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essefs | How do airlocks work in submarines/space | I see them in films and stuff and have never understood how theyre supposed to work | Engineering | explainlikeimfive | {
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"if you opened a door on a submarine it'd fill the whole place with water, so you just make one little room with a door to get into it and then a door to the outside so when you open the outside door only the little room fills with water. That's about it. Then you pump air in or water out once the person is gone.",
"The point of an airlock is to allow safe transit between air pressure between two different environments. i.e. between a vacuum and normal earth air pressure. This works by having two airtight doors both leading into the same pressure vessel (sealed room). Outside one of the two doors is low pressure, outside the other is high. To transit from one to the other you follow this process: * equalise the pressure to one side (e.g. low/vacuum) * open the door on that side * enter that door * close that door * equalise the pressure to the other side (e.g. normal earth air pressure) * open the other door * exit the chamber In a sub, there's only really a few ways to get out 'normally' and they aren't airlocks. They're watertight hatches that lead to the deck. Once submerged you are not really supposed to be able to get in or out easily. Internal doors are watertight, and again are not airlocks. In an emergency it's possible to use the torpedo tubes as emergency evacuation airlocks but that's dangerous as hell and nobody wants to go through that unless they really really really have to. One place I know that there are internal airlocks is on nuclear subs. There tends to be an airlock to access the reactor. There are more exceptions, so I know there are subs with airlocks for divers to exit/enter, but these - as I understand it - are an exception rather than the norm.",
"They are essentially just airtight doors. However, the airlocks in space are very different from submarine airlocks. Usually there are two doors and a room between them. In a submarine, the doors open outwards (towards the sea) and in space it’s the other way around. This is because they want to use the pressure to their advantage. In a submarine, the water presses hard agains the door, so if we make the door open outwards, the pressure will keep the door shut. In space, the air inside the spaceship wants to get out, so the pressure is directed outwards. This means the doors open inwards, so, again, the pressure keeps the door shut. The two door system is to allow an astronaut or diver to get out without the whole spacecraft turning into a vacuum or the submarine flooding. Let’s take the astronaut for an example. Imagine an astronaut at the ISS wants to go walk his dog. If they just opened the door, all the air would be sucked out of the spacecraft. So what they do is have two doors. Here’s the process: 1. Both doors are shut 2. Air is pumped into the space between them. 3. The inner door opens. 4. Astronaut + dog go into the space between the doors. 5. Inner door closes. 6. Astronaut + dog suit up 7. Outer door opens. 8. Astronaut and dog go for walk 9. They enter the airlock. 10. The outer door closes. Inner door is still shut. 11. Air is pumped into the space. 12. The inner door opens.",
"Everyone is talking about just opening the door and the water comes in for a submarine. My understanding is that rush of water would be too great and could cause harm/damage to the person/thing waiting to exit. The same pump that gets water out probably also lets water back in to fill the room so the door can be opened without the violent rush in. I’d also assume the same for space stations. You want to equalize the pressure before making any attempt to open the door to exit/enter submarine and space station."
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esvbqy | How do we keep air in space stations breathable? | Engineering | explainlikeimfive | {
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"It's mostly made from water. Water as H2O can be split and create 2H2 + O2. That hydrogen is then actually combined with waste CO2 from breathing, creating CH4 (methane) and H2O (more water, fed back into the system). There's loss everywhere in the process no matter how efficient the reclamation systems are. We send constant supplies of water up to the station. Similar systems already existed on submarines. Of course, they could provide their own water.",
"There's a few different ways, but the primary source of oxygen comes from electrolysis, passing electrical current through water breaks the water molecules apart into hydrogen and oxygen. Water is brought to the space station when a rocket goes there. Electrical current is provided by the solar panels. Edit: The other methods are oxygen tanks replenished from earth and they also have a backup system called a solid fuel oxygen generator. These are canisters that contain a mixture of sodium chlorate and iron powder. When ignited it burns like a candle / torch and releases oxygen (and salt and rust)",
"**NASA Engineer here**, I have worked with the life support system on ISS. Tl;Dr: We regularly fly up nitrogen, air, and oxygen. We also produce oxygen on ISS by splitting water into O2 and H2. We also scrub the air on board with a machine that cleans the Co2 from the air, and we have cabin air filters that catch the particulates (hair, fodder, etc). Trace chemicals are scrubbed by yet another machine. Supply: We bring Air (a mixture on of Nitrogen and Oxygen) up to ISS often, along with seperate tanks of pure Nitrogen and Oxygen. On Earth, your air is around 78% N2 and 21% O2, so we try to maintain that balance on ISS at a pressure of 14.0 - 14.9 PSI. Crew members also sweat, and produce humidity through their breath. Our air conditioners collect this moisture, and we use cleanse this and the crews urine to produce water, which we then can take and split into H2 and O2, O2 goes back to the cabin. Cleaning the Atmosphere: CO2 scrubbers scrub out the CO2, a Trace Contaminatant scrubber cleanses hundreds of other trace chemicals.",
"How do they keep particulates (dust, clothing lint, water vapor from breathing) from accumulating in the livable spaces?",
"So how do they maintain oxygen levels within breathable range but not explosive range? Is N2 used?",
"People think ELI5 is a chance for you to sound smart using big terms but fail to realize what ELI5 is actually for",
"the are constantly replenishing their air with the air and water they brought from earth, when you run electricity through water it will release more air. they also have lab-made materials that can absorb the bad air(CO2) that they breathe out and release it in to space.",
"They're currently testing [THIS]( URL_0 ) which should cut down on required supply runs. Will be interesting to see how this works for long term space travel!",
"As mentioned by several comments, oxygen is primarily made through electrolysis (electro = electricity, lysis = breaking) which is basically breaking down molecules into its constituents using electricity. In this case, water (H2O) is broken down into H2 and O2 (2H2O -- > 2H2 + O2). Another source would be liquid oxygen brought in tanks up to the space station to be then melted into gas and diluted (liquid oxygen is 100% but you don't breathe 100% oxygen, you only breathe 21% oxygen in the air) for comfortable breathing."
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eswmp1 | Are solar panels used in space the same as the panels used on Earth? Do they generate more electricity in the same amount of time? | Engineering | explainlikeimfive | {
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"No, cheap panels most commonly used are about 10~20% efficient. The best most expensive panels can be 30~40% efficient. Guess which is more expensive, launch more cheap panels to space, or launch less but more expensive panels to space."
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esxke3 | how do tiny airplane wheels withstand the speed and impact of plane during landing? | Engineering | explainlikeimfive | {
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"1. They're not actually that small. It just seems that way relative to the airplane. [Take a look.]( URL_0 ) 2. They're built specifically for airplanes to land on, including having a seriously powerful shock absorption system. 3. Planes are lighter than you'd expect. That's kind of the point; the lighter the airplane is, the faster it can fly and the further it can fly on the same tank of fuel. Making the tires as small as reasonably possible directly helps the plane and the tires both do their jobs.",
"These tires are very tough, but they don't get as many miles as your car tires, only 500 miles or so. They are filled at high pressure and pure nitrogen gas to prevent ice forming at very low temps."
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eta5pf | How does towing a FWD car from the rear work? | I found a YT channel about a guy who posts funny videos of cars getting towed from his business private lot. One thing I was curious about is how towing of a FWD car from the rear works. The trucks will come, and lift the rear of the car and tow it out a bit. The front wheels do end up turning somewhat. But once the car is out of the parking space, the truck will drop the car and turn around to lift the front so the rear wills will be the ones turning (freely?) I'm curious how the front tires wouldn't break the transmission or whatever part of the car when "moved" like this. Thanks! | Engineering | explainlikeimfive | {
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"Don't they normally just put those little dollies under the front wheels to get it out?",
"There are lots of variables here such as if it is an automatic or manual gearbox and if it was put into neutral, park or in gear when it was parked and if the e-break was on. If the gearbox was in neutral then the output shaft would freely rotate. This does not damage the gearbox as the output shaft is designed to rotate and is not connected to anything. The issue is that if the car is being towed for longer distances like this there is no way to lubricate the gears and bearings in the gearbox as the oil distribution system is usually connected to the input shaft. But for shorter distances like across a parking lot there is no damage. If the e-break is enabled it may keep the wheels from spinning which just causes them to be dragged across the pavement. This can create flat spots in the tyres but again due to the short distance there will not be much damage. And a lot of e-breaks is not able to keep the wheels fully locked up either and the e-break will slip a bit. This sounds like what you are describing. If the car was in gear then the wheels are connected to the engine. So as the wheels rotate the engine will also rotate. It does take quite some force to rotate an engine around as the compression in the pistons create a lot of resistance. This will usually case the wheels to lock up but it is possible that the engine does indeed rotate a bit. But again it is done for a short distance at low speed so there is little chance of damage. The throttle is shut and the ignition is off so there is nothing bad that can happen. Even if the engine turns backwards there will not be much damage if any. If the car is put in park then that would lock up the wheels completely which would cause them to be dragged across the pavement. A lot of gearboxes does have a hidden button or leaver which would put it in neutral or even a special tow mode. This can often be accessed from the bottom of the car so if you see a tow truck driver go quickly under the car with a screwdriver he is likely putting the car in neutral. So as this was at slow speed and a short distance there is very little damage done. However there is a reason why the tow truck driver only pulled the car out from the rear and then switched to towing from the front. Towing a front drive car from the rear can cause serious damage over longer distances. But for short distances like getting the car out of a parking spot there is little chance of damage. Most tow trucks does have dollies and jacks which can be used in cases like this if there is fear of damage. However it is not always needed or there may not be enough room to use the dollies. It does take a bit of time to assemble the dollies under the car."
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etbqzo | Why are submarines so hard to detect even with modern equipment? | Engineering | explainlikeimfive | {
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"_~~Cobb~~ COB, I was just teaching_ seaman _Beaumont here the intricacies of modern sonar.._ Yeah, I ain't Cheif of the Boat, Im Sheena, Queen of the jungle. So, there are two types of sonar. One is active. You send out GIANT acoustical pings like a whale or dolphin use for echolocation and they bounce off another submarine, or ships, or rocks or schools of fish. Give you a very clear picture of what's underwater. Now, whether or not it's a loud reverberating CLONG like in Red October, Ill leave to an actual submariner, but the problem with active sonar is... well, its loud. It gives away YOUR position as much as the bad guys, so we're not gonna talk about it here. Passive sonar is just listening to sounds transmitted through the water. Problem is, the sea is _extremely loud_. And noises, particularly low-frequency ones, travel quite a long way. So if you are lucky to pick the sound of noise out of the clutter of the surface waves, the squid and fish and methane bubbling out of volcanic vents, it could be a ship or submarine that is very very far away (_Including one waaaay out of Pearl!_). So lots of computer processing is needed. On the other hand, naval surface ships to some degree, but submarines as a matter of course, have been designed for the past 80 years specifically to be as quiet as possible. Anything that can vibrate, cavitate, or make any noise is isolated from the outer skin of the hull by an air gap or rubber padding or both. The hulls of submarines are streamlined and smooth, possibly coated with sound-absorbing/dampening rubberish material, and designed to sleekly open a gap in the water ahead of them and let the water merge back together behind it. Stealthy like. Nuclear submarines have a lot of motors and pumps and stuff that have to run continuously, so they're actually quite noisy (the tradeoff is they don't need fuel for decades). When they talk about a diesel submarine sneaking up and killing a carrier say, what they mean is a Deisel electric submarine, running on its batteries and electric motors only. The diesel engine is off and is only used out of battle to recharge its batteries.",
"It's a complicated topic that takes a fair amount of training to comprehend and utilize, but the key point is that the sound a submarine makes simply doesn't reach the detectors. * Submarines are designed to be quiet. The details of these design features is classified. * Detection ranges in naval warfare are great enough that they are typically rounded to thousand-yard increments. * Any detector needs to overcome its self-noise, noise from sealife, and other ocean noises (like waves) and pick out and identify the specific noise of the Submarine. * Sound doesn't travel linearly in the ocean. Due to changes in temperature, pressure, and salinity, sound waves will refract in their path through the ocean, which means that the sound waves simply won't reach certain areas regardless of how good the detector is.",
"What makes you think they are hard to detect first off? I personally tracked a Russian Victor III at over 100 miles passively from onboard the USS Leyte Gulf. What can cause hardships: 1. The detecting unit doesn't know ASW. Its a different type of warfare and the ship is married to the mission. It has to be practiced and that is not done these days. 2. Water is fucky. It can make sound bend based on pressure, temperature and salinity. Attenuation. Spreading. Snell's Law. There's a lot of sciencey shit that complicates things. 3. Active (ping), passive (listen), sonobuoys (active and passive), SOSUS, SURTASS, Submarines, MAD, LIDAR....each has its use case and challenges. 4. There are also differences between submarines in terms of modern quieting and application of stealth. Some countries have them strictly for coastal defense. Some never get underway and are only there on paper. The quietest sub operated by a dickbutt will get found faster than a relic sub operated by someone skilled. MOST countries land solidly in the dickbutt category as their submarines never get underway."
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etgdrp | why do you have to check engine oil and transmission fluid? Why can't there just be a gauge like there is for your gasoline or for the engine temperature? | Engineering | explainlikeimfive | {
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"Engine and transmissions fluids move, quite violently in fact, in an engine or transmission. That is why there is a proceeds for checking each. Engine should be off and vehicle level. Transmission should be running, In park, and vehicle level. Notice when you pull a dipstick it is more or less reading beyond full, but when you clean it off and check it again its much lower? Also, its important to check the quality of the oil and fluid, as well as the quantity Oil goes bad, gets contaminated, even absorbs water. This also must be checked.",
"It's not always about checking the level of fluid, it's also about checking the contents or quality of the fluid. A level gauge similar to your fuel tank isn't going to tell you that there are metal shavings in your trans fluid of that your oil is black and burnt.",
"Depending on the car these thing's do exist. For example, the BMW M series no longer has an oil dipstick - it's monitored by a sensor now."
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etgrin | What's the difference between a standard drill and an impact driver? | Engineering | explainlikeimfive | {
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"a standard drill is like. pushing downwards with a constant force (or however hard) on something... except. it does it rotationally. An impact driver is like hammering something in... except rotationally. Therefore, like the hammer strike, you get a higher \"maximum force\" at the time of impact strike by using the momentum of the \"hammer\" to slam something rotationally. Thus, you can achieve higher forces that a drill wouldn't be able to do... like screw in bolts really tight or unscrew rusty bolts."
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etm9we | Programming code tells the computer to do something, but what makes the code actually mean anything to the computer? | Engineering | explainlikeimfive | {
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"Programs are usually written in a \"programming language\" that is easy for people to learn and use. Then there is \"machine language\", basically a string of 1s and 0s arranged in complex patterns that a computer can understand. In-between the person and and the computer is a special program called the \"compiler\". It takes your programming language and turns it into machine language. They're like an interpreter; if I need to talk to somebody who speaks Russian, but I only speak English, I have to find someone who speaks both to translate what I'm saying. Why don't programmers all just learn machine language? Well, it's really, really hard. And it takes a long time to say anything. So the smartest ones who can speak it come up with a programming language that the rest of us can understand. Then the first things they do are write a compiler and publish a dictionary and rules of their language. Source: am programmer. EDIT: If you're also curious about what the 1s and 0s mean to the computer, check out some of the excellent engineering comments.",
"The computer's built so that coded patterns of 1's and 0's physically open / close different paths for electricity, to make it do different things. These coded patterns are called \"machine code.\" The details of exactly what patterns are available, and what they mean, can be different for different models, brands, or kinds of computers. A CPU manufacturer typically publishes a manual with a complete specification of the patterns. Working directly with the coded patterns the computer actually uses is inconvenient for human programmers. It would also be more efficient if the same program could be used on multiple models / brands / kinds of computers. So people created programs (compilers, interpreters, shells, JIT's) that allow the computer to \"understand\" English-like commands. This involves a \"translation\" process, sort of like translating from German to Italian. (Except the computer is, well, a computer, so it expects programmers to use perfect spelling and grammar, but will happily translate a buggy or completely nonsensical program as long as it's grammatically correct.) It can be done in a few ways: - A compiler works like translating a novel. A long program's translated all at once, then the result's saved in a file that the computer can run. - An interpreter analyzes one \"sentence\" (line of code) at a time, runs that one, then moves on to the next. Sort of like translating a novel out loud as you read it. - A shell lets you type a line of code, immediately runs it, then shows you the result. Sort of like when a businessman or government official goes to a foreign country, they might bring a human translator who translates each sentence immediately when they say it.",
"A lot of people are giving you metaphors, or just repeatedly using the phrase 'the computer interprets' as though no matter how deep you drill down there is some sort of ineffable, intelligent gremlin that performs the magic of understanding. So, here is what's done. It may be a bit harder to follow than ELI5 ought to be, but it should actually answer the question in as simple a form as I can make it. The most basic kind of process that would resemble a computer is an arithmetic processing unit. But we'll focus on an even more basic kind of processor than that - something that just lets us store numbers in memory, and add them together. We'll do this with 4-bit numbers. What you need to make this device is an adder circuit, and a bunch of memory circuits. You can look up how to make these from logic gates - but all you need to understand is their basic input-output behavior. For an 4-bit adder, you'll have 8 input lines which you can make high or low (first 4 represent first number, last 4 represent second number) and 4 output lines, which will represent their sum (with any carry-over truncated.) This circuit acts more or less instantly - whatever you assert on the input lines, the output will automatically match. For an 4-bit memory circuit, you have 5 input lines. You have 4 input lines which you assert as high or low to represent your number. And then you typically have a one more input line which, when asserted, will 'store' each of these bits, so that the 4 output lines match the current value of each of the 4 input lines, and will continue to output them until they get another 'store' command. Without that 'store' command the memory slot will just ignore the current inputs. To make our super-dumb calculator, you'll arrange these kinds of circuits together as shown in the following diagram, with 4-wire buses (4 wires in parallel that link outputs of circuits to inputs of others). The horizontal and vertical lines represent these buses. The sideways arrows - > represent 'gates'. A gate is just an electrically-controlled switch. Not drawn are a bunch of single wires connected to these gates. If that wire goes 'high' the gate is opened. If the wire is 'low' the gate is closed. I'll mention what the ARB is for in a minute. We'll attach the input to our gates at the memory-inputs to the memory's 'store' function as well, so when the gate is opened it'll store the value. > |||| - > memory 0---Adder......|||| < - ARB 1 |||| ------------------Adder -- > |||| < - ARB 2 . < - ARB 3 . < - ARB 4 |||| < - memory 1 < -----------|||| |||| < - memory 2 < -----------|||| |||| < - memory 3 < -----------|||| |||| < - memory 4 < -----------|||| |||| < - memory 5 < -----------|||| So how would we use this to do operations? Well, let's say we want to add the numbers 3 and 5 together. For now let's just say that the value of 3 (0011) is stored in memory slot 1 and the value of 5 (0101) is stored in memory slot 2. So how do we do that? Well, they have a single set of 4 wires along the left-hand side attached to the outputs of all the memory slots. If we 'open the gate' at the memory 1 output, then the value of 3 (0011) will spread across the four wires. It will run up against the input to the adder, and the input to the memory 0 slot. We can't also open up the gate at the memory 2 output, because that would put both the values of 3 and 5 (0011 and 0101) on the bus at the same time, so you'd probably get a random result, or the superposition of the two (0111 = 7). So we can't just open both gates and let them flow into the adder. And two 4-wire buses would be inefficient, since we'd need two gates for each memory circuit, one to connect it to each of the two buses. That's why memory slot 0 is there. We open the gate from mem1, which will deliver its value (0011=3) to the adder and the input of memory 0. Then we open the gate on memory zero input (which is also tied to the 'store' line) so the value in mem1 gets delivered to and stored in mem0. Now the value that was in memory slot 1 is continually being input to the adder via the memory 0 output. So, then we close the gate leading from memory 1 to the left bus, and we close the gate leading into memory 0 so it won't get overwritten with a new value. Then we open the gate on the output of memory 2, so that the value there (0101=5) flows directly into the Adder's second input. With this gate open connecting memory 2 to the adder, and memory 0 deliverying memory 1's value to the adder, the output of the adder will be the sum of the values in memory 1 and memory 2 (1000 = 8). This value will be output constantly at the output of the adder. If we open the gate on the output of the adder, and open the gate to the input of memory slot 3, then the sum will get stored in memory slot 3. Thus we will have added two values and stored the result. Going back to the ARB thingy - we need a way to place our desired values into memory in the first place. How do we get the values of 3 and 5 into memory slots 1 and 2 to begin with? We have to put them there. So ARB_IN is actually just a source of high voltage connected to the 4-wire bus with 4 individual gates. We open or close those gates to place a total value on the bus, and then open the input of a single memory slot to store the value. So to store the value 3 in memory 1, we open the memory 1 input gate, and then open ARB_In gates 3 and 4 while leaving 1 and 2 closed (0011 = 3). We do a similar thing to place the value 5 (0101) in memory 2. Thus, we can input ARBitrary values into arbitrary memory by opening the right combination of gates. This is also why we need a gate on the adder output - so we can block off the result constantly flowing out of it if we want to put an arbitrary value on the memory input line instead. So this really just breaks down into 4 steps. Leaving all other gates closed: > 1) Open gate mem1_in, ARB gate 3, and ARB gate 4 2) Open gate mem2_in, ARB gate 2, and ARB gate 4 3) Open gate mem1_out and mem0_in 4) Open gate mem2_out, adder_out, and mem3_in This will: > 1) store the value 3 (0011) into memory slot 1 2) store the value 5 (0101) into memory slot 2 3) store the value in mem1 into mem0 4) deliver the value in mem2 to the adder, adding it with mem0 and storing it in mem3 This is our program. *This* is what we need to tell the computer to do, at the most basic, fundamental level. Build it so that we can make it do different, useful things by opening and closing gates, and then tell it what gates to open and close in what order to make something happen. So what does this *program* look like when written for the computer? Well, we have 16 total gates. We'll label them 0-9 and the remaining six A-F. > 0) ARB 4 1) ARB 3 2) ARB 2 3) ARB 1 > 4) mem0_in 5) mem1_in 6) mem2_in 7) mem3_in 8) mem4_in 9) mem5_in > A) mem1_out B) mem2_out C) mem3_out D) mem4_out E) mem5_out > F) adder_out So our 4 instructions above become: > 1) open gates 5, 1, and 0 2) open gates 6, 2, and 0 3) open gates A and 4 4) open gates B, F, and 7 These gates are all blocking (no signal gets through) if they receive a low voltage (0) and are connecting if they receive a high voltage (1). So that's exactly what our instruction looks like. Our instruction is formatted as 16 high/low signals delivered to the gates in the format of: > FEDC BA98 7654 3210 (spaces added to make it easy to identify individual bits) So our 4 instructions, finally, in fundamental 'machine code' are: > 1) 0000 0000 0010 0011 2) 0000 0000 0100 0101 3) 0000 0100 0001 0000 4) 1000 1000 1000 0000 That's it. That's the machine code. There's no interpretation going on. There's no Gremlin. These are the physical instructions that make the machine go. You could deliver these instructions, say, in the form of a punch-card. Have a cardboard card with lines of 16 perforated holes that can be punched out. Place it between a piece of metal with high voltage, and a line of 16 spring-loaded contacts each attached to a gate. Any holes that are punched out will let the contacts connect to the plate, delivering voltage to their individual gate. Perform each instruction by pushing the card through, to the next line so all 4 lines occur in-sequence (with all gates closed in between to prevent any instruction mixing). All computers are just [much] more complicated combinations of this fundamental mechanism. No matter how many layers of abstraction there are, at some point the system just turns into 'telling which gates to be open and closed for each step to occur\". And the computer doesn't have to 'interpret' anything. At the fundamental level, the instruction *is* the set of signals that electro-mechanically open and close the gates. If you read through all this, well done. Let me know if it was helpful, or if any part was unclear.",
"If you want to dive deep in this topic, pick up Code: The Hidden Language of Computer Hardware and Software. It starts with basically wire and electricity and explains how to build a computer from scratch",
"At the lowest level, the CPU chip has a few storage slots, called registers (which typically hold one number of a binary length equal to the number of bits the CPU is designed to handle) , and a bunch of simple operations it knows how to do involving the registers. The operations are somewhat arbitrarily assigned number codes. So for example, your CPU might have operations like: 001: Add a number n to register X and store it in register X 002: Put a number n in register X 003: Copy register X to register Y 004: Read memory location z to register X 005: Decrement register X 006: Skip the next instruction if register X is zero And so on. These commands are based on operations that can be performed using hardware logic, such as AND, OR, and XOR, and by turning dedicated circuits in the CPU on and off. To run a program, we just feed the CPU a list of these operation codes and data to use in the operations. For example a some program might be: 002 008 005 001 005 Which, based on the instructions earlier, would put the number 8 in the X register, then decrement it to 7, then add 5. After the program is compete, if we were to read the value of the X register, it should be 12. Because the CPU operations are usually very simple we use higher level languages and compilers to convert easier to use commands into these very simple instructions. I also recommend Ben Eater's 8-bit computer videos if you want to understand it more deeply.",
"I think what op is asking is how does a computer take binary machine code and know to run it. Is there code built into the processor that accepts the machine code as a \"fuel\"? What decides what code to run at what times (queue, priority etc)",
"**A computer is basically a HUGE electric \"marble race\" game, with the track shaped by the program.** You start with logic gates. LOTS of them. The power tumbles in lots of different ways according to the way the \"track\" is set up, and after a lot of applied ingenuity you get it to actually do something useful. What do I mean by a logic gate? OK, let's say you design a tiny electronical circuit that has two wires (A & B, say) going in and one wire (C) coming out. And that it's designed so that there's an output signal if (and only if) it's getting at least one input signal. If both are missing, nothing comes out. That's basically a logical OR - C gives a signal if and only if it gets one from A OR B. Then you design another that gives an output when, and only when, it has no input on a specific wire. That's a NOT operation. You can go on to work out how to build basic circuits that do other logical operations, but with OR and NOT you've now already got enough circuit designs to combine to give all the possible logical operations - AND, XOR and so on. [You can make an AND with three NOTs and an OR, for example: feed each of A and B into their own NOT gates; feed the two outputs into an OR gate; feed the output from that into the third NOT gate; what comes out is basically A AND B. Proof left, as they say, as an exercise.] So now you start working out how combine all the gate types into bigger combinations that do something more interesting. You can combine them to tweak a set of electrical values that represent a number so that you effectively add 1, for example. So you keep going, building the complexity. What you're aiming for is a heap of circuits that will copy the values from one place to another, then do interesting things based on what those values are, then move on to the values in another place, and so on. And those values that make it do the different interesting things - are the program. Add power. Electricity tumbles in all sorts of different ways, and the track ticks into a different shape. Add a bit more power, and it ticks into a new shape again. And the shapes are controlled by whatever values we put in some special places - those values are the program. Keep adding power and with enough ticks, suddenly you're browsing Reddit. You've got a computer. Big marble race, like I said. You could, quite seriously, design a \"computer\" to run a modern operating system using marbles. It would be enormously big and INCREDIBLY slow - and the engineering challenges to make it work would likely be insuperable - but in principle you could do it.",
"There is a free course available called “From Nand to Tetris” and it teaches you how to build a Tetris game from scratch, and by scratch I mean Nand gates, which are (one of) the most elemental electrical circuits. It teaches you how to assemble these gates into building blocks of a cpu, and then machine code, assembly, a compiler and an operating system right up to a working Tetris game. It is fascinating and makes you really understand what is going on.",
"A computer at the very basic is just a machine with an on/off switch. 1 is the command to turn it on and 0 is the command to turn it off. Modern computers are a complex assembly of bajillions such machines which can do a lot of different stuff based on the right on/off configuration. The most direct way for humans to configure computer to do their bidding is by inserting the right string of on/off configuration with a bunch of 1s and 0s. These are what is known as machine language. But due to the sheer complexity and huge numbers of machines involved in a modern computer, this is not really efficient nor human friendly so we developed a shortcut. We saved a bunch of frequently used on/off or 0/1 configurations to words we can recognize. So for example 0100110101010 010110010 1010001011 1010111010 can probably be the configuration needed to display a simple apple on the screen based on which pixel should be turned on and which should be turned off. We are going to need that a lot and we don't want to waste time typing that long string of 1 and 0s each time so we automate it by saving the whole string as \"draw apple\". Nicely short, understandable and easy to remember. This process of translating human words to 0 and 1s is called compiling. So the next time we want an apple displayed, we just type in \"draw apple\" and the compiler automatically transform it to a bunch of 0 and 1s and set the computer to the desired state. Overtime we managed to assemble a vast collection of such commands enabling us to do more and more complex configurations by using a relatively short and understandable way. These are the programming code we end up with.",
"The compiler translates code from the words we write into numbers the computer understands.",
"Machine doesn't \"understand\" anything. It just ends up being a series of circuits, gates and switches that go on and off in whatever series we want. And we in turn create \"meaningful\" states to put the machine in. As short of an answer I can think of."
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etqqzf | why does a referee whistle need a little ball inside | Engineering | explainlikeimfive | {
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"A normal whistle gives a constant note which is something that the human brain will automatically ignore as just a background noise. Lots of things make constant notes in nature and most of them is unimportant. Most important or dangerous things makes changing sounds so we tend to focus more on sounds that change instead of the constant notes. Musicians will change the notes of their flutes by blowing through them differently and covering up holes in different patterns. They will sometimes add vibrato to make a sound more noticeable by vibrating their finger over a hole. Referees are not musicians and just wants a whistle which grabs the players attention without having to do anything fancy with it. So instead of a finger to vibrate over a hole they stuff a cork ball into the whistle which will swirl around in the turbulent air and cover up the hole in the whistle changing the sound. This gives the whistle its characteristic vibrato sound which grabs peoples attention. It is also possible to change the speed of the ball by changing how hard you blow into the whistle which is something that is easier to interpret then a change in volume or note.",
"Only old whistles have peas (the cork ball, because it looks like a pea). It's job is to rattle around the air chamber to create variance in the sound of the whistle, because a human brain really HATES flat soundwaves, and will ignore them. Unfortunately the pea mutes the whistle slightly (because it's absorbing the sound waves, being made of a squishy material), and can swell when gotten wet with rain or saliva and get stuck inside the whistle, which makes it almost useless, and most referees work in the rain quite often. Modern whistles don't have the pea, instead using multiple chambers to create harmonic resonances in the whistle to create a shrill, oscillating tone that is both louder than a pea whistle (because you're removing the mute) and more attention grabbing (because you can intentionally design the chambers to vibrate at the right frequencies). The modern standard is the Fox40 classic, a three-chamber whistle used by both football and american football referees."
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ets4mn | How does the tab on the bottom of a car’s rear view mirror work? | When you flip the tab down to reduce the glare from the light of the car behind you, how does that work? How can you still see everything behind you as if the mirror didn’t move at all? | Engineering | explainlikeimfive | {
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"They basically made of two mirrors, placed in an angle opposed to each other. When you dim it, the \"inner\" prismatic mirror reflects your cars ceiling (making it darker) while the front glass reflects the bright car lights behind you. Edit: this video explains it best [ URL_0 ]( URL_0 )",
"The glass in rearview mirrors isn't actually flat like it seems. It's a wedge-shaped piece of glass that is thicker on one side than it is on the other. So when you move that tab, you see the reflection from a different side of that wedge.",
"The mirror is behind a sheet of clear glass. Imagine looking into a store window. Just inside the window is a mirror. Stand directly in front of the mirror looking through the window and you see what you'll see when the car's mirror is in its daytime position. Now, stand off to the side where you can no longer see yourself in the mirror inside the store. You can still see a dimmer reflection of yourself in the store's window. This is like when the car's mirror is moved to the night position. You are now just seeing the reflection from the front of the glass."
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etvz61 | IP subnet masks and classes. | For some reason this topic really confuses me when I try to comprehend it, I'm hoping someone can break this down in a way that is very basic that can help me grasp it. I don't know why but I can't get it straight in my head and the different videos I've watched have been confusing. Thanks a billion! | Engineering | explainlikeimfive | {
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"An IP address in binary looks like this: 00001000000010000000100000001000 (that's 8.8.8.8) And a subnet mask looks like this: 11111111111111111111111100000000 (that's 255.255.255.0) The subnet mask lets your computer know whether another IP address is on the same network or not. If all the bits in the IP address, where the subnet mask is 1, are the same as your computer's IP address, then it sends data directly to that computer. Otherwise, it sends data to a router. 00001000000010000000100000001000 < - your IP 8.8.8.8 11111111111111111111111100000000 < - subnet mask 255.255.255.0 00001000000010000000100000001001 < - 8.8.8.9 - same subnet ^ 00001000000010000000100000001000 < - your IP 8.8.8.8 11111111111111111111111100000000 < - subnet mask 255.255.255.0 00001000000010000000100100001000 < - 8.8.9.8 - different subnet ^ The subnet mask is always a bunch of 1s and then a bunch of 0's - you can't have a random 0 in the middle with 1's on both sides (or vice versa). So instead of 255.255.255.0 it's a lot more convenient to just write the number of 1's, which is 24. If you write the IP and the subnet you put a slash in between, so you would write 8.8.8.8/24. Classes: In the early days of the Internet, the subnet size was based on the IP address. If your IP address was 0.0.0.0 up to 127.255.255.255 it was a /8 subnet. If your IP address was 128.0.0.0 up to 191.255.255.255 it was a /16 subnet. If your IP address was 192.0.0.0 up to 223.255.255.255 it was a /24 subnet. (224.0.0.0 and upwards are used for other purposes and your computer shouldn't have them). We don't do that any more.",
"I could only answer half of the question, but it will be (I hope) enough for the first time. The other half will be one another user's work. So: An IP address is 32bit long logical address, which we use for communication with other networks. Subneting is needed for the network equipments for dividing subnets. One subnet is a range of Ip address, which from a router can assign us one IP address. There are different subnet lengths, depending on our needs. If we want to assign 2 IP address to 2 different routers, which is connected to each other, we would use a one what contains 2 host addresses (which we can use for the interface IPs.). This one is the /30 or 255.255.255.252 (the first one is the number of bits we use to identify the network, the remaining 2 is the bits we use for the host addresses). On the remaining 2 bits we can display four different states (four of hosts), 2 of them are network address and broadcast address ( to identify and to send broadcast messages for the whole subnet), and two hosts which will communicate to each other. The 192.168.0.0 network address with a 255.255.255.252 subnet mask (The abbreviation for the subnet mask is /30) is the following: 192.168.0.0 < === Network address (identify) 192.168.0.1 < === First host address 192.168.0.2 < === Last host address 192.168.0.3 < === Broadcast address (Broadcast messages) 192.168.0.4 < === Next subnet's network address. Of course larger subnets has larger host IP address range, but it was simplier to describe with smaller ones. IF YOU HAVE ANY QUESTIONS I PLEASED TO HELP YOU. There are no silly questions, just be sure, you learn in your own pace, don't speedrun your life. I wrote it on my phone, and I'm Hungarian, so it is possible to have poor grammar, and short explanation. Tomorrow, I will be able to write longer."
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etwiev | Why is it that operating a car or bike in lower gears is better for going uphill? | I’ve had this explained to me before but I just don’t get it. Gears and transmissions in general are confusing to me. | Engineering | explainlikeimfive | {
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"Next time you open a door try this. First, open the door normally by pushing roughly in line where the handle is. Then, open the door by pushing close the hinges. It will be noticably harder. What your experiencing is “torque.” Essentially, it is easier to rotate an object if you apply a force farther from the axis of rotation (i.e. this is why you push a door open far from the hinges) since you produce greater torque, which is essentially a rotational force. Now look at your bike gears. If you look at the gears near the back wheel, your “lower” gears are the big gears close to the wheel, and the “higher” gears are the smaller gears farthest from the wheel. When you’re in low gear, the larger gear means you chain is pulling on the gear at a larger distance from the center of the axis of rotation, thus generating more torque and making it easier to turn the wheel. As you get faster, however, higher gears will help you produce greater speed. A smaller (higher) gear turning the same distance as a larger gear (not angular distance but actual distance around the gear) will result in greater angular velocity and thus greater angular velocity on your wheel, which means greater speed. It’s a bit tricky to explain without a physics education, but hope this helps!",
"At lower gears, the engine (or pedals) need to turn faster in order to turn the wheels one revolution, but it also takes less force to do so. Picture riding a bike, in lower gears your legs might be going like the clappers, but you aren’t having to put a great deal of effort into each stroke."
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eu1ju5 | Why do some keys fit into a lock but not turn it? | Engineering | explainlikeimfive | {
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"The key is made from the same key blank. The basic shape of the key (it cross section) matches the lock. Many many many keys and locks are made off the same blank. It is the teeth of the key that are different and prevent (or allow) the key from turning.",
"Because the key has the right shape to fit into the opening but the right cut to align the pins. [Pin tumbler locks]( URL_1 ) have a set of pins that block the lock from opening unless [they're aligned the right way by the bumps on the key]( URL_0 ). It's not only possible but also very common for a key to have the right outline to fit into the opening of the lock but not to align the pins the right way to open it, because most keys are made from a relatively small number of blanks, and most keys made from the same blank will it into fit into the same lock (but won't open it)."
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eu25y7 | Why and when did farms change from square parcels to circular? | As a city folk who never was on a farm, I notice, with the help of Google maps, that a lot of farms seem to be circular. I presume it's easier for a long arm to have a center point and make a circle to spray water, pesticides, etc. But why does it seem like this wasn't the case 30 years ago? And doesn't a circle waste an ample amount of space in a given square? | Engineering | explainlikeimfive | {
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"[Center-pivot irrigation]( URL_0 ) was invented in 1940 by farmer Frank Zybach, who lived in Strasburg, Colorado. It is recognized as an effective method to improve water distribution to fields. Writer Emily Woodson characterized the increased use of the center pivot irrigation system as part of a profound attitude shift towards modernism (expensive tractors, center-pivot irrigation, dangerous new pesticides) and away from traditional farming that took place in the mid-1970s and 1980s in the United States.",
"Can't answer when. In most modern farms and most wealthy economies that still have farming, land area is seldom a constraint. It is more typically efficiency in capital and labor costs that dominate the economics of farming. The circular irrigation is simpler and cheaper capital wise, easier to repair and install (and move). The loss of not farming the \"extra\" bits is relatively unimportant (ie you wouldn't spend a LOT more money to irrigate only to make relatively LITTLE additional output)",
"It does waste a percentage of the corners of each plot, however they now have automated swing arms at the end that can overcome most of that issue. Technology has improved immensely with electric motors and gps control. Circles used to be fairly rudimentary. Nowadays the increase in yield easily can offset the cost, and the improved circle technology is somewhat more resistant to issues and headaches(nowhere near perfect). Some crops remain better served by alternative irrigation methods. Drip lines for example can produce superior onions compared to pivot based."
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eu8k04 | Why do straight rear windshields have wipers, while angled rear windshields don’t? | Engineering | explainlikeimfive | {
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"More dirt collects on a straight rear windshield due to aerodynamics. The shape of near-vertical rear ends on SUVs and hatchbacks creates a large lower-pressure zone that sucks airborne dirt and grime onto the glass.",
"At speed Rain runs off the slope of the rear windshield. Whereas it beads up on a straight windshield. There are a few sedan/saloon and coupes that have the angular windshield and a wiper."
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euei9z | How do car engine sizes work? For example a 1.4 L, 1.6 L, 2.0 L | Engineering | explainlikeimfive | {
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"it's the total capacity of the cylinders at bottom dead centre, that is, with no compression, a 1.6L 4 cylinder engine has that 1.6L spread out over 4 cylinders, each one being 400cc or 0.4L. Typically the displacement corellates with power/torque, but other factors can affect the characteristics of the engine.",
"An internal combustion engine is just a fancy pump. Air goes in the intake and comes out the exhaust. The displacement is the total volume of air that can be pumped through the engine in a single revolution. For example, a 3.0 L V6 has six cylinders that are each 0.5 Liters when the piston is at the bottom of the stroke. The engine generates power by taking that 0.5 L, adding fuel to it, then squishing it down to about 0.05 L before making it violently explode. Each explosion in series one after the other provides the propulsion that keeps the engine spinning. For another way to imagine it, think of a hypodermic needle used for injections. Medicine is drawn into the cylinder by pulling back the piston, then the mediocre is pumped out by depressing the piston. The volume of the dose is dictated by the diameter of the cylinder and the distance the piston is pulled back (known as the stroke)."
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eumixx | How does a tilting steering column work? | A picture or video showing the exposed steering column while the wheel is being adjusted would help a lot. Or a simple explanation. I can’t find an easy to understand explanation anywhere online. | Engineering | explainlikeimfive | {
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"Simple explanation: a universal joint or flexible shaft coupler allows rotary motion at various angles. Eli5: rotate a bendy straw by holding one end in each hand and observe how it still can rotate without being perfectly straight."
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euvpps | How are CPUs and GPUs different in build? What tasks are handled by the GPU instead of CPU and what about the architecture makes it more suited to those tasks? | Engineering | explainlikeimfive | {
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"My favorite description was that a CPU is like having someone with a PhD per core. A gpu is like having an army of millions of kindergarteners. Want to do complex math on a lot of data? Hand it to the 8 PhDs. Want to fill in a bunch of tiny spots with a different color? Pitch it to the kindergarteners. Edit: haha, glad you all enjoyed this description as much as I did.",
"CPUs use a few fast cores and are much better at complex linear tasks and GPUs use many weak cores and are better at parallel tasks. To use an analogy, the CPU does the hard math problems and the GPU does many, many easy problems all at once. Together they can tackle any test quickly and efficiently.",
"GPUs are good at solving a lot of simple problems at once. A good example is graphics.... I need to take every pixel (and there's a million of them!), and multiply each of them by .5. Anything you can convert into adding/multiplying large groups of numbers together, it can do really fast.... which is frequently needed to render graphics. But they can't do all operations. They are very specialized to working with big lists of numbers. Working with a large list of numbers is all it can really do, and it can only do a handful of operations to them. But if the operation isn't supported, you're basically totally out of luck. Luckily the things it can do are common ones. These operations share some commonality with artificial intelligence and physics simulation as well. But it doesn't do well with directions with a bunch of decisions. GPUs want to work on a whole list of things at once. CPUs are good at doing a bunch of different types of tasks quickly. It's a jack of all trades. It can work with big lists of numbers... but it's slower at it. But it can do all sorts of things that the GPU can't. CPUs are good at following directions that have a bunch of decisions. Everything from making the keyboard work with the computer to talking to the internet requires a lot of decision making. With this ability to make a bunch of decisions, you can come up with some kind of solution to any problem.",
"A typical CPU these days will have something like 8 cores/16 threads meaning that it can do up to 16 things at once. Each core is very powerful and designed to be general-purpose so they can do a wide range of things. The things that are best done on CPU are tasks that are serial meaning that the previous step needs to be finished because the result of it is used in the next one. A typical GPU may have something like 2304 stream processors, meaning that it can do up to 2304 things at once, but what each stream processor can do is much more limited. What a GPU is most suited for is doing math on a big grid of numbers. With a CPU, it'd have to calculate those numbers 16 at a time (actually, less than that because the CPU has to do other things) but with a GPU, you can do math on those numbers 2304 at a time. But it turns out that graphics are pretty much nothing more than a big grid of numbers representing the pixels. And a lot of scientific calculation involves doing math on huge grids of numbers.",
"A CPU can do a few things quickly, and a GPU can do a lot of things slowly. Imagine you have to get from New York to California and back as fast as you can. You can take any car you want, but only you are allowed to drive. You'd get the fastest sports car you could, and drive it as fast as you can. But if you had to take 30 people, you'd want to take one trip with a bus instead of 30 trips with the sports car. CPU and GPU is the same idea. When you make a picture for a game or video, each pixel can be done without worrying about the other pixels - so you have a few million pieces of math that have to be done, it would be better to do them slowly but in big batches than quickly but one at a time. (ELI25 notes) There's also some fundamental differences in the memory model and instruction sets between CPUs and GPUs. GPUs are designed to perform operations important to graphics programming quickly - for example, trigonometric functions that take many cycles on a CPU typically complete in few (usually only a single) GPU cycles. GPUs also have many areas of memory with different sharing characteristics, while CPUs generally just have the RAM and varying levels of cache.",
"In addition to what others have said, CPUs are good at things like: - Compare the coordinates of the bullet object and the opponent object. - If they are the same, then: * Read the score stored at a certain location in memory. * Add 10 to it. * Write the number back to the memory location where the score is stored. * Look up the memory location where the start of the “show opponent dying animation” routine is stored. * Remember what part of the program we’re currently at. * Temporarily go to the “dying animation” part of the program we found earlier. And so on, and so on, and so on. CPUs are really, *really* good at doing relatively complicated steps like each of the above. But because each step might have lots of nitty gritty details, they take a lot of work for the CPU to actually do them. (Read about [instruction pipelining]( URL_0 ) if you want to go down the rabbit hole of how complicated a modern CPU actually is behind the scenes). GPUs can’t do anything nearly that complicated. Their “programs” are more like: - Find the chunk of memory starting at a particular location. - Add 3 to the first 1,000 numbers you find there. Or: - Here’s a list of 10,000,000 decimal number, like 2.3 and 4.7. Add each pair of numbers and divide them by 2, and put the results in another list. Oh, and if it lets you go a little faster to pretend that 2.3 is really 2.9999999987, go for it: raw speed is more important than perfect math here. They can’t do things like make complicated decisions or jump around to just another part of their programming. They don’t have the circuitry to do that stuff. But those simple little instructions like I described? They’re smoking fast at those things, and at doing *a whole awful lot* of those simple little instructions at the same time. A CPU can do all the same things a GPU can, but it doesn’t have the circuitry for “do this one thing a gazillion times” kind of operations. Or TL;DR: - A CPU is like having a mathematician sitting at her desk solving hard problems. - A GPU is like having a thousand kindergartners counting to 10 on their fingers, but all at the same time.",
"Further to the other answers, [this Mythbusters/NVIDIA video]( URL_0 ) gives a good ELI5",
"A CPU has a few cores clocked very high. The Ryzen R7 3700X is a pretty mainstream CPU and has 8 cores. A GPU these days has a few thousand cores clocked low. A Radeon 5700 XT has 2560 cores. That's 320 times the cores of one of the most popular desktop CPUs. This difference in clock speed is down to many things but mostly power consumption and heat. Double something's clock speed and its power usage *more* than doubles because physics. (This is why downclocking a video card just a little bit can save a lot of power for a small loss in performance.) In addition to the core count, the underlying architecture of a GPU and CPU is different. Keep in mind, a GPU is basically a mini computer on a card. It has its own CPU, which we refer to as a GPU, and its own RAM. * GPUs are very efficient at one particular problem: multiply-add. This is *very* common in 3D rendering. They can take three sets of 4 numbers, multiply the first two together then add the result to the third. CPUs are capable of this too but it's almost cute given the difference in core count. * The bigger difference comes in how a video card can use its local memory vs a CPU using system memory. System RAM traditionally (DDR4, these days) is built to be accessed in lots and lots of small chunks. One number here, four numbers there, two numbers yonder. It is low latency but relatively low bandwidth (not a lot of data at once but a very small delay). A GPU's RAM (GDDR6, most recently) is high latency but much higher bandwidth (a shitload of data but often a large delay). This difference in architecture means that the two can serve polar opposite functions. A CPU can process a long string of calculations with data coming from all over RAM very quickly, but don't ask it to do too much at one time. A GPU can process a shitload of calculations all at the same time but don't ask it to access lots of different bits of RAM. And finally, one of the shitty parts about how computers are built is that the CPU controls data going in and out of the GPU. This communication can be slow as shit. See: the purpose of DirectX12/Vulkan over DirectX11/OpenGL.",
"CPU \"waste\" silicon trying to predict the future (branch prediction), to remember the past (cache) and to have it's different cores try to agree with each other (coherency protocols). GPU is the dumb but effective approach: every body does the exact same thing, on data that are right next to each others. They can't do anything else, they can't wait, they don't \"think\", they don't talk to their neighbors, they just do.",
"Imagine a CPU like a sports car moving at 100kph. It holds 2 people and gets them to point B very very quickly. Now imagine a GPU like a big ass bus moving at 10 kph. It can hold 50 people. But gets them to point B very slowly. Basically, a CPU does a few things fast. And a GPU can do multiple things at the cost of speed.",
"Adding onto others, think of a CPU as a pocket knife, good and useful for anything that needs a knife. Now, think of a GPU as a surgeon's stencil, useful for one specific task but not good for anything else. When you are doing brain surgery, you could use a regular pocket knife, but it would be better to use a stencil instead. The same thing applies to the CPU's and the GPU's functions. The GPU has many weak cores (processing units) that allow it to process graphics very quickly, but not much else outside of that. A CPU, however, has fewer cores but, since they are more powerful, it can do a variety of tasks, albeit slower than the GPU.",
"The basic unit of each is called a \"datapath\". Given an instruction, a datapath will load data from memory, do a bit of math on it, write it back to memory. In both, the datapath can run multiple instructions in parallel, but in slight different ways. In a CPU, the goal is to optimize through put, to have the most instructions in a sequence completed. Imagine it a CPU trying to do multiple steps in a recipe at once to get it done as fast as possible. In a GPU, the datapath runs the same instruction over multiple sets of data at once. This lets it do complex mathematical operations, such as matrix multiplication, for large sets really quickly. Since most 3d-graphics and machine learning problems transform into a giant number of matrix multiplications, GPU tend to get used for these. CPU can do one specific thing that GPU's are not good at: branching. When there is a choice that has to be made, the CPU decides which path to take.",
"CPU are general purpose calculator. It is excellent at nothing, but also bad at nothing. GPU are specialised calculator. It is excellent at graphic stuff, and bad as a general purpose calculator. The reason is simple: graphic is a set of instructions that repeat itself alot, so it is worth to combine many standard instructions into one single one and super optimise that function. Since this function will be used only in this context, they can sacrifice the flexibility of it for the gain of speed. As a wrong example, it's like if you had to calculate the volume of a polygon. The CPU would do it the hard way, like you would do it by hand. But the GPU would have a \"gimme the 3d coordonates and I will tell you the volume\" function. So the GPU you throw in the 3d points, it use it's super optimised function (maybe even get help from some look up tables), and return the result in a fraction of the time it would normally take for a CPU. Also, a CPU will have a few cores, while a GPU now have often several thousands of cores. They are slower, so you have to split the problem in many small pieces. Which is fine for a 3d image: it's full of polygon, just send a few thousands at a time to be processed. A cpu may do each faster, but can't compete at all with the thousands of the other. Another thing that a GPU is good at: sorting matrix. Feed it a list, here come a sorted one. A CPU do not have such function. Reason being, a GPU deal with that. Alot. But... Thousands of slow cores... It also mean that each result take more time to come out. For a single, simple task, the CPU will most likelly do it faster: it's single core performance is higher for general purpose use. And sometime by a big margin! However, if you have thousands of repetitive tasks that can be done in parallel, then the GPU will probably beat it.",
"During the 80's and 90's, computers were commercialized and slowly made their way into people's homes and got used more and more in businesses. The internet started out, the first online businesses sprouted up. That meant the chip manufacturers were very busy developing the next generations of CPUs. At first, that meant increasing the *clock speed*: the number of instructions a CPU can handle per second. Around 2004, they ran into a problem though: once they got to around 4 GHz (4 billion instructions per second), they started having a very hard time to get their CPUs working reliably when increasing the speed even more. So they had to find other ways of getting more performance out of the computers they were making. They briefly experimented with installing 2 CPUs in 1 computer, but that also had all sorts of trouble, mostly related to syncing data between the two. The alternative they came up with, was to integrate 2 CPUs *on the same chip*. That's what we call a core today. Now, what is the difference between CPUs and GPUs? A CPU is a chip that can handle all sorts of different tasks: it can do math, it can read and write to/from your hard disk, it can handle data from the internet, it can process the input from your mouse and keyboard, etc. It does a lot of stuff. That also means it's some really complex machinery, which constrains the number of cores you can fit on a single chip. You could in theory make the chips bigger, but that means all the signals have to travel farther, getting you back into that data syncing problem. Power efficiency is also a big factor. This all means that you usually see CPUs with 2, 4 or 8 cores these days. GPUs on the other hand have 1 specific goal: drawing graphics. You give them some *textures*, the actual images you want to draw, and the positions and shapes you want them drawn in, and the GPU will do all the math required to figure out the color for each pixel on the screen. That math is not very hard, but you need to do it for millions of pixels, ideally 60 times per seconds. That's why your CPU struggles with this task: it just can't handle that number of instructions. A GPU on the other hand, often contains 100s or 1000s of cores, allowing it to perform an incredible amount of math every second. These cores are much simpler than those in a CPU because they only have to do 1 thing."
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ev0p4y | How do surgical masks protect you from getting infected when there are huge gaps near your cheeks and the bridge of your nose? | Engineering | explainlikeimfive | {
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"Wearing a surgical mask is not an effective way of preventing they wearer from getting infected. (As you suspected) They are fairly effective in preventing the wearer from spreading their own droplets (sneezing, coughing, just breathing), thereby decreasing the chance of them infecting another person.",
"They don't protect you from disease, they protect those around you from your disease. Surgical masks make it so that if you cough, you aren't spraying germs all over the place."
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ev13r4 | How do large rockets, shuttles etc. keep their balance when launching? | They seem to take off so slowly and I never see any kind of auxiliary propulsion near the nose to help keep things straight. | Engineering | explainlikeimfive | {
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"First, they're designed and built so that they're aerodynamically stable and will tend to remain pointed in the same direction as they move through the air. Second, they're steered, just not from the nose. There are a couple of ways to do this. Many rockets have what are called gimbaled engines. This means the engines can move around and point in different directions to steer the spacecraft. On the space shuttle, the SRBs and the orbiter's 3 main engines could gimbal. Another option is to have the main engines be fixed but to have smaller engines called vernier engines located around the side or the base of the rocket be movable to steer it. The Soyuz has these. Once outside the atmosphere, this becomes irrelevant because there are no aerodynamic forces acting on the vehicle, and it just uses small thrusters to change its orientation."
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evewaq | Three phase power into a single phase transformer | Engineering | explainlikeimfive | {
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"To clarify a bit you still have the same problem with single phase power. Electricity still wants to run from one wire to the other. Its just that stuff like transformers and light bulbs get in the way. Current in three phase power will happily run from any one wire to the other. Three phase motors and power supplies just happen to draw current from all three wires evenly. Things like pulling power from only two wires instead of three will unbalance the current flowing through all three wires. Its not too bad, but it does waste some current carrying capacity of the wire that isn't being used.",
"The two legs are connected to either end of the same conductor that is coiled. When first energized the only thing providing resistance is the wire resistance. The current goes extremely high when first energized. The current flow creates a magnetic field which builds up and collapses as the alternating current changes polarity. As the produced magnetic field from the current flow builds up and collapses with the alternating current it induces a voltage that opposes the applied voltage. It's inductive reactance, kind of like resistance. This causes the current flow to drop back down. The\"input\" side is called the primary. This same magnetic field in the primary induces a voltage into the output windings called the secondary."
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evkazd | Why do guitar brands like Fender and Gibson release models and guitars that stick so strictly to a specific look? | I am sure people enjoy the feel and classic look of a strat, but they literally all look so similar. Wouldn't they want to release newer, more modern body shapes and use more innovative ieeas? | Engineering | explainlikeimfive | {
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"If you can make and sell the same design of something over and over, there's no incentive to innovate. People like and want the classic guitar shape - familiarity, ease of playing and carrying, fitting into standard guitar cases, the look, etc",
"They do. But there are only so many ways to skin a cat, and you're talking about two of the most iconic instruments ever. People will always buy Strats and Les Pauls because of their cultural significance.",
"As buyers, people tend to have values other than pure functionality. Aesthetics and emotional attachment play a huge (some might say predominant) role in why people choose to purchase something. This is why advertising works - packaging, messaging, hiring famous people to tout the products. Guitar players or aficionados might be attached to a famous player who used a particular guitar and associate that guitar with positive attributes. Manufacturers understand this and will cater to this sensibility. Also manufacturers are not emotionless things - the people within these companies have a sense of pride and tradition as well.",
"Fender has actually been innovating a fair amount in recent years. Unfortunately, a lot of those innovations don’t sell so they get discontinued. Recent Fender is actually a great marketing case study. I read and article where their CMO stated that they don’t have an awareness problem or a reputation problem like most brands; they have a attrition problem (the entire industry, really) because the guitar can be a difficult instrument to learn. So they pour a lot of marketing dollars into content aimed at keeping beginners interested. That’s why they push Fender Play so hard. If they can get that person, who got a starter kit but doesn’t know what they’re doing, to learn songs they know, they will increase their overall customer lifetime value. Eventually that player will be in the position to buy an expensive guitar and they will think of fender, who was by their side the whole time. But, my guess is they will still buy a strat/tele/conventional body style because that’s what sells.",
"Probably the same reason the playstation controller has changed so little over the years. The design is iconic to their brand, and if they tried to change it people would get mad and get them to change it back, like the original ps3 boomerang controller."
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evlw1x | Why do cars automatically start moving after you release the brake? | When you come to a stop at a traffic light, you stop the car from moving. When you release the brake, why does the car still move even if you don’t press the gas at all? | Engineering | explainlikeimfive | {
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"Automatic cars have what's called a \"torque converter.\". It's basically a fluid coupling between the engine and the transmission. When the engine is at low RPM, the fluid isn't spinning all that fast so it's easy to overcome the torque with the brakes, but it's still applying a force (but with barely any friction because of three fluid, as opposed to a clutch). When you speed up the engine the coupling applies a greater force on the transmission and you go faster. This is not only simplified for ELI5 bit also because that's the extent of my knowledge so hopefully I didn't mess it up too bad. Like most things in automatics, torque converters are 80% magic.",
"The engine is still kind of tugging on the wheels. You're just holding the wheels back from turning. Once you turn off the break then the engine moves you forward unless there's too much resistance.",
"Doesn't happen in my can unless on a hill. I suspect your driving an automatic transmission which is always engaged with the engine. Brake stops, no brake go",
"An automatic transmission connects the running engine to the wheels with what is essentially a liquid clutch. This liquid clutch is called the \"torque converter\". The torque converter is designed in such a way as to apply very little torque to the wheels ( it allows a large RPM difference) when engine RPM is very low, like when at idle. As the RPM increases the converter no longer allows a large RPM difference and the wheels get full torque from the engine. In short. The engine is never really disconnected from the wheels. The transmission allows enough slippage so that you can hold the car stationary with brakes.",
"The engine is always turning when it's on, even when you're stopped, and in an Automatic car it's always connected to the wheels, so at any point with the engine turned on, the wheels of your car want to turn. The only thing stopping them is you pushing down on the brakes. As soon as you take that brake force away, they start turning.",
"when a manual transmission is sitting at a red light its in neutral, releasing the clutch with stick on first gear begins to pull it forward same as the automatic. if you dont like it you can pop your auto in neutral as well. still hold the brake tho so you dont roll",
"Follow up question. On a manual transmission , if I engage the engine to the wheels, the car will move unless I press the clutch. I can half press the clutch, and the car will slightly move without stalling. But that causes clutch wear down. What is wearing down on an automatic if the engine that is constantly connected to the wheels is forced to stop by pressing the break pedal?",
"From watching a lot of Dashcam videos, i have come to the conclusion that a traditional Torque Converter type Auto-box is actually quite dangerous, especially in a vehicle with a powerful engine. I have often seen secondary and tertiary accidents happen due the the car driving on by itself after the driver has either been stunned by the initial crash, or by feet slipping off pedals after the impact. A regular manual will usually stall but an auto will just idle on, back into traffic or over a person if they are stood/laying in front after an accident."
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evp9jn | Who do some shoelaces stay in a knot for WEEKS while some keep undoing themselves for no reason every few minutes? | Engineering | explainlikeimfive | {
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"The knot that you use has a lot to do with it. If you tie the loops together and tugging on both ends causes the laces to move, then they are backwards. For correct tension, the only part of the knot that should move is the tail. Believe it or not, there is a TED talk about this specific topic. [ URL_1 ]( URL_0 )",
"Knots work by friction. If laces are soft compressible fabrics like those of most sneakers you're able to tighten them down, squeezing the fabric on itself and creating a lot of friction between the surfaces of each piece of the lace inside the loops of the knot. Other laces, like those found on some dress shoes or boots, are cylindrically shaped woven cord. These materials are often stiffer, and don't compress in on themselves as easily when tied into a knot. Additionally, they may have a slick surface texture due to the material they're made from. In these cases those laces don't generate as much friction and the knots more easily loosen and eventually untie themselves. Adding a second overhand knot with the resulting loops from the first knot can help bolster the knot from untying, but even then you might still run into the same issue. If it's a recurring problem, there's nothing in the rules that says you can't buy sneaker-style laces and re-lace the shoes with them on your own.",
"Three things really matter when it comes to shoelace knots holding or untying unexpectedly: the way the knot is tied, the material being tied, and the environment that that knot has to exist in. Shoelace knots are meant to be easily tied and untied rather simply and quickly. This limits the type of knots used and generally only a small handful of those are used by a large number of people. After lacing one's shoe, the laces are crossed and the uppermost lace is passed under the cross and this knot is pulled snug against the surface of the foot. Then, two loop are formed, often referred to a \"bunny ears\", and the same cross and pass method is used to form a second knot that is pulled snug against the first. This is the basic, \"single knot\" tying method, even though it uses two knots. It ties and unties quickly, and even very young children can learn to tie it - but it doesn't hold very well. One solution is to do the same \"bunny ears\" knot again, often called a \"double knot\". Another option, and my personal favorite, is to pass both \"bunny ears\" under the cross when tying the first \"bunny ears\" knot. This holds remarkably well and the knots sits level across the face of the foot. [Here]( URL_0 ) is a great video of that knot. The material that make up the shoelaces matters too. Often found in leather boots, some laces are made of a coarse, somewhat rigid cord that doesn't like to bend into very tight turns. As a result, the knots made with these laces are often not as tightly compressed when pulled snugly against the foot. Laces that are made from thinner, smoother, and more flexible material can bend into very tight turns, which leads to a much tighter, compressed knot. Finally, the environment matters because some knots have to do their job in the rain, mud, during a marathon, while sitting on the couch, while sitting at a desk, and many other scenarios."
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evpmfq | Why, after building millions of cars and seeing that all of them rust, do automobile makers still not spray a rustproof coating or use stainless steel wherever appropriate? | Engineering | explainlikeimfive | {
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"Stainless steel is expensive and harder to work with. Spraying an undercoating at the factory costs money. They pass those savings onto the customer who hopefully will have a rusted out car in 6-10 years and buy a new vehicle."
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evugsc | How can a ships anchor prevent a ship from drifting away, but can easily be redtracted at the same time? | Engineering | explainlikeimfive | {
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"The anchor can be retracted when you are over it. When the anchor is holding the boat you should have 5-7 times the depth of rope or chain out to keep anchor embedded [ URL_0 ]( URL_0 )",
"Long time boater here. Agree with those earlier and I will add that on lighter boats (not cargo vessels), the anchor is attached to several feet of chain which is then attached to rope up to the vessel. The chain is heavy so it keeps the final few of the rope/chain attachment parallel to the sea floor. This way any force of the wind and tide on the vessel is applied horizontally to the points of the anchor causing them to dig in deeper. As previously stated by others, this is negated by being above the anchor and applying vertical force to lift it. By the way there are calculators online that help determine how much length of chain/rope (\"rode\") you need based on the depth, among other factors. It's called \"scope\". From [ URL_0 ](https:// URL_0 ): The amount of rode you put out, or *scope*, combined with weight at the *anchor* end of the rode, determines the angle of pull on the *anchor*.",
"When you’re pulling up the anchor you’re directly above, whereas when the ship moves it tries to drag the anchor making it snag on things and either only move a small amount, or become lodged on something"
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evy0n3 | how does all the digging of tunnels and construction of tall heavy buildings not lead to land cracking and breaking apart? | Always wondered that especially for dense cities like Singapore, Tokyo and New York, how do engineers continue to dig deeper and build higher without risking the land cracking apart like the ice age squirrel's nut cracking the glacier, and having all the infrastructure just sink into the ocean? | Engineering | explainlikeimfive | {
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"Tunnels and foundations aren't dug haphazardly and right underneath the surface. Engineers and geologists study the ground to determine where to dig tunnels and foundations. What they're looking for is bedrock. Bedrock is the extremely hard, sturdy rock that lies under softer material like dirt, mud, clay, or sand. Bedrock is extremely strong. If you build your tunnels and foundations down to bedrock, the weight of of everything on top is distributed over a huge area, and can easily support the weight of anything on top.",
"The ground is really strong. Also, there are engineers who basically only deal with figuring out if the ground can support the loads of buildings and other structures. URL_0"
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evz403 | Why are the backs of chairs curved in such a way that they oppose the curve of our backs? | Engineering | explainlikeimfive | {
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"Like car seats. Yeah. I know. Why *are* car seats designed to push you into a hunched position?"
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ew1e0r | How do bandsaws work? | I'm talking about the handheld bandsaws that appear to have 2 large (circular) drums on either side of the blade I always thought that they went back and forth really quickly but I recently watched some slow motion video of them and it doesnt look like that's the case I assume then that the only way it can work is if it bends the blade but that really doesnt seem likely, I mean it's a solid blade that doesnt seems as if it would bend that easily, and probably put a lot of stress on the blade, would probably also make it hard to change the blade when it gets worn out??? | Engineering | explainlikeimfive | {
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"The blade is a continuous band that loops all the way around. The drums spin at a high speed, driving the blade sort of like a tank track. The blade can handle the bending perfectly fine, and the blades usually only need to be replaced when the teeth are physically worn down.",
"They only go in one direction, one drum is typically the drive drum and the other is just a bearing/tensioner. The blade is flat the whole rotation with one side with teeth and the other flat metal. The blade really isn't hard to change, you just need to release the tensioner. Then when you put a new one in you re-tighten it. The force between the drive and tensioner is what keeps it tight enough to spin. It's like the serpentine belt on your car, but with teeth."
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ew2ye1 | How does a well work? | Are there underground rivers all over the place? How do you know where to dig? Why is the water safe to drink? | Engineering | explainlikeimfive | {
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"There is what’s known as a “water table” where, if you just simply dig deep enough, you’ll reach water. Most modern day wells use a pump and filtration system to extract the water, but if you dig deep enough, the pressure can be enough to shoot water up the well without a pump. The water still needs to be filtered, though."
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ewrsjt | What's the difference between a pipe and a tube? | They seem the same. | Engineering | explainlikeimfive | {
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"Very little. The term tube is usually used for something with a bit more flex, whereas a pipe is most often rigid. A tube and a pipe perform more or less the same function, but pipe vs tube is primarily dependent on where you’re building something or what materials you need to move through it.",
"A tube is any hollow, open-ended cylinder-shaped object, it doesn't matter what it is being used for. A pipe is a kind of tube. It directs a continuous flow of some substance from one location to another and is usually rigid. A toilet paper roll isn't a pipe, because it doesn't transport anything. A subway tunnel isn't a pipe because while it does transport, it doesn't do so in a continuous flow.",
"A pipe is measured by its internal diameter. A tube is measured by its external diameter. So a 20mm pipe and a 20mm tube are not the same size.",
"I used to work in both a pipe factory and a tubing factory at different times, when I was a younger man. They made CLEAR distinctions, though I think it was out of hubris. The pipe factory was in Wisconsin, and they cast large diameter pipe from bronze and steel, as I recall. They had large cylindrical molds, with a gear ring about the middle. The whole thing was set in a machine by something that looked like a front loader with a big rod as the attachment on the front, and this was machine just a pair of roller wheels on either end. The middle set into a drive gear. The whole thing was spun like an axle. On one end, another big loader came by with a crucible of molten metal. While the mold was spinning, they poured it in, where it splayed out, cooled, and shrunk enough for the first loader to come and pull the pipe out. I worked next to the x-ray pit, which was long enough to hold a whole cast pipe. They checked it for cracks and faults. Workers would grind the ends and weld flanges. My job was to wrap the welds in thermal blankets and heat them to 1,750 F to temper them. The process took about 8 hours. We'd rig up a dozen pipes to two transformers wired in series, the transformers were each on their own 12' trailer. I've no idea how much power I was in charge of or how much danger I was in. I can't believe they hired me. I can't believe I took the job, but fuck the money was good for a kid and it's gotta beat hookin'. Pipe holds pressure. That's the big stink they made about it, what distinguished them from tubing. Now, my father works in steel. These days, it's steel stamping, though it used to be in the mills in Chicago, before they all shut down. So sheet steel I understand. The stuff comes in rolls, like tape. It'll be \\~3' wide and the roll will weigh between 1 to 4 tons, and be as thin as paper. As they unrolled it, they sliced it into several narrower rolls. These would be fed into the line, where it would be uncoiled, then gradually rolled into a continuous cylinder, welded along the seam, and then cut, all in a continuous process. When the cutter would come down, it would shake the floor. The whole factory was several football fields long. They would use this green coolant stuff that would flow like a fire hydrant out of the pipe as it went through this part of the process. The tubing would be covered in a caustic oil. The stuff would eat through anything not steel, eventually. It corroded my work boots eventually, they literally just crumbled to grime and grit after I stopped working there. I pressed one end of the tubing in a dye, a cylinder with a reduction. Hardened steel. I was weight lifting like an animal at the time but GOD DAMN were those things heavy. What this did was reduce the diameter of one end so they could thread a rod with a ball on the end through the tube, and then grab onto that and pull the tubing through a stretcher, which thinned out the tube and increased it's length. Let me tell you about the furnaces. They were a football field by themselves. They burned a special filtered natural gas. The VERY purple flames burned \"cold\", in that you could stick your hand in it and not be hurt, or you could throw greasy cardboard in it and it wouldn't catch. I don't understand what I saw, either, but that was part of the pre-heat. Inside the furnace was all ceramic lined, with little peep holes all along so you could see in. The ceramic was so hot inside it glowed almost white. I learned from my dad about molten steel, and knew well enough to not look directly into the furnace without eye protection, similar to welding goggles. We heat treated the tubing. That caustic oil would be cooked off, and you couldn't see one end of the factory from the other. And we breathed that shit in. We were saturated in it. I went to college afterward and got into software development, but I had to throw away all my clothes, everything stunk of that caustic oil shit. Tubing is structural, or doesn't hold pressure. We made tubing for dish washers, hospital beds, cars, god knows what else. Wire might be routed through it. You were \"educated\" (RE: chewed the fuck out) if you called any of their product \"pipe\". Are these definitions rigid? No! We use the words tubing and pipe interchangeably, so long as it's use is consistent."
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j2y52l | How do bicycle and motorcycle wire spoked wheels hold the weight of the bike, support the tension from the rotation, and ensure there is even force all around the wheel? | Engineering | explainlikeimfive | {
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"Well, the \"tension from the rotation\" isn't much. For the rest, steel is pretty strong stuff. The wheel hubs (and all the weight of the frame, rider, etc.) hang from the top of the rim via the top spokes. The horizontal spokes keep the wheel rim from collapsing. The bottom spokes are waiting their turn to be useful.",
"Any external force applied to the wheel is transferred to the hub via the wheel and spokes. Because there are numerous spokes laced between the wheel rim and hub, the load is shared by more than one spoke. As well, spokes opposite each other cooperate in a push-pull manner. At rest, the spokes above the part of the tire on the ground push up against the hub as much as the weight of the bike is pulling the bike towards the ground and applying force from the top down. In motion, centripetal force is trying to force the spokes outward against the rim...which is, itself, trying to expand against the spokes (pulling) and the tire (pushing). Force is “evened out” due to the application within a 360° contained arc. It can’t be applied too unevenly (assuming a decent balance). Because the focal point for all this inertia is pretty small (the hub) it takes a low-friction surface like a bearing to reduce the amount of energy that gets turned into heat from motion."
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j332qv | How are oil drilling platforms and wind turbines built in the ocean? How are they stable? | Engineering | explainlikeimfive | {
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"They stand on pretty solid legs that are buried into the seafloor. Water current is stronger than wind, but with thin but strong steel constructions thats not a much bigger issue than building a tall building on land. For bigger depths there are also concepts with floaters and ropes connected to anchors.",
"I don't know about wind turbines, but a lot of oil drilling platforms are built in shipyards and floated/towed to their locations. These kind are stable because they basically float on giant pontoons that can be filled with water to raise/lower/level the rig depending on the weather and what they're working on. They also have dynamic positioning systems that can hold them in a precise spot.",
"They aren't built in the ocean. Oil platforms are built on/near land and floated out to their destinations and then anchored to the sea floor. They're stable because of the anchoring and their massive size",
"Where the seabed is shallow, (im guessing 200-300ft) the bases are embedded in the sea floor. Where the floor is too deep, the base is mostly submerged and floating. The base is anchored in position by many anchors and long chains. The base and the platform are prefabricated on land and towed out to the site. Oil platforms usually have the base submerge under the transport ship and the structure is floated over, then bolted to the base. The water is then pumped out of the hollow legs, raising the platform to the required height. The above the waves portion of wind turbines are erected by cranes, just like on land. The difference being the cranes are floating. The cranes are held in position either by dropping long legs to the sea floor, or more commonly, by anchors and thrusters keeping them in position."
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j35c6t | What is the difference between octanes in petrol? Will 95 octane have a significant difference over the cheaper 93 octane? | Engineering | explainlikeimfive | {
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"Only if your car needs it. Higher octane gasoline can withstand the compression cycle without prematurely detonating. This is called spark knocking. You would be able to hear your car knocking. If you don’t hear it knocking, it isn’t. If your car isn’t knocking than higher octane gasoline is a complete waste of money. There are no other benefits. No increased fuel economy, no additives.",
"Octane is simply the anti knock rating. On a normal car, the difference is minimal, but in more compressive motors, such as high performance cars, they need higher octane to reduce the knock possibility and not destroy there engine. Any difference in a normal car doesn’t correlate with the knock itself, rather other additives put in the higher end fuel by the fuel maker. The best way to find out if your car needs it is in the owners manual",
"Weird coincidence, I read about this only yesterday! (must have been on Reddit, I don't read anything else these days....) The higher octane value means a fuel can be compressed more in an engine before it explodes spontaneously. That means it can be used in a more powerful engine and produce more power. If you use a lower octane fuel than the engine was designed for, the fuel can ignite before the piston is in the right place in its cycle (called \"pinking\" because of the noise it is said to make)."
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j35s8v | How do radio stations know how many listeners they currently have? | To my understanding the radios you find in cars or homes are only receivers and wouldn't be capable of sending a signal back to the transmission point. How does this work? | Engineering | explainlikeimfive | {
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"Already answered: Arbitron is the biggest ratings firm for radio. They have random people track their listening habits in booklets, record data from equipment they send to select families, and hold focus groups. They then use that sample data to try to create a statistically relevant guess based on the size of each market.",
"I don't think that they can, I think that's why they are always doing radio contests and giveaways. To determine how many new and unique calls they get. Just a guess though, I don't work in that industry.",
"Poling companies conduct surveys of radio listeners, where you self report what you listened to and when. I've done it once - it's just a diary you fill in over a short period. I think mine was a few weeks."
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j3ma5b | Why are shopping karts the shape that they are? Is there an optimal design that we just haven't embraced? | Engineering | explainlikeimfive | {
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"I think that the shape they are is the optimal design. They can pass one another in an average grocery aisle, they can nestle into each other for storage, they're cheap, what else could you want?",
"Think about what a shipping cart needs to do and imagine what shapes it might be. You need it to be stable and not tip over, but also be able to be pushed and steered. It also needs to nest so you can store a lot of them in a small space. There are limits to how long or how wide they can practically be. A square basket makes sense to maximize the amount of cargo space in a limited length and width. The depth is determined by how far the average person can reach, you don't want items on the bottom to be too difficult to retrieve. At this point most reasonable designs have the same basic shape, a square bin a distance off the ground with four wheels, the front two able to change angle. Making the area below the basket an accessible storage area supported on one side just makes sense. Finally you need to nest the carts, which means one of the sides needs to fold in. The most convenient way to push one cart into another is the front into the back, and hinging at the top means gravity will do all the work of keeping it closed when not nested. So the basic layout of a shopping cart is established by the requirements of the tool, and there don't seem to be any obvious other options.",
"It’s the culmination of a lot of factors, and quite optimized. They have to stack into each other, hold a lot of groceries at a comfortable height, use the minimum amount of material as possible, be cheaply made, stand up to being outside in rain, and be cheap enough that it’s not too bad if one goes missing or is damaged. The different sized carts cater to different store use cases."
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j3mucg | How do underground water lines stay hot, and do no freeze is places where its -40c. | Does our poop and hot waters keep it warm? Or is there a heating system down there? | Engineering | explainlikeimfive | {
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"In any cold-climate area, there's a certain depth in the ground which is the limit of 'frost penetration', below which it stays warmer than freezing all year. That's where the atmospheric chill from above, reaches equilibrium with the geothermal heat from below. You want to bury water lines below that depth."
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j3pfio | Why all racquet sports have oval racquets? Why not any other shape? | Engineering | explainlikeimfive | {
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"Modern tennis rackets have been quite a few different shapes over the years. And some of them have been quite close to round. But current tennis rackets have the more elongated shapes they do for a few reasons: Most rackets are made by just a few companies, and the brands tend to copy each other. Changing the most common shapes now would take a very clear indication that the new shape was way better and would provide more sales. Generally speaking, the longer the strings, the more responsive they will be. So racket designs try to put the longest strings where the player will want to hit the ball. Rackets designed to shift the sweet spot closer to the handle will be more egg shaped than oval, with the wide part near the throat. Those made to place the sweet spot closer to the tip will be more like an upside down egg shape. Since the main strings have more of an effect on power and performance than the cross strings, those are lengthened more, causing the racket to be elongated rather than round. This shape also allows more margin for error in terms of how close to the body the ball is hit, making the racket easier to use. And distance from the body is a bit harder to judge than height. Making a racket wider also makes it a bit less streamlined and aerodynamic. So oval rackets are larger than the equivalently wide round racket while compromising aerodynamics a little less. Psychologically, they also look and feel more streamlined. When a racket is swung, it actually isn’t just level, it rotates around a central point (the hand). When you diagram the swing path, you can see that the oval racket actually covers more area more efficiently than the round frame. The rules of tennis state that a racket’s “hitting surface cannot exceed 15 1/2 inches (39.37 cm) in length and 11 1/2 inches (29.21 cm) in width”. This means that the width is the limiting factor in terms of head size, and racquets can be longer than they are wide without breaking the rules. All that said, as rackets evolve, we may see that we find new reasons to change the shape of the head further, based on new learning and technology.",
"Ovals are an easy shape to make. So back when sports are being invented and played for fun they use simple tools (think of the vast majority of sports, they’re all a ball, some kind of goal/target, and maybe a stick. I don’t know the exact history of Racquet sports, but I would bet money that this is the answer. All you need to make an oval shaped racquet is a relatively bendy stick and some string/twine. Bend the stick so the ends come back together, in a roughly oval shape, tie them together, and then weave in your string or twine. This is way simpler than doing something with more pieces/hard angles like squares or triangles, in which you’d need to reinforce each corner."
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j43pzg | What’s the difference between an engine and a motor? | Engineering | explainlikeimfive | {
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"Mostly equiv nowadays but engine is supposed to use a fuel to translate to motion. Motor translates one type of energy to motion. Gasoline engine, steam engine. Electric motor, pneumatic/hydraulic motor.",
"Engine originally meant \"mechanical device\". Later the most popular type of engine was the \"steam engine\". The meaning of engine became more narrow to mean \"device that converts energy to mechanical power\". But we still use it more like it's original meaning \"graphics engine\" for example. Motor comes from Latin and means \"mover\". Meaning latter narrowed to \"machine that supplies motive power\". If it creates movement, it's a motor: \"Outboard motor, electric motor, etc.\" And it's usually assumed to be one contained unit. A \"steam motor\" is a small contained unit that burns coal and produces movement. A \"steam engine\" would be larger and integrated into whatever it is powering. The words are almost interchangeable, where all motors are engines, but not all engines are motors.",
"There's no real difference. They have different connotations but can be used interchangeably. Even MIT doesn't make a distinction: URL_0",
"The main difference is the power source. Generally speaking: A motor **receives** power from an external source. * an electric car has a **motor** because the source of power is from batteries. The power is stored in the batteries. An engine **produces** its own power. * a car that uses fuel has an **engine**. The fuel itself is not power; the engine has to convert the fuel into power through the combustion cycle.",
"An engine does work and a motor produces kinetic energy. Motors have to do with creating movement, so muscles are motors. Engines do things, so the CPU of a computer is an engine, even though it has no moving parts. In most common uses of the words, they are interchangeable though, as usually people use them to refer to a machine that produces motion."
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j4b2r7 | How do atm skimmers collect data? | Don’t they need power memory or etc?? | Engineering | explainlikeimfive | {
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"The amount of electrical power needed to read a magnetic stripe and store maybe at most a few kilobytes of data for a few hours/days isn't that great. If the skimmer is designed to fit over an existing reader, it may be possible to disguise a small batter and a few electronics in some fairly creative ways.",
"Many years ago I case a case with some skimmers. The skimmer itself went over the card reading entry to the vestibule where the atm was. Then, at the atm itself they had a small camera looking down on the keypad. They had a guy outside keeping track of who was matched to what. Then, with that data they punch out a duplicate card and go to town. Then they used the new cards on those smaller units that didn’t have their own cameras. They had a group guys doing it here, and a second group in Montreal. If they had just traded their fake cards, they never would have been convicted. Logistically those trials are complicated. Flying cops from Vancouver to Montreal, and witnesses from Zmobtreal to Vancouver..., We got him. He got deported to Romania."
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j4kd0l | Does a disconnected battery still drain? | I got a question regarding batteries. In winter when I don't ride my motorcycle, my battery drains bit by bit and if I don't charge it, it's dead after a few months. What happens if I disconnect it and take it out? Does the battery still drain, but less? Does it not drain at all? | Engineering | explainlikeimfive | {
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"A lead-acid battery will have a slow intrinsic self-discharge rate, even when it's not connected to anything. It happens because of the internal chemistry. So it has to be maintained with a proper charger, if it's left for many months. If the battery sits around with a partial discharge, the internal chemistry causes irreversible sulfation of the plates. That lowers the battery's capacity & max output current. Degraded plates can later lead to rapid self-discharge & even dead cells."
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j4kw9i | Why are graphic cards often manufactured by so many brands? Why does Nvidia not have one dedicated manufacturer? | Engineering | explainlikeimfive | {
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"Nvidia is fabless - this means they only do the design work and then order the GPU chips from a semiconductor *fab*rication plant. They then ship these, along with a basic card design (called the \"reference card\" that Nvidia also sells out of their own webstore) for the board designer companies to base their design off of. They then put those GPU chips onto various designs derived from the reference - such as blower cards, water cooled cards, cards that are shorter to fit into a small form factor case, etc. and lots of aesthethic designs. This way Nvidia doesn't have to cater to every buyer's wish by themselves.",
"Supply chain diversification. It prevents delays, failures, recalls, or other supply risks from causing catastrophe for the company"
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j4mvub | If trains take so long to stop, how do subway trains stop so quickly | I know subway trains probably weigh alot less than freight trains, but I'd imagine they are still super heavy so how do they manage to stop so quick? | Engineering | explainlikeimfive | {
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"I mean, it's an understatement to say they weigh a lot less than a freight train. A subway train car is SUBSTANTIALLY lighter than a freight train car, and the subway train is not nearly as long as a freight train normally is. A freight train can be 100+ cars, with each car weighing over 100 tons, compared to 30 or 40 tons for a subway car. A full freight train would be many multiple times heavier than a subway train.",
"A freight train weighs about 150 times more than a subway. Not 150%. 150x. It’s a massive difference in scale between the two."
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j4odl6 | Why most disposable things are made of looong lasting materials like plastic? | Engineering | explainlikeimfive | {
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"Plastic is typically pretty cheap to manufacture, is fairly resistant to heat, water, and most food-related compounds, and is fairly strong.",
"Well. Its more like most things are made of plastic in general. Plastic is cheap, can be injection molded or extruded to make complicated shapes or films easily, can be sterilized to be used with food, etc. Its just really really useful.",
"Disposable does not mean 'does not cause an impact'. It means, it is so cheap you won't mind tossing it and buying more. For better or worse, plastic is very inexpensive.",
"All in all 99% of the time it comes down to cheap and trying to spend as little money as possible",
"Cigarette butts last pretty much forever. Chewing gum is used by archeologists to date soils levels. During a dig, once they get past the lumps of chewing gum, they know they’ve hit the 1850’s. Glass is like Frodo’s ring, except it’s “Mt Doom” that created it is the inter-tidal action at the beach. Otherwise, we’re still digging up glass bottles since the shit was invented 2000 years ago. Ceramics. We’re still finding that shit from 30,000 years ago. Nuclear waste. That shit will still be killing nature long after humans are long gone",
"Plastics are a super-convenient material to manufacture with, and it's mostly a coincidence that they're also very resistant to biological decomposition."
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j4xqzg | How does water in the public water supply obtain enough pressure to move tens of km/miles and into the taps without losing any of the pressure? | Engineering | explainlikeimfive | {
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"Big pumps and large gravity-fed water towers. If you put a million tons of water high up, the pressure problems pretty much solve themselves with only the \"uphill\" bits needing specific pumping.",
"Water is hardly compressible, so no matter how much you have, and the distance it has to travel, the pressure is nearly uniform throughout the entire system. So all you have to do is create enough pressure somewhere in the system and it will remain pretty much constant from the nearest tap to the farthest tap. One way this is done is through water towers. Water towers are generally not a water storage instrument (not their main function anyway) - they exist to provide pressure from the downward force of gravity on the water perched high above ground. To pressurize the system, all one needs to do is pump water up into those towers, and then they'll help maintain constant pressure throughout the system. In certain water systems, there will also be pumping stations, or individual water towers on top of buildings to supplement pressure. Those mini towers work the same way as the larger towers, but their impacts are localized to the building they're sitting on top of.",
"Simple answer Water towers - by raising the water higher than the outlet pressure is created by using gravity. Also there are pressurized water tanks that can be used and pumps from treatment plants that can be used to maintain pressure.",
"To add to the other comments which mostly discuss how the water pressure is generated an maintained, I want to point out that there is some pressure loss over that distance when the water is flowing or when the water has to go uphill. My understanding is that the piping is designed to give a reasonable flow of water despite this pressure drop.",
"Simple hydraulics? Water doesn’t compress. Push here, it squeezes out there. This is the way.",
"By something known as head pressure. Picture putting a bucket of water on top of your house with a hose connected to it leading to ground level. If the hose is capped off and a pressure gauge is attached at the ground, due to the forces of gravity on the water, you will have pressure just due to the weight of water sitting on water. Beings how water is non compressible, the hose will have all the force of the water up in the bucket. For every foot above your gauge, you can plan on .43 PSI of pressure on the gauge. So assuming your bucket is 15 foot in the air, your gauge would read somewhere around 6.45PSI. In an ideal city, the water treatment plant (the place that prepares the water) would be located uphill of the town so that just gravity can do all the work. But in some cases, that’s not an option. So in typical mankind fashion, we worked around it by building water towers and holding tanks that are elevated. If said tank is built say, 200 foot in the air, you will then have about 86 PSI at ground level. While that is a bit too much for most houses, it does give you a bit of wiggle room. Large electric pumps are used to fill and keep full the water tank when needed but then afterwards, the gravity is used to push the water out for distributing to end users. This system is far more efficient than having a dedicated pump constantly running to keep pressure up. Source:I’m a dude that makes all of this happen and am responsible for keeping it running."
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j4yilw | Why do multiple screw heads exist? | Engineering | explainlikeimfive | {
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"Different heads are optimal for different purposes. Slot heads are the cheapest to manufacture. Robertson (tapered square drive) heads allow one handed loading of the fastener and high torque capability. Philips heads can prevent overtorquing because they cam out at high loads. Hex (Allen) heads offer the best torque capability to fastener weight ratio. Torx heads offer the best resistance to cam out, and so the highest torque capability.",
"I know that this isn't really the place for linking to videos, so I'll try and explain on my own first. Multiple standards is a common problem. Things develop independently, then those multiple forms come together. Then someone decides \"We have too many standards. I'll make a new *better* one.\" Now there is an *additional* standard. Same kind of thing with screws. Here's an XKCD about multiple standards: URL_1 And here's a Real Engineering video I saw the other day about screw heads: URL_0"
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j4zfpp | Is there a machine that can translate brain activity into pictures? | Engineering | explainlikeimfive | {
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"Technically it exists, but it’s not clear enough to really see what they are thinking. Basically they showed people basic shapes like squares and triangles while they are getting their brain scanned. They found that they can kinda predict what they are seeing, and recreating the image got a super blurry thing that kinda resembled the shape."
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j56xfo | How are train engines able to produce so much power and pull so much weight? | Engineering | explainlikeimfive | {
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"Pulling a train car is, in fact, relatively easy. A train car might weigh, say, 50 tons. The rolling coefficient of friction of steel on steel in a railway is about 0.001. This means that, to move a 50 ton car on flat ground, you only need 0.05 tons of force, which is 50 kilograms or 110 pounds. This is reasonably achievable by a single human. Hopefully, this shows that being able to move the cars is relatively easy. Easier than you'd expect, at least. For 100 cars, it would be more like 5 tons of force. That's really... Not a whole lot. Meanwhile, train engines are huge. A quick google indicates that a train engine may have around 10,000 horsepower. That's reasonable, given the huge size of the thing. I mean, the entire vehicle is just engine. 10,000 HP is 7,457 kilowatts. On flat ground, without air resistance, that could sustain our 100-car train at a speed of 152 m/s or 340 mph. On a slope, or including wind resistance, that reduces significantly, but is still plenty fast. The difficulty is speeding up and slowing down, as even though the engine is strong enough to move the train, it cannot produce enough power to *quickly* change the speed of the train.",
"Specifically because of the very low friction/resistance because of the steel wheels on steel rails. Steel on steel is very efficient in moving freight. The most power/costly part is starting to move, and stopping the train. Once it gets going, it tends to stay going due to the low resistance."
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j5cp0y | how does the sink/shower handle(s) adjust the water temperature? | Engineering | explainlikeimfive | {
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"Basically, it's a valve that lets in more or less cold or hot water from two pipes with 1) room temperature and 2) hot water from your water heater."
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j5ik7z | How does an architectural arch work? | Is it correct to say an arch provides better / stronger / more stable support than a flat beam? How does it do this? What about an arch vs a triangular structure? Thank you! | Engineering | explainlikeimfive | {
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"This video shows you an example. Watch when the truck drops the key stone, the one in the middle, and pulls away. The some settles into place and pushes the weight down. URL_0",
"It has to do with the materials used. Materials like concrete are strong under compression, but weak in tension, so the goal of an unreinforced concrete structure is to keep all of the concrete in compression. An arch does this, because at every part of the arch, the weight of the portion above it keeps the concrete in compression, and the top is under no stress at all. This doesn't make an arch \"better\" than other kinds of structures, it just has different applications. You couldn't make flat beams out of concrete, they'll crack and fail quickly, so we don't, we use other materials that have better tensile strength, like steel. Likewise, building a footbridge out of steel would be impractical and expensive."
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j5jtw3 | How do jet engines handle water in them (rain)? What happens to the water? Is there a point where there could be too much water? | Engineering | explainlikeimfive | {
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"I don't know all the specifics, but jet engines pretty much just eject the water out the back as if it were air ([here's an example]( URL_0 )). You could burn out a jet engine with water, but it takes a lot. The FAA requires jet engines to be able to ingest something like 4.5 tons (about 1200 gallons) of water per minute without affecting thrust. I'd wager most jet engines exceed that number (for overall safety purposes), so if you significantly exceed that value you could flood one enough to put out the flame.",
"Water is ingested into the engine and into the combustion chamber. There is is exposed to the high temperatures and pressures of combustion where most of it evaporates. However the energy is not lost as the evaporated water have a much higher volume creating additional pressure for the engine. So a jet engine can ingest a lot of water before it starts loosing performance. They are designed to handle more water then we have ever observed in any rain cloud no matter how extreme the weather is. There is however a point at which the water will cool down the flame enough that it losing performance. But at that point the engine ingest almost as much water as air.",
"The simple answer is the water just goes in. Most of the air that enters the fan of a jet engine goes through the bypass flow, and most of the rain will go with it, straight out the back to no effect. Some of the rain will enter the core engine where the compressor/combustor/turbine are. Rain droplets are big, so they will not be able to follow the curved flow path within the engine very well, most will end up on the hub, casing or hitting blades. If rain hits rotor blades most of it will be centrifuged to the casing. If water hits stator vanes, it will stream off the trailing edge and be re-entrained into the flow. In a compressor the temperature rises. The temperature in the HP parts of the compressor will be over 400 celsius, and any water that makes it that far will almost certainly evaporate or boil to steam. In very extreme conditions, heavy rain has in the past caused problems in the combustion system. This is not normal for modern engines, though. As part of the type-approval for new engine designs, there is a rain ingestion test, where water sprays are mounted at the engine inlet and an enormous volume of water is sprayed directly into the engine intake, far more water than is likely to be possible by any actual weather phenomenon. The engine has to pass the test by basically being unaffected by it. [Here]( URL_0 ) is a video of such a test taking place.",
"Most jet engines use centrifugal force to channel water and other heavier things that might go into an engine around the actual power generating part of the engine. You can see just how much water this system can handle looking up jet engine water tests. What water remains is harmless and may even increase thrust. In piston engines stalling is the biggest concern due to water being much more difficult to compress. This usually results in a lot of broken parts depending on your speed. In a jet engine what's more likely to happen before the compressor gets overloaded with water is a flameout(engine isn't broken but fuel has stopped burning) If the issue that caused the flameout can be fixed, the engine can usually be restarted but that takes precious time.",
"Yes, there is a point where it's too much. A Boeing USAF C-17 experienced a 4-engine flameout due to water ingestion over Pakistan on 17 Sept 2010 (Combat camera was onboard and had a video camera running and it was found that the reported lightning was not the reason.)"
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j5juoj | how air or water are used to cool buildings throughout the summer | Engineering | explainlikeimfive | {
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"Heat always wants to balance itself- if you touch a hot thing to a cold thing, heat will transfer until they're approximately an equal temperature between the two. If you have hot air inside a building, you can circulate air inside that will slightly cool the environment as it pulls heat from the surroundings. But that heat isn't actually going anywhere so the effect is limited. Of course, we can do this more efficiently with water- which holds a lot of heat energy and pulls it very rapidly from whatever it touches. (which is why cold water kills so quickly). By running that warm air through a heat exchanger, we can transfer that heat in the air to the water in the exchanger, and then send it outside to be vented to the environment and send the cooled air back inside. This is the basis of modern air conditioning."
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j5mml3 | Why do cars get better miles per gallon when doing long distance/motorway driving at high speed compared to when doing city/short city driving at low speed? | So I'll get around 85-90 miles per gallon when I do cross country drives but only 25-40 miles per gallon when I use my car to commute | Engineering | explainlikeimfive | {
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"So when you drive, look at the tachometer. When you're on the highway, the car is in a higher gear and the RPMs are lower. This is an indication of how hard your engine is working. When you are driving in the city, you are having to accelerate and brake a lot. That's momentum that you are having to just give up when you brake, and the engine needs to work hard to get you back up to that speed when the light turns green. However, once you have reached a speed, the car can maintain it with relatively lower energy cost. So, your car will work far more efficiently at higher speeds where it doesn't have to stop and accelerate as often.",
"Think about it this way: when you slow down or come to a stop, the energy of your car moving forward has to be entirely converted to other forms of energy, most of it being heat discharged by the brakes. That energy is now gone, and to get moving again you have to burn fuel.",
"Because of gears. The higher gears require way less power to move you forward, but the downside is that theyre weaker. Its the same system on a bicycle. The first one is very easy and makes you start fast, but requires more strength to power (fuel) and it only takes so far until your legs cant keep up anymore (engine rpm). The 2nd gear requires less strength to operate since for example one spin of the pedals doesnt spin the wheel once, but two times now. The big difference that a bike is very simple and light and the car engine moves up to many tons by combustion. Driving on max rpm in 1st gear, will burn your fuel incredibly fast, while driving only in the 6th gear wont even make your car go. Try to push something heavy on wheels. Its really hard to move it in first place but once it starts rolling it requires almost no effort at all."
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j5uipt | What is the closest thing we have to a 100% efficiency machine? | Apologies if this doesn't fit in the sub, first post I know that machines can't have 100% efficiency, but what is exactly do we have that actually comes very close to a perfect machine? | Engineering | explainlikeimfive | {
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"The highest efficiency machine we can produce is one that produces heat, so, a space heater. Those actually are 100% efficient at their goal, because even the energy turned into other forms like sound, eventually make their way to random molecular motion, aka, heat. As for heat engines, where we want to make motion. The efficiency of those machines is capped by the Carnot cycle. The Carnot cycle efficiency is determined by the temperature difference between the hot side, and the cold side, so theoretically, you can make it arbitrarily high, but in practice, we don't get quite that high (~60%).",
"Not sure if it is the correct type of machine you are looking for. But a bicycle has a reputed 98.1% efficient transfer of energy applied to turning the pedals in to forward movement."
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j5x99u | How were open wells built back in the day? | I’ve got a 32’ deep, 6’ wide well I’m told is an artesian well under my office floor. It’s kinda low right now so my kids dad climbed down to take a closer look today and it made me wonder how did they install it? It’s cinder blocks with a spiral of stairs to some concrete thing and then other stuff deeper. How did they keep the hole dry to get all that work done? My water table is so high it’s only down ten feet by this time of the year and overflows in the winter. [well ]( URL_0 ) water is actually seeping in from above the waterline. The water table is so high I doubt that hole was ever empty or low enough to do the work without some cool engineering feats. My home is in Northern California and the well is older than my 80 year old home obviously. | Engineering | explainlikeimfive | {
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"Wells don't fill instantly, the water seeps in slowly. So basically they just dig down till the water flows in faster than they can bucket it out and then build up the brick walls from there."
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j69s2f | Why do guitars have tuned much more often than pianos? | Engineering | explainlikeimfive | {
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"text": [
"A piano's strings are held on an iron harp while wood holds guitar strings. Wood tends to move a lot more than iron."
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j6itl2 | Why is concrete so loud? | ELI5 Why is driving on the concrete parts of the highway so much louder than the blacktop parts? It is night and day different. All of a sudden you'll switch from concrete to blacktop and realize how LOUD concrete roadways are. | Engineering | explainlikeimfive | {
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"The groves is concrete also serve a as what is called control joints. Concrete does not give. It will crack. A control joint is a way to try and have a crack follow that line not a random one it chooses. These cracks do not take away from the strength of the concrete. Blacktop gives a little. It does not need control joints because it does not crack to the same extent as concrete."
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j6j5sp | Why do turbos need time to “spool up” before they can have a significant power boost? | Engineering | explainlikeimfive | {
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"text": [
"A turbo is driven by the exhaust gas. At idle the exhaust gas Is comparatively low pressure. As the rpm increases the pressure and flow of exhaust increases. This spins the turbo which spins the intake side. Increasing boost."
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j6mr9n | how did ancient sculptors achieve such flawless and smoothed marble sculptures? | (I.e. : sculptors like Bernini and Michelangelo) | Engineering | explainlikeimfive | {
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"Firstly, these sculptors were not ancient, they were working only a few hundred years ago. They had access to surprisingly advanced machinery (think Da Vinci). That said, they spent a lot of time smoothing and polishing. Modern technology lets us do the same thing faster, but the underlying principle is the same: if you repeatedly remove any high points then eventually you end up with a smooth surface.",
"* Flaired as engineering for lack of ‘art’ flair",
"Files, pumice stone powder, hay, depends on what stone they are carving and what texture they require."
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j6o3np | Car brake stops working when the engine is turned off | Why does the brake stop working if the engine is turned off while running (which may happen if the car is in a wrong gear in manual transmission). How is this feature helpful, Isn't it more dangerous? | Engineering | explainlikeimfive | {
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"Modern cars typically use hydraulic brakes assisted with engine power: they will usually function without engine power, but will require significantly more force to activate. There's also often a parking brake that actuates the rear brakes with a cable, completely independently of the hydraulics. However since this usually only uses the rear brakes and bypasses ABS protections, it may be possible to accidentally lock up those wheels.",
"Many brake systems are vacuumed assisted. This provides more power to the hydraulics and the brake pads then what’s required at the pedal. When the engine is off the vacuum drops and the brakes fade. They don’t stop working completely but you need a lot more pressure on the pedal to get the same force on the pads.",
"It doesn’t stop working, it still works, but it’s a lot harder to press, this is because we use a system called a vacuum brake booster to reduce the force you need to apply to the brake pedal, which is incredibly helpful, but without the engine running there is no vacuum and so no brake boost"
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j6shj8 | How did large sailing ships long ago get moving out of the dock? | I doubt they could just let down the sail at the dock and get going, they didn't have motors and it would appear they are too high or too large to use something like a paddle. | Engineering | explainlikeimfive | {
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"Depending on the port, raising some of the sails may be a viable way to get out of dock. Generally they would raise one of the triangular sails which can work a much larger angle off the wind. Another option is called [warping or kedging]( URL_0 ) and involves dropping a small anchor and pulling the ship to that. They could put it on a small boat and have them paddle it out ahead so that the ship could pull it in and thus pull itself along. While this seems slow, remember that most ships of this era were rather slow even under full sail with good wind. The HMS Victory had a top speed of 11 knots and the Mayflower would do 4 knots. Raising full sails while in a harbor wasn't done often because harbors are inherently low wind places but could have pockets of high wind. Raising topsails that catch the occasional strong gust could cause a ship to tip dangerously far over as the [Vasa]( URL_1 ) learned the hard way",
"They did raise their sails and sail away from the dock. They could not do it when the wind was against them. And they could not sail away from shore while the tide was coming in. Sailing ships were very dependent on the weather and tides. They could not just depart whenever they wanted. Nor could they sail in whatever direction they wanted.",
"Ships would be warped along a quay or across a dock to put them into a position from which they could sail. Then they would sail. Warping a boat basically means pulling it around with ropes. As an example of the issues faced by sailing ships, in 1938 Moshulu departed Belfast bound for Australia. She tried to beat down the Irish sea against the wind, but was unable to do so as the sea was too narrow. So after several days of trying this she turned around and sailed North around Ireland and into the Atlantic where she had enough space to make way to windward.",
"In many harbors, sailing vessels wouldn't dock, but would anchor offshore and be unloaded by smaller boats. In addition to the various methods mentioned by other commenters, one of the early applications of steam was for precisely this problem. Some of the earliest steam vessels were actually tugboats, whose job was to tow sailing vessels in harbors and coastal waters. The first steam-powered paddle tugboat entered service in 1801, and steam tugs were in use for most of the 19th century. By comparison, the first seagoing steamships date to the 1820s and 1830s, and steam didn't start to really replace sail for a number of years after that.",
"Have you ever heard the phrase “we sail with the tide”. ? A lot of ports, such as London and New York are on tidal rivers. If you release the ropes at high tide you can float gently away from the dock on slack water, but then get carried out to sea on several knots of current from the falling tide. You only need sails to adjust course enough to avoid other ships."
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j6zey0 | Why are Allen Wrench (Hex wrenches) made so different that traditional screw drivers with normal handles? | Engineering | explainlikeimfive | {
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"A big reason is how they are made. A standard screw driver has a forged tip. You take a round rod head it up to red hot and mash it into the shape you desire. This leaves you with a rod with a tip on it but you can't get much leverage on a narrow round rod so a handle is added. Hex keys are either milled or more often extruded into shape. Since they are hex shaped and not round all the way through you can get a decent grip on them, add a 90 degree bend on one end and you can get even more leverage and have the choice of high torque or low torque. What people think of as typical screw head designs also have an issue that internal and external hex head fasteners don't have - the driver will pop out of the fastener unless downward pressure is applied. You need the big handle on a screw driver to keep the driver in the screw. With an allen head screw you don't need to put any downward pressure at all, you just need to apply torque. This is also why you don't see Philips or flat head screws used in applications where there is a need to torque the fasteners down to prevent backing out. You just can't get much torque onto a Philips or flat head screw. An Allen head screw will stay seated on the driver until there is a material failure. As said elsewhere you can get Allen head screw drivers but they're not popular because there just isn't much need for them. Either it's a low torque application where an Allen key is sufficient or torque matters and something like a socket wrench is better suited.",
"As others have said, you can buy hex keys in screwdriver form. But, I, for one, enjoy the L shape of the traditional hex key. It gives you \"low torque\" and \"high torque\" options, depending on which end of the L you use. That comes in handy. And I'm sure they're cheaper to manufacture that way, as opposed to molding a handle on one end.",
"Think backwards, the screw or bolt that is driven by a hex key is usually what’s called a ‘machine screw’ which means it is blunt ended, normally to fasten metal parts together instead of a self-tapping screw (pointy end) that are usually used to fasten into a material like wood or plastic. Because of their more industrial application, torque (the amount of twisting force, measured in pound-feet/inch, Newton meters, or kilogram meter squared) is more of a principle feature. A Phillips or slotted head commonly found on self-tapping screws are designed to ‘cam out’, where the screwdriver head slips out at high torque. Initially square drive was used to get around this, but the industry went with hex or Allen heads. Trying to apply 50Nm of torque through a screwdriver in a Phillips self-tapping screw is unlikely to happen, but there are many industrial instances where that level of torque, or even more, is required. How does this relate to the tool itself? Well the need for torque means leverage is more important, having a longer lever makes for more and easier torque. The long side of the L is there to apply either more, or more accurate, torque to the fastener. Having the smaller part of the L means that you can be closer to the head of the fastener and have less chance of rounding it, and works well for confined or harder to reach areas. The industrial environment normally equates to high usage, so the tool will inevitably wear more meaning it will need to be replaced frequently and therefore cost and ease of manufacturing needs to be low. In their basic form, standard hex keys are made from long steel rods formed in a hexagonal shape at different sizes, these are then pushed through a machine at matching size that cuts them at the right length, then they’re heated at one spot and bent, so the manufacturing process is incredibly cheap and easy. This being a key factor for the growth of hex keys during WWII when they became more common and less specialist. You just need to cut and bend metal and you’ve got a tool with built in handle, no need to waste precious materials on plastic handles and such. There are, of course, many different forms of hex keys available, from standard L, S-shaped, ball-end, short-arm, hex-plus, T-handle (and sliding version), P-handle, screwdriver style, folding sets, and more. Personally, I wish Torx was more standard than Hex, but that’s another kettle of fish.",
"For leverage. The Lshape gives added leverage in some tight spaces to break the screws torque.",
"Another reason is storage, most of the time they are for small or specialty jobs that may require a few different sizes of key. So being able to take 10 different size tools in your pocket is a big plus",
"You can find them in the shape of regular screwdrivers too. You like to search for \"Allen screwdriver\" or \"Hex Screwdriver\". Allen key is a trademark by a single company the generic name is a hex key. Amazon for example has lots of them You can also find them as bits that can be very practice but can be problematic if the increased screwdriver diameter does not fit in a hole that the screw is located in The L shaped is common because you can make them from six-sided bar stock of the right size that you just cut and bend. You then get a tool with long is that can be useful to have high torque but more problematic to turn a lot of times. So if it is provided as a tool for putting something together they will provide the cheapest variant that exists and can do the job. For other common types of screws that L shape is problematic because it is not stuck in the hole as hex is. But you can find the same design for Torx and other similar with a deep hole that has the same shape all the way down so you do not need to press down to tuen it.",
"In addition to the points already made, Philips and flat screwdrivers are traditionally straight to allow you to bear down on the screw to prevent cam-out. The geometry of the hex head helps secure the wrench to the screw while turning, reducing cam-out which allows a greater range of cheap, viable form factors depending on torque and/or reach requirements"
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j72yoi | How do our phones charge? Do the cords transfer new, highly energized electrons to the battery or something? | Engineering | explainlikeimfive | {
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"No, so a lithium ion battery takes chemical energy, and turns it into electricity through a chemical reaction in the battery. This is how your phone powers itself. This process is reversible though. If you input electrical energy into the battery, it reverses the chemical reaction, turning the chemicals back to the form they had before you used your phone. The reversibility of the reaction is what makes your phone rechargable, while common AA batteries are not. Those use different reactions, that are not as reversible."
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j7c9cd | Why is it bad to use a copper slug (or put a penny in it) to a fuse box? | Engineering | explainlikeimfive | {
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"The purpose of a fuse is to cut the supply of electricity to things in the case of a short circuit in order to prevent a fire. If there's no fuse and there's a short somewhere it will start a fire.",
"The point of a fuse is to cut the circuit under overload or short-circuit conditions, in order to avoid damage or fire. A penny is just going to keep the current flowing, and you'll have damage, or fire.",
"The fuse has a carefully designed wire in it that will blow out if you try to draw too much current from it. Its whole purpose is to protect devices and wiring from dangerous overcurrent events that can start fires. If you replace the fuse with a penny you have no protection anymore. Everything downstream can pull as much current as it wants so when something goes wrong in a device and it starts dumping 100 A and heating up extremely fast, nothing will stop that event except the main breaker. Don't bypass safety devices, they're there for a reason",
"To state what others have said in a slightly different way, fuses are designed to be the ***first*** part of the circuit to fail if there is too much current, and to fail ***safely***. If the fuse does not fail as intended (usually because it is bypassed) some other part of the circuit (like the wires in your wall, or the outlet) is liable to fail, and they will ***not*** fail safely.",
"If you're talking about substituting a penny for a fuse, it's because you're essentially removing any overcurrent protection from that circuit. If something downstream short circuits and begins to draw excessive amperage, then the fuse in that fusebox will melt and break the circuit, preventing a fire or damage to the rest of the circuit. By using a conductive metal instead of a fuse, you're just making a circuit that can't break itself if there's a dangerous overcurrent."
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j7cifj | How do aeroplanes fly when they are so heavy? | Engineering | explainlikeimfive | {
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"There are a number of forces at play when it comes to flight. First, of course, is gravity. a plane is very heavy and so you need to consider the force of gravity in regard to every other calculation here. Second, is drag. Like gravity, it is a negative force when it comes to flight. As the plane moves through the air, the air itself pushes on the plane, slowing the plane down a bit. Third is thrust. Thrust is the forward pushing power of the plane, given by the engines. More thrust means more forward speed, counteracting drag. Fourth and final is lift. Lift is the upward force that counteracts gravity and keeps the plane up. Lift is generated as the plane moves forward and air passes over and under the wings. As the speed increases the wings direct the air in a way that pushes the plane upward. The bigger the plane, the more lift is needed, and that can happen with a) more wings, b) bigger wings, or c) more speed. This is why cargo and transport planes tend to have enormous wingspans, because they can't thrust hard enough for more speed (the larger size means more drag), they need larger wings to generate the lift they need. Obviously, this is all pretty technical, so the best suggestion I can make is to try it out yourself... on a flight simulator.",
"Airplanes fly because of lift. The wings of an aircraft are shaped so that they generate lifting force as air passes over them. In order to get that air moving, they need thrust from one or more engines pushing them forward with enough power to overcome the aerodynamic drag holding them back. A heavy plane needs a lot of thrust to generate enough lift to overcome the force of gravity holding them down and the force of drag pulling them back. An aircraft flies when all these forces are equal.",
"Next time you're in a car moving fast, open the window and stick your hand out a little. If you hold your hand flat horizontally, you won't feel anything except the drag force pushing it backwards. Now, tip your hand a few degrees so that the front edge is up and the back is down. You'll feel a strong force pushing your hand upwards! As the airstream hits your hand, some of it bounces off and is forced down by the angle of the bottom of your hand. Its basically acting as a \"scoop\" to redirect air down. Because you're forcing the air down, the air exerts a force in the opposite direction: up! This is exactly how plane wings work, they force air downwards to generate lift. You can see this if you're able to watch the wings of a plane during takeoff. As the plane first lifts off you can watch the wingtips flex upwards a few inches as the wings take the weight of the plane, now that the wheels are off the ground."
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j7fv9t | what are the advantages and disadvantages of the multi-sail masts of the ocean ships during the age of sail vs the one sail masts of the Mediterranean ships? | Engineering | explainlikeimfive | {
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"more masts = more space to hang sails. Also, the larger the sail, the more stress on the mast. So if you're concerned about snapping the mast with a single ridiculously large sail, you'd do better with 2 masts. And Mediterranean ships had multiple masts too. It comes down to what sail plan you wanted; each sail plan has its own advantages and disadvantages. URL_0",
"Multi-mast = can carry more canvas (sail area) without the mast getting ludicrously tall and bendy. This is good when you need speed, or need to operate in light air. But it's complicated, expensive, and takes a lot of people to operate. For combat, it also offers \"engine\" redundancy to some degree. Single-mast = much simpler rigging, easier to build, cheaper, can be operated by a very small crew. If you don't have to go very far, or can mostly rely on good winds (i.e. the Mediterranean), or can put out a bunch of smaller boats instead of one big one, this is a much more cost-effective option."
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j7ogtp | - Why banjos sound so different from other kinds of "guitar". Their notes appear to have a decay little out of tune? Why is that? | Engineering | explainlikeimfive | {
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"They sound different because the strings are suspended over a drum vs over wood with an open sound whole. Banjos are often played with metal finger picks giving them a sharp attack. Banjos are a lot louder than guitars size for size most of the time as well. As to the out of tune-ness I think it depends on your ear, the quality of the instrument, the setup, and the player. I don’t hear it, personally.",
"The below is in regard to acoustic instruments. The bridge (part the strings go over near the strumming hand) sits on a membrane (sound board) that's essentially a drum head. The body is also usually metal. Most banjo strings are single strings. Compared to a guitar where the body is usually wooden and the bridge sits on a wooden sound board. Metal strings are most often a single string with another wound around them. The playing styles are also different. Guitars are usually strummed or picked with a single flat pick (let's ignore classical fingerstyle for now) and banjos are usually picked with 3 or more individual finger picks. All of these affect the sound of the instrument. In addition the banjo is tuned higher than a guitar usually is and has one string that's significantly shorter than the others (5 frets IIRC)",
"Like many drums, the head can be tuned to a particular pitch. If it's tuned to something that is harmonically out of step with the tuning of the strings, it will affect the pitch. Many bluegrass players swear by tuning the head to G#, while the most typical keys for playing stringband music are G, D, and A. Also, the strings rest on the bridge, which rests directly on the head, so you get sympathetic ringing on open strings when you play a note. Same is true for other string instruments, but since the head is more flexible than a soundboard, and the strings are lower tension, it's a stronger effect. And yeah, especially with metal picks, the attack will be a bit sharper than the decay."
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j7x4iy | What are the different types of bridges, and how do they function? | Engineering | explainlikeimfive | {
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"The choice of bridge type is partly the span and partly an architectural choice. Suspension bridge: You have a giant tower at each end and an enormous cable suspended between them. The giant cable carries a lot of smaller cables that hang vertically to carry the deck. The towers are tied back at each side to balance the forces from the curved cable between them. The cables are all in tension, the towers at each end are in compression. Forces in the deck are relatively low. This is the “maximum span” bridge option. See the Golden Gate Bridge for an example. Cable Stayed Bridge. Similar to a suspension bridge but instead of a single big cable between the towers the cables all fan out from each tower in a triangular shape. Cables in tension, towers in compression. Deck is complex as the cables put a lot of compression into it, trying to pull the deck to the towers. Spans are a little less than suspension bridge, but you don’t need the “tie back” cables, can use only a single tower if spans permit, and gives a different architectural appearance. When used for very long spans you can use multiple towers, each with a fan of cables. After suspension bridge this is probably the next longest span. See Viaduct dr Millau for one of the more impressive examples. Arch bridge: The opposite of a suspension bridge. The arch is all in compression. The arch can be either entirely above or below the deck, of cross over it. When it’s above the deck the deck is suspended by vertical cables. Unlike a suspension bridge you don’t need cables tying each end back. This is probably the third longest spanning form, albeit les efficient than either of the above two, but also used a lot in older small stone bridges. See the Sydney Harbor Bridge for an example of a new one, see the Roman Viaducts for an example of an old one. The above three examples all need significant height for the long spans Draw Bridge: Typically bridges over rivers where large ships need to pass under but they don’t want to build the deck high enough for various reasons. Typically the bridge sections are giant beams of some sort (steel or concrete) between a series of towers. One section will have a mechanism to lift up in some manner. Beam Bridges: You have a beam system (steel, concrete) that spans between as many piers as you need to cross a given span. Technically one of the less complicated bridge types, economical when used for appropriate spans, suitable for a range of spans from very small bridges a few feet across up to larger bridges a few hundred feet In length). For appropriate spans these give a relatively flat profile - see almost any bridge over a highway for examples. Truss Bridges: similar to a beam bridge, often used at the longer end of the span range. A truss is constructed each side of the bridge (Looking along the bridge, not at each end), or possibly a series of trusses underneath. Generally the truss form allows a more economical use of material than a beam bridge for the longer spans and a larger depth due to challenges in transporting very deep beams. Can span somewhat further than beam bridges. Choice of this vs a beam bridge is either architectural (they’re more expensive) or driven by spans that are outside the reasonable range for a beam bridge."
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j8295d | how does a synchronizer in a manual gearbox work? | Engineering | explainlikeimfive | {
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"In order to engage a gear, you need the input shaft to be spinning at the right speed for that gear - otherwise the teeth won't catch and you'll just grind the gear. In very old vehicles, you had to double clutch. You'd press the clutch and put the transmission in neutral. Then you'd press the gas pedal to speed the engine up until it was at the right speed for a lower gear, and then you'd press the clutch again and shift into the lower gear. Nowadays you can single clutch because your forward gears have synchronizer rings on them. The synchronizer ring puts friction on the input shaft, speeding it up or slowing it down so that it's at the right speed for the gear. Your car basically does this instantaneously, so you only have to clutch once to shift gears."
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j8vre7 | Master/Skeleton Keys - how are they made and how are they able to open any door in the house/building? | I’ve always wondered this. If every lock in the building is different, how is the master/ skeleton key made to be able to open all of the doors? | Engineering | explainlikeimfive | {
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"Without getting too into how locks are made; most locks are made with 1-5 pins. If your key matches each pin, it opens the lock. You can then make a skeleton key that exactly matches a specific combo, lets say 1,2,3,4,5, with a gradient upward to 2,3,4,5,5 or even 3,4,5,5,5. This gives you dozens of possible combinations between 1,2,3,4,5 and 3,4,5,5,5, plenty enough for your very precise skeleton key to open every door in the building. Your key is shaped in such a way that it precisely matches 1,2,3,4,5, but has a gradient upward to fill in spaces between 1,2,3,4,5 and 3,4,5,5,5, and it works about the same way as picking a lock. Skeleton keys aren't very popular anymore because we can make locks much more precisely and gradients don't work anymore (generally speaking). Edit: The gradient upward from 1 to 2, 2 to 3, etc allows you to \"match\" the lock position \"well enough\" to convince the lock you have the right key. You have a very thick \"1\" position and a thinner \"2\" position, so the lock doesn't even register that you have a \"1\" and instead just takes your \"2\". Again, this only works on locks that are very weak and not precisely machined."
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j8xh8u | How does a (MOS)FET differ from a BJT and How is it capable of fast switching? | Okay so i have two questions. Firstly, I know that FETs have G,D,S pins while BJTs have B,E,C pins. I also understand that you can use a BJT like a relay by feeding current to the B pin. My question is: can you use a FET exactly how you would use a BJT with different pin names? Secondly, let's say that I have an arduino that has an analog pin capable of giving 1000 pulses of current each second(I am not aware of the actual specs). In most LED strip arduino projects, the circuits have a MOSFET in them because it "can switch on and off more quickly". My question is: wouldn't the MOSFET's higher switch capability per second be bottlenecked by the arduino pin's switch capability per second? I know that I am triggering some engineering majors by making up strange words to compensate for aleady existing terms(ie switch per second). Sorry for that and I would deeply appriciate any tips on what they're actually called. | Engineering | explainlikeimfive | {
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"BJTs and MOSFETs are both transistors, but they are constructed differently and work a bit differently. Probably the main difference is that a BJT is current controlled, the MOSFET is voltage controlled. A BJT is turned on/off due to the Base current. A MOSFET turns on/off due to the Gate voltage. You can't generally just swap one for the other and expect things to work right. MOSFETs are not intrinsically *faster* than BJTs. But since BJTs are current controlled, it can require a bit more power to make them switch. I suspect (but do not actually know) that the Arduino's driver circuits might simply be a type that is better at driving MOSFETs than BJTs. Current drivers and voltages drivers aren't the same, although you can often make one into the other with a bit of additional circuitry. Some driver outputs can do either if correctly programmed. Of course switching speed is always going to be limited by the slowest thing, whatever that is. And \"switch per second\" is perfectly acceptable. Any electrical engineer who doesn't understand that should go back to school.",
"While a BJT can be used as a switch, you wouldn't want to in this application. This is not because of switching frequency, but because BJTs require a current load to push the BJT into saturation, closing the switch, whereas a MOSFET needs a gate voltage potential and no current. Devices like arduinos and raspberry pis are notoriously sensitive to supplying output current loads, and designing solid state switches to operate on switched voltage instead of current is safer."
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j92grc | How are Nokia 3310’s built? Why are they so durable and long lasting? | Engineering | explainlikeimfive | {
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"A Nokia 3310 is quite thick compared to a modern smartphone and is at the same time shorter and narrower that results in a that is harder to physically bend it. It has a cover by thick plastic on all sides and it can be removed and you have a nine plastic shell. The outer shell ben and often detach if you drop it and that absorbs lof energy. There is not exposed to a critical part. The screen is small and is quite far behind a plastic window. The keys plastic and ten a membrane that can bend so not a mechanical switch. The screen is an important factor as it is quite small and can survive a lot hight forces then the larger screen on a phone today. It is not a touch screen so it can do not need to be exposed to the outside but has a plastic cover and an air gap. This is a key part of why it is very hard to destroy, small screen and an air gap The electronic in it is nothing special just wells designed and made phone of it era. There are not as complex chips with so fewer solder points and a bit larger component so they are physically better attached to the circuit board. You today get a phone to have a similar physical strength just look at a tough case that makes it bigger but a lot stronger. The screen is still a weak point"
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j97n3i | How does a vehicle slow down without applying the brakes when you reduce the cruise control speed? | Engineering | explainlikeimfive | {
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"Take your foot off of the gas pedal and watch what happens. That should explain it like your 5.",
"By letting off the gas and lowering the gear. This is what you do in a standard instead as well. It is called engine braking i believe.",
"It's as simple as your ECU (engine control unit) communicating with your TCU (transmission control unit) and they both start to spin at a lower RPM, resulting and slowing down your car.",
"A car will slow down if the engine is not producing more forward forces than the opposing forces such as friction of the road against the tyres, internal friction within the power train (engine/clutch etc) and the air/wind against the outside of the car. This is commonly known as ‘engine braking’. If you are cruising with the CC set at 60mph, then set it to 50, the CC just lets off the accelerator for a while allowing the car to slow down using friction until the speed gets close to 50. It won’t generally use the brakes to do this. Auto-drive is a very different thing."
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j9dtl5 | Why are brakes in a new car so touchy but in a used car they're never like that again? Even after a full brake job. | Engineering | explainlikeimfive | {
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"If the \"full brake job\" replaces the rotors, the pads, and the fluid with the same components as the factory used; then you should get the same performance you had at the factory. Of course your car will still be older, with more suspension play, softer shock absorbers, worn springs and mounts; which all contribute to brake feel.",
"If the braking system is in good condition, the brakes will be just as touchy as they were on the day the car first left the factory. It's possible that what you're seeing are actually differences in the design of new and older cars."
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j9f485 | How does recycling work? What do the different plastic recycling numbers mean? Can you put soda cans holding liquid in the recycling bin? | Engineering | explainlikeimfive | {
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"**No Post-Consumer Plastics are Recyclable in practice.** In theory, they can be shreaded and turned into fill fibers. However, the worldwide demand for this kind of plastic bottle recycling can be one with one plant in a small city. All those plastic bottles you throw in the recycle bin end up in a landfill, often a foreign landfill where many of them wash into the ocean. 100% of the plastic in the bottles you buy is virgin plastic, it's a blow-molding industry requirement. If you want recyclable bottles, buy glass, or aluminum. These are recyclable materials. The Aluminum in the cans is headed to a furnace where it's hot enough to melt aluminum, and no drinkable liquid will survive that. The recycling company would rather you emptied them, so they would weigh less and consume less fuel in the truck on their way to the recycling plant. Please be green and save the planet with aluminum.",
"Most plastic is washed because its melting temperature is lower than the gunk on them. Aluminum, however, is much easier prosess. Its melting point is 1,221°f (660°c). The liquid will evaporate and the residue will be burned to ash, smoke and slag (the non-aluminum that floats to the top.) Then the pure aluminum is poured into ingots and shipped out. There is more to a can than the metal and the drink. There's chemical coating, labeling, and a rubber gasket. All of that sorts itself out. Source: I own a backyard aluminium forge.",
"The numbers tell you what kind of plastic it is! Different plastics have different properties. Here's the well known ones: **1 polyethylene terephthalate (PET/PETE)** single-use bottled beverages **2 high density polyethylene (HDPE)** this one is all over your house, almost all non-transparent jug or bottle is made with HDPE **3 polyvinyl chloride / vinyl (PVC/V)** You have pipes in your house made with PVC.. and probably vinyl in several forms. **4 low density polyethylene (LDPE)** you encounter this one a lot too. Trash bags and grocery are made from this kind. **5 polypropylene (PP)** ~~not used too much in home plastics.~~ It's got a high melting point though, which means it can hold hot substances, which is it's main use. **6 polystyrene (PS) (aka Styrofoam!)** Take out containers and disposable plates/cups/bowls! **7 Miscellaneous** There's a lot of plastics out there, we'd have symbols for days if each one had it's own, so all the others get lumped into this one.",
"Per NPR and a PBS special, while most plastics are recyclable no one actually does. URL_0",
"It doesn’t. The vast majority ends up in landfills. It’s a feel good program designed to keep you spending money without interruption by your conscience.",
"In my county, we place recyclables in a rolling bin, separate from our trash, which the county picks up every other week. It then takes all those recyclables and buries them in a landfill. Allegedly they can be dug back up again if there’s ever a market for recyclable material. There isn’t currently, since China and other countries stopped taking our crap a couple of years ago."
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j9s5e5 | How are sea cans stacked on cargo ships like in this video not moving at all? | Engineering | explainlikeimfive | {
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"One critical design feature of cargo containers is [the bolt holes in the corners]( URL_0 ) that allow them to be connected together. Cargo containers aren't just piled on top of each other and left to gravity and friction to hold together. There are bolts and clamps that go in the corners and link all the cargo containers together like giant LEGO blocks so that a ship carrying 10,000 containers behaves as though it is carrying a few really really big containers rather than thousands that are each moving and sliding independently. Poorly mounted containers can shift in high seas and risk capsizing the boat so its really important to secure them correctly.",
"Shipping containers have slots on all 8 corners that the dock workers slide locking pins in when they load the container ship.",
"They have locks (twistlocks) at their edges that connect them with the container above and below. Or with the ship, the transport vehicle or the truck that transports them. On cargo ships the stacked containers are lashed with iron bars. The bittom three lines are lashed, depending on the heigth of the stack. Look at this [Video Lashing]( URL_0 ) This is a fast way to connect and disconnect them. The rows higher than the third are connected with twistlocks."
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j9u8w9 | how does my (analog) gas gauge work? | Engineering | explainlikeimfive | {
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"There's a little bulb in the tank that floats on top of the gasoline connected to an arm - the higher the position of the bulb/arm, the higher the gauge will register. This is also why your tank will show within like 5% of full and 5% of empty for way longer than 5% of your drive time - When it's crammed against the top of the tank, it's going to register as full even if the tank's full, or pretty close to full. Same deal if it's sitting at the bottom of the tank."
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ja3jzi | How are office chairs able to raise and lower the height of the chair using air without any moving parts? | Engineering | explainlikeimfive | {
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"text": [
"There's a piston full of pressurized gas inside. It's like the chair has a really tough balloon in it, and it's really full. This balloon is attached to a brake that can freeze the chair in place or let it move. & #x200B; When you get off the chair and release the brake, the balloon expands due to the gas inside, making the chair rise up. When you sit on the chair and release the brake, the pressure of your weight compresses the balloon and the chair sinks. You can set the brake when the chair is at just the right height."
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jabqbu | How does an iPhone know a charger is an “approved” accessory? | Engineering | explainlikeimfive | {
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"Apple has an authentication chip inside their lightning cables, the piece that actually goes into the phone. The chip inside when connected to an iPad or iPhone let's the device know that it is an apple-approved device. This small authentication let's the device know that the manufacturer did not go through Apple's certification program. That is why Apple-Approved cables are always over 20$. You can see if they are approved by the small white box on the cable itself."
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jak4lu | Why do cars shudder sometimes when idling at a light? | Engineering | explainlikeimfive | {
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"Usually if your vehicle shudders intermittently or continually while idling , it is being caused by a misfire. Typically misfires are allowed within a certain threshold, exceeding that would trigger a check engine light.",
"Cars have multiple cylinders that fire in a specific order. Lets say you have 4 cylinders and they fire in a 1-2-3-4 order. Sometimes, the fuel in a cylinder doesnt burn or starts burning early. This causes the shudder. This is relatively normal if it occurs infrequently. If it happens too often, you will get a check engine light.",
"There are some good answers here. One other reason is if you replaced the battery recently the computer memory usually gets wiped. It needs to relearn the ideal idle speed. It should correct itself after a while.",
"Sometimes the car is turning off or turning on the alternator or air conditioner when it’s idling. That reduction or increase in engine load is noticeable when the RPMs are already low from idling."
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janyo3 | - Why does an automatic car creep forward in gear at low speed without pressing the gas but manual one will stop and die? | Engineering | explainlikeimfive | {
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"The engine is always spinning when the car is on. In a manual transmission, you engage the clutch while you're stopped. The clutch disconnects the engine from the transmission (and the wheels,) so the engine can just spin freely on its own without making the car move. If you let out the clutch, you will stall, because you've suddenly massively increased the load on the engine and it can't increase its torque fast enough to deal with the increased load... hence needing to gently let out the clutch as you gently step on the gas. Automatic transmissions have a component called a torque converter. When the engine is spinning at a low speed, the torque converter absorbs almost all of the energy from the engine, which allows you to keep the car in place just by putting your foot on the brake. That's why you don't need a clutch. If you let your foot off the brake, the car creeps forward because the small amount of torque making its way through the torque converter is now reaching the wheels and causing them to spin."
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jawmm5 | Why do table fans velocity goes OFF-3-2-1, instead of OFF-1-2-3? | For clarification, I'm referring to those fans with a radial controller in its base. | Engineering | explainlikeimfive | {
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"oh! i know this one! the fan starts off giving more power to the blades in order to overcome inertia. If it were to go OFF-1-2-3, you would run the risk of 1 not turning the blades and causing the motor to burn out.",
"Technology connections actually has a really good video on this on YouTube. Essentially, the motor in a fan takes a lot of power to start up properly, but it only needs that power for a short amount of time. the amount of time that it takes for someone to move the switch from off to one is enough time for the fan to do its startup.",
"The type of motor that they use in the fans have a hard time getting started but when they are first rotating they are easily able to get up to speed. You may have seen issues with older fans where they have stalled and just makes a whirring noise without rotating the blades (until they catch fire shortly afterwards). If you manually start the fan by pushing on the fan blades it will work perfectly fine. To avoid this situation it is recommended to start the motor on the highest setting so that it have enough power to overcome friction and get started. The switch is therefore configured in this way so that you always turn the fan to the highest setting first before turning it down."
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jaxsve | . Why are sports wheelchairs slanted inwards compared to traditional wheelchairs? | Engineering | explainlikeimfive | {
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"As others have said, the slant helps with stability. But the sneaky flip side to your question would be why aren't all wheelchairs slanted? The main reason is probably because that weakens the axle. A straight axle will be stronger than a bent one with an angled connection. So to compensate, sports chairs need to be better engineering, making them more expensive. Since your average pensioner isn't going to be doing too many doughnuts, the extra stability just isn't needed.",
"Its to do with the distribution of forces that the wheelchair goes through. In a sports wheelchair, it is assumed that the user needs a more dynamic wheelchair with the ability to take sideways forces, as they will be leaning/throwing/catching and making contact with other players. It Wouldn't be helpful if all the wheelchairs kept falling over during sports games. The angled wheels achieve this in two ways. The first is it makes the base off the wheelchair wider. Things with a wider base take more force to tip (when being pushed from the side). Secondly the angle of the wheels changes how far it would need to be tipped before it begins to fall over. These allow things like better turning when going fast, and a more stable platform to throw/catch from."
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jb4qz1 | Given how deep the ocean is, how do transatlantic or transpacific cables work? | Engineering | explainlikeimfive | {
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"They are not laid in the deepest parts. The ocean, just like the surface of dry land has peaks and valleys, plains and canyons etc. So you plan the route to avoid places like the Mariana Trench...",
"Depth of the cable isn't really a problem down (up) to 6000m, cables are made of essentially all solid materials plus a gel to fill the gaps, so they don't crush. Most of them are fibre optic now which is solid glass. The vulnerable parts are the joints, which are often signal boosters so are electronics but these too can be selected and designed to cope with the very high pressures."
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jb62jc | What’s the difference between all wheel drive, 4 wheel drive, and 2 wheel drive? And why is AWD/4WD best for slippery road conditions (eg snow)? | Engineering | explainlikeimfive | {
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"The different types of drive dictate which wheels are receiving power from the engine All-wheel-drive means that all 4 wheels would be receiving power from the engine, similarly with 4-wheel-drive all the wheels are powered but the front wheels can usually be manually ‘locked’ or ‘unlocked’ to provide them power or disable it, this allows better traction since the engine power is being channeled through all 4 wheels. 2-wheel-drive can vary between Front-wheel-drive and Rear-wheel-drive, simply mean that the power is either only being delivered through the front of rear wheels. They’re usually cheaper, but can provide less overall power and traction. Hope this helps",
"2WD is just one axle being driven. 4WD means all four wheels are being powered by means of an additional drivetrain on the front axle that is getting power from the transmission. This is achieved with a geared transfer case, effectively coupling the front and rear axle together. This has advantages- torque is split between both axles and all wheels are being driven, improving traction. It also has disadvantages- because your axles are linked, they have to move at the same speed. Off road, this isn't a problem. On-road, your tires need to be able to rotate at different rates (like turning). AWD fixes this by adding a clutch assembly to the link between the two axles- allowing them to \"slip\" against each other without damaging the drivetrain. You some of the benefits of 4WD without the drawbacks of using it on paved roads."
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jb6kla | what technology are we missing in order to build a space elevator? | Engineering | explainlikeimfive | {
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"Mostly it is the materials which need to be both light and strong, currently there isn't anything that could take the strain and be light enough to get to the required altitude. URL_0",
"Materials science. Any material we have that's strong enough to hold a space elevator, is too heavy to be one, and any that's light enough, isn't strong enough. Any materials that are both can only be made in small quantities.",
"A material with high specific strength A space elevator is effectively a strong cable pulled tight between the surface of the Earth and a counter weight up in orbit. The tension in the cable depends on the weight of the cable, a heavier cable is going to require the counter weight to pull on it harder to keep it from sagging in the gravity, this means you need a really strong but really light material. Specific Strength is the measure of maximum pulling pressure versus density of a material A space elevator needs something with a specific strength around 50-100 MPa/(kg/m^3 ). Strong metals like Titanium top out around 0.25 MPa/(kg/m^3 ) while strong fibers like Kevlar come in around 2.5. Carbon Nanotubes have gotten up to 60 MPa/(kg/m^3 ) but only in very precise manufacturing conditions, once you start braiding short strands to get a long cable it'll drop off. The best materials we can actually make notable volumes of come in around 1/10th the required value and that's the main problem now"
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jb9ull | What parts of the Soyuz are re-useable? Surely they don't have to re-manufacture and rebuild the whole entire thing to go to space? Is it just the module which isn't reuse-able? or is it the entire whole rocket part as well? | Engineering | explainlikeimfive | {
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"Well you see Billy, back when the Soyuz was originally designed the idea of spacecraft reusability was still theoretical. The act of launching and returning a Soyuz leaves every major system damaged or destroyed by design. Since neither the rocket or the capsule were designed for reusability, the rocket is cheaper to build, but nothing can be reused without significant risk to absolutely everyone involved. Perhaps more notably, it is only relatively recently that economic and governmental pressures have been aligned to drive the creation/ design of truly reusable space vehicles."
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jbj134 | What the hell is the Large Hadron Collider | Engineering | explainlikeimfive | {
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"Imagine a big circle made of pipe, where you send balls very fast, so that they meet at a certain point. At this point, you have set cameras to film the crash. That's the LHC. Except that the balls are small particles, and that the cameras are really precise instruments. The goal is to understand how the balls are exploding when colliding, and what they are made off.",
"The large hadron collider is basically a giant ring that accelerates particles. The goal is is to smash to subatomic particles together at incredible high speeds. When you smash particles together they tend to break apart allowing you to examine what they are made of. This is the final goal of the large hardon collider. Break apart subatomic particle and examine the pieces left behind."
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jbn16e | What is micro in microcontroller/microprocessor? | Engineering | explainlikeimfive | {
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"* Computer processors used to be made from what are called discrete components. * Literally small individual pieces that had to be wired together. * Then it was discovered that all of those circuit elements could all be made from the same material if we were clever about how we applied certain chemicals to it. * This allowed the circuits to become very very very small (by comparison) to the original designs. * \"Micro\" basically means very small. * Same as microphone and microscope.",
"Lots and lots of things. Microcontrollers specificallly mean a CPU, RAM, and Program Memory all on one chip. Micro just means that the individual chip as a controller is smaller than a non integrated system (like your PCs motherboard, CPU, RAM and Hard drive). Think like an Arduino. They are generally cheaper and less capable than a full on PC, but are super cheap and useful for controlling things like microwaves and cars. Thus microcontroller. Microprocessor refers to CPUs that do processing only and rely on lots external electronics like RAM to function. Before microprocessors, a processor would need to be built out of several other chips and transistors instead of just being on one chip. Imagine one or more boards about the size of a motherboard wired together. Shoving all that onto one chip makes it micro.",
"Micro in these instances does technically refer to circuitry at the micrometer scale (of course you can call anything “micro” even if it’s not actually). Technology has improved enough that we are now attempting to develop nanoprocessors, which refers to nanometer scale.",
"They are called microprocessor because the was designed for use in a microcomputer. All PC we use today are microcomputers The first computer was room-sized, you got was is called mainframe computer that would be like multiple refrigerators in size. In the mid-1960s smaller computers come on the market. The was called a mini-computer and the size was more like a single refrigerator. They cost less than the mainframe, a suggested definition was a computer with a cost of less equivalent to $165000 today. But it makes it economically feasible to use them in more places The processor in those was in the beginning individual transistors in a capsule with other components on a circuit board. It moved to multiple transistors in a chip. The apollo guidance computed that was build in 1965 was the most advanced in used to integrated circuits by you still needed 4100 chips for the computers. It 1971 Inter release the Intel 4004 that was CPU in a single chip. A new class of computer was created. The was smaller than a minicomputer so the natural name was a microcomputer. Mainframe and minicomputer use CPUs on multiple chips for a long time because they want to use more transistors that could reasonable fit on a single chip. You can look at [this video]( URL_0 ) with a teardown of a mainframe CPU from 1990. Today mainframe has CPUs in single chips. Minicomputer is almost gone today as the performance of the microcomputer has caught up. But some like the IBM System i still exist. It resulted in that CPU that is on a single chip was a microprocessor. A microcontroller is just a microprocessor often simpler and designed as a part of a larger system as a way to control it.. Today memory ext is usually integrated into the chip. So a microprocessor for control applications."
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jbu7jr | Why do car/truck manufacturers not provide covers or protective plates for the underside of vehicles where the most water and dirt is liable to collect? | Winter is coming and I just made an appointment to get the underside of my car and truck rust proofed and it made me wonder - I clean, wax and keep my car every year because I want to keep it from rusting or getting damage but I can't do the same to the underside of my vehicle which has a lot of its machinery, wires, cables, pipes and interior panels all completely exposed to the worst possible road conditions every single day. | Engineering | explainlikeimfive | {
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"Probably because they want that area to be able to drain and dry easily...enclosing it would trap the moisture, which would be MUCH worse"
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jbwrsl | Why aren't Hybrid cars more popular? | I know that Hybrid cars greatly improve your MPG, so how come every car that's coming out isn't a hybrid? It doesn't seem too far off from a gas-only car, and it being placed into a different naming scheme instead of marketed as an "Efficiency Improvement" for existing cars is beyond me. | Engineering | explainlikeimfive | {
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"> and it being placed into a different naming scheme instead of marketed as an \"Efficiency Improvement\" for existing cars is beyond me. Because it *is* different. It's a *hybrid* car -- its propulsion system is not fully electric, and it's not fully gas. It's a *hybrid* of the two, where the electric motors do some of the work, and the gas engine picks up where needed. As for why they're not more popular, well. They're more complicated to manufacture, and they're more complicated to maintain. If you do a fair amount of highway driving, you don't save any mileage.",
"They are very popular on the US West Coast where fuel is really expensive. There are several reasons. First, there are more hybrids on the road than you think. Most of them look like regular sedans like Honda Accords or Toyota Camerys. Hybrid cars are thought of as under powered and as a Prius owner, it isn’t my old Camero or my big Expedition. I made a choice that I didn’t need to feel the rumble in my seat and that 50mpg was wiser than 14mpg. Fuel prices impact hybrid sales. When gas is over $3 a gallon and it takes me $100 to fill up that expedition but like $20 to fill up the Prius, the economics are very in favor of the Hybrid, but at sub-$2 a gallon that cash flow pressure is off.",
"Until recently, they were mostly pretty ugly and generally small econo boxes. On a more practical matter, the price premium for the CUV hybrids doesn’t have a good break even vs the incremental cost of gas on the non hybrid model. Modeling the new CRV ex-L vs the hybrid variant had a 8.5 years break even on the $1,200 higher purchase price. Do you really want to wait 8.5 years to start saving money on fuel costs?",
"They are becoming more popular, at least from what I've observed from my limited point of view. I work at a Toyota dealership, and the amount of hybrid vehicles that exist in the range has greatly increased over the 10 years I've been here. It started with the Prius, then the Prius C. Now the Corolla, Camry, Rav 4 and C-HR all have hybrid varieties. I've heard talk of a hybrid Land Cruiser too. The downside of these vehicles is the eventual need to replace the battery, which doesn't come cheap.",
"There are more hybrids on the road than you think. Depending on the cost of gas the savings from running a hybrid may not pay for the price difference in the lifetime of the car. So as a purely cost savings mechanism, it depends where you live. Some downsides of hybrids is that they are more complex therefore have more parts that can break. This makes them less attractive to people that don't replace their car the moment it's off warranty. The batteries will eventually have to be replaced and they are very expensive. Hybrids like the Prius are unnecessarily ugly. To quote Jay Leno \"It's the Hollywood thing to do, I drive an ugly car because it's good for the environment\" If they made a hybrid look like a mustang instead of Prius they'd have an easy time selling them."
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jc7exh | If a hybrid car uses a petrol engine to charge the battery, how is this any more efficient? | I mean, I assume it is something to do with heat efficiency. A petrol engine powering propulsion generates more waste heat? | Engineering | explainlikeimfive | {
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"Two effects - first, because the electric motor can recharge the battery during braking, you can recapture some energy that you lose to brake heat with a regular drivetrain. That's particularly significant in stop-and-go driving, which is why the hybrid does so much better in the city. Second, it allows the petrol engine to operate closer to its optimum speed, allowing it to be more efficient.",
"Kinetic energy recovery. The electric motor replaces moderate braking and returns most of that energy on the next acceleration cycle. Recovery is imperfect of course.",
"the first thing you´re going to have to accept is that a gasoline car is VERY inefficient. most of the energy produced by the gasoline is lost to heat, mechanical friction, noise, light... and thats without taking in to account transmission, brakes and such, around 60-70% of the energy you put in to the gas tank in form of gasoline is lost to the environment. A hybrid car has several systems, like regenerative breaking (when a dynamo is used instead of breaks and the force of the car is reabsorbed in to the battery), excess power made by the engine that dosnt end up in the wheels is passed to the dynamo as well. Basically recovering energy that would be usually wasted in a normal car, so you get a bit better fuel economy, the next step is Plug in hybrids which allow you to recharge the battery at home from the plug and use that for smaller daily travels, Then there the range extender, basically a mostly electric car with a gas engine that only turns on when the battery is low, so you get a low range electric car like 70-100KM range, which is enough for usual stuff like going to the shops or to work every day, but when you want to go on the road, you have a backup gas engine to charge the battery.",
"Efficient question-answering engines. Seriously I went downstairs to make a coffee and already have the answer. Thanks everyone!"
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jcbbve | How do those giant cranes get on top of skyscrapers during construction? | Engineering | explainlikeimfive | {
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"URL_0 The crane build itself. The crane tower is made up of a bunch of pre built sections, so to kind of over simplify all the crane down is Jack itself up above the previous tower section, slide the next tower section in, work with that, and then when it needs to go higher again Jack itself up again and slide in another section below it."
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jcjlf7 | how do people build oil rigs in the oceans? How do we put the giant pillars into the ocean floor? | Engineering | explainlikeimfive | {
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"We don't actually anchor them to the floor. Those deep water platforms actually float there with anchor lines to keep them stable. The drill and pump mechanism is sent down some somewhat flexible tubing. There was an article in The Economist about towing one to a scrap yard in Turkey."
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jcmwly | If nuclear power plant is helpful, what's preventing modern countries to operate one? | Engineering | explainlikeimfive | {
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"Modern countries do operating them. For example, in France, 71% of their power comes from Nuclear power. However, it's very expensive to get started. So some countries don't use it because other methods of power generation is cheaper for them. And Nuclear power can be safe. Think about how many disaster's you've ever heard of. It's very few. However, when things go bad, they go very very bad."
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jd6qlh | Why is gardening equipment (lawn mower, leaf blower) so fucking loud? | Engineering | explainlikeimfive | {
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"Gas powered ones especially have the same little explosions powering them that power cars, only without all that extra mass+exhaust system to dampen the noise. Most manufacturers probably figure the extra cost and weight added by potential quieting features just aren't worth it."
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jd8vhk | why is it ok to leave the pilot light on in your gas fireplace? | ...like I know it’s ok. I had an oven with a pilot light growing up. But for some reason it feels wrong to leave a flame lit 24/7 even when the house is unattended. | Engineering | explainlikeimfive | {
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"Back in the 1980’s standard equipment for a household were candles and matches. When the power went out, you lit a candle. Now, people can also burn their house down when they light candles. So now it’s common to not light candles anymore for safety. So what is safe is relative. Having an open flame poses some risks. But these are minimized because pilot lights are internal to appliances. If you have a pilot light without physical guards, that is dangerous! Pilot lights, however, do a great service for safety. They ensure that there is an ignition source whenever natural gas is released, guaranteeing it will burn. If it does not burn, gas will collect and either suffocate people or explode. Yikes.",
"Not sure about fireplaces but I know it's pretty safe for a continuous pilot on a furnace. I would suspect a similar reason. Your furnace is basically just one big simple machine that has nothing but safety switches/triggers. Aside from modern furnaces with the control board (high/mid efficiency furnaces) the concept was so incredibly basic. You have a pilot ready to ignite the gas when the thermometer sends a call for heat. It opens the gas valve and the pilot ignites the burners. Every step from then on is designed only to prove its safe. There is a flame sensor that is making sure flame is available (so the gas doesn't keep spilling out) if it doesn't sense the flame it shuts it all down. Then you have high limit switches that will shut everything down if temperature gets too high.. then you have pressure switches to make sure there is continuous negative or positive pressure down the line for the inducer motor (whichever it was designed for) or it .. shuts everything down. There are flue gas spillout switches , making sure you're not spilling flue gasses into the house .. but all the system is really doing is lighting a gas and then pumping air through a fan .. it's simple but the complexity of furnaces comes from the bajillion safety switches/limits and 90% of the time when your furnace isn't working its just because one of the safety's were triggered.. so a technician comes out to fix the \"safety\". They are incredibly safe because they are 90% safety and 10% fan blowing hot air. It's easy to realize how dangerous pumping a gas onto a flame can be so it makes me sleep alot better with that realization. That I have this huge machine that does something very simple , but costs me an arm and a leg and is breaking down or ever not working only because it probably wasn't being safe. They literally won't work at all in any unsafe scenario . I only listed a few of the safety triggers, there are more . Any scenario you could think of there is probably some type of safety for it."
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jd9e7g | How does a nail hold two things together? How doesn't it not fall back out of the hole it created over time? | Engineering | explainlikeimfive | {
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"The nail rams the wood out of the way, but the surrounding wood tries to push the displaced wood back into place, the force from this results in significant friction that holds the nail in place. This is also why nailing into the end grain (into the end of a plank) is much weaker than nailing into the side of a plank, as the wood fibers are much better able to try squash back together when you nail into the side.",
"Friction. The nail is being squeezed on all sides very tightly because it was forced into the wall. But if there's enough vibration, over the course of time it could fall out. But it's still unlikely.",
"Nails can work their way out over time, but it will not simply fall out because you are compressing the material when driving it. So there is pressure acting against the nail to keep it in place. However the pressure depends on the material, its density, composition, and integrity. (Imagine nailing two pieces of cheese together, or nailing drywall / particleboard.) How quickly would those nails \"fall back out?\" However, you will notice that even in an ideal medium like a pine 2x4, screws, or glue along with nails are recommended over nails alone for reasons of durability.",
"It is just friction. Often on things that get a lot of movement (decks are a good example of this) the nails do slowly push themselves out of the holes. You've got to tap them back in. Screws aren't really any different except they have larger contact areas and the movement needs to be directional."
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jdco7r | what do washers actually *do* in the fastening process? | I’m about to have a baby in a few months, so I’m putting together a ton of furniture and things. I cannot understand why some things have washers with the screws, nuts, and bolts, but some don’t. What’s the point of using washers, and why would you choose to use one or not use one? | Engineering | explainlikeimfive | {
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"In general, a washer is used when the material you're fastening is softer than the material you're fastening with... Eg a metal bolt on the wooden leg of a table, and its purpose is to spread the pressure of the bolt across a broader area, so you can tighten more without the bolt just sinking into the soft wood Edit: you do also see rubber or plastic washers for metal on metal fastenings, this is usual to prevent vibration from loosening the bolt over time. Edit 2: wow - thanks everyone! Many people have pointed out other reasons why washers are used in addition to the above including to prevent certain types of corrosion, to carry the wear for fastenings which are frequently used (like on access panels) and to seal against moisture. There have also been comments about the validity of the anti-vibration washers (both polymer and \"anti-lock\") so I guess do your research if this is a concern for you! There are many many great links and comments in this thread.",
"A few reasons for washers: They spread the load of the screw/bolt head over more area - rather than just the inside rim of the bolt pushing down on the piece fixed, you have the much larger washer. This is especially important fixing softer materials, where something like wood could get crushed beneath a concentrated load. You could just use a larger bolt head instead of a washer, but these are bulkier and more expensive, so a washer is preferable. Washers also create a buffer and slip plane between the bolt and material - so when you tighten the bolt down, the bolt isn't twisting against a softer material and damaging it, but against the tough steel which will be fine. You also get special use washers for specific jobs too - the funny washers with a kind of star shape pressed into the inside ring for example act as locking pieces and help to hold the bolt in place and prevent it unscrewing, as do certain types of nylon washers which purposely crush down and hold everything in place, or you can get things like rubber damping washers that will absorb vibrations, or rubber/nylon washers that isolate different types of metal (certain metal types can react when in contact with each other and oxidise or weld together, which is not always a good thing).",
"Assuming you're not talking about lock washers they effectively make the head of the screw larger (like snowshoes) helping to spread out the load of the screw to prevent damage to the surface you're screwing against and to hold more securely. If you're fastening metal they can help to prevent corrosion. Some washers used in fluid containers, pumps, ect. are designed to deform and create a seal to prevent leaks. There are washers used as spacers, or to stop vibration. Most likely the first paragraph is the answeryou're looking for.",
"There is actually a bunch of engineering theory behind washers. For furniture, the most common use for them is to prevent the screw from sinking into the soft wood. The washer is stiff enough to spread the force on a larger area, so the pressure on the wood is lower. Same usually goes for anywhere where plastic is fastened to metal... This is not eli5, but a little basic machine element engineering theory...: Otherwise, properly torqued/tensioned screws on metal flanges also usually have washers. There is a lot of things to consider there - high clamping forces means the screw could also sink into the metal slightly over time, which would loosenvthe connection, and the (usually stamped sheet metal or rarely special milled/turned out of a solid) washers make that procedure a lot slower or less important. Another thing - the ratio between the screw diameter and the flange thickness tells you if the screw will unscrew by itself. A screw is self-locking a lot more, if the flange thickness is far greater than the screw diameter. This is why e.g. for engine cylinder head, you have relatively thin studs which are very long. If they were thicker, that effect would be much worse. Also, for sealing surfaces, if the distance between the screw head/nut to the sealing surface is longer, the pressure on the sealing surface is distributed over a greater area. Washers add up to that distance... And lastly, there are countless standard variations for washers, most are of course just plain washers but you also have lots of lock-washers using different methods, usually based on increasing friction, to prevent the nut from unscrewing over time...",
"Washers protect the surface under them in two ways: 1. they distribute the pressure of the screw head over a larger area, to prevent the marring or indentation of the material that the screw is holding down. 2. they protect the material from friction. As the screw turns the underside of the screw head can grip and twist the material around for the last couple of turns.",
"Hey, aviation mechanic here. Washers do a great number of things. The washers you are probably thinking of are called plain washers, they look like a squashed donut. These plain washers are used as spacers, if the fastener is too long. They also help protect against rubbing that can happen from turning the fastener. Large plain washers, which are like a coin with a small hole in it, is used to apply clamping force to fragile materials. If you, say, took a tiny screw and tightened it down through some plastic, the plastic will probably break because the force is being applied over a small area. If you use a large plain washer, it \"clamps\" over a wider area, reducing the stress and potential for damage or cracking. Think of it like a needle vs a mallet, which is more likely to poke through your skin? There are trim washers too. They are often also called grommets, but they are used to grab onto fabric. They look like half of a bagel, and are hollow inside with a sharp edge pointing down to dig into the fabric. There is also lock washers. These come in many forms, from a \"c\" shaped bent washer to a washer that resembles a starfish, called star washers. These are meant to create friction between the fastener and whatever it is being fastened to, so as to make it harder for that fastener to loosen on its own. There are many, many types of lock washers, but the c-shaped and star-shaped are the most common I see in my work, but there is also spring washers, tab washers, flip washers, and many more. There is also anti-corrosion washers. There is some complex chemistry involved, but to super simplify, some metals don't like other metals, and will corrode if they touch each other. This is primarily what plastic washers are for, to stop that touching. Another type of anti-corrosion washer is a sacrificial washer. These washers are made of a metal that really likes to corrode, that way the washer corrodes instead of the fastener/whatever being fastened. That's why they are called sacrificial washers. There is one other washer, too. Phenolic washers. Phenolic is a fancy term for layered and compressed paper, and it is reasonably strong but really good at insulating against electricity. This is used for a lot of wiring stuff, if you don't want electricity to travel through the fastener. Hope this helped, I tried to simplify this stuff best I could, but if I forgot to mention something or didn't simplify something enough, tell me!",
"Another use of washers that I'm not seeing here is for shoulder bolts. You don't want threads in bearing in many applications (the threaded part of the bolt inside the material being joined). You'll spec out a fastener that has a certain grip length to match the material stack thickness. However, you might not have a fastener that matches exactly. In that case you would go the next higher grip length and use a washer of enough thickness to ensure your threads protrude. Even the fastening spec document will allow up to two washers to be installed under the nut. At least this is the case in aerospace design...",
"Reasons can vary, from spreading the load out on low-density materials, protecting finish, or isolating dissimilar materials to protect from corrosion.",
"There are many other types of washers and reason you might use them - lock washers that prevent bolts from loosening on their own, rubber washers that act as a seal or dampener, inhibitor washers that prevent corrosion, etc... but in your case, with wooden baby furniture, it's about spreading out the load force. Grab a piece of styrofoam and try to push a finger through it. Pretty easy, right? OK, now try to push your fist through it. Same amount of strength, but somehow it's not as easy. Why? The force is being spread out across more material. That's effectively what a washer does - spreads the force of the screw head out across more material, allowing it to be very tight without just tearing through the material. Screws that don't have washers probably aren't required to be as tight.",
"Just imagine holding something against a wall with your finger (no washer) or your palm (washer).",
"Distributes weight along a larger surface area. Usually best when the material is really soft like wood. Think of it like wearing snowshoes.",
"Washers spread the force of the screw or bolt more evenly across a larger surface so that the bolt or screw does not dent or break through whatever material you are putting it through",
"Washers act as a cushion for the material used in the furniture, as screwing the bolt people tend to overdo it to make sure the screws aren't going to loose and fall off over time.",
"Metal washers spread stress out and reduce it. Rubber ones quiet things down and prevent leaks. Soft metal ones do a bit of both. Love the rubber ones. If you have something vibrating in your car you can often wedge a rubber washer in the gap to silence it.",
"When you screw a bolt down tight, what is happening? The threads of it are trying to go down but the flat head can't go down the hole also. This makes a pulling force in the metal shaft of the bolt called tension. The highest forces metals can withstand are called ultimate tensile, tension. So to get the most out of a bolt you want to take advantage of this property. When you bolt two things together that may slide around the bolt will physically stop that. The force a bolt can withstand before failing like this (shear) is less than it can withstand in tension. So how do I convert some of that sweet tension strength into shear strength? By tightening it down. The friction between the things you're bolting together increases when forced together. Now to your question. Bolts work by being under a lot of tension. The tension in the bolt must be resisted by the members you are tightening together. Washers help spread out this force so the softer or thinner members aren't damaged by the head of the bolt. I noticed a lot of answers mentioned the distribution of force but that left the question of 'why not tighten it less'?",
"They do 2 major things. 1 they spread the load of the bolt head over a larger area, so you can get tighter hardware without destroying the wood or material. It also is usually made of a harder steel which allows the bolt to slide easily along its surface. This makes it so your bolt doesn’t try to dig into the wood or material, instead of tighten. That refers to flat and fender washers only. There are other washer types as well. The 2 most common are lock washers and carriage bolt washers. Lock washers are made of spring steel and they are the ones that are cut and bent. As you tighten the washer puts pressure back on the nut so that it cannot vibrate loose. Carriage bolt washers are for carriage bolts. (The ones with the square peg and smooth round head) the washer has a square hole in the center, and teeth. The teeth dig into the material, and the square head locks into the carriage bolt. My personal opinion? Use a washer. Always. I can’t think of any reason not to use one except maybe space? Any time there will be rubbing between the bolt, or nut, and the material, use one.",
"They have 2 main purposes: to spread the clamping load out over a larger area and to compensate for oversized holes. I'll explain the second one first. When you're fastening 2 things with a bolt, you have to drill a hole in both of the things for the bolt to go through. Because nothing is going to be perfectly lined up, you make both holes a little bigger than the bolt so there is some extra room. Sometimes when you do this, the hole is big enough that the bolt or nut won't press down on the thing really evenly - part of it will press down on the hole itself, which is not useful. So you use a washer, which has a small hole in the middle (because it is easy to line it up) and a big diameter so it is sure to completely cover the big hole in the material. When you fasten 2 things with a bolt, the joint is strong because the bolt squeezes the 2 things together really hard (we call this clamping load). This clamping load, among other things, helps the bolt and nut to stay tight. Most of the time, the bolt is made of a stronger material than the things it is fastening. When the bolt is MUCH stronger, like with a metal bolt into a wooden thing, the clamping load the bolt puts into the thing might be strong enough to crumble the thing. So, we spread the load out over a larger area with a washer."
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