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iejbrk | Why does an engine not produce the same amount of torque at low RPM? | I understand that it drops off in the high end because air can't get into the cylinder fast enough, but what limits are there at low RPMs? Why does an explosion at say 1000 RPM not produce the same torque as one occuring at 3000-4000? And is it the same reason in both gasoline and diesel? | Engineering | explainlikeimfive | {
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"Each combustion event (the bit where the air-fuel mix burns) takes a finite amount of time. The burning of the fuel generates high pressure in the cylinder which, of course, is done to push down on the top of the piston to extract work. Maximum mechanical advantage (and hence most torque) happens with the piston half way down its stroke, as the throw on the crank is at 90 degrees and thus has the most leverage to turn the crank. If the crank is rotating slowly (low RPM, near to idle speed), the combustion event and its peak pressure on the piston crown happens before this point. Thus the pressure on the top of the piston from the expanding gasses doesn't get maximum mechanical advantage to turn the crank. The same is also true at very high RPM, when peak cylinder pressure happens 'late' in the travel of the piston, and again torque is lost. Ignition timing (when the spark is fired) is adjusted on-the-fly by the engine computer to minimise this and centre the combustion event as well as possible on the piston movement, but you can't stretch or compress the time the combustion takes.",
"Engine seals aren't that perfect. Gas can escape, given time. Engines are also tuned for specific RPM's. They're most powerful/efficient at these RPM's. This RPM is usually pretty low, since engines spend most of their time at low rev. However, at *even lower* revs, they go beyond the range they're tuned for. By changing timings and such, this can be partially worked around, but things like exhaust geometry don't really change easily. There are probably other reasons that I don't know about, too.",
"There are undoubtedly more than a few reasons, however I’ll attempt to explain briefly the ones I know. 1.) Momentum of air coming from intake manifold. The higher the rpm, the higher the flow rate of air into the cylinder until a point. When the intake valve is opened, the faster the air is flowing, the more can get into the cylinder before the valve closes. This would then create a more powerful explosion and thus more torque. (Comparing between 1000-mid to high range rpm) 2.) Increased mixing - the quicker the air coming into the cylinder, the better the air and fuel would mix to create an essentially better explosion. Edit: the top of some pistons are shaped in order to enhance mixing"
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ielfkc | What is the "TSSSS" sound a bus or a truck makes? | Engineering | explainlikeimfive | {
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"In addition to the air brakes, buses and trucks use air suspension, so you may be hearing them releasing air from their bags. Most times when a bus stops, it releases air to lower the bus and make it easier for passengers to hop off.",
"An interesting (I thought) aside - the air pressure holds the brakes off, and each brake has its own spring that is always trying to apply the brake. Then the air pressure from the control system is run to all brakes via lines. That way if there is a leak or some other failure where you loose air pressure, the brakes go on. I always thought that was a cool example of a 'fail-safe' design - where the design tries to predict a failure that is likely to happen, and defaults to the safest option. *edit*: turns out this is misleading (unintentionally). I thought nearly all air brake systems worked this way, but it sounds like this is only in the case of the parking brake. See other comments below. Thank you to those who have taught me something here.",
"Trucker here: That noise you hear could be a few things. All relating to the brakes. The trucks brake system relies on pneumatic (air) pressure rather than hydrolic (fluid) pressure like in your normal car. When the driver applies the brakes air pressure is applied to the system, the air expands inside the brake chamber which turns an S-cam which moves a rod that pushes the brake pads to make contact with the disk or drumb (usually drumb) and the truck stops. When the driver releases the brakes you can hear a hiss as the air pressure is released. The hiss you hear that most people associate with trucks is when the driver sets their parking brakes. They pull out a valve in the cab that in turn sends a rush of air pressure from the air tanks to the brakes. And that holds in place as long as the trucks compressor is running. After a long while, the air may bleed off and once it reaches a predetermined pressure (20psi) the emergency spring brakes are automatically engaged. That truck ain't going anywhere. The last hiss ill talk about is a safety check valve on the air tanks. You'll hear this hiss after pressure in the tank builds to 125psi. At that point the valve opens and quickly releases some pressure and a satisfying hiss and closes again once the tank is back below 125psi. This whole thing happens in less than a second. Its a complicated system, but when dealing with heavier loads, air brakes are the bees knees.",
"So why do these big boys use air pressure and not what ever the rest of us smaller rides use?",
"As most have already said, trucks use air pressure to both remove the parking/secondary brake and to apply the service brake. A compressor is constantly running which charges several large tanks which in turn provide air to release the parking brake and for service brake applications. When the system reaches a set pressure a Pressure Relief Valve will vent to atmosphere to keep the system pressure as close to constant as possible. This is one occasion where you might hear a release. The louder releases that you can hear are more than likely as soon as or very shortly after the truck has come to a complete stop. Some of the axles have a Spring Brake Actuator fitted. These use pressure to apply the service brake and to compress a spring. When applying the secondary or parking brake, that pressure is released sharply allowing the spring to reassert itself, applying the brake mechanically. The spring also acts as mechanical fail safe in the event of an air leak. It's required by law in the UK that all vehicles are fitted with a form of mechanical brake. In short - apply parking brake, big release of air, gigantic spring applies brakes.",
"I see a lot of right and wrong answers here. I think the TSSSSS your thinking of is the air dryer. When ever you use air in the air brake system, it needs to be replaced, with dry air. Once the air tanks are refilled the air dryer purges itself with a loud TSSSSSS. Source: Am heavy truck mechanic",
"I responded, but for some reason it was removed. My answer was simplistic,a nd answered the question. The noise is from the air dryer expelling moisture from the air system. Trucks use compressed air for brakes and other functions. That requires that the system have as little moisture as possible. They have an air dryer plumbed in, and as it removes moisture, it has to empty itself sometimes.",
"It’s the brakes. Cars like yours or mine use hydraulic braking fluid to compress the brakes. This isn’t loud enough to provide a distinctive sound (unless something is wrong with said brakes). Trucks and busses used compressed air. This air needs to be kept at the right pressure for the brakes to work properly, and the use of the brakes causes the pressure to increase, so a valve needs to release pressure to keep that in check. The hissing sound you hear is that mechanism at work, releasing the air.",
"People talking about the brakes releasing air are leaving out one point. The air brake system relies on a compressor to provide pressurized air. The compressor runs constantly, always pumping air into the system. It runs at very high pressure so that it con provide a large volume of air to the braking system, enough that frequent braking will not deplete the braking system of its stored air. The air is stored in tanks that are large to provide high volumes of air on demand, but they cannot support the maximum pressure that the compressor produces. When the tanks are full, as between stops while the compressor is running, the tanks have to bleed off air to keep their pressure at a safe level. This is why the tanks let air escape from time to time.",
"Rule 2. Straightforward questions are not allowed. You can find this from a web search.",
"It’s our air brakes. They use air to apply instead of brake fluid - which is what cars use. so what you are hearing is them releasing their brake pedal which is venting the air.",
"Air brakes are common on larger vehicles for various reasons, but mainly because the air is constantly recycled, bleeding off system heat as they go, unlike hydraulic systems which just use the same fluid which can get hot and even boil to failure. Also, the way that airbrakes work is to \"fail on\" rather than \"fail off\" like hydraulic brakes do. Here's what that means. In a hydraulic system, system failure means you got no brakes. That's bad. Airbrakes, however, have a failsafe built in called a spring brake, which, upon system failure, applies the brakes, hard. There's a very stiff spring that pushes the brakes on, until air pressure pushes against the spring and holds it open. If you lose air pressure, the brakes turn on, not off. The vehicle stops, hard, upon system failure. I think the benefits of that are obvious. The compressor that provides the compressed air for the system is engine driven, so whenever the engine is running, it's making compressed air. What this means is that the PSSHT sound comes from three sources: 1.) The operator releases the air from the system to set the spring brake, which also functions as the parking brake of the vehicle. This will happen whenever the operator pulls a yellow, diamond shaped button on the dash out. It sets the spring/parking brakes and makes the vehicle immobile. Buses do this for safety whenever they stop at a bus stop to ensure the vehicle doesn't move as people get on and off. PSSHT 2.) If the operator applies the brake pedal at all, when they let off the pedal, the air that was fed into the system to apply the brakes is vented so that the brakes unapply. So, anytime you hit the brake pedal and then lift off, PSSHT. 3.) Because the compressor is engine driven, it is constantly making compressed air. Eventually, it makes more than the system needs, and a pressure actuated relief valve will blow some un-needed air out of the system to maintain the proper pressures and prevent overpressure. PSHHT."
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ieojqw | How does turning a digital device (like a phone) on and off work without a mechanical switch (like a lamp) | I understand how individual pins control different functions of digital devices, but today I realized I don’t understand how this works in small electronics. Is there a very small mechanical switch or is there a different mechanism going on when something is switched off and on? | Engineering | explainlikeimfive | {
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"Transistors! A voltage (or lack thereof, depending of the type) at the base pin of a bipolar junction transistor will allow current to flow between the collector and emitter pins, acting like a switch!",
"When you press the button, it mechanically closes two different circuits. The first one triggers a pin on the CPU and then the CPU can run some code to sleep or wake or whatever it wants to do. But what if the CPU has totally crashed? And you need to do a hard reset? Then there will be a complete separate analog circuit that runs a simple timer, and once the timer hits it's set value, it will open and close a switch to physically turn the CPU off and back on again."
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ieolui | How do engineers expand roads to create new lanes without moving the houses/businesses that already exist along the side of the road? | For example, how do engineers create 6+ lanes where there were only 4 before? How are they able to create additional lanes when there are solid structures that exist close to where the old lanes were? | Engineering | explainlikeimfive | {
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"They don’t. They buy those homes and businesses and bulldoze those buildings to make room for the extra lanes. It’s called eminent domain. The government has the right to buy those buildings at any time and the owners are forced to sell them in order to make room for a Public good.",
"Unless they’re going to buy up the surrounding land and bulldoze it. All they can do is just try to squeeze in more lanes where they have space Extra space can come from removing parking spots along the road, or shrinking the sidewalks. Or removing things like bike lanes. But really if they aren’t really making any physical changes to the road, they’re just shrinking the actual width of each lane. For example a 60 ft wide road might have 4 15ft lanes. If they wanted they could squeeze that to 5 12ft lanes. (12 ft is the typical width of highway lanes). In some extreme cases like dense urban areas lanes can get shrunk even further to 10ft, possibly under special circumstances (with city council aprroval) to even smaller, but that generally comes with rules like banning buses/trucks from using that road."
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iesduw | how manufacturers made precise things, like needles and measurement tools, without modern technology | I sometimes think about how you could create a mold for a needle *without* their being something the size of a needle, or how something like a regulation basketball was made perfectly round when they had no way of producing *perfectly* round. I might be missing something here, or am just wording the question very poorly, but how the heck did people make stuff so precise without a way of telling? | Engineering | explainlikeimfive | {
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"The short answer is that they didn't...even today it's very rare and very difficult to make it \\*perfectly\\* anything. You could make it astonishingly precise though; there are relatively simple ways, like scraping surface plates, that you can make incredibly precise reference surfaces with just hand tools. Then you use a known good reference to make other things. Complex shapes are harder; that's why tool & die makers or \"patternmakers\" were very well paid and highly skilled. You did it by hand and cleverness until you have a really good reference piece, then use regular techniques to replicate it over and over. Round things aren't super hard if you have a lathe, a grinder, and patience. The invention of Johansen blocks, known good and very precise standard size blocks that would let you repeat a measurement with very high (but not perfect) accuracy was a big step forward.",
"You don’t need a mold for a needle. Stone Age people made needles some 50,000 years ago. You can conceptualize what the end product needs to look like to deliver on the purpose you’re making it for. Then you work from there backwards."
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ievfnl | Why does letting air out of your tires let you drive on sand? | Engineering | explainlikeimfive | {
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"The part of the tire that hits the sand becomes larger and doesn’t allow you to sink as far down. Makes it easier to move through sand since there’s less in front of the tire that it will need to move through.",
"The reduction in tire pressure allows for an increase in the tire’s contact patch, which spreads the load of the vehicle over a larger area. It’s kinda like how a snow shoe allows you to walk on top of fresh powder by effectively doubling or tripling your footprint."
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ievwkb | BIOMECHANICS Can prosthetics move faster if wired into nerves? | I know work has been done on prosthetic limbs connected directly to nerves, allowing easier control, and tactile feedback. What I'm wondering is, if a prosthetic limb was connected to a persons nerves, and maybe even muscles, would they be able to make prostetics that move at the speed of normal limbs? | Engineering | explainlikeimfive | {
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"If the user was able to control them well enough, yeah. Prosthetics that can move very quickly but cannot be properly controlled by the user would be dangerous. I'm really not an expert on prosthetics, but I'm fairly confident in saying the mechanical actuators that move prosthetics are intentionally limited in how fast they can go if the user can't control them precisely."
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iex5mm | Why do old tube lights make that buzzing sound when they're switched on? | Basically the title. Unsure about the flair, but this one seemed the most appropriate. I'm at my uncle's house right now and the tube light in one of the bathrooms is an old white halogen light. It buzzes loudly when it's switched on, and then a low hum when it's lit. | Engineering | explainlikeimfive | {
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"That is the 60hz AC power (60 alternating waves per second) passing through the starter which boosts the voltage to a few thousand volts to start the gas glowing in the tube (florescent), then it guns at 60hz as the gas in the tube is excited by the current."
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if76c7 | Why do tires need air pressure? | Wouldn‘t it be more reasonable to use a solid material instead? | Engineering | explainlikeimfive | {
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"We used to make wheels of solid materials. They kept breaking. This was back when the vehicles the wheels were used on were only moving at the speed a horse could run (and usually much slower than that). See, the problem with solid materials is that if you move one part of a solid just a tiny bit compared to a different part of that same solid, you cause permanent damage. Meanwhile, moving one part of a gas a tiny bit compared to other parts of the same gas does.. absolutely nothing. It's a gas, doesn't matter which bits are where. Now you might ask why we don't just make the wheels out of *more* solid material to make them stronger. The answer to this is that solids are great at transmitting shocks which other solid parts like the axle might be broken by, and if we make everything infinitely strong and solid then every single bump you roll over will be smashing your vertebrae together."
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if9trb | Why isn't lightning being harnessed with supersized capacitors for electrical storage? | Engineering | explainlikeimfive | {
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"A lightning strike is around 1 billion joules of energy. 1 kWh is 3.6 million joules. So a lightning strike is 277 kWh. The cost of 1kWh of electricity in the US on average 13.19 cents for residential customers so the energy of a lightning strike is worth 277\\*0.1319=$36 You can find info about supercapacitors storage for electrical grids that costs $100 per kWh. So to store the energy of a lightning strike would cost 277\\*100= $27 700. This is ignoring any problem of getting them into the capacitor in a way that does not destroy anything. You would need 27000/36 = 750 lightning strikes to break even for the cost. That is more than a lightning strike per day for two years How many places at there where you get enough lighting to strikee so charge the system and then discharge for the lifetime of the device to have a chance of breaking even? Remember this is cost of supercapacitors not cost of anything that could make it be possible to charge them without frying the system. I doubt that they can be charger in fraction of a second without melting. Even before you look at that problem it has huge economic problems. The better option is to use solar or wind power that is more reliable. If you add storage with capacitors or batteries it is better to do that for solar as you have can get data of how many days there is with sunlight per year. 750 days of sunlight to is not unreasonable during 3 years of solar and then you do not need some extra unknow way to get the lighting into them without destroying them."
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if9wsu | How does a product go from an idea to mass-production and distribution? | Say I came up with a killer baked beans recipe, and I want to share my cooking with the world. Or I created a prototype of a new electronic gadget that would make everyone's lives easier. What are the next steps? I know I'll need to secure a good deal on raw materials, spin up a production line, and get stores to sell my product, but whose job is it to coordinate all of these daunting tasks? | Engineering | explainlikeimfive | {
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"Whos job is it? Well, it's your job. Or, you can hire some people who are knowledgable about those areas and delegate responsibility to those people, but now you need to pay those people with money you don't have yet. Also, you are still responsible if those people screw up. That's why being the owner of a business is high risk/high reward. You have all the responsibility in the world, but can reap the most rewards from it."
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ifda5o | How are disc breaks on a bicycle superior to rim breaks? Wouldn't the greater surface area of the rim require less force than a disc break? | Engineering | explainlikeimfive | {
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"The fact the rotor is an easily replaceable component also means that manufacturers can use more harsher brake pad compounds, giving a lot more friction between the rotor and brakes and increasing braking force there. Also, a disc brake isn't sensitive to the rim being out of true (not perfectly round/flat) and avoids issues of a tire having to clear the brake pads as the wheel is inserted/removed"
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ifj76r | When your car is in a tight spot (like exiting a parallel parking spot), you turn the wheel all the way to one side while stopped, you lurch forward slowly, after after a half tire rotation the car will suddenly turn a little more despite the steering wheel not moving. What's happening there? | I hope I described this OK. I notice it every time I pull out of a parallel parking spot. It's like a little turbo-boost of turning radius. | Engineering | explainlikeimfive | {
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"Probably the power steering is unable to fully turn the tires while stationary, but rolling forward allows the tires to finish physically turning. If you're on a bicycle you can experience this easier, as turning the front tire while stationary will cause audible grinding between the rubber and the ground."
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ifjvgm | Why can electronic plugs be plugged into an outlet and it doesn't matter which prong is in which hole? | Engineering | explainlikeimfive | {
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"Household outlets are alternating current, which means the current flips back and forth - it flows out of the left hole and into the right hole for a bit, then reverses and flows out of the right hole and into the left hole. It switches directions 120* times per second. So plug-in devices can use current in either direction; they don't care. Don't like the direction it's going? Wait 1/120 of a second. In contrast, batteries give you direct current, which always goes the same way, and you've probably noticed that if you put batteries in a device backwards, it will do a whole lot of nothing unless it's a really simple device. *120 per second in North America, 100 per second in Europe. For the rest of the world I'm not sure. [Edit: I checked a bunch of countries and it seems like Canada, the USA and Mexico run at 120 switches per second (60Hz AC) and everywhere else likes 100 per second (50Hz AC).]"
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ifmfur | Why do some electrical plugs (USA) have 1 large prong + 1 small prong and some have 2 small prongs? And then some larger things, like portable heaters, have all 3 prongs (large + small + circular prong)? | Engineering | explainlikeimfive | {
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"So the plugs that have a large prong and a small prong are to keep polarity correct. The plugs with two of the same sized prongs are not polarity specific. And the plugs with all three require an equipment grounding conductor (small round prong). Source: am electrician",
"For many decades, homes were wired with just two wires to each switch or outlets. In terms of basic electric properties, being alternating current these wires were electrically equivalent, so lamps and appliances were wired with two identical small prongs (North American outlet design). But, in fact, the two wires going from the breaker/fuse box to the outlet weren’t strictly identical. One of them was connected, at the box, to ground, typically either through a connection to a water pipe entering the house or to a copper stake literally hammered into the ground. This side of the circuit is called *neutral* while the other side is called *hot*. Later on, the people responsible for electric codes realized there were easy ways to make these safer. Consider a standard light bulb socket. A light bulb has two contacts, one a small circle in the center of the bottom of the base and the other the metal shell of the base that has the screw grooves. Obviously it’s much easier for a person to accidentally make contact with the shell of the socket than with the contact point all the way at the bottom. If you could guarantee that the shell was always connected to the neutral side of the circuit and the center point always connected to the hot side, it’s much safer. That’s because a person’s electrical potential is much closer to that of the ground, which is connected to the neutral side. Polarized plugs were a simple answer to that. By making one blade bigger than the other, and one side of the outlet bigger than the other, a plug can only be inserted one way. And this doesn’t require any rewiring of an older house. All it takes is an electrician or other skilled person to make sure that the correct sides (neutral vs ground) are connected to the correct slots on the outlet, and that the lamp manufacturer follows the same convention in connecting the plug. At some point, I think in the 60s or 70s, it was realized we could do much better by running a separate wire, called the grounding wire, all the way to each outlet. This wire is normally expected to carry no electric current. In fact, it often doesn’t have any individual insulation, the way the other two do. Like the neutral wire, it is connected to ground at the box. But no properly working device deliberately sends electricity to it from the hot wire. The grounding wire is connected to that third rounded socket on the outlet. Instead, the ground wire is there in case a wire inside the appliance comes loose and makes contact with the case of the appliance. Cases such as toasters and mixers are often metal and conductive, so an internal wire contacting the case is an electric hazard. These devices will have the case and other metallic parts that aren’t part of the electric circuit connected to that grounding pin on the outlet. But, as an option available to manufacturers, they can choose instead to make a device *double insulated*, meaning there need to be at least two failures of insulation for one of the live electric wires inside to come in contact with the case. This is a policy decision by the people writing the national electric standards. It doesn’t necessarily address the risk of the light bulb socket mentioned above. Finally, the grounding wire is a pain to get right in older construction without rewiring the entire house. Hence adapters. These often aren’t as safe. Anyone who can afford to upgrade an old two wire installation should consider doing so. Standard electric cable that you find at places like Home Depot is going to have three wires, though I think it’s still be possible to get two wire cable for special applications.",
"* Two small plugs means the device will work just fine no matter which way you plug it into the socket. * One large, one small means that it needs to be plugged in a certain way. * This is because one slot has the +/- voltage on it and the other one is \"neutral\" so it's basically 0 volts. * Some circuits need the the voltage on side and the neutral on the other. * Some don't. * All three prongs is the same as one large and one small except there is an extra safety pathway for electric current to return back to the source. * This is in case something inside the device gets damaged and exposes live voltage to some place it shouldn't be, like the metal case of the device. * If that happens, the safety pin helps conduct that current back to the source where it can trip the circuit breaker and shut off the circuit."
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ifof09 | How do portable/rechargeable batteries know to charge the connected device rather than drain it? | If you have a portable battery that's 75% charged and you connect your phone which is at 25%, what prevents the battery from draining the phone? | Engineering | explainlikeimfive | {
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"You use a different port for charging a device with the power pack than you do for charging the power pack. Different circuits.",
"A portable battery like a power bank it not just a battery in a box that is connected to the outside. You have electronics in it that controls charging and discharging. The barrel is usually at 3.7V and the USB in and output is at 5V. So you have to have electronics that increase the voltage for output and decrease it to charge the battery. & #x200B; If you look at a power bank that not use USB-C connector the input and output connector are different. You have large type-A connector for the output like on the back of a computer and small type-B for input today mostly micro USB. So the power bank have the changing part connected to the small Type-B connector and it can only charge from that. The large Type-A is connected to the part that increases the voltage and power can only go out from a port like that. You could charge the power bank with a \"USB on the go adapter\" adapter that has a Type-A connector but you have to intentionally use it. The adapter has an extra pin so the phone knows that one is connected the phone has to charge electronics for the battery and electronics that cover the correct voltage for the phone. If it support \"USB on the go\" it can output 5V but only it detect a adapter with an extra pin. So before USB-C input and output connector are different. & #x200B; For USB-C the power can go in any direction. It is the device that selects if iy output power or receive power. That can happen by communicating with the device on the other end. I have read that power can sometimes go in the incorrect direction. I do not have a device that uses that but I suspect that on a phone if you connect it to something that you could charge you get a notification where you can choose what to do just like if you connect it to a computer to transfer images etc. It is unlikely you charge a power bank from a phone but to use one phone to charge another is a lot more likely to happen. You could add a button on the power bank that can be used to change the port from output to input if you connect it to something that is not just a wall power adapter. What direction the power can be chosen by the electronic in the device. The same is true if you connect a power bank to a computer then you might like to change it if the computer is connected to a power outlet but you might like to charge the computer if not. I suspect that you add som program in the compute where you can select what happens. I do not have or have used a laptop with USB-C",
"The batteries aren’t simply connect to each other directly, there’s circuitry inside that controls which controls battery charge and drain, you can’t drain your phone with a charging cable or change the power bank from the USB outputs. The difference is with USB C power banks, where the same port is used for changing and discharging, but in that case the two devices send data to say which one charges and which one is accepting charge"
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ifvc5y | Why do we use regular seatbelts in street cars when the ones used by racing cars are much safer and could save tons of lives? | Having seen the kind of seatbelts those cars use and the crashes those drivers go through it impresses me how unscratched they leave their cars, even though they don't have airbags Wouldn't it be much safer if race cars also switched from the current seatbelts and air bags to those and no air bag? | Engineering | explainlikeimfive | {
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"Racing seatbelts are expensive, inconvenient, and uncomfortable. They also generally require a car to be caged to have the right number of anchor points, and may require the use of a helmet and/or HANS device.",
"There’s more to it than just harnesses. First off, if everyone was asked to use a 5 point harness for every trip anywhere, a lot more people just wouldn’t. Those things are a pain to get in and out of. The appeal of the three-point belt is that it’s convenient and easily adjustable for different people. Beyond that, though, race cars are engineered in many ways for driver safety. The cockpits are reinforced in strategic ways to protect the drivers who also where full face helmets and HANS devices. Your proposal leaves all of that out. An airbag is essentially the more convenient HANS/helmet combo that people actually use instead of ignoring because it’s too complicated and cumbersome. If a race car comes to a sudden stop, the driver doesn’t fly forward because they’re attached to the car in six different places, not to mention a radically different seat and driving position. Three points are sufficient for most regular cars because combined with the cushioning of airbags, the results are good enough when weighed against the convenience of daily usage.",
"There are always going to be safer things we COULD be doing, but there is always a balance to strike between effectiveness and convenience. Racing type harnesses are simply too unwieldy and inconvenient for regular people to wear all the time, despite their effectiveness. The car needs to be designed in a certain way, and they are uncomfortable to wear. People would just stop wearing them entirely. The same reason we don't wear helmets when we drive, despite the additional safety they provide. There is a balance that needs to be struck.",
"I mean, don't they also drive with helmets on and fire-retardant suits?",
"1) Non-racing cars aren't normally travelling at 150 mph or faster - so harnesses aren't beneficial 2) They need more anchor points and to be welded to a roll cage to be effective 3) Roll cages and harnesses would take much longer for emergency services folks to cut if Jaws of life are needed in a wreck."
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igamho | what does a turbo do in a car? | Im not a big car guy sorry | Engineering | explainlikeimfive | {
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"A turbo(charger) is really two things: a turbine and a compressor. The compressor - it compresses the air that goes inside the engine. If there is more (compressed) air per unit of volume, that means there are more oxygen molecules, and you can inject more fuel, to make more power on each engine revolution. The turbine - it sits in the path of exhaust gases. The passing gases spin the turbine, and then the turbine (connected by a shaft) spins the compressor. This is a way of using mostly waste energy - the pressure of the exhaust gas - to do the useful work of spinning the compressor. In some engines, the compressor is driven directly by a belt and pulley from the engine's crankshaft. That's called a supercharger. A supercharger robs some of the engine's own power (rather than using the wasted power of exhaust gases), but has the advantage of keeping the compressor spinning all the time. This is better than a turbine, which only works when the exhaust gases reach a sufficiently high pressure, i.e. the engine works at a sufficiently high RPM. Whether the engine builders choose a supercharger or a turbocharger depends on how they want the engine to behave, where that engine will mostly be used, in how heavy a car, etc.",
"It’s compressing the air which is used to fire up the engine in addition to the fuel. A normal engine has to get his air from ( I think it’s called negativ pressure in english) which occurs when the empty Zylinders open. A turbo can support the engine by applying pressure to the air.",
"Combustion engines need both air and fuel to get power. to make more power, you need more of each. sometimes the engine is made \"larger\" so it eats more air, so gets more power. Other times we can make the engine eat a lot more without making it any bigger. One half of a turbo squeezes the air and forces it into the engine. After the engine makes power from the burnt air and fuel, it makes a lot of hot burnt air and fuel, which is called exhaust. This exhaust comes out fast and still a bit squeezed, which powers the other half of the turbo. both halves of the turbo are connected."
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igau56 | Why do bike brake discs have so many holes in them? | Wouldn't it be more efficent to have a solid brake disc, so the brake pad will touch more disc surface, and hence, stop the bike faster? Plus, removing the holes would make the disc more resistent to breaking/cracking? | Engineering | explainlikeimfive | {
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"They’re to dissipate the heat. Braking uses friction to stop the movement of the body. The energy needs to go somewhere, so it becomes heat. Too much heat energy in the metal (or whatever material your brakes are made of) can warp them, making the brakes stutter, and cause them to fail.",
"Two main reasons: 1. To aid cooling as brake discs do get hot when in use (transfer of energy from kinetic to thermal); 2. Brake pads are applied to a brake disc at a certain pressure. If the area that pressure is excerpted on is smaller (a disc with holes in it) and the force remains the same, the amount of force applied to the brake disc is higher as it is spread over a smaller surface area. Holes are drilled in carefully calculated places to try to reduce breaking/cracking. Same thing with uprated clutches in cars - usually stage 2/3/4 clutches have a smaller surface area for the flywheel to adhere to, but tend to grip much better, as the force is spread out less, so the clutch is being pushed into the flywheel harder."
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igjott | Why do warplanes have little-to-no armor compared to tanks? | In my case, I think it probably has to do with the fact that they're flying in the air, and they need to be as lightweight as humanly possible in order to fly high and better, and that adding armor just weighs them down. Tanks, on the other hand, are ground vehicles, so they're not as encumbered by their own armor as warplanes and whatever armor they could have equipped themselves with. Right? | Engineering | explainlikeimfive | {
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"Just as you stated, armor on a plane means more weight which reduces range and maneuverability. Especially these days, fighting aircraft rely on a combination of weapons range, speed, stealth, and electronic countermeasures to prevent being hit in the first place.",
"You've pretty much answered your own question, yes. A lighter plane could fly better than a heavy one. Another thing to consider is fuel and ammo. The lighter a plane, the more fuel and ammo they could carry, and thus the longer they could stay in the air and fight. Airstrips were often not that close to the battlefields, so the plane had to use a good amount of fuel to get there and back. Planes would be somewhat useless if they were so heavy, that they could only engage in combat for a couple of minutes, then turn back. Or, they only had enough ammo to shoot for a few seconds. It is much easier to refuel and resupply a tank during combat. If a tank ran out of fuel, it could still shoot and provide cover, and at least draw fire from the enemy. Also, a plane that runs out of fuel crashes. A tank that runs out of fuel only become a better target, but isn't guaranteed destruction. All it would take is a truck to come up to the tank in the fuel to refuel it and re-arm it, and now they are good to go again.",
"Airplanes' best defense is the ability to not get hit. Enough armor to stop a .50 round or a missile would be impractical to apply to most of the plane, and is reserved for certain parts of the vehicle."
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igjut2 | what is it about a laser pointer being able to be seen from far away but not the same with a high powered flashlight? | Engineering | explainlikeimfive | {
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"Photons/light waves coming out of a flashlight spread out in all directions from the bulb, causing them to get fainter the further away you get from the bulb. Reflective housings can help some, but its still going to spread out. Laser light is formed differently, so its photons/light waves all travel practically parallel to each other, meaning it can still be detected much further away. The waves haven't spread out nearly as much. In both cases, some amount of light will hit a distant target as long as nothing is in the way."
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ih3kqh | Why do batteries need to be charged for a long period (8-12 hours) before the first use? | Engineering | explainlikeimfive | {
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"They do not anymore. It used to be that electronics had poor ability to measure the existing battery level. So you had to be 100% sure the battery was 100% or else the system would incorrectly report battery as being full when it was not quite full. This has long since no longer been required, however many still keep saying to do it."
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ih4z0k | V6 V8 V10 V12 - what to pick, when? | I understand they mean the number of cilinders in an engine. But why would you pick a V6 over a V10 or V12? Would bigger not always mean better? What are the key differences you look at as an engineer when choosing a certain engine type for a certain job, e.g. rally, formula 1, drag racing, ... | Engineering | explainlikeimfive | {
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"Yes, those numbers are strictly referring to the number of pistons/cylinders in an engine. There also was a great straight 6 produced by AMC and later Chrysler that used to be in their Jeep line for 4 liter engines. That's why those vehicles had longer hoods. There are far, far more considerations that make up an engine's power. A couple of them are cylinder displacement and compression ratio. Cylinder displacement refers to how much space is taken up by the cylinders. That's where terms like \"4 liter engine\" or \"350 engine\" come from. Some are measured in liters (metric system) and others in cubic inches like the 350. Compression ratio relates to power as well, how tightly the pistons compress the fuel/air mixture. Consider a larger engine will also weigh a lot more, and be more mechanically complex. Depending on these and other factors, cylinder count is less critical as it relates to horsepower. A 4 cylinder engine with larger displacement may well generate more power than a small V6. Also consider the purpose of the engine. Are we talking a race car where every last ounce of weight matters and there are incredibly strict standards on what you can do to an engine? Are we talking a family sedan for getting groceries and bringing little Jonny to soccer practice? Are we talking a big pickup truck for a contractor to pull his large job trailer to the work site every day? They will all have different requirements based on the task.",
"V refers to the shape of the piston arrangement. There are other shape such as in-line, opposed/flat or radial. All these arrangements have pros and cons. V arrangements are popular for automotive because they sit inside a cars engine bay nicely and give good access for matainance. The number is, as you said, the number of cylinders the engine has, however whats is also important is the displacement, which is the total volume of all the cylinders. So if an engine had big enough cylinders it could have more displacement than engine with more cylinders that are smaller. Displacement determines the total energy that an engine can produce. Bigger means more power, but that's not always better. A small compact city car could use a flat-4 90 HP engine just fine. It would be a waste of money, space and weight to put a V12 1500 HP engine in it since it would never use that extra power. When talking about performance vehicles for racing, then you intend to use all of an engines available power so you look for an engine that fits your power requirements and has the best power to weight ratio (how much power it produces divided by how much it weighs). This is where number of cylinders is determined. A company might not have the tooling to make large bore cylinders so they make more cylinders to get the displacement required, or another company may find a better way to seal piston rings so they can increase the size of their piston and get rid of some cylinders. Every cylinder requires its own set of spark plugs, valves, lubricant, bearings, cooling, etc so by removing a cylinder, it can save on the total weight of an engine."
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ih64zn | Why would they build a control center (Houston) for a rocket all the way in Florida? Couldn't they have just built the control center right next to Kennedy? | Engineering | explainlikeimfive | {
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"The control center at Kennedy Space Center has operational control during the launch and ascent stages, but after the rocket is in orbit it doesn't matter much where the control center is. The Houston Control Center dates back to the early days of the manned space program and was built not only to support space flights but also serve as a hub for R & D, manufacturing, astronaut training and much more in support of the space program. Houston checked all those boxes due in part to its location and strong infrastructure available.",
"the control center for the rocket launch IS in Florida, at Kennedy. Houston is in charge of the mission AFTER the launch succeeds. This only applies to manned missions. Unmanned missions are usually controlled from JPL in California. The reasons for Houston are political, geographical, financial, etc. Houston was picked when LBJ was a powerful Senator from Texas, and officially opened when he was Kennedy's VP. It's located in the middle of the Continental US. It was near a major university (Rice) and in an area that would be home to the growing oil & gas business, providing a good pool of engineering talent. The land was donated by the Humble Oil company.",
"Not really an ELI5 question because it has a simple answer. The control center was going to be big and employ a lot of people. So they needed land near a place where a lot of people could live. Houston ticked the boxes. Nasa got a good deal on some land there. The control center doesn't need to be near the rocket launch pad.",
"As other comments noted, control doesn't \\*need\\* to be near the rocket so they had free choice and there's lots of reasons Houston is a reasonable choice. They \\*could\\* have built it in Florida but the space program was a huge multi-billion $ government program and they intentionally spread that $/jobs/prestige around. That's part of the reason you've got major facilities in California, Texas, Alabama, Florida.",
"The launching site needed to be as close as possible to the equator, because the earth is rotating faster there, giving a boost to rockets leaving the atmosphere. So Florida was, scientifically speaking, the best location for the launch site. However, at the time they were exploring a site for the NASA headquarters, Sam Rayburn (from Texas) was Speaker of the House and Lyndon Johnson (also from Texas) was senate majority leader, then vice president, and finally, president, and they used their influence to get the space center moved to their state of Texas. They didn't *need* to move to Houston--prior to the establishment of the center in Houston, NASA was located in Virginia, where there were plenty of people to work there and space to do so. Whether they would have chosen Houston without the influence of Johnson (who had been working to advance the space program since 1957, and became head of the Space Council in 1961 as Veep) is unknown. It was definitely a prize for any politician to have in their district or state so lots of politicians jockeyed to have their location chosen. JFK had wanted the space program to be centered in the Boston/Cambridge area, a perfect place for Harvard and MIT scientists, and they broke ground for some buildings. But ultimately Boston was passed over for Houston, despite JFK being the president at the time. If you want more detail: the site of Houston was chosen while Johnson was Vice President and head of the Space Council, but he had been already working on advancing the space program since 1957, which was before JFK became president and declared his man on the moon mission. So there were a range of years where Johnson had a lot of power where NASA was concerned and he was able to use that to help push through what he wanted, but it wasn't until he became veep that the site was chosen."
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ih7zhc | How does mAh convey the capacity of a phone battery, as opposed to Wh which reduces to joules? | Engineering | explainlikeimfive | {
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"If you know the voltage of the battery (probably about 3.7 V), multiply the mA-h figure by that to get the energy stored in W-h."
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iha4wd | Integrated Circuits | I realize this is a fairly specific topic, but I am learning about integrated circuits in a class and something just isn’t clicking - even though everything I read is about how they revolutionized computers. My understanding is that they are just very small, predefined circuits. Why is this revolutionary? And why does having a very small circuit help with anything anyways? | Engineering | explainlikeimfive | {
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"They provide an easy way to manufacture incredibly complex circuits. A modern CPU for instance has billions of transistors and wires running between them. Imagine trying to wire that by hand, or even by machine. The earliest computers such as the ENIAC were done this way, took up entire rooms, years to build, and are millions of times slower than phones in terms of processing. ICs themselves are made using a technique called photolithography which uses chemicals, light, and a “stencil” to etch the circuit into a slab of silicon. This is significantly easier than having to wire things manually, it also produces a device with no moving parts and can be made pretty small, which reduces material used and turns out to allow the components to “switch” faster, which speeds up computation a lot.",
"The first ICs had a few transistors, each equivalent to a lightbulb-sized vacuum tube. The transistors could be, and were, scaled down radically. Now, fingernail-sized chips have *billions* of transistors."
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ihgr70 | Why do we connect positive to positive when we jumpstart a car? Electricity should form a current, so shouldn't positive to positive be fighting itself? | Engineering | explainlikeimfive | {
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"The car’s electrical system is already a circuit. You are just hooking up two batteries in parallel.",
"A discharged battery is very roughly analogous to an empty water tank. (Electrical potential is analogous to some water's gravitational potential). If you want to fill an empty water tank, you can connect it side-by-side to a full water tank. Current will rush into the discharged tank. If there's another car nearby with a charged battery, then that's the source of the higher voltage. Connect (+) to (+), then make sure they have a shared \"ground\", and *bingo!* the electrical current flows straight from the charged battery into the discharged battery, to begin the charging process."
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ihqyq4 | Why are dedicated blenders and food processors more popular than 2-in-1 models? | I do understand blenders and food processors serve for different purposes. But from an engineering point of view, those 2 machines are identical. I only noticed their differences in cups and blades. My point is the same motor base should work just as well for different blades and cups. A good modular design should produce a 2-in-1 with similar performance to the dedicated models but at a much cheaper price. I expect to see 2-in-1s dominate the market. The reality seems to be the opposite. Why is that? Any design difficulties I failed to see? | Engineering | explainlikeimfive | {
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"Food processors motors require a bit more torque than a blender to break up more solid foods. But high end powerful blenders can easily process solid foods (ie those “will it blend” videos). It’s more on the lower end, of you don’t really care too much and you just need it for drinks, you can get a blender that doesn’t have the power to blend up solid foods for cheaper."
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ihy7xk | How do big ass ships like aircraft carriers actually float on water while carrying the weight of aircraft, engines, controls, etc? | Engineering | explainlikeimfive | {
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"Buoyancy is what holds up a ship. A ship displaces a certain volume of water — the ship “makes a hole” in the water of a certain size. If the volume of the ship inside the hole is lighter in weight than the water would be, it floats. Water is _heavy_, and the interior of a ship is mostly air, really. A cubic foot of air weighs very little (like, .08 pounds). A cubic foot of seawater weighs 64 pounds.",
"* Two things can't occupy the same space at the same time. * So when the ship goes in the water, it takes up space. * The water that used to be in that space gets pushed to the sides. * But there was already water to the sides, so that water gets pushed up. * So the weight of the boat is actually lifting the weight of the water that it pushed out of the way. * As long as the weight of that water is heavier than the weight of the boat..it floats. * Don't forget that shape matters. * IF the boat was super skinny, then it would only have to move a little bit of water out of the way. * But boats are designed to take up enough space in the water to make the water it moves weight more than the boat.",
"It's proportional, so the bigger the boat the more weight they can carry. Those aircraft carriers are ABSOLUTELY MASSIVE and the buoyancy grows accordingly. Also having a large volume displacing water maters. Use the same weight but as a pole and the pole would sink, the amount of water displaced is more than the weight of the ship. So the force of the water pushes the boat \"up\"."
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ii2fyh | How in the world does a faucet work? | Engineering | explainlikeimfive | {
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"Imagine a [water dispenser / water cooler]( URL_1 ) like you might find in an office building. The water is at the top, and the spigot is at the bottom. When you press a button or turn a knob, all it's doing is opening a hole. Gravity pulls the water down. When you release your finger or screw the knob back, the water stays inside. The faucets in your house work basically the same way. When you're turning it, you're just opening a hole. Water pressure is what causes the water to come out. It's exactly equivalent to if the water was coming from a big tank on your roof. And in fact, that's exactly how water works in many areas - have you ever seen a [water tower]( URL_0 )? As for mixing hot and cold, it's a pretty cool mechanical invention, but it's nothing more complicated than opening two holes so that both hot and cold flow at the same time."
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ii5lij | What are the specific reasons we cant scale up a model proportionally? Eg. a small bridge design that works well but fails catastrophically when scaled up proportionally. | Engineering | explainlikeimfive | {
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"The square-cube law the strength of a material is usually proportional to its cross section (area) the weight of a material is proportional to its volume if you double the size of a bridge, it’s strength increases 4x but it’s volume increases 8x as you continue to scale up the weight quickly overshoots the strength",
"The mass of an object is proportional to the volume. The volume of a cube is side\\*side\\*side so side\\^3. So if you make a bridge is uniformly scaled to twice the size the mass is 2\\^3= 8 times higher. The strength of the material is proportional to the cross-section area of the material. The cross-section area is side\\*side= side\\^2 The result that the strength of a bridge is uniformly scaled to twice the size is 2\\^2 = 4 times higher. So you have 8 times the mass and only 4 times the strength this is a problem. The result is that a bride you just scale that way will soon collapse under is own weight. This is called the [Square–cube law]( URL_0 ) You can see that in animal bones where small animals have very thing bones in the legs compared to the size but large animals have comparable thick legs. An elephant-sized mouse would break its lege if it attempted to stand up.",
"What others mentioned about the square-cube law is right, and is the main reason a bridge can't simply be scaled up and not collapse. I'd just like to add for a moving object, the hindrance (or aid) of drag is introduced. Weight depends on volume, while drag depends on surface area. Again, square-cube law. A larger plane would find it easier to counter drag and move forward but harder to stay aloft than a smaller one."
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ii7rtb | Why is it that I get amazing cell phone reception in some buildings but in others I don't? | Engineering | explainlikeimfive | {
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"It depends on what type of material is used for the building. Lots of metals used in construction cause more interference than for example wood."
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iictsp | Why aren't dashcams preinstalled into new vehicles if they are effective tools for insurance companies and courts after an accident? | Engineering | explainlikeimfive | {
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"The biggest reason is that if the manufacturer includes them, then they are liable for them. Dashcams and SD cards fail all the time and Ford or GM do not want to be on the hook if it's some defect in the camera. Given that there is a huge market for dash cams, giving the end user a plethora of options, and given that you can pick a really good camera up for under $200, there is absolutely no reason for manufacturers to engineer embedded cameras at the normal consumer level. Some luxury cars do have them. Tesla has cameras. I believe some Mercedes do as well. Cadillac has started including them.",
"A camera is just as likely to implicate the driver (and their insurance company) as it is to exonerate them",
"I could be wrong but people who are paranoid already about being filmed or recorded at home or tracked elsewhere, probably wouldn't get a car with a camera that will do all that while they drive too",
"What incentive does a car company have to include something that benefits insurance companies and courts? How does that make money for the car company? Rest assured, if car makers could increase their profits by including dash cams, every car would have one.",
"Tesla does have I think 4 different dashcams installed factory. There are other cars with cameras but they are special cameras that help with driver assists. However, as previously mentioned, there are plenty of paranoid people. I wouldn’t get a car with a dashcam factory. What if it’s recording audio? Now I did put an aftermarket dashcam that also record audio in. Thing is, I am the only one who can access the recordings.",
"I asked my State Farm agent if I have a dash cam do they offer any discounts? You know for like safe driving or to easily prove who's at fault for an accident. She almost laughed, said no, and moved right on to whatever else we were talking about. Was a little strange.",
"Most consumers don't want them because most people break laws all of the time (speeding, not stopping at stop signs, not wearing seatbelts, texting while driving, etc). Insurance companies know that their customers constantly break laws so they don't want cameras either (so they don't have to pay to the other party when their customer breaks the law). This is why you don't get an insurance rebate for having a camera. So no one is pushing for dash cams and there is a good incentive to not mandate them. So it laws did get proposed I am sure insurance companies would fight against them. It might make sense when we have more self-driving cars.",
"Former OEM interior engineer here. Primary reason is it’s not something most customers are looking for an it increases the cost a fairly sizable amount. Anything built into a vehicle needs to be able to last the life of the vehicle. The testing and development needed to add dash cams simply isn’t worth it. Not enough people would choose it as an option. We did start including USB ports in the mirror covers on newer cars, but mostly in foreign markets where dash cams are more widely purchased (Russia, China, etc.)",
"A $100 camera turns into $1000 for the consumer. They sell more cars if they are cheaper. Until it becomes a requirement, car manufacturers don't really have an incentive.",
"They are illegal in Germany because you are recording where other people are going to or what they're doing that thus violating their privacy. Being German is annoying, I'm telling you...",
"The internet has a tendency to concentrate information about stuff and to make rare things seem much more common than they actually are. In this case, dash cams don't matter in the vast, vast majority of car crashes. Only a tiny percentage of car crashes have any dispute about liability. Of the crashes in which there is disputed liability, only a tiny percentage of those occurred in such a way that a dash cam will show what happened - you need something like what Teslas have with full camera coverage. And of the remaining crashes, only a tiny percentage have more than trivial damage. The internet just makes dash cams seem useful because the handful of instances each year in which they were have facts so bizarre that they make interesting posts on the internet. It costs thousands of dollars to do the full camera coverage that Teslas come with. But those cameras aren't there to protect you from liability. They're there partially because they're necessary to run the autopilot and partially to protect Tesla. Tesla is a huge, well financed corporation producing a *legally* untested technology that can easily hurt or kill other people. The cameras on a Tesla are necessary to deter people from filing frivolous or fraudulent litigation against them. But that isn't a real concern for you unless you live somewhere, like Russia or China, where insurance fraud is common.",
"Because they can make more money on it as an option. People expect a new car to be about $21k. So you can't charge much more than that, but let's say you want to install a discreet dashcam in your new car. Well, you could just include it and decrease the profit margin, or you could add it as a buy-on for an extra fee, negotiate with financial institutions to lower the interest rate of anyone who gets it and move on.",
"You mean like built in navigation systems that cost $1000 to update the maps?",
"I mean I want less unremovable tracking in my car, not more! Some car \"security\" systems that have internet connection through the cellular network are already a problem I rather want to use my own dashcam only, that I have (more) control of"
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iil49o | Why do things turn red when heated? | Engineering | explainlikeimfive | {
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"Radiant heat is infrared which is a form of light that's lower energy than visible light. As something gets so hot and energetic that light moves up the spectrum and into visible light starting with red. If it gets hot enough it can even turn blue like the very base of a flame."
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iiurug | With electric trains that use a third rail, how come when it rains all the water doesn't make a short circuit? | Engineering | explainlikeimfive | {
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"There's no path for the electricity to follow to the ground. The rail is raised up on insulators, and these insulators are designed so that they have a dry band around them even when it is raining. For top-contact third rails, these are supported from below by [mushroom-shaped insulator 'pots']( URL_0 ); these stay dry under the mushroom 'cusp'. For side-contact and bottom-contact third rails, the support arm shape and covers can be used to stop rain reaching the rail. These also have significant safety benefits to track workers. In all cases, it comes down to there not being a continuous layer of water which is substantial enough to allow significant current leakage.",
"Water isn't actually conductive, the dissolved minerals in it are what give it any sort of conductivity. Rainwater contains next to no dissolved minerals so it's about as non-conductive as liquids get.",
"The most important answer here that I have not seen yet is that a vast majority (but not all) third rail systems for subways and trains are DC power. DC power is very tolerant of water. I have personally witnessed (via camera feed until we lost it) a DC switching system run in hurricane flood water. This was rising salty sea water. Ice and snow on the line can pose a contact problem, but the rail can be heated or the system may have maintenance cars run down the track scraping and spraying antifreeze on them.."
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ij1u9g | Why do all street race cars in movies/games/shows have manual transmissions? What is better about them for racing over automatic transmissions? | It just seems that all race cars in video games and movies have manual transmissions. Really, would automatic cars just not race as well? | Engineering | explainlikeimfive | {
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"In video games and movies - because it's \"cool looking\" In real life - because it allows more control over the transmission shift points",
"You've got more control over when to change gear, so you can let the car rev much higher than an automatic transmission would.",
"Manual transmissions give better control of the car overall. It allows for rapid gear changes that automatic transmissions just don't let you do, and it's that kind of control that allows for drifting, much more rapid acceleration overall, and it's easier to prevent the engine from blowing from too high of an rpm. Stunt driving is done pretty exclusively with modified manual transmission cars, shits wild man",
"There may be lots of reasons but the first one I can think of is control of power to the wheels. Automatic transmissions are specified to change gears based on RPM and speed. A manual transmission allows the driver to accelerate and gain speed based on whatever they need for their race.",
"Automatic transmissions have a lot of losses and are heavier than a strictly mechanical gearbox An automatic transmission generally includes a torque converter which is two fans blowing air at each other to transfer power. This has a fair amount of losses, especially when you're trying to transmit large amounts of power during heavy acceleration. This big fluid filled donut is also reasonable heavy Your basic manual gearbox will have a dry clutch which is two plates that get pushed against each other and ideally they don't slip so you have no losses. Manual transmissions of a couple decades ago offered more gears and faster shifts than automatic gearboxes of the same era with a 5 speed manual being common but only a 3 or 4 speed automatic. Combined with the reduced losses of clutches vs torque converters it made them better for ambitious driving Modern cars prefer dual-clutch transmissions for maximum performance. They're basically two manual transmissions in one box with one clutch engaging the odd gears and the other engaging the even gears, and a clutch for each set (hence dual clutch). In sports cars with paddle shifters this is the transmission, and it can complete an upshift in tens of milliseconds. Dual Clutch Transmissions are what you get if you go \"How do i make the best transmission using clutches and manual style gears\"",
"A manual transmission allows for operator to control how many RPMs each gear gets whereas an automatic transmission utilizes computers to shift gears. Getting the maximum RPM potential from each gear will result in more speed and power. Having control over this manually in a race typically results in more efficient and effective use of each gear. (I would argue to say that today’s modern technology has made automatics extremely efficient in shifting, especially in the super car category. 0-60 in less than 3 seconds is a ridiculous feat that a manual car shouldn’t be able to do.)"
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ij8jgi | How could ancient civilizations carve so finely inside volcanic rocks, granite or other type of tough rock? | Engineering | explainlikeimfive | {
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"Volcanic rock is generally tough, but iron chisels can dent it, or granite at least. You only need to cut it deep enough that you can insert wooden wedges into it. Then you soak those wedges in water so they expand, and the expansion of enough wedges causes the rock to crack. You can't carve granite until you have invented iron though, cos bronze tools are quite soft.",
"_Inside_? The techniques for shaping stone are ancient but I haven’t seen rocks carved internally."
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ijfx4r | Why isn't pumping loud noise underwater widely used to defeat passive sonar? | That's pretty much it. Lots of different wave-based detection and tracking systems can and have been defeated by creating "noise" in that system. Airborne metal chaff can create noise for radar and render it useless, for instance. So why isn't it more common to just overwhelm the ridiculously sensitive listening devices on passive sonar by just dropping underwater drones that blast Sabaton, or something? I mean, this could theoretically even make a torpedo miss, right? Or do they do this and I'm just unaware of it? | Engineering | explainlikeimfive | {
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"Underwater, the point is to not be seen. Emitting a ton of noise is a great way to be seen and give away your location. Chaff is used when the enemy has already found you and is shooting at you. Submarines do use decoys to confuse torpedoes, exactly as you suggest. Once you know where a submarine is it’s relatively easy to track and kill in a a way the submarine can’t defend against. So the whole point is not to be found.",
"Maybe not exactly what you are looking for, but there is something called \"Prarie-Masker\" that is a system on the underside of some Navy ships that pumps out noisy air bubbles to mask the acoustic signature of the ship. This makes the ship noisier in general, but makes it harder to classify or blade-count, which makes it more difficult to do acoustic intercept on.",
"> Or do they do this and I'm just unaware of it? There are devices that do things sorta like this, they're called \"sonar decoys\". You're describing a particular kind of sonar decoy that was used back in WWII and shortly thereafter. [Here is a US patent for a \"Hammer\" decoy]( URL_0 ), The Germans in WWII had a device known as \"Siegmund\" which was designed to setoff a bunch of explosions to deafen enemy sonars. There are also a wide vareity of \"bubble\" based sonar decoys that operate a lot more like chaff used to - generate a body of water that is hard to operate sonar in. These are usually launched from the submarine in an effort to confuse people (or torpedoes) actually hunting for the sub. The US has a device called a \"Mobile Submarine Simulator\" which is basically a torpedo that is designed to sound like a submarine, so that if you're hunting a submarine launching missiles you're forced to run down multiple targets. These are all generally reactionary devices however, because a submarines best option is to just remain undetected."
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ijh8ki | Metal on metal seems like a terrible option for traction. Should trains use rubber or tires or something else? | Engineering | explainlikeimfive | {
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"> Metal on metal seems like a terrible option for traction. That's a feature not a bug As your car rolls along it's rubber tires squish and deform a bit which burns off energy as rolling resistance Steel wheels and steel rails don't deform significantly so the rolling resistance is extremely low This means that trains can't speed up/slow down quickly but they can travel long distances with massive loads very efficiently and that's more important to a train that 0-60 times Trains are about 4x as fuel efficient as trucks thanks to their low rolling resistance",
"Trains are really heavy. Rubber tires would not last. The friction of the weight alone is enough to get a train moving.... The secret is in the coupling mechanisms between all those freight cars. There’s roughly a foot of slack between each car in the train. When they want to start the train moving, the freight engineer first gets rid of all the slack by backing up enough to compress the entire train. Then, when he starts the locomotive moving forward, the slack is gradually taken up and the train starts moving literally one car at a time. Once all the cars are moving, the locomotive can keep them rolling, even speed up and slow down. But it was the slack that got them all started.",
"The low traction, and thus the low rolling resistance is the entire point. That's something you want and its a huge reason why trains are so energy efficient.",
"Train tracks are generally designed to not require more traction than metal-on-metal can provide. In cases where additional traction is desired the standard solution is to put down sand.",
"I know of one train used in logging that had tubes near the drive wheels so that sand could be poured down to help with grip.",
"Trains are heavy enough that it doesn't matter too much. They don't accelerate or decelerate very quickly and if they did have rubber wheels, I suspect they would be destroyed by the weight. Lastly, trains are on tracks so it's not like they really need the traction to steer.",
"The reason why the rails are in steel is because how steel is resistant and easy to produce compared to other materials. And the reason why the wheels are in iron is because they need to keep their circular shape so it's easier to pull something (1 man could pull 15 tons of materials if they are put in a wagon). Now, you're right when you say that it's harder for the locomotive to roll on the rails. But steel is still the hardest easiest material to create on an industrial level, and maybe theorically we could use another material for the rails or the wheels that would be as hard as still without being steel, but in today context, it would be not costworthy."
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ijon2c | How do we build bridges or off shore oil rigs where deep water is involved and how do we know it’s safe? | Engineering | explainlikeimfive | {
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"Oil rigs are actually really complicated. Sometimes they have to construct a solid base under water, but sometimes the rig itself floats and is just securely tethered to the ocean floor to keep it in place. And lots of methods in between. The rigs are engineered specifically to the location they're going. With bridges, there are probably just as many methods, if not more, but my favourite is the cofferdam technique. Because it's [literally insane]( URL_0 ). This is actually a super old technique, but they basically build a damn around the area they need to work on and trust that it doesn't collapse while they're doing it. They use that while they build the structure and then dismantle it and move on. As for how they know they'll be safe? Engineering. The architect designs the structure and then the engineer makes sure it's actually feasible and safe. And modern engineering is basically reasonable overkill. They plan to ensure that it can withstand more force than its likely to encounter. But there have been some spectacular failures. The collapse of the [galloping gertie bridge]( URL_1 ) is pretty famous. Wind caused the bridge to ripple dramatically and it collapsed just months after it was constructed."
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ijqdvj | Why is binary with transistors used in computers? Why not other states like 3 or 4? | I saw this in a video and they said that it was because if there are more states, there'd be "interference" from other devices? What does it mean? Transistors make use of semiconductors and flow of electrons, why not divide certain voltages for more states? I apologise if I got any info wrong, but please make me wrong. Layman terms would be appreciated. | Engineering | explainlikeimfive | {
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"Two states are easy. On and off. This is very easy for transistors to compare. You don't need to be careful about what exact voltage the transistors output - just on or off. Making a system that sets exact voltages and differentiates them would likely just end up being a bunch of different interwoven binary systems running at different voltages. Not really a step up. Now, analog computers have been attempted, but they are less reliable and more difficult to make than digital ones, and ultimately digital was the one that humanity chose to use.",
"It’s a lot cheaper and simpler to use only two states. Electricity seems like a constant, but it’s actually constantly fluctuating a little bit because of tiny things like magnetic fields, static electricity etc. So if say you had 3 states. High, low and off. You walk past one of those grocery store anti-theft gates. It’s not much, but it’s enough to switch some states from low to high. This causes stuff to break. Whereas if it’s only: on and off. If something was on, and the voltage dropped a bit, it still reads as on, so nothing happens. Making the difference between multiple states big enough would also require you to build circuits that can tolerate a huge range of voltage.",
"The \"interference\" issue is true, but it's not the main reason. When a circuit is using different values to represent different things, using more voltage levels means that they are closer together, so it's harder for the reading circuit to discriminate between them. The \"signal to noise ratio\" goes down. Once it gets too low, you get errors. You *can* use multiple voltage levels to construct logic circuits. It's been done. There are two main reasons why it isn't done routinely. The most important one is power. If you have the transistors either in the \"mostly off\" state or \"hard on\" state, then you can design circuits in such a way that there's very little current flow most of the time (other than during state changes). This is a huge issue when you are putting billions of devices into a small area. And no one has come up with a way to do it with other logic systems that doesn't require a huge area (size/cost) penalty. You can design trinary circuits that are power efficient, but you have to use far more than 50% more transistors to accomplish it. So you lose any possible benefits. The other main reason is that we've been doing binary for decades. There's a huge infrastructure invested in designing and using binary digital logic. For a technology to replace it, you need to get some major, major benefits. That may happen at some time with a technology like quantum computing, but something like trinary computing just doesn't merit the change at this point.",
"Not quite the question you asked, but there's similarities between this and evolution of solid state storage. It started off with SLC (single bit per cell) where, any significant charge is a \"1\" and anything below that is a \"0\", then they moved to 2 bits per cell (MLC) up to 3 and 4 (TLC, QLC). These have the advantage of offering much higher data density but at the expense of reliability - the charge degrades over time and its much harder to distinguish a degraded QLC cell vs a SLC cell, so they get written off faster. Once you run out of the buffer of spare cells, the drive is essentially unable to write any more data. Guess what I'm saying is it is possible to divide voltages to represent more states, but it comes at a cost.",
"As several people have stated, binary logic is easier to interpret and takes less space when considering other systems. Another consideration, and this is mostly how technology is evolving relates to the actual size of the electronic devices (mostly transistors) and how it physically behaves. As technology has evolved, transistors have been gradually shrinking. In the 80s-90s transistor gates were on the 20-40 micrometers size. On this size it is relatively easy to control how much current a transistor drives and it has quite ideal on/off states. Nowadays modern computers have transistors with a size of about 7nm, about 2000 times smaller. On this sort of technology the previously on and off states do not really exist. A transistor is never fully off and never fully on. It no longer behaves as you would expect and leakage current, i.e. current that happens when a transistor is off, becomes really relevant and accounts for a full chunk of the power consumption. Furthermore and this is mostly to design considerations, voltages to power those systems has consistently lowered. From TTL (transistor transfer logic) that had a 0-5V level, current transistors tend to work below 1V. All of this issues have made it harder to define given states on transistors and would require even more precise devices to be able to interpret multi-voltage states."
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ijrfdq | Why are cars built to go 100+ MPH when most speed limits usually don't allow over 70? Is there a point to this? | Engineering | explainlikeimfive | {
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"It's to do with efficient gearing For a given engine you can gear a car to accelerate really quickly, or to reach a higher top speed. When racing, this is changed depending on the track (does the track have a lot of tight corners and hairpins, or a lot of long straights?) For road cars, you want to gear it so that it can navigate tight streets and hills at slow speeds without using lots of fuel, as well as go on motorways at higher speeds without using a lot of fuel. They do that with a good range of gears. The engine size required to be able to provide decent acceleration at low revs in low gears, at higher revs in higher gears can achieve 100"
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ijtqhp | if an anchor is deep seated in the seabed enough to stop a 50,000 tonne ship from moving, how do they get the anchor out when they want to resume a journey? | Engineering | explainlikeimfive | {
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"An anchor is like a claw. Go outside, find a patch of soil, dig your fingers right into the earth and try to drag your hand along parallel with the ground. Difficult, isn't it? Now do the same again - really dig your fingers in, and then pull it straight up. Your hand lifts right out! This is how an anchor works. The anchor and chain prevent horizontal movement (like the wind and tide) by digging in like a claw, and when the ship comes to leave, the crew winds in the chain and rope until the ship is above the anchor, and it pops right out. Edit: A spelling. Edit 2: Thank you for the Reddit silver, kind stranger! To all of you who commented on the weight of chain doing most of the work, I'm aware of that, but this is ELI5 not ELI15. I don't expect a child to understand friction, shear strength and fluke angles. Happy sailing!",
"Anchors are designed to resist a horizontal pull, but to break out of the seabed when subject to a roughly vertical pull. Thus the ship winds in the anchor rode until it is straight up and down, and the anchor releases.",
"I think [this image]( URL_0 ) shows fairly well how an anchor works: It only prevents the boat from moving away from the anchor due to the anchor and chain dragging over the ground. But the boat is free to move towards the anchor. So the boat can just move to where the anchor lies on the ground and pull it up into the boat.",
"For heavier ships, the chain does most of the work. The anchor point is mostly for the initial grab of the sea floor. It's designed wedge itself into the sand when dragged. As the chain is put out, more and more of it is laid on the sea floor while a good portion of it remains taught between the ship and the links on the floor. The total weight of chain on the sea floor vastly exceeds the weight of the anchor and greatly contributes to holding onto the sea floor. To get out, as the ship retracts the chain, the ship is pulled closer and closer to the anchor point as the chain is peeled off the surface. At some point the chain is near vertical. The anchor is designed to be easily pulled vertically away from the sea floor. The force it takes to rotate the anchor towards the surface is very small compared to the force it would take to pull it across the sea floor",
"It's not the anchor that holds the ship in place, it's the long heavy chain that does that. All the anchor does is hold the end of the chain in place on the seabed. As most seabeds are covered with a think layer of silt it's not hard to pull it out.",
"In anchoring an important concept is Scope. This is the length and angle of the anchor line. The longer the scope the greater the holding power, due to angles and leverage. Typically you drop the anchor, and then let the current push you back while letting out anchor line, in calm seas you want a scope that is at minimum 5x the water depth. In rougher seas or very strong current you might extend the scope to 10 times or more of the water depth. When you want to pull the anchor you start taking in line, and reducing scope by moving toward the anchor, when you are directly over the anchor with zero scope, you are just lifting the weight of the anchor back into the boat. If the anchor has has \"claws\" they will not be able to dig into the ground with zero scope. Just as an example that might be easier to visualize, I can easily anchor my kayak that weighs about 300 lbs (with me and all my fishing gear) with a 1.5 lbs anchor and about 25 ft of anchor line around the grass flats where the water is only a few feet deep.",
"Anchors are designed that if you pull them sideways they dig into the sea bed but if you pull them upwards they come free. What stops the ship from moving is the weight of the anchor chain rather than the anchor itself. In general you let out something like 3 times the depths of water in chain, so there is a long length sitting on the sea bed.",
"A question that( as a seafarer) I can finally answer, sort of! As stated above removing the anchor vertically is far easier than dragging it along the seafloor. However sometimes an anchor never even needs to touch the seafloor at all! Interestingly enough the actual weight of the anchor chain plays a large part in keeping the ship steady. Based on wind and current speed you pay out a certain number of shots, (15 ft lengths of chain) in order to remain steady. Of course anchor chains for modern cargo ships are intensely large and heavy for this reason. Imagine if you were swimming in deep water (with floaties, no drowning please) and had a 40 to 50 lb weight dangling below you. It'd be pretty difficult to swim around I'd say.",
"There’s a lot of good but incomplete answers, so here’s what happens when a large ship anchors. First of all, the areas of harbors that are designated for anchoring generally have a sandy bottom. The ship positions to the anchoring point, reduces speed to almost a dead stop, then drops the anchor. A large amount of chain is then let out. The ship has a designated area in which it can drift around the anchoring point. If the ship drifts too far from the anchoring point, the engines are used to reposition the ship, which can include retrieving and re-dropping the anchor. When it’s time to leave port, the anchor chain is brought in, and MOST of the time, the anchor just comes right out of the sand. If the anchor is stuck, a combination of moving the ship and pulling the chain up and down are used to free the anchor. The anchor can be used to stop a ship in an emergency, but that’s going to put an insane amount of stress on the components of the anchoring system and the ship, itself. Edit:grammar",
"The same is true for smaller boats. My sailboat is only about 14 tons and our anchor keeps us attached to the Earth in > 40kts of wind. And yet our windlass can pull it out of the seabed without pulling the boat down into the water :D Depending on the design of the anchor, and there are many designs, it's likely more of a plow than a \"hook\". When you pull it horizontally along the seabed it actually pulls itself further down into the mud. But when you pull it up toward the surface the plow end pivots out of the mud and breaks free. That said, I've certainly had several instances where we spent ten minutes or more just slowly working the anchor out of the mud in order to move the boat.",
"It's the weight of the chain that holds the vessel. You go slow astern and drop the anchor, paying out the chain along the sea bed as the ship moves backwards. To weigh anchor, you winch in the chain until it is \"up and down\" (ie vertical), which means the bows of the vessel are directly above the anchor where you dropped it. Wind it ( \"weigh it\") aboard and you're floating free.",
"Former Officer Of The Deck Underway, USN. It's not the anchor that stops the shop. The anchor's job is to give enough friction to help pay out the chain. The chain is what stops the ship. You pay out a long enough length of it - I don't remember the exact equation, but it was something like 3 times the depth (which of course means you are not going to anchor in very deep water). The sheer weight and direction of the chain is what holds you in place, as well as placement in relation to current."
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ijuri3 | how a hollow point round could be hard enough to enter a body, but soft enough to then warp/expand/break-apart in a body after entering. | Engineering | explainlikeimfive | {
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"Being hard is not a requirement for going into something. A baseball is softer than glass, but will go through a window if thrown with enough force. And bullets are thrown with a hell of a lot of force. That same amount of force is what causes the bullet to expand on impact. Even water will cause the bullet to squash and expand. But because it was going so fast, the squashed and expanded bits are still strong enough to go in. But almost certainly not enough to go straight through."
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ijvtov | how does throwing a rock in the san roque funnel cause flooding to cities? | URL_0 Saw this post and I dont understand how this can flood cities | Engineering | explainlikeimfive | {
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"That is a discharge channel of a dam, it’s meant to drain excess water if the dam overfills, but if it breaks, then all the water could flow out, causing a flood",
"I'd say that statement was something of an exaggeration. This is an overflow to the reservoir, and as many people in the original have stated, made from reinforced concrete many metres thick. A little rock like this isn't going to do anything. And even if it did, the water would simply follow the river course, just as if the dam was overflowing.",
"Dams and obviously funnels are constructed with the force of the water, not a rock. If there are any dents or cracks the entire construct becomes unstable. In this situation, if you fill the funnel and it breaks... probably the entire thing breaks, which unleashes all the water at once.",
"Dams are built to respond to various forces. The number one force is of all that water pushing against the dam. Then there are earthquake forces and the like. Throwing a heavy rock against it is like shooting at it with a cannonball. It's not just constantly getting peppered with cannonballs, so it is an unusual force. Now, where the rock hit is lots of concrete. Probably fine against the rock. But it is still unusual. So they had to come out and visually inspect the dam to make sure it didn't take any weird damage. If the rock had chipped a big chunk of concrete out, that wouldn't cause the dam to fail - but once tons of water start flowing through that tunnel, the water would start to expand the divot, and that could eventually cause part of the dam to fail."
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ik2qfc | How do recommendation engines work? | Engineering | explainlikeimfive | {
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"There are many different ways to do recommendation engines. It depends on the data you have and your goal. The first goal is to determine what people like. You can assume that if they buy an item they like it, or if they view an item on the website they like it, or if they click a like button they like it. Those assumptions may or may not be true. And relying on something like clicking the like button may not give you enough information. Then you try to associate different items. You can organize movies by director or actors. If you liked Steven Spielberg's movie X maybe you are more likely to like other movies he directed. Or you can organize them by genre. If you liked a sci-fi movie maybe you are more likely to like other sci-fi movies. So a simple recommendation engine determines that you watched 9 sci-fi movies and one romcom. It therefore recommends 90% scifi movies and 10% romcoms to you. A more complex recommendation engine looks at the movies you watched and tries to match you with other people who watched those movies. Then it sees what else they watched. If you are a fan of The Matrix and Dark City then you will likely enjoy movies that other fans of The Matrix and Dark city enjoyed. But what it recommends also depends on the goal. If the goal is just to recommend sci-fi movies you will like, then it recommends the most popular sci-fi movies - probably Star Wars. But every sci-fi fan probably knows about Star Wars and has seen it. So recommending Star Wars is not helping the person find something new. Your engine should try to recommend something the user has not seen and possible not heard of, but that they will like. So a recommendation engine may exclude the most popular things in a category because they are too obvious."
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ik3f6s | How does a water jet nozzle not get destroyed very rapidly by the water and abrasive coming out of it? | Engineering | explainlikeimfive | {
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"This is because of Bernoulli's principle. Inside the nozzle the velocity of water is low and the pressure is very high. The nozzle is made to sustain the high pressure. Hence as the velocity is less the wear and tear is less. When the water exits out of the nozzle, the pressure suddenly drops to atmospheric pressure and there is a corresponding rise in the velocity. Hence inside the nozzle there is some but not too much wear and tear."
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ik5i23 | How does a turbocharger in a car work? | I've been watching videos, but it's a lot for someone who isn't an expert in physics. I understand that the compressed air in the chamber is even more compressed. But that's about all I know... | Engineering | explainlikeimfive | {
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"When the piston comes down on the intake stroke it's going to pull in air. However much air you have is the limit of how much fuel you can burn. A piston in a naturally aspirated engine is going to have a maximum amount of air it can take in: the amount of air that can occupy the displacement of the cylinder at atmospheric pressure (1 bar). If you compress the air to 1.5 bar, you have (roughly) 50% more air in the cylinder when the intake valve closes. You can then burn 50% more fuel and output 50% more power. The question is how do you compress the air? Well the exhaust gases coming out are hot and still have a lot of energy in them. They're trying to expand as they cool. So what if we fed the exhaust gases into a turbine to drive an intake compressor? There's only a minimal amount of drag on the engine from back pressure and you can get a compressor going really well from the energy still left in the exhaust that would just go out to the atmosphere as hot air. So we take the hot exhaust gases, use the energy in them to compress more air, which lets us pack a cylinder with more air, which lets us burn more fuel per power stroke which delivers more torque and more power."
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ik7c8a | How do water jet cutters work? and why would you use them as opposed to this like saws and the like? | Engineering | explainlikeimfive | {
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"first, water is pressurized. Then it goes through a nozzle that accelerates the water to a very high speed (like mach 3) and abrasives are mixed in. The high energy water combined with the abrasives are capable cutting through metals. The advantages over a saw are very obvious. A saw is capable of cutting a straight line while water jets are capable of cutting 2d shapes out of flat materials (although some 3 d cuts are possible). In more general terms, they are very accurate and can produce very small cuts allowing them to produce complex, intricate pieces. They also don't produce much heat, which is actually a pretty big deal for metals. Techniques such as welding and plasma cutting mess with the properties of the metal near the cut. They're also very versatile. They can be used for metals, ceramics, fabric, glass and so on. While some materials need special attention, they can all use water jet cutting. Compared to a drill where you'd need different bits for metal (even different bits for different metals), ceramics and glass as an example."
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ikdbt6 | How do computer engineers make it so when the signals on the bus go into a register, the signal and/or timing isn't affected by the longer wire on the outside of the bus? | Engineering | explainlikeimfive | {
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"In designs where the propagation delays could alter timings, the length of wires are extended to ensure the signal arrives at the same time. That feature on a PCB is called a “meander.” Example: the blue trace in the top right of [this image]( URL_0 )",
"timing, in design it is taken into account as per /u/jimy12 says by a meander, in these sort of instances, it is essential that both components are able to sync timing of their signal and response, against the clock component.",
"the mechanical correction with wire length is a common way to address this, as stated. routing of circuitry both on physical board traces/wires and within chips is checked by math for the delay effects made by circuitry and components, otherwise known as propagation delay, or with the same clock arriving at different times to different components, known as clock skew. there is a fixed amount of time a signal must be present at a register before it can be safely clocked in by a separate clock signal known as 'setup time', and similarly it must be stable for a minimum period afterward known as 'hold time'. these times are known and based on the frequency of the clock and calculated delays/skew between the data and the clocking circuitry, extra slack can be added to compensate. this can be done mechanically with a longer wire/trace, or by adding additional delay circuitry in-line to synchronize each register to the data it is registering."
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ikiufe | How does a torpedo work? | I love naval history and was wondering about this question. | Engineering | explainlikeimfive | {
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"A torpedo is just a self-propelled underwater bomb. They use a few different kinds of propulsion systems. Steam, compressed air, compressed oxygen, electrical, etc. All basically do the same job of making a propeller spin to make the torpedo go forward. Some are guided, and some are \"dumb\". The dumb ones just run at a preset depth in a straight line until they either run out of go-juice and sink, or hit something and explode. The guided ones are either trailing a long wire through which they get commands from the launcher, or have an onboard sonar that they can use to look for targets by themselves. Once the torpedo gets where it's going there are a few option for how it explodes. The simplest is a contact trigger, where the torpedo hits something, and kaboom. More complex detonators use things like magnetic influence (detecting large metal things) to determine when they're near a ship. These aim to detonate under the ship rather than beside it, because that's more destructive."
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ikndr8 | Why is it when you touch the metal part of a plugged in phone charger you don’t get shocked? | I’m confused why when I touch the tip of my plugged in my phone charger it doesn’t shock me. | Engineering | explainlikeimfive | {
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"Because it's an absolutely tiny voltage--the charger is probably only providing about 4V, which isn't much more than the batteries in a torch, which similarly wouldn't be able to give you a noticeable shock. (Even the more potent 9V batteries won't shock you if you touch the terminals with your skin--your tongue, on the other hand, is a different matter entirely).",
"Aside from all the earlier explanations: the exposed metal part of connector (in case of most USB) carries no voltage potential. Typically it's GND (Ground) or in badly designed chargers it's NC (Not Connected). Connecting charger to a phone the GND will connect first to drain potential static charge (like you get rubbing balloon along hair) before other pins make contact. Same goes for Lightning, the grey part of plug is GND. The gold-plated pins require to do source-sink 'negotiaton' I believe (correct me please) as part of Apple's Made-for-Iphone certification. So as others have said, there won't be any (noticeable) voltage/amperage on the pins, other than maybe 3.3 or 5V at incredibly low amps.",
"The same reason why when a baby punches you in the face it doesn't hurt but if a grownup does you could be seriously injured. Baby voltage vs daddy voltage.",
"The output is totally insulated from mains. There's a tranformer to lower the voltage and this part consists of two seperate coils of insulatded wire \"connected\" only by a magnetic field. In some really shitty transformers there's only the µm thick lacker of the insulation of the coil wires to protect you from mains. Look at YT for DiodeGoneWild. This czech guy with a funny accent has lots of dissassembling vids and show you the details by taking apart those adapters.",
"It’s not high enough voltage to hurt you, a phone charges at 5 V, and you typically start to feel it above 30 V. And the output is not connected to the input so you can’t get a shock form the mains electricity However some parts of the body are more sensitive, if you were to lick an iPhone charger you will feel it as slight tingle and, but I don’t recommend you do that. Usb connectors also hide the contacts so you can’t touch them directly anyways, which is why I specified iPhone charger",
"The answers that it's only 5v, etc., are basically correct, but more could be said. In a well designed and manufactured charger, the high voltage side (plugged into the mains) is \"electrically isolated\" from the low voltage side (the part plugged into your phone). What this means is that there is no direct path for current from the mains to your phone. Touching the metal bits is fine in that case because there isn't anything trying to drive current from you to the ground. But I said \"well designed and manufactured\". Cheap phone chargers from disreputable companies cut corners on designs and the quality of parts in order to save money. Some of these chargers either are not electrically isolated or have isolation that isn't very good. I've seen pictures of chargers where a high voltage wire is 1mm or less from a low voltage wire with no insulator between the metal. As a rule of thumb, it's best to always treat anything plugged into the mains as if it could give you a shock. Don't touch the metal bits. Don't plug it in near the bath. Don't use it when you're wet. Etc. If you have a metal cased phone, it is also a good idea to have a plastic or rubber cover for it.",
"You mean the part that goes into your phone? Your skin is a moderately good insulator, meaning electricity that doesn't have a ton of force (voltage) behind it will not pass through your skin. Phone chargers only emit 5V at the phone end, they use special electronics to turn the 120V wall electricity into the 5V phone electricity. You can get a shock around 20V with wet, salty skin or around 40V with dry skin. Anything over 100V is considered dangerous for the average person.",
"You can feel it if you meet three criteria: 1. You bridge the connection (+ to -) with part of your body. 2. You do it with a part of your body that is more sensitive to touch. 3. The part used has much less resistance than your average epidermis. Ooh, I know. Lick it.",
"I have been shocked by doing this while plugging the charger in. I was doing the ok’ find the outlet hole with your finger and guide the charger in and when the chargers metal tip touched the outlet it electrocuted me. That’s the only time it had ever happened to me out of the million times I had done that. I was shocked.",
"Electricity is like water in a pipe. Voltage is pressure, current is flow. Of course you need pressure to cause flow, but the width of the pipe (resistance) decides how much pressure is needed for a certain flow. You feel a shock when there is flow - but you need some pressure to make it go through you - and it also needs somewhere it wants to flow to; it's only ever relative between the high pressure to low pressure; never just flowing \"out\". Touching wires together is like connecting pipes. Separating the wires is like sealing the pipes/blocking them off. 5 volts like a charger, is a very low pressure; and most of your skin has high resistance (like a very narrow pipe); so almost nothing flows. Your tongue, being wet/salty/dissolved ions, has less resistance, so needs less voltage to cause the same flow. Also, except for iPhone, the cable only has one piece of metal you can touch - so there's nowhere to flow to - no 2 points with a pressure difference between them; so even then the voltage doesn't matter. For fast charge, sometimes they use higher voltages, but typically it's just by disabling the normal *\"if too much flow, something is wrong, turn off\"* that's built in to everything. Higher voltages in chargers are still very low, 9v-12v on some phones; up to 20 volts on laptops; but anything over USB will only go over 5 volts after sending messages back and forth to confirm it's plugged in normally and is safe But I still wouldn't worry about touching those with my dry, clean fingers; but don't lick it over 10 volts. The limits are mostly to avoid overheating wires and catching fire; not about electrocuting people. Wall power is dangerous because when voltages get high enough, over about 60 volts, is enough pressure to cause it to flow through you, into your feet, and through the dirt back to wherever it wants to go. USA=110 volts; civilized world = 220 volts.",
"The voltage from the outlet is 110V AC or 220V AC depending where you're from, that voltage would easily not only fry you but your phone as well therefore that big \"block\" that is connected to the outlet lowers the voltage to around 5V DC which you can't even feel. By the way, it's a safety standard that those 2 different voltages be as isolated from each other as much as they can (unless you buy a shady 2usd phone charger) There are many ways to lower said voltage for example some use a transformer and rectify the lowered AC into DC. Source: [Electroboom]( URL_0 ) and my 6 months of electrical engineering i took",
"It takes about 50v to penetrate skin, but it only takes a tenth of an amp to kill you, so amperage is the real killer when it comes to electricity. This is what my electronics teacher taught me in highschool.",
"Because you didn't buy a cheap Chinese import charger, which can output 115 and 120 volts at the connectors (the difference being the 5 volts required for charging). Have a look at a \"capacitive dropper\"."
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ikrk1g | How does heat affect the efficiency of a computer? | Engineering | explainlikeimfive | {
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"If you heat up transistors they take longer to switch states. So if your processor overheats it starts giving wrong answers to its calculations as the transistors will be in the wrong state. This usually results in strange computer crashes. To prevent this modern processors have thermostats built inn which will detect that the heat becomes too high and reduce the clock speed so that the transistors have a bit more time to switch states. It also reduce the voltage supply to the processor which makes it use less power and therefore not generate as much heat but by reducing the voltage the time needed by the transistors to switch state further increases meaning it have to further decrease the clock speed. However by reducing the power it can prevent the processor temperatures from climbing higher. The relation between supply voltage, clock speed and temperature is something that is carefully designed and tested in order to give you the optimal efficiency in all conditions. Most applications only require bursts of processing which means it can run on higher speeds and power when needed and still allow the processor to cool down when not needed. But if you continue to load the processor it will heat up and throttle down to prevent overheating and crashing. What modes it finds best depend on how much the processor is able to cool. If you allow the fan to suck inn lots of cool air it will work better and cool the processor enough that it will run in a higher power mode and give you higher speeds. But if you restrict the airflow or if the ambient air is too hot the processor have to go to a lower power setting and lower clock speed.",
"Not that much, really. The problem is if your components go above 125°C or so (meaning silicon chips here) they get irreparably damaged. A modern CPU without cooling blows itself in about 10 seconds from room temperature start if the safety throttling fails to kick in, for reference. This is why you need to cool the components effectively."
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ikts6o | Why cant cars turn all 4 of their wheels at once, making parallel parking super easy? | Engineering | explainlikeimfive | {
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"It's doable but impractical. Moving rear wheels using traditional mechanical linkages would require a second steering rack and complex connections and hydraulics. Using actuators or hydraulics to do it is also possible but impractical. Basically it makes it too expensive to implement and makes the car to difficult to maintain for something that would honestly be a gimmick.",
"It’s been done, and was deemed superfluous. As you gain more experience... Parallel parking is super easy. Practicing in a truck or longer vehicle will help your confidence tremendously when doing it in your car again. Like anything, practice makes perfect; You can’t only practice it when you have to. As for the production side... It’s incredibly expensive to engineer all 4 wheels to be able to turn 90 degrees; The front wheels on all cars that haven’t been specifically designed to do otherwise aftermarket, only go to about 60 degrees MAX, as is. Long story short, for many reasons... It’s unnecessary and not feasible in mass production",
"[Some can]( URL_0 ). Though the rear wheels usually can't turn as much as the front ones. It's not common because it makes the steering system much more complicated and expensive. For it to work well, it generally needs a computer to control it, so it wasn't that viable until relatively recently."
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il2495 | Why do powerful, heavily tuned engines like those in big muscle cars, or drag racers idle so poorly, hunting around and spluttering and popping, only smoothing out when under load? Why can't they idle nicely too? | Engineering | explainlikeimfive | {
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"Because their camshafts are optimized to run well at high revs and full throttle. The camshaft is what controls the lift and duration of the valves opening during the intake and exhaust strokes of an engine. More lift and duration means more air/fuel mixture reaches the inside of the cylinder. The hunting and spluttering you hear is the sound of an engine at idle whose valves are opening for too long. When that engine is under full load, the valves are opening for as long as is needed *at full load*, and that's why the engine works smoothly at higher revs. It's possible to build an engine that works smoothly both at idle and at high revs - that's called Variable Valve Timing, and most regular passenger car engines have had it for a couple decades, in one form or another. But for race engines, it's added expense, complexity and unreliability. Drag racers and people who build competition engines don't really care that it works badly at idle - that's not important for them. Of course, people think that race engines sound cool, and so you will sometimes see regular passenger cars that have been modified to sound like that at idle. That's just pure aesthetics. The best example is Harley-Davidson motorcycle engines - they sound that way at idle because it's traditional, and they're intentionally built to this day to run slightly badly at idle."
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il3wzr | why is it when my arm/wrist touches a certain part of a laptop (like, along the side on the casing seam(?)), it stings/gives a small electric shock? | Engineering | explainlikeimfive | {
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"It's usually caused by improper grounding. By right, there should be 3 prongs on the plug for your laptop power supply. Sometimes some of the electricity for the stuff in your laptop \"leaks\" out. The exposed bit catches some of this electricity. It's supposed to be connected to the \"ground\" prong on your power supply, and flow out into the wall socket and to a place you don't care about. If there isn't a ground prong or it's broken. By touching it, *YOU* become the ground prong, so it flows out of the bits into you, and to the ground, giving you a mild shock.",
"Macbooks do this. They have an aluminium casing which conducts electricity and there must be some reason why their voltage is slightly higher when plugged in because if you disconnect them from mains electricity, that weird vibration is no longer felt. I'm not sure why it feels like a vibration - it seems slower than a 50hz AC frequency and it shouldn't be AC anyway as the transformer (power brick) converts mains AC to DC."
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il7m3j | Why use brick and mortar in construction? | Hi guys, I'm from the UK and for the most part, the majority of basic houses over here are made of bricks and mortar. I was watching a video on why mortar was used in historical buildings that used undressed stones, AKA: Rubble Masonry, as it helps to settle the stones such that they have good contact with the other stones that make up the wall/building/structure. However, many buildings over here use standard red/orange dressed bricks that are uniform in size and shape, yet mortar is still used in the constuction of the wall. I'm aware that it's possible when using these kinds of dressed stone to not use mortar, whilst still having a strong and sturdy wall to show for it. With all this said, my question is what is the need for the mortar in these kinds of construction projects? Is it simply that the bricks themselves do not weigh enough such that the wall can remain stable on its own? I'm no architect, but stone structures that I've seen myself that do not use mortar seem to use very large stones (such as those at the ruins of Mycenae), and those that use smaller stones/tiles (such as those in Ancient Roman ruins that litter landscape here in the UK) often use mortar. Or perhaps simply that modern mortar is much stronger in some way that historical mortar, and as such it serves its purpose better? Apologies if this seems like a **really** basic question, but I couldn't find anything to answer my question online, though perhaps I wasn't using the right search terms. | Engineering | explainlikeimfive | {
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"Mortar is important because it acts as both a binding argent, as well as preventing water from getting in between and behind the masonry Yes the mortar does help set the bricks and keep the stable and from moving, but it also serves an important purpose in keeping water out. Something that Is next to impossible to do with just masonry. You would need laser precision brick laying to make it so no water would ever get in the joints. For all intents and purposes, that’s impossible. And this extends past just preventing leaks, the quickest way to destroy masonry without actively demolishing it with a sledge hammer or wrecking ball, is to let water get into it and freeze, because when water freezes, it expands, and the force of that water freezing along is enough to crack rocks and masonry. Then once there’s on crack, more water is able to get in, more water is able to freeze, and more freezing leads to more cracking. Keeping a surface that isn’t penetrate to liquid water is very important for maintaining the structure edit: also yes, a single layer of bricks on their own would be relatively easy to topple, if the wall is multiple bricks wide or made of larger stones then it could be relatively structurally sound without mortar (would work for shorter buildings, no so much for y’all many stories ones). But they still then have the problem of water getting in and causes havoc",
"U/tmahfan117 covers a lot of it. One other reason is the mortar forms a cushion between the bricks. It’s a softer material than the bricks so allows a small amount of differential movement between layers to distribute forces in the wall without damaging the brick. A common error when repairing older brick walls is masons use modern mortars that are much stronger than the old lime mortars. They can also be stronger than the old bricks too. This is bad because the bricks are brittle, so when they’re the weak link they crack. The most common manifestation of this is when the faces of the bricks pop off after mortar repairs."
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ilc8qw | I have watched videos where a person can unassemble a rifle or gun. Is it true for all guns and do they not have screws or bolts to keep different parts together? With so much recoil, how does a gun not unscramble on its own? | Engineering | explainlikeimfive | {
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"Depends very much on each different Firearm. Some, as you saw in the vids, can be easily disassembled and reassembled using just your fingers. (To a certain point... even those usually have parts that require special tools to entirely take apart.) Others require tools... some require simple everyday tools, other require very special tools. In all cases, the weapons have been designed by engineers to hold together tightly, even in margins of pressure and/or recoil beyond what the firearm would experience in normal usage.",
"Most of those videos you see, the weapon is only broken down to its maintenance level. That breaks the bolt down, removes the upper and lower from eachother, and the buffer and buffer spring. There are parts such as the barrel, buttstock, trigger housing group that can be broken down with special tools. Besides those special components, the maintenance level of parts include the upper, lower receiver, bolt housing group buffer and buffer housing group are designed so that they are inserted in a specific order that locks them down. The buffer assembly is held down in place by the bolt housing group, and the bolt housing group has little pins that hold it together. These pins are held through friction and are placed perpendicular to the force of recoil and when placed in he chamber, is not allowed to move out of place. With the bolt and buffer in place, the upper and lower receiver are held together with one or two pins that are also held in place by friction. For weapons with higher recoils, those pins are larger and also have a locking ball bearing that needs to be depressed before it can be removed."
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ilhjdl | Why are the bottom sides of cars exposed? | Everything I've experienced from flooding and water getting into the engine/transmission to low-riding cars getting fucked from potholes and other road objects, you'd think an area that's so susceptible to damage would have a tough bottom covering. | Engineering | explainlikeimfive | {
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"Any covering wouldn’t make the vehicle waterproof. You’d be adding a load of extra metal, increasing the weight of the vehicle, for no benefit, and when you take the car to a garage and put it on a high ramp they’ll only have to remove the covering to get to what they need to fix.",
"Over heating, access to repair, and efficiency of space are possible answers to that. There is only so much space to put things in a car’s mechanics. But interested in answers from any professional autobody mechanics who would know more. Following."
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ilnwsj | Statically could my key fit somewhere else? | Engineering | explainlikeimfive | {
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"Tumbler locks tend to have 5 or 6 pins. Let's say 6. The question then is how many distinct pin positions they can have. Let's say 8. That would give a total number of unique keys as 8^6 or about a quarter of a million. This ignores different lock designs and such, but still, you can see it's actually a remarkably low number and many lock manufacturers have probably made well in excess of a million locks. So yeah, just based on the odds there are probably lots of other locks out there your keys will open. Good luck finding them. EDIT: I understand that keys have physical restrictions that mean you don't really have the full range of possible positions on every pin. I was trying to set a reasonable upper bound, not come up with an actual accurate estimate.",
"Many locks and their keys are standards. For example, in the US, an estimated 75% of recreational vehicles use a CH751 key. If you own an RV, it is likely that the key for lock you use to gain access to your vehicle will work in another. Filing cabinets, desks, and many other small locks use a limited number of keys. I used to run a charity, and we had locking steel filing cabinets donated to us without keys. It was simple and inexpensive to look up the lock number, and order new ones on-line. Lock standards like this are cheaper for manufacturers. The chances that any one lock and its key has a duplicate is much greater than chance.",
"In all likelihood your key fits someone else's home in your own city. Locks provide a certain degree of comfort to a resident but are unlikely to actually deter anyone who really wants to enter your home. There is a proverb in the US and likely elsewhere that says \"Locks keep honest men honest.\"",
"You're in Russia - remember the old Russian (Soviet) film Ирония Судьбы? This is part of the plot there, I think. :) In reality, it's not just the limited number of tumbler combinations. A poorly made or worn-out lock will allow *close* positions to open it. So yes, it's definitely been known to happen.",
"Please remember that top level comments must be *explanations.* Personal anecdotes of having experienced a matching key or similar, with no explanatory material, are not allowed at the top level.",
"Locks are only there to keep honest people out. Picking most locks is trivial. If your lock cost under $100 then it can be picked in less than a minute. For most locks, less than 10 seconds. Look up Bosnian Bill or the Lockpicking Lawyer on YouTube. Prepare to have your mind blown.",
"I once locked myself out of my new house. I had been living there about a week. I never got given a key for the deadbolt, and while I was out, it had managed to bolt itself closed due to an earthquake. I still had a key to my old place, and had keys to my dads house, and I tried them all. Oddly, the key to my old place was a perfect fit, thank goodness",
"I live in a house that’s two single family homes connected by a closed in breezeway. We live in one and rent the other. When we bought the house we replaced the lock on our door and then a few years later replaced the lock on the other. Ended up discovering both locks have the exact same key. So yes totally possible",
"So in college, we were out at a field practicing. Rob, a friend, was playing the part of a coach for the practice. He asked John to drive back to the apartment to pick up some gear and come back. Rob gives John his car key, and we start the practice. A few minutes later Rob looks up, and sees his car still parked. He's confused, and looks for John. John has left. And Chris says, \"Hey, where's my car?\" Turns out that Rob's a s Chris's cars were the same make/model, and that the keys for these two specific cars were interchangeable. So, I've seen it happen. (This is pretty much impossible today with electronic keys).",
"You've never seen [Ирония судьбы, или С лёгким паром!]( URL_1 !) (the [Irony of Fate]( URL_0 ) for the English readers)? It's a very regularly shown movie on Russian TV. And yes, it definitely happens for real, since locks have limited combinations to them. Better locks have more combinations, but with something like lockers at a gym it's quite likely that there is a key that opens another locker.",
"I have a friend with a 1965 Cessna. Back then there were only 14 different Cessna keys. Aircraft mechanics just had a complete set of all 14.",
"My sister locked her keys in her car once and after trying to coax her cat over to step on the power door lock button, she called AAA. The tow truck driver couldn't jimmy it open, so he took out his truck door key and said \"this works sometimes\". And it did.",
"Statically? No Giving a key a positive charge nets no benefits to its use around lock tumblers. Unless, say, the charge was so great, it semi-melted the key in the lock, forming it to the shape you needed. This would require absolute timing and precision.",
"Fun story. In college I had 2 friends buy Suzuki GSX-R 600 from the same dealer. As a joke one got on the other, put his key in the ignition and pretended to turn it. Sure enough, same key. They would randomly take each other's bikes after that.",
"As everyone has answered already, I'll add another random fact-- there are different kinds of keys. My family in Argentina has keys that are like a metal stick with little bubbles carved into the side, and my dutch family's keys are metal sticks with the normal key shame you imagine from US keys carved into the middle. My key to my house in the UK is like the old fashioned keys, a rod and a little piece at the end. So your key would not even go into a lock in a lot of places. [ URL_0 ]( URL_0 ) Here's what I mean in picture format.",
"Back in the day two dark green sedans, same make year & color, were parked in front of my ex’s building. Guy runs out late for a meeting, hops in, drives away. Thing is, he took the wrong car. Realized it like 20 minutes later & came back to the shocked older lady who thought her car had been stolen. The key worked despite odds similar to 1 in 250,000 like you mentioned, confirmed later by the dealer so no charges would be pressed. Make - I *think* it was Honda or Acura, some super common model, had some too-small varieties of key produced that year. Interestingly, crypto wallet addresses work on that principle - if the code (digital ‘pins’) is long and unique enough the odds of collision fall to effectively zero.",
"You watched the irony of fate too many times and trying to hope that it could happen to you one day",
"Back in the 90s, my mom had a Camry and got into another Camry, same color and model year and had started the car before she realized that she was in someone else's car.",
"One flat I moved in, the landlord was trying mail boxes, to show us ours. Later on we noticed we got shown the wrong one, our key fit into the mailbox lock of a neighbor, and the other way around as well. Wasnt even a big house, just 8 flats",
"At the place we used to live I got one set of keys in which one of them opened the lock at the front building, my door knob, the deadbolt and even the basement door for garbage disposal. None of the other keys in the set did that and they just opened what they were supposed to open.",
"This actually happened to my friend in high school. He was leaving the supermarket and unlocked his car with his key, sat in it and turned on the ignition, when he looked around and realized something was off... Pink seat covers, a drink that was definitely not his, et cetera. As if on cue, a lady walked up to the car and started screaming that he was a thief and such. Turns out both of them had the same color and model of car, as well as the same key."
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ilueeg | Why does a car in reverse sound so whiny when no other gear does? | Engineering | explainlikeimfive | {
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"The gears are cut differently. Forward gears are used more, and so they're cut helically. This makes their engagement smoother and the gears last longer. The reverse gear, since it is used less, has straight cut gears. These are cheaper, but add that whine.",
"In addition to what the others have said, the reason that reverse gears are straight cut is that they have to slide past each other in order to engage reverse. This is not possible with herringbone or helical gears. The forward gears are constantly meshed so don’t need to slide past each other.",
"Most cogs in cars' gearboxes mesh together with > > > patterns (helical cut or constant mesh) as it is quieter than straight cut gears III. Actually Citroen's logo looks this way > > as this type of gear was invented by someone at the company. Reverse gears however are usually straight-cut as they take up less space and are much more simple gears. Reverse gears aren’t used as much as the rest of the gears so it is a good compromise. Straight cut gears are strong however and in applications where being quiet is not so important (heavy machinery and rally cars) you hear whiny gears."
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ilyh99 | How Do Cars Work? | Engineering | explainlikeimfive | {
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"They take gasoline and burn it in small controlled explosions to push the pistons. The pistons are connected to the crankshaft. One piston goes up one goes down (that's greatly simplified) the crank connects to the transmission. The transmission is geared to take the power from the engine and transfer it to the axles. The axles turn the wheels. Pretty simplified explanation",
"Take gasoline Put it in container, Seal container with piston, Attach piston to rotating shaft. Light gasoline, gasoline explodes, pushing piston, which then turns the shaft. The shaft then turns the wheels by using a set of gears."
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imemce | the difference between x86 chip and ARM chip | Engineering | explainlikeimfive | {
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"More of an ELI5: they understand different languages, for example your have to talk in French to one of them and in German to the other. They also think in different ways but in the end the result is the same. However, due to these two differences one or the other will be faster in different tasks. More advanced: AMD64 (the proper name of the 64 bit extension to x86, commonly and incorrectly written as x86-64) is a CISC architecture: the instructions to the CPU are large in number and they can be with different sizes (for example different number of arguments). The instruction set is regularly updated with newer (generally faster but now always) instructions. ARM is a RISC architecture where there is a limited number of instructions and their sizes are the same (may need a correction here). Following from that single instruction execution is faster than in a CISC architecture but you may need more instructions to achieve the same goal. CISC: complex instruction set computer RISC: reduced insurrection set computer",
"Think of them as cars: x86 is closer to a traditional gas car. They can range from the very slow (a Smart Car) to the extremely powerful (a long-haul truck). The issue is that these engines (and processors) aren't super power efficient. It's why laptops with things like a core i7 or i9 require massive batteries to get more than a few hours of screen on time. ARM is more like an electric vehicle. They're the new kid on the block (not actually, but for all intents and purposes they are), and for a long time, while they were more efficient and leaner than x86 systems, they also had a much lower ceiling, and couldn't get as powerful. This is why they were perfect for smartphones which didn't require as much processing power as a desktop, but also needed something that wouldn't eat up all the battery. For a long time ARM vs x86 was like comparing a Prius to a Ram Truck. Both were good at what they did for their specific task. However, much like with electric cars, year over year ARM has gotten better while x86 hasn't seen a big leap forward in quite a few years. It's to the point that now ARM can now out-perform many x86 chips on a fraction of the energy costs. Just like with cars: Tesla's new big-rig truck isn't just possible, it's inevitable, because it's just so much more efficient than what's on the road today. But even without the massive performance improvements we've seen with ARM, it still would have inevitably replaced x86 because of a pretty simple economic fact: 1/10th of the performance will still be worth it if it's 1/100th of the price, both in terms of upfront cost and cost-per-watt. This is why we started seeing experiments with Desktop operating systems on ARM chips as far back as Windows RT, even if the chipsets weren't quite as powerful as they are today. In fact, if you have the disposable income, the Surface line is a great way to compare the two: if you compare the Surface 2 running Windows RT, and the Surface PRO 2 running traditional Windows 8.1, I think you'll see that in 2020 the Surface 2 still runs reasonably well (in spite of the OS) while the Pro 2 will have poorer performance, battery life, and overall usability."
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immsqy | What is the advantage of using the recycled air button the car’s A/C? | I understand it’s pulling air from inside the car vs outside but why does the recycle option seem like it blows a lot harder. | Engineering | explainlikeimfive | {
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"If you pull air from outside the car you have to heat or cool it a lot more to make it the right temperature then when pulling air that is already close to the desired temperature from inside the car. So the climate control slows down the fans to make sure the air spends more time over the coils to get to the correct temperature. The disadvantage of recycling air inside the cabin is that any smoke or humidity will take a long time to vent out. So the option is there so you can select between good ventilation or good temperature control.",
"To keep out outside air, like when car puts out a black cloud of smoke, you pass a smelly section of road, etc. To keep your heated or air conditioned air in the car. This only seems to have a small effect, though, as far as I can tell. I've always thought it meant \"recirculated\" air.",
"When some big diesel truck drives past you, spewing it’s filthy, stinking exhaust, if you *don’t* have the recycled air on, your system sucks the diesel fumes into your car and you’re stuck huffing that shit until you open a couple windows. Just keep the air recycle on and you prevent that from happening. You’ll have to open windows if someone inside lets a fart rip, though.",
"The recirculation button pulls air from within the cabin through the system rather than pulling air from outside. This means that when you're warming up the car on a cold winter morning, you're heating air that's already been heated from before. Thus, your cabin air heats up faster. The problem is, that the humidity is also confined to the cabin. So your windows will fog up. The way you use it is to start the car, hit the recirc, then grab the snow brush and start clearing the snow and ice off of your car. When you've got it all cleared off (hood, trunk, roof, fenders, mirrors, and all of the windows) you can go into a nice warm car, stow your snow brush, and return the system to outside air. You'll have a lot less problem with fog that way."
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ims5dj | Why did the nuclear direct air/non direct-air aircraft fail where nuclear powered submarine/boats was a success? | It seems like there are a lot of nuclear powered engines that go in the water, and create steam for the major part(correct me if im wrong) to create thrust, but why did the engine for aircraft created by GE and P & W not work after 15 years of R & D and 1 billion in cost? | Engineering | explainlikeimfive | {
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"Submarines and ships are bigger than aircraft - it's a heck of a lot easier to set up a reactor and control the reaction and have enough space for all the necessary systems and loops to keep it cooled and operational. Aircraft require smaller reactors - the smaller it gets, the more complex it becomes and the more chances there are of something going wrong. Also people don't want nuclear materials flying around everywhere in the sky - traditionally planes have a much higher rate of accidents than ships or submarines.",
"To put it simply... it did work The US government just realized, and quite rightly, that a crash of a single nuclear powered airplane would have resulted in an unmitigated ecological disaster, so they stopped development. The problem was the risk was too high. The chances of an aircraft crashing or having an accident are much much higher than a boat. Boats are also large enough to have adequate shielding and safety devices in place, while planes are too concerned with weight. If you had a fleet of nuclear powered B-52's for example, it's not a question of **if** you'll lose one, it's a question of **when**. That would scatter highly radioactive material all over the better part of a state. The principal was sound though. Super heating molten salt with a nuclear reaction can take the place of fuel in a jet engine by superheating the air passing through to generate thrust. Once we develop appropriate Nuclear fusion reactors thermonuclear turbines will make a come back."
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in24qx | Rocket fuel injectors | like how the hell do they work | Engineering | explainlikeimfive | {
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"They're actually pretty similar to the injection system on a car or the ceiling-mounted fire suppression sprinklers, just much beefier. They also are intended to provide a constant spray of fuel (or oxidizer), rather than intermittent pulses. In short; you pressurize the fuel and oxidizer (collectively, propellant) behind the injectors using a very very powerful pump, and then the fuel and oxidizer sprays into the combustion chamber (with the streams usually designed to run into each other in order to aid in mixing). Somewhere in all of this, you provide an ignition source (or, for some fuels and oxidizers, they'll combust on contact with each other), at which point the rocket will have stable(ish) combustion in the chamber so long as you keep feeding it with propellant."
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inaaos | how do modern ship anchors work? What happens when they get stuck? | Engineering | explainlikeimfive | {
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"An anchor isn't meant to hold the entire force of a ship against the wind and current. Instead, it acts in conjunction with a length of chain laid on the bottom, so that when the forces on the ship are strong, more chain lifts off the bottom, but the weight of the suspended chain acts to absorb energy and draw the ship back towards the anchor. In general, the more severe the conditions, the more scope (ratio of deployed chain to water depth) is let out. The anchors themselves are generally designed to increase their holding power when subjected to a pull which is parallel to the seafloor, such as the pull of a ship at anchor via the bottomed chain. At higher angles of pull, such as when the ship has shortened chain in order to retrieve the anchor, they are designed to break out."
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indkhm | Why do busy city roads take longer to degrade than lesser used county roads? | Engineering | explainlikeimfive | {
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"Former paving contractor here. Busy city roads are usually built to a higher standard and get more maintenance than low-use country roads. To the causal observer, roads all tend to look the same. But underneath the black asphalt you see, busy roads are built stronger. More gravel base, and often a layer of concrete provide a strong long lasting structure that can support lots of traffic. But this strength is expensive. Municipalities often cannot justify the extra expense of building this strength on country roads that do not get used much. So they sometimes degrade more rapidly.",
"1. Weather has a significantly reduced effect when buildings are either side of a road. 2. More effort was spent making city roads good. 3. They don't necessarily take longer to degrade, often they just get better maintenance"
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indrfl | How do tunnels work? | Engineering | explainlikeimfive | {
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"A tunnel through solid rock will stay structurally stable because the rock has enough strength to maintain its shape. However, tunnel through dirt, gravel,or loose rock will usually be stabilized in some way. most often with a concrete lining. [this video from practical engineering]( URL_0 ) is very interesting, if a little technical at some points. sorry if my answer is a little vague, your question is quite broad. But feel free to ask me any moire questions."
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inf74o | Why is some plastic hard and some plastic "soft"? Is it the same kind of plastic with more layers or what? | I was at home today with a plastic container in one hand, and a plastic bag in the other. It got me wondering, are these plastics the same material or are they different composition altogether. Then what about like Saran Wrap, also seems kind of different. Do these all use the same raw material created differently? Plastic seems extremely diverse | Engineering | explainlikeimfive | {
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"They are different in composition and in material. Plastic is a word to summarize a type of material, not the material itself. Like gold is a metal but metal not a material itself.",
"There are different types of plastics, and there are different ways to form or extrude those plastics. Think about it like baking, take eggs, flour, sugar, butter and you can make several hundred different food items. It's all about the ratio of one ingredient to another and how you combine and process those ingredients. Plastics are the same way."
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inl990 | how an air conditioner makes cold air. | Engineering | explainlikeimfive | {
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"When you compress a gas, it’s temperature goes up. When you decompress it, it’s temperate goes down. Air conditioners compress the gas and dump the heat outside of the building, then let the gas decompress in pipes in the aircon box. Then a fan in the box blows the cold air into the room.",
"The same way fridges work! There's a compressor, connected to a closed pipe network with a gaseous refridgerant loaded up in it. The compressor compresses it. Compressing things heats them up, so it gets hot. It's then allowed to cool to room temperature. Then it's allowed to re-expand. Expansion cools things down for the same reason compression heats it up. Letting the refridgerant cool while it's compressed means that when time comes to expand it, it cools down further, and becomes cold. The air is then run past the pipes and blown out into your living room. Very clever application of engineering.",
"One of the things that helped me really grasp it was \"you can't 'make' cold air you can only remove heat from the air\". Its basically removing heat from one area (evaporator) and taking it somewhere else (condenser) and blowing said heat off it with a fan."
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intsk0 | Why do screws have different heads? (Phillips, Flat, Star, etc.) | Engineering | explainlikeimfive | {
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"They all have different advantages and disadvantages. Almost all screws were flat heads before as this is the easiest screw and screwdriver to make. You still find flat head screws where it is expected people will use improvised screw drivers. But flat heads wear out quite fast as there is only two points of contact. So when industrialization kicked off good with assembly line factories people started looking at screwdrivers with more points of contact that would be self centering to help assembly line workers and also have a taper that pushed the screwdriver out instead of overtightening the screw. This is where we have the Phillips head and the Posidrive screwdrivers from. But it can be quite costly to form the correct geometry of these screw heads and drivers. So where cost were a bigger factor then helping manual assembly lines people would use simpler geometries like hex drives. These gives six points of contact and can only go in the center which makes them better then flat heads but the geometry is still very simple so the cost is the same as flat heads. But they have the disadvantage of the walls not being in line with the force which can quickly damage the screw and driver, especially if the sizes does not match well. So a slightly different variant called Torx were made that improves on the hex drives by having the forces go straight into the walls instead of at an angle. This means you can apply a lot more force and have better tolerances for your tool then the hex drive.",
"Flat heads came first, there easy to make and so is the driving tool, whe have used flathead screws for hundreds of years. But flathead screws are flawed badly as the driver can \"camout\" screwdriver can jump out the grove and its also harder to keep the driver in alignment. So crosshead screws and philips heads were developed, less camout and the driver stays in place. Then there is torxhead, these are a star pattern for a good reason, much harder to camout and they have much greater surface area being driven. There are odd triangle shapes and torx with a stud in the centre...these were designed as security heads as the driver bits were not as near widespread. Tldr we came up with better head and driver designs over time."
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io2wsv | What is the most common cause of big projects over running on their estimated budget? For example, I recently learned that the HS2 train line in the UK will be nearly £75bn over the estimated budget! How was the estimate so wrong? | Engineering | explainlikeimfive | {
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"When a job is bid and an estimate is given, that’s all it is, it is an estimate on material and labor and some wiggle room for profit and mishaps, not much though. The bigger the job the more problems can arise and bigger the problems can be, for example, you can look at a topographical map to plot the train line but maybe the map hasn’t been updated in awhile so you throw a good number at it and turns out someone threw a house right where you want your line, or what is more than likely the case as it happens most often here in the US, they plan on buying the owned property along where they want the line and the owners of said property refuse, so they keep offering more and more until either they sell or the company decides to just go around, both are very expensive as they cost both time and labor. I’ve had a $20,000 job that tanked to $500,000 job, and the company just had to eat that loss, it’s not often a big loss like that happens but it’s rough when it does.",
"With HS2 specifically one of the big reasons for the original estimate and current estimate being so different is the Chiltern hills. The original estimate was based around running the HS2 line at surface level, with some cut throughs and some small tunnels, but during the consultation phase, the local residents and environmental groups got this changed so pretty much the whole thing will run through tunnels. Some of this is pure nimbyism (my idylic views will be disrupted by trains running through them!), some of it is genuine issues (like train tracks creating noise near villages), some if it is environmental (sites of special scientific interest, areas of outstanding natural beauty etc). tunnels are expensive and when they started actually working on the geological side of it, they found the hills are more difficult to tunnel through than thought, so the costs keep going up. There's a good FT article about this here: [ URL_0 ]( URL_0 ) It's not the only reason and the stuff they talk about at the end of the article is going to be an increasing issue as more and more of HS2 gets built. Once Curzon St, Birmingham Interchange and Euston Station are finished, they won't be giving up on this project no matter how much costs rise, and this gives an incentive for the private companies contracted to do this to push up their costs to make more profits. Add to that the government's tendencies to accept the lowest credible bidder, means companies put in bids they know are too low, intending to push the price up afterwards. Inflation has a part to play, mostly the original estimates (which were in 2010) are quoted at around £30bn and played against £100bn, but with inflation that would be £38bn now. Also original estimates ranged up to abound £37bn, which would be nearly £48bn now. But there's also genuine social/engineering issues that have caused the cost of HS2 to rise so far above original estimates.",
"[ URL_0 ]( URL_1 ) > \" Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law. \"",
"I’ve had a 25 year career in enterprise software. The kind of solutions that have a 1-2 year procurement process and a multi year implementation process. I’ve seen a LOT of projects run long. By far the biggest cause is change. The customer changes their minds about what they want, or, there is a clarity gap between what they described in the tender and what they meant. The customer will be adamant that when they said they wanted a chair, it should be obvious that means a chair with arm rests. The supplier, who only has chairs without arms, will be equally adamant that the chair they are supplying will do the job and adding arms is a change - a change that will impact the project timelines (because they need to design and build arms) and needs to be paid for. There will be literally hundreds of things like this in a major programme.",
"Because when there's no consequences for going over an estimate, there's no real incentive to make sure you stick to your estimate or to estimate a number you can stick to.",
"In this case the budget overruns have happened *before* construction (they’ve started on construction but that’s not the cause of the overruns). It looks like it’s coming in at about twice the original budget, which was from a schematic phase, about a decade ago. The bust appears due to several factors: 1. Inflation. This starts to be impactful over a decade. The original $ amount wouldn’t have been in 2020 money. The project is still over budget but not quite as much as some newspapers might be pushing. 2. Poor ground conditions. During prelim geotechnical world as the project has been finalized they’ve found sections of the ground work are going to be much more expensive than planned. 3. Possibly over specifying the project requirements. The rail speed required is apparently higher than typical HSR, which the initial estimates were prepared for. This is a common cause of budget overruns during initial design - as the owner first decides what they want the go with their “Option A” for everything from tile selections to air conditioners to light switches, and then the project is way over and everyone needs to have meetings to work out what the Owner really needs/wants and what they can afford and where efficiencies can be found. This stage happens on every project ever. It’s possible they’ve just done a poor job of reining in these types of additional costs. 4. Land values are higher, and rising faster, than originally planned for. Once construction really begins I’d expect more overruns as either late design changes are made which cost $$$, or £££, as they contractor already has the job and doesn’t feel much pressure to give the best price possible. They go high on the add service/change order fees and it’s not easy to negotiate down. There will also undoubtedly be cases where they find additional unforeseen conditions that require costly additional services, again not at competitively bid rates."
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io4whd | Why is it more difficult to cool a room down in summer than it is to heat up a room in winter? | Engineering | explainlikeimfive | {
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"Your intuition is correct that the amount of energy required to heat or cool a material by the same amount should be similar theoretically. However, the difference in practice is caused by [thermal inefficiency]( URL_0 ): A cooling machine is not 100% efficient, and so it will always produce some heat during operation, wasting energy. However, a heating machine is *always 100% efficient* if you think about it! Any waste heat it produces is heat all the same, so it's not actually wasted.",
"The laws of thermodynamics make heat more naturally from hot to cold. Reversing this always takes a lot of effort. Heating things is very easy, because you don't have to move the heat inside, you can simply release energy and it will naturally convert to heat. But to make things colder, you need to take heat and move it outside, while also preventing the tendency of the heat to move to your newly created cold basin."
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io5pzt | Why are there disks, USBs and memory cards with more storage than others of the same kind of a storage unit? | I have always had the doubt about how it is possible that a 4GB USB memory can be the same size as a 256GB one. How is it that an SD memory can be so small and be 256 GB, and at the same time only 2GB. Why are there so many types of storage units? Why does a computer have to use a hard disk instead of an SD memory of the same size? | Engineering | explainlikeimfive | {
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"What you see is the casing that has to be big enough to fit the USB connector and your fingers to hold it. The actual memory chip is (nowadays) so small that it doesn’t really influence the size of the actual drive that much.",
"Computers nowadays \\*do\\* often use the equivalent of SD memory instead of a hard disk. The reason they don't just use SD cards directly is because those have a limited number of write cycles before they break, and computers write a lot more to the hard drive than you might think.",
"If you've ever cracked open a usb stick, you've probably seen that the actual memory chips are pretty small. Higher capacity USB drives just use more and higher density chips, but they all fit the same familiar form factor."
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ioag3v | When you slowly turn up a faucet, why is there a certain point that makes a louder sound and as you turn up more it's gone? | Engineering | explainlikeimfive | {
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"Only a \"fully open\" valve will allow the water to flow through a (mostly) perfect cylinder. Water flows smoothly and easily though this shape. There will be no noise. Any about of \"partially open\" will mean there is turbulence - the more water flow, the greater the force exerted by the turbulent water. This means the volume (of sound) will increase as you open the valve, increasing the water flow. It will then stop when the value is fully open. This is interestingly how blood pressure can be measured. Edit: little bits and pieces"
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ioh69q | why are most motorcycles so much louder than most cars? Shouldn't a bigger motor mean more noise? | Walking around the city is crazy how I can always spot a motorcycle but most cars just have a white noise type of sound | Engineering | explainlikeimfive | {
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"Motorcycles don't have to be loud. When they are, it's choice or bad maintenance. Internal combustion engines are loud. Consider your typical lawnmower. They tend to be a lot louder than cars. This is curbed with mufflers and controlled exhaust. This can be easier on cars, which have more space and can carry more weight. This allows more baffles and decompression to occur before the exhaust coming out the back. This can be changed by choice, as many muscle cars or trucks rumble louder than most cars. Notice also that cars with bad exhaust have sound problems, too. There is a lot of nonsense about loud exhaust saving lives. The belief is that if you can hear it, you're aware of it. Unfortunately, anyone driving in front of a loud vehicle knows most of its noise is cast backwards, and doesn't meet that bar of helpfulness. Then it falls to loud exhaust sounding cool or tough or whatever. There are also arguments of the lack of back pressure resulting in performance improvements. For the same reasons muscle cars do this. I have a motorcycle with a large engine, bigger than some small cars have. It's quiet enough that people hear the tires before they hear the motor.",
"A car engine is wrapped inside the engine bay and body of the car, and at least one side (the side against the cabin) is specifically insulated against sound. Plus exhaust goes through the muffler and a long exhaust pipe. Altogether that means the engine noise is more likely to stay in the engine. Motorcycles are just the engine exposed to open air with nothing to quiet it. Add to that that a lot of people deliberately modify them to be extra noisy because they're dorks and it's super loud.",
"Far, far shorter exhausts even on std non modified bikes. There's physically nowhere on a bike to put the amount of exhaust a car has, especially with the size of the boxes in car exhausts."
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iovohc | Why do cars in Audi's RS class (like the RS6) become almost completely silent as soon as the driver releases the throttle after completely flooring it? | I once was driving home and there was this Audi RS6 driving nearby. When it started driving, it made a loud and mighty racket and then when the driver decided it was enough the car went completely quiet. Like I couldn't even hear the revs go down. I'm not sure if this applies for other car manufacturers/models, but this is the only one I have experienced. Does anyone know what causes this silence? | Engineering | explainlikeimfive | {
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"This setting for the exhaust valve is automatic on a lot of cars, rpm or throttle based. Alternatively, it’s likely in sport plus settings that it may become always open. So either it was automatic in D and it closed once throttle and rpm was low, or sport more was on for takeoff then the driver turned it off after and the exhaust valve closed for a more quiet experience. Sources: I work on Audi and Porsche’s all day. Own a new Beamer that does this as well.",
"Most likely this is due to a valve within the muffler of the car. When needed, the valve will open allowing a bit more airflow for more power, but more importantly will make the car louder for the sensation. Then, once the car is cruising, there coffee will shut to improve passenger comfort by reducing noise. Some people don't want their cars to be loud all the time, but like it when accelerating. Edit for ELI5: The car is loud to be faster, but quite so people can enjoy their music or conversation."
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ioyjf0 | Why have premium cellphones shifted to glass bodies that are prone to shatter (like on phone backs)? | Engineering | explainlikeimfive | {
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"There's a few reasons to choose glass over other things like aluminum or plastic. 1. It's aesthetically more pleasing, I know I like it more than plastic 2. It is more conducive for wireless charging pads. 3. Glass can actually be quite resilient and could last as long/longer than other backings."
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ioyox1 | If the wind is blowing East, how does a boat travel West? Or vice versa | Engineering | explainlikeimfive | {
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"I assume you mean a sailboat. You do that by \"tacking\" You can't sail west, but you might still be able to sail Northwest and Southwest if your boat is rigged right. So you just constantly zig-zag towards the wind to get where you're going. Your path ends up looking [like this]( URL_0 ).",
"Something a lot of the other answers are missing is how sails work. There are two main kinds of sails. Mind you, I'm not doing a proper taxonomy, but there are two main kinds for the purpose of my examples. One kind catches the wind like a parachute. The stereotypical old pirate ships with square or rectangular sails do that. Modern sailboats have a sail called a spinnaker that does that. These sails allow the boat to be pushed by the wind and go in the direction of the wind. The other kind is often triangular. They're the sails you see on a modern sailboat. They work the same way airplane wings work. Air moves past the surface of the sail, but faster on one side than the other, which causes higher air pressure on one side and lower pressure on the other, and that propels the boat in the direction of the lower air pressure. That allows the boat to move *mostly* in the direction opposite of the wind. IIRC, the best speed is generally at roughly a 30% angle to the wind, assuming head on to the wind is 0 degrees. So, if you want to go a direction head on to the wind, you need to tack and jibe, which means go a zigzag pattern, like others have mentioned.",
"Good responses already but yeah, you angle your sails to catch as much of the wind as you can, but it's gonna push you off course so you'll have to constantly adjust, resulting in that zigzag path they're mentioning. You've also still got a rudder and the aquadynamic shape of the ship to help keep you going the right direction, so once you get some forward momentum going just a little bit, on water it's pretty hard to stop that momentum, so you just have to make adjustments side to side.",
"In the early days of sailing this was a problem, and trade ships first headed south and followed the “trade winds” that blow east-to-west near the equator, then would sail north and take the west-to-east “westerlies” back to Europe. This triangular route was the basis for the “Triangular trade” If you had to sail directly into a headwind, you have to zig-zag side to side with the sails sharply angled - a time consuming process called “tacking” that lets the ship gain momentum sideways and then turn into the wind to make some progress."
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ipglld | Why are old structures often found buried under the ground? | Engineering | explainlikeimfive | {
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"Wind in an open area can get fast and pick up dirt. When it reaches a structure, the wind slows down, and it drops the dirt that it picked up. The wind can't get fast enough in that structure to pick up that dirt again, so it stays there. Repeat this process for a couple hundred years and you can get buried structures."
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ipmj3i | How can Earth observation satellites take pictures all the way down from space? | Engineering | explainlikeimfive | {
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"A lot of the high resolution Google Maps stuff comes from aircraft; zoom in on the good stuff and you've got about 6\" per pixel. Even the best commercial satellite is only about 16\" per pixel. It's called \"Satellite\" mode because it's from a satellite's point of view, not necessarily actual satellite imagery. Satellites capable of high-res Google Maps imagery belong to the military, and they use both techniques you describe...huge sensors + really amazing optics."
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ipupf5 | Why are aeroplane windows circular? | Engineering | explainlikeimfive | {
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"Because square corners in the openings create cracks in the aluminum. This was discovered in the de Havilland comet.",
"At first they made the windows square. Like normal windows everywhere. Thing is a jet airliner flies very high, and there isn't enough air for people to breathe there. Since they didn't want everyone wearing oxygen masks, they made the air pressure inside more than it is outside. Meaning as the plane took off and landed, the difference in pressure would cause stress to the the parts of the plane around the cabin, and the windows were the weakest part. The square windows meant that as the whole thing got stressed, the stress would focus in the corners. Over time as the plane took of and landed many times, the metal would start to get weaker and eventually break. Leading to a bunch of the planes crashing and killing a lot of people. They found that if they made the windows round, there wouldn't be corners for the stress to be focused on, so it would spread out over the curve. First they went with circle windows, later they went with squarish windows with rounded corners. And that stopped the planes from breaking that way. You can read more about this by searching \"de Havilland Comet\". This was the first jet plane airliner and the one where they figured out square windows kill people. I honestly don't know where /u/packflipper is getting his info from, it isn't really true.",
"they arent, the window mount is tho, it's to avoid having more corners than required moreso in seams between different materials. Each corner you have in a pressurized cabin is a potential point of failure that can be mitigated if you just design so it doesn't need to have them."
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iq5zni | Why do helicopters/choppers need to do circles in the air before landing? | Engineering | explainlikeimfive | {
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"They don't, but it's good practice to overfly the landing zone to get a good look at it, make sure it's clear, and get an idea of the wind.",
"Circling is the most compact (in terms of land overflown) was to descend. You can go down more quickly than just down-hovering. As an added bonus is allows the pilot an excellent opportunity to scan the landing zone for obstacles and convey to people (and animals) on the ground where some helicopter stuff is about to occur so they can clear out.",
"Even if helicopters are capable of hovering and translating backwards or side to side it is much easier for the pilot to move forward as this provides much better viability over where they are going. So it is much easier to do circles over the landing site as you do your final preparations then it is to stop and hover. These final preparations includes slowing down to landing speed as the helicopter still have quite a lot of momentum, checking for any obstacles in the landing area like tree branches, wires, fences, people or animals, checking the wind direction, speed and conditions as well as configuring the helicopter for landing. Once the helicopter is ready for the final landing it is also easier to do so while still moving forward. And to reduce the relative speed to the ground and prevent the wind from blowing them off the landing area they will try to land against the wind. So you might see a helicopter do a couple of circles above their landing site before landing, once to prepare for landing and observe the landing area and once to do final checks and get into position for landing."
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iqef87 | How have the Voyager probes not hit anything? | Given the large number of micrometeorites etc that are so small that we can't detect them, How have the probes managed to make it to the edge of the solar system? | Engineering | explainlikeimfive | {
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"To give some scale as to how little stuff there is in space compared to space, one of the most dense regions in the solar system is the asteroid belt, and the average distance between asteroids is > 600000 miles. This means that even in the most dense part of the solar system, you could fit 75 Earths in between every asteroid. There really is no worry about collisions in space, at least on a human time scale.",
"Space is really empty, and we aimed them at the empty space. They weren't supposed to go this long so its certainly possible they could have hit something after their planned path but it'd be like winning the lottery.",
"Space is very very very very big. There is dramatically more debris, large and small both being drawn towards earth's gravity well or even orbiting it than there is out in the middle of nowhere, and yet the vast, vast majority of satellites don't get destroyed by collisions because well... Again, space is huge."
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iqilp3 | Why do car engines need gears and a clutch but propellor planes don't? | Engineering | explainlikeimfive | {
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"While stationary, the force required to spin the wheel is substantially more than when moving, and so to get the car moving, you'll need a lot of torque, or force at the wheels. This requires a gear that amplifies torque while sacrificing speed. To move faster, the engine cannot simply ramp up the RPMs at first gear and go at 100km/h. So, some more gears are needed to trade torque for speed. To move efficiently at any speed, the engine should be operating at an optimal RPM. So, to maximize efficiency, you add enough gears with varying ratios so the engine can stay at that RPM as frequently as possible. Also, a gear is needed for reverse, as the engine cannot spin backwards. A plane has no problem spinning the propeller at any speed, and so does not need a gear to get it moving. A plane's engine still needs to operate within a certain optimal RPM, and thus cannot simply speed up and slow down to vary all the needed speeds. While you can add a gearbox to a plane, the much easier solution is simply changing the angle (or the bite) of your propellers. This mechanism is very simple and does not put additional stress on the propeller as it spins at constant speed. Also, to reverse a plane, you simply need to reverse the bite of your propellers."
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iqj6wt | If Air Brakes Are More Reliable Then Hydraulic Brakes Why Are They Only Found In Large Commercial Vehicles? | Engineering | explainlikeimfive | {
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"It isn't inherently more reliable. It's more complex and requires more moving parts. The main advantage is there is no brake fluid to boil off if the brakes overheat and you can maintain braking pressure when the vehicle is off. In most cars a simple hand brake is enough to provide adequate braking pressure to make sure the car doesn't move while it's shut down and most people don't get their brakes hot enough for overheating to be a problem. If they do they just upgrade the braking system and use different fluid. Air brakes are also very twitchy and hard to get used to."
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iqjn7x | How are roads built on deserts? Or for that matter on any surface. | I've always wondered how roads were built on desert lands, islands, steeply curved mountain roads, crossing river/lake surfaces, marshy lands? How the paths of the roads get decided before construction, what parameters decide if a tunnel is to be built through the mountain/hill or go around it. How are steep turns of the roads inclined, how are road speed limits set? | Engineering | explainlikeimfive | {
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"Here's a civil engineer talking precisely about some of these issues, and then some. URL_0",
"I'm sure there is an absolutely mind blowing amount of other things considered in an engineering study before all of those situations are finalized and ground is broken, but as far as \"technologies\" or techniques used as the base of an enormous portion of roadways (and a lot of foundations in general)... Mechanically Stabilized Earth (MSE) [ URL_0 ]( URL_1 ) is a great illustration of the principles behind it.",
"There are some protected parts of Peruvian desert where they simply drove in trucks with (salt?) water and made mud that they then pressed flat. That way they had roads with a limited “footprint”"
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iqlhsq | What makes the classic blinker sound in a car? | Engineering | explainlikeimfive | {
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"It's an electrical component called a relay. Basically it's an electronic switch that lets you turn on/off a high current electric circuit with a much much lower current circuit. Think of it kind of like a light switch in your house, only controlled electrically with another switch. For high current circuits in a car (such as headlights and turn signals), you want the shortest possible route between the battery and the light and it also needs to be pretty thick gauge wire. This is to limit the resistance of the wire due to length, as well as to help prevent any major shorts that could potentially lead to a fire. This is where relays come in handy. You can switch on/off a high current circuit (thick wires) with a much smaller current circuit (very small wires). That way you don't have to run a super thick wire from the battery in the hood all the way inside the car to the turn signal switch and back out to the actual turn signal bulbs. Instead, you can connect the bulb directly to the battery and just control it using a relay with a really small wire coming from inside the car. The audible clicking noise is just this relay turning on and off. All relays make noise, it just happens to be beneficial in this case since it lets you know if you left the blinker on. I should mention that some modern cars purposely make a clicking noise through a speaker or something similar, but originally it was just a result of using a relay and was probably not intended.",
"Back then: a magnetic switch called a relais. Nowadays: a speaker. I'm not sure this answer is extensive enough by ELI5 standards, but there really isn't anything else to it.",
"That clicking sound is what's known as an electromagnetic relay. Relays are used to help switch something on and off but the way they do it is quite interesting. It's a safety mechanism to protect a small voltage or current circuit from the absolutely massive voltage and currents used within the car circuitry. A small voltage is used to turn on the electromagnet which clicks shut and completes the high voltage circuit. The high voltage and low voltage circuits are not connected to each other so they won't end up blowing up and fizzling out. Once you hear that click or clunk it's immediately recognisable. Relays are awesome in that you could use a simple circuit from a pocket calculator to turn on a high voltage circuit using relays, for example. & #x200B; Nowadays I'm sure they use something like solid state relays that don't click or clunk and that sound is emulated by the software since it's a throwback to the good old days and people would feel a little strange if that sound wasn't there."
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iqn6bw | How does pressing the gas pedal lead to the engine working, and then how does the engine make the wheels spin? | Engineering | explainlikeimfive | {
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"In a petrol engine, pressing the throttle opens a valve that allows air into the cylinders. More air allows more fuel to be burned, so the computer injects more petrol into the cylinders. The burning of this fuel pushes down on the piston, resulting in a torque on the crank shaft. More fuel means more torque. This is transferred through the drivetrain to the wheels, accelerating the car.",
"The gas pedal sends petrol into a chamber which sets it on fire. That fire creates pressure which spins something, and that spinning gets sent to the wheels via gears! (Am highly unedilucated on cars this is based on my very limited knowledge on such things)"
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iqu5bn | Why manual transmission order is the same in both right and left hand drive cars? | Engineering | explainlikeimfive | {
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"Because left and right drive cars are mostly identical. Only the things that have to change are changed, for every other part it's cheaper to make one version for both cars. Transmissions and engines are expensive and not steering-side dependent, so they are the same parts.",
"Moving the steering wheel is not cheap, but it must be done, changing the signal and wiper stocks around doesn’t really change the cost so they do that, but the transmission is quite expensive so you don’t really want to manufacture two different transmissions"
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ir37f3 | Why did older cars not shut off immediately but take time to turn off and when they did, they made a loud bang? | Engineering | explainlikeimfive | {
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"backfire. unburned gas/air detonating in the hot muffler. this is an oversimplification but the whole explanation is s too long"
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ir5cfk | How come helicopters don’t plummet to the ground in the event of an engine failure? | Engineering | explainlikeimfive | {
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"They actually do plummet to the ground, but there is a clever trick which can be used to make it survivable. When the engine fails and the helicopter starts to fall the rotors and attached machinery has inertia. As it falls the pilot can adjust the blades such that the air passing through them causes them to rotate faster, like blowing air through a turbine. Then when close to the ground the pilot can switch the blades so that instead of being pushed by the air they instead push air down with their stored inertia. If done properly this can give enough lift to slow the helicopter into a survivable crash.",
"Autorotation As the helicopter falls, the air moving up through the rotor rotates them, reducing the speed of decent and producing forward motion as if the rotors were being powered by an engine. It’s analogous to an airplane gliding when the engines are off."
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ir9h8t | If a circuit breaker at home will trip in a fraction of a second. Why is it dangerous to touch a live electricity wire? | Engineering | explainlikeimfive | {
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"It takes a lot more electrical current to set the house on fire than it does to stop your heart. The breaker detects amounts of current that might damage household wiring and shuts off. Your body doesn't draw that much current, usually.",
"Because the amps that would kill you have already traveled through your body by the time the breaker does it’s thing. The amps need to be drawn before the breaker can engage so you already stopped your heart before the breaker is triggered.",
"It’s kind of hard to explain electricity to a 5yo. Basically electricity is like a push. And a breaker is there to stop electricity when it pushes too hard to stop the wires in our walls from getting to hot. But electricity doesn’t have to push anywhere near that hard to kill you."
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ircby5 | Why were ridiculously fast planes like the SR-71 built, and why hasn't it speed record been broken for 50 years? | Engineering | explainlikeimfive | {
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"Before we could use satellites to take pictures from space, if we wanted to see what was going on in enemy territory, we had to take pictures from a plane. Enemies didn't want us taking pictures so they would try to stop the plane - usually by blowing it up with missiles. We didn't have \"stealth\" technology yet to keep from being seen, so if we wanted to avoid getting hit with missiles, we needed a way to avoid them. The best way we could come up with was to go so fast they couldn't catch up. Being really high in the air helped this, because it's easier to go fast up high, and because it would take missiles so long to get up to you, you could be out of the area before they reached that height. As a result, the SR-71 was designed to go as high and as fast as possible. Since then, we learned to build space satellites to take our pictures, which can't be hit with missiles. We also developed \"stealth\" technology for planes, which keeps them from being seen on radar. This means we no longer need to develop planes for high and fast work, so the SR-71 remains the best at that. (Edited to remove error related to a missile strike)",
"For the “why hasn’t something faster been built”: There’s no need for anything as fast or faster. Flying at M3.2 requires Ramjet engines, custom fuel that won’t spontaneously ignite when the aircraft gets hot and a shit ton of maintenance time on the ground. Theoretically, a Ramjet engine is good up to Mach 5 at which point the intake temperature exceeds the working temp of all known materials. The SR-71 showed that even getting 2/3 of the way there requires buckets of money, R & D and maintenance, so we’re pretty much at the limits of that technology. The next step up requires a new generation of engines, either a Scramjet (Supersonic Combustion Ramjet) being developed by NASA on the X43-A) or the Sabre engine being developed by a British company. Shit like this takes a looooong time to develop and test, when I was studying aerospace engineering in the late 80s I wrote a paper on the design and development of both engines. They’ve only started testing them in the last few years!",
"It technically was broken by the A-12. Additionally, faster air breathing planes exist, but they are pilot-less, like the scram jet prototypes",
"Where’s the bot?! I came for the story.",
"Its speed record for \"how fast can something go\" has been broken a bunch of times. The North American X-15 went 4520 mph. & #x200B; There was even a direct competitor to the SR-71 called the A-12 that went pretty much the same speed, they just look pretty much the same. & #x200B; The design challenges to make something that flies that fast is where the economics falls apart. The SR71 was extremely expensive, and it was only able to hit those speeds because of the altitude it was flying at. Flying at those speeds at lower altitude would have destroyed the plane At sea level the aircraft was limited to much slower speeds, normally under 1 mach. (500 mph or less) & #x200B; so basically \"How do you go really really fast in a plane?\" - go really really high... why don't we do it anymore? there is no need & #x200B; btw - the ISS is currently going 4.76 Miles per second... thats over 18k mph. Its just up really really high. & #x200B; edit: guys - I get it the ISS isn't a plane, it was just a cool tidbit about shit going really fast",
"*unzips* There were a lot of things we couldn’t do in an SR-71, but we were the fastest guys on the block and loved reminding our fellow aviators of this fact. People often asked us if, because of this fact, it was fun to fly the jet. Fun would not be the first word I would use to describe flying this plane. Intense, maybe. Even cerebral. But there was one day in our Sled experience when we would have to say that it was pure fun to be the fastest guys out there, at least for a moment. It occurred when Walt and I were flying our final training sortie. We needed 100 hours in the jet to complete our training and attain Mission Ready status. Somewhere over Colorado we had passed the century mark. We had made the turn in Arizona and the jet was performing flawlessly. My gauges were wired in the front seat and we were starting to feel pretty good about ourselves, not only because we would soon be flying real missions but because we had gained a great deal of confidence in the plane in the past ten months. Ripping across the barren deserts 80,000 feet below us, I could already see the coast of California from the Arizona border. I was, finally, after many humbling months of simulators and study, ahead of the jet. I was beginning to feel a bit sorry for Walter in the back seat. There he was, with no really good view of the incredible sights before us, tasked with monitoring four different radios. This was good practice for him for when we began flying real missions, when a priority transmission from headquarters could be vital. It had been difficult, too, for me to relinquish control of the radios, as during my entire flying career I had controlled my own transmissions. But it was part of the division of duties in this plane and I had adjusted to it. I still insisted on talking on the radio while we were on the ground, however. Walt was so good at many things, but he couldn’t match my expertise at sounding smooth on the radios, a skill that had been honed sharply with years in fighter squadrons where the slightest radio miscue was grounds for beheading. He understood that and allowed me that luxury. Just to get a sense of what Walt had to contend with, I pulled the radio toggle switches and monitored the frequencies along with him. The predominant radio chatter was from Los Angeles Center, far below us, controlling daily traffic in their sector. While they had us on their scope (albeit briefly), we were in uncontrolled airspace and normally would not talk to them unless we needed to descend into their airspace. We listened as the shaky voice of a lone Cessna pilot asked Center for a readout of his ground speed. Center replied: November Charlie 175, I’m showing you at ninety knots on the ground. Now the thing to understand about Center controllers, was that whether they were talking to a rookie pilot in a Cessna, or to Air Force One, they always spoke in the exact same, calm, deep, professional, tone that made one feel important. I referred to it as the “ HoustonCentervoice.” I have always felt that after years of seeing documentaries on this country’s space program and listening to the calm and distinct voice of the Houstoncontrollers, that all other controllers since then wanted to sound like that… and that they basically did. And it didn’t matter what sector of the country we would be flying in, it always seemed like the same guy was talking. Over the years that tone of voice had become somewhat of a comforting sound to pilots everywhere. Conversely, over the years, pilots always wanted to ensure that, when transmitting, they sounded like Chuck Yeager, or at least like John Wayne. Better to die than sound bad on the radios. Just moments after the Cessna’s inquiry, a Twin Beech piped up on frequency, in a rather superior tone, asking for his groundspeed. Twin Beach, I have you at one hundred and twenty-five knots of ground speed. Boy, I thought, the Beechcraft really must think he is dazzling his Cessna brethren. Then out of the blue, a navy F-18 pilot out of NAS Lemoore came up on frequency. You knew right away it was a Navy jock because he sounded very cool on the radios. Center, Dusty 52 ground speed check Before Center could reply, I’m thinking to myself, hey, Dusty 52 has a ground speed indicator in that million-dollar cockpit, so why is he asking Center for a readout? Then I got it, ol’ Dusty here is making sure that every bug smasher from Mount Whitney to the Mojave knows what true speed is. He’s the fastest dude in the valley today, and he just wants everyone to know how much fun he is having in his new Hornet. And the reply, always with that same, calm, voice, with more distinct alliteration than emotion: Dusty 52, Center, we have you at 620 on the ground. And I thought to myself, is this a ripe situation, or what? As my hand instinctively reached for the mic button, I had to remind myself that Walt was in control of the radios. Still, I thought, it must be done – in mere seconds we’ll be out of the sector and the opportunity will be lost. That Hornet must die, and die now. I thought about all of our Sim training and how important it was that we developed well as a crew and knew that to jump in on the radios now would destroy the integrity of all that we had worked toward becoming. I was torn. Somewhere, 13 miles above Arizona, there was a pilot screaming inside his space helmet. Then, I heard it. The click of the mic button from the back seat. That was the very moment that I knew Walter and I had become a crew. Very professionally, and with no emotion, Walter spoke: Los Angeles Center, Aspen 20, can you give us a ground speed check? There was no hesitation, and the replay came as if was an everyday request. Aspen 20, I show you at one thousand eight hundred and forty-two knots, across the ground. I think it was the forty-two knots that I liked the best, so accurate and proud was Center to deliver that information without hesitation, and you just knew he was smiling. But the precise point at which I knew that Walt and I were going to be really good friends for a long time was when he keyed the mic once again to say, in his most fighter-pilot-like voice: Ah, Center, much thanks, We’re showing closer to nineteen hundred on the money. For a moment Walter was a god. And we finally heard a little crack in the armor of the HoustonCentervoice, when L.A.came back with: Roger that Aspen, Your equipment is probably more accurate than ours. You boys have a good one. It all had lasted for just moments, but in that short, memorable sprint across the southwest, the Navy had been flamed, all mortal airplanes on freq were forced to bow before the King of Speed, and more importantly, Walter and I had crossed the threshold of being a crew. A fine day’s work. We never heard another transmission on that frequency all the way to the coast. For just one day, it truly was fun being the fastest guys out there.",
"The SR-71 could evade air defenses with raw speed and altitude. Air defenses have improved to the point where it would take a truly revolutionary leap to make an airplanes that could use its speed and altitude to do so. Couple that with satellites and stealth and the cost/benefit/practicality doesn’t make sense. At least on paper. Who knows what remains classified.",
"My dad flew the SR-71 in the late 70’s early 80’s. I would get to watch him suit up, what a neat experience as a kid! I also heard him break the sound barrier a few times when coming back to base. Dad absolutely loved flying this plane. I’ve seen him cry very few times in my life but the day the last flight of the blackbird came into DC, flown by JT Vida, he cried hard. So proud of my dad, Gene Quist 💕",
"The replacement for those spy planes is top secret. We won’t know about them for another 30 years, if ever. I’ll bet there are aircraft out there right now that have Radar and optical stealth and are going in and out of sovereign airspace at will. They may or may not be manned. As other people have pointed out, satellites can be planned for. There will always be a need to put eyes on a target from the air. The alternative would be to send in special forces with drones. Either way, satellites cannot be the final answer.",
"First off, the SR-71s record has been shattered by the X-43, which flew three times as fast as the SR-71 As for why the SR-71 was so fast, it was to prevent it from being shot down by Soviet air defense. Whenever a SAM site targeted the SR-71, it would accelerate until,it was going faster than the missile.",
"The Blackbird was built to fly high and fast over the Soviet Union to take reconnaissance photos. Then we started putting cameras on satellites and it became unnecessary.",
"Obligatory Sled Driver: . . . **There were a lot of things we couldn't do in an SR-71, but we were the fastest guys on the block and loved reminding our fellow aviators of this fact.** . . . Nah, just kidding. Here's a DIFFERENT excerpt from Sled Driver: Walt continues to update me with numerous reactions he sees on the DEF panel. He is receiving missile tracking signals. With each mile we traverse, every two seconds, I become more uncomfortable driving deeper into this barren and hostile land. I am glad the DEF panel is not in the front seat. It would be a big distraction now, seeing the lights flashing. In contrast, my cockpit is ‘quiet’ as the jet purrs and relishes her new-found strength, continuing to slowly accelerate. The spikes are full aft now, tucked twenty-six inches deep into the nacelles. With all inlet doors tightly shut, at 3.24 Mach, the J-58s are more like ramjets now, gulping 100,000 cubic feet of air per second. We are a roaring express now, and as we roll through the enemy’s backyard, I hope our speed continues to defeat the missile radars below. We are approaching a turn, and this is good. It will only make it more difficult for any launched missile to solve the solution for hitting our aircraft. I push the speed up at Walt’s request. The jet does not skip a beat, nothing fluctuates, and the cameras have a rock steady platform. Walt received missile launch signals. Before he can say anything else, my left hand instinctively moves the throttles yet farther forward. My eyes are glued to temperature gauges now, as I know the jet will willingly go to speeds that can harm her. The temps are relatively cool and from all the warm temps we’ve encountered thus far, this surprises me but then, it really doesn’t surprise me. Mach 3.31 and Walt is quiet for the moment. I move my gloved finder across the small silver wheel on the autopilot panel which controls the aircraft’s pitch. With the deft feel known to Swiss watchmakers, surgeons, and ‘dinosaurs’ (old- time pilots who not only fly an airplane but ‘feel it’), I rotate the pitch wheel somewhere between one-sixteenth and one-eighth inch location, a position which yields the 500-foot-per-minute climb I desire. The jet raises her nose one-sixth of a degree and knows, I’ll push her higher as she goes faster. The Mach continues to rise, but during this segment of our route, I am in no mood to pull throttles back. Walt’s voice pierces the quiet of my cockpit with the news of more missile launch signals. The gravity of Walter’s voice tells me that he believes the signals to be a more valid threat than the others. Within seconds he tells me to ‘push it up’ and I firmly press both throttles against their stops. For the next few seconds, I will let the jet go as fast as she wants. A final turn is coming up and we both know that if we can hit that turn at this speed, we most likely will defeat any missiles. We are not there yet, though, and I’m wondering if Walt will call for a defensive turn off our course. With no words spoken, I sense Walter is thinking in concert with me about maintaining our programmed course. To keep from worrying, I glance outside, wondering if I’ll be able to visually pick up a missile aimed at us. Odd are the thoughts that wander through one’s mind in times like these. I found myself recalling the words of former SR-71 pilots who were fired upon while flying missions over North Vietnam They said the few errant missile detonations they were able to observe from the cockpit looked like implosions rather than explosions. This was due to the great speed at which the jet was hurling away from the exploding missile. I see nothing outside except the endless expanse of a steel blue sky and the broad patch of tan earth far below. I have only had my eyes out of the cockpit for seconds, but it seems like many minutes since I have last checked the gauges inside. Returning my attention inward, I glance first at the miles counter telling me how many more to go, until we can start our turn Then I note the Mach, and passing beyond 3.45, I realize that Walter and I have attained new personal records. The Mach continues to increase. The ride is incredibly smooth.",
"Satellites go about 17,000 miles per hour. Sr71 chugging along at 2,193 mph. It's like trying to break the fastest walking speed record. You could do it, but why?",
"Because right around 50 years ago, the people with all the money and power stopped caring about the progress, welfare, or even the survival of humanity, and they reoriented their efforts towards getting richer at all costs.",
"The US wanted to spy on Russia to see where ICBM's and other military installments were located, back in the 50' & 60's the only feasable way to do this was with spy planes. The clever engineers at the time decided to make the U-2 spy plane, this would fly at 70,000ft which the US was above the ceiling of the russian radar system for the Surface-to-Air Missiles (SAM's). They were wrong. The russians could track and even shoot them down, they did so with Mj Gary Powers piloting the craft, the US then stepped back and never over-flew the Soviet Union ever again. To combat the SAM's, the US decided to create a plane that could outrun these high-speed, high-altitude missiles. This became the A-12 and then the SR-71 spy plane. The SR-71 is a magnificent piece of engineering, requiring new materials, new engines, whole new design philosophies. What came out of this was Mach 3 (3x the speed of sound), 80,000ft capable super-jet that nothing could touch, it used on-board camers with very long zoom lenses to peek into the soviet union as far as they could without over-flying the territory. As technology advanced, the US developed spy satellites, these would originally use film and send them back to be recovered, they eventually moved to digital and also launched more. These satellites could cover the entire world with imagery every day to a very high detail, basically they have \\~20 hubble space telescopes, but pointed at the earth instead of out. The SR-71's did find a use, they could target specific areas quicker than waiting for a satellite to pass overhead, they were also used in Korea and Vietnam and other places. There was never a need to make a new SR-71, so nothing has been made since. Although an apparent successor called the SR-72 is in development. It's unmanned and can possible achieve Mach 5+. This would be used for targeted imagery that space based systems would take time to image.",
"If they had something faster, do you think they would let us know?",
"Why? Because they could and the Cold War. Why it hasn’t been broken? Because that’s hard to do and dangerous and because it’s a lukewarm war now.",
"There's a 95% chance there is a replacement plane for the SR-71 that's been operational for 25+ years. People are bent on satellites taking up the spy role, but the big problem with satellites is they follow a known trajectory/path. You can cover up activity when they are overhead. So the DoD is using a mix of new spy plane + satellites, most likely.",
"I'd like to add that I'm sure manned aircraft *have* been built that go faster, but they are most likely classified. My Dad works does engineering for military aircraft and he's met some engineers who have hinted that they've seen some weird shit that they're not allowed to talk about. Besides, the military has the technology to go faster than the SR-71, so I have no doubt that they've stuck a human on something quicker than it by now."
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irflhm | How do new build houses in the middle of nowhere get their power/water? | Engineering | explainlikeimfive | {
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"A lot of homes in the middle of no-where rely on well water/under ground water reserves and septic tanks unless they somehow have access to a city’s municipalities, which is typically not the case. I’m not sure on the power.",
"Water/sewage can be handled with on-site wells and septic tanks, so it’s not a big of a deal. A lot of suburban areas start out that way, but may get city water service as towns grow and expand. For electricity, the power company, eager to get new customers, brings the service to them. In real estate listing for land, you’ll often see lots described as developed or undeveloped, and that basically means that they do or do not have utility service ready to go at that location. If you buy undeveloped land, then you, as the owner, have to work with the utility companies to figure out what can be done as you begin planning your construction."
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iri0nt | How do gear shifts in cars work? I've been driving for a while and now I'm too embarrassed to ask. | Engineering | explainlikeimfive | {
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"The gear changes the ratio between the engine speed and the wheel speed. So in gear 1, the engine has to spin a lot of times before the wheels spin once. In gear 5, the engine has to spin less times before the wheels spin once. But *why*? Basically engines don't have a very big speed range. If you only had gear 5, the engine couldn't go slow enough to drive into your garage. You'd have to start the car at like 20 km/h. If you only had gear 1, you could start the car and drive into the garage, but wouldn't be able to go *faster* than 20 km/h. And then there are more in-between gears."
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8
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|
irip0h | why is it mandatory to have a minimum amount of water in the electronic water boiler in order to prevent damage? | Engineering | explainlikeimfive | {
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"g4ys3zs",
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"text": [
"If you mean a small electric boiler for making tea and such (i.e. an electric kettle): The boiler has a heating coil at the bottom which heats up very quickly. If there is water around it, that heat goes into the water and heats it up until it boils, so the heating coil never gets much hotter than 100°C. If there is no water in there, the coil will heat up a lot more because the heat isn't absorbed, and that may damage the coil or start a fire. Though often there is an additional safety switch which *should* turn the boiler off before that happens. Another reason there's a \"minimum amount\" is to ensure there's always enough water to produce enough steam to trigger the automatic shutoff when it's boiling. Otherwise it might keep boiling for a long time and boil all the water off, in which case we get back to the damage/fire situation.",
"the heating element can destroy itself otherwise. boiling water takes a tremendous amount of energy. without that water, the energy has nowhere to go so it just melts the heater. this is particularly likely to happen to a water heater because it's an enclosed space. air is actually a *terrible* conductor when it can't move. most forms of heat insulation, from your home to your clothing, is actually just trying to trap air. it's also particularly bad for an electric heater, as electric heating elements change how conductive they are (and therefore how much heat they generate) based on how hot they are. unlike gas units which send out fuel (and therefore energy) at a fairly fixed rate."
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9,
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|
irojn3 | why do some prosthetic legs tend to hand a backwards curve when human legs are straight? | Engineering | explainlikeimfive | {
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"text": [
"Prosthetic legs aren't designed to simulate human bones, but rather to support the weight as close to how an entire leg would as possible. This means they need to simulate not just the support of the leg, but the flexibility and cushioning of the foot and ankle. That flexibility isn't usually possible from a straight structure, unless it's soft, but prosthetics need to be durable because they aren't made of constantly regenerating cells.",
"Because that curve form lets the prosthetic to flex everytime you take a step, similar to the way your leg stretches and contracts when you walk. Imagine going up a staircase with a stick that can't contract itself when you put it on the next step.",
"In addition to what others have said, our feet are actually four points of contact. We are constantly adjusting pressure to our toes and heels to stay balanced. Amputees can't do this with prosthetics, so the curve allows better control over their balance. Source: my buddy is a bilateral amputee.",
"The curved ones are carbon fibre which flexes when you weight bear on it then springs back giving you energy back as you step off the leg. It has to curve one way and forwards would get in the way more than backwards. Source: i’m a prosthetist."
],
"score": [
20,
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5
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irue96 | How do people turn slabs of wood into wooden barrels that can hold water without leaking? | Engineering | explainlikeimfive | {
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"g52jnuh"
],
"text": [
"The wood is cut at a slight angle so all the pieces fit as a large polygon which all edges touch. They are then banded tightly with metal bands at the top and bottom to form a barrel. This isn't perfectly leak proof, but when you add liquid to the barrel, the wood swells and absorbs a small amount. This makes a pressure seal between all the pieces of wood."
],
"score": [
33
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Subsets and Splits