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hym18v | how are negative decibels possible? | I saw a couple posts about the worlds quietest room and it had over -20 decibels of noise. How is that possible? | Engineering | explainlikeimfive | {
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"Normal units, like meters or gallons, are linear. Two gallons is twice as much water as one gallon. Four is twice as much as two. This is what humans are mostly used to. Similarly, you can't have negative gallons (except when subtracting, but that's different). I mean, zero is zero - nothing, zilch... Now, we're going to leave the realm of sanity (and linearity) and talk about log scales. Decibels are a log scale, but we're actually going to make up our own based on gallons, since gallons make a bit more sense than \"watts per square meter). So, we're making a new unit called the Kahoot. The kahoot measures volume (just like gallons), but unlike gallons we want the kahoot to be applicable to a wide range of volumes. In short, we want to be lazy and write fewer numbers. So, we make an equation: 10^kHoot = gal The number of gallons is equal to ten to the power of the kahoots. Bear with me. We'll do one kahoot. 10^1 = 10. So, one kahoot is ten gallons. Two kahoots? 100 gallons. Three kahoots, a thousand gallons. Let's go the other way. Zero kahoots? 10^0 = 1. One gallon. Negative one kahoots? 10^-1 = 0.1 gallons. Negative two kahoots? 0.01 gallons. -3kHt? 0.001 gal. Hopefully you see how this works. Even -1,000 kHt is still more than zero gallons. It's such a small number that I won't write it out (999 zeros is a bit much), but still not quite nothing. Decibels are also a logarithmic scale. 0 decibels is not actually zero sound - iirc it is the minimum amount of sound that a person can hear. Something like 1 milliwatt per square meter. I don't remember exactly. Decibels for sound are kind of arbitrary. Mathematically, they work similarly, but the exact numbers are different from our kahoot system.",
"Decibels are on log scale with an annoying factor of 10. To find the decibel of 100Watts for example, you do 10xlog10(100), which gets 10x2=20dB. If you want to go backward you divide by 10 and then put your result as the power, and 10 as base. So if you have -20dB it becomes 10^(-20/10) = 10^-2, which is 0.01 watts, which is still positive",
"Simply put, 0 decibel isn't a complete lack of sound. It's just the level where the average human stops hearing it. That's why you can have negative numbers."
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hyobbw | How do Stormwater drains work? | Ok I'm an idiot.. & #x200B; Theres been heavy rainfall and the huge stormwater drains running through my city have been completely filled up and rushing like a strong river. They go for miles and end up joining to the ocean. There usually empty and kids just play in them or skate or whatever... I dont understand how the whole thing doesnt get filled up when its high tide? How does it all drain to the ocean and not fill up, particularly the points where the ground is equal to or below sea level.. how does it flow out but not flow in? & #x200B; Thankyou for not shaming my dumbness. | Engineering | explainlikeimfive | {
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"They are built so that the mouth of the drain is higher than most high tides. From several miles inland to the ocean, the land will, on average, slope downward, so even though the actual elevation might be a bit up and down, the storm drain is made to have a continuous downward slope in order to ensure quick removal of excess water."
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hyp5ak | Why do we prefer QWERTY keyboard over ABCD? | Engineering | explainlikeimfive | {
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"Because when we used typewriters, letters that were used a lot were typed in quick succession, and that make the typewriter get jammed. So they spread out the letters to stop it from jamming.",
"Most frequently used letters are located in the upper and the middle row, so you don't have to move your fingers to type them. Put your hands over the keyboard in a relaxed position, each finger will be over the more used letters. Letters are also spread between left and right side, in a way that you alternate hands when typing most words, so you can achieve better typing speed. That was the theory for it anyway, some typists now say that the historic QWERTY layout is not ideal and DVORAK layout is the best, as it was developed later with better understanding of most used words and letters."
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hytylc | How do the corners stay attached, but can move around freely, on a rubix cube? | Engineering | explainlikeimfive | {
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"Here a yt vid of a man building the world's biggest. You get to see how the inside works. URL_0"
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hyx2an | What determines when an appliance, etc. needs a 3-pronged plug with a ground vs. just a 2-prong plug-in? | Engineering | explainlikeimfive | {
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"Basically, if the exterior is metal it's a three prong plug and if it's a nonconductive exterior like plastic it's a two prong.",
"The two-pronged ones requires something called *double insulation*, a safety measure that makes the ground connection unnecessary. Look at the type sticker. there should be a symbol there with two squares (a small square inside a larger square) that indicates that the appliance is double-insulated. All appliances that are not double-insulated (i.e, their cover is metallic and can potentially have a galvanic connection to something with live current) must also be provided with ground, or Protective Earth, as it's called in most standards."
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hz5onc | How does the vibration dampener on a tennis racket work? | Engineering | explainlikeimfive | {
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"Full disclosure, I'm no expert on physics, but I do play a lot of tennis and this is how it was explained to me. The logic is that every time you hit the ball with the racket, the strings vibrate after, kinda like hitting a tuning fork. Now if you hold that tuning fork in your hands, you'll feel those small vibrations. If you pinch harder, you'll absorb more vibrations in your finger and slow it down quicker. Imagine the racket as one giant tuning fork. The vibrations pass down the handle fairly easily. In extension, they go into your hand and arm as well. The most susceptible points are the ones that have the most motion (ie-your joints). That's where the vibrations will have the most impact. If you put something on those strings that add extra tension, it can absorb the vibrations with expansion and contraction (akin to pinching the tuning fork). Basically the vibrations go into the dampener and it expands and contracts ever so slightly. This is enough that fewer vibrations make it to the handle, and in turn, your hand. Now, if you are a casual player will you feel the difference in those vibrations? Probably not. If you're playing every day for a few hours a day? You'll probably feel the difference then."
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hzchom | How can internet cables laid on the ocean floor for thousands of kilometers remain effective... while an HDMI cable can lose its effectiveness after as little as 5 meters? | Engineering | explainlikeimfive | {
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"Fiber Optics has much higher range and deep sea cables are made specifically for the that purpose, the longest range Fiber Optics cable you can have on land is about 120 km without amplifiers or repeaters. In the deep sea cables there are amplifiers about every 80km, this is also why it must be constantly supplied with electricity.",
"You are comparing very different cable technologies. An HDMI cable is a copper cable that have been built the cheapest way to conform to the standard. Similar with the equipment at the ends. But an ocean floor cable is a fiber optic cable with much stricter tolerances making it much more expensive and also with much higher quality and more powerful equipment at the ends. In addition to this the long transoceanic cables often have amplifiers on them at regular intervals. You can also get \"active\" HDMI cables with similar amplifiers to reach longer distances.",
"Are those cables actually on the ocean floor or are they \"floating\" somewhat meters under surface? Genuinely asking",
"Your HDMI costs like 5 dollars a foot, those cables cost thousands of dollars per foot. They also have little computers in them that also boost their signal so the signal doesn't die in the wire.",
"Copper in HDMI transports electricity. This means it can be influenced by magnetic fields around it, which your house is full of. Also every radio signal produces interference, the longer the cable the worse. Ocean cable conducts light. There is no other light at the bottom to interfere. There are repeaters at regular intervals so the actual length of each fibreoptic is some 50 miles.",
"Can I add something to this? I heard that mankind barely discovered the deep ocean because of its sheer depth. So... are deep sea cables laid and attached on mellow parts that are discovered or are they just floating around in the sea?",
"So, how was this funded? The the countries split the cost?",
"Who pays for all this? And how much electricity is needed to power all the repeaters?",
"Everything is made to do a job. If you want it to send lots of video/pictures/stuff then it needs to be fast. HDMI cables are fast, but thy don’t need to be long so they can be cheap. If you need it to be long then you need to do things differently. Sending stuff using electricity is easy & cheap, but electricity needs metal & metal is slow because it knows when other metal is near it (capacitance) and it doesn’t like changing the amount of electricity in it (inductance). That’s OK if the metal is short, but not OK if it is long, because those two things smear our signal/stuff out & stop it working fast. Beaming light down a hose made of glass is another way to send stuff, light is very fast electricity, it moves a bit differently & so doesn’t get slowed down & smeared out in the same way. The only thing is that the special torches that send light down this glass hose cost lots of money, so we only use them when we have to. If we want to make a glass hose really long, the signal/stuff gets quieter as it goes along, this means we need to make it louder along the cable, which means more special torches, which makes it even more expensive. Edit: spelling",
"Between these videos I think it explains it pretty well Fiber VS copper as fast as possible URL_1 Why does cable length matter URL_0 Bonus video All HDMI cables are not the same URL_2",
"It's a mix of cables really. Power cables provide repeaters built-in the cable with power to amplify the data signal which is carried over fiber optic cables. Light is essentially undisturbed by electric signals so it carries much further. HDMI does everything over copper with multiple signals in the same cable. It's much more susceptible to signals from outside.",
"Amplified repeaters are of course part of the answer, but I'd argue the fundamental reason fiber optic cables can transmit much greater distances compared to normal copper is by exploiting the phenomenon of total internal reflection. When light strikes the edge of the fiber at a shallow angle it reflects with nearly perfect efficiency. This is also how fiber optic cables allow light to be \"bent\" along their length."
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hzcs8t | Can a phone battery power a car? | Engineering | explainlikeimfive | {
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"A gasoline-powered car might need about 1.5-1.6 amps per hour to run the electrical components of its engine, plus the other electrical stuff. Not to move the car itself. :) That said, Tesla batteries are fundamentally a huge stack of the same *type* of battery cell as in consumer electronics. But of course much more of them, and manufactured to higher standards. EDIT: Forgot an obvious thing: a car battery is much bigger than a phone battery because it needs to retain enough charge over days or weeks of non-running, and then when you are starting the engine, the starter briefly draws hundreds of amps.",
"It’s not possible to use a phone battery to run a car for several reasons - phone batteries are 3.3V and car batteries are 12V - cars need a lot of current to start, I’m talking around 200 Amps, even if for a short time, small lithium batteries cannot really take that without Puffing up or even catching fire, and after that, the battery gets just charged all the time - a typical car battery is usually around 70 000 mAh, at 12V rather than 3.3, so it’s about 40 times the energy as a phone battery - lithium batteries don’t really like too much heat or too much cold, while lead batteries are much more forgiving, the engine bay gets quite hot Sure you could some of those problems with more batteries, but it’s just more expensive and not worth it",
"It’s probably 1.5(ish) amps once the car is started but in order to start the car you would need somewhere between 300-1200 amps. So in theory, yeah you could power a car with a phone, especially if you consider the alternator keeping it charged, but in order to start it you would need a much larger power source.",
"> Amps per hour Very uncommon unit, since amps are already a measure of \"charge flow per time\". The issue is likely in this unit. > huge phone battery If you make the battery large enough you can power anything with it. Ever heared of a Tesla? Its battery *is* indeed just a huge phone battery (Li-ion battery)."
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hzj55d | how is that just by powering something, it can move? How does electricity make a piston or an axle move? | Engineering | explainlikeimfive | {
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"Because electricity is not an independent phonemenon. Electricity is intrinsically tied with magnetism. That's why you constantly hear EMI, EMP etc. Where there's magnetism, there is electric current and vice versa. When you give electric current to a circular metallic arm, the magnetic field causes it to rotate. Attach a shaft to this rotating wheel and you got a rotating pole. At the other end of the pole, attach a gear and you got a rotating gear. Where you got 1 rotating gear, you got an entire machine moving.",
"Electricity and magnetism are related concepts. If electricity flows through a wire, it creates a magnetic field. The more current (or the more wire,) the more magnetic field you get. You might have seen the experiment in Jr. High science class where you wrap a coil of wire around a nail, connect the wire to a power source, and then pick up metal objects with the magnetic field created by the wire. Electric motors use this principle. Imagine a very simple electric motor consisting of an electromagnet hooked up to alternating current, placed in between two permanent magnets. As the current flows, it generates an electric field that attracts the electromagnet to one magnet. When the current reverses direction, the electromagnet gets attracted to the other magnet. This constant alternation of current causes the electromagnet to rotate. If you put a driveshaft on the same axis that the magnet is rotating around, now you've got a basic motor that can do some work for you."
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i0dv5i | Why are midwest roads so awful | I was in a large midwest city recently, and I'm not exaggerating at all, every single road that I've been on is under construction. I asked a friend who lives here, and she said yeah, they're never NOT under construction. It's like this every week, every month, year after year. My question is, why are all the roads so shitty and constantly having to be ripped up if they're always being replaced / fixed / touched up? Do they just put down super shitty roads that break and tear and heave every six months so they'll get a new contract? | Engineering | explainlikeimfive | {
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"Bad weather — freezing and thawing, storms, tornados — causes a lot of wear and tear to roads, and the weather is worst in the Midwest.",
"Because it’s all about the base and clay is terrible. It expands and contracts with moisture content which will eventually cause the road to heave and need repairs."
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i0f0iz | How do Chinese Finger Traps work? | Engineering | explainlikeimfive | {
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"The weaving of the material used to make the trap is loose until you try to remove inserted fingers. Once inserted when you try to remove your fingers the weave tightens as your fingers pull the weave in opposite directions. In order to remove the trap you must hold the center of the trap forcing the weave to stay loose and not contract when you remove your fingers."
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i0h79k | Why do almost all power plants rely on steam to generate electricity? | It seems like almost every method we use to generate electricity (with the exception of solar, wind, hydro and maybe some others) involves some form of using heat to warm up water. Nuclear fission, fossil fuels, even future fusion reactors will ultimately create energy by boiling water. It seems like such a 19th century way of producing electricity. Isn't there a more efficient way of transferring heat to electricity than turning a turbine with steam? How efficient is steam? | Engineering | explainlikeimfive | {
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"Except for solar, electricity is generated by turning a wire coil around a magnet. To do that, you need something to move the coil (or the magnet). Easiest way to do that is by having air or water move some kind of turbine - windmills do this by wind, hydro by water, everything else relies on air movement generated by steam because how else do you get the movement? Is it efficient? In terms of energy in vs energy out, not really, but it's an awful lot more efficient than the presently fictional alternatives.",
"Heat by itself isn't very useful as an energy source, especially for generating electricity. The energy source we're good at using for making electricity is rotation. Boiling water and using the hot steam as a source of pressure may be crude but it's effective. Then you can use the pressure to spin a generator.",
"Steam turbines is the most efficient way to convert heat into electrical energy. But a modern steam turbine have very little in common with its 19th century ancestors. They might run at 30MPa at 700 °C to get between 40% and 50% efficiency. Direct thermal engines like internal combustion engines and gas turbines rarely get more then 30% efficiency. The reason to use steam is that water have a very high expansion rate compared to most other gasses. So you get a lot more efficiency out of it then anything else."
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i0jqn8 | How are tires the only thing that support a planes entire weight? | Engineering | explainlikeimfive | {
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"Rubber is incredibly tough. Think of the pressure on them when a car driving at, say, 60 mph hits a pothole... it's amazing they don't just burst. The fact that air can compress, and rubber is elastic and can expand is obviously relevant, but even so...",
"Considering their size, planes are actually not that heavy. If you take a Boeing 777, a typical long range wide-body airliner, the empty weight (no passengers, cargo or fuel but including seats, engines etc) is somewhere in the region of 160 tonnes, and at maximum takeoff it's around 100 tonnes more. It rides on 14 tires. An \"18 wheeler\" truck-and-trailer is somewhere in the ballpark of 40 or 50 tonnes, so a maximum takeoff weight 777 is about as heavy as 5 or 6 truck-and-trailers. While those are heavy trucks, compared with the size of a 777, the aircraft actually isn't that heavy. Sure, it has fewer wheels, but the tires on the 777 are very much larger, so the demands on the tires aren't that extreme.",
"In two words, higher pressure. 777 tires run about 8 times the pressure of car tires, and have a *lot* of steel-wire reinforcement in them.",
"Plane tires are quite different from the regular ones. It is a composite of various rubbers reinforced with aluminum alloy, steel, nylon and aramid. And they are filled with a nitrogen."
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i0o8h9 | What keeps the helicopter shaft from flying out of the engine? | It is not just in helicopters. But what makes the drive shafts in electric motors for example from just falling out of the engine? What holds it back so we can not just drag it out? I believe it is not metal against metal that holds it back. That would be a lot of tearing. I know about bearing? But are they really that strong, and are they used for this? | Engineering | explainlikeimfive | {
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"URL_0 I present to you....the Jesus Nut!! Aka... the God Nut",
"Bearings are way way stronger than you are giving them credit for. I'm not sure about the case of a helicopter but in a car the crankshaft rests on bearings that connect it to the rest of the engine. As long as bearings are kept oiled they can withstand an incredibly amount of pressure. That's, among many others, the reason you have to keep your car oiled."
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i0od4a | Why do you have to turn the switch on a lamp twice to turn it on? | On some lamps they have a turn switch and you have to turn them multiple times to turn it on, why is that? | Engineering | explainlikeimfive | {
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"You have a one-way light bulb in a fixture that supports three-way bulbs. If you put in the right bulb, one click would get you dim light, the second would get you medium, and the third would get you bright before the fourth turns the lamp off.",
"Because out of three point one is off one is dim and another is full. Lamp bulbs are designed with two power settings which enables to dim the light. But nowadays bulb used in lamps come without dimming point, but you can buy that 2 point lamp bulb from stores.",
"That is a lamp made for a trilight bulb. A trilight bulb has two circuits in it, a higher voltage and lower voltage circuit. As you click, you first turn on the low circuit, then (only) the high circuit, then both circuits, and then off again. When you put a non-trilight bulb in, it only makes contact with the high circuit. This means it turns on when the lamp is in either the High or Both positions, but it is effectively off in the low position."
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i0zpik | How do they keep water-pipes clean without using dangerous chemicals? | Got reminded about the post about the guy installing a soup pipe-system that households could tap into but everyone kept pointing out how nasty the pipes would get. So even if it's just "clean drinkingwater", never ever cleaning the pipes have to lead to some nasty stuff building up? | Engineering | explainlikeimfive | {
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"That's a big part of why there is chlorine in the water. Chlorine binds to organic materials. When it does it kills the bacteria in water. Another important point is that water really shouldn't be left to sit in pipes for too long, as the chlorine will be used up and then what tiny amounts of bacteria may be in there can flourish.",
"You ever seen the inside of a water pipe? They are nasty. But they're not organic nasty -- it's not bacteria (chlorine takes care of that) -- they're just FULL of mineral scale. The scale builds up on the inside of the pipe over time."
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i17s3x | What makes bells different sounds/pitches/tones? | I just went to a bell museum but all she said was the combination of materials. But she played music on a bunch of different ones. | Engineering | explainlikeimfive | {
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"Have you ever seen a xylophone? The largest bar makes the lowest pitch and the smallest bar makes the highest. This is true with stringed instruments too. Thick string generally equals low pitch, while thin generally means highest. Same with the bell, they’re different size and thickness equate to different pitches",
"It's a combination of material and shape. The material, like copper, brass, or iron, will vibrate differently based on natural resonance of the material. The shape and size of the bell modifies that resonance, and allows for fine-tuning of the sound to a desired tone and pitch. It's like when you tap on a glass. It plays a single tone while it is empty, but if it is half-full it will play a different one.",
"Size, thickness, shape, and material the bell is made out of. An analogy might be to find glasses of different thickness and ping them with a fork. You can also fill a glass with water. The smaller amount of free area the glass has as the water increases, the higher the frequency/pitch."
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i17w4t | why are fishing poles so bendy? | Engineering | explainlikeimfive | {
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"Sorry, most the answers you've been given are either incomplete or incorrect. Fishing rods bend in order to keep tension on the line while the fish darts in different directions. Slack line can cause the hook to become dislodged from the fish's mouth. The reel typically has a \"drag\" on it they allows line to be pulled out when the fish is pulling hard enough, this allows the fish to run a bit without breaking the line, or the rod, or the fisherman's arms.",
"Which one is harder to break? A dry wood stick or a wet(young) one? In the nature most of the things try to cope with enviroment. If it resist adventually it breaks.",
"A flexible pole absorbs sudden stresses on the line. Lets say you were a linedancer walking across a rope attached to two poles. And then you jumped up and tried to land as hard as possible on the rope. When you come down you'll exert a force much greater than your own weight. Lets say the rope can just take a force just somewhat greater than your weight (like 50% more). So if the rope was tight between two sturdy poles it would snap. But if the poles were flexible, then they would absorb a portion of that force and spread out that extra force from your jump across a much longer period of time, and the rope would hold. A flexible fishing pole does the same thing. It acts as a way of keeping the line tight, but by bending it absorbs any sudden stresses that could snap the line.",
"You kind of answered your own question here, part of the reason the line didn't break because the pole is so bendy, a flexable material disperses the tension far more effective than a rigid one will.",
"To reduce torque exerted by the fish. Fish pull really hard so if the pole is stiff than the torque point will be on tip and you have to pull much harder,and if the pole bend the torque point shift towards you and make it harder for dish to pull. Another example is wrenches, longer the handle easier to open the nut. And second point is explained by other posts."
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i1gkum | How is electricity made? | Engineering | explainlikeimfive | {
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"There are 6 ways to make electricity: 1) piezoelectric effect - when you compress certain crystals, a large potential (10kV) can be created. You can create a spark using this and is used primarily as pilot lights in gas burners for instance 2) thermocouple - when two dissimilar metals are joined, a potential is created across the join as temperature changes. Very small voltages, only used as temperature sensors 3) photoelectric/photovoltaic cells - when light shines on a semi conductor junction, the photons of light can encourage some electrons to move out of their cells by giving them energy, creating a voltage across the semi conductor. Obviously solar is the use here. 4) chemical - dissimilar metals have different affinities for charge. Put two together like zinc and carbon, and if there is a acidic chemical known as an electrolyte between them, there is a reaction allowing electrons to move from one metal to the other. This means one has a positive charge and the other a negative. Put a circuit across them and you now have a battery. 5) friction - rubbing certain items together will encourage electrons to move from one surface to the other, creating a difference in charge. The charge can't move ordinarily, unless you touch a metal object and get a static shock. Other effects include objects sticking to you, hair standing up, lightning. It can be dangerous to electronics and is generally unwanted except in a few instances, like car painting - make the paint positive and the car negative and the paint will be attracted to the car and settle evenly. 6) magnetism - relies on the concept that electric fields and magnetic fields are closed intertwined. Think of the law as this - *when a conductor moves relative to a magnetic field, a current will be induced in the conductor*. You have three elements there - a magnetic field, a current in a conductor, and relative movement between conductor and magnetic fields. Any two and you'll get the third. A current through a conductor, through a magnetic field, and you'll get relative movement, which we use in motors. Relative movement through magnetic fields will induce a current, and this is how a generator works. That relative movement is created by a burning fuel to create steam to turn a turbine, burning fuel to turn an engine, creating nuclear reactions to create steam to turn a turbine, water flowing through a dam to turn a turbine, wind flowing through wind turbines, geothermal steam flowing through a turbine etc - basically every method you know of power plants except for solar. We use rotational motion as it is easiest and most compact and doesn't have to \"reset\" itself. Even a hand crank or workout bike could be rigged up to produce electricity. The amount it produces is very little, so we need to have lots of the conductor in the magnetic field to produce more, so we make the conductor into a coil with hundreds or thousands of turns. At each end of the coil, there is a voltage. Attach that to an electricity grid and you have electricity. The nature of how this works means your have to use what's generated immediately. The electricity you're using right now turned a turbine somewhere mere seconds ago. Unless you can store it in a battery (which is not possible for the power grid to do right now, battery technology isn't good enough), which works because current flowing into a rechargeable battery can force the chemical reaction to happen again, effectively recharging the battery. The technology can be used small scale on solar panels on your house, allowing you to use the energy generated by sunlight at a later time.",
"Electrons are constituents of matter. In metals, some of their electrons are highly mobile, and will drift in a direction defined by the local electric field. We can create those local electric fields in an electrical circuit in different ways. One way involves putting different chemicals in a battery. The chemical reactions cause electrons to \"pile up\" in some places, so that the two battery terminals are at different voltages. Another way involves a fundamental physical law of electromagnetism: any wire loop exposed to a changing magnetic field will have an electric current induced in it. To make a large electric generator, you can engineer a magnet design to spin on a shaft, in the middle of many copper wire coils."
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i1i29r | How are fired bullets unique to a riffle? | With modern production techniques and controls, how are they able to create a unique ballistic signature? | Engineering | explainlikeimfive | {
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"They're not unique. At best you can reliably say that the bullet is right kind to have been fired from a particular gun. If someone is caught with an M1911 chambered in .45 ACP they definitely aren't holding the weapon that put a .22LR into someone's head. Matching rifling marks is one of nunerous forensic techniques that turned out to be bunk.",
"Each gun is very, very similar; but no two are identical. The scratches inside the barrel, left by the machine tools that make it, are unique. That's the most common variation, but it's not the only one. If the brass casing can be recovered, for example, the firing pin leaves a unique impression on the primer. The expansion of the brass casing into the chamber of the weapon is also variable from weapon to weapon, but is not totally unique. Then, of course, some bullets of the exact same size can be fired successfully from one gun but not from another of the same caliber; for example, if a round is pure lead and is fired from a barrel that spins it very fast, it will rip itself apart in midair. Such a bullet must be fired from a gun with a more moderate twist rate."
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i1oki0 | Why are Laypeople with little scientific or engineering background put in charge of scientific or engineering projects? | I've been watching a marathon of disaster documentaries and the reoccuring theme in so many disasters is that scientists / engineers warn... managers ignore those warnings... disaster happens. Space shuttle Columbia and Challenger are two good examples of engineers bringing up their worries and then just being totally shut down by managers that aren't experts in that field. You can see how certain events are happening now where scientists are being ignored and that has lead to disaster in 2020. But Rule 2.. | Engineering | explainlikeimfive | {
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"For what it’s worth, there are plenty of times, jobs, and places where a team of experts can be reasonably led by someone who isn’t an expert. A good manager knows how to get good results from a team. And trusting the people under you to effectively execute their jobs to the highest of their capabilities is really all any manager is doing anyway. Many of these kinds of things are exactly this. A good business person, or money cruncher, or number mover, or manager is put in charge of a group of engineers or scientists or whatever. And that person leans on the team for the science stuff, and they take care of putting the pieces together. For an analogy I can reasonably communicate, Bill Bellichick has never played a down of professional football. But he’s one of if not the best coach of all time. Because someone needs to move the pieces on the board.",
"I'm an engineer. You ask me to run calculations, make design drawings, explain technical issues to you, I can do it in a heartbeat. You ask me to make scheduling, handle budgets, negotiate with outside contractors and vendors? I'm in way over my head. I've done project management work, and while I don't mind it, it's not something I went to school for, it's not something I'm versed in and not something I'm super comfortable with when it comes to big budget projects. But I've seen this problem come up before. Project management is more concerned with getting it done on time and in budget. They will cut whatever corners they need to make that happen. Usually they have enough experience/knowledge to know what corners to cut. My job is to make sure that whatever we are doing, it's as good as we can make it, and while I take budget and schedule into account, I would prefer to push things back and spend more money rather than make it worse. A good project manager knows when to listen to their engineers, that's why they have them on their team.",
"Usually, for highly technical projects, the manager is not a non-technical person. S/he is someone who has in some capacity served at lower ranks, and after doing an MBA got into managing. But it is not uncommon for managers to be technically sound on one aspect of a project while not knowing the rest. The reason why such people are put in charge is that noone can really have a mastery over all the aspects of a project. You need someone who is not entirely ignorant of the technical things, but is adept at bringing together people from disparate aspects of the projects and ensure that a synergy is maintained. A manager failing to heed the technical specialist is a failure because of s/he is a bad manager, not because of his/her lack of technical knowledge.",
"To add to the management answers of others, there's also the issue that most people who get into science and engineering do it because they enjoy doing it. Once you start getting into management you're often taken away from that thing you love doing.",
"The biggest reason is costs. Massive scientific and engineering undertakings are massively expensive and often times run over budget and over schedule. The funding of these projects typically come from a mix of private and governmental investment. As such the investors need someone to ensure that the project will be completed as close to the budget as possible because if it goes over budget it may not be completed at all and thus a total loss for everyone involved. Unfortunately that means weighing science vs cost vs time. Which is a business decision, so someone with a business background is given a managing position in the project. Occasionally they'll miscalculate what's important with disastrous consequences, but it's worth noting that it does work well a vast majority of the time. And by vast majority I mean every day."
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i1pxk4 | How does my car key only open my car | Engineering | explainlikeimfive | {
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"your car is a phone that only answers to one call - all others are spam. That car key/fob is the only phone it will answer.",
"It’s got a code inside, it transmits the code as a radio signal, and only if the car gets the right code, it unlocks",
"If it's an old school key, you know the metal things, it can open other cars. There are only so many combinations you can do. With fobs it's a completely unique signal code, though."
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i1ztep | What are the differences between an amp, watt, volt, and ohm? | Engineering | explainlikeimfive | {
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"An ampere measures the flow of electricity through a circuit; think of it as the water flowing through a hose, or over a dam. A volt is potential energy; the water sitting behind the dam (or behind the faucet) awaiting its release. An ohm is a measure of resistance to the flow of electrons, like the diameter of the hose (or the size of the dam's passages). A watt is a measure of energy transfer; how much water is flowing over how much time; higher resistance (smaller hoses) for a given wattage will mean less energy transfer over time.",
"Amp= measure of flow of electricity. Speed so to speak Watt= how much power something draws Volt= set source power ie 9 volt battery Ohm= measure of resistance on a circuit. It’s something that pushes back on the flow of electricity or amps. Change one you change both. Edit: to understand these and how they all correlate search Ohms law.",
"An ohm is a measurement of resistance, which is how much harder it is to transmit electricity in the circuit An amp is how much (or the volume of) electricity passes one point in one second. A watt is the rate of power consumption (volts x amps) And a volt is the force of the electrical flow, so high voltage is Sonic and low voltage is a snail Edit: See [this image]( URL_0 ) to find out how they link",
"An amp is how fast the river flows, watts is the amount of water flowing, voltage is the force exerted by the water, and an ohm is anything in the way of the river. To that extent, amp is how much electricity is flowing through the wire, a volt is the \"pressure\" of electricity between 2 points, watts is the total amount of power, and ohms is resistance"
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i24wxj | How do tires not fall/pop off the rim? | I know some tires do indeed just pop off the rim in freak accidents. What I am trying to get to the bottom of is how do great condition tires not pop of the rim with all the weight from a car and the pressure they are in. Tires don't have any adhesives connecting them to the rim. Is it the pressure itself or something else? & #x200B; Edit: Thank you all for saving me from this tire hell. | Engineering | explainlikeimfive | {
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"The rim is not a flat piece. It’s a long tubular structure . Length as in the line along the width of the car. The tire sits on top, and around the wheel and when fully inflated the tire is pressured around the rim, sealing the air inside and preventing it from falling URL_0 Take a look at this picture to see the width of a wheel",
"The bead wire anchors the tire and locks it onto the wheel. URL_0"
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i2cfdn | Why are electric cables installed outside suspended in midair when lightning strikes can easily damage them? | Engineering | explainlikeimfive | {
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"Because they're way cheaper to install and service that way, as opposed to digging tunnels from the power plant to every single structure that needs power.",
"Running wires underground can encounter other risks, like plant roots or even ants damaging the wires coatings and causing damage. Replacing damaged wires underground is also a lot more dangerous and more expensive than replacing damaged suspended wires. Speaking of ants, it's more likely to loose power even above ground because of ant damage to the wooden pillars than for the wires to get hit by lightning. It's just not a common enough event to be the primary concern.",
"Because it’s cheaper, a lot cheaper, and lightning strikes don’t hit power lines that often anyway You could make them underground, but it’s only done where there is no other option, like in cities, because underground high voltage power lines are incredibly explosive",
"As most other answers tell you, it's just cheaper to construct them that way. But even when hanging out in the open, they're usually not defenseless from lightning strikes! Lightning favors the most direct path to ground. Jumping directly through the air itself is hard, so if it can take a shortcut through something, it usually will. [This What If article]( URL_3 ) by xkcd goes into more detail (still ELI5 friendly), but the key takeaway is that you can imagine rolling a sphere 60 meters in diameter across the landscape, where it has to roll up and over any obstacles on the ground. Anywhere that sphere touches is a prime lightning strike target. Some high-voltage transmission lines carry extra sacrificial cables that hang above the actual power-delivering ones. [Here's an example of a tower carrying such lines.]( URL_1 ) You can notice the actual power cables are held separate from the tower structure by those long, dark insulators. For AC power (which is most transmission lines) they also tend to come in bundles of three. Any \"extra\" cables hanging above these towers with no insulators are there to provide lightning strike protection. These cables are fused directly to the towers they rest on, or to a cable leading directly into the ground to redirect the lighting strike away from the sensitive parts. What's more, you might find the lines decorated with what looks like more, redundant insulators. They may be casually dangling off the lines [like this]( URL_0 ), or they may be directly mounted onto those insulators [like this]( URL_4 ), or they may take the form of [these rectangular box thingies]( URL_2 ) whenever the line taps off to go underground or into a transformer for delivery to a customer. These are all called *lightning arresters*, and they're essentially giant fuses. Depending on what kind of lightning arrester it is and where it's mounted, when lightning strikes, all that extra current will cause the arrester to melt, which either severs a path to prevent current from passing through, or creates a new path to a ground diversion to carry the current away."
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i2ec61 | What's the obstacle between us and automated driving? | It seems like we have all we need. Is there something big in our way? | Engineering | explainlikeimfive | {
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"The technology and hardware isn't there yet. I remember viewing a vide on the topic once, and fully autonomous driving is still way far off. In terms of steps, 1-5, we're currently at about step 2, where step 5 is where we want to be. & #x200B; It's mostly a matter of time, software gets developed and fleshed out, and the hardware gets progressively stronger without requiring more space or power. But it won't be next year, or the year after."
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i2gc1k | How does a PC needs a big stick of RAM to fit 8GB, but a phone can have the same amount in a much smaller space? | Engineering | explainlikeimfive | {
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"The actual chips of RAM in a PC are roughly the same size as the ones in your phone. They're just soldered onto a PCB and sold as DIMMs for modularity and compatibility.",
"Phones are not modular. Phone hardware is more expensive, specialized hardware. PC's could choose a smaller RAM spec, but this would have the consequence of both increasing prices and breaking backwards compatibility.",
"Your PC doesn't actually need a big stick for 8gb of ram, but there is a standard that manufactures use that allows them to create many configurations of of memory sticks and have them be comparable with whatever system you want to put them in. You can get a 64gb stick of ram that is the same physical size as the 8gb and fits in the same slot. Phones ditch this compatibility and versatility and say what you get is what you have. This let's them ditch the dimm form factor and integrate the ram chips directly only the motherboard."
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i2ilx9 | If today was the first splashdown from space in 45 years, how have astronauts been coming back from the ISS during all these years? | Engineering | explainlikeimfive | {
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"From 1981 until 2011, the US sent Astronauts to space using the Space Shuttle which has wings and glides well enough that they landed them on a longggg runway in Florida The Soviet and later the Russian Soyuz capsules land on the ground generally in Kazakhstan. They've been using Soyuz capsules similar to the modern day one since 1967. The Apollo capsules were the last things to need to return by splashing down and the last Apollo mission was in 1972",
"Today's event was the first splashdown of SpaceX's new Crew Dragon capsule while humans were onboard. Dragon is a new privately-constructed vehicle for transporting humans to and from low earth orbit. Prior to this new vehicle, ISS astronauts returned to Earth using the Russian Soyuz capsule. This capsule lands on land, not water, so even though American astronauts have been using it for decades, it doesn't count as a splashdown. Prior to purchasing rides on Soyuz, American astronauts traveled to and from space on the Space Shuttle, which lands like an aircraft on a runway. Also not a splashdown. Capsule splashdowns have not stopped for 45 years though, only human ones. The next most recent capsule splashdown that did NOT contain astronauts was on April 07, 2020: URL_0",
"Like people have said: the Russians (and the Soviets before them) have lots of fairly empty land, so that's where they prefer to land. The actual landing apparently range from \"whap!\" to \"eaaaaaagghhhhh! WAP!\" :-) And once (in the sixties?), a Soviet capsule was off-target, and the crew was nearly attacked by wolves.",
"Soyuz capsules come down slow enough that they can hit the ground and be okay. They're built like tanks and the Russians have been using them pretty much since they invented them. The Americans had the shuttle, which came down as a glider. Everyone else hitched a ride with the Americans or the Russians to get up or down so those were the only crewed missions for a long time. And when the shuttle went away, *everyone* hitched a ride with a Russians. NASA invested a lot of money into Dragon because it was expensive to buy a ticket on Soyuz, and Dragon capsules splash down instead of hitting the ground."
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i2mqxv | Why do cars make little popping and crackling noises after they’re turned off? | Engineering | explainlikeimfive | {
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"Car engines (and other stuff in the drivetrain) generate a lot of heat and things that are hot expand. When the engine is turned off things will start cooling down and hence contract. So yeah there's little pops and creaks as the metal slowly shrinks a bit.",
"All of the parts that are hot, such as the motor and exhaust are cooling down and contracting, making the noises you are hearing. Normal and nothing to worry about."
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i2rbz9 | why does “hoo” produces cold air but “haa” produces hot air? | Engineering | explainlikeimfive | {
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"When you hoo you make your mouth more close then when you haa, so you change the speed of blown air and evaporation. Hoo evaporates more water then haa and you feel more cold",
"Hoo and haa are “the same temp” leaving the mouth but it’s the speed that the air leaves the mouth that affects the temperature. Faster moving air = lower pressure Lower pressure = lower temperature PV = nRT Pressure Volume R - gas constant n - moles/amount Temperature",
"Nobody mentioned about joule-thompson In haa hoo thing about of 50 percent bernoili and 50 percent joule thompson Joule thompson is basicly when you increase presure of air inside your mouth you also bondin air molecules ( or increase bonds powers) which is exotermic rx (that means heatin up your mouth) and when air comes out from your lips its presure goes back to normal and molecules bonds weakens or brokens which is endotermic rx ( blowin way gets colder ) And its how air conditioners work too"
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i2tqi7 | Why can’t the whole world be supplied by one electrical power plant if we can step up and step down voltage with transformers? | Engineering | explainlikeimfive | {
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"Unfortunately, no metal we have found is a perfect conductor (under sustainable circumstances). That is to say that when we pass current through metal some of the current is absorbed. Typically it's not a large amount, but over greater distances you lose more and more \"flow\". Meaning it's inefficient and costly to even try to send power that far. This is what's called \"grid loss\" On top of that, there is a practical maximum a turbine can produce. After that you need more furnaces and more turbines. Essentially leaving you with the same amount of power plants in operation but this time the energy has farther to travel and you lose more. However, in a perfect world yes it could be possible. You'd need transmission lines made of superconductors that have a perfect or near perfect efficiency.",
"Step up/step down transformers trade voltage for current or current for voltage, but in both cases the power remains the same That's the problem with this plan Its not that a house needs 10 amps so if we use a step down transformer to feed it 10 amps at 10 volts everything is fine. The house needs 1250 W of power, and millions of other houses need about that much. If your power station only generates 1.25 MW then it can only power 1,000 houses no matter how crafty you get with your transformers because it simply can't provide the *power*",
"In a textbook question: Yes. In the real world: No. Our electricity grids are largely alternating current: The current and voltage are changing direction 100 or 120 times per second (depending on the region). Alternating current is easier to transform up and down, but if you want to transmit it over very long distances you run into a problem. Just like everything else, a change in voltage can't move faster than the speed of light. Make the cable too long and the customer gets \"out of sync\" with the power plant: The current changes direction again before it even arrives at the customer. This wastes a lot of electricity in the cables. For this reason long-distance transmission lines use direct current. It's a bit more difficult to step up/down but it avoids this problem. That doesn't mean unlimited electricity transport: The cables still have electric resistance. Higher voltages need better insulation and there are practical limits what you can do. Superconductors have zero electric resistance. A worldwide superconducting network powered from a single place would work *in principle*. But superconductors need expensive cooling. Less technical concerns: It's literally a single point of failure. If something goes wrong there the world wouldn't have electricity any more. And it's politically completely unfeasible, countries don't want to rely on other countries that way. You would also need to ship everything to that site, any local resource demand (like cooling water) would be really scarce. And what do you gain? You still need to produce the same amount of electricity. Stepping the voltage up/down just makes transmission easier, it doesn't change the power. Instead of 10000 power plants all over the world you now have 10000 next to each other, which doesn't really help."
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i2u7nu | How does a jet engine work? | Engineering | explainlikeimfive | {
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"Inside there is a spinning shaft running front to back. At the front there is a set of fan blades that suck air into the engine and compresses it. Fuel is mixed in and burnt which causes heat and a large expansion in gas volume. That hot gas rushing out of the back end pushes the plane forwards by Newton's Law \"for every action there is an equal and opposite reaction\". Also on the shaft is a second set of blades which are turned by the hot gas. These turn the shaft and therefore the compressor blades at the front, which sucks it more air, so the process carries on. Variations on this sometimes use the rotations of the shaft itself to drive a propeller in a turboprop aircraft or the blades of a helicopter rotor. Fighter jets inject extra fuel into the exhaust to get more thrust, that's called an afterburner.",
"I did work experience at Rolls Royce Aerospace when I was in school (across fighter jet engines, Navy ship engines and helicopter engines) and for the easiest explanation and way to remember, they used to say... Suck, Squeeze, Bang, Blow. (Sounds like a great Friday night plan to me) Sucks air in the front (Suck), compresses it (Squeeze) fuel is added and ignites (Bang) and is then forced out the back (Blow) causing the propulsion. Simple!"
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i2vs29 | . Why are the two astronauts that just came back such a big deal? Don't we have astronauts going to and from the space station all the time, what makes this case so special that everyone's talking about it? | Engineering | explainlikeimfive | {
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"Usually it’s a *government* agency, like NASA, is sending astronauts up and back. This is the first time a *private* company has sent them up (and back), a new era in space history has begun.",
"It was the first time that the new spaceship \"Crew Dragon\" did a manned reentry. it was also the first time in 45 years that a capsule \"landed\" in the sea. Also it was the first time that a private american company sent and retrieved astronauts from the ISS."
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i3d0ld | AWD vs. 4X4 vs. 4WD? | What is the difference. I have a understanding of transmissions and differentials but what are the differences in the mechanisms and performances? | Engineering | explainlikeimfive | {
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"Not an expert. I have a Jeep and family member has a Subaru so this conversation came up before. What I gathered was: Awd - all four wheels are used for drive. You get the same torque or power to all four wheels at the same time. He doesn’t have the option to disengage this. 4wd - option to have all four wheels used for drive. When engaged you can get torque to all four wheels at the same time. You also have the option of 2WD. I parlay stay in 2WD until on a trail with a higher difficulty of terrain then I’ll switch. I can also get independent power to each wheel. 4x4 - same as 4wd"
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i3d1hc | How do they know exactly where to paint the water line on new ships before they are launched? | Engineering | explainlikeimfive | {
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"Humans have been building ships for 1000s of years. Hence the math that comes along with ship building has been evolving and getting more accurate over those 1000s of years. If done right, the ship builders have pretty much have it down! When a ship is ordered to be made, it usually comes with guidance of how long, wide and deep it needs to be. It also demands how much inside space(volume) it should have and how much weight it should be able to carry. Hence the engineers already know the approximate weight the ship has to carry. Using this, they can do the buoyancy and force balance math/physics and figure out where the water line needs to go. BUT, It's an approximation. The water line can be slightly higher or lower depending upon how much weight the boat is carrying. So not just math but math and physics along with appropriate approximation gets you the water line. I am not a boat builder so the accuracy of boat building might not be exact. My answer is only based on math and physics expertise. Hope this helps :)",
"With a ship that large, yes they can weigh every component. After all, everything was planned and drawn and approved long before the keel was laid. Every joint, weld, wire, bolt, and component is approved by multiple people in an engineering department. There is some amount of error with welds adding a small amounts of weight and other small inconsistencies in some components, but these are relatively miniscule and it takes many tons for a large ship to have it's water line rise even an inch. So yes they calculate the exact location of the water line.",
"> It seems unlikely to me that they can figure this out exactly with math No, they can do it fairly exactly. I mean, every single component of a ship was *put there* by someone (probably a welder) at the instruction of the engineer, who has all of the plans written out. Every steel beam or sheet has a known weight. It's not really rocket science. Sure, they're not accurate down to the pound, but they don't *need* to be.",
"Adding onto the idea that we are actually really good at math, the line isn't exact anyway. A large ship's height above the water is going to change based on it's cargo/fuel/passengers. These ships will pretty much always have ballast tanks that can be filled with water in order to load them down because when unloaded they would tend to ride too high above the water and be very tippy. So even if the ships weight is wrong by a bit they can raise or lower the height above the water to get the correct height.",
"There's software for determining the stability of a vessel based on load out. You drop too many containers on one side... Oh o, your stability goes to rats. Load the vessel up with fuel and operational equipment and your water line is now void. It doesn't matter. Close enough, is close enough."
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i3et1t | Why do airplanes fly so high? | I understand why planes must fly high enouph to avoid hitting buildings and mountains, but airplanes fly much, much, higher than (most) mountains, why? | Engineering | explainlikeimfive | {
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"The air is dense near the ground. The higher you go, the density of air goes down, which means there is less air around at high altitude. A good thing of less air being around is that it is easier to move. It is similar to walking on ground surrounded by air vs. walking in a swimming pool surrounded by water. It takes much more effort to walk in the swimming pool. Since it's easier for the engines to push the airplane forward, it also saves a lot of gas/fuel. Which means it saves a lot of money. Hence airplanes fly so high to save gas money."
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i3f96b | How does changing voltage affect the life of a battery? | So the post title might not make sense as I don't know what I don't know lol. If I have a 12v battery in a van, and it's got a 100ah capacity. I understand that a 12v device can pull 1 amp for 100 hours (I know it's not as easy as that, as it's not perfectly efficient etc, but I'm keeping it simple). If I was to use a converter to use a 60v item, which also pulled 1 amp, would it just drain the battery in 20 hours? (again, keeping it simple). Since 12v x 100 amps is 1200 watts, and 1200 watts / 60 volts = 20 amps, so 1 amp for 20 hours? I feel like this can't be right as it's too simple, but I'm struggling to Google it because I don't really know the words to search for. There's probably a really common phrase that will throw up loads of useful search results once I know it. As an extra Brucie Bonus ELI5, if this was right, could you scale it up to 240v (standard UK house supply)? If I used an inverter on the same 100ah 12v battery to provide 240v (which is common in campervans), would you be able to use a 1200 watt microwave for an hour? | Engineering | explainlikeimfive | {
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"Yes, it's totally that simple. The 12V device pulling 1A is dissipating 12W of power, while the 60V device at 1A is doing 60W, exactly five times as much, so it will drain the battery five times faster (in an ideal situation--as you point out, stuff like the battery's own internal resistance will change that slightly). The inverter situation is likely a bit more complicated because (a) the inverter itself is going to be adding its own inefficiencies and (b) a 1200W microwave will actually be drawing more than that due to heat losses, lights, and fans, but if you had a theoretical perfectly efficient inverter, a device that actually drew 1200W, and a battery with no internal resistance, it would run it for an hour, yes. In reality, when you ask the battery to supply 100A (as it would need to do in this situation) its output voltage is going to dip below 12V due to internal resistance.",
"Assuming perfectly efficient voltage converters - like you did - all you care about is the actual energy stored in the battery. In your case, that's 12V \\* 100Ah = 1200Wh or 1.2kWh. You can then do whatever you want with that energy. You can use it at 1W (at whatever voltage / current configuration you like, as long as \\[V\\] \\* \\[A\\] = 1) and it'll last 1200 hours. At 10W, it'll last 120 hours and so on. & #x200B; > As an extra Brucie Bonus ELI5, if this was right, could you scale it up to 240v (standard UK house supply)? If I used an inverter on the same 100ah 12v battery to provide 240v (which is common in campervans), would you be able to use a 1200 watt microwave for an hour? Yes, you can do that. However, your battery has another restriction in it's specs, and that is the max discharge rate. IIRC, a regular 100Ah car battery is usually rated at around 10A continuous current. So you cannot draw more than 120W out of your car battery for more than a couple of minutes without risking that it catches fire. Or in other words, you cannot safely drain your 100Ah battery in less than 10 hours. So, to power your microwave at 1200W safely for a longer period of time, you'd need 10 batteries. Note: the 10A is a fictional number, I don't know the actual max current rating for car batteries, but every battery (or in fact any real life electricity source) has such a limit."
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i3hi1p | How do standard transmissions work, specifically downshifting? | Engineering | explainlikeimfive | {
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"A clutch is basically a disk brake that connects the engines' shaft with the gear box. If you kick down the clutch pedal, you loosen the \"brake\" and decouple the rotation of the engine shaft from the drivetrain and have no torque applied to the gears, which allows you to pull them apart and set together another pair at different RPM. If you slowly take your foot off the clutch pedal, the disk brake in the clutch starts syncing the RPM of the engine with that of the selected gear by friction.",
"Your engine can only supply a limited amount of torque and can only spin to a limited rpm speed. The transmission uses 1st gear to get you moving from stopped, until you hit high rpms, then the 2nd gear takes low rpm to high rpm again and so on. It's just like a bike, your legs can only move so fast and you can only pedal so hard, so as you go faster, you change gears when your legs cant move fast enough, then you pedal slow to fast as you move through the gear. For down shifting. When you start moving slower and need to go to a lower gear, your engine is at its slowest rpm at the bottom of the gear, and you need to shift to the top of the next gear, so you need to shift out of the gear then speed the engine up, then shift into the lower gear. 1st (low rpm) -- > (high rpm) /shift 2nd (low rpm) -- > (high rpm) / shift 3rd (low rpm) -- > (high rpm) So for down shifting, you have to follow the same flow but in reverse, and you rev match to the high rpm of the top of the gear you are down shifting into.",
"To set up the scene, the path from the engine to the wheels has 2 disconnection points: the clutch, and the gears. If both these things are disconnected (clutch pedal down, gear lever in neutral) then what's in between - the clutch itself and transmission's input half - are spinning freely and by friction will slow down. However when downshifting you're moving to a gear where the clutch speed actually needs to come up. And since you're moving metal bits inside a transmission engaging two metal gears into each other requires them to be moving at about the same speed or you're just going to grind metal together. In the old days people were expected to double-clutch... You shift to neutral, rev the engine to the speed you want, and then release the clutch pedal while still in neutral. This connects the clutch and transmission input to the engine and brings them up to speed. Now you can press the clutch pedal again for properly shifting into your new low gear without grinding gears. Nowadays transmissions have synchronizers on the gears. When you push the lever into a gear there's a bit of rubbing of the synchronizers to bring the clutch+input to the correct speed before the gear goes in. You may notice that downshifting may involve putting a bit of extra pressure on the gear lever to go in and it takes a moment before it wants to happen - that's this mechanism. However they are a component that can wear out over time, replacing them is expensive since it involves removing and dismantling the transmission/gearbox itself, and honestly they have limits. They are not meant for shifting from 5th to 2nd while remaining at interstate highway speeds, and they are most certainly not able to handle changing gears without pressing the clutch. Don't abuse them. Also not all gears have them - commonly reverse may not have any synchronization or it may cheat by borrowing another gear's synchronizer meaning you should not shift into reverse unless you're absolutely stopped and the engine is at idle. Older cars may not have one on 1st gear. Consequently some drivers still choose to perform the double-clutch procedure even on modern cars. The synchronizers will last longer and it should make the gear lever easier to move."
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i3p3pn | How does a single outlet power multiple electronics on a power strip? Is there a maximum limit of how many things can be plugged in? | Engineering | explainlikeimfive | {
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"Simple answer is yes. Most power outlets are on a 15 or 20 amp circuit. So the max device for the outlet depends on the amperage draw for the connected devices. If you get over that 15 or 20 amps the breaker will trip.",
"To go a little further, The electric service delivered to your house is capable of providing WAY MORE POWER than you could ever reasonably need. In fact, your electric service can provide way more power than any of the wires themselves can sustainably deliver so the main line can provide service to all the subscribers both at the end of the run and under peak load. Due to inherent internal resistance in the wires, some energy is transformed into electromagnetism (all conductors are also antenna) and HEAT. When you have a closed, unimpeded circuit, electricity will flow freely. Too freely. Electrons will flow as fast as they can over the surface layer of the wire (which is why stranded wire can carry more current than solid wire), and this will raise the temperature of the wire. What happens when the temperature goes up? Conductivity goes up. What happens when conductivity goes up? Temperature goes up... And what you get is thermal runaway. The wires in your house can flash into plasma in an instant, and your house is on fire. Enter fuses, breakers, GFCI, and ground. These devices are designed to limit the flow of current to prevent your wires from catching fire. There is also safety in limiting the amount of power that can go through a circuit because GOD DAMN what sort of industrial mixer are you running in the kitchen that needs 800A? Fuses are glorified incandescent light bulbs. If they flow too much current, they have a tungsten element, with high impedance, that will burn out, breaking the flow of electricity. The nice thing about fuses is they can't fail. Breakers can fail, which is why you don't see them in cars. They work by either a huge electromagnetic pulse, or by thermal deformation of a spring. You can't just turn a breaker back on, you have to reset it, flex that spring back into shape, before you switch it back to the on position. GFCI will trip due to a huge induction load, which tends to make them incompatible with stand mixers and garage air compressors. Ground is a place to dump current that isn't through your body and across your chest and heart, but the current will still flow high enough to trip the breaker. All your devices have impedance and resistance, so they'll only draw what they need. The limit to the number of devices you can plug in is set by the lowest rated segment in the circuit. So you might have a 20A breaker, but the outlet might be limited to 15A. Manufacturers also warn against overloading any one component - power strips, for example, are not supposed to have more power strips or extension cords plugged into them. And bear in mind you have to think about the whole circuit, not just one particular outlet in a room.",
"An outlet will accept as much power as you put demand on it. The only limiting factor is the circuit breaker that it's circuit is on. The typical max load you can put on a receptacle outlet is 16A, or 1920W for a 120V circuit.",
"In your house multiple outlets are connected to each other through the wiring in the walls. The limit to what you can plug in depends on the current draw. In a typical US house, the outlets are on a 15-amp circuit breaker, so you can theoretically plug in enough items to draw close to 15 amps into a single outlet (as long as nothing is plugged in to the other outlets)."
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i3rc2c | What is actually happening when the power *almost* goes out? | when there's a lot of wind or rain, and the lights dim or flicker for a second, and then immediately kick back on, what is actually happening? I'm asking because it seems like if the power is going to disconnect, it would be from some wire breaking or something. So what is happening when it almost goes out, but it doesn't? | Engineering | explainlikeimfive | {
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"A lot of power grids are designed with automatic fail over. If a part of the grid goes down, say from a blown transformer or a power pole being knocked out, the system is designed to detect that and reroute power through alternate paths. While that system can react extremely quickly, it can't react as quickly as electricity flows, and the sudden change in load can briefly cause power levels to dip, so the flicker you see is the brief drop in current before the system can compensate. The flip side of the coin is the people for whom power *does* go out, but only for a few seconds until the system switches over. Their power coming back on is what causes your power to \"almost\" go out."
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i3ynqy | Why did the Beirut explosion damage buildings so much but not people? | Engineering | explainlikeimfive | {
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"There are thousands of injured people, how is this not a damage? Last I heard also 70 dead but I think those were the ones closer to the explosion. (Around 4000 injured at least)",
"A big thing is the sudden pressure difference. A building can’t move air out that quick so it puts pressure on the walls to move. In a human you can easily breathe out/burp and you can withstand a greater pressure difference because buildings aren’t built to stand that type of force."
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i3z18i | do certain gears of a car have a set range of speed | I’m mainly asking because i can’t wrap my head around the concept of stick shift. ex: would 1st gear be good from “X” mph until “Y” mph and then you need to switch to 2nd gear? | Engineering | explainlikeimfive | {
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"Yes and no. For a given setup, yes. First gear can work from, say, 10 to 30mph. Second from 20 to 60. Third 30 to 90. So on. If you got a different car or transmission, then it could/would be different. In general, you don't want to run it all the way to the max. You'd run first gear until shortly after you could switch to second, and second until shortly after you could switch to third. This keeps the engine rpm's lower, improving efficiency and making for a smoother/quieter ride.",
"Gas engines only really work well in a certain RPM range, too low and the engine makes too little power, too high and you risk damaging it and use a lot of fuel. Gears work by sort of trading speed for acceleration, so in first gear you trade off a lot of speed, to get a lot of force in order to start, which is why the engine revs up very high even at low speeds, but you accelerate really fast. Second gear you keep more speed, and so less acceleration. And finally in 5th or/ 6th you actually trade away acceleration in order to get more speed, and higher fuel efficiency. This in short means the speed of the car is limited by how the speed of the engine and much speed the gear “trades away” so you have a speed range for every gear This is absolutely the same in an automatic and a stick shift, just switching e tween these gears works is achieved in very different ways"
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i437c9 | Why do cars have tachometers? | Engineering | explainlikeimfive | {
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"If you ever try and drive a non-synchronous truck using a crash gearbox (e.g. Eaton Fuller Roadranger) then you have to be reasonably accurate with your gear changes, double de-clutching on the way down the gears waiting for the engine speed to drop ~300rpm (depending on the vehicle) before engaging the higher gear. In a manual car with synchromesh that is far less of an issue - but it still helps to know when you're in danger of redlining the engine speed using the throttle. And in an automatic you can still hit the red zone by simply putting the car into \"neutral\" and hitting the accelerator. Managing engine speed is one of the more important things about car health so it makes sense to give that indicator priority on the dashboard.",
"You weren't born with an innate sense of when to change gears in a car. You learned by using the tachometer*. You relearn whenever you get a new car and has to get used to how it feels - especially if it uses a different engine type, for example switching to diesel (or back) requires you to completely relearn how a car should feel. Once you've learned how your car (or other motorized transport) feels at all speeds and gears, you don't need any of the instrument panel except maybe a way to estimate how much fuel you have left. *) Edit: unless you either never got professional driving instruction and didn't bother maintaining your first vehicle or got it from an instructor who didn't bother maintaining his vehicles. In that case you almost certainly learned from someone who learned from a tachometer somewhere upstream and just skipped the lessons about using your full rev range.",
"When you start your car, but haven't pulled away, the RPM is useful to check the engine is behaving properly. If your car is idling at abnormal RPM it's a sign something is wrong. It's useful on a manual car for gear changes, although sound and feel works as well, it's less precise and less useful for deaf people."
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i43vpb | How does a petrol gauge in a car work? | How does the gauge know how much petrol is in the tank? There can't be any electrics involved as that would be unsafe, surely? | Engineering | explainlikeimfive | {
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"Inside the fuel tank is a little hollow plastic float (almost looks like a plastic bar of soap). That will be attached to the fuel delivery module with a rigid metal wire. As fuel level rises and falls the float travels along an arch as that metal wire pivots around its attachment. At that pivot is a device called a potentiometer which is able to translate that radial position of the wire into an electrical voltage by way of changing electrical resistances along the path of motion. Your car's electronic brain reads that voltage and translates it to a fuel level.",
"As far as I know, they put a ball floating on fuel and a sensor attached to that ball measures the level of the ball floating. All the electronic stuff is outside the tank. Edit: typo"
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i45z8v | How big a factor does heat play in space travel? | I was always under the impression that effective dissipation or cooling was a major problem in space travel. Is this true because the vacuum doesn't move heat? Edit: is this one of the largest factors in longer distance space travel? | Engineering | explainlikeimfive | {
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"You can still radiate heat away in a vacuum it’s just slower to use radiation only. Craft and instruments need to be designed in a way that doesn’t produce more heat than can be released into space. (unless its primary purpose it to heat up to some given temp)",
"Yes it is. You need radiator to dissipate the heat or you spacecraft will heat up and destroy itself. [ URL_0 ]( URL_0 ) On the Space shuttle the radiator are inside the cargo door, so the space shuttle need to keep it's cargo doors open when they operate in space. [ URL_1 ]( URL_1 ) On the ISS the white panels are the radiator.",
"It's a massive issue, because heat works so much differently than what we're used to on Earth, where it is moved automatically all the time. 1. It moves slower. The only way to move heat in a vacuum is by radiation. Every hot object radiates electromagnetic waves in a frequency depending on the temperature (lower temp = lower frequency). And at \"room temperature\", this is really really inefficient. So you need a lot of cooling capacity in order to move heat. The massive cooling panels on the ISS only radiate 70 kW at maximum capacity, while a 70 kW AC can fit on a pickup truck bed. 2. It's directional. If you're exposed to the sun, you take on heat rather quickly, that's even true on Earth. But on Earth, things in the shadow also heat up over time by conducting heat in from the air. In space, if you're in the shadow, you get ZERO heat. That leads to massive temperature changes between day and night, or between the front and back of your spacecraft."
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i46a88 | Are electric motors nowadays vastly more efficient than an electric motor from 100 years ago? | I've disassembled electric motors from about the 1950's, and they seem identical to the ones we have today. So have there been any advances in electric motor technology in the past 100 years? I realize that things have become smaller and more streamlined, and permanent magnets have become more powerful, but these seem like simply incremental changes. The only thing I can think of is brushless motors, but beyond that has anything else substantial changed? | Engineering | explainlikeimfive | {
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"Electric motors pretty much maxed out on efficiency when they were first created, we have motors today that can hit 99% efficiency, but that doesn't give you the right picture A motor that you just want spun up to a constant speed can be made very efficient and you just connect it straight to power and you've got yourself a highly efficient motor. But what if you want to control the speed? Well now you need a motor controller and this is where most of the efficiency gains have been had. Advances in switching electronics allow us to feed the motor exactly what we need to and only draw what is needed from the batteries, earlier systems would generally have to throw a lot of the unneeded power away as heat which isn't efficient and drains your battery. So while motors have remained around the same efficiency as components, the systems involving motors have increased in efficiency as we could build motor controllers with fewer losses.",
"Not all electric motors are the same. The basic electric motor designs were perfected around 1900, so there hasn't been much change in the motors used for every day items like household appliances. What has changed is the high tech motors used in high performance applications like electric cars, or in flying drones. These motors haven't changed much in terms of electrical efficiency (which was already high), but they produce much more power in a much smaller, lighter package. The motors in a Tesla are about the size of a watermelon, but produce several hundred horsepower each. If you were to look at the motors in electric cars from the early 1900's, they might be about the same size, but produce only 10 or 20 horsepower. The advances that allow this include brushless motors, which are more reliable and more powerful than older style brushed motors. The use of new materials such as rare earth magnets allows the creation of smaller, more powerful motors as well."
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i4lsqr | why do people talk about the maximum life of a car as the cost of the last repair it'll get vs it's current value, rather than the price of repairs over a set time/mileage vs the same for another newer car? wouldn't this be easy data to collect and graph for mechanic companies? | at some point every car is going to be bought by someone who drives it into the ground. with hundreds of millions of cars on the road we should have a better idea of how long they last, and how many miles you lose out of a cars life for each bad thing done to it | Engineering | explainlikeimfive | {
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"Cars aren't perfect. One your car hits a low enough value there's no point in major repairs. If your car is worth 500$ and the repairs are gonna be 3500$. Just buy a 3500$ car at that point"
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i4par2 | Why are cars exhaust pipe always located at the rear, not side? And truck exhaust pipe located at the front but high up? | Engineering | explainlikeimfive | {
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"Side exhaust tend to not do well if a fair number of people burn their clothes and skin getting in and out of the car from the side. Most cars don't have entry ways from the rear. Trucks used to (perhaps still do) spend a lot of time running idle (in cold weather, many truckers used to keep their engines running all night even while parked and the driver is sleeping in the cabin). The container or load at the back is detachable and people tend to work there attaching and detaching stuff while the engine continues to run. The high exhaust makes it more comfortable and safe."
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i4rogv | Why does a bullet not hit and break the barrel of the gun when they’re fired? | Engineering | explainlikeimfive | {
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"g0k3c9c",
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"text": [
"The bullet is fired through the barrel, not into it. It just skims along the inside surface. Poorly made/maintained guns have certainly been known to explode during firing if the barrel or receiver isn’t strong enough to control the expanding gunpowder blast.",
"Guns are like spit balls. Bullets are much softer than the barrel. Most (if not all guns) the bullet is already loaded in to the barrel partially before it's shot. (Revolvers have cylinders and should be considered part of the barrel here.) The thing that propels the bullet is essentially air. An explosion pushes the bullet out of the barrel. And like a good spit ball, the sides of the bullet is just touching the sides of the barrel/straw."
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i4t9fo | How do mechanical speedometers work? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"There is a spinning magnet below a magnetically sensitive needle. The faster the magnet spins, the more it tries to rotate the needle. A tiny coil spring tries to hold the needle on 0. These forces balance, and this is a measure of the speed of the magnet's rotation. A cable and gears connect the spinning magnet to the drive shaft that powers the wheels, so it spins at a speed proportional to the speed of the car."
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i5e0em | how homing missiles work? How do they actually track the target that the weapon that fired them was targeting? | Engineering | explainlikeimfive | {
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"g0ogc6j"
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"text": [
"For the purposes of this question, we'll consider two categories of missile: *semi-active radar homing* and *infrared homing.* * A semi-active radar homing missile relies on an external radar source to provide the tracking data. The radar source sweeps the sky with a beam of radio waves; when the radio waves strike a target, they bounce back and paint a characteristic signal that the source can then send to the missile. All the missile does is listen to the source, and adjust its navigation based on constant tracking updates -- the radar source can tell how the target is moving, and provides the necessary angles for guidance correction. * Infrared homing missiles are comparatively simpler: infrared radiation is heat, so these are also called *heat-seeking missiles.* They operate by pointing their \"eyes\" at a source of heat, and then tracking towards it in much the same manner as a SARH missile."
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i5mnar | What causes the electricity to go out for a second or two during a thunderstorm? | The power often flickers or goes out for a few seconds during afternoon storms in Florida. What is the cause? Thanks! | Engineering | explainlikeimfive | {
"a_id": [
"g0q5my0"
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"text": [
"Automatically resetting circuit breakers in the power grid The power company has breakers spread throughout the power grid that will trip if something bad happens like a short to ground from a tree branch hitting the line, but rather than just sending the neighborhood dark until someone can come out they'll wait a second and retry, if it trips again it'll try in another second, and again. After 3 attempts they generally wait for a signal to be sent before trying again or someone has to physically reset them after the fault has been cleared. This is why you'll sometimes get quick flashes of restored power before it goes out for long periods of time, or may only have 1-2 second blackouts during a storm."
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i5wr8j | How do container ships secure their cargo such that the shipping containers at the top of those tall stacks do not fall off into the ocean? | Engineering | explainlikeimfive | {
"a_id": [
"g0rz8m1",
"g0rz4ec"
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"text": [
"ISO containers (aka conexes, shipping containers,) are modular, they have points where you can attach each container at each corner to the containers around the one you're mounting. When you do this, the set of containers act as a single block and not singular containers.",
"The containers are connected together by single or double stacking cones or twist locks. The entire stack or container block is lashed using lashing wires or rods and turnbuckles. If you want me to explain in ELI5 what a turnbuckle, a twist lock, a stack, a stacking cone, a rod or a lashing wire is, just let me know."
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i6i71l | waterjet cutters, how the hell do they work and keep such a high pressure and have such a straight cut | Engineering | explainlikeimfive | {
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"According to Pascal's law, pressure exerted on a liquid is distributed evenly throughout the liquid. So when liquid is exerted with high pressure through a small hole, the pressure remains the same but the area is extremely small. The makes the force exerted by that small jet extremely high. This makes cutting objects extremely easy.",
"Very strong hydraulics force water through very small openings. Water doesn't compress (well, that's not exactly true, but it's pretty darn incompressible), so when force is applied to water it either moves away from the force or breaks the thing applying the force. Build strong enough hydraulics, pumps,tanks and tubing, and you can produce an extremely powerful and focused stream of water - powerful enough to cut through steel and other hard materials - and the more focused it is, the more effective it is at cutting since force is focused on a very small area. Sometimes abrasive materials are mixed into the water that provide additional cutting power."
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i6offa | How does one-way glass work? | Engineering | explainlikeimfive | {
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"text": [
"One-way mirrors (or one-way glass) have a light mirroring layer applied. They are made to be reflective, but not as reflective as a typical mirror. The way that they are used is that you light the room on one side brightly and leave the other side dark. Since there is a lot of light reflecting off of the mirror on the brightly lit side it appears as a mirror. In the dark room it appears as glass because there is a lot of light still passing through from the other side but very little reflecting off of it. The key takeaway is that a \"one-way mirror\" would really work from either side if you lit the rooms in the opposite way.",
"It only has 50% of the reflective coating applied. You turn off the lights in one room so that 50% of the dark room's light is transmitted and 50% is reflected. But for all intents and purposes 50% of 0 is 0. But if the other room is very bright, 50% reflected light still leaves enough transmitted light to be seen in the dark room."
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i6tlrb | Large Hadron Collider Question | If the Large Hadron Collider has produced the hottest known temperature in the Universe(5 trillion kelvin in 2012), how do the materials of the LHC not instantly vaporize from the heat? How can anything withstand that heat, or do the particles not actually “touch” anything besides other particles? | Engineering | explainlikeimfive | {
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"g0xwdpm",
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"text": [
"A very small amount of particles are at that temperature and they are suspended in a hard vacuum by magnetic fields. They never touch the walls of the collider and even if they did they contain so little energy in total that nothing spectacular would happen on the macroscopic scale.",
"Temperature and heat are different things so something as small as sub atomic particles reaching high temperatures don’t have sufficient energy to cause the damage you mentioned. The energy will be able to dissipate to the surroundings. I know that other nuclear physics research sites use toroidal electromagnets to keep the particles in a donut shape and from touching the sides; the example I remember reading about was for plasma though so unsure if it would translate to the LHC in the same way."
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i6yuu6 | Why do front loading washing machines take so much longer than top loading? | Hellos! My new front loading washing machine has a standard wash cycle of 2 hours. My old top loading one took under an hour. Why is this so please? | Engineering | explainlikeimfive | {
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"text": [
"You’re using less water to complete the same job. So you need longer wash cycles. For the most part."
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i71k34 | Why do some fighter jets have two engines side by side and others just have one? | Engineering | explainlikeimfive | {
"a_id": [
"g0z8vp4"
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"text": [
"It's just a design difference based on the role the specific jet is intended for. There are pros and cons to both (although as technology advances, these are becoming less apparent), and the choice depends on which factors are considered important. A fighter with twin engines is generally faster, climbs better, has better maneuverability, and provides extra thrust for take-off (which is ideal for aircraft carrier based jets). Twin engine fighters also provide more range because the extra thrust mean they can carry bigger fuel tanks and more fuel, and that extra power can often let them carry larger payloads. You also have a safely margin in that if one engine fails, the plane can still fly on the remaining engine. The flipside is that They're more expensive to build and maintain, require more maintenance, use more fuel, and since they're larger, tend to be less stealthy (although this can be offset by using stealth technology)."
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i788fo | Why are digital displays, car tachometer or aircrafts cockpit backlights often green? | I noticed, that especially older japanese cars had tachometers with green lights. Aircrafts like the C17 or Ilyushins also have green cockpit lights. Are there any benefits or some special reasons for using that colour? Maybe like easier to read? For example the cockpit colours of Soviet aircraft were turquoise, because it was confirmed that this colour is affecting the pilots psychologically positive. | Engineering | explainlikeimfive | {
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"It is easier on the eyes, and is less likely to cause eye fatigue. There is a reason why most current phones have blue light filters.",
"Our eyes are naturally more sensitive to green than any other color, likely because we evolved in nature between green trees and green grass, so at the same power, it’s brighter and easier to see"
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i7b20f | how motorcycles make so much horsepower with small engines but cars need bigger engine or turbochargers? | Most 600cc super bikes make more power than many entry level passenger cars. | Engineering | explainlikeimfive | {
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"The short version is that the PWR (power to weight ratio) is much higher in motorcycles since most of the bike weight is in it's engine. It doesn't have to waste much power getting all the mass of a full car moving.",
"Revs. Power is energy over time. Energy is coming from fuel, so in case of a combustion engine, it's power is fuel burned in a unit of time. Motorbikes can spin their engines up to 15k RPM while most standard cars red out at 5k. This means the bikes use the volume of their engines 2-3 times for every time a car does, can use 2-3 times as much petrol and gain 2-3 times us much energy in the same time. Now, there is a price to pay. Bikes are super loud, the quick-revving engines don't last nearly as long as car engines and they are generally not as efficient as cars (because they sacrifice efficiency for light weight). What happens if you use the same trick in cars? F1 happens. Their engines rev up to 20k giving them incredible performance.",
"They dont have to worry about many things that cars do. The big ones that come to mind are weight, sound, and emissions. Weight: motorcycles can remain very fuel efficient without very efficient engines. Cars have to worry about remaining efficient while also lugging a LOT of extra weight. You lose some overall performance compensating for that. Sound: cars typically come with engines that run quieter, which isn't a concern for a performance bike. You lose performance making sure that people can still hear each other over the sound of the engine. Emmissions: Way more stringent emissions regulations on cars. Manufacturers will build to that standard and sacrifice performance as a result. Motorcycles are not bound by the same regulations. When you boil it down engineers simply have less limitations designing a bike engine and can get more power out of it when compared to a car engine with the same displacement.",
"Economies of scale. Larger engines can produce more torque, but smaller engines can produce more work. This is because smaller, lighter components can move faster. It's not unreasonable for a motorcycle to have a redline of 14,000 to 22,000 RPM. A larger car engine would rip itself apart at engine speeds typically above 7,500 RPM. Formula 1 can achieve astronomical engine speeds, but they're using insanely expensive engineering and materials, with a stroke less than an inch for a piston skyward of 4 inches across, they're massively over-square, and they have a lot of combustion challenges in this configuration. Their engines are only good for 2 races before needing to be replaced. But car engines, even in Formula 1, need all the torque they can get to move those absolutely massive vehicles. Not only do cars weigh tons vs pounds (F1 is an exception, some bikes are heavier than the curb weight of these cars - pre ballast, F1 cars are so light they have a regulation minimum weight), they also have the dynamic weight of their dynamics, both pushing down on the car, and having to be overcome."
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i7dkuv | How can a heat pump make heat when it's very cold outside? Where does the heat come from? | Engineering | explainlikeimfive | {
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"text": [
"The outside is not cold in winter. It has a temperature of 260-270-ish Kelvin, while summer has a temperature of about 290-300 Kelvin. 260 kelvin is cold to humans because we've evolved in a way that's not compatible with those temperatures, but 260 Kelvin is not objectively cold. Objectively speaking, summer is just about 10% warmer than winter. Heat pumps utilize the fact that \"phase changing\" of a substance requires a lot of energy. Phase changing is what we call it when a material goes from for example liquid to gas, aka \"boiling\". You can change the boiling point of a liquid by changing the pressure around it, so a heat pump lowers the pressure on one side, causing the liquid to boil and turn into a gas. This process requires energy to do, which it takes from the environment (outside, in this case). As we have already established, there is plenty of energy to suck up even in winter. This gas is transferred to the inside of the house, along with all the energy it sucked up from the outside, where the heat pump suddenly increases the pressure, causing the gas to turn into liquid again, and at the same time dump all the energy it took from outside into the inside environment. A cold winter day is so cold that it would be very difficult to make water boil by just changing the pressure around it, but many other substances are still liquid at -10 celsius, and those are more ideal to use in a heat pump. The efficiency of the heat pump does go down as you approach the limits of the refrigerants in use. If it gets cold enough, the refrigerant won't really boil even if the heat pump is trying its best to lower the pressure around it. Likewise, if it gets too hot, the heat pump won't be able to compress the gas hard enough for it to turn back into liquid."
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i7l9xd | Rev matching. What is it and why is it important (or not) for manual transmissions? | Engineering | explainlikeimfive | {
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"In order for two gears to mesh, the teeth need to be at the same speed. If they're close in speed and you push sideways on one gear it will \"snap\" into the other but if the speed difference is large the teeth will just skip past each other, making that horrible grinding noise we associate with people leaning to drive a manual transmission. Modern manual transmissions have a clutch on the side of the the gears called a syncromesh (\"synchro\") that spins the free gear up to speed when you push the shifter so that the gears mesh nicely. This is what's responsible for the slight \"squish\" you feel in some transmissions as they go into gear. This matches the gear speeds for you. Old or large transmissions often don't have synchros so you have to manually match the gear speeds by speeding up or slowing down the gear you can control (the one connected to the engine). That's rev matching.",
"if the working gear is revolving waaay faster than the one it's about the link to for a different gear, that causes damage. think of a spinning disc with holes the size of your finger. it's spinning faster than you can accurately poke your finger into a hole; this will not end well for your finger",
"Not a mechanic but going to school soon to be one so I thought I'd give it a crack. Rev matching is a technique used to shift gears efficiently. Essentially what's happening when you rev match is you press your clutch in and rev until you're in the \"sweet spot\" then shift. What's really happening inside of the drivetrain is this: 1. You're disconnecting power to the gear you're in 2. You're getting your \"engine gears\" up to speed with your transmission. 3. You change gears and release the clutch 4. Go zoom zoom"
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i7m5hu | Early warning systems for intercontinental missiles, how do they work? | Engineering | explainlikeimfive | {
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"text": [
"The earliest warning systems are satellites that watch for the rocket exhaust from an ICBM launch. Rocket exhaust is very very hot and moving fast, it's relatively easy for a satellite that can \"see\" infrared to spot it. It's also really hard to hide. The satellites can't tell if it's an ICBM or a regular rocket, which is one reason why countries are pretty open about launch schedules...they don't want someone accidentally thinking they're launching an ICBM. Once the ICBM gets above the horizon, some countries have very large radars that can see the rockets going up (and over and back down). Google \"SBX-1\" for an example. This is one of the advantages of submarine-launched ICBMs; they can be parked relatively close to the target, minimizing the time between the warning system detecting the launch and impact."
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i7qq2t | Why do houses always tend to have triangular roofs, whereas office buildings and flat blocks always have a flat roof? | Engineering | explainlikeimfive | {
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"There are a few reasons we do it this way and they vary from building to building. For smaller commercial buildings such as an apartment building with store fronts on the ground level in a generally residential area, say 4 stories, we do it because of the height and lot restrictions. Commercial properties have different concerns than a residential home. They try to cram in as many units as they possibly can, which means making the building footprint as large as possible and maxing the height. A roof counts as height so by making the roof flat you can sometimes add an entire additional floor worth of rental units. There’s also the issue of mechanical units. A residential home generally puts things like ac condensers at ground level next to the house. Here at the Jersey shore we elevate them slightly because of flooding concerns but they’re generally speaking still placed on the side of the house. AC condensers for an apartment building are huge and you need a lot of them. This assumes the apartments come with ac included which most modern buildings do. To solve this space problem we stack mechanical units on the roof. They’re are also some safety concerns to consider in regards to mechanical units being better suited for a roof installation we don’t have to get into here. There’s also an issue of how the roof appears when seen from the ground level. Homes are actually quite low so having a nice roof design is a plus from a cub appeal standpoint. But for a building 6 stories tall, you won’t see the roof line unless your either really high or really far away. Adding a roof instead of going flat is just a waste. Not all single family homes have pitched roofs these days. A quickly growing trend here in NJ are modern home designs with flat roofs. Check this post out if your into those types of designs. [source]( URL_0 )",
"Houses retained that traditional shape which helps rain (and snow in colder regions) fall from the roof. That has been the case for centuries everywhere except desert regions where there's no rain and houses have flat roofs. Offices and flat blocks appeared later when it became more practcal to have a flat roof for utilities (ventilation pipes etc) and use other methods to remove water from the roof such as draining pipes. Small one-family houses don't need this but large condos are built with flat roofs.",
"Houses have wooden roof structures usually, and commercial buildings usually have metal truss structures. You can make flat roofs out of wooden truss' but it's more difficult. Peaked roofs shed rain and snow better also. Plus commercial buildings often need to span a large interior area, so that span would be larger than you could comfortably do with a peaked roof. Plus a lot of it is tradition also.",
"A couple reasons — commercial buildings are much wider than a home, so a peaked roof would need to be super tall to have any noticeable slope. That would hurt usable space since there are often height restrictions, or simply not doable at all due to height. Secondly, there are often mechanical systems that need to go somewhere, and a roof is a place that doesn’t take up ground. And flat roofs are harder to maintain, more prone to leaks, need to support more snow load, but that’s all less of an issue with the economics of building and running a commercial building."
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i80uml | Why there aren't better safety measures built into oil tanker ships to prevent spillage in case of an accident. | Engineering | explainlikeimfive | {
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"That's not an oil tanker, its a bulk carrier. Bulk carriers transport ore and grain. In the case of the Wakashio, it was empty at the time of the accident but appears to have been headed to pick up rice from Brazil. They also didn't dump their cargo - again, they had no cargo on board. They struck an underwater reef. The reef tore the hull of the ship open, causing it to spill fuel oil. Large container ships run on fuel oil, which is basically whats left after more valuable substances, like gasoline, have been refined out of the oil. That's why ships always spill oil when they aground - they're all using it as fuel. It isn't possible to design a ship that isn't going to get ripped open when it collides with an underwater obstacle. Overall ships weigh a huge amount - they're basically skyscrapers that are floating on the ocean. When a ship collides with an underwater object, 100% of the ships weight ends up being focused on the small chunk of hull that was impacted on. There just isn't a material known to man that is strong enough to survive that. Even heavily armored military ships - like WWII battleships, which were surrounded in armor plating that was measure in feet - would have their hulls ripped open when they collided with underwater objects. But cargo ships can't have armor like a battleship - they need to be loaded with whatever that it is they're carrying. In order to float despite being fully loaded, the average density of the ship's hull needs to be substantially lower than the density of water. That means that the hull needs to be relatively thin in order for the ship to function as a cargo ship. You also can't just put the fuel in some small, out of the way area of the ship like you can with a fuel tank on a car. The fuel that a ship is carrying adds a significant amount of density to the ship. If you put all of the fuel in the back of the ship then it becomes back heavy and sinks. If you put the fuel in the top middle of the ship then it becomes top heavy and capsizes. The only way to keep the ship stable is to evenly distribute the fuel along the bottom of the ship.",
"Well the main reason is that you don't hear about ones that DON'T dump their cargo, they aren't newsworthy. Ships break down and there are tugs all over the world which can go out and drag a ship, no matter how large, back to the nearest port. That's what happens 99% of the time. Nothing spills, no one freaks out, they get the engines repaired and go on their merry way. But ***\"OIL SPILL RUINS THE ENVIRONMENT\"*** gets everyone spazzing out and makes headlines. That's why you notice them happening. The general reason is probably that waves slam into it and crack the hull when it's unpowered and unable to steer itself into the wave. Large waves hitting a ship broadside during a storm can impart tremendous forces and destroy any ship no matter how well constructed. As a side note, these ships are double hulled, [built to very rigorous maritime standards. The front generally won't fall off.]( URL_0 )",
"First of all, that ship is not an oil tanker. It is dry bulk carrier. That oil spill comes from her fuel tanks, not cargo tanks. It looks like that ship ran over a shoal and punctured her fuel tanks. Ships are fragile and steel is not as strong as you think it is. It doesn't take much to puncture a tank. Ships have gotten a lot safer over the years. Since the Exxon Valdez grounding 30 years ago, and other incidents, ships are stronger, the crew are better trained, and accidents like these are more rare. However, nothing is perfect and everything can still fall victim to error, both human and mechanical. A ship could be built with several protections, but then they would be less efficient. Ships make money by carrying cargo. The more steel and reinforcements you put on her, the less she can carry. Due to shipping expenses, a ship only profits on the last few hundreds tonnes she carries. By adding an extra layer, the ship would no longer make any profit, thus it would not operate. So, people are faced with the dilemma; do we make ships safer but non-existent, or do we take risks but continue to feed the world's economy?"
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i83i5f | Why does the arm that connects the cable to the chair/ski lift have a curve to it instead of being straight? | Engineering | explainlikeimfive | {
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"text": [
"There are wheels at each of the towers along the route. The arch allows the arm to go around those wheels so it can continue along the path of the cable pulling it. If it went straight, it would block the path of the wheel and it just wouldn’t work."
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i8by7f | Why did Steam Locomotives not cool and recycle the steam/water back to the boiler to increase the range, like the primary loop in a power station? | Considering that they had to bunker large amounts of water, limiting their range between refills and also increasing the weight, why did steam locomotives not feed the spent, cooled steam back into the boiler/water reservoir after expansion in the cylinders in a closed loop, instead of venting it out the chimney? If it works in e.g. nuclear power plants with a closed loop, why not in a locomotive? | Engineering | explainlikeimfive | {
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"Mainly, because in most cases it wasn't worth it. Water is cheap, and mostly everywhere. And they got some benefit from the waste steam - the used steam was blown up the chimney in a jet, which drew air along with it, pulling the fire through the boiler and more air into the fire - which meant that the fire would burn more fuel and the boiler produce more steam the harder the engine ran. But in places where water was scarce, [condensing steam locomotives]( URL_0 ) were used.",
"Water simply wasn't that hard to come by. So why bother with a closed loop system if you dont have to? Its more costly to build and maintain. But arid locations and some other circumstances like underground trains did use them: URL_0",
"As well as what everyone else has said. Most steam trains didn't actually need to stop to resupply water either. The flying scotsman and mallard for example was fitted with a water scoop and at certain points along the east coast mainline there would be water troughs. First class where kindly informed to close the windows before they got soaked. Source. A plaque I read in front of mallard at the national railway museum york",
"You can't get the used steam back into the boiler while it's still steam: that would take huge amounts of pumping work. You have to *actively cool* it first, until it condenses back into liquid; then you can pump it in with a small amount of work because its volume is small. In a train, the only coolant medium you have is outside air, and that would take a gigantic heat exchanger; it's more practical to just build water tanks and make frequent stops. Ocean-going steamships have the advantage of an endless supply of cool seawater, so they cool their used steam by running it through pipes immersed in the seawater. And they *have* to do that, because there's no way to erect water tanks at sea, and seawater won't work in a boiler.",
"You're forgetting that power plants are strategically located next to MASSIVE bodies of water in order to cool the steam enough. This simply isn't portable or practical if water is readily available.",
"I can speak from a stationary steam perspective, which I may or may not apply to locomotive (train) engines as well: In stationary steam engines, there are drips of oil that are inserted into the ingress pipe before the valvebox. The methods to do this are clever and numerous, as many 18th/19th century problems ended up with lots of brainpower pointed at them (displacement, mechanical injector, venturi injector... etc.) This oil lubricates the slides of the valves, and also the cylinder itself, as there is no splash lubrication or other method to get oil in between the cylinder rings and piston sleeve. (Well, there were some engines using spray injectors or other fragile systems, but they were atypical - I am betting locomotives have additional methods for lubrication.) So this oil then exits in the exhaust stroke and is mixed with the rapidly-cooling steam. The oil in itself is not a problem in the system at low volumes if recycled, but if you were to mix that oil back into the boiler, it would float on the top of the water and accumulate in a \"scum ring\" around the top of the water level where the heat from the fire was highest. This would cause either a thick nasty goo of oil to need to be removed frequently, or would (if the engine had a superheater which was hot enough) coke on the inside of the pipes, making removal exceptionally difficult. There are special oil/water separators for this purpose on some engine installations that recycle the water but it is often imperfect. Doing this at \"locomotive\" scale and speed would be difficult given the constraints of size and weight, I suspect. The oil itself for my \"low pressure\" needs is tallow oil, and while there may be man-made substitutes these days I have only ever seen tallow oil for sale in any of the catalogs that I frequent. There are discussions about using tallow vs castor oil vs mineral oil - the reader can fall into those rabbit holes if they have time. The arguments about efficiency, size of radiator required and other points are all also valid. This is just yet another reason not to re-use the water or which requires lots of engineering to solve this problem.",
"The short story is there were. The long story is innovative thinking and design like that didn't come about until the 1930's. If you look at the advancement of locomotive technology (especially in the US) designs mostly stayed single expansion due to diminishing returns of building double and triple expansion systems (reference UP 4014 which was also the only Big Boy converted to run on bunker oil) as the the pistons have to progressively get larger in diameter and travel shorter distances as the pressures reduce (reference the size difference in the first stage and third stage pistons in the USS Texas.). Other than that, the only way to effectively cool the steam would be to condense it which would require a (making the locomotive larger and heavier). GE made two superheat plus reheat turbine-electric locomotives in the late 1930's for UP that did use a closed loop system but they were deemed uneconomical due to them not creating the same amount of power for the amount of fuel burned compared to a supercharged diesel engine. From what I remember, those two engines were later converted to diesel electric. For further reading, UP did also commission turbine-electric locomotives which operated similarly to the turbine engines in turbo-prop aircraft.",
"Power plants have access to large bodies of water or enormous cooling towers. Otherwise you cannot condense all that steam.",
"If the diesel electrics had not been invented, and we had developed steam technology these last 70 years, what advances might we have seen and what sort of increased efficiency would have been possible?",
"One of the major reasons that people aren’t mentioning is because of water treatment, one of the major drawbacks of a closed system is that any impurities will build up over time (this is known as cycles of concentration), these can cause a plethora of problems from pitting and grooving, to build up on the heat transfer piping in the boiler. The chemicals required to remove impurities from the system are extremely expensive, and in some cases didn’t really exist back when steam locomotives were predominantly used. So the easiest method of preventing this is to just keep adding fresh water while allowing water to escape from the system along with any impurities. The concept can be described as continuous and intermittent blowdowns. And is something that is rather methodically exercised based on the results of water tests, as it’s the only way to remove impurities and dissolved solids once they’ve entered a boiler. Long story short, more fresh water = less bad in boiler."
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i8d2u4 | Why do train railways have wooden planks along them? | Engineering | explainlikeimfive | {
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"[Railroad ties]( URL_0 ) attach the two rails together and keep them the proper distance apart. Without them the rails could bend, stretch, or sag which could cause a train to derail. They also help to spread out the weight of the train over the whole width of the track bed.",
"Those wood planks (railroad ties) serve two purposes. They increase the surface area that the trains weight is distributed over to prevent the ground from shifting too much underneath the tracks. The main purpose is to... Well... Essentially tie the rails together and hold them in place."
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i8hri4 | SSD vs HDD | Engineering | explainlikeimfive | {
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"A hard disk drive is a spinning disc that uses little heads to read and write information on it. Think of like a vinyl record being played on a phonogram - the needle \"reads\" the data. A faster spin speed usually means faster read/write times which means it can support faster installation, faster downloading and faster loading of files. A solid state drive is more or less like an SD memory card you'd use on your digital camera. These are significantly faster than a disk since there's no moving parts - the specific information that needs to be loaded can be directly loaded without needing to read around a spinning physical disk.",
"A HDD is like public transportation, you have to wait for the train you need to come around and even then, it doesn't go that fast. A SSD is like owning your own car, you go directly where you need to go and get things done.",
"nobody actually ELI5 so I'll try : HDD is actual, very tiny, written stuff, on the surface of a tiny metal disk. The tiny writing is actually the information the computer reads. It takes a lot of time to read and write everything so small, on a hard surface, with a tiny needle. SSD doesn't actually have tiny writing to read and write when using it. It writes instantly using electricity, and it just logically knows what the data is. Basically, an HDD is an old vinyl record, SSD is an mp3 file. edit : formatting is hard"
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i8p3x3 | How are suspension bridges able to support more weight than normal bridges? | Engineering | explainlikeimfive | {
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"They don't, really. The only reason most of the world's largest bridges are suspension bridges are because they are an extremely cost-effective design. Consider a famous example, the Golden Gate bridge. Look at its [design]( URL_0 ). See that shape the cable makes across the main span? You could have, theoretically, designed this bridge instead by constructing an arch under the bridge with that same shape. But that presents many challenges. Perhaps the largest one is that a compression arch isn't stable until it's completely built. You can't just build an arch like that out from either side piece by piece. You'd need to prop up both ends through the entire construction process until you've completed the entire span. You'd also likely need way more material to build that arch. Compare that to a cable, where all you need to do is build the two towers, then drape the cable across. It supports itself, no temporary framework required. And once the cable is in place, you can start attaching segments of the bridge deck piece by piece, since the cable is already there to support them."
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i8wvy7 | Why are Diesel engines used in trucks for heavy work and pulling over gas engines? | What makes them better? | Engineering | explainlikeimfive | {
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"They produce more torque, meaning more force, they are slower than gas engines, but that doesn’t really matter for a heavy truck, also Diesel engines are more efficient because of higher compression, and diesel fuel is a bit more energy dense, so you can go farther with the same amount",
"They are cheaper to run due to the cost of diesel and the amount of energy you get out compared to the same amount of \"gas\""
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i95aio | Why no tidal power plants in the US? | I just found out about tidal power plants and was wondering if there were any near me in Texas. Turns out there aren't that many in the world, and there are none the US. It seems like a really reliable way to get energy. It doesn't rely on the weather as much as solar or wind. Is there some reason that makes it really impractical? | Engineering | explainlikeimfive | {
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"Texas doesn't have worthwhile tidal fluctuation to make tidal energy cost competitive with Texas's existing petroleum energy production or even it's growing solar/wind production. Even in areas with powerful tides, I don't think I've seen a grid scale project that's cost competitive. To clarify, I'm not against tidal power, just don't see it as more than a niche provider in general, limited to certain geographically advantageous areas. It should be part of a diversified, renewable grid, but will likely never be a big player on the global scale.",
"In addition to what listed here, every piece of marine equipment is maintenance intensive. The ocean is a harsh place and the wear and tear on things in the ocean is heavy.",
"The US has: -cheap energy from other sources -a lot of population centers that are *really* far from the ocean -relatively few areas with really strong tidal flows This makes it hard for tidal power to compete effectively at scale.",
"Tidal plants have two major problems: they don't produce a lot of energy, and they cause major economic and environmental damage. Let's take for example San Francisco Bay. If you could extract all its tidal energy, [this report]( URL_1 ) says you could get 170 megawatts -- about 20% of what the city of San Francisco uses, and a tiny fraction of what the entire Bay Area uses. And it's impossible to extract *all* this power. The same amount of energy could be produced by a very small natural gas power plant, or a large wind farm, costing [a few hundred million dollars]( URL_0 ). Current technology for tidal energy extraction requires building a dam across the mouth of the bay. (Nobody's figured out how to create an underwater \"wind turbine\" that works well and can stand up to barnacles and algae and stuff growing on it.) Damming San Francisco Bay would make it impossible for ships to get in and out without a lock, and would cause immense environmental damage: fish and other species wouldn't be able to get through the dam, and neither would the nutrients, salt and fresh water, and other water properties they depend on. Even setting aside the environmental consequences, is powering a few neighborhoods in one small city worth causing huge damage to the shipping, fishing, and tourist industries? Probably not. And the same calculus plays out everywhere. America's coastlines are one of our most valuable resources, and it's difficult to justify monopolizing them for tidal power.",
"Tidal requires a big variation in tides in order to actually generate meaningful energy, but the tides around North America generally aren't strong enough to do that, so it's not worth the investment.",
"There's only a single tidal power station in the entirety of North America. The [Annapolis Royal Generating Station]( URL_0 ) is located in the Bay of Fundy which has 13 meter tides unlike most places in the world which average 1 meter. It only outputs 20 MW for 50 GWh. Even the largest tidal power plant comes in at just 254 MW of capacity. For reference, offshore wind turbines are generally 5-10 MW *each*. 3 offshore wind turbines generate more power than Annapolis does, and 32 can generate more than the largest tidal generator in the world. The UK Hornsea Windfarm is currently at 3 GW of capacity with another 3 GW under construction. Wind and solar are just easier to work with than building a tidal station that will have to be unique and will have environmental concerns."
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i9da33 | Why aren’t car tires just made out of solid rubber instead of filling them with air? | Engineering | explainlikeimfive | {
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"1. Because rubber is expensive and it would cost more. 2. Because solid rubber is waaayyyyyy more rigid than air. Sure something like a rubber bouncy ball might bounce, but trying just squeezing it in your hand and see how much it gives. You’ll find that although it squished a little bit it’s actually pretty hard. You don’t want this hardened sin your tires, you want some of the soft cushion that air provides to smooth out the drive over bumps and cracks in the road.",
"Several reasons: (1) Rubber is expensive; solid rubber tires would cost many times more than pneumatic tires because of the price of the materials. They would also be extremely heavy, reducing fuel efficiency. (2) Tires are not just round donuts, they are highly engineered components that do much more than just roll in a circle. They have tread that is designed to have specific characteristics, such as biting into snow and ice, sticking to hot dry roads at high speeds, moving through mud, evacuating water from between the tire and road surface. This part of the tire would wear down on a solid tire just the same as on a pneumatic tire, and they would still require replacement at that point. (3) Modern radial tires look flatter at the point where they contact the road because they are designed to do exactly that, to have as much of a contact patch with the road surface as possible without generating enough heat to damage the tire. That several square inches of contact patch is what transmits all the forces the car generates during braking, steering, and acceleration to the road surface. The smaller the contact patch, the easier the tires will lose grip resulting in loss of steering or braking ability. A hard rubber solid tire would have a very small contact patch, so the car would have to be driven very slowly. (4) The side wall of the tire is actually a spring; it deforms and absorbs impacts and shock from driving over rough or uneven surfaces. With solid rubber tires you would feel every small stone or joint in the road surface, making driving an unpleasant experience. Here is what actually goes on inside a tire while you are driving: URL_0 What intrigues me is the fact that in the US alone millions of tires are replaced each year; each one of them having been driven long enough to wear off a half inch of tread rubber. That is likely tens of thousands of tons of tire rubber worn off each year, possibly far more. How come we don't see black rubber dust accumulating along the roads, especially busy 8 lane highways that are heavily traveled daily? Where does it go?",
"In order for your tires to grip the road, they have to be made of a rubber that's on the softer side. If the whole wheel was made of that material, then it would be both way heavier and it would get squished down by the weight of the car itself so that the wheel would get destroyed as soon as you tried to drive. Air-filled tires let us use the type of rubber that gets good traction and can hold up the car. The rubber is filled with mesh and wire layers that make it strong enough to hold the high air pressure."
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i9k2a3 | Why do racing tyres last just some track laps, while regular tyres can last for years? | Engineering | explainlikeimfive | {
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"Racing tires are made of much softer rubber. If you touch them, they are soft and sticky.this gives them a lot more traction but also means they don’t last long",
"In general racing tyres have much softer rubber compound so they deform more in contact with asphalt. This gives much more grip than regular road tyres but also means that the tyres wear out faster. They are also under much higher stress than on regular road car and will heat up more during racing. This contributes to wear. And once tyres are out of their optimal performace window they get changed",
"In addition to the other answers, some categories such as Formula 1 use tyres that cannot last the entire race because they want to add another layer of complexity to the strategy, so they design them to degrade in a specific way.",
"Not only is the rubber softer as others have pointed out, but they tend to spin the tires when accelerating, lock them when braking, and skid around corners. They try to keep them just on the edge of losing traction on every maneuver. This creates a lot of heat and causes lots of wear on the tires. You can wear out a set of regular car tires very quickly if you spin your tires every time you accelerate, brake as hard as possible, and go as fast as possible around every corner just on the verge of spinning out."
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ia20z5 | () Why do Buses & Trucks use 2 skinny wheels put together on each side of the axle? Instead of just using one fat wheel? | Engineering | explainlikeimfive | {
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"Not Five Explanation: Trucks and buses generally have double wheels at the back to increase the area of contact on which their weights acts and hence reduces the pressure on the ground. It also provides the ability to replace one side if it is punctured, as well as being more cost friendly. Five Explanation: two wheels is more stable, two wheels is cheaper than big fat wheel, two wheels is easier to replace if one side is broken. two wheel good. Edit: Listen, I haven’t talked to a kid in years. I don’t know how smart they are.",
"Because it's easier to make it flat that way. Anything pressurized wants to be round, but tires work best when they have a nice flat surface to meet the nice flat road. This problem gets worse as the tire gets bigger. That's why your bike tire can basically have a circular cross section and it's not big deal, it just squishes some as you roll on it. But if you do that with a really big tire at speed all that flexing in the sidewall generates a lot of heat and the tire fails. A truck or bus is so heavy that you need a tire about about 2 feet wide to provide enough surface to take the weight from the axel, but a single tire 2 wide will bulge out way too much. Two skinnier tires side by side has almost as much surface but doesn't bulge nearly as badly because you have a sidewall in the \"middle\" to hold everything down. You also have the advantage that if one goes flat the whole wheel doesn't drop.",
"Some trucks run super singles, it's basically one big tire instead of two smaller ones. Every trucker I've talked to that has them absolutely hate them. I guess they are horrible on ice and snow",
"Here's something that no ones added yet, All the individual double wheels and front wheels on buses and trucks are actually identical and the outer double wheel is just flipped around, which is why the rear wheel looks concave and the front wheels look convex. This means that they can all be easily rotated and replaced, and you can theoretically pull a rear wheel off to replace a flat in the front and still have plenty of wheels left to drive on.",
"One reason I'm not seeing mentioned here is snow and ice. In a truck, your fat ass takes a looooong time to slow down, even in perfect dry weather (take note, drivers, this is why you shouldn't swoop in front of trucks two feet off their bumper when passing). In snow? Your time to maneuver is effectively doubled. What's the form of a snow tire? In its most simplest form, it's a tire with deeper treads that avoid being filled completely with snow, and softer rubber to help grip the road better in cold conditions, where rubber will harden. That first one is especially important, as deeper treads help get grip on packed snow and ice. With dual tires, the space between them basically acts as one very deep tread, allowing greater control in the snow. Which if you're running super singles (which is what the \"one big tire\" would be called -- they do exist), you don't have. Source: was truck driver for a year. Not recommended unless it's your only alternative to homelessness.",
"If you look up \"wide base tires\" One fat tire is also an option. I see it in mexico a lot, I've been told they do better on washed out roads, but the guy that told me that isn't a truck driver.... and doesn't own a car.",
"despite what you may think its actually the air pressure in the tire that holds the weight and not the rubber itself. to hold more weight you can increase pressure, but a single tire can only hold so much pressure safely. this is where adding more tires comes in & #x200B; each tire is rated to hold a specific amount of weight at a specific pressure, so if you need to hold more weight you add more tires.",
"Price, mostly. The price of two standard sized tires is less than one specially made tire. Also, there are extra wide tires called 'super singles'. and their performance leaves a lot to be desired. They have less traction on snow, ice, and water than 2 regular tires. And when one goes flat, it's far more problematic than when a regular tire goes flat. They do give about a 0.5% better fuel mileage - which will translate into a bunch of money saved over the course of their lives. But professionals generally do not like them as much due to their traction issues and troubles when one goes flat. Source: was a trucker for 18 years.",
"Probably because of tire explosions. If only one of the two skinny tires blows up, it's a smaller explosion and easier to replace than one big tire.",
"Adding to the other responses. A single big fat tyre is also more prone to hydroplaning. Hydroplaning is a dangerous condition when the tyre floats over the water on the road instead of cutting through it leading to skidding and well...crash"
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ia840x | when you blow through a straw, you can feel it from over a foot away but when you suck air through it, you only feel it when you're almost touching the end? | Engineering | explainlikeimfive | {
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"Blowing through the straw pushes the air in one direction. It's energy dissipates slightly to push away air it encounters in other directions, but it is mainly going in that one direction. Sucking in air pulls it in from nearly all directions. The load is spread out. Think about how switching a hose from one stream to spraying in all directions affects how far the water goes. Same principle."
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iaciyk | How can a networking wire carry multiple channels at once? | To my knowledge, a copper cable carry's data by changing the voltage. For digital, it is either high or low for 1 or 0. For analog, it is a wave pattern that gets altered over time to express some information. But if the cable can only have 1 voltage at any time, how can multiple channels be created? As for fiber, I think I understand that one. If you send blue and yellow light (for example) through in pulses, then you could send digital 1's and 0's based on the received color: blue = blue:1 yellow:0 yellow = blue:0 yellow:1 green = blue:1 yellow:1 none = blue:0 yellow:0 Maybe I'm wrong on this though... | Engineering | explainlikeimfive | {
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"Regarding fiber optics: Multiple channels of data can be sent over a single fiber using a technique called [wavelength-division multiplexing]( URL_4 ). It basically works just like you said, multiple colors (wavelengths) are sent over a singe fiber using a multiplexer (think of this as a reverse prism, where multiple color beams enter the prism and a single one comes out) . At the end of the fiber there is a de-multiplexer (a normal prism, one beam of light comes in, multiple color beams come out) [This]( URL_3 ) is a very interesting way of multiplexing - demultiplexing. Now for the cables: Back in the days of the [OG ethernet]( URL_1 ), a singe coaxial cable was used to connect all computers on a network. Each computer had its own [vampire tap]( URL_5 ), just like you can connect multiple TV sets to a single aerial using those t adapters. Since all computers were on the same cable, each one had to know when the cable was not in use in order to send its data. This had several drawbacks such as [collisions]( URL_0 ), where multiple computers would talk at the same time and no one would understand what was said. But when twisted pair ethernet was introduced, each device on a network had its own cable to a central station, the [switch]( URL_6 ). A perfect analogy to the switch would be a post office. Each device has its own PO box (the IP address), and each letter sent to the post office (the switch) is a [network packet]( URL_2 ). The switch knows the sender of each packet and its destination (which PO box to send the packet to). A packet can have one or multiple destinations. And also, if the switch receives two packets destined for a single PO box, it will send them in succession (just like you get bulk mail in your PO box). Cables also have two variables, speed and bandwidth. Speed refers to the highest speed of data transfer the cable can achieve and it is measured in Mbps. So you can have a cable that can carry up to 100 Mbps, and another one that can do 1000 Mbps or more. Bandwidth is how much data you can simultaneously transfer. Essentially, this is how many times a cable can change its state from 1 to 0. Some cables support 100 MHz (100.000.000 state changes per second), some can do better. So, speed and bandwidth combined form the categories of cables that exist, or what's known as CAT (CAT5e, CAT6 etc). The higher category a cable is, the faster it can transfer data. To summarize everything, ethernet cables cannot carry multiple signals. They can carry multiple packets destined for multiple computers, but a switch is needed to take that single ethernet cable and turn it to multiple cables."
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iady1z | Why do the motion censors for paper towel machines in restaurants always get broken | Engineering | explainlikeimfive | {
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"* no one bothers to replace the paper * no one cleans the sensor or cleans it with something that messes up the plastic * no one replaces the batteries * people yank to hard or early so the despensor thinks no one got the paper towel off after the last one. You can often fix this one by pushing up the cutting piece."
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ib2hqy | Why do back car windows have lines on them? | Engineering | explainlikeimfive | {
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"These are metal resistance heating elements. These are used the defrost setting. Electricity will be passed through these to create heat."
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ibbhsd | Why do processor die look colorfull like rainbow in pictures/videos? I have searched about it and it is mentioned it is something related to diffraction grating and also some camera polarization effect? | I myself has never opened up a processor package before so don't know how it looks like in person | Engineering | explainlikeimfive | {
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"Remember the weird rainbow effect you would see on the bottom of a CD? Same process The die is covered in little lumps and pits that form a [diffraction grating]( URL_0 ). Light comes in, and hits all the little pits and lumps and goes off in one direction or another depending on its frequency so you get a rainbow effect with differing colors depending on how the pits and lumps are arranged. Since sections of the die tend to have similar layouts you can get large blocks of color indicating Cache portions or duplicated portions showing you the 4 distinct cores. Also, don't ignore the chances that the image is color enhanced as well to really show you the different sections clearly"
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ibx4qr | how do Refrigerators work? How can they keep things cold in hot weather? | Engineering | explainlikeimfive | {
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"A refrigeration cycle consists of a cool refrigerator and a warm exterior. A cool refrigerant is compressed. When fluids are compressed, they heat up. The cool refrigerant is now hot. The hot, compressed refrigerant is pumped outside, to the exterior. Since it's hotter than the warm exterior, it cools down until it's warm (usually with a fan blowing on it), releasing heat. The warm, compressed refrigerant is allowed to expand. When fluids are allowed to expand, they lose heat. The warm refrigerant is now cold. The cold refrigerant is pumped inside, to the refrigerator. Since it's colder than the refrigerator, it warms up, absorbing heat, until it's cool. The cool refrigerant is compressed, and the cycle repeats."
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iby8vm | Why is superhard suspension better than no suspension and why is it used almost exclusively by race cars | So i understand that suspension makes riding in a car more comfortable and the softer the suspension is the more smooth the drive will feel. I know there is a trade off between comfort and handling and that the softer the suspension the harder it os to handle a car. That said surly the best racing suspension would be to not have any suspension at all? Wouldnt this make cars handle really well by not havong a system that allows momentum to affect turnying or handling of the car? | Engineering | explainlikeimfive | {
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"Suspension is also needed to keep all four wheels in contact with the road. If one wheel lifted off as a car was cornering at the limit then it would quite probably spin out. Of course there is some suspension in tyres but there may be performance benefits to having a higher pressure tyre and a separate suspension (there are)."
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ic522e | Why can't waste plutonium from power plants be turned into RTGs for spaceprobes? | I found a similar question here before: [ URL_0 ]( URL_1 ) However the answer to that question is that nuclear fuel rods are too dangerous. I am thinking about waste Plutonium as a byproduct from Uranium fission specifically. Surely if they are being used for spaceprobes where no humans are around then it would be a lot safer? | Engineering | explainlikeimfive | {
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"It's the wrong sort of plutonium. Pu-238 has a half-life of 88 years. It decays so fast that the heat produced makes lumps of it glow orange. But waste plutonium is mostly Pu-239, with a half-life of 24k years. Not a useful source of heat for RTGs."
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icdjde | How do the white noise machines used in therapist offices work? | Engineering | explainlikeimfive | {
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"White noise machines are typically just simplified digital music players that contain a library of pre-recorded sounds edited so that they can be played in an endless loop. If you listen to the average white noise generator carefully enough you'll find that the loops last as little as 30 sec to a couple of minutes. Which for something like a fireplace that's supposed to be random it can be a tad disconcerting. Prior to this they sold CDs and tapes that served the same purpose. Playing white noise in the background helps keep part of the brain busy and for a lot of people it has a calming effect. In my case I use one to help me sleep. Not only does it have a calming effect but more importantly it helps drone out my persistent tinnitus."
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icjui9 | How software controls hardware | Engineering | explainlikeimfive | {
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"The software has a physical existence when it's executed as a pattern of electric currents within the processor. These currents can be redirected to the output contacts to exchange data with external devices and, if necessary, amplified with different devices such as relays.",
"Software does physically exist. It's stored on disk and memory; some types of memory are non volatile meaning their contents don't go away when rebooted or machine turned off. Basically it's very small pieces of software that are tied closely to the hardware which allow the more complicated software to run. It's called bootstrapping."
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icljh4 | how does the sensor which measures the level of fuel of a car know pretty precisely how much fuel there is in the tank? | I mean this might sound dumb, but hear me out, there are lots of bumps while you drive and the liquid always moves due to acceleration and breaking. What type of sensor is this? How does it work so well? Edit: You guys are insane, thank you so much for the answers! Oh my god, I love this subreddit. | Engineering | explainlikeimfive | {
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"Ahhhh finally my time to shine. & #x200B; I actually sell fuel level sensors to the major OEMS. The 3 main sensing technologies are ultrasonic (super super accurate), Float + reed switch (most commonly used), and capacitive . For your question regarding sloshing - software is used to filter the rapidly changing signal (due to sloshing). Its able to smooth out the output and give you a good idea of the real level. Float and reed switch is essentially a float with a magnet it in that rides up and down a vertical shaft with the fuel level. As the magnet in the float passes reed switches at various levels on the vertical shaft, they become triggered. Edit as requested: A float and reed switch assembly is essentially foam donut with a magnet inside of it. That foam donut rides up and down on a vertical shaft inside the tank as the fluid level rises and falls. Inside the vertical shaft is a switch technology called reed switches. These reed switches either make or break an electrical connection - they are actuated magnetically by the float as it passes by. Hope that helps clear it up for those still confused. Edit: a word. To be clear, this is ONE form of technology. There is also a Resistive sensor that functions like the float switch in the back of your toilet - as float rises, it rotates a sensor that changes the resistance value. Hope this helps. Last edit: Suppose I should take the moment to shamelessly plug my company. If there are any engineers out there looking for a liquid level sensor (doesnt have to be automotive), let a brotha know. Happy to connect via LinkedIn and set up a conference call. Already had one awesome redditor reach out. Next time my boss gives me crap about cruising reddit....... & #x200B; One more edit: Common question - how does ultrasonics work? Ultrasonic operating principal is all based on TOF (Time of flight). Ultrasonics generate a sound wave (by hitting a ceramic disc with a crap ton of voltage causing it to vibrate). Sound wave bounce off the surface of the fuel and returns to sensor face. As Speed of Sound (SoS) is a fixed value, you can tell how far away the fuel is (level) based on how long the sound wave took to get back to the sensor. & #x200B; Last edit, PROMISE: As many have pointed out, float on a swing arm + resistive (like a potentiometer) is the dominant solution in the passenger car world - Ive worked most recently with on-road tractors (semi-trucks) which use much larger fuel tanks that would destroy the little mechanical float arm. This is why they use reed switchs + float vs what on-road cars use.",
"This float is the reason why when we fill the tank all the way it seems like it gets better gas mileage in the first half of the tank than the bottom half. At full it takes longer for the float to start going down because it’s fully submerged in gasoline and it won’t move until it you have used enough gas for the float to “float”",
"There's a little ball that floats in there. This is attached to an electrical component whose resistance changes depending on the height of the ball. By passing a current through that electrical component, the car can tell how high up the ball is and thus how full the fuel gauge is. & #x200B; You'd need to be doing some absolution crazy flips for it to register meaningfully on the fuel gauge, though parking on a steep hill can still give you an incorrect reading as the angle of the tank causes the ball to appear higher or lower, depending on which way you're pointing.",
"To add to the others, there are also little walls inside your fuel tank called baffles. They sort of make a little maze inside the fuel tank, which reduces sloshing. It's not a complicated passage way or anything. Usually just a big X in the middle of the tank, or sometimes a snake pattern back and forth, from to back.",
"It consists of a float, usually made of foam, connected to a thin, metal rod. The end of the rod is mounted to a variable resistor. A resistor is an electrical device that resists the flow of electricity. The more resistance there is, the less current will flow. In a fuel tank, the variable resistor consists of a strip of resistive material connected on one side to the ground. A wiper connected to the gauge slides along this strip of material, conducting the current from the gauge to the resistor. If the wiper is close to the grounded side of the strip, there is less resistive material in the path of the current, so the resistance is small. If the wiper is at the other end of the strip, there is more resistive material in the current's path, so the resistance is large.",
"The float itself sits in a tube that is open at the bottom so the level isnt buffeted by waves sloshing around the tank. But often the sensor is in the front or back of the tank so going down/up steep hills can change the level.",
"In modern cars, the fuel level sensor looks like a variation of [this]( URL_0 ). The white part attaches to the same housing that holds your fuel pump, and the black part floats. The float moving up and down changes the electrical resistance, telling the computer how much fuel there is. The computer isn’t constantly looking at the sensor. It does so when the key is turned on, and then every few seconds. If it gets several readings saying the fuel level is going down, it moves the needle down...if it gets a few down readings with some up readings mixed in, it ignores the whole batch.",
"Go to your bathroom. Take the back off the toilet. Flush. Thats how car fuel tanks work. They have a float (the rubber ball thingy). It stays on top of the liquid. As liquid comes into the container the float rises along with liquid, and as liquid leaves the container it sinks. As the float rises and falls, it pulls a lever. In the toilet the lever is attached to the water cutoff. In your car the lever is attached to the fuel gauge. Essentially the gauge/lever are weighted so it moves slowly up and down (thus countering car movements). But if you park on a significant incline/decline you will see a false reading on your fuel gauge because it had time to adjust to the false fuel level.",
"It isnt precise at all, evidence: according to my car's gas meter the top 1/4th of my tank accounts for 50% of the gas. Found this out by putting $12 in when empty for it to go to 3/4 tank and another $12 for it to fill up.",
"In 99% of cars there is a float on a arm / pivot. As the fuel level goes down the arm pivots lower and lower. At the end of the arm is a resistor that changes it's resistance based on the position of the arm. In it's simplist form your fuel gauge is just measuring the resistance and displaying the results. In old cars that meant your fuel gauge would move as the fuel sloshed and moved in the tank. Later on they added circuits to smooth this reading out and kind of average it. This worked well for old school rectangular fuel tanks since the fuel level was directly related to the remaining fuel. Modern cars still typically use the same sensor. But now it goes into the engine computer and it can do all sorts of smoothing and adjustments. Since modern fuel tanks are all sorts of weird shapes your fuel level no longer changes in a linear fashion. So your cars computer nowadays has a correction table to normalize it and actually can report a fuel remaining amount in gallons for things like remaining range calculations. You will basically never see the exact calculated amount without a scantool or obd device to read it out though. Ever notice how your gauge will stick on full for a while after filling up which makes you feel good? There is another table that takes our nice precise fuel percentage reading and converts it into what the gauge says. So the car can lie to you basically. When your fuel level is 80% or higher it will simply show a full tank. Then when your fuel level gets below 15% it will simply show empty. This is because humans are stupid and would not enjoy immediately seeing the needle come off of the full mark and would run out of gas since the needle would show empty only when truely empty. I actually have the software to change that on some cars and usually change my gauge to tell the truth but it can definitely mess with some people.",
"The sensor is fairly simple, however the computer that reads the signal from the sensor will filter the results (like a running average) so that large changes don't appear immediately at the gas gauge. This way changes due to short bumps and acceleration will not be seen, but parking on an incline for an extended period might.",
"former mechanic. It's just a atandard float sensor. That is, there's a bob in the gas attached to an arm, that runs to a potentiometer. The reason the gauge doesn't go all over the place is cuz the computer knows that sudden changes are just a shift. Kinda just averages out the last minute or so of readings. If you go up a long hill you can watch the level change",
"On some of the fuel pumps/sensors I've seen in fuel tanks, they use a float on a coiled piece of metal. The float would move around the coil and therefore up and down when the fuel level went up and down, but because it was on a coil instead of a perfectly vertical piece of metal, it would \"filter out\" any sloshing about. (It takes time for the float to move up and down the coil, instead of instant like it would be on a vertical piece of metal.) Simple, yet effective.",
"This reminds me of my first car: 1976 Tatra 613. It has two fuel tanks, interconnected but with fuel level sensor only in one tank. Meter has no damping/filtering of fuel level, so it is basically \"immediate fuel level near float\" turning left? no fuel. turning right? full tank! acceleration? 1/4 tank. braking? 3/4 tank. To add a little fun, it has no daily counter, only odometer. I stopped counting how many times I have run out of fuel with that car :) Very cool, air cooled, rear-mid mounted DOHC V8 powered car, by the way, but it has it's perks",
"The most common system is the same as is used to refill your toilet after each flush. There's a bobber attached to a rod. When a tank is full the bobber floats ontop of the water/fuel and is attached to a central point or switch. As is the bobber is too close to the switch to do anything interesting. As the tank empties and the bobber falls away it's weight pulls on the rod and the switch its connected to adjusting your fuel gauge and eventually turning on a warning light. Alternatively as the tank refills the bobber floats again putting less weight on the rod and gauge.",
"Great answers here, I’ll jump in as well. I work for a major OEM and on one of our units we have the option of telling the vehicle to either a) Calculate the fuel level based of actual usage/demand of the vehicle or b) a float as described by the top comment. Option A works by calculation of the vehicle engine control module in conjunction with the float. Let’s say you fill the vehicle up from a 1/4 tank of gas to a full tank. The float sends a signal to the engine control module to tell it how much the level has risen. The control module knows the given value of the float equals a certain amount of gas ( calculations input by the Engineers). Once the car starts driving it monitors the demand for gas ( the fuel air mixture ). It knows how much each injector is spitting out per engine cycle and calculates the amount of fuel used. Every time the car stops for a period of time it checks back in with the float to cross compare numbers. Hope that made sense."
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icwi2h | How does a car's speedometer measure speed? | Engineering | explainlikeimfive | {
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"* There is a sensor on an internally rotating part of the car (not the tires like others have said). * The sensor counts the number of rotations per second. * The car's computer knows the circumference of the tire so it can do a little math to convert rotations per second to miles per hour. * This information is then displayed to the driver. * For this reason, if you put the wrong size tires on your car, your speedometer might be off by as much as 10 miles per hour."
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icxwj6 | How do we build in the middle of the ocean? | How do we build in the middle of the open sea? Do we have to find a more elevated spot to lay the foundations? ELI5, if you wanna explain it like I'm 25 that's cool too. | Engineering | explainlikeimfive | {
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"We usually don't. If we're building anything out there, it's probably some sort of oil rig like \"building\" that floats. Usually the bottom of the ocean is too far down to build on, and even if you could build on it, it's squishy mud that won't support the weight. In places we do build, it's usually shallow enough to do so and the area has firm enough ground to lay foundations on.",
"In the case of more permanent oil rigs, they use concrete or steel legs anchored to the seabed. Here's a more detailed page with the different types. URL_0"
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icy3w9 | If the propellers of a helicopter accelerate to raise it from 0 to 50 feet what happens once it reached the altitude, keeps the same rotation speed otherwise it descends? At each altitude there is a specific rotation that keeps the helicopter there? | Engineering | explainlikeimfive | {
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"Most helicopters have constant speed rotors. They change the pitch of the blades, basically how hard the rotor bites the air, they don't change speed. When you're near the ground, the air coming down from the rotor hits the ground and spreads out. This causes something called \"ground effect\" that makes it easier for the rotor to lift the helicopter. You need to keep increasing pitch on the blades to \"climb\" out of ground effect. Once you're out of ground effect this isn't nearly as pronounced but you still need to keep increasing pitch as you ascend because the air is getting thinner...you need to push more of it down to maintain lift. This is what determines the maximum altitude of a helicopter, it's how high they can go with the rotor at maximum pitch. If they can get into ground effect, like scooting up a mountain slope, they can go higher. There are a very few helicopters that use variable speed rotors; there's a bunch of technical vibration reasons that this is hard to execute in practice but \\*they\\* will have a particular rotor speed for a particular altitude, not including ground effect.",
"That's not how it works. There are two parameters that control the rotor, speed of rotation and angle of attack. To go up, you apply more power and more angle of attack. To hover, you apply less angle of attack. Helicopters never struggle in the first 50 feet, as the first 25 feet have ground effect enhancement of their efficiency. Helicopters struggle at altitude. As the air gets thin neither control provides enough lift."
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iczh2n | How does the electricity generators keep up with the uneven demand? | I’m interested in knowing how come the electricity generation guys always generate as per the demand? What happens to the extra electricity that gets generated? They ensure that the lights are on for the entire city or sometimes states, I’m sure they have some complex logic to get it done right, I’m interested in understanding that logic in simple words. Cheers. | Engineering | explainlikeimfive | {
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"Generation never perfectly matches demand. This can be seen in a change of frequency in the grid. An excess of generation will result in a higher frequency and a deficit will result in a lower one. There is also a change in voltage. Not a huge amount, but still measurable. Some forms of generation take hours to run up and shut down, but others can be turned on and off in less than a minute. The grid has a good idea of what the demand is on any given day. So the more expensive forms of generation are only used when there is high demand. Most system have an agreement with high volume users to get them to reduce demand in periods of exceptional demand. For minor changes in demand the system just soaks it up. Your stove may boil a pan of water a bit faster or slower, but the difference is so small you won't notice it.",
"They don't generate (much) extra electricity. The generators spin at constant speed to make sure that the AC power frequency is constant. The amount of torque it takes to spin a generator depends on how much power the generator is producing. All the generation guys do is make sure the generators stay at the right speed. When power demand goes up, the current through the generator goes up, the torque on the generator goes up, and the generator starts to slow down (a tiny bit). Whatever is driving the generator has a controller, like cruise control on your car, that opens up to provide more power to the generator and get it back up to speed. If it's a steam plant, a valve opens to let more steam into the power turbine. If it's a hydro plant, the floodgate open a little to let more water through. If it's a gas turbine, they feed it a little more gas. Most real generators are pretty big spinning masses so they tend to act like their own big flywheel and that helps even out any small transients. This is kind of like having cruise control on in your car and then heading up a hill...the speed of your car doesn't change but the gas pedal goes down as the engine takes more fuel (puts out more power) to keep you at the requested speed. When power demand drops the torque on the generator drops and it all reverses. In a real world power grid, there's a bunch of complicated flows between generators and between different transmission lines that help even out any momentary spikes. This is one of the reasons that you need to have a generator up to speed \\*and in phase\\* before you connect it to the grid, otherwise Bad Things happen to the generator. Edit: the demand on a large generator is also pretty even over the short term...it's the sum of all the individual loads and a lot of that balances out. You turning your kettle on might be a 50% jump in power demand in your house but it's probably a .001% demand change to a municipal generator.",
"Previous answers are good but I will respond as well. The grid as a whole has multiple generators connected at all times. Usually none of them are running at full capacity. When demand fluctuates they all share the up and down so the change to any unit is negligible. \"Extra\" electricity only exists for fractions of a second and it doesn't get noticed by consumers. The grid frequency rises for a few cycles but then everyone ramps down and things are balanced again. Human intervention is only required in cases of sudden capacity loss or to adjust for economic efficiency."
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id0vvt | How does striped toothpaste continue to squeeze out consistently striped product from start to finish? | Engineering | explainlikeimfive | {
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"To answer your “what does the inside of the tube look like” question, you can see the contents of a tube [here.]( URL_0 )",
"Basically the different colors are all the same thickness and behave the same way under pressure allowing them to keep their relative positions even when being squeezed. For a less eli5, look up thixotropic rheology.",
"[here is a video]( URL_0 )that shows the whole process, filling the tubes @ around 4:00"
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id3zfs | how does the sensor that detects cars on turning lanes work? | It has to be a robust mechanism that doesn't break down despite being out in the open and repeated uses, right? | Engineering | explainlikeimfive | {
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"Do you mean the sensor for traffic lights? There are a few ways but a very common one is a copper wire underground which works similar to a metal detector to tell if there is a car. This has no moving parts and is very protected from weather. Other ways include cameras which have had the entire history of security cameras to figure out how to keep it protected.",
"It's not out in the open. It's a couple of coils of wire that are embedded within the asphalt of the roadway itself. One coil creates a magnetic field, and the other detects the field. When a vehicle passes over the coils, the magnetic field is distorted, and that distortion is picked up by the second coil. This information is sent to the light sequence controller, which alters the timing of the traffic lights."
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id97g1 | - Why do planes look smaller from the outside (in the terminal) than on the inside? | Engineering | explainlikeimfive | {
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"Only thing I can think of is that when you are in the terminal and look through the glass, the plane is still always a good 50-60 feet away from the gate opening. You also stand a little higher than the planes inside floor making it also seem a little less tall than if you were on the ground next to it."
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idpmlp | Why phone flashlights use blue and orange lights together. | It may just be my phone, but if I look at the shadows casted by my phone's flashlight, there are blue and orange outlines on the object. This means that there is a combination of blue and orange lights to make the white light. Why not just use a white LED? | Engineering | explainlikeimfive | {
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"These are both white LEDs, they're just each a different Color Temperature. The orange one is a \"warm\" white, like that of a candle. Blue is \"cool\", like a dingy operating room might be. They might choose to combine these two, on opposite sides of the spectrum, to achieve a better range of colors for your picture—although I'd argue a standard 5000k \"neutral\" LED with high Color Rendering Index would be preferable anyways. See the bot replies to me for more info on these terms! u/brokenrecordbot cct"
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idrzu6 | How does the '4 low' option generate so much torque with such little effort compared to '4 high' in Jeeps and other 4x4s? | Engineering | explainlikeimfive | {
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"Gear ratios multiply torque in the same proportion that they reduce revs. If you've got a 10:1 gear reduction, and an engine revving at 5000rpm on one end with 100 lb-ft, then at the other end you will have an output shaft spinning at 500 rpm but with a torque of 1000 lb-ft. The \"4 low\" option is like that, a very big gear reduction. The output shaft spins very slowly, but the torque is multiplied by a lot too."
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idw998 | why fans have a flash of light/spark when you turn them off | Engineering | explainlikeimfive | {
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"It’s called arcing, when you disconnect a thing that is drawing a large amount of power, if the contacts aren’t broken fast enough, the current can jump though the air and create a spark or more technically an electrical arc. This doesn’t happen only on fans, but by the nature of those it’s more likely to happen since the coils in the motor act as a generator when the power is disconnected and can create a short pulse of high voltage Also by the way this is the reason switches make click sounds, it’s to avoid arcing here’s a Technology Connections video URL_0"
],
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11
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ie525x | How does the Space Station use Oxygen? | Engineering | explainlikeimfive | {
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"text": [
"It's recycled...in a sense. If you didn't know, there's a process called *electrolysis* (from the words for 'electricity' and 'to unbind') that uses high levels of electricity to break common water apart into hydrogen and oxygen. This can be done with literally anything -- waste water, sweat, even urine. It all gets split into oxygen and hydrogen, and then the hydrogen is combined with carbon dioxide to reclaim water from the process.",
"They have external oxygen tanks. They can also produce oxygen from water using a process called electrolysis, which separates the hydrogen and oxygen that make up the water. Believe it or not, the whole space station isn't exposed to vacuum when they open the door. That would be kinda poor design. They have an airlock - a kind of hallway with a door at either end. The astronaut goes into the hallway, and closes the internal door. Then they depressurise the airlock, and open the external door. Then they do that in reverse when they come back in.",
"Everything they have on the ISS was supplied with rockets in one way or another. They have several re-supply missions per year. They bring new science experiments, food and water. Water is mainly oxygen plus some hydrogen. On the ISS water is split into components, the oxygen goes into the station. The astronauts exhale carbon dioxide which has to be removed. Here the hydrogen helps - the ISS has a module that can convert carbon dioxide plus hydrogen to methane and oxygen. The methane is discarded, the oxygen is again used for astronauts. That's recycling. In addition to the water that is sent up, the ISS also recycles some of the water from the toilet. For space walks the astronauts go into small airlocks: Keep the outside door closed, close a door on the inside, get into the space suit, then the station pumps out the air out of the airlock. A bit of the air is still lost in the process, but that's acceptable."
],
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iea4qt | Why does drywall exist? What purpose does it serve? | Engineering | explainlikeimfive | {
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"text": [
"1. It's a barrier between the exterior and interior walls to hide everything run inside the walls and the insulation. 2. The substance it is made from helps prevent heat loss and gain working along with the insulation. And exterior walls to form a thermal barrier. 3. Drywall is extremley affordable and easily modified for how ever you need to use it. Ex: odd shapes, outlet locations patches and repairs. Most can be done with simple hand tools. 4. Paints easily due to the paper coating on it vs many types of wood panning. And is easily smoothed and finished with experience. Tldr; drywall essentially is stupidly affordable thermal barrier that hides the ugly inside your walls and can be fixed for cheap. And tastes terrible.",
"It covers up all the wires, pipes, and studs in the wall. It's faster to install and smoother than other solutions. It also doesn't require the skill of plastering.",
"As others have pointed out, it's just a very economical and versatile way to cover up the ugly. That's really most of it. A fully insulated garage could be more or less just as effective as a finished one in terms of keeping out the elements and insulating the space. It just won't look as nice. More things than you'd expect follow the principle of \"absolute mess on the inside, with a pretty cover thrown on top to hide the ugly\"."
],
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iec57y | How can tyre pressure increase when driving? | I understand how it can decrease, continuous pressure would force that out, but I can't wrap my head around why sometimes, I check the pressure and it'll say like 40psi??? It should be 32??? | Engineering | explainlikeimfive | {
"a_id": [
"g2er5w8",
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"text": [
"Friction between the rubber and the road, and internal friction in the rubber as it flexes, heats up the tire, and then heats up the air inside. If it's summer and the road surface is hot, that'll contribute too, and of course so will sunshine on the rubber. Assuming the walls of the tire are fairly rigid, if your tire starts out at room temperature, every Celsius degree it warms up should raise the pressure by about 0.3%, or an extra 0.11psi if it started at 32. Now, having said that, a jump from 32psi to 40 is an awful lot and I'm not sure heating can explain all that unless your tires are too hot to touch. Is there a chance your pressure gauge is inconsistent? [Edit: Or have you ever used one of those spray-can repair kits that mends a flat tire? Those can leave residue in the tire that will evolve fumes.]",
"Air volume increases as the temperature increases. When you drive, your tires heat up, causing the air inside them to increase in temperature and expand.",
"Depending on your manufacturer's specs written in the door jam, it should be around 30 cold, meaning you haven't been driving it. As you drive, the tires flex and get warm. That heat transfers to the air in your tire which increases pressure."
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iehfvl | How do underground bases in the ocean keep water from entering when someone enters or leaves? | Engineering | explainlikeimfive | {
"a_id": [
"g2ggukf",
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],
"text": [
"Even submarines do this. 2 doors. You open one. Fill the space with water. Close the first and open the second. This a works for all places that regulate pressure. Such as airlocks in space stations.",
"From Wikipedia: “An airlock may also be used underwater to allow passage between an air environment in a pressure vessel and the water environment outside, in which case the airlock can contain air or water. This is called a floodable airlock or an underwater airlock, and is used to prevent water from entering a submersible vessel or an underwater habitat.” Source: URL_0"
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Subsets and Splits