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gjgk4m | What makes the power go out in a small chunk of like 500 homes and how does the electric company fix it within just a few hours or less? | Engineering | explainlikeimfive | {
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"Electric service starts as big transmission lines, and breaks out into smaller and smaller distribution sections. When something goes wrong with _one_ of those sections, everything served by it has an outage. If it’s something simple — one broken powerline, say — then they de-energize what they need to de-energize, repair the break, and start everything back up. Sometimes the outage is caused by something for which there is a near-immediate backup, or an alternate option — those are some of the little short outages.",
"Areas are serviced by Sub-stations from where high power lines get voltage is reduced and distrubuted throughout a neighbourhood. If a part of the substation fails, they have cut the power to the substation to safely make the repair. It's ussually an easy fix as they will have replacement parts waiting on-site to be prepared for this.",
"I actually used to intern in an energy control center and have some hands on experience with this. Power grids are usually chock full of redundant connections. So it’s pretty hard to knock out power to too many people at once because there’s usually a second power line somewhere else that can pick up the slack while they fix the broken line without a real interruption in service (things break literally all the time but, at least in the US, it is incredibly rare to actually have a power outage). Inevitably though as you get down into it you can’t run multiple power lines from multiple different generator sources to every single building. There will be some smaller places where there is just a single point of failure. Like if the transformer on your street is damaged there’s probably not a second redundant one at that local of a level, so the street will lose power. On a larger scale the problem could occur in a substation which can distribute power to a larger number of houses on its own. If it goes down it could cut power to most of a town. The grid is really complicated and has a lot of components though, there’s not one single thing that’s always the cause of blackouts. It’s usually a multiple things going wrong or just more of a smaller section of the grid that’s not connected at multiple points being hit. As for how they fix it, they usually just replace what’s broken. They have a huge database showing most of the lines in the grid and all of the transformers, switches, substations, etc. connected to it. It even lets them control a lot of the switches and such. Once they become aware of a problem they’ll send out a crew to figure out what’s wrong. If it’s something like a broken line they’ll just cut power to that line by turning off a switch, replace the line, and then connect it to power again. Something like a substation can be trickier but they have portable substations which are basically just trucks with everything a basic substation needs to function on the back. They can divert power through one of these portable substations pretty quickly, fix what’s broken in the regular substation and then reconnect power once it’s working again with minimal impact to a customer."
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gjsb4l | What goes in to disinfectant chambers? What components are there to bump the sprays and what is the stuff inside it made out of. | Engineering | explainlikeimfive | {
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"There are many schemes. You can use dry heat (commonly called an autoclave), live steam, gamma radiation, chemical gases (commonly called a gas autoclave), chemical liquids, ... ."
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gkcx1j | Can anyone explain to me the navier-stokes equation for fluid ? | Engineering | explainlikeimfive | {
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"There's a few properties of fluids that explain how they move. One is called viscosity, which is a measure of how much a fluid resists being sheared (you can imagine something like honey or molasses as a high viscosity fluid - it likes to stick together and doesn't pour very quickly.) Another property is momentum - a moving fluid has momentum based on its density and the speed it's moving at. We can apply Newton's laws to describe the motion of fluids. The problem is that viscosity and momentum makes it a lot harder to apply Newton's laws to fluids. The Navier-Stokes equations are a series of equations that try to solve the problem of conservation of momentum in a moving fluid. There are 5 equations - a time dependent conservation of mass equation, a time dependent conservation of energy equation, and three time dependent conservation of momentum equations (for momentum in the x, y, and z directions.) Together if you can solve these equations for every set of x,y,z coordinates within a fluid, you can completely describe how it will move, where it will eddy, etc. Unfortunately the equations are very complicated, they're partial differential equations, and you need to solve them at very very small intervals. So that's why we can't solve them by hand, and that's why NASA uses super computers to run fluid simulations."
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gkmh6k | Why do cars automatically start moving after you release the brake? | Engineering | explainlikeimfive | {
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"That only happens in an automatic transmission car. It's part of the automatic function, to help prevent roll-back on an uphill stop."
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gksbpf | Why do foreign countries use over 200 volts 50hz while the US uses 120 volts and 60hz for main electricity? What effect does this have? | Engineering | explainlikeimfive | {
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"Usually historical reasons, 120V at 60Hz in the US worked fine, so they stuck on using it and used it as the standard In Germany they tried 230V at 40Hz and it was too little, so they increase it to 50Hz and that worked, and then that was also made the standard The advantage of higher voltage is that it is more efficient at transmitting power, you can draw more power over the same wires, but it’s also more dangerous. The advantage of higher frequency is that the transformers can be a little smaller, and you have less flicker with the light, but that also causes a bit more losses",
"In the uk we can draw power at a rate of 3120watts(13amps of current at 240Volts) from any wall outlet. That means our kettles boil twice as quickly, and our lawnmowers/hairdyers/everything else can be twice as powerful as a US version.",
"At the end of the day, power is power. Voltage is the energy per 'packet' Current is how many 'packets' per cycle And Frequency is how many cycles per second. These factors are incredibly relevant for designers and engineers but are largely irrelevant for regular people and the reason each reason has what they have are largely traditional and it's simply too costly to unify power systems (Never mind the squabbling on which one to change to)"
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gksml8 | What's the difference between Water Proof and Water Resistant? | The guy in the Apple store kept correcting me to water resistant whenever I said water proof. | Engineering | explainlikeimfive | {
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"Water resistant means you can use it in the rain, but not in a bath. It can stand getting wet but not submerged in water.",
"Because no product is ever really *anything*-proof. You were probably intentionally correct to make that point across. It’s like the other comments said, but I want to add that this is very intentional correction. It’s the same deal with anything “bulletproof”. Nothing is bullet proof. It’s bullet *resistant* up to certain calibers. Waterproof implies that you can just do whatever in water, and it will probably be resistant to certain depths, but yeah, eventually something will go wrong."
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gkuw1g | How are these things so fast? Where is the torque coming from? | URL_0 | Engineering | explainlikeimfive | {
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"They're likely using three phase brushless motors like those used on multicopters, but with big fat motor controllers capable of putting out a lot of current. Those types of motors can be precisely controlled to turn an almost exact number of degrees and can put out a lot of power so they're good for robotics unlike single phase DC brushed motors which just spin until you take away power.",
"They use two motors which both have about 1.4 kW motor, probably more as the reference I am using was not as professional. They weigh less than 3 kg and have strong magnets under their chassis. So they have a lot of downforce with a shit load of torque, thanks to high reduction and a lot of power. The motors are the most important thing in these things, so a lot of the budget and work goes into these. As well as the other person says, the motors are three phase brushless motors, which are capable of producing a lot of power in a small size"
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gli4hh | Given how old most USPS mail trucks are, how are they still able to make the routes they do and not break down constantly? | Engineering | explainlikeimfive | {
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"They were designed for durability, aren’t very complex as far as vehicles go, and because they are standardized they are able to keep parts at the ready and know how to fix them quickly.",
"Continuedly Maintained? I mean, big rigs will drive 14 hours a day, 6 days a week, for 30 years. As long as you maintain a vehicle and service it, it will keep running.",
"They break down all the time. The mechanic I go to is contracted to fix the ones in town. He always has AT LEAST one or two in his garage.",
"Just because the truck itself is old doesn't mean that the engine is. I imagine they have a standardised parts with standardised repairers and a strict maintenance schedule with lots of working replacements on standby. Pretty much how London buses and taxis would be if we didn't chance the model every few years - there's still working models from the 50's and 60's, and if we'd only had that model and a ton of affordable spare parts, you could keep them going basically until the shell rusts through."
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gll441 | Why does adding weight not increase tire pressure? | I'm puzzled by the fact that car/bike/truck tires maintain about the same pressure regardless of the weight they are supporting. If I take my the tire off my car and air it up to 35psi, I would think that the pressure would significantly increase after I add the 3000lb+ weight of my car to it. But it doesn't. Why not? Google say's it has something to do with the volume of air being unchanged, but I'm still having trouble wrapping my mind around that. Can someone please ELI5? | Engineering | explainlikeimfive | {
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"The part of the tire that actually touches the road is called the [contact patch][1]. When you add load, the tire deforms slightly and the area of the contact patch increases. When the vehicle is at rest the area of the contact patch times (in square inches) times the pressure (pounds per square inch) will always exactly equal the weight of vehicle (in pounds) because the downward force of gravity and the upward reactive force of the ground must exactly balance. (When the vehicle is in motion and going over hills or bumps it's not quite so simple, but the forces still roughly balance.) The pressure inside the tire stays the same because it's volume, temperature, and number of atoms stay the same. According to the [ideal gas law][2], unless you decrease the volume by squeezing it equally from all sides (by submerging it a hundred feet under water, say) or increase the temperature by heating it up the pressure will not increase. [1]: URL_1 [2]: URL_0",
"The volume and pressure do change: just not by much. Here's an imaginary experiment: Jack the wheel off the ground and measure the interior volume of the tire. Now let it down to the pavement. The tire flattens over a small area called the *contact patch*. Measure the interior volume again. What do you think the ratio of those volumes will be? Does 0.99 (i.e. a 1% reduction) seem reasonable? I do. OK, the ideal gas law says the pressure will now be 1/0.99 times what it was before. So if you had 30 psi in the tire, you now have 30.3 psi. Do you think you'd see that change on your tire gauge?",
"Gasses expand to fill their container. Adding weight to your car may make the rubber of the tire bend, but the tire is still the same size holding the same amount of air. It doesn't matter that the overall shape is different, the actual size of the container and amount of gas within haven't.",
"First you don’t add 3000lbs. You add 3000 pounds on 4 tires. So about 750lbs per tire. Then your tire isn’t a balloon. It’s rigid even when completely deflated. What does a tire look like when it’s not yet on a wheel? A pancake?Nope. Now. Your wheel receives 750lbs. That’s coming from the shaft and applied to the rim. The rims sits on the tire sidewalls. The lower portion of which. It supports an additional 750lbs. The upper portion of your tire does nothing except be read for the next half turn. The air in your tire does not support your car. It tensions the side wall so this one does not collapse under the weight of your car. If your air pressure is high enough, the side wall of your tire is rigid and your car stands. If the pressure is not high enough, the side wall can’t cope with the weight and flexes. This lowers the volume in the tire and raises the pressure. You reach and equilibrium with a lower wheel and a partially bender side wall. If the pressure is too high, but doesn’t make your tires explode, the wheel is akin to a rigid body and doesn’t flex. Driving is super uncomfortable and every bump is sent directly through to the suspension. If pressure is too high, the tire material can’t take it anymore and ruptures. No more air pressure, side wall collapses. And towing. The most important part of your tire is the side wall.",
"Pressure is basically the amount of air divided by the space you squeeze it into. Lots of air in a big space = low pressure. Not much air in a small space = low pressure. Lots of air in a small space = high pressure. If the tire doesn't squish very much because of the car, then the pressure won't go up very much."
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gln68o | What's the difference between different wing sweep types on planes (straight, swept back, forward swept etc.)? | Engineering | explainlikeimfive | {
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"straight wing just means both wings are at 90deg angle to the fuselage. \"straight out\". easy to make design that does the job just fine for low speed aircraft like general aviation. back swept just means the wing tips are further back than attachment point to the fuselage. it does better for efficiency. you'll see this on almost all commercial and most military planes. forward swept is very experimental. don't know of any ones other than the X-29. the design is inherently unstable and requires computer corrections. & #x200B; then there's F14 tomcat's variable configuration between backswept and delta"
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glutbx | Why is it that chainsaws need a pull cord to start? Couldn’t they just be turned off or on with a switch? | Engineering | explainlikeimfive | {
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"In order to do that it would need to have a battery, an electric starter motor, and a coil to generate electricity to recharge the battery, all of which would add a bunch of weight which you don't want with a handheld tool.",
"You could build in an electric starter to your chainsaw but then you'd have to haul around the electric motor and the battery, which adds a lot of weight and bulk (and cost). An engine that small is easy enough to start that getting it going by hand usually isn't an issue, so it's not worth the headache that a self-starting unit would have.",
"An engine that runs on gas or gas/oil mixture is generally one that explodes that fuel to drive one or more pistons, etc. You can't start such an engine just by applying electricity to it, you have to get process of firing the spark plug to turn the crank started. If you fired a spark plug when the piston mechanism was in the wrong position, the piston would drive the engine in the wrong direction. So the way to get such an engine started is to move the whole mechanism a little bit in the proper direction while electricity is available for the spark to fire at the correct time. Really old cars had a crank; manual transmission cars can still be started by turning on the ignition, pushing the car forward at a mile or two per hour with the clutch pedal pushed in, and then releasing the clutch suddenly (to move the pistons, etc.). In order to start with a switch, the chainsaw would need some equivalent to an automobile's starter motor: something that would take stored electricity (like a car battery) and jerk the motor forward. Such a mechanism would increase the weight, cost, and complexity of the chainsaw mechanism, so they don't normally do it. Chainsaws have to be small and light enough that they can be manipulated while working, so increasing weight is likely the biggest factor."
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glx7hh | what is the difference between the two wires in an AC circuit, if the current is constantly switching direction? E.g. why do they say to always put the switch on the “hot” side? | Engineering | explainlikeimfive | {
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"One of the wires switches from trying to push to trying to pull electrons. The other wire is by itself often inert. Those are hot and neutral respectively. There is also the possibility to use another hot wire that's always in the opposite phase of the push-pull cycle as the other wire, which gives you double the voltage (that's how 240V outlets work in the USA).",
"Because the neutral side is connected to the earth and the ground wire, so if you touch that, nothing happens even if you are standing on the ground, but if you touch the hot, suddenly there is voltage between you and ground, and current flows"
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gly3h9 | What is Kubernetes in software development? | Engineering | explainlikeimfive | {
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"Unfortunately, trying to explain Kubernetes to a 5yo, or even to an adult who has no previous knowledge of software development, is going to involve a chain of \"first you have to know this\". A computer program is a set of instructions for a computer to execute. All computer programs are written with some assumptions about the computer and the computing environment in which that program is to run, and so the program is dependent on those assumptions, i.e., they have to be true in order for a computer to execute the program. The assumptions vary widely, i.e., different computer programs assume and depend on different things. Some computer programs can be put into \"containers\"; you can think of a container as a collection of things needed for a particular computer program to run. Some might need a database connection, some are written to be executed within a web server environment, some might need a library of instructions or a \"virtual machine\". Once a computer program has been written, assuming it is able to be packaged with a particular type of container, is put together in this software container with all the libraries, database connections, other programs, etc. that it needs to execute. Kubernetes is a set of tools for dealing with a particular type of container. It lets computer people (programmers, system administrators, etc.) list, add, delete, execute, move, observe, etc. a collection of these containers.",
"It's a set of tools for managing containers. Containers are basically a way of packaging software in a lightweight unit that contains everything needed for the software to run. It's meant to speed up the deployment of applications by making them portable, easy to set up and configure, and easy to scale. Kubernetes is a system for managing many containers. It lets you configure and manage things like automatic application scaling, load balancing, deployments etc."
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gm3iz6 | Why do some V8 cars have more horsepower than other V8 cars? | For example, a V8 Bi-Turbo G63 AMG has 577 BHP and a Twin-Turbo V8 Koeniggsegg has 1160 BHP. How do virtually the same engines have such a large discrepancy? | Engineering | explainlikeimfive | {
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"V8 only tells you how the cylinders are oriented. it doesn't tell you displacement, flow characteristics, stroke bore ratio, etc etc. and as both a turbo'd, V8 doesn't tell you how much boost they're running the turbo's at. the G63 run s 17.4 psi boost. the Koeniggsegg runs 24.7 to 31.9 psi. the G63 is a 4.0L. Koeniggsegg runs a 5.0L",
"It's like trying to measure your FPS in a video game SOLELY by how many cores your processor has. There are LOTS of other variables involved with the various other parts - RAM speed, bus speed, video card, settings, etc. In a car you have total CC displacement (i.e how big the cylinders are), intake manifold, exhaust manifold, air intake, lubrication, fuel, transmission, exhaust layout, just to name a few.",
"Cylinders and displacement is not a good estimate of a cars performance. There are many more design elements. It's like say two people weigh 250lbs but one can bench press 300lbs while another can do only 150lbs. Why?",
"Your definition of \"virtually the same\" is incorrect. The G63 is luxury SUV and the Koeniggsegg is a barely legal race car. Yes, both have dual turbo 5L-ish V8 engines, but all the fuel management and engine computer controls are completely different.",
"At it's core, an engine is an air pump. The more air it can pump, the more power it makes. There are four main ways to get an engine to be able to pump more air: * Make it bigger (displacement). This is the most direct way. * Make it pump faster (rpm). If it goes faster, it will pump more air in the same amount of time (i.e. you go farther running for a minute than walking for a minute). * Pressurize the air going in (turbo/supercharging). If the air is \"smaller\", more fits in the pump at once. * Remove restrictions to airflow. If the pump is less restricted, it can move more air. Think about trying to breathe through a straw versus breathing through a snorkel. If one engine makes more power than another, it's doing it by one or more of the above."
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gm4ro8 | If the airplanes wings are shaped to create a lifting force , how can acrobatic airplanes fly upside-down ? | Whenever I see an explanation about how airplanes can fly, I see that the shape of the wing is different on the top side to create a dragging force that pushes the airplane up. The top is curved and the bottom is flat. If a airplane turn upside down, should it fall faster because it's dragging down ? I saw airplanes doing acrobatics on air , and some of them looks impossible because of this. | Engineering | explainlikeimfive | {
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"The shape of the wing has more to do with being aerodynamic than creating lift. The vast majority of lift comes from the angle of attack, which is the angle of the wing relative to its motion through the air. You can create lift with a flat wing, it just won't be very efficient and will have a higher stall speed. There are several different wing shapes depending on the needs of the aircraft, like how fast it is designed to cruise at, how low the stall speed is, etc. They might have more curve underneath, which creates more lift but also more drag, or even diamond shaped to reduce the negative effects of supersonic flight. Acrobatic planes that are designed to spend an unusual amount of time upside down have wings that are symmetrical from top to bottom. They are more of a teardrop than most wings, which are more like a flattened teardrop. The symmetrical wing is less efficient in normal, level flight but is equally efficient when flying upside down.",
"This is because the lift that a wing generates is also impacted by the [angle of attack]( URL_0 ), or how the plane's wing is angled towards the oncoming wind. In the picture that I linked, you can see that it has a positive angle of attack (the wing's leading edge is pointed slightly upwards) and most airplane wings are optimized to generate lift in in this configuration. However, if you gave the wings a negative angle of attack (so they're pointing downwards) they would actually generate lift downwards. This is what airplanes do when they fly upside down. Aerospace engineers can use something called a [lift curve]( URL_1 ) to examine the relationship between the angle of attack and the lift that a wing generates. In this image, you can see that a negative lift can be generated at a negative AoA.",
"Most explanations of aerodynamic lift vastly overstate the effect of Bernoulli's Principle, leading to your confusion. Wings generate most of their lift by pushing air down, not by pressure differentials.",
"the wings provide force in relation to the angle in relation to the direction of airflow. just like when you put your hand outside the window in a moving car and the air forces your hand up or down depending on what angle you hold it at. if the plane is upside down but pointed above the horizon, then it's still going to be pushed up"
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gm5v3k | Why do batteries last longer in a remote control than a Xbox One controller? | Xbox Batteries = 1 day Remote Batteries = 3+ months How is that?? | Engineering | explainlikeimfive | {
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"There are a couple of basic pieces here that contribute to higher power consumption. TV remotes aren't connected to your TV, instead they only send out instructions when a button is pressed. This requires very little energy and also means that when you are not pressing a button there is no power drawn. Xbox controllers are actively connected to the console, this requires some amount of energy to maintain. While it is not a lot(modern electronics are good with power consumption) it is a non-0 amount so you get a slow drain throughout. The other (bigger) difference comes from the way instructions are moving. TV remotes only send instructions in short bursts and don't receive anything. This is pretty simple and doesn't take much energy. Xbox remotes have a back and forth with the console, you are sending and receiving many instructions per second (button presses, holding a joystick, rumbles etc.). This consumes much more energy because of the sheer number of things happening. Apart from that, the rumble motors, various LEDs etc. all draw a bit of power and this adds up to reduce battery life.",
"A remote will usually only use power at the moment you press the button to transmit the button press while a controller is staying on and transmitting how far the buttons are pressed which directing the analog sticks are pointing and similar. Basically the controller has a great deal more information to transmit and needs to stay powered to transmit it all quickly while a remote can just transmit the button press and go back to its off state."
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gm69sa | How do sod farms never lose elevation after years of harvest? | Engineering | explainlikeimfive | {
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"Most of the mass in plants comes from photosynthesis which use carbon dioxide and water, both comes from the sky and not the ground. There is just a small amount of dirt in the sod as most of it is roots. In fact it is possible to grow sod without any dirt at all and just float it on nutrient rich water.",
"I one asked my Earth Science teacher why there aren’t huge craters at the base of every tree. You know, since trees use up the soil to create trunk, limbs, leaves, etc. He looked me like I was stupid. All that mass is actually taken from carbon in the air. The same is true of sod. That said, I do think they lose a bit of dirt every time they harvest sod.",
"Lived across the street from a sod field my whole life. They do lose elevation. The one across from me is down about a foot over 30+ years."
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gm8hry | How did/does the Apollo missions and Voyager missions transmit data through the Van Allen belt to Earth? | Engineering | explainlikeimfive | {
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"By radio. The Van Allen belt redirects charged particles, but not radio waves because photons are uncharged particles."
],
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7
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gm9ax9 | How can a multimeter measure higher voltages then it battery? | Basic multi meters only take a 9 volt battery but has the capability to read much larger voltages. Does it just wear it out faster? | Engineering | explainlikeimfive | {
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"fr2bx1y"
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"A very simple explanation: The electric circuit you're measuring goes in on of the wires and out at the other. The only thing it goes through whole inside the multimeter is the sensor. It doesn't go through the rest of the multi meter. Meanwhile the battery powers the sensor and the display. So the sensor is able to measure what is going through it, but the two electrical circuit are not connected."
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gmog6d | When building something, why are bricks laid in a very specific pattern on top of each other? | Every alternate row of bricks perfectly align with each other. But the successive ones don’t. Is there an engineering reason for this being the only way to lay bricks? | Engineering | explainlikeimfive | {
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"for strength, if all the seams were aligned the wall would be easier to knock down or fall apart. a good example of this is a pallet stacked with boxes, they alternate every level to \"lock in\" the boxes underneath making the whole stack stronger.",
"Stability and strength if the vertical joints are directly in line it produces a weak point, the varying combinations called bonds are cosmetic to some degree,and depending on particular bond can be extremely strong. The purpose of it is to make wall as strong as possible."
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gmw2ad | The purpose of fans that blow air on you when you enter/exit a mall or a supermarket. | Engineering | explainlikeimfive | {
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"Oh, an air curtain. The doors are opening all the time, and spending some electricity making a vertical column of air saves a lot of money over letting all that air conditioned air out. I believe some of those open-air coolers use the same effect so they can be open-air yet cool.",
"Large buildings try to maintain a positive pressure (higher air pressure inside) so that air always blows *out* when the doors open. This is done so that dirt and bugs and birds and leaves and snow and whatever else gets blown away instead of drawn in.",
"There are several reasons, which vary from site to site. 1. By having a \"wall of air\" it prevents the indoor air from escaping the building from the door that keeps opening and closing. This keeps in the heated/cooled air. 2. It keeps bugs and other things that are floating in the air out, to a limited degree. 3. Some installations negatively charge the air with ions, and then as it blows over you it knocks off all of the dust and dirt that was gonna fall off anyway, and then those charged particles are captured by the HVAC filters. It is kind of ironic that the public has a \"neutral to negative\" image of these blowers, mainly because nobody really knows the reason why some stores have them and some stores do not... They question why their hair/hat gets messed up at some stores, and not at other stores. Those 'other' stores probably have what is known as a \"positive pressure\" system, in which filtered/cleaned air is pumped in to the building. And then, all doors become 'vents' which blow the indoor air out. Typically used on big buildings, but it sees some use in speciality stores where they need to keep the dust levels down. Any store where dust would be a huge negative on the product, probably has one. Jewelry and Camera stores are the ones that spring to mind. This is also how 'Clean Rooms' work, but with more cleaning of the air. I used to work at a place where they had one, and whenever the power went out for more than 40 minutes they had to tape all the doors/passthroughs closed. Since with the fans off, some dust will sneak in as the pressure equalizes.",
"Receiver for a major grocery warehouse here. We also have these setup on smaller openings as well as some internal areas to keep bugs from flying in",
"Not so sure about with supermarkets, but industrial warehouses have them on pretty much all large external doors. They are air curtains, and they are intended to keep bugs and birds and other such flying pests out of the warehouse."
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gmxwzp | How are we able to manufacture incredibly small things such as computers processors? | Engineering | explainlikeimfive | {
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"fr6eyfk",
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"It's different for each small thing. Computer processors specifically are made by using light that is projected through several lenses to etch the components on the silicon. Think of a reverse microscope. The places on the processors where the other components of the computer connect are orders of magnitude larger due to the need to make a connection that is removable.",
"With great difficulty. People have been working for over half a century to be able to make smaller and smaller features on Integrated Circuits (ICs). It takes a lot of work from various disciplines to do....physics, electrical engineering, mechanical engineering, optics, chemistry, etc. etc. The key to it all is a process called \"photolithography\". Special chemicals called photoresists are coated on the silicon wafer. After exposure to light, these substances change their ability to be etched away. So by selectively exposing or not exposing areas, the photoresist can be removed in some areas and left in others. This allows us to transfer a 2-dimensional pattern onto the wafer. After the photoresist has been exposed, developed, and etched, it forms a barrier in the places where it still exists. So we can do things to the wafer and the exposed areas get affected and the areas covered by the photoresist don't. Then we strip off the photoresist and move to the next step. For example, let's say we cover the entire wafer with a thin layer of Cu metal. But we don't want it everywhere, we want to use it to form \"wires\" to connect up the transistors. So photoresist is applied. We expose the resist in certain areas and not in others, then strip away the exposed areas. After that, the wafer is exposed to something that etches away Cu but which can't get through the photoresist. So the pattern we made in the photoresist gets transferred into the Cu. Then we remove the photoresist with a special chemical and we're ready for the next thing. This is done literally dozens of times for each wafer. How do we expose the photoresist in some areas and not others? We use a \"mask\"....a plate of very transparent quartz glass with the pattern etched into a layer of metal like chrome. That mask is typically 5 times bigger than the pattern we want on the chip, and it gets reduced down with lenses. The mask is made by using a process like the photoresist/wafer process, but instead of using light we use an electron beam aimed with electromagnets controlled by a computer. It's a much slower process, but able to create very tiny patterns. There's a LOT more to all this, as you might imagine for a technology that has taken decades to perfect and had billions of dollars spent on it."
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gn267v | Why does electricity need a closed circuit? | Engineering | explainlikeimfive | {
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"text": [
"Electricity most certainly can go from one place to another without a connection to it's starting place. The most striking example of this, of course, is lightning. Less shocking examples would be things like static electricity. The problem with that model is it is unpredictable, unstable, and once all of the electrons have moved from one place to the other, it's spent. No more electricity. Generally speaking, we want our electronic objects to be more than one use, which means once electricity has gone from one place to the other, we need some way of getting electricity back to the starting place so it can go from one place to the other again. And again, continuously. And the best way to do that is to put it in a continuous loop. A circuit."
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gn3o7x | Would it make sense for a government to invest huge sums into a very strong, entirely renewable power grid? | Engineering | explainlikeimfive | {
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"It would make lots of sense.b the question is would it maken somone lots of money, or take money away from somone who already has lots of money. Either of those is your problem",
"This is more of a personal take on the issue but who’s going to do the labor? There are over 500,000 renewable jobs in the US maintaining and developing our currently small amount of renewables. There are 50,000 coal miners in the US right now. Even if you re-educated all of them, that would be a 10% increase in our work capacity. There’s 150,000 in oil, so even with that, you’re taking about a 40% increase in labor at best. Now consider the fact that as of 2018, renewable techs in Canada recieved half the wage of their former job in oil plants, after a year of unemployment during their re-education. So 40% is incredibly optimistic at best in given conditions. Now take into account that we have approximately 33 deaths per year on wind farms. It’s an inherently dangerous job, so that 40% increase from the re-education and labor deployment of fossil fuel workers is basically a fever-dream. So with that in mind, who would do the labor of building huge wind farms, maintaining solar farms, and rewiring all of America? The last time we tried something of this scale, we were in World War 2, where the government had greater authority, more people were unemployed to a level of desperation, and America as a whole was a more labor-intensive economy. Even then, we came up with myths about bodies buried in the cement of the Hoover Dam because we associated the projects with a huge sacrifice of America’s laborer. Just my two cents on the fact that the debate is so obliviously technical that it forgets that these wind farms don’t just spring up from the ground if you plant some money in the ground. There are social and economic systems that influence human labor decisions. Edit: coal miners in the US*, not the world. Hopefully people have already guessed that that was a typo"
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gn7kgq | Why are bridges vital on flat body guitars that have tailpieces? | I’m a decent guitar player but I hardly know anything about the guitar itself. I know how they work, like how the string vibrates and makes sounds that resonate in the guitar. But for the life of me, I don’t understand why bridges are important for flatbody guitars that have tailpieces. Curved body guitars have special curved bridges for the strings to lay on and I understand that, but I don’t see why flatbody guitars have bridges. Can’t the tailpiece just hold the strings in place and you can tune it? Sorry if this makes no sense, it’s kinda hard to explain if you don’t know anything about guitars. | Engineering | explainlikeimfive | {
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"fr81gho"
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"Your understanding of guitars lack one step. Strings by themselves make very little sound when played. You need to somehowe get the vibrations from the string into the resonant body of the guitar case in order for it to be audiable. And this is where the bridge come in. It transfers the vibrations of the string into the wooden body at the right spot where it will get amplified the most. If you tap the body of the guitar both at the bridge and at the tail you notice how much different it sounds."
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gnkj3p | Why does a closed room still get stuffy with a window fan? | Shouldn’t in theory new air be pushed in and old air be pushed out thus circulating the air inside? | Engineering | explainlikeimfive | {
"a_id": [
"fraapy9",
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"text": [
"You need one of those dual fan window units that allows you to set one fan in each direction. You have to exhaust air from the room while adding in fresh air. You cant just blow a fan into a closed room.",
"There’s no “new air” if the room is closed. You’d need an open window or at least an open door for “new air” to enter the room. A fan does not filter air, it simply blows the same old air around."
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gnmw89 | - how do you build something like the Eurostar? I thought the seabed would be far too porous and uneven to do something so grand - do they get on huge boats and drill down into the sea to secure the foundations? how do you build underwater? it can’t be a bunch of builders in wetsuits | Engineering | explainlikeimfive | {
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"If you're referring to the Channel tunnel, you use a tunnel boring machine (TBM). Since the sediments under the channel were pretty solid and suited for drilling the machines that dug the channel were open faced. Which is basically a big cutting-wheel the same size as the tunnel, pushers that grip the tunnel walls and push the cutting-wheel forward when drilling and then a huge train-like structure that provides power and sends the dug-out materials backwards. In softer material the TBM would be slightly more complicated and would have a mechanism to build its own tunnel walls as it moves forward so that only the front part of the tunnel is open to the silt & mud. The weight is not really a problem. Even in relatively soft material the tunnel is designed to be relatively weight neutral, it displaces close to as much material as it weighs so it neither has a desire to float up or sink down. & #x200B; A method for flatter riverbottoms is to dig a trench, sink pre-fabricated concrete tunnel segments, attach the segments with divers, pump out the water and then remove the bulkheads between each segment. Then you add a layer of rock on top of the tunnel segments to protect it from anchors and boats and stuff and you're done.",
"The seabed, or at least the underlying geography in that area actually is not that porous. The tunnel runs through a layer of Chalk Marl, a dense, fine grained material that allows digging, but is largely water impermeable. Of course, as they dug, they immediately reinforced the tunnel with concrete sections, and they had to constantly pump water. The workers basically wore typical work clothes, though fresh air still had to be pumped into the tunnel for cooling and oxygen.",
"The Eurostar isn't a tunnel running through the water, it goes *under* the seabed. It was done more or less the same way any tunnel through any solid is done, with tunnel boring machines."
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gnqhd2 | Sawed off shotguns. | What's the big deal with them anyway? Why wouldn't someone just buy a gun with a shorter barrel? Does it have something to do with how lethal it is? I just do not get it. | Engineering | explainlikeimfive | {
"a_id": [
"frbaybu"
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"Any rifle with a barrel less than 16 inches, as well as any shotgun with a barrel less than 18 inches, are federally regulated by the National Firearms Act (NFA). As well as many state laws. Per federal law they must be registered and extra taxes paid to keep registration. Sawed off weapons are a means of circumventing that registration, and also possessing one is a federal crime. The benefit of a shorter barrel is in concealment and handling, it will actually reduce the power. Not typically something desirable for anyone others than a criminal who wishes to sacrifice performance for concealment without having a registration."
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gnrb9k | Why do flying machines always have so many buttons and switches even in these modern times? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"There are good answers here but also consider the need for separate failsafe systems and redundancy. Tying together many functions through more consolidated interfaces also makes failure \"chokepoints\". You don't want a single broken screen/switch/button/sensor to have a pilot lose access to multiple controls/functions.",
"Because they are complex machines and to have control over it you need a lot of buttons. These days those buttons work not only as buttons but as indication too. That is very important for modern cockpits. Buttons are arranged as schematics of the certain system and they can be illuminated. Simply you can see eg. your fuel system scheme to be made of buttons just connected with drawn lines and when the button is dark you know everything is ok. When the button shows yellow (amber would be correct name for the colour) FAULT you immidiately knows that this fuel pump in this fuel tank feeding this engine is broken. When you push it it turns into white OFF and yo again know that this pump is turned off. It really depends how detailed answer you need and it can vary from type to type.",
"If something breaks in a car. You can turn off the engine and pull over to the side of the road. If something breaks in a plane and you're 20,000 feet up in the air, that's going to be a problem. You really want the ability to turn just the particular broken thing off and see if you can do without it until you can land. Otherwise the thing might catch fire. So you got a switch to turn off just that thing. It's based on things already going wrong, so your computers might not be working properly. So you want something simpler than that. Also, you might really want to turn it off quickly, and fumbling through menus is going to take a lot of time. If the thing is already on fire, then you really want to stop putting things into the place that makes the fire worse. So you got things that stop that."
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go0dh2 | - How does Lyft bike continuous gear shifting work? | I rode a Lyft bikeshare bike from a dock (in some cities it may be run by a different company) for the first time and was perplexed by the gear shifting. Rather than shifting up and down in steps like bikes I'm used to, the Lyft bike has a dial on the right handle that can be twisted at any increment and the resistance on the pedals changes smoothly rather than with sudden jumps of the chain. How is this possible? Is this some different kind of gear? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Its a CVT (continuously variable transmission) which uses a belt wrapped around two cones. By adjusting where the belt sits on the cones, the gear ratio changes smoothly."
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5
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go0m0w | What's the difference between the horsepower and break horsepower of a car? | I'm trying to get into cars but know absolutely nothing about them. This is my first question on the topic | Engineering | explainlikeimfive | {
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"Brake horsepower is the power measured by a brake type dynamometer, and its measured right at the crankshaft on engines Basically the engine is setup with an exhaust system, water pump, alternator, and all the standard components hooked up to it. crank shaft is hooked up to a Dynamometer instead of the transmission like it normally would be and the horsepower is measured that way. Its called a brake type dynamometer because it applies brakes until the spinning shaft reaches the target RPM. If it knows how much force is being applied by the brakes (torque) and it knows the RPM, then you can calculate the horsepower. Brake Horsepower is different from the horsepower at the wheels or under real driving conditions as there are other inefficiencies at play in the real world",
"Brake characteristics (particularly brake power and brake torque) are measured by an engine dynamometer, i.e. without all of the various parasitic losses associated with an automotive drivetrain (e.g. transmission, alternator, etc.). If you want to measure a *cars* horsepower (i.e. with all of those losses in place), you use a chassic dyno instead. It's called brake horsepower because of the way dynos classically worked; they basically serve as a brake for the engine in order to keep it at a constant speed. If the speed is known, and the torque of the crankshaft can be measured (typically with a torque transducer), then you know the brake torque, and can directly calculate the brake power. At the same time, the usage of the word \"brake\" is actually kind of a traditional term as braking dynos are actually being (kind of) phased out in favor of electric motor/generator dynos (which aren't considered \"brake\" dynos as they can also be used to drive the engine)."
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go85k8 | -What is a charge? | I hear it many trillions pf electrons but what about protons? What makes a charge positive or negative, is it the way they occupy space time? How many electrons or protons are in a charge. If I = Q/t what does that mean? | Engineering | explainlikeimfive | {
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"Charge is just a property of matter. Charge is measured a lot of ways, but it always is a multiple of the charge of 1 electron (or proton; they're the same, but opposite), which is called the elementary charge, or e. So, a simple way to measure it is to say a proton has a charge of 1e and an electron has a charge of -1e. An atom with more protons than electrons will be positively charged, and an atom with more electrons will be negatively charged. If they balance out, it results in a charge of 0e. The names positive and negative were initially just assigned arbitrarily and we keep them out of convention (even though it might actually have made some later discoveries a little more intuitive if they had been reversed, since a lot of electricity stuff deals with the movement of electrons). There's nothing about the charges that makes them inherently \"positive\" or \"negative,\" they just needed opposite names."
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gommi4 | How does the petrol pump know when my tank is full? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"There is a second smaller sensing tube going down along the main fuel filler. This have some small airflow through it from a pump in the handle which again is driven by the fuel flow. When the fuel comes up to this sensing tube it slightly changes the backpressure which will then trigger a mechanical device in the handle that shuts off the fuel flow.",
"There's a small inner tube in the nozzle, visible for example in this stock photo: URL_0 . This small inner tube goes up into the handle where it's connected back to the main petrol flow tube with a small hole. Thanks to something called the Venturi Effect, the fast flow of petrol past this little hole creates a suction force that pulls out air from the little tube to move along with the petrol in the large tube. Think of this as sucking air in through a straw. If the level of petrol in your tank is high enough, the entrance to the small inner tube will be submerged, making it harder to suck up more air. Imagine sucking air through a straw and slowly lowering it into a glass of water (or just blocking it with a finger) - once you reach the water it becomes much harder to suck it up the straw. Now this inner tube is also connected to a membrane in the handle that reacts to changes in pressure by bending. Once the petrol hits the tube, the membrane is sucked in and bends (as it is easier to move than sucking up the petrol through the tube), and attached to that is the hook that releases the handle. There's no sensors, it's all mechanical with some clever use of fluid dynamics."
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gon3ip | What is metal fatigue | How come you can bend metal back and forth and eventually break it. What is happening at a molecular level. How does movement allow for such weakening of certain metal (all metals? idk). | Engineering | explainlikeimfive | {
"a_id": [
"frgria8",
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"text": [
"As you bend the metal, the outermost region is being stretched while the innermost is being compressed. Metal is not very elastic, so this stretching and compressing breaks some of the molecular bonds. Each time you bend it, more bonds break until the entire thing snaps.",
"There are two types of \"bending\" in metal: 1) elastic and 2) inelastic. If you bend a piece of metal elastically, it springs back and it unchanged. This is how the springs on your car hit bumps for years and never lose their springy-ness. Inelastic bending leaves the metal \"bent\" afterward. This means the bonds are deformed and the atoms moved around. It also produces an effect called \"work hardening\". This means that the atoms are harder to move around after they've been moved once. If you do this over and over, the hardened parts of the metal focus the strain on the remaining parts, which causes bonds to fail and cracks for form. As the cracks spread, the metal fails and the item breaks."
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gorcun | How do barrel attachments on guns help control recoil? Or is this just a video game thing? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"What you're referring to is commonly known as a muzzle-break or compensator. These devices have channels cut into them to specifically vent some of the hot gases that escape the barrel in a direction that helps control the muzzle. Basically a gun recoils because of physical (every action has an equal but opposite reaction, bull goes away from gun, gun comes towards you). My venting some of that hot gas in the same direction that the gun is wanting to travel, the gas essentially becomes a little jet engine that pushes the gun back down. To see this in action, check out the below video. This Barret rifle has a muzzle break that vents gas out and to the sides, which helps push back as the rifle pushes towards the shooter with recoil. URL_0 That one is noticeable enough that you can be setting 10 feet behind the shooter, but in line with that muzzle break, and you'll feel a little tap on your chest."
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gouuin | Why is glass the dominant window material, as opposed to higher-grade plastics? | I understand why car windows should be glass, given the high speeds, and potential benefits in a crash. For home windows or buildings, I would guess that plastics might be more durable, longer-lasting, and potentially cheaper. I assume I'm wrong and someone must have put far more thought into this than me, so I'm curious to hear what that is. | Engineering | explainlikeimfive | {
"a_id": [
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"friuq2n",
"fri46qm",
"frivl9g"
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"text": [
"Glass is far more durable than any plastic, most significantly it doesn’t degrade due to UV exposure. It also does not let UV through which protects the interior. Items in plastic conservatories will bleach much faster than in glass ones.",
"Cause plastic starts scratching with the #3 pick, with deeper grooves on 4. While glass is more scratch resistant, starting to show scratches at 6, with deeper grooves with the #7 pick.",
"Glass is cheaper, and doesn't scratch as easily. Plastic is lighter, but considering the weight of things, it is a minimal amount of weight compared to the rest of the load. Glass doesn't deflect near as much under pressure, so when you have double or triple paned windoes with evacuated cavaties between layers the glass doesn't distort. Also, any idiot can scry glass.and replace a panel, much harder to DIY a plastic panel replacement. Hope that helps.",
"Windshields actually have at least one plastic layer sandwiched into it to keep the glass from completely shattering into thousands of free flying pieces."
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gowvtl | Why are air conditioners so heavy? | Engineering | explainlikeimfive | {
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"Air conditioners are heavy because they need 1. a relatively high pressure compressor which requires everything to be *very* solid on the inside to avoid failure or leakage. 2. a lot of metal to help condense the water vapor into a liquid 3. a relatively large motor to drive all this. 4. metal tubing to transfer all this All these parts often are best as heavier metals for better heat transfer and durability and they all require tight fittings to ensure it all works properly."
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18
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gp4h1k | What are the rudders on planes used for? | I sort of understand the other ones but don't really get what the rudders do. | Engineering | explainlikeimfive | {
"a_id": [
"frjoncs",
"frjp34j",
"frjovdu"
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"text": [
"Basically rotates the nose of the plane left/right while the wings stay level. Imagine balancing a toy plane on the tip of your finger, with your finger in the middle of the belly and spinning the plane left/right.",
"Ailerons control roll, elevators control pitch, rudder controls yaw. Coordinated turns require manipulation of all three.",
"Rudders are basically the handlebars on a bicycle. When you turn the handlebar on a bicycle, it changes the direction in which the front tyres point. Rudders to the same with and change the direction in which the nose of the plane is pointing. However, to turn a moving bicycle, you generally have to lean the bicycle slightly in conjunction with a slight handlebar turn and coordinate between the two. Same goes for a plane where rudders are generally used in conjunction with ailerons to make a coordinated turn"
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gp6966 | Why are there so many different screws with different screwdriver needed? Why cant it just be a Star Screw and you only need star screwdrivers? | Engineering | explainlikeimfive | {
"a_id": [
"frjzaht"
],
"text": [
"There’s actually several reasons. Torquing capabilities, cost of manufacturing, and difficulty of manufacturing. Flathead screws are cheap but can not withstand the torque that other screws can. Phillips head screws can handle more torque than flat head but do cost more to manufacture. Allen head screws can withstand even more torque but once again the cost of manufacturing increases. It’s an inverse relationship. Depending on the situation and clamping force required, each type of screw serves a purpose. If you’re sending a shuttle to the ISS you definitely want a screw that’ll provide adequate clamping force but the cost is very high. If you’re putting together a desk from Ikea, well...you don’t need a fastener approved by NASA nor would you want to accrue that cost. Hope that helps some! - Mechanical Engineer"
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27
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gp7zuj | Why didn't all the bomb tests during the Cold War set off a nuclear winter? | Engineering | explainlikeimfive | {
"a_id": [
"frk9kt8",
"frkdsks"
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"text": [
"There wasn't enough, they were spaced out, and they're detonated in remote, barren areas. If you have thousands of nuclear bombs going off at once in populated areas, there's more material that can be launched into the atmosphere.",
"In addition to all the answers about the spread out nature and the fact that many were underground a key factor is that nuclear winter theory was based on the danger of *burning cities*, not the exploding nuclear weapons themselves. During WWII scientists gained perspective on just how much soot can be put into the air by burning cities like Dresden as well as how that soot comes back down (or doesn't). Extrapolated out to a war where hundreds of cities around the world would be burning all at once because of a simultaneous nuclear exchange they concluded that there would be so much soot that a large enough volume would be pushed into the stratosphere to cause a 'nuclear winter', since once in the stratosphere the soot would takes as long as years to come back down, resulting in the sun being blocked out for a long time."
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gp9ols | What are we actually hearing when a house is "settling"? When hearing a crack or pop sound I've always heard this term. What is actually happening to create the sound? Could we see it occur visually somehow? | Engineering | explainlikeimfive | {
"a_id": [
"frkkp23",
"frl83xq"
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"text": [
"Mostly caused by soil expansion and contraction. The most common cause of the pops and cracks are the unevenness of the expansion causing uneven stress on the wood and other materials the house is made of. The best way to tell if this is what is causing it is to look at the corner of the door frames if there are cracks coming from the to corners it is evidence of soil expansion.",
"A house settling is caused by the weight of the house compressing or moving the soil below it over time as rain, temperature changes, etc loosen or compact the soil. But I don't think you can normal hear that process as it is hopefully quite slow. Houses did often groan, creak, or pop during sudden temperature changes, or when a heating system is warming up or cooling down, as different parts of the house expand or contact at different rates."
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gpd9ee | What did ancient underground cities use as a light source? Did they always have fire going all over the place? | Engineering | explainlikeimfive | {
"a_id": [
"frl5wfd",
"frl60qm",
"frm101r"
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"text": [
"Yes, and it was a constant fire hazard. Some places burned oil from animal fat, others just torches coated in pitch.",
"Yeah, usually it was torches or candles. some places they would even carve the bowls into niches in the wall, and fill them with oil, drop a wick in it and voila! instant wall sconce!",
"Eli5: what ancient underground cities? I know many old cities had catacombs , but never really heard of complete cities."
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gpi22c | When a new product gives 10-15 years part warranty, example washing machine with digital inverter, how do they measure that without actually observing it for that long? | Engineering | explainlikeimfive | {
"a_id": [
"frm1c4u",
"frm0ygx"
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"text": [
"My statistics professor had done warranty research for years, so I'm not answering first hand but he talked about it a lot, and Ill answer from my memory. 1. They have data from components that have existed in older models. 2. They build little devices that wear out pieces. Say they need to test a spring. They build a little thing that contracts the spring 100 times a minute and let it run until it breaks. That allows them to make educated guesses about the lifespan of the spring in normal use. All the estimates are combined into one number which they use to make profit and losses projections.",
"Well, as I understand it, they have a testing room. And they run cycles over and over again. Like constantly. And when the machine breaks down they kind of divide the usage into normal time factors that most people would use said product. So of course it isn't 100% accurate but a good guess."
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gpx67s | - how does cruise control work on a car? | Always was curious as to what parts of the car's engine were being controlled to make the car stay at an exactly consistent speed. | Engineering | explainlikeimfive | {
"a_id": [
"frpcjxh"
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"text": [
"Just the throttle is being controlled Cruise control on a car is a simple control loop. Above target speed? Reduce throttle Below target speed? Increase throttle. Continue until target speed is reached This is why you'll sometimes get sudden high revs when climbing a hill in cruise control because the engine didn't preemptively push the gas to maintain speed because it didn't know there was a hill"
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5
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gpydjk | What is happening when ships/tankers have water constantly flowing out of the sides of the hulls? | Is water intended to be flowing in from somewhere, and pumped out? | Engineering | explainlikeimfive | {
"a_id": [
"frpktoy",
"frpy92y"
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"text": [
"Sea water is used to cool the engine coolant and any generators too. Sea water cannot be used directly in the engines as it is corrosive , but is continually fed to heat exchangers and discharged overboard, keeping coolant fluid at the correct temperature.",
"There's a few sources of this water. It's engine coolant. Boats don't recirculate their coolant like a car does. They pump in cold water directly from whatever body of water they're in. This is also the reason why you'll see a stream of water coming out the back of jet skis and outboard power boats. Even the motors and electronics in small hobby grade RC boats are cooled this way. It's used for ballast. Large ships have tanks in them that can be filled with water or drained to help balance the ship. It's bilge. Water sometimes comes up the \"stuffing box\", the tube that separates the interior part of the prop shaft with the part in the water outside. Normally it's filled with grease, but some water will work its way in over time. Water will also ingress in rough seas, rain, or through small leaks. It's collected in the ship's \"bilge\", tanks at the bottom of the hull, where it's pumped out. Wastewater - Yep, sometimes it's good old fashioned sewage. Newer cruise and military ships will treat the water first. So it's more grey water that's being ejected. Small boats will out pump their sewage tanks at marinas. Though many ships, including large passenger ships, do still eject their raw sewage into the ocean. However, they're prohibited from doing this in port."
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11,
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gq0khk | In low visibility conditions, why can’t a helicopter just inch down vertically until they hit the ground? | Title pretty much says it. I used to do helicopter work and obviously visibility was our top priority. If there was even a threat of losing it, we weren’t going up. Given that helicopters can hover, why can’t they move down slowly in a vertical position until they hit they ground lightly instead of running into mountains in a low visibility situation? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It’s not just vertical movement you need to worry about. If you’re clear just below you, then a gust of wind pushes you into trees, you’re fucked. Or if it looks fine, but you didn’t notice you’re about to lower your rotor into a building or lamp post.",
"Not practical. You don't know what's around you. It isn't just what's directly underneath you that matters. Here's an example. One issue helicopters may encounter when trying to hover is called *vortex ring state*, which results in severe loss of lift.\\* The primary way to get out of this state is to re-establish forward flight. Imagine you're hovering, going down slowly, and suddenly feel a loss of power. You adjust the cyclic control to angle the rotors, pitch the nose down, and attempt to re-establish forward velocity. You start moving forward and...WHAM! You've just crashed into a tree that was hidden by dust or smoke in front of you. That's just one possibility among many. Helicopters are pretty incredibly complex and hovering alone is pretty demanding. It isn't just a matter of putting out exactly enough power to not fall; if you want to hover a little higher or lower you would raise/lower the collective to induce ascent/descent, but then that increases/decreases air resistance on the main rotors. This makes the fuselage of the helicopter want to start yawing, so you also have to apply pedal to increase/decrease pitch on the tail rotors as well to prevent that. But then, because the tail rotor faces sideways, changing its thrust output can make the helo drift sideways a little (this is called *translation tendency*), which you then have to compensate for with the cyclic. You can see pretty quickly that a hovering descent doesn't automatically mean zero lateral velocity. Drift happens. It is very much more about constant correction for constantly-changing circumstances than anything else, so going perfectly straight up and down isn't always possible or practical. Plus, at low speeds and in low-vis conditions, you might not even notice you're drifting until you hit something. If you don't know the terrain and the surroundings, you might get blindsided by something. No bueno. ^(\\*In a very simplistic nutshell, the main rotors push air down which then gets sucked back up only to be pushed back down again. Just like how you can't pick yourself up off the ground by pulling yourself upward by the scruff of the neck, a helo can't stay in the air by just recycling the air it's pushing down, so it falls.)",
"I'm on mobile so I'll give a very short answer. The reason is spatial disorientation. At low speed in low visibility you cannot tell exactly what the helicopter is doing and your inner ear conflicts with what your eyes see."
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gq3ryc | How do bicycle gear shifters work? | Engineering | explainlikeimfive | {
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"frqj2it",
"frqjk5k"
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"text": [
"Answer: As you turn the gear shift thingy it pulls on a metal cord. That metal cord pulls on a “guide” that surrounds the chain. Depending on the way you turn the gear shift thing, the guide moves closer or farther away from the tire/frame of the bike. This pulls the chain in a horizontal manner which cause it to skip off of the current gear and get caught on the next one. Those black plastic tubes that usually run down the frame of the bike house the metal cord. Sorry for the lack of terminology, I know how it works but I’m not a bike mechanic.",
"I can't tell you how certain three-speed hubs work, but most multi-gear kinds are really pretty simple. The chain runs through a derailleur which is a pair of guide wheels. These wheels have a spring action which takes up slack in the chain when it's on the smaller gears. Also, the derailleur is made so it can move inward and outward. This is controlled by a cable connected to the shift lever. Moving the lever moves the derailleur in or out, which moves the chain from one gear to another. A similar device moves the chain from one chain ring (front gear) to the other on the crank set."
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gq45n6 | Why is it bad to dry fire a bow? | Engineering | explainlikeimfive | {
"a_id": [
"frqmppw",
"frqjvku"
],
"text": [
"When you draw a bow, you load it either energy and the arms curl in. Letting go means the the arms snap out. If they snap out too fast, they can overextend and crack. The weight of the arrow slows down their snap back and absorbs energy. Without that arrow, they can snap back much harder.",
"The energy that usually propels the arrow forward instead travels through the limbs and can cause breaking."
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gq67hn | Why do door hinges squeak louder the more slowly you move them? | Engineering | explainlikeimfive | {
"a_id": [
"frqweku"
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"text": [
"The squeak is due to the surfaces alternately sticking then slipping. The faster they're moving the harder it is for them to stick."
],
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7
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gqgelg | Why do pipelines have U shaped bends every now and then? | Wouldn't that make impossible for "pigs" to go trough resist flow, make cavitation acumulate grime and other piping problems? Surely they have a reason to be but I have no idea what it is | Engineering | explainlikeimfive | {
"a_id": [
"frsj6rv",
"frsjfqg",
"frskost"
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"text": [
"As the horizontal pipes expand and contract with temperature changes the U sections can flex to absorb the length changes.",
"What you describe sounds like a water trap. Every sewage pipe have a water trap before it is exposed to the inside of a house. As the name suggest these trap water so that there is no contact between the air in the sewage pipe and the air in the living space. This ensures that the smelly gasses from the sewage will not seep into the living space and make it smell like sewage. These water traps is usually detachable so that if you need to maintain the sewage line you can remove the water trap.",
"As somebody that has worked in the design and construction for the Oil and Gas industry in Canada for years, I can say that /u/old_liberal is correct. These are for thermal expansion. You may understand that some items increase or decrease in size as the temperature changes. This also happens with steel, and is captured with 'bends' or larger elbows (usually 3x or 5x the diameter of the pipe). This will permit the 'pigs' to still pass through the pipeline to either clean or inspect (most inspection pigs would require a minimum 5D bend (5x diameter of pipe). Let me know if you have other questions, as I no longer work in O & G but I still enjoy the design of the systems."
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gqgl6p | Why are car tires filled with air and not just made completely of rubber? | Engineering | explainlikeimfive | {
"a_id": [
"frsjzig",
"frsk33o",
"frsktly",
"frskv68"
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"text": [
"Air provides a cushion on which the tire can absorb impact, move laterally in turns, and decreases rolling resistance. If they were solid rubber, they would have very little pliability, would be extremely heavy, and wouldn't be able to be patched/repaired. I'm sure they would be a great deal more expensive too. Google \"tweel\" to learn more about alternative to air tires.",
"A fully rubber tire would be heavier. A heavier tire means it takes more energy to make it speed up, but also more energy to make it slow down. This means that it will take a longer distance to brake. In addition, the air in the tires acts to absorb minor bumps in the road, along with your shocks. Solid rubber tires can't really deform as much, so you'll feel every bump full on. Also, they would be significantly more expensive.",
"There are actually designs of no-air rubber tires, so it is a relevant question. There are several factors: Cost (current design is cheaper) Performance: most people don't stop to think just how awesome is that tires can take a beating for literally thousands of km. It's harder for no air tires to retain their properties for so long. Also it's hard to beat air tires in shock absorbance.",
"Your tire is an air spring that softens the ride and allows the tire to deflect - to bend to the shape of the road, increasing surface contact and thus traction. By being solid, deflection would be minimized and traction would be greatly reduced, and the rid would become very uncomfortable. Further, the weight. Not only would such a tire be outrageously heavy, but it would put additional strain on the materials used to hold the tire together, as well as on the suspension. Just keeping that much rotating mass attached to the car would require much, and I mean much larger structural suspension components, which would make the car heavier. You'd need larger springs, larger shocks, and they'd all take on WAY more load and wear. You'd need MUCH larger brakes, and they'd be drum brakes like you'd see on a semi, just to stop your car, which comes with more weight and greater maintenance and material costs. It would take a lot more energy to accelerate the vehicle, you'd generate a lot more heat just trying to stop it, and you'd have lots of problems with inertia, not just within the wheel itself, but also in suspension travel, and the whole car. Your fuel economy would tank."
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gqqt2g | How does velcro lose its adhesiveness? | Engineering | explainlikeimfive | {
"a_id": [
"fruc5ii"
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"text": [
"Velcro works by having a bunch of teeny tiny hooks hook around a bunch of teeny tiny loops, so the two surfaces “stick” together. With extended use, the repeated attaching/detaching of the loops and hooks causes the hoops to stretch and break, so the hooks can’t get a very good grip on them anymore. When this happens the Velcro loses its “sticky” property. Also, annoying things like dust and lint can gather between the components and reduce their ability to interact."
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gqu77o | Why some SUV's and pickup trucks have air dams under their bumpers? | Engineering | explainlikeimfive | {
"a_id": [
"fruxjyp"
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"text": [
"I'm an auto body tech and have taken apart many front ends of cars. If you are talking about the slats in front of the condenser they just help with directing air."
],
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4
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gqw8c0 | How do tunnels prevent deadly carbon monoxide buildup and why is it that many garages aren’t built the same mechanism? | Engineering | explainlikeimfive | {
"a_id": [
"frv5s7c",
"frv6o2s",
"frv5v94"
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"text": [
"Road tunnels have a giant hole at either end at often large fans to keep air moving. Many garage owners want their garage to have walls on all sides, a roof, and a floor, leaving no room for giant holes. Many home garages do have at least one giant hole making carbon monoxide build up impossible.",
"Tunnels have huge ventilation fans every few hundred meters to ventilate the tunnel. There is often seperate ventilation shafts for longer tunnels allowing for better ventilation throughout the tunnel. Garages built as workshops do have similar ventilation systems as it is required for mechanics to be able to work on cars safely. However if a garage is built as storage then this is just a waste of money and resources.",
"Through designed air moving ventilation ducts. Garages are not designed this way because the gas load is only short term"
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gqykar | What's the difference between turbofan engines and turbojet engines when built into a supersonic aircraft? | The Concorde had 4 Olympus 593 turbojet engines and the Tupolev 144 had 4 Kolesov RD-36 turbojet engines. The upcoming supersonic aircraft, the Boom Overture, will be a trijet turbofan aircraft. How are these engines different from one another in terms of power, thrust, and efficiency? | Engineering | explainlikeimfive | {
"a_id": [
"frvkjcv"
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"text": [
"a turbojet burns fuel and uses the hot exhaust as thrust. a turbofan burns fuel and uses the energy to turn a big fan in the front as thrust. turbojets make more thrust and high speed but at low fuel efficiency, that's why they're used for combat aircraft. turbofans are used for lower speed and higher fuel efficiency, used on commercial and transport aircraft."
],
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9
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gr40q9 | How do fiber optics transmit data using light? | I understand how light physically gets from one place to another, but how does the other end know what data is being sent? | Engineering | explainlikeimfive | {
"a_id": [
"frwj40t",
"frwjjp1",
"frwk7m5",
"frwlsn5"
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"text": [
"Through pulses of light. The transmitter flashes the light on and off and a sensor on the other end picks it up - much in the same way that an electric signal turns on and off to transmit data through a USB cable.",
"Every time step (which is probably in the neighborhood of nanoseconds) the light receiver records if it sees light coming out of the optic fiber. If it sees a light on, mark down a 1. If it sees it's off, mark a 0. In such a way, it can transfer any series of 1s and 0s. Nearly every modern digital file is in binary, meaning it's a long series of 1s and 0s that computers know how to translate.",
"Imagine we're in opposite ends of a dark tunnel. We both have a flashlight. Before we went in though we agreed that we would follow the standard morse code to communicate. So if I want to send SOS (the only thing I know) I blink 3 times fast, 3 slow, 3 fast. Since we agreed beforehand I know how to send you a message and you know how to interpret it. It's the exact same thing in networking.",
"The Information being transmitted over most networks (including fiber) is binary (1’s and 0’s) and each blink of light represents one of the two. There is quite a bit more to how it all works, but to ELY5: You send a message to someone The message is converted from text to binary (010010100101110100101...) The data is sent over several different networks in the following format: [info on where the data is going, what type of data, if it can be lost or must be delivered complete, etc.] (your message) The data transmitted may change mediums several times during transit (fiber, Ethernet, cable) but in the end it’s always just 1’s and 0’s. (Sorry for formatting, typing this from a phone)"
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gr58q5 | why do guitar pedal clones of super famous (like Klons) never sound the same even when they are made with the exact diodes, capacitors, etc? | Engineering | explainlikeimfive | {
"a_id": [
"frwz6u8"
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"text": [
"Ahah finally one for me. I build guitar pedals and usually the older ‘vintage’ pedals that are commonly cloned used parts from that era. These parts are now harder to source but still can be found. Usually more modern parts are used as replacements and get a very close sound but to get the exact sound, you would need to use all of the era-specific parts. This is because the sound you hear from the pedal is just the guitar signal being put through a series of components that cause resistance (ICs are an exception) and any small difference will affect this resistance."
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gr67qs | Why aren't any small engines like generators pressure washer etc, quiet like a car engine? | Engineering | explainlikeimfive | {
"a_id": [
"frwxfrk",
"frwy109"
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"text": [
"Car engines aren’t quiet by any means. Pop the bonnet, and kick the throttle: it’ll make a racket, just like any other combustion engine. It only seems quieter because of acoustic insulation of the engine bay, and isolation of the passenger compartment.",
"A car is an expensive piece of machinery that is trimmed to be as quiet as possible while being ok reliable. A generator is an reasonably priced piece of equipment that's trimmed to be incredibly reliable and sturdy and to have good economy. Generators are missing things a car has, which are: a long and precisely engineered exhaust for quietness, advanced engine mounts that reduce vibration, extra balancing shafts that cancel out vibration, and especially lots of insulation against sound. Whoever uses machines like these is aware that it will be loud, but reliable and effective, and manufacturers know that."
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gravlz | How can a vehicle in extremely hot conditions remain cool enough to not overheat. Also how much of a strain is put on vehicles due to high temps and having to keep from over heating? | Engineering | explainlikeimfive | {
"a_id": [
"frxsh5e",
"frxshbb"
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"text": [
"Vehicles have cooling systems. They usually use liquids like water or antifreeze that run around all the parts that could get hot, run to a piece called a radiator that spreads out the liquid and blows air on it pushing most of the heat out of the engine area. The heat from the engine is extremely high so this system doesn't have to work that much harder if its hot outside. At a certain point though it absolutely will stop working, its just higher than what we consider extremely hot to us. In summary they don't, extremely hot for a vehicle is just much hotter than what is extremely hot for a person",
"because of the cooling system. you can overheat a car in extreme heat conditions. the car cools itself by pumping water to the engine and extracting that heat into the water then getting pumped to the radiator to dissipate off into the airstream. if the water pump or radiator is not functioning at enough capacity, the engine will overheat and damage itself, possibly catastrophically. in addition to airflow from car movement, there is also a fan that can be triggered by the car computer. if that fan fails, again you have possibility to overheat"
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grjs1c | How do dehumidifiers work? | How do dehumidifiers take the humidity out of the air? Why does the water not eventually go back into the atmosphere of where you have the dehumidifier? | Engineering | explainlikeimfive | {
"a_id": [
"frz74hs"
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"text": [
"Air can only hold so much water, and it can hold more when it’s hot and less when it’s cold A dehumidifier simply gets cold so the colder air can’t hold the water anymore and it condenses out There is nothing stopping the water from evaporating again, but the dehumidifier pulls water in faster than it can evaporate"
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grk4f1 | When something falls into a drilling hole on an oil rig, why is it so catastrophic and expensive to fix? What goes into fixing it? | Engineering | explainlikeimfive | {
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"Drilling into the ground for oil or gas is expensive. If, during a bit change or other time there is an open hole, a piece of metal falls in, it can damage the tri-cone or hammer bits used to do the drilling. The carbide buttons on the bits do the work, and are very hard, but brittle. Metal in the hole can snap these and slow or halt the drilling process. A bit can cost around $2000 per inch of the diameter of the bit. Sometimes, the bits can fail if the bearings go out, due to too much weight put on them, or from a manufacturers defect. The entire drill stem needs to then be \"tripped\" back out of the hole, to gain access for what is called a \"fishing trip\", where magnetic ended, barbed, or other means of grabbing what fell in or fell off back up out of the hole. At any time, there are 2-4 large diesel engines running on a rig, to drill, pump fluids, or to compress air for drilling purposes, which can use around 55 gallons or more of fuel per hour. That fuel cost, plus cost of the 3-5 man crew, the waste of time for the setback, the possibility of a downhole pipe casing cementing crew being on location and on hold due to unforseen problems like an idiot dropping a pipe wrench down the hole when breaking apart a flange on the casing and leaving it in a precarious spot...wait time and fishing trips can cost hundreds of thousands of dollars in added expense."
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18
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grl5pq | Why is the grill on the back of a refrigerator really hot? | Engineering | explainlikeimfive | {
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"The grill is hot because that's where the heat is going. A refrigerator works by moving heat from one place (the inside of the refrigerator) to another (the outside of the refrigerator). Thermodynamics says that this process cannot be 100% efficient (moving heat from the inside of the refrigerator to the outside requires a work input) so moving 100 joules of energy from inside to outside will actually put close to 200 joules outside. That is why the back of the refrigerator is hit and why you can't cool down a room by opening the refrigerator.",
"The refrigerator is moving heat from inside the fridge to outside. The thing at the back of the fridge is where it gets rid of the heat from inside the fridge. The heat gets inside the fridge through the insulated walls, in the warm air when you open the door, and when you put warm food or drinks in the fridge. The fridge will not have to get rid of so much heat if the walls have thicker insulation. Choosing a fridge with better insulation will reduce your electricity bill and the back of the fridge will not get so hot. Letting hot food cool down before you put it in the fridge will have the same effect - all that heat you put into the fridge will have to be moved out of the back of the fridge. If you look at the back of the fridge you will see the \"grill\" thing that gets hot has got little tubes going through it. The tubes at the top have gas in them and by the time the gas has gone through the tubes to the bottom all the gas will have turned into liquid - the gas will have condensed - like when the clouds rain. The tubes at the bottom only have liquid in them. The proper name for this thing is the \"condenser\". When a gas is close to becoming a liquid it is usually called a vapor rather than gas, but that's the same thing really. And we sometimes call the gas/liquid/vapor a \"fluid\" because it gets boring writing gas/liquid/vapor and we sometimes don't want to say if it is gas or liquid or mixture of gas and liquid etc. \"Fluid\" is just a name for something that can change shape to fill a container. The tubes are sealed in a loop that goes inside then outside the fridge. The same fluid goes round and round and round the loop for ever. It changes from liquid to gas to liquid to gas etc. If the tubes ever leak the fridge will stop working. We call this fluid a \"refrigerant\" because it is the fluid that moves the heat out of the refrigerator. Inside the fridge there is another thing like the condenser. This has tubes where the refrigerant evaporates from liquid into gas. This is called the evaporator. It's usually very cold and sometimes gets ice on it. The ice is water from the air like when it snows or gets frosty. The liquid refrigerant goes into the tube at the bottom of the evaporator and by the time the refrigerant goes out of the tube at the top of the evaporator it will all be gas. Both the condenser and evaporator have a large metal surface to let the heat transfer quickly to the refrigerant. This allows the fridge to cool things quickly and makes the fridge more efficient. Allowing the air to move past the condenser and the evaporator will make them work better. If you block the air flow over the condenser at the back of the fridge - or if it gets clogged with dust - it will get hotter and the fridge will use more electricity because it will have to work harder. The refrigerant gets pushed through the evaporator and condenser - round and round the sealed loop of tubes - by a thing called the \"compressor\". You might be able to see the compressor in the back of the fridge - a round black thing with tubes connected to it. The compressor also makes the pressure of the refrigerant higher in the condenser and lower in the evaporator. The higher pressure makes the fluid change from gas to liquid at a higher temperature. So the condenser has a higher temperature than the evaporator and it gets rid of the heat from the fridge into the air in the house.",
"It's where the thermal energy from the inside moves to. Using a compressor, the air from the inside is compressed, which makes the temperature hot. Then the heat is radiated away via a radiator, clever huh. Then onces the air becomes cool inside of the compressor, the air/coolant is decompressed, which chills the air/coolant inside, providing a \"cold source\" to cool the rest of the air inside the refrigerator."
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grokvr | How does water-resistant technology work? | I just saw an ad for the new iPhone that said it was water resistant "for up to two meters for 30 minutes". How does that work? I assumed that the depth thing was always a mater of water pressure but I never got the time limit, like the phone can tell when it gets wet and starts a timer, and when time's up the floodgates just open and destroy the phone or something. | Engineering | explainlikeimfive | {
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"The seal isn't perfect. At two meters, the seal is under enough pressure that some water will slowly make its way in. However, the tolerances of the electronics can deal with a small amount of water vapor. However, the longer it is under, the more water will make its way in and the more likely it will interfere with the electronics.",
"It's important to keep in mind that the [IP rating]( URL_0 ) is a guarantee of how much ingress the device can survive. Not a direct reflection of the amount of ingress. The seals are not perfect, as someone else has already pointed out. The tests for an IP rated device will have shown though, that it can survive for 2 meters, for 30 minutes. After that, there may or may not be too much liquid in the device to survive the submersion.",
"The phone is probably sealed and has a really good SIM card/microSD port closing sistem Since it's sealed, the only problem it has with water is pressure, if it gets too deep (+2mts in your case) the sealing breaks quickly, and if it lasts too much under relatively high pressure (those 30m), consider pressure as a consistent damage to your phone, it's low damage but if you give it some time, well your phone sealing breaks too The reason a phone doesn't last as much as anything else underwater is that each port has to be well sealed, and weight, carrying a 1kg water resistant phone is not a good idea"
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grrq5j | How does weather affect a rocket during launch? | I just saw that the SpaceX/NASA launch was cancelled due to "bad weather". This isn't the first time I'm hearing about bad weather stalling a rocket launch. The Falcon Heavy unmanned launch was also on alert for unfavourable weather. How exactly can a bit of bad weather influence something as mighty and powerful as a rocket? | Engineering | explainlikeimfive | {
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"There are a few big factors that get them 1. Ground level winds - a Falcon rocket isn't permitted to launch if the wind at the launchpad is over 35 mph. When the rocket is traveling slowly at ground level the winds can cause significant tilt or drift of the rocket 2. Upper level wind shear - [Musk was nice enough to tweet a plot of the upper level winds for one scrubbed launch]( URL_0 ) and you can see that at 10 km the wind gets up to 70 m/s (156 mph). That speed of wind alone isn't a huge problem as the rocket is traveling around 2000 m/s at this point, but you can see that from 8km to 10km the wind went from 30 m/s to 70 m/s, this quick change in the wind speed is called Wind Shear and means that the top and bottom of the rocket are experiencing different wind levels which can cause it to tilt beyond what it can correct for 3. Launches near thunderstorm clouds - Those towers around the launch pad are lightning rods designed to protect the rocket while its sitting there, but once it gets off the pad it becomes a fresh target. You don't want to launch and have a lightning bolt pick your rocket. It might be alright, but if you can just wait until a sunny day that's a much safer option 4. Thick clouds - They have restrictions about launching through thick cloud layers that extend up to freezing temperataures because you could build up an ice layer on the rocket. Rocket flight profiles rely on knowing the exact weight of the rocket and power of the engines. Picking up 500 pounds of ice on their way through the clouds will change their flight profile and could have ice chunks break off and damage the rocket. Most of these things come down to \"Could this might maybe possibly be a problem? Yes? Cool, Saturday looks sunny lets do Saturday.",
"Something as mighty and powerful as a rocket must maintain an extremely precise flight path for insertion into the proper orbit. There are weather parameters (usually wind speed, but also turbulence, visibility, and others) that affect whether or not the rocket can safely to what it needs to do. If the weather is outside of the limits set for the launch, the launch is scrubbed.",
"If the rocket is flying through said weather it can interfere with visibility and communications. It just adds too much risk compared to a day with clear skies.",
"The reasoning was something along the lines of harmful electrical fields in the clouds that could pose adverse effects on the launch. Better be safe than sorry. Don’t want all the computers on the rocket to malfunction and cause issue.",
"Ths problem for this flight was a risk or lightning strike that could hit the rocket and damage or destroy it. Apollo 12 was hit by lightning and the primary radio system was if I remember correctly. If the could have launched 10 minutes later it might has been ok but you have to launch on the correct moment to get to the space station. To high win can also be a problem that stops a launch. It is especially wind shear, rapid changes in wind direction in the air that can be a problem & #x200B; For crewed launches, you need the wether in the possible emergency landing sights to be good enough. You do not what to try picking up a capsule from the sea in a storm. This is not just off Florida but also around Nova Scotia and even Ireland because if there is failures in the flight you might land there. For Falco Heavy the center stage attempted landing on a drone ship so the sea has to be calm enough where it is. The first stage of the Falcon 9 that would be launched today will attempt land on drones too. So if there is some risk of failure you abort the launch because you can always try again later. Arriving on the space station 3 days later is better the risking never getting there. A delay costs a lot less than a failure.",
"There are many different ways. Most famous was the Challenger disaster which was the result of cold temperatures making a rubber seal shrink and stiffen up so it did not work. The launch was initially successful though with sot and debris from the rocket sealing the rocket in place of the rubber seal. However they experienced another weather event, a wind shear, further into the flight. This put a lot of sideways forces on the rocket shaking the plug loose allowing hot exhaust gasses to escape and destroy the spacecraft killing all crew. The weather conditions that were worst today was the buildup of electric charge. This is what happens before a thunderstorm. Even though lightning was very unlikely the rocket exhaust is very electrically conductive as it is a plasma. So the already tall rocket would be much taller once it have launched. This can make lightning strike the rocket even though lightning would not have struck the ground. Apollo 12 experienced this during launch which disrupted several electrical systems including the three redundant power generators on the spacecraft. They were seconds from aborting the lunar landing before they were able to find a way to work around the problem by flipping the now famous SCE switch to the AUX position. Once in orbit they had to conduct further repairs and start the power generators again before they could head to the moon. The Dragon spacecraft and the Falcon rocket is not designed to handle such lightning strikes and they did not feel like risking the lives of two astronauts by flying the rocket into a situation it was not designed for. A big reason for the Challenger disaster was that they were flying it into conditions that they knew the spacecraft were not designed for and the components had not been tested for those conditions."
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gs94e0 | Why was the Demo 2 launch window "instantaneous"? | If I understand the default parameters correctly, they were going to do a couple of orbits with one burn before arriving at the ISS. I'm obviously not an expert in orbital mechanics, or I wouldn't be asking the question, but, in my naivete I don't understand why they couldn't adjust for a later launch time. Is it a lack of fuel in the 3rd stage? | Engineering | explainlikeimfive | {
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"The ISS doesn't orbit around the equator. It's not quite a polar orbit, but it's North-South enough that it can pass over Argentina and Russia in one loop. It takes about 90 minutes to make an orbit, and the earth continues to rotate beneath it as it orbits. That means by the time it comes back around to the USA after one orbit, it'll probably be flying over a different time zone than it was in the previous orbit. That's a huge difference and it wouldn't be practical to include the mass of that much extra fuel.",
"The Falcon 9 is only a two stage launch vehicle. It's because they're sending people up into space, and they want to minimize the amount of time it takes to reach and dock with the ISS. Even though a few minutes might not seem like a long time to us here on earth, the ISS is traveling at over 17,000 miles per hour, so even if they delayed it by ten minutes that would mean re-adjusting launch trajectories, require more fuel, and a longer flight time (which is already pretty long, at 19 hours)."
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gs97d1 | If alternating current goes both ways, why do some plugs only allow you to put them in one way? | Engineering | explainlikeimfive | {
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"text": [
"Safety. AC (hot wire) goes both ways, but it needs a center point to push-pull against. We call that center the \"neutral\" wire, which goes back to the power station, but also to earth-ground. The metal cases of appliances also have a grounding/bonding wire, so that if a wire ever came loose inside the power would go to ground through that wire, instead of through you when you grab the handle. That's different from the neutral though. The neutral and ground are connected, so that the center point \"neutral\" can't float to some undefined value, with the hot going along for the ride. Why it might float is beyond what I can explain here. Reversing hot and neutral would connect the case of the appliance to power, through the neutral-ground link in your power panel. Risk of death. Some appliances don't have a ground and the hot and neural can be flipped because there's no metal casing or polarity sensitive devices inside (some kinds of motors care about polarity, etc.)."
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gsa1ea | Why does rebar or other wire/steel strengthen concrete? | Engineering | explainlikeimfive | {
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"Concrete is really good at deal with compressive forces, you can put a massive amount of weight pushing against concrete or cement and it will be fine But what if you were to make a cement house? Well it can take the weight of the walls pushing downward, but the walls may also want to lean out a little bit meaning that the corner experiences a pulling force rather than a squishing force that its good at and you get cracks This is where steel comes in. Steel has really good tensile strength meaning its great at resisting those pulling forces without breaking. The combination of steel and concrete gives you something with good compressive strength (concrete) and good tensile strength (rebar/steel)",
"Concrete is very, very difficult to compress. It can be broken, if the concrete is put in tension. When you have a beam that's carrying a load, the top side is being compressed but the bottom is in tension. Steel is very strong in tension, but it can be bent. Steel in concrete is the best of both worlds. The steel takes the tension load, so the concrete doesn't crack, and the concrete prevents the steel from bending because to bend the steel you'd have to compress the concrete."
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gsbdqt | Is there a physical limit to the size of a single CPU core? | I was reading online that CPU cores can be less than a square millimetre per core. I'm wondering if we are going to reach a limit with how small we can compress them. | Engineering | explainlikeimfive | {
"a_id": [
"fs44cxq"
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"text": [
"We already have reached (in lab experiments) the limit for how small a transistor can be before quantum mechanics take over and electrons are as likely to pass through an off transistor as an on. With transistors that size, the lower limit to the size of a CPU core depends entirely on how many transistors you want in it. The upper limit to the size of a CPU core is generally set by how far an electric signal can travel in a single clock cycle. For a 3ghz processor this is about 6cm. Edit to add: the limit of the size of a transistor is the size of a medium sized molecule, so the limit for how small a CPU core can get is probably around the size of a virus as long as you don't need it to do anything but basic arithmetic."
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13
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gsbl83 | Why can't a fridge be laid on its back? | Engineering | explainlikeimfive | {
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"text": [
"Leaning a fridge over on it's side can cause fluids like the refrigerant and oils to move and pool in the wrong place. If you tilt over a fridge to move it it's recommended to leave a fridge standing up 24 hours to let the fluids settle back to their proper position to prevent damage. Fridges also have a number of sensitive components, leaning one over risks damaging the fluid pipes and a radiators."
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15
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gsclm0 | How does street paving work? | So, every time you drive on a road that is newly paved, but not painted. I see these white tabs sticking up. I know they'll eventually make the lane markings. But, they are never straight. & #x200B; How on earth do these tabs create lane markings and are decided upon? | Engineering | explainlikeimfive | {
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"text": [
"The tabs are just a placeholder, so people can still drive before lines are painted. The actual painting is done by a paint truck later, it may not follow the tabs. If you look closely, you may see some faint chalk stripes where they want the paint to go, that’s laid down using chalk lines. Basically a string thats covered in chalk. They stretch it between two points, pull it back and let it snap against the ground. The painters will follow those markings."
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4
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gsg0q8 | In a normal piston-cylinder combustion engine is it more beneficial to have a larger bore and fewer cylinders or smaller bore with more cylinders? or does it cancel out? | Engineering | explainlikeimfive | {
"a_id": [
"fs50kla"
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"text": [
"It really depends on the application. Surprisingly there is no overall optimal engine design. Every engine makes tradeoffs. This one might be small, light and powerful - but it's expensive and doesn't last long. This one might be super efficient, but isn't very responsive. This one might be amazing in all aspects, except its really polluting so needs an expensive aftertreatment solution. Generally: A long stroked engine with fewer big cylinders can be more efficient and produce a decent amount of torque at low speeds for a given displacement (Big truck diesel - lots of torque and good efficiency) A short stroke engine with more little cylinders can rev fast and be power dense, but sacrifices low speed torque and often doesn't last as long. (motorbike - lots of power from a tiny engine). A short-stroke big cylinder engine is unusual. The reciprocating mass is too high to rev it fast, and you don't gain the efficiency benefit of the long stroke. A long stroke small bore is difficult/impossible to make because the conrod hits the cylinder wall. Then there are considerations like low cylinder counts are quite unbalanced and don't sound great. This is why car engines are generally 3 or more cylinder."
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11
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gsgto5 | How are bridges over a river built? More specifically, how are the pillars that end up in the middle of the water built? | Engineering | explainlikeimfive | {
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"text": [
"They build walls around the area in the center of the river and then they pump the water out , that allows the construction crew to lay foundations and pour concrete",
"They build a big barrel in the water by driving a bunch of pieces of metal into the mud at the bottom and locking them all together. Then they pump all the water out of the inside of the barrel so they have a dry area in the middle of the river to start building. It's called a cofferdam. It's pretty scary looking, but they've been doing it for a long time, so I guess it works."
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gsm92x | how do pens work? Like, how does the ink get out and how does the ink stay in the pen and not slosh around in it? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"There’s a small metal ball(smaller than a BB for a BB gun) on the writing end of the ink cartridge, it holds the ink in and when drug against a surface the ball rolls, grabbing ink as it does and laying it down on said surface."
],
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8
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gt1u2q | Why are rockets so difficult to successfully launch into space? | Not sure if the flair should be physics or engineering. So the recent Space X and other space launches in the past have been aborted due to weather or mechanical issues even after years of prep work. I'm not a rocket scientist (obviously) but why does it seem so incredibly complex to get a rocket or ship into space?? | Engineering | explainlikeimfive | {
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"text": [
"It's not hard, unless you want 100% chance of success. When NASA has cut corners, launching at temps a little lower than they had test data for, they've had things like the Challenger Disaster. After killing the \"First Teacher in Space\" and Greg Jarvis (who was a work colleague of mine) it doesn't look like NASA's going to be pressing the edge of the weather envelope again on a manned mission for a while",
"This was said recently in a similar question: This is an example of existential risk. Would a tornado have hit the SpaceX launch pad while the astronauts were in the capsule? Probably not. But the damage could've been total and complete obliteration of not just the rocket and the astronauts, but the very *concept* of manned spaceflight itself. NASA would be grounded for years. SpaceX would go out of business, period, or be so harmed in the public eye as to never recover in the same way. You get to launch the rocket only *once*."
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gt7uxw | How do they discover ancient ruins underneath the floors/foundations of buildings? Don’t they have to do soil bores before laying the foundation? Wouldn’t they dig down to pour the concrete footings? | Like this: [Link]( URL_0 ) | Engineering | explainlikeimfive | {
"a_id": [
"fs9ybtd"
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"text": [
"In a lot of places, and for a lot of buildings, digging a few feet down to the compressed dirt beneath the topsoil is enough, and no footings are added. Even when footings are used, they may be pounded in place, or any bored-out material may not be examined. Archeology is probably not on the minds of most as they finally get their product underway. Certainly in some cases, they may even turn a blind eye to some artifacts to avoid delaying or stopping expensive projects on a tight timeline."
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6
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gt8vom | ] Why do all self-assemble furnitures use hex screws? How are they superior to flat head or Philips screws? | Engineering | explainlikeimfive | {
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"fsa49wn",
"fsa4nt2"
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"text": [
"This is actually a very simple answer. It is simply because it is much harder to strip hex screws. More points of contact = more torque for tighter fit. This is equally untrue for flathead screws. Even by hand, I could drive a hex screw far tighter than a wood screw.",
"A hex screw lets a person install the fasteners well, and even remove them, without collateral damage. If my aunt is anything like a typical consumer, every single Phillips screw would get mangled because she'd always [cam out]( URL_0 ) the screwdriver. Every single screw that takes a flat head screwdriver would lead her to slip and impale her other hand."
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gtetpr | how do pipes work? | How does water get from ground level to the penthouse of an 80 story building? I feel like it’s mostly just pressure but how does that work for huge heights? I have a general idea of how things like water towers work but i can’t wrap my mind around this. Thanks in advance! | Engineering | explainlikeimfive | {
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"It’s complicated. City pipes provide an initial pressure but it gets in to the basement so usually not enough to got past a few floors at a significant flow. Any high rise building will have a set of strong pumps to get that water up to a top reservoir or, if it’s too high, to a series of step reservoirs each sending water up again. [Burj Kalifa does it like this. ]( URL_0 ) Then the water from that top reservoir is allowed down to secondary pipes on each floor, but first though pressure restricting valves so the floor at the bottom doesn’t have extreme pressure and the others have less and less.",
"Plumber here! City pressure doesn't usually pump hard enough to get up past about 3-5 floors. We try to keep pressure so that at max flow, the water will go down the drain slightly faster than it will come out the faucet... Sometimes it even works out like that! High pressure also puts lots of strain on your fixtures, risks breaking them much faster and to greater effect. For taller buildings, we install booster pumps at the bottom of the building, and many buildings use an industrial size boiler and chiller at the top of the building (the Mechanical Penthouse, we can it; above the to for, but below the elevator winch). This stores water up high, so it flows down to you. In REALLY tall buildings, the pressure coming down from to high up would put to much strain on your fixtures (same problem, different reason). We can install Pressure Reducing Valves, but eventually even that fix isn't perfect... So we get a 2nd mechanical not-so-penthouse, halfway up the building to serve the units below it."
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gtngm2 | Space is huge, but how do you make sure that you won't get hit by debris or other satellites when you launch one? | Engineering | explainlikeimfive | {
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"text": [
"Space is huge. We track all the bigger stuff, and the rest of the time you rely on how big space is to minimize the probability. Then you engineer your spaceship/satellite/... to be able to withstand a tiny impact.",
"Bad answer: you don't. This is literally the nightmare scenario that keeps space programs up at night. There are space trash tracking programs that are trying to figure out how to recapture all of this junk, but to this point in time no one has cracked it. Eventually, one of these orbiting pieces of junk/trash will potentially end a mission or kill some astronauts; unless we can create a workable solution."
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gtripl | How is gasoline octane level measured and why are some cars only supposed to use higher octane fuel? | My 07 subaru legacy gt says to only use 91+ octane fuel in it and I was wondering what the octane rating actually means and why some cars such as mine only use higher ones. | Engineering | explainlikeimfive | {
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"Octane rating is a measure of how hard it is to accidentally ignite the fuel in the engine. This causes a phenomena known as \"knocking\" which if left unchecked will cause permanent (potentially catastrophic) damage to the engine. Modern engines will detect knocking and do things to prevent it from happening, but this generally significantly degrades the performance of the engine. Engines that require higher octane ratings are designed in a way that makes them more likely to accidentally ignite the fuel. Engine designers do this because it turns out that the things that make that more likely also can help improve the performance of the engine. How octane rating is measured depends on where you're located. Europe uses something called the \"Research Octane Rating\" (RON) which basically is just an engine that subjects the fuel/air mixture to varying levels of compression to determine when it starts behaving badly. The US uses something called the \"Anti-knock Index\" which is the average of RON and a 2nd test called the \"Motor Octane Number\" (MON). The MON subjects the fuel/air mixture to a bunch of other abuses, and results in a lower rating. As an aside - this is why octane ratings in Europe are much higher than in the US, they're actually different measuring techniques."
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gtt8t4 | As a crew member, how loud is the ISS? Do astronauts use noise cancelling headphones to drown out the hum, and get a good “nights” sleep? | Engineering | explainlikeimfive | {
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"It used to be a much bigger problem. They have since attempted to limit the noise and add baffles to the ISS so that people can sleep. URL_0 If you have ever seen a livestream from the station you can pick up only faint noises in the background. I cannot find a link to the video, but I know one astronaut mentioned that there are noise requirements to stay within unless performing a critical task. The number I remember is about 70 decibels being the normal operations (they reduce noise at night), which is about the same you would get on a busy city block. Many astronauts do listen to music or put in headphones when they sleep.",
"There’s a couple videos of them giving tours, and you can hear multiple equipment and machines going.",
"Watching the livestream from SpaceX's Crew Dragon today I was surprised how loud the capsule seemed to be on orbit but perhaps the microphone was near a circulation fan or something? Will be interesting to see more video in the future. Especially the higher quality stuff after the capsule returns."
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gtvy8g | How do they cool computers in space where normal fans wouldn't work? | Engineering | explainlikeimfive | {
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"Same way they cool everything else in space: by radiating the heat into space. Everything in space is covered my a special white paint that has two important properties: it is really good at reflecting light (which is why it is white) and it has really good thermal conductivity. This means it absorbs very little heat from the sun, but lets the heat generated in the spacecraft (including heat from computers) escape into space.",
"This is kind of an aside (looks like others have given you an answer more broadly) but fans are actually very important in space. For something like a computer, there's no 'up' so warm air won't rise on its own. It just sits where it is. The inside of a computer could get very hot, hitter then they would on earth, without a fan. Likewise, astronauts have to sleep with a small fan, otherwise their exhaled co2 can build up near them in the less turbulent air. If you watch videos from the space station it is very loud."
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gu5p9t | How do portable electronic devices not get some sort of overload when you leave them charging/plugged in past a full charge? | Engineering | explainlikeimfive | {
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"The charge controller circuit inside them simply shuts off electricity flowing into the battery when it detects that the battery has reached maximum safe charge level. In super simple stuff like solar garden lamps there is no such circuit and the batteries actually do get overloaded, but the energy input is so low that the batteries can survive it well enough by shedding the extra energy as heat (this is dependent on battery type - don't try this on Li-Ion, but Ni-MH can survive it at very low power).",
"They cant get past the \"full charge\". There is electronics on them that control the charging process and will stop charging when you hit certain limit. Fun fact - its not optimal to charge batteries up to 100% (simplifying a little here). So a lot of the phones will display 100% charge, while the actual charge is at optimal limit to extend battery life. Fun fact no2 - you can see example of overcharging when charging car battery with some of the older chargers that don't check for charge level. If you leave it on long enough, acid inside the battery will start boiling, which can lead to a nasty accident if you allow it to happen..",
"Any correctly designed device to charge batteries vill monitor the changing and stop it before they are overcharged. You not connect the batteries directly to an external power source but have control chips in between. If you connect directly the control electronics is in the external device."
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gucsy2 | What are the main setbacks that prevent us from having robots with fluid/human-like movements like in films? | Even the most advanced robots, whether bipedal or quadrupedal, move in a clunky clumsy fashion. All their movements are sluggish. Is this merely a software limitation? Considering how fast computers nowadays are, and how fast and complex engineering wonders like rockets are, I'd like to understand why it is that robots are still so sluggish. What's so hard about them? Feel free to go a bit in-depth if necessary. | Engineering | explainlikeimfive | {
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"My understanding of this is relatively rudimentary, but the basic reason is that human movement is produced by contraction of many many muscles, and it’s difficult to cram that many motors and other components essential to motion into spaces the size of a human arm or leg.",
"The actual movement is quite easy, it's fairly simple to get smooth motion from a robot. What's difficult is determining the path of that motion; humans can sense our surroundings in ways that robots generally can't, because we have brains highly optimized for spatial awareness and we process that information far more efficiently than a computer can. The main reason that humans are better at navigating our environments is because we're good at *ignoring* information. We get a lot of input from our eyes, our inner ears, our kinesthetic senses (the thing your doctor is checking when they ask you to close your eyes and touch your nose), the feeling of the ground under our feet... there's a lot there and a computer would have to actively process all of it, while the human brain can constantly prioritize the information we need most."
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guly0x | why can four 1/4 full batteries make an electronic work but one fully-charged battery cannot? | Engineering | explainlikeimfive | {
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"Each battery provide a certain amount of voltage (usually 1.5V-ish). So 4 quarter-full batteries provide the needed 6V; one battery alone, even full, provides only 1.5V.",
"Imagine it like moving furniture: Your big old wooden dresser is so heavy that you need four guys to carry it. One guy just can't lift it, no matter how well rested he is. Four tired guys can lift it, but will probably not go very far.",
"Batteries for consumer electronics are often wired \"in series\". That means that the positive terminal of one battery is connected to the negative terminal of the next line line. (This is also the reason why most consumer electronics require batteries to be positioned with the batteries alternating orientation... it saves on wiring costs and space). When batteries are wired in series, their voltages are added together. Four typical 1.5 volt batteries wired in series end up producing 6 volts. When you say \"full,\" what you're really talking about is how much current the battery can supply--how much electricity is inside. A battery produces the electricity at the same voltage pretty much until it's totally dead. So, a fully charged battery might not have the voltage to run the electronic in question, whereas 4 1/4 full batteries will.",
"A battery's voltage decreases when it's drained but doesn't reach 0 V when empty. AA batteries have a voltage range of 1.65 V when full and 1.4 V when empty. Four 1/4 full batteries would have ~1.5 V x 4 = 6 V. A single fresh battery is only 1.65 V. Draining batteries beyond the empty voltage can cause chemical changes that could cause the battery to leak."
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guobll | How are "hollow" objects extruded? | Example: Penne pasta, metalwork such as non-welded pipes, etc. | Engineering | explainlikeimfive | {
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"You make a dire so the center part is supported from behind and the material is allowed to flow around the center part and form a single extruded part. Here is [3D printed]( URL_1 ) nozzle for pasta. [Here is an]( URL_0 )[ animation for the same for aluminum]( URL_0 ) I have to say that I am not sure how you do that for steel but I would assume the same thing and cooling the die made of a material that survives higher temperature.",
"Usually you have a pin that forms the hole that is attached to the extruding machine only at the back, therefore giving time for te material to flow around it and fill the gaps I’m not sure they do that for non-welded pipes though",
"Don't know if this is always the case but at least some pipes are made with centrifugal casting. Spin some liquid metal in a long barrel and let it cool.",
"There is a plug in the center to make the interior hole. That plug is supported by a connection back in the extruder, but the concept of extrusion implies the substance being extruded is plastic enough to merge around the connection."
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gur7w4 | how does carpet stay down when vacuuming? | If carpet is just rolled out and hammered into the tack strip and tucked into the baseboards, how is that enough to keep it anchored during vacuuming and not suck it up off the floor? My Dyson is pretty powerful. My thinks-he’s-handy husband says it’s that easy! | Engineering | explainlikeimfive | {
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"The vacuum is pulling the carpet towards it right? But where is the vacuum? Sitting on the carpet. If the vacuum is lifted off the carpet it becomes really easy for outside air to rush in. Even with the vacuum down air can also go through the carpet and in fact that is what you're doing with the vacuum: pulling air through the carpet fibers to try and get debris out. If the carpet were a sheet of plastic you might have issues but basically all carpet is just mesh and threads which allow air through them.",
"Carpets are breathable. So, if it were a wind proof plastic mat, it would suck solid to the vacuum. But because the backing of carpet has room for air to Woosh through... it sucks the air past the mat and the fibers."
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guyqrw | Can we approximate the future of the world using numerical methods? | Engineering | explainlikeimfive | {
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"If we have a model that can describe how something changes with time, then we can make approximations about what will happen in to the future. This relies on the model being sufficiently accurate, and the time steps being sufficiently small (which calls for heavy processing). If we had perfect knowledge of everything about the earth, we could in theory predict the future. However you need look no further than the weather forecast to know how difficult that is.",
"In theory? Maybe. However, mathematicians have shown that even the smallest error margins can mean drastically inaccurate predictions after a short time. That’s why we are pretty good at predicting the weather for a day or a few days, but most models are garbage after as little as a week. We have gotten good at predicting short term behaviors using these methods and we’ve gotten good at predicting larger trends (e.g. we can predict the average temperatures over a year REALLY well, but predict any given temp on a given day is shooting in the dark) but long-term exact predicting is still really tough."
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gv1hwi | Where does the water go? | If you turn on the hose and it has a hand sprayer nozzle on it, but after watering you forget it’s on and a day later turn off the hose... where did all the water go? I ask because I am at a place where I have to conserve water... and I feel like an idiot asking this question, because I guess it just stays in the well right? If so.. what about all the pressure that built up? | Engineering | explainlikeimfive | {
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"The hand sprayer on the hose holds the water back. The pressure is there and is constant but is manageable. Same as a kitchen sink. The pressure is there until you squeeze the hand sprayer or turn the knob on the sink. .. the water stays in the hose and within your plumbing. Same as if you turn the sink off."
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gvffqj | Why can't we just build higher to solve housing problems? | Was looking out the window and this thought came to me. There doesn't seem to be anything apparent (other than money) stopping us from building higher, so why can't we just build one extremely tall building instead of multiple shorter ones to solve housing? | Engineering | explainlikeimfive | {
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"Many cities do. But the taller you buildings get, the more expensive they are to build and maintain, so not just anyone can simply build higher. Furthermore, many cities, especially smaller suburban ones, have ordinances preventing buildings from exceeding a certain height. They are afraid of tall apartment complexes ruining the aesthetics of their city.",
"The housing problem isn't that we lack enough housing. Some estimates put us as having more vacant housing in the US than homeless people. The problem is the lack of AFFORDABLE housing.",
"NIMBY! In many, many places, existing zoning restrictions favor current homeowners and protect their equity; increasing density is strongly opposed. Case in point SF",
"There are lots of costs involved with building higher... while it solves for high land costs, the additional engineering, difference in building techniques and materials, extra mechanicals (elevators, safety sytems, giant HVAC systems, presurized plumbing, etc.) that go into high rises result in much higher costs per sq. ft. to build and maintain. Sure, it can help in a super expensive, super dense place like New York City or Singapore, but not so much in less dense/rural areas.",
"Engineer here. 1) Building high is more expensive per square feet than building on the ground. That said, building vertically decrease some cost per square feet, the main one being the cost of land. Depending on all the variable there is an optimal high to build, building higher than that will increase the cost. This optimal high will vary from city to city, but can also vary within the same city. Usually the more costly the land is the higher the optimal heigh it. Like I said it vary greatly, but usualy it's between 8 and 12 stories. 2) Urbanisation. Cities have rules that limit what type of building and which characteristic a building can have in different zone. One of those characteristic is the height of the building. If you look at Washington DC, they have aggresive limitation on height so that building don't block the view of national monument or important building. 3) Remember that the goal here is to build enough affortable income building, not just build more building. So you need to able to build cheap building, but also cheap apartment. It more often easier to build higher quality or larger apartment that you can sell to people which better finance than to build smaller apartment to sold to people with less money. It's more risky, the chance of having trouble might be higher and so a lot of people just prefer to build higher price appartment, which doesn't help the housing crisis and might even make it worst."
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gvy3nv | Why when my power goes out during a storm is it only for a second or two? What happens to the power line to cause only a brief loss of power? | Engineering | explainlikeimfive | {
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"You are seeing the automatic response of the power system when something has caused a transient fault. That means it is not long lasting and many time can clear itself without anyone having to respond to it. For example during a storm you will often get rain, wind, and lighting. Trees are a big cause of outages so the wind blowing trees into the lines or other random debris can cause a brief short circuit, the automatic switches see this, open for fractions of a second to allow the fault to dissipate, and close back in. Rain can cause tracking down poles or other paths to ground, lighting can damage equipment. The end user, you, sees the lights flicker, blink, or go out for a few seconds and up to a couple minutes. This is purposeful to help clear momentary faults and avoid having to investigate every possible cause of a power outage which takes much longer if you need to send a crew out."
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gvyf9p | How can a chainsaw cut through wood without jamming ? | Wood is kind of pretty hard and the chain of the chainsaw is made of "blocks" I suppose, can't really find out what it exactly is but anyway, to me, it seems like that chain would just get stuck in the wood at the very moment it touches it. Even more when cuting deeper into the tree. | Engineering | explainlikeimfive | {
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"Key is the speed. Try it with a barely moving chain and it gets stuck. Get enough speed and the wood it gets stuck in can’t hold it and breaks, allowing the next block to eat a little more inside. As the saw goes in, it goes in a straight plane and touches nothing else. From the saw perspective, it’s just the wood below it that is present. The rest doesn’t offer resistance. Also the sides of the blocks are relatively flat and can slide should there be a small misalignment. But torque it enough and it will surely Jam. Edit key is the speed. Not isn’t.",
"A chain saw blade is mostly covered with cutting [teeth]( URL_0 ). But yes, a blade can jam but not due to the actual cutting. It is more common for the tree or whatever is being cut to pinch the blade, causing it to stop or bind. Wood is structurally strong (for the most part) but cuts fairly easily.",
"There are two sorts of blocks. One cuts on the left and one cuts on the right. The chain goes left-right-left-right-... . By cutting a slot that's wider than the chain and the bar, it's easy to avoid problems. Of course, you have to be smart, and but the tree in tension rather than compression. If you cut wrong, the blade will be pinched."
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gvynym | How do you store energy/electricity? | If i were to build a dam in a river, to focus the flow of the water and try to harness it. I guess i would create some sort of wheel that would be spun by the power of the water. How do i turn this into energy and eventually even store it? | Engineering | explainlikeimfive | {
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"Imagine you have a long line of golf balls, all touching and side by side. This is a wire, lets say its a copper wire because copper is easy to make into the long wire and its something the imaginary golf balls have an easy time rolling in (it could also be made from steel and some other metals). These golf balls are electrons, a metal, like copper, is an element whose electrons can \"move\" around. If we push on the balls without them rolling (imagine on the other end something was blocking the way that will move if you push hard enough) we have just created Voltage, its the pressure pushing on the electrons. If they move we have Amperage, the number of electrons that move or flow down the line. How hard we have to push is the Resistance. Now, we can't just push the golf balls into nothing, that would make empty spots in our line and it wouldnt be a line anymore. So imagine the line goes off into the distance and comes twisting back around so that the other end is touching our starting spot. Now you can see that by pushing the balls forward they will roll like a train and fill up the spot where you moved them from. This is the flow of electricity, electrons move out but simultaneously move in from the other way. We could say the direction they go is positive and the direction they come from is negative. Now let's create some power. Magnets, or actually the magnetic field magnets make can gently push on those balls without touching them, very useful! If we spin the magnet we can push one ball forward every spin. This is nice but its not a lot, so let's take our wire, the long line of balls, and wrap it around outside the spinning magnet many, many, many times. Now when the magnet spins it can push alot of balls at once and with a lot of pressure. We need a way to keep the magnet spinning, we could do it by hand but that isnt a real job. So lets hook the magnet up to a big fan and spin the fan. We could use wind, or steam (coal, gas, nuclear all heat up water to make steam to push the fan to turn the magnet) or we can use flowing water. We could also make a special type of wire that makes sunlight move the electrons but we can focus on the basics. Now we have a big spinning magnet and lots of wire pushing electron and creating electricity. We can do way to many things with it for me to cover everything, but ill be happy to answer specifics. As for how to store it, we can use batteries. We actually use so much electricity that our magnets are practically spinning all the time, but sometimes we need batteries. There's many types, but the basic idea is to take two different metals and submerge them in an acid. The acid has holes in it that want to be filled with electrons and the two metals have plenty to give. So if we add electricity to the battery it will \"charge\" and fill up all its spots. We can then take electricity from battery by connecting to it later. The actual number of electrons in the battery doesn't go up or down they just change locations from the acid to the metal and back.",
"One way would just to be hold back as much water as you can, and then release it to generate the amount of electricity you need at that given moment.",
"To force electrons to move through a wire, you move a magnet along a wire. Many materials will conduct electrons, but copper is the best all-around material for that, so let's look at a copper atom An atom has a blob in the center, like the sun, and it's made up of protons and neutrons. All you need to know for electricity is that electrons orbit the nucleus, just like planets around the sun. Each element has a different number of protons, neutrons, and electrons. Copper has 29 electrons per atom. Electrons can be pulled out of an atom and shoved into the next atom by moving a strong magnet near it.. Imagine a row of copper atoms in-line along a section of copper wire. When they are at rest, each atom has 29 electrons. However, when you pass a strong magnet along the wire, just behind the magnet the copper atoms have 28 electrons, and just under the magnet, the copper atoms have 30 electrons. Current will only flow if there is a continuous loop, called a circuit. When you turn a switch on, you are closing the switch-air-gap, and completing a circuit. Now when you move the magnet, the copper atoms with 30 electrons are pushing electrons ahead of them to flow away from the magnet (so they can get back to 29 electrons), and the copper atoms behind the magnet with 28 electrons are pulling the electrons from the circuit to bring them back up to 29 electrons, which is where the copper atom is in balance with all its forces being stable. Since its impractical to move magnets along a long straight wire, the copper wire is cleverly packaged into coils, and they are arranged in a circle like the numbers on an old analog clock. Depending on how the internals are configured, this device could be called a generator, an alternator, or a dynamo."
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gw5we1 | Why can't we just 3d print human-sized legos and build working structures/vehicles with them? | What would go wrong with upscaling legos? | Engineering | explainlikeimfive | {
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"For manufacturing large amounts of anything, there are much less expensive materials and processes to achieve that goal. 3d printing with plastic filament takes forever, and costs a shit ton.",
"In some ways you can. I’ve seen precast concrete pieces that work in a similar way to connect to each other, but with grout or some sort of sealant in the joint as well to hold everything in place and prevent water from getting in the cracks.",
"3D printing is slow so for mass production you like to mould stuff just like you do with lego. Plastic can be quite strong for small stuff but for large stuff, you start to notice that is is quite weak compared to other material. There is a reason you do not build houses in plastic. Lego is held together by the friction from the extruding studs and it will not scale with the increased mass so comparably larger lego parts will not be held together as good as small. The manufacturing tolerance is also quite small for lego. The moulds have to be accurate down to 20 micrometers and because of that, you need to replace them after a lot fewer users than other common plastic parts. Lego is one of the consumer plastic parts that is manufactured with the lowest tolerances The molds cost a lot of money. This is why lego clones that exist on the market often do not stick together as lego does. they do not make good enough mold or they use them for longer so the dimension of the part is not correct. & #x200B; But there are lego inspired parts to construct larger object but the are molded concrete block make do be stacked together. [ URL_0 ]( URL_0 ) So you can use them in situation where you in the past used to concrete or stone blocks."
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gw7203 | How do doorbells work? | Engineering | explainlikeimfive | {
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"Depends on the type of doorbell, many new ones are wifi enabled, but traditional doorbells that most people are familiar with are buttons/switches with electrical wires running through them, through the wall, and to a chime usually built into a wall somewhere closer to the middle of the house, though some are right inside the door. Pushing the button completes an electrical circuit which causes the \"bell\" to go off"
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gwl07x | Why does modern concrete/asphalt break so easily compared to ancient/brick roads? | Engineering | explainlikeimfive | {
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"Because brick roads were uneven and people had a lower standard. Ancient roads accomodated foot traffic and relatively light vehicles. They needed only to not be dirt, so the surface of the road doesn't matter. Modern roads carry much heavier loads and the surface must be smooth. An uneven road quickly destroys heavy vehicles movung quickly. Modern roads are much more durable than brick and stone roads. They are just also used significantly more.",
"The last thing you want to do is drive a motorized vehicle at highway speeds over brick. Initially it would be OK, but bricks will dip and rise over time making it dangerous to drive on at any high rate of speed. The best solution is to install concrete in chunks (like the autobahn) so you get all the benefits of concrete - resistance to cratering in the sun, water channels help keep water off the tires, rough concrete is safer to brake on, concrete roads can last an awful long time. The problem is cracking, especially in colder climates where you will get water expanding and contracting seasonally. Solution, put them down like huge bricks, that way when one cracks it won't spread, and it is a fairly simple task to replace the section.",
"The indestructibility of old roads is a popular meme just now. That idea suffers from a load of data sampling errors. Yes, I can take you to a Roman [180AD] pool in Tunisia still holding water. Yes, I can show you crumbling concrete culverts from 1956. There are millions of tons of modern concrete/asphalt infrastructure holding up very well and nobody's photographing it. Most of Rome's concrete is at the bottom of the Tyrennian Sea...",
"They weren't building roads that had to endure up to hundreds of thousands of vehicles a day that all weigh more than a ton. That shit is hard to do without spending money. We don't like spending money up front to get things that will last longer, so they fall to shit after a decade. They built roads for ox carts and shit. No where near the wear and tear of a modern road.",
"Asphalt roads have a noise damping and cushioning effect, and are inexpensive to repair and source materials for. Ancient roads use very expensive materials that are costly to transport and require large amounts of skilled labor. I'm not aware of any types of durable ancient roads that are smooth and friendly toward rubber tires and hydraulic suspension systems either. They're all fairly rough in texture. Also, \"solid\" roads don't handle repeated freezing and exposure to deicing materials any better than modern roads do, and this is the cause of most road damage. In my state they have several concrete interstate highways and they are not any better than asphalt highways because not only are they maddening to drive on (clack, clack, clack, clack) but they have to be regularly shaved to even out frost heaving or they develop stress cracks and get potholes the same as asphalt.",
"A real simply way to think of it is like this: Ever think \"hey, these tires would last a lot longer if they were made of something more durable than rubber!\" The problem is that when you go for a more durable material, you are sacrificing other properties that make it safer to drive on.",
"Brick and stone are more durable, but they cost a lot more to install and don't provide as smooth a road surface. So it's a compromise to get something that's cheaper to build and that you can actually drive more than 20 mph on without too much noise and vibration. Brick streets are now sometimes built in areas where the city is trying to get traffic to go slower.",
"It's probably mentioned elsewhere in here but the most important part of the road isn't even the surface, it's what's referred to as the base. High traffic roads designed to handle heavy loads will actually have several feet of gravel and compacted dirt underneath. For a time I worked with a soil testing company and they had the road plans for the nearby city, the owner showed me that some roads are actually designed to handle things even heavier than fully loaded trailers such as tanks and heavy lift aircraft. He showed my the original ground plans for an emergency runway and it actually had 14 feet of base underneath it! From the surface it looked like any other road!",
"There seems to be a misconception that ancient concrete was somehow superior to current methods. This is a myth. We have way bigger, way more efficient, concrete structures today than ancient civilizations had. And our structures have to deal with cars and truck weighing up to several tons. Ancient civilization's concrete wouldnt stand up for long under those loads. But it didn't need to. They didn't have cars back in those days, and even vehicles of the time were light relative to modern standards. Concrete itself is actually kinda crappy. It handles compression (squishing forces) really well, but handles tension (pulling forces) really, really poorly. So in order to make it handle tension better, we put reinforcing materials in it. Like steel rods (rebar). The steel handles tension really well. Unfortunately, steel also corrodes over time. So the concrete needs to be replaced periodically. Making it seem weaker as it degrades. Bonus: It is actually pretty common to 'prestress' the concrete so it is stronger. Essentially, you put the rebar under tension (pull it really hard) while the concrete is curing. Then when you release, the metal tried to shrink, which puts the concrete under compression. It's like a rubber band squeezing the concrete. We can think of squeezing the concrete as having a negative force here. So now when tension is applied (which would be a positive force), the force has to be positive enough to get the concrete above zero before the concrete goes into tension. Like how you would have to re-stretch that rubber band to get it back to zero. And remember concrete does bad in tension, so this makes the concrete + rebar combo able to resist stronger tension forces. Making it even stronger."
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gwloba | Are we really wasting water when we let the faucet run? | Another way to put it is: what happens to the water that goes down the drain? I understood this water is recycled. As such, what are we wasting? It would be more wasting the power/water used to recycle this water but not the actual water we let run? Thank you for the insight. | Engineering | explainlikeimfive | {
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"You are not wasting the water, per se, but you are wasting the resources (energy/money/manpower) needed to treat that waste water. All the water that goes down your drain needs to go through the water treatment plant. You’re also wasting money if you are on a water meter.",
"Letting water run for no other purpose than to do so is wasteful by definition. All systems (ostensibly) have losses, and the waste system will lose water due to leaks and evaporation. This may not seem like a big deal where water is already abundant, but in arid regions, that's water that can't be reclaimed and reintroduced back into the system. If your water source is an aquifer in the western states, like Colorado, they're draining their water supplies way faster than they are replenishing them, and once that's gone, water prices will skyrocket due to scarcity, and on demand water won't be possible in those regions anymore. You're also wasting all the coal and oil burned to deliver that water to your tap in the first place, for all the chemicals used in treating, for all the pumping, for all the facets of producing it in the first place. You do pay for it, it comes out of your water bill, so do what you want. As of right now, water, for you, is so cheap you're here asking this question, and in the scheme of things the world won't notice you've poured money down the drain like that, but if a society were reckless, they would only burden themselves in the long run.",
"Fresh water is a relatively limited resource, in many areas rain water is limited and the other option is aquifers underground sources of water which either don't get replenished or it takes thousands of years to replenish. In addition the water is treated before it gets to the faucet and that is expensive. URL_0",
"Well yes and no. Some water is cleaned and then put back into rivers so in that case you could consider the water wasted. Sometimes it is fully recycled and you are just wasting the energy and time needed to do so and transport it.",
"3 Reasons 1) You are not wasting the water itself, but the drinkable water. The more drinkable water we use (or let down the drain) the more drinkable water and waste water the city have to treat to provide their city. That's money, infrastructure, chemical, etc. 2) Pipes in the ground are not that good. Most are old, with holes and fissures. Depending where you live as much as 40% of the water we use is lost in the ground. This water will eventually reach an underground water flow and eventually end up somewhere, but it could take decades or more because the water reach a location where we can use that water again. It could also go through radiactive or chemical residue in the ground (natural or not) and that water might never be used by human ever again. The more water we use the more we gonna lose in the ground. 3) This is probably the most important. Cities get their water from a source and that source isn't infinite. There is a limit on how much water get regenerated into the source. If we use water at an higher rate than the natural regen rate then we slowly syphon the source until less and less water will be available. By wasting water now, you might (depending where you live and what is the source of your water) cause serious water issues for other people or future people. [ URL_0 ]( URL_0 ) [ URL_1 ]( URL_1 ) Now of course this is more complex than just people letting the faucet run. It's about agriculture, bad infrastructure, industry, etc. But wasting water is a part of the problem."
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gwwxlt | Why do wheels have spokes? | Engineering | explainlikeimfive | {
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"It's important for wheels to be light in weight as much as possible. Imagine you had a bicycle wheel, and you were trying to get it spinning by by twisting the axle with your hand. Now imagine doing the same thing with a heavier wheel such as a car wheel. It would be much harder with the car wheel, right? (That rotational \"heaviness\" is called \"moment of inertia\" or \"angular mass\" in physics, by the way.) We want to make things as easy as possible for the engine (or the person pedaling in the case of a bicycle), so that's why we want the wheel to be as light as possible. The lighter the wheel, the faster the vehicle will accelerate, and the less energy will be wasted. So, the reason they use spokes is because they are strong yet light.",
"Functionality and safety. Solid wheels generally have higher moment of inertia. This means given the same torque, the wheels accelerate slower. At a cruising speed, they \"maintain\" their speed better. But if there is less constant speed travel, the added inertia is a disadvantage. When the vehicle needs to slow down, all that rotational energy in solid wheels means that brakes have to work harder. This will heat up brakes more (wear and tear) and also result in longer braking distance (safety) It generally also results in poorer fuel consumption as more energy is lost to heat. In things like cars, most of the weight of the car is carried on compliant suspension systems. This makes the care more comfortable. Too heavy wheels make the suspension system more difficult to design and can result in poorer traction (safety) or poorer ride quality.",
"reduces vehicle weight and conserves material. Also the old saying, \"if it ain't broke don't fix it\" comes to mind since wheels have been somewhat consistently made for quite a long time to the best of my knowledge.",
"have you seen those [tensegrity tables]( URL_0 ) that were all the rage recently? spokes are basically like that. they hold tension from the wheel and distribute the load evenly along all the spokes attached to the hub.",
"The spokes can use materials designed to handle the mechanical *compression*, like the old wood wagon wheels, or modern alloy car wheels. The spokes can also use materials under mechanical *tension*, like the lightweight spokes of bicycle wheels. They're designed to be strong enough for each application. Any extra materials would only add costs and dead weight.",
"It is to reduce unsprung weight. This increases the responsiveness to the road because the inertia is less (keeps the tires in contact with the road). In bicycles, it's to reduce the crosswind load and also weight. Steel in tension will support more load than steel in compression given the same weight."
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gx1xow | How is every single lock in the world different? | Engineering | explainlikeimfive | {
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"> How is every single lock in the world different? They're not. Many different locks use the same key. It's just very unlike that you'll find one.",
"^(Disclaimer: I'm not a locksmith nor a subject matter expert, so I might be mistaken.) They're not unique. Rather there are a sufficient number of variations that using duplicate keys for multiple locks is fine, so long as it is not know which locks are opened by the same shape of key. As for how they keep track of this, I'm assuming there are nation-wide registers for such things, or perhaps just manufacturer-wide registers.",
"As a lot of others have explained, they aren't and there's really no way they could be realistically. The basic standard lock you'd see on anyone's front door is a cylinder lock with pins. To unlock you need rotate the cylinder to move the latch out of the way so the handle can turn. Inside that cylinder there are typically 5 or 6 sets of pins depending on brand and cost. Each set is two pins. A small one that's the same in every slot and a second one below it of variable length. For a decent quality lock there's 9 or 10 possible lengths for those variable pins. Lastly there's a small spring behind both sets of pins pushing it all down. If you try to turn the cylinder without a key you won't be able to because the pins are across the shear point where the cylinder meets its housing. When you insert the correct key, the various bumps and valleys push the pins up different amounts so the gaps between the flat pins and the variable pins all line up with the shear line and allow the cylinder to rotate. So a lock might have a key code something like 25463 meaning the first pin is length 2, the second 5 and so on. So, the number of keys you can have is determined by the number of pins and the number of lengths. There are some additional limiting factors however. Let's imagine a lock with 3 pins and 5 lengths. First off any key like 222, 333, etc would be terrible because if they're all the same all you would need to do to unlock it is jam any old thin object in and wiggle it up and down a little till it lined up and turned. Likewise for anything in a smooth line like 123 or 246. On top of that you can't make too large of a jump between pins. If you tried to make a lock keyed 161 it wouldn't work because the changes are too steep and you wouldn't be able to slide the key in. So if you have a 5 pin lock with 9 length options (average residential lock) mathematically there are 59,049 possible combinations. Once you take those other limits into account though there are fewer than 20,000 useful combinations. This isn't really a problem though because tens of thousands of combinations makes the odds of finding another lock at random that fits a key you have pretty low. Even lower for someone with malicious intent managing to randomly find a lock of a place they actually want to get into. The other thing too is, for a typical lock like that, there are lots of easier ways to get around it if someone REALLY wanted to than stumbling across the matching key. A good solid kick near the handle will break most doors with a wooden frame fairly easily. You could also break a window or whatever. Locks keep people from just opportunistically walking in but at the end of the day it's not going to stop anyone determined to make entry.",
"they (the locks) arent and they (the locksmiths) dont know it. BUT there are many different types of keys and many different possible configurations per type. think of it a bit like a password. let's say most people in the UK use a 10-digit-password for their door consisting of random numbers. some people use 9-digit-passwords that contain letters. and now lets say it's the inverse in Germany, where most people use the 9-digit-letter-passwords and few people the 10-digit-number ones... if you took any random German key to the UK it would be already highly unlikely it would fit the type there (since youd use a letter-password and most doors wants a number-password) and even if it did, the chance of your key fitting a lock of the same type would still be so close to zero that you'd need to try millions/billions of doors before you find one that it would open. thats why locksmiths dont need to know what locks other countries/cities are using. HOWEVER sometimes you have similar locks for a building, say your appartments door-PW is ABCDEFXYZ. Often the lock on the building door is designed so that any key beginning with ABCDEF can unlock that one, and the last few digits distinguish the appartments. In that case it is important for the locksmith to keep in mind which keys have been used in that building (since it's much easier to accidently create 2 keys with the same 3 letters than to randomly create keys with the same 9 letters).",
"[You're in for a wild ride, my friend]( URL_0 ), since locks are very much not unique. That video isn't quite ELI5, but it's the best I've got. I hope this, in conjunction with the other answers, will help answer your question :)",
"It’s not, at all. It’s sortof a game of chance. There are only like 100,000 key types effectively (just an arbitrary value, I don’t actually know) so it’s sortof a random chance of you do happen to have the same key. Burglars arent likely to not only carry around 100k keys, much less have the time to test them all. It wouldn’t work. So 99.99999999999% of the time, the lock system we have is effective. Funny story, we were rebuilding a house, and brought a lock into the local hardware store to find one that would fit in our antique (70s lol) handle fixture. We find one and chat for a bit with the guy behind the counter. (It’s a small town) and he was fiddling with the old lock and the new key. As it turns out, it worked! Different locks from decades apart seem to work together! It was pretty interesting and funny. Also pen testers, or people who are paid to break into buildings to test for weaknesses, often have a set of every day keys. A lot of brands of doors, key boxes and call boxes are keyed the same way from the factory, just as a place holder, and installers install new locks, usually so every thing can be keyed the same. Installers almost never change the locks. So it’s great, there are a lot of keys that work all over the world because no once changes from factory locks! Always change your locks"
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gx4pcf | How does trim work on an aircraft? | I understand that there's pitch, roll and yaw, controlled by the yoke/sidestick and rudders, but what does trim actually do? I've heard that pilots set it to 5 degrees or thereabouts before takeoff, but it doesn't really make sense to me. | Engineering | explainlikeimfive | {
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"Trim is what we use in order to \"center\" the flight controls. On each control surface that has trim, there is a [trim tab]( URL_0 ) which is what actually moves in order to trim that surface. You can think of these tabs as a 'mini-elevator' or whatever control it's on. As an example, lets say I want to trim nose down. When I move the trim wheel in that direction, the tab will deflect upwards (opposite) into the airstream above the elevator, which then will push the elevator slightly down, relieving some of the nose down force I would've had to apply to the yoke. This goes in a similar manner for all the control surfaces. Also, takeoff trim positions depends from aircraft to aircraft, generally rudder and aileron trim is set to 0 (centered), and there is either a placarded or a calculated value for the elevator trim.",
"Trim is usually referring to pitch when you hear it. Think of it as micro pitch that's always on. Specifically they are smaller flight surfaces meant to stay in place during flight. Think of it as being able to change and correct the alignment on your car while you're driving down the highway so the car will drive straight in a heavy crosswind.",
"Trim is an offset of the controls, if the plane isn’t going perfectly straight, instead of holding the controls in the position you need, you can leave the controls at their neutral position and trim the aircraft so that it stays level Trim works by rotating the whole horizontal stabilizer up and down, which is why on the tail of planes you see a flat surface where the stabilizer meets the fuselage"
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gx6wi7 | How do card readers work? | Here’s an example: URL_0 . It doesn’t connect to the internet but it gives you codes to log in and stuff, I find it strangely fascinating. | Engineering | explainlikeimfive | {
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"So on your card is a little smart chip. It happens to be a computer that is powered by the reader. That smart chip has what is essentially a secure key-store. It has stuff programmed on it that cannot be read externally^1. When you put your pin in the machine, the machine asks the card to confirm the pin. The card can confirm on itself yes or no, and return that response. The little computer on the card is actually advanced enough to even do things like rate-limiting. If you start putting in incorrect entries, it slows down how long it will take to reply to the next request. It can even disable itself entirely until it is brought into a branch and reactivated by a trusted reader. 1: The card can only be accessed externally by a reader with the right security certificates on it. These will be bank-specific terminals, which is why you can change your pin at your bank branch's ATM, but not at one at the gas station."
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