting yard where the trains move slowly, you can see the bends in the rails. This isn't a problem at low speeds, so they let it be. On high speed tracks it is a problem, and that's why high speed tracks need more maintenance."
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bcw23t | Why do auto makers make concept cars that look nothing like the final car? | Engineering | explainlikeimfive | {
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"Just think of it as what you say in an interview vs how you perform when hired. Same concept.",
"They want to get media attention, and to show the purest version of their ideas to test public reaction. But they haven't yet factored in things like the cost of manufacturing, or whether the right parts will be ready very soon."
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bczhrx | How do electric cars modulate regenerative brakes? | I get how the motors act as alternators, but don't quite understand how pushing the brake harder stops the car faster and creates more electricity. I'm guessing there's no clutch or movement of the motor coils, and that the drive motors are the generators? Thanks in advance! | Engineering | explainlikeimfive | {
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"Brakes on an electric car work a bit differently than an internal combustion car. There is still a regular mechanical brake pedal, that works identically to what you're familiar with. This is used for fast braking, and to hold the car stopped on a slope. The regenerative braking happens whenever there isn't power supplied to the motor. What this means in practice is that when you're driving along at a steady speed and you decrease the pressure on the accelerator, it immediately starts to act as a brake. In a conventional car, you will start to slow down if you take your foot off the gas, but it will be more gradual, and mostly due to air resistance. In an electric car, it is a more dramatic effect. You end up driving almost entirely by manipulating the accelerator, and only use the actual brake pedal for emergency stopping."
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bd0oqm | Extensive grid plans are common only in North America, and in other rapidly emerging cities, especially in East China, city blocks are like toddlers' drawings on the wall (ie full of curves). What are the factors for this discrepancy? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Different philosophies. US cities were built on grid patterns because they're seen as efficient, easy to zone and therefore very easy to adhere to town planning guides which attempt to optimise layout. More recent planned cities (like the new Egyptian capital I watched a video about recently) like curves because they are seen as aesthetically pleasing and sleek and, well...modern, whereas grid plans can create somewhat soulless districts. Other new cities in less developed countries (I haven't looked at any Chinese city plans so can't comment on which category they are in) likely are built with less of a plan at all, with developers able to add new blocks however they wish."
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bd20g7 | In the 15th and 16th Centuries and before, how did they build bridges over rivers? | Engineering | explainlikeimfive | {
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"Building temporary cofferdams to have a dry environment to build the foundation for a pillar of a bridge is a old idea. Temporary earth dams to diverted a river was used in 539 BC when King Cyprus of Persia captured Bablyon, they diverged the Eupjrates river. There is known example of temporary wooden coffer dams that the roman used for a bridge over the Danumbe in 102 AD . They down down a wooden pilings into the riverbed around where the bridge pillars should be perhaps in two rows with clay in between and the removed the water from the inside. It is done the same way today but with u shaped metal pilings. A illustration of a roman coffer dam [ URL_0 ]( URL_0 ) I suspect the the distance between the outer in inner wooden wall might have been larger Depending of how deep or shallow the river is it might be the case that there was a temporary earthen dam so half of it was dry when the build the bridge. Just google for cofferdam and you find a lot of modern coffer dams made of metal and earth. You could make wooden one just lik the the metal one but is required more work. Diverting rivers and making small dams is not that had and humans have done the for millennias. Is it just a loft of work and material you need to move."
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bd7i8r | How do they construct oil rigs out in the middle of the ocean? | Engineering | explainlikeimfive | {
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"text": [
"Like a giant Lego set really. They ship out the components to sea and slowly assemble them in place in stages."
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bd92lf | Why is it that when a rocket launches into space it looks like starts to curve to the side? | I live in Central Florida and have always watched the launches from KSC from my back yard. I've always wondered why instead of going straight up, it starts to veer off to the side. Is it because of the Earth's spin? A flat earther told me that it does that because they are going to land on the other side of the disk lol. Thanks in advance! | Engineering | explainlikeimfive | {
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"The goal of space flight is not just to reach space, but to stay there for a while. The most efficient way of doing that is to turn onto a tangent of the orbital sphere (sideways, as seen from the surface). This increases the forward momentum of the craft, allowing it to begin to \"fall around the Earth\". In practice, having enough forward speed allows the craft to miss the planet as it falls due to gravity, creating an equilibrium in the height gained by moving forward and height lost to gravity. Moving faster will increase the orbital distance opposite to the current location, increasing the perigee (lowest point) and apogee (highest point) of the orbit. Slowing down does the opposite, and allows the craft to land.",
"Because they do. To get into orbit, you have to do more than just get to the altitude of space, you also have to be moving to the side really fast. Things in orbit aren't in zero-g because they're in space, it's because they're constantly falling. If you just go straight up, you will fall straight down. If you move to the side fast enough, you just continuously \"miss\" the atmosphere as you're falling.",
"It's not an illusion. To orbit the planet, a spacecraft needs a *horizontal* velocity of 17000 mph. So the rocket needs to get the satellite up to space, but it also needs to accelerate it to a gigantic sideways speed.",
"The primary reason the rocket turns to the side is to most efficiently gain both the vertical and horizontal speeds necessary to establish an orbit. At the start of a launch, they have to be aligned straight up in order to maintain stability and not fall over. Once they get enough speed going, they can begin to angle themselves to the side without tumbling end over end. Their goal in almost any space launch is to get going fast enough sideways to cancel out the force of gravity pulling down on them. Turning shortly after getting off the ground gets them horizontal movement as early as possible. If they can manage to reach the necessary speeds, they can get in orbit. While in orbit they are falling toward the ground, but they are also moving sideways so extraordinarily fast that, because the earth is round, the ground curves down away from them at the same speed that the fall toward it. Without turning sideways the rocket would just come straight back down when it ran out of fuel and the precious cargo (usually satellites that are supposed to go into orbit) would be destroyed leaving everyone involved very unhappy. There are lots of other things that go into this which is commonly referred to as a \"gravity turn\". I encourage you to look more into it. There is a multitude of great resources on this and other spaceflight related topics online if you're willing to look for them and trust their expertise."
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bdd45j | How don't we run out of air to breathe if we don't open windows in our house for long periods of time? | Engineering | explainlikeimfive | {
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"Your house is more exposed to the outdoors than you imagine. While it's mostly water-tight, it's far from air tight. Generally your attic is opened to the outdoors as well as your basement or crawl-space.",
"Your house is not sealed so it does let some air in and out. But let's say it didn't. Human use about 550litres of oxygen a day. That's just over half a cubic meter. So oxygen in air is about 20% by volume so you need 5x as much air to get that oxygen so you need 2750 litres or 2.75m^3 of air. So to use up all the oxygen in air in a day your room would need to be tiny at 2.75m^3 that's not much more than a 1x1 meter floor room at a normal height for a room. Although I agree you woul feel ill way before that your not going to suffocate. And again your house is not sealed so even that would be getting replaced. Edit: oxygen in air"
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bddsdg | why does a car start when we push it ? | Engineering | explainlikeimfive | {
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"A car starts when you turn the engine manually. Normally this is done by the starter motor, which turns the engine when you turn the key. But because the wheels are connected to the engine (assuming you're not in neutral and you don't have your foot on the clutch pedal), pushing the car turns the engine. So it starts. This is why, when you're working on your petrol-powered lawn mower, the manual always says that you should disconnect the spark plug first. Because otherwise, when you're turning the blade by hand in order to remove junk and grass, the engine could start. Ever seen those videos on Youtube when they start the engine of a plane by turning the propeller by hand? Same thing.",
"From my limited mechanical knowledge a push or bump start is used when the starter motor is failing to provide the needed power to cause a spark and start the engine. By pushing a car up to speed and then putting it in gear you are in effect forcing the engine to turn over which I believe is the mechanical parts of the engine are then forced to move which causes the spark and starts the engine bypassing the starter motor. But, I could be so wrong ha"
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bdfq8c | How have cars increased in horsepower so much in the last 15 years whilst the engines are the same size or even smaller? | I drive a 15 year old car with a 3 cylinder 1.2L engine, it had around 65 horsepowe when brand new. I was looking at upgrading and I noticed that the modern version of the same model has a smaller 1L 3 cylinder engine yet the horsepower is 108. | Engineering | explainlikeimfive | {
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"Turbos, higher compression, less frictional losses, more efficient induction - take your pick just about everything has been tweaked and it adds up",
"None of the responses have gone into super detail but they have touched on the important thing. An internal combustion engine is merely a container for explosions. In order for explosions to happen there needs to be air and fuel. Balancing the ratio is the answer to everything. Older air-cooled engines were cheap and easy to design/build/maintain, but they have to run rich (fuel heavy) to keep the temperatures of combustion down for reliability. By adding water cooling, the ratio of fuel can be dropped and the explosion can be higher temp as the waste heat will be drawn away by the cooling system. Bigger, better, booms, more engine power. Now lets go away from carburetors (how we mix air/fuel for the engine) to fuel injection. You can now more finely tune that air/fuel ratio and get a little more oomph out of each explosion. NOW add on top of all that the magic of computers! The engine management systems in modern cars know exactly how much air is being ingested by the intake (cars before computers made ALOT of assumptions and had wide margins of error) and will calculate exactly how much fuel to spritz to get the explosion JUST right. Then it will read information on the exhaust side to verify that the boom went as expected. If it didn't, it will adjust. But wait, there's more! As I said earlier, you need the right MIX of air/fuel to create the perfect explosion. So now what if you want a BIGGER explosion? There's only so much air outside right? Well not if you use a Turbo or Supercharger, these devices suck air in harder than the normal movements of an engine meaning you can now ingest larger amounts of air in one cycle. If you have more air, throw a little more fuel at it and you've got yourself a bigger boom! Finally, as one of the earlier responses mentioned, the engines themselves have gotten lighter despite the increases in explosive power fuel/air delivery has provided. It's possible now to create a container that will not rupture during use and either uses less materials and/or uses lighter materials. This helps overall efficiency as that weight can be spent on other parts of the vehicle.",
"The easiest way to get more power from a smaller engine is by turbocharging. If the new car is turbocharged, that is your answer right there. But there have definitely been advances in other areas too. Specifically, more computer power at the design stage and in engine management, and in materials and friction management. Modern engines can run higher compression ratios (and thus run more efficiently) without risking damage from pre-ignition.",
"Tighter emissions standards have forced manufacturers to make more efficient engines for their vehicles. This is primarily done by adding turbochargers to everything, but lighter, better built engines overall have also helped. This is nothing new either. the land barge cars form the 60s and 70s have terrible power given their size."
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bdmxvy | Why do manual cars make that whining sound when reversing? | Engineering | explainlikeimfive | {
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"text": [
"The forward gears mesh at an angle and that reduces noise. Reverse uses straight cut gears which whine. Muncie made transmissions which used straight cut gears for forward and they had a distinctive sound.",
"Straight cut gears for reverse. 1) Reverse gears are cut differently than forward gears. Forward gears usually have helical gear teeth and reverse has straight teeth. ... The extra gear often contributes the most to gear noise. The abnormal sound of reverse is actually a combination of the extra gear and the straight cut teeth."
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bdnhnt | what is “back pressure”? I work in a facility where the word back pressure is used. I understand pressure, as in our reactor is under 10 psi of pressure however I don’t understand when people mention “back pressure”, as in “that pipe work has back pressure”. | Engineering | explainlikeimfive | {
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"It is pressure opposing the desired/intended direction of fluid flow through a pipe. a simple example is an air pump filling up a car tire. Your car tire is pressurized (hopefully), and when you connect the air hose to the tire, the hose becomes pressurized. If you want to add air to the tire, you need to overcome this backpressure in order to force more air into the tire. If the pump or driving force in your pipe system is not strong enough to overcome the back pressure, you will have no flow in the pipes, or possibly flow in the opposite direction. URL_0",
"Think of the pipe as a one way street you want the gasses flowing on one direction. Pressure keeps it flowing in that direction, back pressure is when there is more pressure where you want the gas to go than pushing the gas so the gas backs up in the pipe or flows backwards.",
"Basically means that the pipe has pressure the opposite direction it's supposed to flow"
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bdpaoz | Why would old structures like Norte Dame or Sisten Chapel take awhile to restore. Don't we have 1000 times better Architecture Technology? What makes them hard to restore in the case of Notre Dame I hear it might take years. | Engineering | explainlikeimfive | {
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"Restoration is painstaking work, because the goal isn't just to build something, it's to preserve as much of the original as possible, while filling in the missing parts. The first question is how much filling in do you want to do? The argument for minimal restoration (make the structure safe, prevent further loss) is that the artworks of the past should be preserved as best as possible, but nothing should be added that might detract from them. The argument for a full restoration (do whatever it takes to make it like new) is that you are bringing the structure back to the state its builders intended it to be seen in, and that trumps preservation of worn, damaged, or partially destroyed works. And of course there's arguments for every tiny step between those extremes. Then comes actually doing it, and hoo-boy. Do you know how many master stonecarvers, or stained glass makers, or fresco artists are still around? The answer is not many. An extensive restoration of a structure like a major cathedral might require re-learning of artistic disciplines that have been extinct or nearly extinct for centuries."
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bdplhn | Why did it take over a century to build Notre Dome? Is it due to resources? Complicated structure? Part time work? | Engineering | explainlikeimfive | {
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"text": [
"It was a massive project, and a massively expensive one. Work often slowed when money for the project got tight. It was also an incredibly complex and ambitious structure for its time, and required a lot of very high-skill work in an age where skilled craftsman were difficult to find (some of those skills are still difficult, if not impossible, to find). And the whole shebang was built with manual labor.",
"Parishes had to finance their own construction work, while still passing money up the chain of command to Rome, so budgeting a huge project like that was very difficult. There weren't banks who would lend money for the construction, so they did what they could each year with the funds available. This either meant hiring a few workers for a very long period of time, and proceeding at a very slow pace, or hiring a lot of workers when the coffers were full and working at a faster pace, but then being forced to lay off most of the workers when the money ran out. It was a delicate balancing act. A good book that covers this sort of construction is called \"Pillars of the Earth\" by Ken Follett."
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bdqa0d | What is the difference between the white and black keys on a piano? | Engineering | explainlikeimfive | {
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"text": [
"The white keys are naturals (a-g) and the Black keys are the flats/sharps All the white keys are one \"step\" apart, and the Black keys represent a half step. So the Black keys are in between tones",
"The black keys are no different than the white keys, strictly speaking. Mechanically, they all cause a felt hammer to hit a string (actually a set of strings that are close together) inside the piano causing a sound at a particular pitch. The difference in terms of why they are black and smaller has more to do with a bit of music theory. If you're not familiar with basic scales, then this won't help all that much, but here goes: The C major scale is composed of all white keys on the piano. You can play it super easily just by starting with middle C (which is right in the middle of the keyboard) and hitting every white key until the next highest C note. In fact, it just keeps repeating at higher and higher pitches. In fact, if you were to play along with a song that was written in the key of C major (or the equivalent E minor), you could hit random white keys all across the piano keyboard for the duration of the song and you would sound in key, and possibly sound \"good\" if you were in rhythm. This is super oversimplified, but hopefully that gives you an idea. If you really want to know more, then you have to learn some basic music theory. There are thousands of videos on YouTube that can help with that."
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bdtnuv | Why will the rebuilding of the Notre Dame cost millions of dollars? | Engineering | explainlikeimfive | {
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"text": [
"It took over 200 years to build back then. Now, we are talking rebuilding it within a handful of years. Maybe a decade. At least that’s what we hope. I’d imagine fixing any faulty structural elements that have worn away over time is much harder than doing it the first time from scratch, too. Thus costing more.",
"Well the renovations before the fire were gonna cost around 170 million anyway, so adding more work to that will put the cost up drastically. However I’m not sure how much it would have cost to build it 800 years ago",
"You could probably write a significant essay on this, for example - how accurately do they want to re-create the original construction, or build modern with period facade ... etc... As for cost, I am certainly no expert but I would think almost about the same. Keep in mind it was a VERY different world then, for example a significant part of the labor could have been slaves, children and very low cost ( but not necessarily low skill) Labor - so how do you account for the cost of that. A good stone mason, may have been one of the higher paid laborers then - but today, they barely exist.... so to make it \"identical\" would get very expensive."
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be5vtf | What happens when someone crashes into a fire hydrant? How does the fire brigade "fix" it? | Engineering | explainlikeimfive | {
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"Fire hydrants aren't pressurized until they are used. So when you see a movie or TV show where someone hits a hydrant and it starts spraying water, that is Hollywood being dramatic and not real to life. There is a five sided nut on the top that controls a valve several feet below the ground where the fire main connection is. It is closed until that hydrant is needed to be used. This prevents the spraying and de pressurizing the line in case of an accident where someone hits it, or if one breaks and springs a leak. Repairing one is a fairly simple matter of removing the bolts at the mating flange and bolting a new one one, assuming the damage is above that point. The flange is typically below the ground, but you sometimes see them above ground.",
"The materials engineering professor that taught our materials class drove a truck into fire hydrants at work for a living. The idea was to test the break away characteristics of the alloys used in constructing the fire hydrant connection to the pipes. I guess this planned breakage saves the main pipe and they re-bolt a new break away section into place after the accident."
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16,
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becj9u | In the days of telephone towers, how were new wires from homes/offices added to the tower without disrupting the city's traffic too much? | Engineering | explainlikeimfive | {
"a_id": [
"el51si2",
"el513zv"
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"text": [
"There would be a central hub that all the lines would be run to, that in turn would be run to a larger trunk that then connects to the overall network. Each part has a certain amount of capacity that is well known to the phone company. So many lines per hub, so many hubs per trunk. The idea is not to fill it up completely and allow for new connections. If the hub is getting full, you build another one while the first one is still being used and connect new lines to that one. Also the lines weren't on towers, they would either be underground or on poles and would go into a central building where the main switching equipment would be. There's something similar today with dark fibre. There's tonnes of fibre optic cable that's been strung up on poles or through communication pipes that isn't being used at all. They are there for future expansion. It's cheaper to run 50 lines at once, than one line 50 times.",
"In POTS (Plain Old Telephone System) you basically have a wire going from the phone to the closest telephone exchange. In the oldest technology, the telephone poles would be set up with extra wires for new connections, so you would just need to take an existing wire that isn't active, and run a connection between it and the building. In newer technologies, they would have intermediate equipment set up that digitizes the calls and compresses them, putting data from multiple calls into a single line- you would only have to run a new cable from the closest such exchange to your new building. And, again, it's likely that spare wires would have been run in expectation of hooking up new connections. In the most modern settings, there are shared data lines that the equipment in your home connect to directly that is sent to equipment that is likely installed right on the telephone poles, with the wire from your house not necessarily needing to even connect to a pole before connecting into that equipment."
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5,
4
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befocg | Why unexploded ordnance didn't explode when it should have and now may blow up just by looking wrong at it? | Engineering | explainlikeimfive | {
"a_id": [
"el5islx",
"el5kxjw",
"el5l81q"
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"text": [
"Some weapons have an *inertia trigger*, the weapon arms itself from the G-forces of it's having been launched or fired. Once armed, they stay armed, and even though they didn't explode, all it takes is one good bump to set them off",
"Ordnance isn't just a container filled with explosive; a sophisticated fuse is required to operate to make it explode. Modern explosives are generally very stable so that a bomb hitting the ground or a shell hitting a solid object is not enough by itself to make the explosive inside go off. The manufacturers usually don't want it to explode like that anyway; the best time for the explosion is usually some time after impact, and the fuses can often be set differently according to the target. Fuses can fail like any other item of equipment, and they obviously have a very severe operating environment, needing to survive being shot out of a gun or impacting with a solid object. So they can fail to operate correctly, or sometimes the don't go off because they don't hit a target in the way expected, e.g., a bomb hitting very soft ground or water, or an armour-piercing round hitting only a weak object might not feel enough G forces to trigger the fuse. As for why unexploded ordnance can explode later with little apparent cause, it depends on the reason for the failure to explode. Some explosive chemicals can degrade over time to become more unstable and can eventually explode spontaneously, independent of any fuse present. And failed or untriggered fuses can go off for a range of reasons, possibly related to the fault, or to minor disturbances. The details of likely reasons will vary with the model of ordnance and fuse involved.",
"Most of the time ordinance doesn't go off because of a problem with the signal that's supposed to set off the charge that ignites the explosives. So if it's knocked in exactly the wrong way it could end up making the connection and setting off the explosion. It's almost like if you were plugging in a string of Christmas lights. They have to be plugged in all the way to light up so if you picture the electronics of explosives the same way an unexploded bomb is only pushed in part of the way and a push in the right way could turn on the lights."
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bemwq8 | 360 cameras? How do they work? | Engineering | explainlikeimfive | {
"a_id": [
"el6y275",
"el71buk"
],
"text": [
"Multiple cameras taking photos in all directions, then software is used to stitch all the individual images together",
"There are many approaches. The \"circlevision\" style of camera from the 1980s uses several (9 in some cases) cameras that are mounted so their lenses point out like spokes in a wagonwheel. [[sample]( URL_1 )] The \"spinner\" kind rotates a line scanner and then combines the lines into a single image. This is the kind of gadget self-driving cars tend to use. The \"parabolic mirror\" kind, like [Lucy]( URL_0 ) points a single camera up at a parabolic mirror. This produces a distorted 360˚ image, like looking at a garden ball, but the math of the distortion is well known and completely reversible."
],
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59,
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"http://paulbourke.net/dome/LucyCamera/",
"https://static.bhphoto.com/images/images500x500/1500579397000_1350726.jpg"
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|
beqe2u | why are bank vault doors round and not rectangular like normal doors? | Engineering | explainlikeimfive | {
"a_id": [
"el7v282"
],
"text": [
"Traditionally, they work by pushing big rods into holes in the door frame. This is easiest if the rods are all the same length, which is what a circular door gets you. The circle shape also means you can't make use of stress concentrations at the corner, since there isn't one, and you can't really use a jack to force the door frame open like you could with a rectangular door, since it will just squeeze the rest of the door even tighter."
],
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27
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berhow | How do airbags "know" when to go off? | Engineering | explainlikeimfive | {
"a_id": [
"el80spa",
"el84ruq",
"el9f6u1"
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"text": [
"There is a sensor somewhere in the car that can measure how much force is applied when decelerating rapidly. When the car stops with a large enough force, the airbag goes off.",
"The airbags in a vehicle are controlled by a central airbag control unit (ACU), a specific type of ECU. The ACU monitors a number of related sensors within the vehicle, including accelerometers, impact sensors, side (door) pressure sensors, wheel speed sensors, gyroscopes, brake pressure sensors, and seat occupancy sensors. Once the requisite threshold has been reached or exceeded, the airbag control unit will trigger the ignition of a gas generator propellant to rapidly inflate the bag.",
"So far the answers are: a highly complex sensor suite and software, a single accelerometer, and a $0.10 SPST switch bolted to the bumper. Perfect."
],
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5,
3
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bew85z | How are magnets made into different shapes if they lose magnetism on impact or heating? | Many are shaped first then magnetised, but what about neodymium ones? Is there a way to shape natural magnetic rocks? | Engineering | explainlikeimfive | {
"a_id": [
"el912xe"
],
"text": [
"Rare earth magnets are made by creating a fine powder, pouring it into a mold, and applying a strong magnetic field to rotate all the magnetic grains so they're parallel. Then the aligned powder is compacted and sintered. Sintering means the magnet is heated enough to fuse the corners of the grains to each other, but not so much that it reaches the Curie point. URL_0"
],
"score": [
73
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[
"https://www.arnoldmagnetics.com/resources/magnet-manufacturing-process/"
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bexluz | Why are there typically three blades in a fan? | Engineering | explainlikeimfive | {
"a_id": [
"el98vqg",
"el9tp8j",
"el9ecum",
"el9bkf4"
],
"text": [
"Two-bladed fans would be prone to a phenomenon known as gyroscopic precession, resulting in a wobbling. Any number of blades greater than three would create greater air resistance, slowing sucking in air fro behind and hence cooling air coming out from the front, thus becoming less efficient than a three blade fan. It kinda cool to see how 2blade propellers were used in ww1 fighters, cuz they are more efficient. But with increased engine power output, rotation and airspeed, by ww2 most fighters had 3blade props cuz of stability",
"Coming from an aerospace masters student that has had to take way too many useless aircraft performance classes, the other comments are pretty wrong. Gyroscopic procession is only a function of angular momentum, not number of blades assuming the system has the same mass and mass distribution regardless of blade number. Stability in a system we can consider subsonic and rigid only is a function of center of mass. If a fan designer's goal is to maximize airflow forward per watt hr of electricity used, they need to balance the impact of each blade on the airflow with the impact of each blade on the other blades. Do to this, they need to consider that the more identical blades they add to the fan, the less efficient each blade will become, due to the turbulence created by the preceding blade, and that the sooner each blade reaches the point where air has already been accelerated by the preceding blade, the less it will further accelerate that air forward. After a certain number of blades, it becomes more power efficient to just increase the speed of the fan rather than the number of blades. To answer the question, I doubt a lot of thought goes into designing fans. The engineering hours to optimize a fan by a small margin are likely not worth the company's time, and so they stick with the same design we've seen since the mid 20th century. Maybe they would be able to get more efficient fans with 4 or 5 smaller blades but also that involves a higher production cost that probably isn't worth it to an uneducated consumer. Looking at all the various number of blades in aircraft propellors and helicopter rotors is a better example of why blade design for the number, size of blades chosen, and operational rpm is much more important than the actual number of blades. Edit: To address the \"chatter\" others talk about with two blades, because the rpm of a household fan is so high relative to its oscillation rate and the blades are rigid enough to not appreciably deflect due to inertia when oscillated, chatter wouldn't be an issue.",
"room fans and ceiling fans are very low pressure. as a general rule, a lower number of blades pushes more air at lower pressure. as for why *that* is, it's rather deep. to explain *very* crudely, the leading edge of the fan blade creates a pressure front. more blades create more pressure fronts, but obstruct flow. this is why turbines have hundreds or even *thousands* of tiny blades. their purpose is to change pressure, rather than flow rate. but you don't want to change the pressure in your house, you want to induce flow. 1 blade is obviously unstable. 2 blades are also unstable if the fan has to change facing (as most fans do), and will tend to \"chatter\"",
"I don't know if I agree with your premise. Small fans usually have 3, larger ones usually have more. Small fans being the most common, the most you see."
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beyo5h | Why is underwater welding so dangerous? | I've always heard that underwater welding is one of the most dangerous jobs anyone can undertake, hence the big pay check. Can anyone explain why? | Engineering | explainlikeimfive | {
"a_id": [
"el9qcj1",
"el9gkva",
"el9xdhq"
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"text": [
"Technical diving is extremely complicated, and there are a lot of risk factors. Decompression sickness and narcosis will both kill you real dead if you aren't extremely careful about monitoring your depth, time, and the amount of gas you're breathing. Any strenuous physical activity will make both of those problems worse. Now add to all the normal diving problems that you have to drag a welding unit with you, and that you're going to be diving around heavy machinery and in areas that potentially have huge pressure gradients (dams, pipelines, water towers, pump stations, etc), and that you'll be doing it all in less than ideal conditions most of the time (cold water, low visibility, strong current, rough seas, etc). It's a tough job that requires mastery of two quite hard to master skillsets.",
"A lot of reasons, first you’re working in an environment where a lot of the time you have 6 inches of visibility, if not less... plus the water currents are constantly pushing you... I understand it’s like trying to weld in a class 4 hurricane...",
"The reason that you hire an underwater welder is, generally speaking, that you can't get access to the workplace otherwise. The only solution you have is to send in a diver who knows how to weld well. That's two very narrow skills combined in one person, and that's a lot of what does it. If you dive underneath a ship that is docked, then maybe the environment is kind of calm compared to a lot of other similar jobs, but you have to keep in mind that some divers are prepared to do their job in a cage *underneath a moving ship*, while they are pulled by a guide-tug on their way to a dock. If you think that the diving welders made stupid money before, it's nothing compared to the money you can make when you are able to cut back on the almost unbelievably expensive hourly docking fees of some major transport docks. Or, you know, if you go out to an oil rig, where the sea is nothing but calm no natter when you go there to do the job. You need to have a skilled welder, who is prepared to do his job while diving. Which is hard enough. And then you want him to be prepared to do his job while diving, despite that the weather is kind of shit. Underwater welders are often working internationally. Are on-call all the time. Travel on short notice. Are delivered to their workplace by helicopter. And so on. You miss your kids birthdays and a wedding day now and then, are never home when important shit happens. And the job is risky if you do it right and dangerous if you do it wrong. It all adds up. If the pay was lousy, no-one would do it."
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bf4jyb | How do fuses blow? Can it be from disuse? | I'm curious and stupid. I bought a Sega CD recently, and it has a blown fuse. How could something like this happen? Because it hasn't been used in a few decades? Or did someone plug in the wrong power adapter? | Engineering | explainlikeimfive | {
"a_id": [
"elata9g",
"elavndx"
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"text": [
"Fuses blow because the amount of electricity coming in was higher than the fuse rating. Could have been a wrong adapter. Could also have been a power surge. Lightening strike or problem with the grid could do that. In theory, age could cause a fuse to decay but the time span required for the metal in the fuse to decay to that point is likely longer than the age of the machine.",
"A fuse blow because of to high current that heat it up or it can happen from physical force so it might have happen if it was dropped or handled uncafrully without any other damages to the device. If it just the fuse that have died you can just replace it with another with the same rating and it will work. & #x200B; There are electrical components that age a lot more and can fail in a way that result in a short or other problem. The most common is capacitors that contain liquids that can and do leak. A quick search resulted in this article [ URL_0 ]( URL_0 ) with pictures of the board where you can see discoloration because of leaking capacitors. There is also packs of new capacitors for the Sega CD [ URL_1 ]( URL_1 ) so it is relative common problem. So it might be a good idea to if the fuse fail when you replace it to open it and look on the board for leaks. To replace them you need to know how to solder and there might be a idea to let someone else do the replacement."
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bf5clj | Why are there always metal foils wrapped around a satellite? What's the difference between the gold and silver colored foils? And why are they always so wrinkly? | I suppose one of the reasons could be for shielding some components from radiation, but if it's true, wouldn't a less flexible material be more reliable? | Engineering | explainlikeimfive | {
"a_id": [
"elazcg9"
],
"text": [
"It's called \"MLI\" - multi-layer-insulation. This exist on the satellite to protect electronics from the crazy temperature fluctuations in space. This serves to regulate heat transfer, more than it really does \"insulate\". It also serves as a bit of protection from dust particles and things that would build up on the surface of internal componentry if allowed to run wild. The different colors are just different materials on the outer layer. Different materials in different combinations have different heat transfer properties so you can assume there was a different desired behavior in the silver location than the gold one."
],
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12
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bfm0bh | How did Charles Lindbergh navigate across the featureless Atlantic with 1927 aeronautical technology (no autopilot) and land just outside Paris? | Engineering | explainlikeimfive | {
"a_id": [
"eleo733"
],
"text": [
"Interesting question: Luck had a lot to do with it. \"Charles Lindbergh’s 1927 transatlantic flight highlighted the limitations of early air navigation technology. Though not the first person to cross the Atlantic by air (over 100 had preceded him), Lindbergh demonstrated that transatlantic flight would soon be practical. Because he lacked any means for fixing position, his flight also illustrated that, until better navigational tools and techniques were developed, this type of flying could be a gamble. Indeed, many who attempted it perished. Lindbergh's Simple Tools for a Difficult Crossing Lindbergh navigated the Spirit of St. Louis on his transatlantic flight with an earth inductor compass, a drift sight, a speed timer (a stopwatch for the drift sight), and an eight-day clock. Despite weather deviations and extreme fatigue, Lindbergh reached the coast of Ireland within 5 kilometers (3 miles) of his intended great circle course. But he knew that chance, not skill or equipment, had allowed such accuracy—winds during his flight had caused no significant drift.\" URL_0"
],
"score": [
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"text_urls": [
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bfoavp | Why are escalator step surfaces jagged? | It just seems to be a extra safety hazard for any escalator accident where the victims falls down while using them. Is there some underlying benefit to this design? | Engineering | explainlikeimfive | {
"a_id": [
"elf1w7d",
"elg8j71",
"elgc9li"
],
"text": [
"There is a comb at the top and bottom that prevents your feet and other stiff from being drawn into the mechanism. People died before this was implemented.",
"the way an escalator works, the stairs as well as the floor want to meet very tightly. this prevents things such as clothing from getting caught in the mechanism, among other things. now unfortunately, the steps can't just be smooth blocks of metal. people would slip. so they are cut in a gripping patterns that can move through a comb that will clear any obstructions",
"If it makes you feel better, probably only slightly better, Macy’s in NYC still has wooden escalators in operation....over 100 years old. [Wood Escalator]( URL_0 )"
],
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bft43d | Why does it feel weird to walk in a new pair of shoes for a little while? | If you go to a store and try on some shoes, it'd feel kinda awkward to walk around in them, but once you start wearing them more, the feeling goes away. | Engineering | explainlikeimfive | {
"a_id": [
"elg4fgt",
"elg5tib"
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"text": [
"After some wear, the shoes start to mold to the shape of your feet. The material will be less stiff and fit you more comfortably.",
"There are two sides to this: -your brain adapting -the shoes adapting. The main thing that happens is your brain adapting. This happens with a lot of tactile sensations. Your brain maps out how the shoe sits on your foot, where it touches, how it behaves when stepped on, etc. It then compensates for how it behaves, so you can walk properly with them on, and you stop noticing them on your feet. This happens because your brain notices something new, and starts keeping track of it, as with anything else. You feel every bit of it. Then after a while when it keeps happening and it's the same for long stretches at a time, it sees no reason to keep tracking it every time, and juat starts ignorin it when it pops up. The same thing happens with new headphones, keyboards, and mice. Oh, and new cars."
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bftpvl | Car water pumps | So, I know that the coolant in the circulates around the engine to draw heat, my question is how does the water pump continue to run with the thermostat closed and not pressurize and explode? | Engineering | explainlikeimfive | {
"a_id": [
"elg9nct"
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"text": [
"The average car water pump is actually very inefficient in terms of operating as a pump. You will notice in most cases, the impeller to housing fit is quite gappy. This permits the fluid being pumped to slip between the impeller and pump housing when pump outlet is blocked. Coolant itself in the engine doesn't require a ton of pressure/force to move around so pump itself is fairly low pressure. Some manufacturers will also plumb the heater core between the thermostat as a bit of a bypass. Most engines will come up to temp (ie. the thermostat will open) within a few minutes so you're not likely to be driving with a closed thermostat for a long time."
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bg22ij | How are lighthouses and bridge pylons built or placed in water while the waves are constantly crashing and moving? | Engineering | explainlikeimfive | {
"a_id": [
"elhrgyq"
],
"text": [
"Some structures are built on shore (or in a dry dock) and barged to the location before being placed. Some of these concrete objects float if full of air and sink when full of sand/water/concrete. The other choice is to use a [caisson]( URL_0 ) to form a pocket of dry air against the bottom of the lake/sea for workers to construct in. It's more than a little dangerous and difficult, so that's why most things are built someplace else."
],
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bg34pd | What makes one car brand more reliable than another? | For example, you frequently hear and observe that Japanese cars are reliable. What do they do differently in the manufacturing of their cars that makes the car more reliable? | Engineering | explainlikeimfive | {
"a_id": [
"elhywuc"
],
"text": [
"This is mostly an \"old\" idea of car manufacturing. Pretty much all modern car makers operate the same way now... the ones that didn't adapt are now out of business! Japanese makers (who also were manufacturing in the US) were using a operations and process that focused on minimal defects in manufacturing. I can throw out some cool business terms and names, but in the end, really the thing to focus on was that Japanese makers focused on quality and perfection in manufacturing, while US brands (until they changed) didn't have a big focus on that and were pretty inefficient and cared more about pumping out cars and marketing rather than getting each car working right and their line operating at the most efficient level (way oversimplified) But again, this is OLD. Now all car manufacturers are producing cars using newer version of the Japanese production system."
],
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7
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bgb47a | Why does tall buildings have a higher chance to collapse when its not swaying than when it is swaying during an earthquake? | Engineering | explainlikeimfive | {
"a_id": [
"eljobny"
],
"text": [
"Because when its swaying, it's absorbing energy. Think about it like this, if you clamp down a wooden skewer (the stick in a kebab), and you grab the top and and wiggle it violently, itll break. If you did it with a straw, the straw is fine. Although the premise is very different, the idea is the same. In buildings, they dont just snap in half, maybe one metal beam, or one load bearing joint or wall cracks, weakening it, then on the next shake, the building above it pushes it down and it buckles, then more walls will break. Have you played a bridge building game? It's always one weak point that breaks everything."
],
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bge5su | What is reactive power? | In the context of power systems. Bonus question: How is it caused and how can it be prevented? | Engineering | explainlikeimfive | {
"a_id": [
"elkdeha"
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"text": [
"Power systems use alternating current to deliver power. This means the current oscillates between a negative and positive value. Sometimes the current is maximal, other times it's minimal, but most of the time it's somewhere in the middle. In such a system, the voltage will also be oscillating. If the load is purely resistive, the voltage and current will oscillate in phase. That is, they will have the same frequency and they will be maximal, minimal, and zero at the same times. However if the load is reactive - if it has inductors or capacitors in it - the current and voltage will be shifted out of phase. When this happens, there will be times when you are forcing current *against* the voltage, and that costs energy. (EDIT:) That energy is not delivered to the loads, and this causes issues with sizing because you need to supply more power to compensate even though the load needs less (see edman007's reply below). You can mitigate this by shifting the phase in the other direction, however this shift will change depending on what reactance is in the load at the time. Inductors shift the phase one way, and capacitors shift it the other way. So you'd need to add capacitance to counteract an inductive load, or inductance to counteract a capacitive load. (Generally reactive loads are inductive - motors, etc - so you don't usually need to add inductance.) EDIT: See edit above. Thanks edman007"
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bgkndg | How do non-pendulum mechanical clocks keep constant time? | For instance, how do small pocket watches keep a constant pace at different windings? This has been surprisingly difficult to find on Google. I have found that typically these sorts of clocks are powered by spring, but shouldn't the force of that spring change based on how wound your spring is? If that's the case then shouldn't your time keeping device slow down as the spring unwinds? In fact in my search I came across Hooke's Law which seems to suggest exactly that. How do mechanical clock designs get around this issue? | Engineering | explainlikeimfive | {
"a_id": [
"ellko66"
],
"text": [
"URL_0 Unsurprisingly, Hooke solved this issue with another spring, again using his law. The mainspring drives a balance wheel, which is hooked up to a balance spring or hairspring. The balance wheel and hairspring form a harmonic oscillator; no matter the driving force (aside from that too weak to force an oscillation or too strong for the material to withstand), the balance wheel rotates at the same rhythm. The stronger the mainspring pushes, the more it compresses the balance spring and delays the oscillation. Similarly, as the mainspring weakens, it compresses the balance spring less, which speeds up the return. The net effect is that the oscillation is regular for the majority of the mainspring’s winding."
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bgyrui | What is the difference between 4WD and AWD on vehicles. | Engineering | explainlikeimfive | {
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"4WD systems typically are user selectable, and there's typically a mechanical lock between the front and rear drive shafts so they turn at the same speed, when 4WD is selected. This is fine on surfaces that will allow some slip, but on a grippy surface, like say a road, as the vehicle turns, there'll be a (slight) difference between the speed the two drive shafts will want to turn at. (Note that this isn't a difference between the left and right wheels, on the front or back axle - that's dealt with using ordinary differentials - it's a difference between the speeds of the shafts that *drive* the front and rear differentials) Because a 4WD system both shafts are locked together that inevitably means that one of the wheels, somewhere, will have to slip in this situation. If it can't, it can put strain on the 4WD system, and in extreme cases, damage or a situation called lock up, where the vehicle can't move because this phenomenon is jamming things up. So you tend to drive with 2WD on the roads. With an AWD system, all the wheels are driven all the time, so there has to be some provision for driving such a vehicle on normal roads. That's normally a third differential which sits between the front and rear drive shafts, allowing them to spin at different speeds, if necessary."
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bh03z4 | When dams are being built, how do they build it with all the water still there? | Engineering | explainlikeimfive | {
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"They dont. They divert the water then build the dam. Then they divert the water back to where the dam is!",
"They typically build a \"[cofferdam]( URL_0 )\" to temporarily divert water around the dam site. Then they build the dam, and once that's built, they remove or destroy the coffer dam. The coffer dam does not need to be particularly big or strong to divert a river. The actual dam needs to be big and strong to hold back the reservoir that's created by the dam Fun dam fact: Glen Canyon Dam in ~~Utah~~ Arizona is one of the largest in the US, and is under threat by all the sediment that the dam has trapped from moving downstream. The millions of tons of sediment are pushing on the dam and may eventually cause its collapse. So just dredge the sediment right? The problem: Some of it is highly radioactive from all of the uranium mining that took place in Utah and Colorado in the middle of the 20th century",
"The Hoover Dam documentaries are pretty cool, in that case they actually made a tunnel beside the proposed dam and diverted the river(the Colorado) through it during construction, I think they still use the tunnel as overflow. This was from memory(what's left of it) so I could be wrong.",
"They don’t. If you think about a dam you normally picture a big lake, but the lake is only there because they built the dam. Let’s take the Hoover dam, as this is famous and there is a lot of documented history. Here they chewed some tunnels through the rock beside the existing river, this allowed them to divert the water from the main channel and construct a giant wall. Once complete, they blocked up the tunnels and let the water very slowly back up and create Lake Mead on the other side. [Spend 8 minutes watching this]( URL_0 )",
"After reading the responses, it appears the answer is that they dam the river before they build the dam.",
"It differs depending on the dam. On the two dam projects I've been a part of, they basically build the dam beside the river, then close off the original river opening so the water goes through the new dam. Edit: I just want to clarify that the dam projects I am talking about are hydro electric dams, not sure if that's what you were referring to.",
"Firstly they tend to wait until a dry season so that there will be less water. In a few cases this might be enough and the remaining water running there will not cause any issues. However in most cases you need to make temporary dams and divert the water around the construction site. The diversion needs to be built above the normal water level to prevent flooding during the construction and might be either temporary or permanent features. When the diversions is prepared a temporary dam is constructed. Often by dumping sand bags into the flow of the river however it is also possible to lower solid structures into the river to block it. This dam does not have to be very watertight as the construction can handle some water and it does not have to be a dam that lasts for a long time. For example if construction takes place during the dry season the temporary dam might not have to last until the annual floods. It is also possible to use pumps to get rid of water on the construction site although this is often not enough on its own. In some cases the diversions can be constructed bellow the normal water line but they leave a section of rock intact to prevent them from flooding. This will then be blasted away diverting the river. This is a technique done as a last effort as it can be hard to divert the river back and it requires a lot of planning and preparations to make sure everything works to your benefit when you detonate the charges.",
"A similar question I’ve always had; How do they pour the concrete for bridge pillars in a lake?",
"They actually build a dam a little further up the river so there isn’t water flowing into the main dam being built"
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bh2ubt | Why aren't all rockets launched from the equator? | Recently I've noticed that quite a few launch sites such as cape canaveral, mid-atlantic regional spaceport, Baikonur cosmodrome are actually quite far away from the equator. Isn't it most efficient to launch from the equator as the rotation of the earth contributes to the speed of the spacecraft? What stops countries such as Russia or America from acquiring a plot of land closer to the equator? Is it simply a political reason? | Engineering | explainlikeimfive | {
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"Do the best with what you have. Florida and California are US launch sites because they are good enough. There's certainly an advantage to an equator launch, but logistically and practically its far easier to launch from home... and cheaper! Baikonur (Kazakhstan) fits a similar idea... although being the USSR's launch site, there a lot of crazy complications regarding that location, that are way out of scope to the core question. > What stops countries such as Russia or America from acquiring a plot of land closer to the equator? Is it simply a political reason? Certainly they could do this, but again, most of this stuff is just cheaper and easier to do at home ... even more so if you don't want anyone snooping on what you're doing, its a lot easier to protect Florida than it would some random place near the equator.",
"There's an additional aspect to this that people aren't mentioning, and it involves math. The orbital speed at any latitude is equal to the equatorial rotational speed times the cosine of the latitude. Therefore, as long as you're somewhat close to the tropics, the rotational speed will be almost as fast as the equator. For example, Cape Canaveral is at a latitude of 28N. Therefore, the rotational speed of an object at cape canaveral is cos(28) = 88% as fast as the speed at the equator. For practical purposes, 88% is close enough.",
"Because not every launch is into an equatorial orbit. In order to maximize the gain you get from launching into the earth’s rotation, you want to launch due east. If you launch due east, your unchanged orbital inclination is equal to your latitude. Any change in orbital inclination is very expensive fuel wise, so you minimize the changes by choosing a launch site with the most efficient and optimal initial inclination."
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bh3gf4 | Like dams, how to they build seawalls when there's the ocean water already there? | Engineering | explainlikeimfive | {
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"It depends on the type of seawall. Some are simply mounds of rocks just dropped into the ocean. The type you're probably thinking of are massive concrete structures like the Galveston Seawall. For those, they pour sections of concrete slabs then erect them in place at low tide."
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bh3ij8 | What are those colored balls that hang above powerlines and why are they there? | Engineering | explainlikeimfive | {
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"Apparently, Google is my friend: The marker balls are placed on power lines to make the conductor crossings visible to aircraft. Helicopters and small aircraft often fly low in mountain passes or freeways and usually fly low while approaching an airport.",
"They're called visibility marker balls or overhead wire markers. They don't affect anything in the electrical wires themselves. They are placed on wires so that if anyone is flying nearby, it's easier for them to see that there are wires nearby and avoid touching them. Wires are thin and generally have a dull color, so having something like a large orange ball on them makes it easier to tell that there is dangerous obstacle that the pilot needs to avoid touching."
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bh449g | How do skyscrapers not topple during an earthquake? | Engineering | explainlikeimfive | {
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"They're designed in a way to absorb energy and not have it directly transfer into the weakest point of the structure. This is done with the choice or materials and geometry. The one word answer to this would be 'engineering'",
"They use a [Tuned Mass Damper]( URL_0 ) which basically counteracts the movement of the building and dampens the swaying from strong winds and earthquakes",
"There are many different methods. Another poster mentioned Tuned Mass Dampers, which are huge balls suspended by some rope and allowed to swing freely. They are weighed and arranged in such a manner that they cancel out earthquake energy waves. Another method is to place the entire building on springs. The earthquake affects the ground below the springs, which absorb the energy. The building placed on the springs wobbles horizontally and vertically far less than the ground does. Yet another method is to place rollers under the building. Image gigantic rolling pins which you place a building on. The building will move smoothly rather than randomly jerking around in an earthquake, which will minimise damage."
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bh6efg | how do you get cranes on to the tops of skyscrapers? | Engineering | explainlikeimfive | {
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"You send a small crane up, and use that to lift the big crane. They break down into smaller pieces. & #x200B; Also there is a method by which a crane builds the structure *underneath itself*, lifting itself up with jacks as it builds the structure.",
"VERY SLOWLY! lol Theres a FEW ways. SOme buildings are built skeltal, then finished fromt the inside out (think of a frame being put up first THEN the insides and exteriors being put on. There are also buildings that do this ALL AT ONCE. They will build a few stories, then , as they go up one level, they will start finishing the lower levels, and start making more floors on the top. They JACK UP the crane, one floor at a time, as each floor is started, then complted. This cuts ENORMOUS time in finishing the building. They can also use SMALL cranes to lift BIG cranes to the top of buildings. That way you dont have to have a 1000 foot tall crane, just a 100 foot tall crane with a REALLY long rope. Lastly, actually BUILD A CRANE ON TOP OF A structure, they use a smaller crane to lift parts then assemble it on top. THOUGH this is getting rarer and rarer and it takes a long time for total constrcution. Take a look that this first example! [crane and building in progress]( URL_0 )",
"keep in mind that in most tall buildings, the crane is built inside the lift shaft. so, there isnt just the vertical portion of a crane standing next to the building, its a part of the building itself. The horizontal part of a crane is also not static - it can be moved depending on how long the crane needs to be or how much counterweight is there. So, a small crane is used to build the first few floors, and then a new crane is assembled (using the small crane to lift the pieces to where they are needed) inside the structure. Once finished, the crane is disassembled from the horizontal portion first. The vertical portion can be disassembled from the bottom, using the same jack system used to build it up."
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bh70yt | Why are the most efficient cars petrol hybrids not diesel hybrids? | When disesel engine by itself is more efficient then petrol. | Engineering | explainlikeimfive | {
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"Since the petrol engines in a hybrid drives a generator, and not the wheels (directly), the engine can be setup to run a more efficient cycle, at a more constant loading. This is very different to a conventional engine role, where the engine is directly connected to the driving wheels via the clutch/transmission/etc. In this role, the engine loading and revs vary considerably - as does the fuel efficiency. You could use a Diesel engine to perform the former role, but it is likely to be heavier, more polluting, and possibly less suited to the stop/start role of the hybrid’s generator engine. At least in Europe, Diesel engines now require a shedload of emission-regulating systems - which are expensive and weighty. Diesel engines are likely too noisy, compared to a modern petrol, for a an electric vehicle. And, I’m not sure if diesel technology is as well suited to variable-valve systems - which help drive up fuel efficiency. I’m sure someone here will give a more, specific explanation; I’ve been out of the trade for too long now :-)"
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bh8fdj | When underwater tunnels are built, why does a crack in the ceiling of the tunnel cause a powerful vacuum effect or a “blowout”? | Engineering | explainlikeimfive | {
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"Neither. An underwater tunnel has high pressure water on the outside and atmospheric pressure air on the inside. If there is a crack, water squirts in, but in no sense is there a vacuum. Some crack geometries might let water in at the bottom and air out at the top, but only in very shallow water."
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bha3hm | When bridge spanning across lakes or seas or any other large bodies of water, how do they build the massive concrete posts or pillar under the water? | Engineering | explainlikeimfive | {
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"They drill down into bedrock to place the foundation for the pillars. Then they will usually build some sort of wall connected to the foundation, pump out all of the water, and then build in the open area."
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bhao66 | How can battery packs for tools only be up to 6aH but us power packs can be 22000mah and be the same size or smaller. | Like DeWalts biggest 20v battery is 6ah but Anker sells a power pack that feels roughly the same weight and it's 22000mah which when convert to ah is 22ah almost 4 times as big Edit: title should be USB | Engineering | explainlikeimfive | {
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"text": [
"Marketing blather is part of it. But also voltage. 22 amp hours at 5 volts is the nearly same energy density as 6 amp hours at 20 volts.",
"Because of the voltage. The anker Pack is probably internally at 3-4V depending on the type of battery. They can then step the voltage up to 5V for USB. Meaning you have on big cell. The dewalt needs to get to 20V, which they will manage by putting several 3-4V cells in series. If they want the same Ah like anker, they would have to take 4-6 of the anker cells to still supply 20V. Also the anker pack is probably a lipo and the dewalt probably a li-ion. Edit: phrasing",
"22000 mAh x 5 volts = 110 watthours 6Ah x 20 volts = 120 watthours So from an energy storage perspective, those batteries have a similar capacity. & #x200B; Packaging also comes into play: Many tool batteries use cylindrical cells (i.e. 18650) whereas a power bank probably uses a rectangular (prismatic/pouch) cell. You waste some space with the round cells, plus power tool batteries probably have padding and thicker housings for durability."
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bhcgp4 | How is higher octane fuel less likely to cause a misfire than low octane fuel | I would've thought it was the other way around. | Engineering | explainlikeimfive | {
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"The octane number describes how difficult it is to get the fuel to combust. The higher the octane, the more heat/ pressure is needed for it to combust. High performance engines are often designed to use higher compression ratios because that way you get more power out of the same amount of fuel. So then to prevent pre ignition from the high pressure u use higher octane fuel.",
"Higher octane prevents auto ignition in higher compression engines. It can withstand higher pressure than lower octane fuel. Low octane fuel will detonate with the heat and compression before the spark plug tries to ignite the fuel causing a misfire.",
"Misfire in a engine is more known as knocking is the because the fuel burn to fast/to early so a fuel that is less sensitive to ignition from compression is better. So the problem is not that fuel do not ignite but that is ignite to early. So a high octane fuel that can sustain more compression is better. That said a engine will not preform better if you have a fuel with higher octane rating. As long as it is high enough so there is no knocking any higher. That is because higher octane make it possible to have higher compression ratio but that is fixed in all normal engines."
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bhmuw9 | Can Sandy’s treedome from spongebob squarepants actually exist in real life? | I know there are several factors to consider here, like the pressure of the water over the glass. However, if submarines can exist, maybe a kind of underwater greenhouse can also exist on the sea floor. That was my thought. Is this really possible? | Engineering | explainlikeimfive | {
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"text": [
"Because Science actually did a video on this topic. [Here's a link. ]( URL_0 ) It depends on how deep the water above her dome is. If Bikini Bottom is at the bottom of Bikini Atoll, then the average height of the water at the sea floor is about 53m (175 feet). The SpongeBob wiki says her dome is 10m tall, so taking that into account and doing some fancy physics math, the force of the water above the dome is just over 32 million pounds. So, now we need to figure out the surface area of her dome to find the total pressure from all that water on her dome. After some more fancy math, we find out it is just about 33psi, or just over the same pressure the sky puts on you at sea level. Now, we need to know the strength of the dome. According to Sandy, the dome is made of polyurethane. Assuming the dome is 1 meter thick, more math says it would be able to resist up to 176 psi, but because domes are very strong, it would only have to be 1cm thick, or 0.4 inches. The problem with her dome isn't the strength but the amount of usable air inside. Assuming she could provide her tree with enough carbon dioxide, sunlight, and nutrients, then it would make enough oxygen for her.",
"In theory, yes. But they would need a way to refresh the oxygen to carbon dioxide ratio as the air is breathed. Think Sandy’s tree for example. The issue is depth. There was actually a study a long time ago where they essentially built an underwater lab that marine scientists lived in for awhile. I don’t remember the study exactly but you can google it."
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bhwn60 | Why are glass bottles so cheap (especially large ones like Vodka bottles)? | Engineering | explainlikeimfive | {
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"text": [
"Glass is basically just melted sand. Sand is relatively abundantly available and humans have been making glass for so long that we have become fairly good at it. However if you think the cost of the glass bottle is the price of the redemption amount you are mistaken."
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