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7nws3h | How does an ECU tune on a car engine affect the performance of the car? What happens? | Engineering | explainlikeimfive | {
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"I did ECU calibration for a major automotive supplier for several years, so I can offer some insight. When an engine controller is programmed by the manufacturer of a car, there are several goals they're trying to meet. Some of those goals are mutually exclusive, so that improving performance in one are decreases performance in another area. The three primary goals that they have to balance between are performance, fuel economy, and emissions. Depending on the vehicle and its intended customer base, those goals will be more or less important. For example power is very important for a high-end sports car, so fuel economy and emissions take a backseat. Having your ECU tuned, or installing an aftermarket ECU alters the way your car operates, usually shifting the balance point of those three things one direction or another. If you wanted to increase your car's fuel economy, you can do that at the expense of performance or emissions. It's something you need to be very cautious with, since many aftermarket tuners and ECUs don't do the kind of testing and validation that OEMs do, so you're getting a less certain product. It may also make your car illegal to drive in certain places (i.e. California)."
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7nwxx8 | Why do some urinals have standing water? | Our urinals at work have standing water in them. I brought this up to some co-workers and the best response I got was to possibly prevent splash-back, but that doesn't seem like a much of a reason to have standing water in a urinal. Any other ideas or explanations? | Engineering | explainlikeimfive | {
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"It forms a liquid seal that prevents odors from leaking up from the drain pipe. Modern waterless urinals use instead a chemical that floats atop, and doesn't mix with, urine."
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7nxc90 | Estimated distance of ICBMs | How do they estimate the maximum distance that an intercontinental ballistic missile can travel and how accurate are these estimates? For example the Hwasong-15 is estimated to be able to travel 13000 KM, but how can they know if it didn't actually travel that far during the test? | Engineering | explainlikeimfive | {
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"When ballistic missiles are tested, it is my understanding that they are fired basically straight up. By seeing how high they go, it's relatively simple physics to derive how far it could travel if it were launched at a conventional angle assuming you take into account things like air resistance and the curvature of the Earth.",
"ICBM range is based on two major metrics: Thrust capability and payload. Thrust indicates how long the engine can burn for and how powerful the engine is. More thrust means longer range. This can be determined based on watching a rocket and measuring its size. Once you know its acceleration off the pad and how big it is (how much fuel it can hold), you've got all the information you need to calculate maximum range. Payload is a bit fuzzier, and also affects range. A heavier payload means the engine has to work harder to lift it (lowering range). Most experts can agree on the rough dimensions of a weapon that can go atop various rockets while still being 'efficient'. Larger warheads lower range too much, and lighter warheads won't do significant enough damage to worry about. Combining the two determines the effective range of the rocket."
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7o29bv | when playing music at a rock show, what's the purpose of feeding a loudspeaker back into a microphone? | Engineering | explainlikeimfive | {
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"Guitar amps & speakers aren't like stereo amps & speakers. They tend to color (or even distort) the sounds coming out of them based on how loud they are. If a guitarist likes the amp sitting at a \"6\" but you need a \"9\" to be heard, it will ruin the sound. You also need to consider that guitar amps just aren't big enough to give you good sound in a large club or stadium. To get that level of volume, you need PA system with much larger amplifiers (that, ideally, don't distort sounds). If you mic up all the guitar amps, you can run it all through a central mixing board where the sound guy and make sure everyone's playing at the right volume to sound good everywhere in the venue."
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7o6woy | Why tires themselves have a max pressure load different than what the recommended tire pressure load is specified on the actual vehicle | For instance, the tires on my Altima have a max load of 44psi - the Altima itself, on the car door sticker states a recommended pressure of 32psi. Why not just follow the tire's recommended load? | Engineering | explainlikeimfive | {
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"Your tires aren't made to be used only on your make/model. They could also be used on other cars that have different recommended pressure setpoints. edit: Additionally: suppose you inflate your tires to target on a really cold day. If you go driving on a hot day the pressure will not only increase due to the hotter weather, but due to the friction from driving. Tires need to be able to withstand this additional pressure."
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7obgct | How is energy from renewable sources, like wind or solar, stored? | I'm all for green energy but it seems to me like there's a serious problem with depending entirely on renewable energy sources. The weather is variable and unpredictable, so is the demand for energy. For example, There's less sun in the winter but the demand for energy is higher. How is the surplus energy produced during the summer stored to be used in the winter? I know about water reservoirs, they are used to store energy. What about flat countries like Denmark or the Netherlands? Do they have gigantic batteries storing the energy? How efficient would that be? | Engineering | explainlikeimfive | {
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"That’s actually a big issue holding us back from 100% renewables that they are still working feverishly on. Right now, though, we can avoid the storage problems by having back-up energy capacity installed. Basically: if the sun isn’t shining or the wind isn’t blowing, we just burn more fossil fuels to compensate for the shortage.",
"Energy storage is a huge issue in general, especially for \"unreliable\" energy sources like solar and wind. Right now the most effective way we have to store it is to pump water uphill into a resevoir, which can then be drained back downhill to spin a turbine (i.e. hydroelectric power) and harvest some of that energy on the way down. The efficiency of this system is terrible, however, you lose more than half the power you generated in the process. The best option we have now to deal with this issue is to simply diversify energy types. Have solar *and* wind *and* hydroelectric, and have a maximum capacity that's greatly in excess of whatever maximum load you anticipate; that way you'll always have enough.",
"Best renewable storage I have seen in pump storage dams for hydro. In short, pump water up a hill to a lake with excess renewable energy and have the water flow down turning turbines producing energy when electric power in needed. URL_0"
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7obnuq | With there being thousands and thousands of satellites (maybe millions? idk) all orbiting Earth at the same time, how are they not constantly colliding with each other? | Engineering | explainlikeimfive | {
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"Space is big, satellites are small. There are 7odd *billion* humans on the surface of the earth, yet almost all of the earth's surface is empty. The orbital space above earth adds a whole third altitude dimension to that area, and is mind-bogglingly huge. Now consider that Nasa and the ESA track all the known satellites and that the satellites often have the ability to alter their orbits slightly if two appear to intersect. Thousands of objects is a lot for a person to handle, but tracking a bunch of orbits by computer isn't that difficult. Collisions do happen though. Not every loose nut and bolt is accounted for, and satellites do sometimes sustain serious damage from a rogue washer impacting the case at 15000mph.",
"The simplest thing is that space is really, really big, and satellites are fairly small, and there aren't really that many of them. On top of that, they're mostly tracked and their orbits are planned to avoid collisions. At a minimum, their orbits are 25,000 miles long, so 4,000 satellites would be at least 6 or 7 miles apart on average. But that's only if they're all in the same orbit, and their orbit is as low as possible. Most satellites are up in geostationary orbit, where one trip around the planet is 165,000 miles, giving them an average of about 30 miles separation. If the nearest car is 30 miles away, you don't have to be a good driver to avoid a collision.",
"There's about 3600 satellites in orbit. There are ~270 million cars in the US by itself. Yet there are broad swaths of the US where you can drive for quite some time before ever seeing another car. Now, that's way more cars than satellites. Also important to note, the space around Earth in which satellites operate is *vastly* larger than the United States. Or the entire surface of the Earth. So you've got a few thousand car-sized or larger objects filling a volume that dwarfs all the land that all the humans live on. That being said, there are certain specific applications, like geosynchronous orbit, where the satellites need a specific 'part' of the sky. These areas *do* get more crowded. But the engineers responsible for putting these devices into space take their neighbors into account and plan a route that avoids them. Additionally, satellites don't fly all willy nilly. They take fairly straight paths and the majority of them travel in the same direction, and if they are at the same elevation, then at the same speed. So they aren't necessarily heading towards their neighbors."
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7oh3br | Why is carbon fibre so strong if just held together by resin? | I've never really understood how carbon fibre is so strong when it's primarily just held together with resin. Wouldn't it only be as strong as the resin is? | Engineering | explainlikeimfive | {
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"[This wiki link is a good place to start if you're curious about fibrous composites.]( URL_0 ) So \"carbon fiber\" the material has some incredibly high tensile strength to weight ratio. It's like a super rope material if you will... But like rope, it doesn't hold it's shape. You can weave the fiber into a shape you want, and then the matrix(resin/plastic) provides the stiffness. Then when there is a force in the direction the shape is designed for, the incredibly strong fibers take a lot of the stress. This means you can make it stronger and lighter. If you're doing a force the structure isn't made for, it can actually make it weaker - because the fiber isn't taking any stress in the direction and can actually cause a failure mode.",
"I think the resin is just to help it keep its shape, the strength comes from the fibers themselves. Carbon fiber isn't strong at all in directions the fibers don't point."
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7oo6s7 | What exactly happens when a fuse is blown? | Engineering | explainlikeimfive | {
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"A wire is in the fuse that is smaller than any other wire on the rest of the circuit and burns up before anything else does.",
"The *fuse* melts, causing a disconnect in the circuit. This is why blown fuses often look burnt. [Here's a video of a fuse blowing]( URL_0 )",
"Inside the fuse there is a little wire, when too much current runs through the fuse this wire overheats and burns out in the middle. If the power is high enough there will be an arc that forms across the gap in the broken wire, this will blow apart the rest of the wire. A fuse literally blows which is why the glass is often blackened when its blown",
"It's a safety to prevent an overload. If too much current goes through, the fuse breaks. Either it destroys itself to prevent catastrophic failure (like in a piece of equipment or car), or it's a switch that flips and opens the circuit if it gets too hot. Fuses are made of material that will break at a predetermined temperature. So a 20 amp fuse is made to bend and break open if it heats up past what 20 amps would cause. A circuit breaker is made of a piece of metal that bends or deforms when heated up, or an electromagnet that gets powerful enough, it causes a switch to flip and open the circuit.",
"The faster electricity flows through a substance (this is called current and is abbreviated as I for some reason), the hotter that substance gets. A fuse contains a portion that is designed to melt/burn/otherwise fail when the current gets to be too high. So, essentially, too many things turn on at once and draw too much power, causing too much current to pass through the fuse, and a little piece of it melts away. Once that piece is gone, the current can't flow anymore and the electricity is cut from wherever it was going. At least, that's how *old* fuses worked. A lot of them now don't actually suffer any damage. Rather, they are switches that flip into the \"off\" position once the current gets to be too high. (I'm not certain how they do this exactly. Maybe someone else knows the mechanism behind it.) That way, instead of having to put in a whole new fuse because the old one isn't usable anymore, you can just flip the switch back to the \"on\" position and resume normal use of electricity."
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7os07p | Why piston engines are less efficient and being used less than turbine engines. | For instance, why sterling engines only require expansive gas to produce energy, yet are being less than turbine generators that require high pressure to produce energy. | Engineering | explainlikeimfive | {
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"Turbines are more efficient for several reasons, but one of the top reasons is that they are not constantly reversing direction. Yarr! Yer not alone in askin', and kind strangers have explained: 1. [ELI5 How Do jet engines work and what’s the benefits of using them over a standard internal combustion or Wankel engine? Is it possible to use a jet engine in a car? ]( URL_1 ) ^(_35 comments_) 1. [ELI5: How do plane engines get more efficient? ]( URL_3 ) ^(_7 comments_) 1. [ELI5: Usage of jet engines vs turboprop ]( URL_2 ) ^(_11 comments_) 1. [ELI5: Plane Turbines ]( URL_0 ) ^(_19 comments_)"
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7oscjw | Why did engineers use Babbitt type bearings in car engines instead of roller ball bearings? | Engineering | explainlikeimfive | {
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"Plain, or journal, bearings with a pressurised oil layer can handle larger radial loads and last far longer than a rolling element bearing. Roller bearings are a bit more fuel efficient and allow an engine to be faster revving, but they don't last very long. The longevity difference can be huge: roller bearings might last for an oil change cycle, while journal bearings will often last for the useful life of the vehicle the engine is installed in. Btw, Babbitt is the name of the alloy typically used for automotive journal bearing shells."
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7otu1h | Why do cooling towers for nuclear power plants have to be so tall? | And does there have to be two of them per plant is just one enough? | Engineering | explainlikeimfive | {
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"Thermal power plants need to reject heat, because not all the heat energy can be captured by the turbine/generator. The plants therefore need some sort of way of getting rid of the heat, called a heatsink. If the power plant is near the sea, or a large lake, then cold water can be used as the heatsink. If less water is available (for example the plant only has a river for cooling water), then another way of getting rid of the heat is needed. Cooling towers are an effective way of doing this. There are two main types - natural draft and forced draft. In both cases, they work the same way. Warm water is sprayed from spray nozzles high up. As the water falls down, some evaporates cooling the rest of it. The cooled water is collected at the bottom of the tower. In a natural draft tower, the tower is tall enough that the buoyancy of the heated air is enough to create a strong up-draft. Cold air is sucked in at the bottom, rises, and the hot air exits from the top. In a forced draft tower, fans are used to blow the air through the tower. These don't need to be very high, because they don't rely on a tall column of air. Cooling towers are designed according to how much heat needs to be removed, the temperature of the water, how tall the towers are allowed to be (there may be zoning restrictions on them due to how tall natural draft towers may be), weather conditions, etc. There are various models and equations that can be used to design the towers. It would be possible to build a single cooling tower for a power plant, even a high power nuclear plant; but it would have to be very large. For example, the new nuclear plants in Georgia have 1 tower each. (See photos at URL_0 ) The same design plants being built in North Carolina (now cancelled) were being built with 2 forced draft low-profile towers each. (The 4 low-profile cooling towers are in the background here - URL_1 )",
"I would like to comment that cooling towers are *not* a feature of Nuclear power plants. Some nuclear plants do not have then, and many non-nuclear plants do have them. [Example.]( URL_1 ) You can tell that the image is of a coal plant by the chimneys (tall and thin towers), which imply that there is something being burned inside. EDIT: [Specific example.]( URL_0 )"
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7ouff3 | Engine Oil Ratings | I know there are different standards to which engine oil is rated for gas, diesel, motorcycle/atv and I am wondering about effects of using let's say a car oil in a motorcycle or vice versa. | Engineering | explainlikeimfive | {
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"This question has many answers. I can answer the car/motorcycle one with authority: motorcycles use wet clutches (engine oil lubricates the clutch). Most modern car oils have friction modifiers which decrease friction between parts. If you used oil with friction modifiers in a vehicle with a wet clutch (ie. almost all motorcycles) the clutch would slip, which is obviously pretty bad. You can use diesel oil in motorcycles no problem. One of the most popular motorcycle oils out there is actual a diesel oil. So a lot has to do with what kind of crap they're including in their product, since no oil is pure oil, they all have additives. The other stuff, like 5w-40, 10w-30 is temperature ratings. The first number is how viscous it is when cold, the 2nd number is viscosity when hot."
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7ovj6h | How would the suicide net planned to be implemented on the Golden Gate Bridge and other similar structures work? | Engineering | explainlikeimfive | {
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"A very large majority of people who jump off of structures like the Golden Gate Bridge and survive say that they immediately regretted taking the jump, and if they were to land in the net it would be unlikely that they were to try again. However, if you block off the sides of the bridge, someone's just going to find something else. On the other hand, since most suicides are impulsive, the idea of netting on the sides may work, at least until word of the netting gets around and people no longer consider the bridge a suicide option. Of course, the same risk occurs with the safety net. It's just a battle over what is the best option when both have their flaws. Source: suicide survivor, and URL_0",
"I guess it would be nice in the case that maybe someone jumps and then realizes while falling that they don’t want to die. Just a sort of second chance opportunity to reconsider.",
"It's meant to make it more inconvenient, not impossible. According to [this article]( URL_0 ) these nets don't significantly reduce suicides, they just make people choose a different place, so the whole thing doesn't seem quite thought out."
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7owxfl | Gas pedal and torque in steep incline. | I don't drive much. Less than ten times a year but it is always a long haul (at least 500 km). So I was driving in my small rental (manual) and found myself climbing a steep hill on icy and snowy highway. I pushed the pedal to the metal but both rpm and speed remained constant. I understand that during incline we need more torque and speed should remain the same but I couldn't figure how rpm remained constant. In normal case you shift to slower gear giving you more torque with same rpm but my car is manual so it can't be doing this. If I push the gas pedal my engine gets more air and fuel so it should run faster (more rpm) and there for my tires should rotate faster (more speed). Then I alter torque by shifting gears. But ELI5 me this: When in steep incline on gear 5 how does my speed, rpm and gear remain constant when I increase fuel to engine? | Engineering | explainlikeimfive | {
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"You don’t have what’s called low end torque in 5th gear. When climbing a hill watch the tachometer. Once you start to see your speed falling but your rpms remain constant downshift to gain a torque advantage. TLDR: don’t climb hills in 5th gears; downshift."
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7oy41y | What is the purpose of an EGR Valve on a car | My understanding is that EGR controls the exhaust gas that goes into the combustion chamber. Why would the exhaust gas go into the combustion chamber when it leaves from the muffler? | Engineering | explainlikeimfive | {
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"Oxides of Nitrogen, collectively known as NOx. NOx is bad. It causes smog and acid rain, it harms the ozone layer, and it has all sorts of bad reactions with biological material. Unfortunately, it's also an essentially unavoidable product of engine combustion; when you take a mixture of oxygen and nitrogen (which is of course what air is), and you bring it up to very high temperatures, the N2 and O2 molecules end up reacting to form NOx. NOx is also surprisingly challenging to get rid of from the engine exhaust. EGR rerouts exhaust gas back into the cylinders in order to starve the combustion reaction of oxygen. In doing so, it keeps the temperatures in the cylinder down, producing less NOx overall."
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7oyf32 | How is time synchronized all over the world? | Engineering | explainlikeimfive | {
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"For the most part, the answer is three letters long: [NTP]( URL_0 ). NTP is, roughly, a system for synchronising clocks over the internet (over any network, really, but \"the internet\" works well enough for our purposes here). Basically, the big difficulty with synchronising clocks is that it takes a small amount of time between me asking you the time and you answering, and some time between you answering and me hearing the response. Therefore, I can't just set my clock to what you said the time was, I have to account for those differences. In practice, what I actually do is ask multiple people what the time is, look at the timings for the responses, and use some clever maths to average it all out."
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7p26ip | OSI Layer Functions | Everything I read makes each layer sound very similar. Anyone care to break it down for me? | Engineering | explainlikeimfive | {
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"Layer 1 (physical layer) is how you transmit your message (through the air, through copper wire, through fiber optic cable, etc.). Layer 2 (data link layer) is how you communicate with the device next to you. You don't care whether you're connected to the device via radios or fiber optic cables or wires, just that you're connected. Layer 3 (network layer) is how you send a message to any other device on the network, even if it's not directly connected to you. Layer 4 (transport layer) is about how you communicate with the computer on the other end. As far as you're concerned, when looking at level 4, the messages may as well teleport directly from your computer to the other computer, but layer 4 will cover things like making sure the message arrives reliably and in-order. The separation between the higher layers is a bit more murky. By the time you get to layer 4, you have your core network working- you can send messages between any two computers. The higher levels are about how applications interpret the data that was sent across the network."
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7pc56j | Why is having a high bypass ratio on a jet engine more efficient? | Engineering | explainlikeimfive | {
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"text": [
"The core of the engine has very high speed exhaust, it takes a relatively small quantity of air and speeds it up to high speed. This is a large change in momentum for a large amount of energy The bypass fan takes a large amount of air and speeds it up just a bit. This gives a large change in momentum but doesn't waste energy accelerating the air up to high speed. Momentum is mass*velocity while energy is 1/2 * mass * velocity^2 The engine core is giving the fan a certain amount of energy to work with, but thrust is determined by how much momentum it can impart not how much energy. Thus taking a huge amount of air and accelerating it a little gives the biggest change in momentum for the smallest energy usage"
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7pe32m | How does an impeller increase pressure? | Engineering | explainlikeimfive | {
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"text": [
"I assume you mean for a centrifugal pump? The impeller is spun by the motor in the pump and has fins that move the liquid being pumped in a circle as it spins. This spinning forces the liquid out of the pump's channel. The faster the impeller spins, the more centrifugal force it generates which pushes the liquid harder. This creates pressure to push the liquid through the pump's tube.",
"The key idea here is that the energy created is kinetic energy. The amount of energy given to the liquid corresponds to the velocity at the edge or vane tip of the impeller. **The faster the impeller revolves or the bigger the impeller is, then the higher will be the velocity of the liquid at the vane tip and the greater the energy transfered to the liquid.** The kinetic energy of a liquid coming out of an impeller is harnessed by creating a resistance to the flow."
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7pihfe | what makes some boats able to cross larger masses of water than others? | Engineering | explainlikeimfive | {
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"text": [
"Fuel capacity, size/ability to deal with larger waves, ability to operate the engine(s) continually for long enough to reach your destination, etc."
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7pjymv | What is the little blade on the back of my razor for? | Engineering | explainlikeimfive | {
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"text": [
"It's for detail work. It's easier to shave a specific part of the beard with the single blade."
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7pmqbu | What do the little numbers on metric steel bolts mean, and how are they measured? (8.8, 10.9, 12.9, etc) | Engineering | explainlikeimfive | {
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"The first number represents the tensile strength of the bolt, the second number represents the yield strength (how much of that load it can take before being stretched past its elastic point and into the plastic point and being permanently distorted). Eg. A 8.8 bolt can hold 800Mpa before breaking. But if loaded with more than 80% of that (640Mpa) it will be permanently stretched/distorted. A 12.9 bolt will hold 1220Mpa before failure, but will permanently distort at 90% of that (1100Mpa) Alot of bolts in special applications are \"torque to yield\", that means they are done up far enough they become permanently stretched. And once undone must be replaced, or can only be used a couple of times (the stretch must be measured before reuse. If they are incorrectly reused they may fail.",
"The number actually has nothing to do with the size of the bolt, but rather the strength of it. The higher the number, the stronger the bolt.",
"/u/StopherDBF has the real scoop, they're grade/strength [markings]( URL_1 ). [Here]( URL_0 ) are other markings (ASTM & SAE) you will see on hardware."
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"https://www.engineeringtoolbox.com/steel-bolts-metric-grades-d_1428.html"
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7pp9q0 | How do car alarms work? | For example,i intentionally or not break a car's window,or hit its door,and the alarm goes off. What makes it to go off? | Engineering | explainlikeimfive | {
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"It's pretty simple, really. A lot more simple than people think. When a window get smashed, you abruptly change the air pressure inside the car. There is a sensor somewhere inside the car that detects the pressure change. The same sensor reacts when you have a large dog barking inside the car too, so most car alarms have a setting where you can turn off that sensor either temporarily or permanently. Added to that, some cars have vibration sensors. They detect when the car is lifted, so that you can't steal the rims without the alarm going off. Incidentally, those sensors also react to things that are unrelated, like earth quakes or when a train passes by a poorly built parking lot. Then, to make it harder to bypass the alarm, it reacts when the car battery gets disconnected. Some alarms also react when you try to remove a light bulb (because, you know, if it ain't blinking people won't react quickly enough) and most of them protect themselves from short circuited lamps because that is one of the oldest tricks in the book to cull an old aftermarket alarm system. To top it off, the alarm often has its own battery so that it can run the siren independently from the cars electrical system for half an hour or so. The rest is about entry control. There is a switch in each door. Including the tank cap and the engine compartment. Sometimes you also replace the central locking motors with motors that are able to lock themselves, because that is also an old trick; if you can physically move the motor in the drivers door, it will typically order all the other motors to open. So if you manage to get access to the motor, the alarm will actually make it EASIER to get into the car. Unless it can lock itself, that is."
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7pqev7 | so today I learned that the last b-52 was produced in 1962 but how are they still operational? | Engineering | explainlikeimfive | {
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"two words: preventive maintenance. you run through a series of checks on a regular basis and if something seems off or on the verge of breaking, you repair/replace it.",
"In terms of the frame, the most vulnerable part of the B-52 is the upper wing. As you can imagine, the wing is stressed by the weight of the engines as well as the lift generated from the wing itself. Engineers have determined that the useful life of that part of the plane is about 35,000 flight hours. That means that after those 35,000 flight hours, the metal in the upper wing surface will have been stressed so much that it would no longer would be safe to continue operations with the aircraft. In reality, the plane could likely fly many thousands of hours past that point, but the risk and cost of continued operation exceeds the levels determined to be safe by the Air Force. Going back to the B-52s still being operated, we're only putting about 300-400 flight hours on our operational B-52s each year. That's a big difference from some of our older B-52 inventory which put up much more flight hours annually. It's important to remember that the B-52 was designed to fly extremely long missions, with bomber fleets providing 24/7 missions ready to drop bombs on the USSR. We knew it was going to log a serious number of flight hours, so it was built to last a while. As we developed ICBMS and other nuclear delivery systems, the need for large numbers of B-52s to be in the air decreased. When the USSR collapsed and the Cold War tensions died down, we needed the B-52 to fly even less. So we had a plane designed to be flown for a long time that ended up not getting used as much. When nuclear treaties were signed that required us to reduce our nuclear-capable bomber inventory, we were able to select aircraft that had the longest usable life left. So now we have an inventory of B-52s that have between 2/3rds and 3/4ths of their expected life used, with limited expectations for how much we'll use them. If, for some reason, the mission demands on the B-52 increased, their life (at least in terms of years of projected service) would be cut shorter. Our estimate that they'll operate until 2040 is based on the idea that we'll use them at our current rate, so a large engagement that involves heavy bombing by the B-52 could quickly eat up the remaining flight hours.",
"I used to work at Kelly AFB where they overhauled the B-52s. They would strip each plane down to its component parts, test everything, rebuild as needed, replace anything out of tolerance, inspect the airframe for cracks, and install upgrades. When it went back together, it was better than new.",
"Would you be surprised if you saw a car from the 60's still operational? The U.S. spent a LOT of money on these aircraft, and they're surprisingly well built. Routine maintenance on them can keep them working for a long time. Not only that, but more modern stuff has come out since then to limit their functional use a bit."
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7prwqd | How do automatic transmissions "learn the driver's driving habits"? Does this truly increase efficiency(mpg)? | Engineering | explainlikeimfive | {
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"Nothing to do with piston wear. And most automatic transmissions do *not* have this feature. Instead they have an explicit switch for you to select sportier, medium, or more economical driving. What it really does: changes gear sooner (at lower RPMs) or later (at higher RPMs)."
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7pwr4n | Why is that sometimes when I’m sharpening a pencil with an electric sharpener, it gets really sharp but if you push the tip in one direction even slightly the graphite tip falls out? Then no matter how many times I resharpen it, it won’t sharpen correctly. | Bonus points if you know a life hack to get around this lol, it’s very annoying for those of us not on the mechanical pencil train. | Engineering | explainlikeimfive | {
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"It's possible you may have dropped the pencil. When you drop a pencil (especially colored pencils, funny enough), the graphite can shatter. Now you have a long tube full of broken graphite pieces that easily break off once they've been exposed by the sharpener. Source: My high school art teacher. She flipped her wig any time she heard a pencil drop."
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7pzhmu | Why does the fuel indicator go down faster at lower fuel? | Well exactly that, it feels that when I just fill up the car, that I can drive for quite a distance before losing a bar on the digital fuel indicator, but as there are less bars, the bars disappear quicker the lower fuel the car has. Thanks in advance Edit 1: I also thought that it was because it wasn't as important to know when you're full as opposed to empty, glad it wasn't just a silly thought. Thanks for all the replies so far | Engineering | explainlikeimfive | {
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"Most fuel tanks are somewhat \"bowl shaped\" and hold less volume at the bottom, making it appear to empty faster. Source: im an auto tech.",
"because car manufacturers have done lots of consumer testing and drivers feel better about their car when the fuel guage shows more than half full. the gauge is not meant to an accurate representation of the actual percentage of the amount of the fuel in the tank. the only marks on the poorly inaccurate gauge are \"full\" (or near overfull), 3/4, 1/2, 1/4, empty (near empty) and warning light for really low.",
"Gas gauges are not exactly linear, meaning 3/4 on the meter does not indicate 3/4 fuel remaining in the tank. I have read multiple conflicting explanations about why, but that's that.",
"I have noticed this and tested it by filling up when the gauge says 3/4, 1/2, and 1/4. Plus we all know that the gauge will stay on FULL for quite some time after filling up. The fractional gauge analog is simply not linear. I believe that is by design. Who cares what the fuel level is between FULL and 1/2? You need more warning as the tank gets closer to empty. If they made the scale non-linear (and thus accurate) people would get confused because 1/2 would not be halfway on the scale. Digital gauges in \"trip computers\" which track gas used while driving are linear."
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7pzr81 | Why aren't commercial airplanes getting any faster? | Engineering | explainlikeimfive | {
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"Most big airliners fly somewhere in the ballpark between Mach 0.5 and Mach 0.8. Going faster than that would require a few things: First, you'd have to use a lot more fuel. Drag increases ~~exponentially~~ geometrically (see comments below) with speed, so going faster requires you to burn a lot more fuel. Fuel is the biggest cost associated with commercial air travel, so a faster plane would be a lot more expensive to fly. Next, you'd have have to redesign the planes. The current configurations of planes aren't equipped to travel at Mach-1 or near Mach-1 speeds. If you look at something like the Concorde (a supersonic commercial airliner) you'll see that it has less room, as wide bodied designs aren't really conducive to supersonic travel. Assuming you want to go supersonic, you'd have to get around the problem with sonic booms. Sonic booms are very loud, and most people get angry when a loud explosion happens over their house. In the past, supersonic commercial flights were conducted almost exclusively over oceans because communities didn't want supersonic jets flying over them. _____ If you're asking why we don't go as fast as possible without breaking the speed of sound, it again goes back to cost and efficiency. If we have a 767 going Mach-0.75, a plane going Mach 0.99 is only 33% faster. A flight that would take 3 hours would be cut down to 2 hours and 15 minutes. Sure you'd save 45 minutes, but you'd burn considerably more fuel, which would drive up the cost of tickets. It's unlikely that the market would support spending something like 50% more for a ticket to only shave off 33% of flight time.",
"You can't get too much faster without having to cross the supersonic threshold, which requires significant changes to aircraft and engine design. Operational costs end up being very high because of the non-linear increase in fuel usage due to increased drag. Look at what happened to the Concorde. It wasn't cost effective en masse.",
"[This]( URL_0 ) video quite perfectly answers your question. tl:dw Passangers don't care enough about getting from point A - > point B on an airplane enough to pay the amount of money it would take to make them go faster.",
"Drag is based on the square of velocity, so increasing speed dramatically increases fuel consumption. The only reason to increase the speed of planes would be if it granted a competitive advantage in the marketplace to compensate for these increased costs. However, it generally doesn't. It's a lot easier to save time at the end points and with routing than simply making planes fly faster - and airlines have figured out that even marginal increases in cost to shave additional time tend to lose them passengers.",
"Because the fuel and regulation cost economics of going faster aren't compensated by the consumer willingness to pay for going faster. Since the 90s boom of electronic and video conferencing, there's much less business travel for meetings. Business travelers pay the premium for speed since time is money. Leisure travelers don't pay as much premium for speed since a few hours doesn't matter as much when you're on vacation.",
"There is a great video about this on YouTube which I would link but not sure of the rules for that on this sub. It’s by Wendover and it comes down to cost. It is basically cheaper to fly slower due to fuel efficiency than it is to fly faster.",
"Because going faster would require the consumption of far more fuel and would likely require more streamlined aircraft that would carry fewer people (like the Concorde did) - these factors would significantly raise the price of airline tickets. Presently, commercial airplanes are in a \"sweet spot\". They're fast enough to be very practical to nearly all travelers while being very fuel efficient - enabling the aircraft to carry a large number of passengers and keep the fuel cost per paying customer to a very low number."
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7q2wd7 | What makes a burning clutch smell the way it does? | I'm trying to find out what causes that clutch smell, as opposed to a purely burnt smell. Are certain chemicals/materials added to create this smell? (Because it is a very distinct scent) | Engineering | explainlikeimfive | {
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"text": [
"Road vehicle friction materials (clutch and brake linings) are typically made from a plastic material with various friction producing additives (steel fibers, kevlar, ceramic beads, sand grains, etc.) The most common plastic used is something called \"phenolic\". This tends to have quite a strong smell when burned or heated, but is otherwise extremely resistant to heat; it won't melt and it burns only with extreme difficulty. Some electronics contain phenolic, which is why the clutch smell is similar to overheated electronic smell.",
"A clutch friction plate is made of heat resistant materials, (used to be asbestos). So it is the materials heating up and eventually burning/smoking. That’s where the distinct smell comes from."
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7q54b2 | If there are bladeless fans you can stick your whole arm thru, why can't that idea be adapted to airline engines to lessen the danger of bird strikes | Engineering | explainlikeimfive | {
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"text": [
"Bladeless fans aren't actually bladeless, their intake is actually just a hole at the bottom and they output the air at the top",
"Because a jet engine needs to move a lot more air to push a million pounds at 600 MPH. Convert that to metric, bot.",
"There is a jet engine that is bladeless it is called a ramjet it works well enough but doesn't have the thrust of a jet engine, requires more fuel, and are less safe. The reason why they are less safe is that if they falter they have a harder time restarting do to the fact they have to dive tward the ground in order to build up the air pressure required for them to work in the explosive chamber. However regular jet engines having their fan blades that can be electrically speed up and pressure maintained until they restart mid-flight they don't flame out like ram Jets can. Also on average bird strikes happened less than 1 in 2000 flights both commercial and private in the United States."
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7q5e17 | Different Types of Metal Strengths | Hello reddit, I'm looking for an easy explanation for different metallic strengths(Yield, impact, compressive, tensile). Any responses would be invaluable. | Engineering | explainlikeimfive | {
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"* Hardness: Scratch-ability. If it wears or rubs against another material, does it wear out or does the other thing wear out? Chalk is one of the softest materials, diamond is one of the hardest. * Toughness: How quickly it can absorb a lot of energy. Example: you hit it with a hammer: Not tough, it shatters (diamond). Very tough, the hammer goes 'clunk' (magnesium steel). Toughness is also called Impact Strength. Dropping your laptop is also an example of material toughness at work. (Protip: do not attempt) * Young's Modulus: Stiffness. Very low modulus means the material is flexible and can stretch (weak plastic). Very high modulus means the material is stiff and does not bend at all (tungsten carbide). Something that is very stiff but not strong is \"brittle\". * Strength: There are several varieties of strength but they refer to how much force can be applied THROUGH the material. The way to measure this is force per area. The area used is the cross section of the thinnest part of where the force will be pushing or pulling through the thing you're examining. Force per area is pressure, so strength is measured in Pounds per Square Inch (PSI), Kilopounds per Square Inch (KSI) and MegaPascals (MPa). * Yield Strength: how much force does it take for the material to begin to bend or stretch *permanently*. (As far as most designs go, most kinds of things \"are broken\" if they reach the Yield point. A bent screw isn't shattered, but it can't do its job properly any more.) If you press on a paperclip, the maximum amount of push you can apply BEFORE it actually begins to change shape is its Yield Strength. * Ultimate Strength: how much force does it take for the material to break into pieces. (Some materials, like rubber, don't have a yield strength. They just flex and flex and flex and suddenly fail.) Bending a ruler until it snaps is an example of ultimate strength for that ruler. * Yield Limit: how much force does it take for the material to bend or stretch, AND still be able to return to its original shape. (Example: squishing a plastic cup in your hand, but not to the point where it snaps the rim.) Different directions of forces have different names, and have different strength measurements associated with them. * Tensile - pulling. How much force does it take to pull a thing until it bends or breaks. * Compression - pushing or squishing. How much force does it take to squash a thing. * Bending - self explanatory. * Buckling - bending caused by compression of thinner parts. * Shear - cutting action, or being pulled and pushed at the same time near the same place in opposite directions It gets more complicated (i.e. worse) the deeper you go. I haven't even mentioned *plasticity* or *stress*, and forces can be far more complicated than just the five I mentioned."
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7q8bh3 | The process for connecting new construction to already existing infrastructure. (i.e sewage, internet, power) | I live in a neighbourhood that has had a lot of quick construction over the years and have seen lots of new development pop up in relatively quick time. How are these construction projects connected to already existing infrastructure? | Engineering | explainlikeimfive | {
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"Permitting and code - you start by getting permission to make a physical connection. The process for a small user (like a home) is probably pretty simplified, but for a large users like industrial and comercial locations, you go through a review on how you would impact the rest of the distribution system. You may be required to upgrade things (new sub stations, pipes, etc) Physically connections - Sewer, water, and natural gas are probably hot tapped. The means you put a saddle on the pipe, then a valve, then a drill assembly goes through the valve, drills a hole on the pipe, then retracts and you close the valve. the distribution system is also build with redundancy, so they can possibly isolate certain legs and drain them if need by. Electricity is done by the utulility company, but can be done live with certain protective measures. I do not have any direct experience with telecom, but i imagine its similiar. I'm an engineer at a manufacturing plant, but i used to be a construction worker and i've actually hot tapped water and sewer. They're building a large Bass Pro Shops in my area, but the opening date was delayed. I spoke with a friend at the local municipal utility authority, and he told me they realized the sewer pipes weren't big enough to handle all the water flow and made them run a new line. I'm trying to get more electricity into my manufacturing plant, I had to apply to the power company for a review of the new connection. They looked at the existing capacity on my leg of the grid and determined that i can take another 200A of the grid (at13.2kv) without impacting the other customers. they told me this is good because my 2nd option would be to run 5 miles of utility poles and install a new sub-station. option 1 is about $100,000 while option 2 would be about $4 million.",
"Water, sewer, drainage and cable are typically under the new roads. The developer has to find the nearest existing connection points that are sufficient to service the new homes and they connect there and construct new lines under the road."
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7q8q7f | What is 'sharpness' and how does serration affect it? | Engineering | explainlikeimfive | {
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"text": [
"Sharpness is correlated to how thin the leading edge of a blade is. The thinner the edge, the easier it can wedge between other materials and thus cut them. Serration is also used for cutting, but instead of relying on a thin edge to cut, the teeth physically dig in and pull on the material, tearing it. Serration is good for tough, fibrous material that might otherwise flex under the pressure of a straight edge. But for softer materials, serration can produce a rough, uneven cut."
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7q96gq | Neural Network vs Alpha-beta pruning | What are the key differences between an 'Artificial Neural Network' and 'Alpha-beta pruning', in terms of how they function? What are the pros and cons for each? | Engineering | explainlikeimfive | {
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"That's a hard question because you really comparing apples and oranges. The mini-max algorithm is useful in very specific situations. You need to have a well-defined state space (game board and pieces), well-defined state transitions (game rules), adversarial gameplay (players have opposing goals), low branching factor (few good moves in a given position) alternating turns, and a good static evaluation function (who has the most pieces). When these conditions exist, mini-max and its various heuristics (which includes alpha-beta pruning) is an efficient way to conduct a brute force search through the move tree. A neural network is an artificial intelligence technique that in some ways mimics the human brain. The network learns by being exposed to a large body of input and being \"rewarded\" or \"punished\" if its response is right or wrong. It is a very general technique applicable to a wide variety of problems but usually does not give as good results as a special purpose solution. The two are so different, comparing them is like asking what is a better food, grain or beef Wellington? Grain feeds the world, but you are unlikely to order it in a fancy restaurant."
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7qcpj1 | Why some drill bits/machining bits are made of carbide when it's a seemingly very brittle material | Engineering | explainlikeimfive | {
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"text": [
"Tungsten carbide is very, very, very, very, very hard. While it may be 'brittle' under certain circumstances, the way the drill bit is formed prevents the kind of cross shear normally associated with it flaking off. They aren't used in a way where it flexes along the lines of it's points of weakness, so the main factor is how hard it is, and it works just great for what it is used for."
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7qn1jn | How does a turbo provide MORE power than it requires to spin? | I know that a turbo uses the exhaust to spin a turbine to push more air into the combustion engine. But how can it produce more power then it requires to run? I can't quite grasp the concept, as it feels like the equivilant of me pulling my self up by a rope without a pulley. And where does the limit go, as you can't just keep adding more turbos to get infinite power? | Engineering | explainlikeimfive | {
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"Your exhaust gases are being forced out by explosive force during the combustion cycle. These gases are then harnessed by a fan. This does, in fact, create back pressure and would slow down the enough slightly. But, by using this waste energy, the turbocharger forces extra air into the cylinder. Your vehicle's computer reads the pressure of this air, and adds more fuel. If you add extra fuel to a normal r running engine, there are very slight gains, and then the engine will run richer and richer, which is very dirty and inefficient. Overall, the extra air pressure far outweighs the 'slowing down' effect from the exhaust back pressure.",
"The turbo does not generate power, it's not a turbine engine. Rather, it's a device for cramming more air into the piston engine -- which uses this air to burn more petroleum fuel in the same-sized cylinder.",
"Most people think that only the \"flow\" of air spins a turbo.. when in effect, most of the energy is from the HEAT of the air getting out of the engine. The turbine in the turbo is shaped to promote expansion of the gaz (air)... since the exhaust gases are really hot, this expansion is what creates most of the energy."
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7qpdan | Why are billet parts structurally stronger than cast parts? And why are forged parts stronger than both? | Engineering | explainlikeimfive | {
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"It's all about the grain structure of the metal. Billets have a uniform grain structure from the extrusion operation that formed them before machining. However the grain structure is not oriented to the shape of the part. The act of forging will reshape the grain structure so that it follows the shape of the part thereby increasing its strength. Cast parts have no grain structure.",
"If you imagine a block of wood cut out to the shape of a hook. It'll have the grain structure of the wood through it, and if you try and lift something heavy, the hook will likely snap along the grain of the wood. However, if that hook shape is made by steaming the wood and bending it to the correct shape, the grain will follow around the curve of the hook, and it will be many times stronger. That's the basic difference between a machined part made from a billet, and a forged part. Cast parts have a crystalline structure which isn't all that tough, because it tends to be fairly hard. Which is why cast iron is known for shattering if it gets hit hard."
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7qr8ne | Why are there suddenly "guardrail famage ahead" signs everywhere? | Engineering | explainlikeimfive | {
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"You drive small car. You don’t need the signs. I drive big truck. I see sign. I may have to readjust my steering. Or maybe not. It just nice to have a sign in case it’s an issue",
"> no one plans to crash into a guardrail No one plans to do it. But everyone should be aware that should they involuntarily crash, the repercussions might be dire up ahead, far worse than normal. It might encourage them to drive more carefully than normal."
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7qshmr | Out of order processing and Tomasulo's algorithm | Engineering | explainlikeimfive | {
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"I'm going to explain this how I would explain it to an actual 5 year old. This will be at a very different level than the other answers, but maybe it will help some things click for you. Consider making dinner at your house. Someone gave you instructions to follow so that the dinner gets made correctly. You are going to make a spaghetti sandwich. 1. Boil water 2. Add pasta to water 3. Boil pasta for 10 minutes 4. Drain water from pasta 5. Add sauce to pasta 6. Pre-heat oven to 400 degrees 7. Put bread in oven 8. Bake bread for 5 minutes 9. Remove bread from oven 10. Turn off oven 11. Slice bread 12. Put pasta between bread slices 13. Eat Now, you could follow the instructions exactly as written and make a delicious spaghetti sandwich. However, you would be wasting time. There is no reason to wait for the pasta to cook before you start the oven. As written, it will take 10+5=15 minutes to make this meal. If you cooked the pasta and bread at the same time, you could make the meal in 10 minutes. You do this by executing the same steps in this new order: 6. Pre-heat oven to 400 degrees 1. Boil water 7. Put bread in oven 2. Add pasta to water 3. Boil pasta for 10 minutes 8. Bake bread for 5 minutes 9. Remove bread from oven 10. Turn off oven 11. Slice bread 4. Drain water from pasta 5. Add sauce to pasta 12. Put pasta between bread slices 13. Eat This is out-of-order execution. It is the processor figuring out that some of these steps aren't dependent on each other, so you can do them in a different order to get things done faster. This is possible because the resources you need to make the pasta (stove) and the resources you need to make the bread (oven) are different. Tomasulo's algorithm is a way of keeping track of which things are dependent on each other, and what resources are free, at any given point in time to get things done as quickly as possible.",
"Well, here goes, to hold you over until hopefully somebody with more background in this answers your question. For out-of-order execution, the first two sections of [this]( URL_1 ) page do a good job of explaining the situation, and also the problems that register renaming, which is a technique used by Tomasulo's Algorithm, tries to solve. Instructions are usually thought of as being processed sequentially by the CPU. However, when an instruction can take a long time, for example because of a memory access, out-of-order execution can allow us to start running some other instructions while we wait. Specifically this is out-of-order because there are instructions later on that complete before one higher up in the instruction set. So there's the potential to use processor cycles much more efficiently if this idea can be implemented correctly. However, naturally there are dependency issues with this idea. There can be trouble if we try and execute an instruction ahead of another instruction that, for example, provides parameters for the out-of-order instruction. Tomasulo's algorithm is pretty uncharted territory for me, but the general idea is that it is a way to implement out-of-order execution to prevent some of the dependency issues we would expect. If an instruction doesn't have its operands ready as it's preparing to be issued, it refers to a flag set to the algorithm to know where to look for the value when it gets computed and will stall until all its operands become available. When each instruction completes, it also puts its result into some logic that will inform other instructions waiting on it that one of their operands has become available. Along this process, register renaming is used so that values are not read out-of-order with reservation stations where instructions can look up operands that cannot be overwritten by other instructions. See [here]( URL_2 ) and [here]( URL_0 ).",
"IIRC when I took advanced arch, variable 1 = 5*9 variable 2 = 2+4 variable 3 = variable 2 + variable 1 on a basic level we have something that does sums and something else handles multiplications, and they take different times. We know that multiplication takes longer, and sums are done quickly. So while we wait for the multiplication to finish, we can start doing the sum. Since our last variable needs both results, it will get the sum first, and its gonna wait for the multiplication to finish.",
"Going to try my best. I'm assuming you mean out of order in regards to Tomasulo's algorithm. To boil it down Tomasulo's algorithm is when you grab an instruction, or a piece of code, you copy it, and begin working on it. Think of this like having a book you want to read. If you take the book to read the chapter you want then no one else can read it. If you photo copy that chapter, then the book can be used by someone else even while you use that chapter! TS algorithm does this by copying the information it needs and running that code with it's own copy of the values. This prevents a bunch of issues which aren't very ELI5 but it basically boils down to more people using the book at once. The out of order part is a little trick the algorithm uses that makes things go a little faster. Basically the program starts working on what it can rather then waiting for every piece to be there. For example say you are making a sandwich. You have to toast the bread, slice the meat then make the sauce. If you start making the bread and it is in the oven, you would still want to cut the meat and make the sauce while waiting for the bread. If the sauce is going to be ready before the bread you wouldn't want to wait for the bread to finish. It would be faster to finish the sauce. The out of order basically means you can start any step that isn't dependent on a previous step and finish that step before the other. We do this every day by multitasking. Non out of order would be like starting the shower then starting to brush your teeth but having to keep brushing till you finish showering. Just because we started the shower first doesn't mean we have to finish it first. It sounds crazy but without OOO a processor has to finish showering before it can finish brushing it's teeth. TLDR: TS algorithm copies everything to prevent issues and can start AND stop a task while another is going on with OOO. Edit: wording and basic restructure"
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7qxffi | How does your cars heat work? | Engineering | explainlikeimfive | {
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"Your car engine makes a lot of heat, that's why there is the big radiator up front. When the engine gets warm it opens a valve and starts the water pump so coolant flows through the engine and to radiator to move heat out of the engine The coolant also flows through a small radiator called the \"heater core\". When you want hot air, it blows through this heater core and into the passenger compartment. The delay is because until the engine gets warm enough to need cooling the coolant doesn't flow so the heater core doesn't warm up(neither does the radiator)",
"in a space heater there are electric heating elements like those on a stove, that warm up almost immediately. For majority of vehicles the heat comes from the coolant flowing through the engine compartment. So before hot air can start flowing, the engine has to warm up the radiator fluid, which will in turn heat the air."
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7r03rw | How do Military drones stay in range when they are so far away from their controllers, compared to normal commercial drones which have small ranges? | Engineering | explainlikeimfive | {
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"[This is the controller of a civilian drone]( URL_1 ). It's built to be held in your hand, run on batteries & operate on low-power shared radio frequencies & be operated by untrained civilians with no or minimal licencings. [This is the controller of a military drone]( URL_0 ). It's designed to operate over long ranges, have power, use protected radio frequencies and be operated by trained professionals. A Predator drone also costs **four million dollars** while your top of the line civilian drones top out at a few thousand dollars."
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7r8py9 | Why does some disposable lighter stop working before the gas runs out? | My fruit for the day. Why does some disposable lighter stop working before the gas runs out? By stop working I mean: 1. Does not light up. 2. Lights up but with very small flame. On the other hand, why does some disposable lighter continue to operate until the gas runs out? | Engineering | explainlikeimfive | {
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"A leaky valve can let some air in. That will dilute the concentration of butane fumes inside lighter, making it harder to ignite it. Butane is heavier than air so the air sits on top stopping so much butane escaping. Less butane coming out = a smaller flame. Depending on the design, you can sometimes tip them to get all the liquid in one side under the valve, which helps because the air moves to the empty side. Or give it a good shake which helps mix butane and air to make it easier to ignite."
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7r96u2 | how do demolition companies knock down buildings in cities with dynamite without destroying other buildings and having all the rubble fall in one place? | Engineering | explainlikeimfive | {
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"text": [
"They carefully calculate and simulate the position and strength of the explosives. It's placed to destroy main holding structures from the middle so that the building would collapse on itself, with outside walls falling inwards, from its own weight."
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7rbh15 | The difference between a church organ and a piano? | Engineering | explainlikeimfive | {
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"An organ makes sound by driving pressurized air through pipes of varying size. Each pipe makes one specific pitch. A piano makes sound by striking strings with a hammer and making the string vibrate. Each string makes one specific pitch. Each instrument uses a keyboard (and the keyboard layout is very similar between the two.) The difference is what happens when you press a key - on an organ, it opens a valve to let air into the corresponding pipe. On a piano, it causes the hammer to string the corresponding string.",
"Organs use bellows or motors to blow air through different sized pipes in order to create different tones, a piano has a number of different size and length strings that a hammer comes down when you hit a key and strikes the wires and creates a different tone."
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7rca6e | Why do New Orleans' pipes freeze and toilets stop flushing in 20 degree weather, yet a place like Chicago has far colder temperatures but unaffected pipes and toilets? | Engineering | explainlikeimfive | {
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"Just experienced this moving from Chicago to MO. In Chicago the pipes were insulated and underground. In my house in MO they were in the ceiling and not insulated. So a pipe burst.",
"Up here in Minnesota most city water lines are 6 to 8 feet deep. The houses also have to have a great insulation r-value to prevent freezing. Older homes still have freezing issues though. My hot water to my sink will freeze every time it gets below zero as it's kinda drafty between my floors but I'm renting so yeah. To simply put most homes are better insulated to save on energy costs which in turn prevent freezing pipes.",
"pipes in Chicago freeze as well if they get to 20 degrees. thing is...up north, people build their houses with alot of insulation and bury the pipes deep underground where the temperature doesn't get that cold. in southern part of the country, people don't spend as much on cold weather insulation because 99% of the time, it's wasted money.",
"For starters, Chicago gets frozen pipes too. [They wouldn't have pages on how to prevent them if they didn't]( URL_0 ). New Orleans doesn't expect to have such cold temperatures. 20F is way lower than the average low, and pretty close to the record low. Chicago, on the other hand, sees 20F routinely, and it gets much, much colder than that. Pipes usually freeze above ground, because even a few feet of earth makes for good insulation. So most pipes in Chicago are insulated above ground to help prevent freezing. In other words, Chicago is prepared for temperatures like that, and New Orleans isn't.",
"Vermont girl moved to New Orleans here. The insulated + underground thing is real for up north cold. Here in New Orleans, our house is raised like most houses here. Pipes exposed to all the elements. We did everything we were supposed to do (drip water upstairs and down) and we still froze and ultimately burst a pipe last night. Every single person I have talked to, burst a pipe. There is no water left ANYWHERE. The infrastructure couldn’t handle the water use (everyone running faucets to avoid freezing) and as a result they slowed the water flow. Which...froze all our pipes. My kid hasn’t been to school since Tuesday and I haven’t been to work since then either.",
"different building codes,freeze prone areas have pipes that are buried deeper,insulation required on exposed piping. the buildings are better insulates.",
"Pipes are not insulated as much (if at all) in the south, and they are not buried as deep either. Freezing temps are rare enough that there is no need to go to the expense of doing it that way most of the time. But in areas that freezing temps are common those protections are worth the expense so they are taken.",
"I live 60 miles from New Orleans in Biloxi MS. Down here our winters usually consist of low 30s and wind chill from the coastal waters. Many houses are built on stilts or off the ground in some way, exposing pipes to the elements. We usually cover pipes with foam insulation and let the faucets in the house drip overnight. New Orleans is also built below sea level forming a big ass bowl for the winds off Lake Pontchartrain to sweep down in to. It get cold down in da bayou too, comme ça.",
"In colder climates, outside (feeder) pipes sit below what is called a frost layer (A layer to which the ground above has insulated it from freezing). Internally, we have insulation inside the house down to the frost layer (where I am its 4 feet from the surface) if you have a sub-surface basement and this prevents cold from \"leaking\" into the house and affecting our pipes (not to mention that it helps prevent heat loss in general).. In the event of no basement, pipes need to be on the heated side at all times. Even where I am (where we just finished a 2 week stint at -40), if our heat goes off long enough, our pipes burst, insulation only does so much when there is no heat source In addition, summer only homes in our area, you need to drain all the pipes and open the taps before the winter to prevent freezing."
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7re6mp | What is a "Flathead V8"? | Engineering | explainlikeimfive | {
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"Flathead engines are ones where the valves are placed in the engine block, alongside the pistons. Compare to overhead valve engines, where it's up top. V8 means it has 8 pistons arranged in two sets of four, which meet at an acute angle, making a \"V\" shape."
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7ri3fu | Why is it that 40-60 year old houses in the US are known to suffer from major issues, while European cities have habitable buildings that are 100+ years old? | Engineering | explainlikeimfive | {
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"You get what you pay for. Create a house of plywood- and plaster-walls you get that. Build a house of stone and solid wood and you get that. Cost decides what you build. There's also the cultural thing of \"moving\": In the US you move very, very often. So if you build a house you build it for 5 or 10 years tops. If you build in Europe* you usually expect to never move again... Build it right and you get places that are 300, 500 or 1000+ years old that are still habitable (this is not saying renovation of those isn't taking in a lot of money; if you have a place that's 80 years old, expect to sink in a lot of money to get it up to modern energy standards even though the substance itself is still good). Build it cheap and it starts to fall apart after 20 years. And there are obviously also cheap houses in \"Europe\" that have the same issues as the US-houses you mentioned, that are build for maybe 30, 40 years and then are not really expected to hold up. --- \\* As always with this: \"Europe\" is not a country but a very diverse place made of many regions and countries and very different building styles and levels of wealth, which is reflected in housing.",
"The ones that last 100 years are the expensive well built ones. Come to my home town and i can point out plenty of falling apart 40-60 year old houses.",
"Your premise is wrong. There are plenty of 100+ year old houses in the US . There are entire neighborhoods with old houses and they are in great shape. Many European cities are older and the buildings have had \"major issues\". Every building needs maintenance.",
"The oldest house in the street I live in was built in 1594. It was an Indian restaurant last but is now mostly empty and used for events. There are a bunch of slightly (decades and centuries) younger buildings in my street that are now used as shops and have people living in them. One might conclude from that Renaissance era people knew how to build buildings that would last for ages. The truth is that the buildings that are left today are the outliers. There where a lot of buildings build in the last decade of the 16th century in my town, due to the place mostly burning to the ground in 1592. One has to assume that they rebuild everything. It isn't a large town today and wasn't one back then but it would still account for a lot of houses. All the houses that were built along side the one oldest house are no more. Out of all of them only one stood the test of time. While a lot of luck was no doubt involved one can assume that the buildings from that time that are left today were the ones that were build the best and maintained the best. If you wait a few centuries until 99% of the buildings from the 1950s in your area are torn down, the ones that will be left will be some of the best and sturdiest built in the 1950s. It is not that they were all built strong originally it is that only the strong survived. There is also the factor of maintenance and being built for maintenance. Most of the really old houses (fortifications and castles aside) in my area are built in the half-timbered style. This style is suited to be easily rebuilt and maintained with new shingles and beams and can even be completely taken apart and built up again elsewhere if necessary. In many cases these really old half-timbered buildings have a ship of Theseus thing going on in that it becomes hard to say how much of them is still the original building. A sturdily built and well maintained building that manages to be lucky enough to avoid all fires and the depredations of the various wars can stand for a really long time.",
"It's the same for modern European houses compared to old ones. In the past houses were built to last forever where as now we build them to last 30ish years.",
"As far as i know, many houses in the US are built differently. In central europe, houses have massive walls (typical example from my country: covering made of plaster plates or wood, layer of isolation, a wall made of concrete, massive wood or bricks, another layer of plaster plates or roughcast resulting in 50-60cm thick walls). In central europe, having air conditioning in private homes is rare too because of this. The houses in central europe are massive, with thick walls and solid materials. The other aspect is that many old buildings are made from stone and get renovated from time to time (e.g. wires, floors, heating, water...). A 60 year old house in my country also has issues - cracks in the plaster or roughcast, the isolation has to be renewed probably, the roof might have to be re-done as well, and the living standards might have changed so you need a better heating system, more electric wires etc. etc. But the walls usually are still solid like a bone structure.",
"Survivor's bias. There have been alot of shitty houses built in Europe over the centuries. Only the non-shitty ones have survived.",
"I live in a house built in 1906 and my neighborhood is full of hundreds as old or older. Not sure where you got your premise.",
"There's plenty of US houses that are that old that people live in. No matter where you live, there's upkeep that needs to be done on properties. In Europe and the US, roofs need to be replaced. As do windows, fixtures, etc. Things wear down after decades of use.",
"Many houses in the USA are simply not built to last 100 years (without significant maintenance issues) because our country is used to a huge rate of change. Especially during the economic boom of the 1950s and 1960s, there was *huge* demand for more and bigger housing, and people would rather buy houses only designed to last 50-75 years, than wait a long time to afford a more strongly-built house. Also, the huge supply of wood in North America has led people to built most homes out of wood, which is less durable than brick and stone."
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7rm9ln | What is filter gain? | What I've got so far is that its something to do with the relationship between the input voltage and the output voltage of a filter circuit but its all quite vague. | Engineering | explainlikeimfive | {
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"The gain is simply the ratio of the output voltage over the input voltage For filters you generally target the gain for certain frequencies to be high or low. If you're making a 1 kHz low pass filter then you want the gain for every frequency below 1 kHz to be as close to 1 (unity or 100%) as possible. A gain of 1 means a signal of that frequency will come out looking the same, if your input signal is only made of low frequencies then it will come out looking the same as it went it. You'd also want every frequency above 1 kHz to have a gain as close to zero as possible, this means they don't make it through the filter and aren't in your output signal In passive filters the gain is always less than or equal to 1, unlike in amplifiers where the gain is generally greater than 1"
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7rxceu | how are themocouples able to detect the temperature? | Engineering | explainlikeimfive | {
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"text": [
"When you join two dissimilar metals, you get a voltage across them. That voltage is proportional to the temperature at the junction. It's called the Seebeck effect: URL_0 You can also reverse it - driving a current through the junction to achieve a temperature change. That's the Peltier effect."
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7rzsso | How do shopping carts "hit the brakes" when you get too far from the store? | Engineering | explainlikeimfive | {
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"What kind of super advanced store has these? Worked retail for 6 years and have never heard of such a thing.",
"I used to work at a grocery store and often had to unlock these carts with a remote fob. At my store, they painted yellow lines along the “electronic fence,” which would stop the cart when the wheel with the lock would approached it. In my case, a single wheel was housed in a grey hood and a yellow brake would come down and under the wheel. Although when the fob stopped working we just filed the yellow brake down to the wheel to allow the cart to move freely again.",
"A cable is embedded underground around the perimeter of the store (or where they want to allow the carts). When a cart passes over them, it signals the locking mechanism to engage, rendering the cart annoying to use. Want to circumvent it? Find where the cable is embedded, and note how close you need to get before the cart locks. Get another cart, and with a buddy, lift it higher than that distance and walk it well past the perimeter. Done."
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7s6nmb | How do 'fuel injection kits' that convert carborated engines into fuel injected ones work? | I understand the basics of engines and how carbs work, but I am no mechanic and I see these talked about quite a bit and don't understand what they are exactly. | Engineering | explainlikeimfive | {
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"text": [
"Here's what a kit contains: 1.A higher pressure fuel pump to supply injectors. 2.One or more fuel injectors, of course. URL_0 Engine Control Unit (computer) to control the injectors. 4.Sensors for the ECU to tell it what the airflow, temperature, speed, throttle position, crankshaft position, and exhaust oxygen level is. 5.A throttle body to control airflow into the engine. The advantage of fuel injection is that the correct amount of fuel for the operating conditions can be inserted into the pistons. That makes for more power and lower emissions. A closed loop control system looks at the exhaust for each firing of a piston and makes corrections quickly."
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7saw31 | does kicking the door knob/handle off of a door actually open the door like in films, and if so why? | Engineering | explainlikeimfive | {
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"No, kicking the handle off won't necessarily open the door. Kicking the whole handle and bolt assembly through the door probably will though. The most effective way to boot open your average cheapo residential door is to apply your foot (with your body weight behind it) right next to the knob. This provides the maximum force against the weakest part of the structure. [A handy illustration]( URL_0 ) If you've had time to prepare though you can do much better with a simple door ram. A 3' length of solid 4\" pipe with flat ends, a couple handles, and filled with something heavy (like shot or cement) will smash most doors right off their hinges with minimum effort.",
"I got locked out of my house recently. My brother came over when my wife, son, and I were on a trip and locked the door into the house from the garage, which I had purposefully left unlocked. We got back from the trip, saw the door was locked, and couldn't get in. I tried using a plastic card to push open the latch, but it didn't work. I ended up using a hammer to break the handle off, push the rest of the handle through the other side, and open the door. Obviously, I replaced the handle soon after. You can get into a house by breaking the handle off, but you still have to get the internal mechanism to move somehow."
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7sd01p | What difference does the layout of pistons in an engine make? | eg. Two stroke, Straight 6, V6, W16 Does it have a significant contribution to power delivery? | Engineering | explainlikeimfive | {
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"[this is more ELI9] It helps to think of a car (or any other piston-engined machine) like a bicycle. Each piston moves up and down inside its cylinder, sort of like your legs do when pedaling your bicycle. Those pistons, just your legs, turn a crank that connects to the wheels and makes the car/bike move forward. - In a bicycle, the pedals are located opposite to each other. In other words, one pedal is at the top when the other is at the bottom (i.e. 180°/180° orientation). This makes it easier for you to pedal smoothly. If they were both at the top/bottom at the same time, or some other orientation (e.g. 90°/270°), it would be harder to pedal, and you would get a more “lumpy” feeling, similar to how it feels if you try to pedal with just one leg. You’d feel a very pronounced pulse on every rotation. - The same principles apply in a piston-engined car; It’s convenient to lay out pistons in pairs that oppose each other. That gives you smooth and efficient power delivery. Unlike bicycles though, an engine can easily have more than two pistons (i.e. legs), which can give you a lot more power. Most cars have between four and eight cylinders, and sometimes up to twelve (16 in _very_ rare cases). You could arrange them like a tandem bike, but that takes up a LOT of space. Instead, engines usually arranges the pistons all side by side, as if bicyclists were sitting shoulder-to-shoulder (like in a paddle boat). This is called an “inline” or “straight” arrangement e.g. an inline 6-cylinder or I-6 engine. - That works well for four cylinders. It doesn’t take up a lot of space, and you get a nice and even 90°-90°-90°-90° orientation along the crankshaft. It also works ok for five cylinders, but you can imagine how awkward it is to have a one-legged bicyclist on your team. It works REALLY well for six cylinders, with a 60°-60°-60°-60°-60°-60° orientation that is extraordinarily smooth because each pulse is so close to the next. Unfortunately, that requires a longer crankshaft, which takes up more space in the engine compartment and makes the hood longer (or wider, depending on which direction you orient the engine itself). - To get around that problem, engines sometimes position the pistons across from each other instead of all in a line side by side. That modification takes up less space. Usually it’s in a “V” pattern (e.g. V6, V8, V12) with pairs of pistons arranged like `•’ around the crankshaft, and occasionally it’s an “H” pattern with pistons arranged like —•— (most notably Subaru and Porsche). V’s are narrower but taller (good tradeoff between packaging efficiency and smoothness), whereas H’s are lower but wider (great for handling due to low center of gravity, but tend to have more vibration/harshness). - If this were an ELI12, we’d go into the differences between different piston and crankshaft angles in V- engines as well as their resulting harmonic/vibrations, why different companies chose certain layouts, and maybe even talk about a few crazy W-shaped engines."
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7sdk36 | what is the advantage of the multi-rotor design used for drones over that of the conventional helicopter rotor setup? | Engineering | explainlikeimfive | {
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"With two of four rotors spinning opposite directions, it eliminates the need for variable pitch blades and a rotor positioned vertically in order to counter the effects of rotation. That’s where a tail rotor on a helicopter comes in, as it keeps the body of the helicopter from rotating in the *opposite direction as the main rotor by “pushing” against that force. Quad rotors have equal rotors spinning opposite directions, cancelling out rotation.",
"The single rotor of a helicopter is a very complex piece of machinery. It needs to be able to change the pitch (angle) of the blades as they rotate. They're also fairly difficult to miniaturize. Small quadcopters, OTOH, use fixed pitch blades & because the electric motors they use can very quickly change speed. When coupled with the microcontrollers & sensors on the drone, this is more than enough to keep a small, lightweight craft in the air and under control.",
"I've met people that do remote controlled helicopters. They are much more complex, expensive and hard to control. This raises the question of why it is that regular, people-carrying helicopters use such a huge rotor, if the quad is so much easier to control. The answer is efficiency. A long skinny blade has higher aerodynamic efficiency. It also covers a far large area, moving more air. When you have to carry a large amount of weight, the efficiency outweighs the complexity.",
"You don't have to worry about collective and cyclic pitch. Just spin multiple motors (the net torque cancels out when simply hovering) harder or slower. Vary motor speeds to steer. Much less complex.",
"> why has the multi-rotor design become more prevalent in the use of drones? It's much simpler as noted in the other posts. It's just four electric motors with plastic rotors. The design is too unsafe to use for human flight because losing a single motor halves your available thrust which probably means going down. So you have four times as many motors but you can't afford to lose any of them, so four times more chance of crashing due to motor failure. The reason that losing one motor effectively means losing two is that thrust from a clockwise motor has to be balanced with thrust from a counter-clockwise motor, or the craft will start to spin.",
"small electric motors are extremely compact and efficient, with minimal mechanical complexity. with 4 rotors, and sufficiently intelligent control software, a drone can maneuver in any way a conventional rotorcraft can through varying the output of its 4 rotors. real helicopters are gas powered. the combustion engine and its support systems are powerful, but work better as large single units. having multiple engines would become wildly complex very quickly. electric doesn't scale well in vehicles because of batteries."
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7sjzx3 | Is this experiment real or fake? | If real can you ELI5 how is this possible? URL_0 | Engineering | explainlikeimfive | {
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"The battery generates electricity when it is connected back on itself via the copper wire touching the magnets. Electric current in loops creates a magnetic field - this is how an electromagnet is made. The magnetic field is only where the electricity is flowing, so only under the battery. This electromagnet repels the magnets on the battery, propelling it forward.",
"You have a battery and two magnets attached to it. Those magnets will keep the 'train' attached to the 'track'. When you place the 'train' on the 'track', it completes a circuit through the coils of the 'track'. That current creates a magnetic field which is essentially parallel to the center line of the coils and which pushes against the magnets on the 'train', causing the 'train' to move down the 'track'.",
"Electricity causes magnetism. This is how electromagnets work, it's also how simple motors work (it's how you take electricity from a wall outlet and turn it into a motor which blends your food or vacuums the floor). So, when you put the battery on the wire, it completes a circuit, which in turn creates a mini magnet both in the battery and in the wire. This magnet can be used to propel the \"train.\""
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7sm5ot | Maximum amounts of watt an appliance can utilize at home? | Engineering | explainlikeimfive | {
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"It depends on how deep you want to dive into the question. Here, in Sweden, the nominal voltage is 400V/230V. Most houses have a 3-phase feed, and quite a lot of flats have a three phase feed too because stoves, ovens and such tend to be two- or three-phased. An ordinary Schuko wall socket is one-phased (230V) and is fused at max 10A. The Perilex socket used for stoves is three-phased (400V) and is fused at max 3x16A. If you have something else three-phased that you need to connect, like...say...a welder, you'll make use of CEE sockets instead (400V), those are three-phased TN-S (that is, the socket provides three phases, Neutral and Protective Earth) and come in literally any size you need them in from 16A up to 250A. This means, if you want to be blunt about it, that any house has at the very least 400V 3x16A as the main feed. I have two-phased electrical heating as well, so my feed is 400V 3x25A. You might have noticed a pattern here. Fuses. A fuse is a safety device. It's there literally to ensure that the cables are not overloaded to the point where they overheat and catch fire. But it's also a damn simple limiter. You can't (alright, you can. but only during a shorter time span) extract more from the power line than the fuse allows, so it's literally the fuse that is the point of the equation that matters. So. Back to the one-phased 230V Schuko with a 10A fuse. It's pretty likely that more than one socket share the same fuse. In fact, often a whole bedroom has only one fuse for all the lights and all the sockets. But if you assume that you only use one socket, it's pretty simple. The max load on a socket is 230V * 10A = 2300W. If you look at the stove, it has 230V * 3x10A = 3x3680W available. Most stoves are a bunch of 1-phased loads that you can turn on and off so you can simplify the calculations and count as if the loads where on a one-phase feed, but in reality you are supposed to complicate the equation with phase offset and whatnot. So, the CEE's, then? They are 400V. But, 400V is extracted between two phases. So when you calculate the load you are supposed to add * √3 to the equation (that part takes into account the offset between the phases, If I remember correctly) but in reality you often have a load that is so even over the phases that you can just calculate the phases separately anyway. I got one of those in my garage, it's a 25A CEE, which means that I got 230V * 3x25A = 3x5750W available there. EDIT: Actually. I'm kind of stupid. 400/230 = √3. √3 is the nominal current increase if you combine two phases that are 120degrees apart."
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7sosjz | why we can't (easily) convert ocean water to fresh water? | Engineering | explainlikeimfive | {
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"We have multiple methods for purifying water (also known as desalination in this case). However, they are moderately expensive to set up, and require a large amount of energy",
"We can, but it is fairly expensive to setup and maintain, and would also only help areas right along the coast without also investing in infrastructure to transport this water. Desalination plants do exist, but taking the salt out of water through normal means (typically by boiling most of the water which leaves behind a salt-rich brine while the water vapor condenses into pure water) is really rough on the pipes (the salty brine is fairly damaging due to the salt deposits it tends to create). So they require a lot of maintenance."
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7sou9l | How does electricity generation adapt to variation of power consumption? | If I were to turn on my lights at my house, does the power generation plant work a little harder until I turn them back off? If so, how does it know? I know that storing a lot of electric energy can be very difficult. | Engineering | explainlikeimfive | {
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"Electricity has to be generated as soon as it is used, this means that demand has to constantly be matched to supply. There is relatively little storage in the grid. The basic way in which power is regulated is called \"frequency control\". Most large generators are rotating machines. They spin at the speed of the grid's electrical frequency (for a 60 Hz country like the US, this means they spin 60 times per second or 3600 rpm). Their rotation is magnetically locked to the grid. This means all the generators in the grid rotate completely synchronised. Generators become stiffer to turn as you take more power from them. If they are unconnected, they turn freely, but as you start to draw power, you have to work harder to turn them. So, imagine that all the power plants are in a stable condition, the engines for the generators are all at a steady power, and the grid frequency (generator speed) is stable and not moving. Now, a big factory switches on some heavy machines. The extra power being taken from the grid makes the generators a tiny bit stiffer to turn - Just like a car driving along the road and reaching a hill, when they see the load, they will start slowing down. The grid operator will see the grid frequency dropping, and will send instructions out to various power plants telling them \"please increase power by 10 MW\". Some plants may have automatic control, so the grid operator can give an automatic instruction like \"Adjust power by 1 MW for each 0.01 Hz that grid frequency deviates from 60.0 Hz.\" This is called \"primary frequency control\". It works, but you have to have power plants available which can respond quickly. The problem is that not all power plants can respond quickly - sometime it takes hours to get the boilers hot enough to get more steam. This means that the grid operator has to plan in advance. They can usually predict roughly how much electricity is needed at some time of day. For example, power consumption is much lower during the night. They also know at that 6 am, power consumption starts rising as people start going to work, factories start turning on machines, etc. So, they will tell slow responders like coal plants to reduce power over night, and the start increasing power in the morning; so that they are already producing power in advance. They then use frequency control on fast responding plants (like gas) to make fine adjustments. So, if there is too much power and frequency starts rising, they can tell the gas plants to reduce power to bring frequency back under control. The idea is that the grid operator forecasts how much power is needed at a specific time, and gets power plants ready in advance, but some fine adjustment is needed from second to second.",
"The power grid is full of devices that \"store\" a (relatively) small amount of energy and ensure consistent, stable delivery of power to homes and businesses. This gives power stations (and switching stations, key word: grid) time to ramp up their power production in response to unexpected usage spikes, \"refilling\" this stored power. Many steam power plants also have huge flywheels which can help keep up with demand."
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7srml8 | How do satellites in orbit around Earth avoid colliding with each other? | I know our Earth is massive compared to the number of satellites currently in orbit. But as more and more are launched, don't the chances of collision increase? Are satellites equipped with a similar system like how aircrafts use TCAS (Traffic Collision Avoidance System), or do we just not hear about the rare occurrence when they do collide? | Engineering | explainlikeimfive | {
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"space is HUGE. satellites are small. imagine a 100 lane highway and there's 1 car per 1000 miles.",
"> I know our Earth is massive compared to the number of satellites currently in orbit. But as more and more are launched, don't the chances of collision increase? Sure, but on average they are about 440 kilometers apart. New satellites are launched into orbits which are planned out in advance so assuming they do their homework and don't launch directly into another satellite on purpose (you would really need to try) it should be fine. > Are satellites equipped with a similar system like how aircrafts use TCAS (Traffic Collision Avoidance System), or do we just not hear about the rare occurrence when they do collide? They don't have such a system, but satellite locations are tracked and new launches take these paths into account. Collisions are extremely rare due to the vast distances involved.",
"As you said, space is the crucial component here. There's an awful lot of room and satellites are tiny. Additionally, orbits are by nature extremely predictable, satellites in high orbit will follow the same path at the same speed for millions of years. Satellites are indeed tracked and catalogued, and their orbits are calculated in advance in order to predict and avoid collisions - I don't know much more than that. I recommend reading about Kessler Syndrome - basically, if a collision does occur, satellites would tend to break apart into a sort of \"shotgun\" formation, further increasing the odds of additional collisions, which in turn \"shotgun\" and further increase the odds of collisions - it eventually corrects itself as eccentric orbits slow down and deorbit, but this happens on a very long timescale and this could potentially make space inaccessible to Earthlings for thousands or even millions of years. See Gravity (film), Planetes (Anime), Cowboy Bebop (Anime) Edit: I also want to add that several collisions have occurred in the past, at least two seem to be deliberately destroyed with EKV or some other weapon, and IIRC there was a collision involving an Iridium satellite which required the ISS to perform evasive maneuvers, and not for the first time."
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7swrkb | Why are sidewalks divided into squares? Wouldn't it be faster to pour long blocks of concrete instead? | Engineering | explainlikeimfive | {
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"Those 'cracks' between the squares are for structural relief - so the concrete/cement can expand and contract without cracking for real",
"As the ground shifts and moves, the long concrete sidewalk will crack and heave most impressively. The discrete squares allow for a greater range of motion. That said, it *is* possible to dig a deeper, more exactingly prepared base, that would minimize heaving a bit better. However, that increases the cost, and still won't provide perfect results ten years later.",
"When they make concrete sidewalk, they do pour it as one long continuous sidewalk. They add the lines that divide it into squares/rectangles because they know that sidewalks will eventually crack on their own anyway, because of use and because of the weather. They add the cracks at the start so that it looks neater. Otherwise the natural cracks that develop would be random, ugly, and potentially unsafe."
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7sx3rz | why aren’t planes designed to have enough overhead space to accommodate all passengers? | Engineering | explainlikeimfive | {
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"They would, except everyone insists on carrying bags on the plane instead of checking them, because checking them now costs money. Years ago, checking bags was usually free, and there was a lot more room in the overheads. Have you ever flown Southwest? Checked bags are free, and there's plenty of overhead bin room.",
"Airlines have started cramming in more rows of seats than the same planes had in the past (by stealing leg room from each row), and airlines have begun charging for checked bags. These two factors mean that there are both more people on the plane and more carry-on luggage than there would have been in the past.",
"* there are more seats in planes then there used to be * airlines often charge for checked bags now, so people have a greater incentive to only have carry-on * airlines mostly care about business travelers first, and most of them have frequent flyer status that lets them board earlier...only the tourists in the back usually wind up checking bags",
"Well, first off, most planes were designed and built before airlines started charging for checked baggage. Prior to that, overhead bin space was not a problem at all. It is very expensive to retrofit a plane, so very few have had significant work done since this policy change the need for overhead bin space. At a higher level, though, there is no reason for them to do so. Adding overhead bin space is harder than it seems - you'd either have to have the bins be longer (which wouldn't help much and would make them more difficult to use) or reduce the number of passengers the plane could hold (which would reduce revenues). Neither of those provide a benefit _to the airline_ and unless you are choosing your airline based on overhead bin capacity (no one does) then improving this aspect of the experience doesn't increase revenues. Businesses will only make changes based on what makes them more profitable. People don't think about overhead bin space when they book a ticket, so there is no incentive for the airlines to care about it either."
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7t2b2c | A car battery can "fail" suddenly due to one faulty cell. How? | Engineering | explainlikeimfive | {
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"A car battery is made up of 6 cells in series, meaning the circuit passes through each cell one after another. So a problem in one cell effects the entire circuit. (The chemistry of lead acid batteries is such that each cell produces ~2 volts, so it takes 6 cells in series to make a 12 volt battery.) Batteries physically fail in two ways: the conducting structure fails allowing an open circuit, or the plates collapse and short that particular cell, reducing that cell to a conductor that doesn't produce voltage, reducing the battery's output by 1/6. There are also failures that effect the chemistry of the battery, but those aren't the \"sudden\" failures."
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7t65p3 | What makes a river like the Mississippi change course? | I understand that sediment from upriver settles and causes the river to change course, but I just can't wrap my head around how the mechanisms for that actually work. It seems like before the sediment could come even close to clogging up the current channel, the force of the river would clear that sediment away. We can assume that we're not even talking about the man-made levees that keep the river controlled now. I just don't understand how starting a 'new' course would ever be more efficient for the flow of the water than even a slightly clogged but otherwise established course. | Engineering | explainlikeimfive | {
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"A new flow does not have to be more efficient totally. Is only have to be locally easier to flow in a direction. A river can start to [meander]( URL_1 ). The only thing that has to happen is that the water flow faster on one side then the other. Then sediment will be deposited on the slower side and removed on the faster so the path of the river will move. If the meander is large the river can intersect in own path downstream and a [Oxbow lake]( URL_0 ) is formed where the river no longer flow. So a river change course not by a sudden clogging of the old path but by a slow move of its path. There can be a sudden change if the land in not even and the river eroderad away natural dam and flow down to a lower land area",
"Water has to be traveling at a certain speed to carry sediment. If you were to take a jar of water + fine sand, and swirl it around, you'd observe that before the water stops moving entirely, it's slowed down enough that the sand starts to settle at the bottom again. So up the river where it's just coming out of mountains and is still taking a steep course, yeah, the water just flushes most of the sediment on. But when the river reaches a flat area before the ocean, it slows down a lot. This slowing causes it to deposit sediment. Some parts of rivers may lose less than a foot of elevation over a mile of their course. In places like this where it's only a very slight elevation difference that's causing the river to flow in the first place, enough sediment can land that it makes some other slightly-sloped course more sloped. That's when the river's course changes. Some rivers, like the Mississippi, have to be dredged and propped up with levees to force them to keep the same course we're used to, because river has \"wanted\" to take a different course for a long time."
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7t6830 | what kind of math, if any, is behind traffic lights especially in major cities? Is it a difficult process to time them in sync with surrounding lights to make sure there are no huge back ups? | Engineering | explainlikeimfive | {
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"Traffic engineers have models that incorporate any new lights into the existing network of traffic lights. Traffic light timing is done both to synchronize the lights with the surrounding network, but also to ensure that people don't have to wait too long at the lights. So there's lots of math behind it, but it's mostly done with computer programs.",
"This is a pretty complex topic and is handled in differing ways at differing intersections in different municipalities. I remember back in university there was an engineering course that tackled the traffic light problem as one of its major topics for the entire semester. The math gets very complicated very quickly. I'll let someone who's actually studied the issue provide the details, but even in a grid situation, not all stretches of road will be traveled at the same speed for various environmental reasons, and traffic shaping will usually try to push the high volume traffic through certain routes. This is also affected by things like how long the amber light should last and how long the pedestrian crossing sign should be on, whether you're having to deal with a lot of pedestrian and cyclist traffic, whether you have separate timings for peak hours and non peak hours, if you have traffic sensors present, etc.",
"Lots of simulations using Matrix algebra with huge dimension matrices. Basically they use observation (cameras and car counters) and computer simulation to make adjustments in response to changes in the system (new roads, lights, population changes)."
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7tgdi5 | Why are car speedometers inaccurate? | I’m well aware that my Japanese car’s speedometer says i’m going 3 to 5km/h (1.9 - 3.1 mph) faster than what I actually am, depending on my speed. I also know this is a common problem in my home town in Australia, nearly every car my friends and family own all present this problem. But why? Can it not just tell us the actual speed? Apparently different countries of origin use different ways to regulate the speedometer and as such, results in a lot of different speed readings for different car manufacturers. I’d imagine there’d be a more accurate way to read speed, perhaps gps? but even that has it’s flaws, i.e. if you lose gps signal. | Engineering | explainlikeimfive | {
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"They are usually quite accurate. Smaller or underinflated tires will make it read high and larger tires will make it read low. Compare your tire size with the specified tires for your vehicle. That info (and the recommended pressure) is usually found inside the driver's door frame. GPS responds too slowly, and as you say, it doesn't always work.",
"The speedometer measures the rotation of your tires. Your tires' effective circumference varies depending on inflation, as well as tire size, tread depth, and construction. Older (analog) speedometers were subject to parts variation; the difference between a 5% accurate electronic part and a 1% accurate electronic part is quite large when the manufacturer has to buy tens of thousands of them. To avoid being responsible for your speeding, manufacturers usually set the speedometer to be on the low side of any error, that is, if your speedometer is only accurate within 5%, the manufacturer prefers them to average 5% low rather than have half of their speedometers read high.",
"Speedometers count how many rotations your wheel makes. Gps would be hugely inaccurate and require you to travel a while before it figure it out. Think of one of those progress bars guessing how long it takes to download something, thats what a speedometer that uses gps would look like. Is it possible that australian regulations have slightly larger wheels than standard japanese ones? A centimeter or two wheel diameter difference would seriously offset your speed measurement."
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7tp1f4 | Why build tanks to drive on tracks instead of wheels? | I understand using it for all terrain purposes like in the forest or wooded areas, but if you were to use a tank on sand or snow why not use wheels instead of tracks, Humvees and other vehicles can drive on these surfaces using wheels, why not tanks? | Engineering | explainlikeimfive | {
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"Tracks spread out the weight of the vehicle, which helps it not sink in soft ground. Tracks are also a lot more durable than wheels, which is important on a vehicle designed to be shot at. Light vehicles can travel on wheels because they are relatively light and so their ground pressure isn't very high. A modern tank weighs upwards of 140,000 lbs (65,000kg). Even with huge wheels its ground pressure would be far too high to travel on anything but the hardest surfaces.",
"Tanks are generally heavier. Wheels provide a smaller surface area compared to tracks. With wheels, a tank risks sinking into the mud/snow.",
"The track of a tank essentially allows the tank to take its own road with it. The wheels of the tank drive on the track and the track lays motionless on the ground like a road as it's being driven over. This allows the tank to drive over extremely varied terrains."
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7tp320 | If one-way encryption can't be reversed or decrypted, how come the same encryption works the same at all times with the same input? | I've recently been digging into one-way encryption and find it more confusing than recursion when I first heard of it. Doesn't encryption mean that there's an algorithm lying underneath when a password X is always being translated as Y, that there's a specific way of X being translated into Y, which can be cracked? What makes encryption one-way and impossible to decrypt? | Engineering | explainlikeimfive | {
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"I assume you are talking about a Hash. A hash cannot be reversed to the original message because the process (which technically isn't encryption) literally destroys information. Since all possible messages (infinite possible input set) maps to a output set of a given, set size (finite possible output set) then information has to be destroyed (and sort of collision inevitable)."
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7tss1v | How do water towers work? | Engineering | explainlikeimfive | {
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"The tower is built to be higher then any of the fixtures it's supplying. Pumps bring the water into the tank at the top through pipes. Then, gravity does the rest. As long as the bottom of the tank is above all the faucets and other things that need the water, you don't even need a pump; the water just \"falls\" out of the tank through the output, which keeps pressure on the system.",
"Pump water up to the tower, and the weight of it provides pressure to the entire pipe system in the region. This means that even in the event of a power outage, you still have water pressure (for a reasonable time), even without anything to power the pumps.",
"the bottom of the ocean has really high pressure because there's a bunch of water above it. same basic concept. the height of the tower serves to pressurize the rest of the system. the water is added to the tower through a pumping station at its base. water towers also serve as a buffer during times of high demand. the water level can drop a bit without a substantial pressure loss."
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7tssq5 | How do clocks become fast or slow over time? | For example, I’ll set my watch to the exact time that’s on my phone and a month or so later, it’s 2-3 minutes slow. | Engineering | explainlikeimfive | {
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"Your watch is not keeping the exact time. There are 86400 seconds in a day, but if it is mechanically measuring 86399 seconds in a day, then after 2 months, it'll be one minute off. We're talking about a 0.001% error here. For many inexpensive watches, it is 'easy' to not build to this level of specificity. This is especially true since after 6 months, you'll be 3 minutes out of date at this rate, and then you change your watch for Daylight Savings time anyways, and you'll fix the error then.",
"Your watch likely uses Quartz, which resonates at ABOUT 32,768 Hz. Hertz are a measurement of frequency and time. 1 Hertz is [This]( URL_1 ). Your watch basically counts the cycles and knows that after 32,768 it needs to move the second hand. Quartz has a clock drift of about .5 seconds per day. Your phone uses GPS timing, which comes from atomic clocks. Atomic clocks use cesium, which resonates at EXACTLY 9,192,631,770 Hz. [Interesting read if you are looking for more info]( URL_0 ) The clock used for GPS drifts at less than 1 second every 300 million years. > Since 1967, the International System of Units (SI) has defined the second as the duration of 9192631770 cycles of radiation corresponding to the transition between two energy levels of the caesium-133 atom. TLDR: Quartz clocks have a drift of about .5 seconds per day. Your GPS's clock drifts at less than 1 second every 300 million years.",
"Have you been travelling at or near the speed of light?"
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7tvo4h | How do elevator systems determine which elevator to send when there are multiple that are equidistant away? | Engineering | explainlikeimfive | {
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"The scheduler will find all elevators that are idle or moving in the proper direction already. From there, it will score them for which one should go. The score is going to be mostly distance based, but it could also be programmed to favour an elevator in motion. It may also factor in some sort of 'wear and tear' factor so that elevators tend to do the same amount of work. Programmers wouldn't really handle a 'tie' scenario. Instead, the easiest way to do this is to just iterate through the list, holding an elevator and comparing it. If you find one that is lower score, you hold onto that one as you continue through the list. There's no specific handling for a tie, it just works because you're not checking for less than or equals, just less than."
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7u54ck | I’m lying on the couch and staring at the ceiling right now. Why is the ceiling bumpy as if there were tiny rocks embedded in the paint? How do they get the paint to be so bumpy like that? Is there a benefit from having it like this. | Engineering | explainlikeimfive | {
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"For multiple reasons. For one, it's cheaper - you can do it more quickly and with less labor. Also, it hides any imperfections, so you can also spend less time working on ceiling seems. And last, it was said to give some acoustic benefits.",
"In the US this is commonly called a [\"popcorn\" ceiling]( URL_0 ) > A popcorn ceiling (slang), also known as a cottage cheese ceiling, a stucco ceiling or formally an acoustic ceiling, is a term for a spray-on or paint-on ceiling treatment. It was the standard for bedroom and residential hallway ceilings for its bright, white appearance, ability to hide imperfections, and acoustical characteristics.[citation needed] In comparison, kitchen and living room ceilings would normally be finished in smoother skip-trowel or orange peel texture for their higher durability and ease of cleaning. > > In early formulations, it often contained white asbestos fibers. When asbestos was banned in ceiling treatments by the Clean Air Act of 1978 in the United States,[1] popcorn ceilings fell out of favor in much of the country. However, in order to minimize economic hardship to suppliers and installers, existing inventories of asbestos-bearing texturing materials were exempt from the ban, so it is possible to find asbestos in popcorn ceilings that were applied through the 1980s. After the ban, popcorn ceiling materials were created using a paper-based or Styrofoam product to create the texture, rather than asbestos. Textured ceilings remain common in residential construction in the United States.",
"Oh god, textured ceilings. I remember those when I was a kid. They must have been all the rage in the 80s because every house in my development had them. I would always accidentally scrape my knuckles on that shit where the ceiling was lower due to the stairs above it.",
"they spray it on. it is called an acoustic ceiling. or a textured ceiling. i think there is a benefit in terms of sound deadening."
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7ub82w | Why are we still flushing toilets with clean, drinking water? | Why are we treating and cleaning water which will essentially be used to flush down the toilet? If costs to implement weren't a factor, why can't we use grey or even salt water? | Engineering | explainlikeimfive | {
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"We certainly _can_ use grey or salt water and many places do. The reason that many places don't is cost of implementation. You have to install and maintain two sets of pipes - potable and non-potable water - to every bathroom. In areas where fresh water isn't scarce, there is little reason to do this.",
"> Why are we treating and cleaning water which will essentially be used to flush down the toilet? We're not treating and cleaning water *just* to flush down the toilet. We're treating and cleaning water, *so that we have treated and clean water*, some of which is used for toilets, because it's already piped to the house for other reasons (drinking, cooking, washing).",
"> If costs to implement weren't a factor That's the reason. Maintaining two sets of pipes. Plus, people often throw things down sinks they shouldn't. Putting that into a toilet would cause even more trouble.",
"The reasons I can think of are: 1. We want our toilets to be clean after we flush them, so we flush them with clean water. 2. It's probably easier on the pipes that cleaner water is used? 3. It's not worth the time/effort to create a new \"dirty\" water supply system and create two parallel plumbing systems in the house (one for clean and one for \"clean\" water), when we can just use the already present and required clean water supply. Basically, the amount of waste (extra pipes, extra water capture systems) generated by implementing a separate, dirtier plumbing system to flush toilets is larger than the amount of waste involved in treating a slightly larger batch of drinking water at a time.",
"Setting up a separate plumbing system just for toilets would be a lot of extra labor and materials during construction. Most buildings just have supply risers that send water straight up the building and it branches out from there. This would make it that a separate supply riser would have to be installed just for toilets, which isn’t very practical. Not to mention having to bypass the water plant to send a separate supply of water that’s just for toilets, which is also impractical. Regarding salt water, assuming you mean water from the ocean, the corrosive effects of the high concentration of salt would most likely ruin cast iron pipes quickly over time. And again, the cost of getting salt water to places all over the country"
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9ket0c | Why do planes need to dump fuel before emergency landing? | Engineering | explainlikeimfive | {
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"They are too heavy, and they are trying to reduce the risk of fire in the event of a crash.",
"Aircraft have both a Maximum TakeOff Weight and a Maximum Landing Weight. For some planes the difference between the two can be quite big. More weight means more inertia and needing a longer runway to bleed of kinetic energy. There is also the fact that aircraft fuel is quite flammable and if you are having an emergency and might possible crash you want as little as possible of that with you.",
"Fuel is very flammable and combustible, by nature of being fuel. The more fuel you dump, the less there is to burn, explode and otherwise be troublesome when you do crash - something that can very easily cause leaks, sparks or other ways to lose or ignite fuel.",
"If a plane needs to land right after take off it usually will still be loaded with so much fuel that it's too heavy to land on most runways (a heavier plane means more airspeed is necessary for lift, so the plane has to either move too fast horizontally to stop on the runway or it is so slow that due to insufficient lift it's moving vertically too fast and will hit the ground too hard). Besides that it can be a precaution to get rid of most of the flammable fuel when a more serious crash landing is likely.",
"Initially, the answer seems fairly basic. Less fuel equals not only less weight but I guess also less unstable weight. I'm sure baffles are used to slow the rate of fluid movement, but removing the liquid completely would Def help with increased handling of an aircraft. That aside, I think more importantly thst removing a highly combustible fuel would definitely be a good thing in the event of a possible crash landing... But u would wonder does that made the fuel tanks more susceptible to possible explosion, considering they are now filled with highly combustible fuel vapour"
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9kftom | what is the difference between a compressed carbon dioxide tanks and a liquefied carbon dioxide tank? | As a bit of a background story, where I work we can only use liquified CO2 for frozen drinks otherwise we would have to have our pipes flushed and machine cleaned/repaired. So what is the difference and what is compressed CO2 used for? | Engineering | explainlikeimfive | {
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"The saturated liquid pressure for CO2 at room temperature is about 860 psi. As such, major gains in storage efficiency are made when you bottle it at higher pressures than that, because it will exist in mixed phase in the bottle. There is much more CO2 in a volume of liquid than in that same volume of gas. Now, mixed phase liquids / gases like that, with the appropriate equipment, can either be drawn off as gas (where e.g. the system pressure is immediately reduced to produce a gas stream), or with a dip tube or submerged outlet, drawn off as liquid at the bottle pressure, where the CO2 is either consumed as liquid or has its pressure dropped somewhere downstream to be consumed as gas. Depends on the equipment and the process. As you consume a product from such a mixed phase bottle,, the pressure in it stays constant. You just drop the liquid level, and some of the liquid evaporates to maintain the saturation pressure. That's why things like CO2 and propane are filled by weight. The pressure won't begin to drop until all of the liquid is exhausted and only gas remains. CO2 in particular can also be solid near atmospheric pressure, if you cool it sufficiently (i.e. dry ice), and you might notice if you ever discharge a CO2 fire extinguisher that you get a few solid flakes coming out of the nozzle with the gas - this is just CO2 that has cooled too much during discharge and solidified - not a problem though, as that state is short lived and quickly reverts to gas again as it warms. It sounds like your particular process requires CO2 as liquid, either for dosing, or for ensuring a particular temperature change when it is evaporated. Compressed gas CO2 is simply CO2 stored at a lesser pressure than the saturated liquid pressure, ensuring that it is all gas, and enabling you to measure remaining contents with a pressure gauge."
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9khk30 | How come none of the bullets hit the propeller in the WW1 fighter planes even though the machine gun is right behind it? | Engineering | explainlikeimfive | {
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"Because of an invention called the synchronization gear ( URL_1 ). It basically times the shots from the gun with the propeller so that they wouldn't hit. Here's a gif: URL_0",
"Interruptor gear. Basically, a gear on the prop shaft would cut out the gun as the blade passed the muzzle."
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9kincv | Why do motorcycles idle at lower rpm’s compared to cars? | Engineering | explainlikeimfive | {
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"They don't, according to Wikipedia. For a passenger car engine, idle speed is customarily between 600 and 1000rpm. For medium and heavy duty trucks, it is approximately 600 rpm. For many single-cylinder motorcycle engines, idle speed is set between 1200 and 1500 rpm. Two-cylindermotorcycle engines are often set around 1000 rpm.",
"It sounds like it because motorbikes have less cylinders and therefore the sound is more pronounced than let's say, a 6 cylinder car."
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9kxesk | Why are jet engines so much faster and powerful than propeller engines | Engineering | explainlikeimfive | {
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"It's worth noting that jet engines aren't *inherently* faster and more powerful than propeller engines (also, as pointed out elsewhere, most propeller driven planes use turbines these days). Rather, the jet engine as a concept has the *potential* to be much faster and more powerful. Piston-driven propeller engines pretty much maxed out their potential in late WWII. They just had *so* many moving parts, weren't all that efficient, and required sophisticated turbo or super-chargers to climb to a useful altitude. Turbine engines can spin far faster, have far fewer moving parts, and can adapt to changes of altitude far better. Even so, the British flew a jet aircraft years *before* the famous German Messerschmidt 262 was terrorizing Allied bombers towards the end of the war. But even though the Brits flew a jet in 1941, it took several more years before they could refine the design enough to even compete with the piston-driven fighters out in the field. It's weird today to imagine a jet that can't keep up with a piston+propeller plane, but that was where Allied (1941) and Axis (1939) powers were from for most of the war. They *had* jets in development, but they couldn't keep up with the far more refined existing technology, though that technology was reaching its limits, while jets were just starting to show what they could do.",
"A propeller is able to grab the air with the curved blade and push it back on the air behind the plane. It's exactly like how you paddle in water. You aren't \"pulling\" water towards you, you push it away. Both water and air are fluids and work the same way. You just need a lot more speed force to get air to care. A jet engine will pull in a bunch of air in front of it (how the engine pulls isn't 5YOF) and squeeze it really tight inside a box. Think a pump nerf gun. Now light gas on fire (think water into mist, you get more \"volume\" because it's hot) with the high pressure air and you are blowing a massive fart behind you. A propeller is limited to the air it can collect by moving forward. A jet engine increase the amount of air it pulls in, adds lighter fluid to the volume, and farts that. TL;DR it's just blowing really hard like a fart you held in too long. 5YOF = 5 year old friendly",
"Very simplified: So at the core of what we think of as jet engines (turbofans and turbojets) is the fact that we have a turbine which has blades (think its own propellers) that is spun by the exhaust from compressed air, compressed by a compressor, which is ignited. In fact, this [NASA explanation]( URL_0 ) sums it up easiest: > All jet engines, which are also called gas turbines, work on the same principle. The engine sucks air in at the front with a fan. A compressor raises the pressure of the air. The compressor is made with many blades attached to a shaft. The blades spin at high speed and compress or squeeze the air. The compressed air is then sprayed with fuel and an electric spark lights the mixture. The burning gases expand and blast out through the nozzle, at the back of the engine. As the jets of gas shoot backward, the engine and the aircraft are thrust forward. As the hot air is going to the nozzle, it passes through another group of blades called the turbine. The turbine is attached to the same shaft as the compressor. Spinning the turbine causes the compressor to spin. Meanwhile, a propeller based engine has to use the external propeller to \"lift\" the aircraft. If you look at a propeller, you will see that each blade actually like a mini wing in that it creates 'lift' - but in the forward direction, which we call thrust. Propeller-driven plane have some significant limits though: as the aircraft moves faster in speed, the blades - spinning super fast- can see the tips reach supersonic speeds which creates a lot of other issues (drag, material limits, noise, etc.). So propeller driven planes can't reach the speeds or climb rates that jet planes can. There is actually a thing that a lot of modern higher-end prop planes use: the turboprop. It uses a turbine engine setup like a jet but at the front it is connected to propellers which can generate much larger amounts of thrust. Of course, none of this comes free: jet engines can burn a ridiculous amount of fuel, and so they are fit on aircraft that need it for performance reasons. For instance, in the T-6B Texan II, an 1100 horsepower turboprop trainer plane the Navy uses, to cruise at 240 knots, we might be at 80% power and burn 400-600 pounds of gas per hour. However, in the F/A-18E Super Hornet, flying at 240 knots - which is roughly where max endurance is (most fuel efficient in terms of time you can stay aloft), we're talking about roughly 2600-3000 pounds of gas per hour... per engine.",
"The difference is that propeller engines just blow air back and can only push so much air back. With a jet engine it sucks air in, compresses that air inside and then creates a bang with igniters inside the engine creating a much more powerful blow out the back of the engine. Suck, Squeeze, Bang, Blow.",
"Some bits of these are right but some are not. Both types of engine pull air towards them (~half the speed change in air due to the presence of a propellor happens before the air reaches the propellor itself). Because it has walls and lots of blades, the jet engine can sustain high pressures through much more of the engine. With a prop, the pressure differences can only be sustained over part of the blade and slowly fades towards zero at the tip because air spills over to the lower pressure areas. This large pressure helps drive a faster speed of air out the back of the engine which gives more thrust and also gives thrust up to a higher speed (you cant fly faster forward than the air comes out the back of the engine because you need the momentum to balance. There is also a trade off between how much air you put through the engine and how fast you push it out, one with give higher max speeds but the other will give more thrust and efficiency at low speeds which is why you get turboprops with huge propellor blades, much bigger than any jet engine",
"Most of these comments are spot-on. Here is a little longer explanation. One thing that is missing is the pressure change mechanism. Propeller has 2-4 cambered blades. The camber, similar to the wing of an airplane, changes the air pressure between the front and the back of the blade. This pressure change “pulls/pushes” the air as it passes the propeller blades. Same principles as the lift vector of a wing. The pressure differences between the top and bottom of the wing provide a changing lift vector. (Many aspects affect the changes to the vector). On smaller and slower prop aircraft, the blades are “fixed”, so you can only achieve so much thrust from that blade. Adjustable pitch blades move to change the aspect of the blade optimizing the efficiency of the blades at different speeds. Most turbo-prop aircraft utilize a smaller jet engine to spin the prop. The prop will typically be a “fixed speed” prop (roughly 2000 RPM for the prop) and utilizing the adjustable pitch to accelerate or cruise at higher speeds and even act as a spoiler to slow the aircraft. The pressure change of the prop is not contained in any manner. The prop spins in free space. This causes a negative aerodynamic effects to the aircraft called P-factor (longer explanation for another time) The jet engine, whether commercial airliner or fighter aircraft, have a contained compressor. All the stages of fans in the jet engine have blades that are shaped to achieve the pressure change designed for the specific engine. Depending on the design of the engine and the compressor, engineers can achieve more powerful thrust output or more efficient output. Airliners we see today, run a high-bypass engine. This simply means a high volume of air is sucked into the engine and by-passed around the compressor. A smaller amount of air is compressed, fueled, and ignited. This does a couple: the by-passed air is minimally compressed. However it is a contained compression (thing of blowing through a straw verses blowing with no straw). The ignited air is highly compressed and to achieve that it will pass through many sets of blades (typically called stages). The compressed and ignited air also drives the entire fan blade system; both compressor blades and by-pass system. The end result is the by-pass air accounts for about 60% of total thrust, while the compressed and ignited air accounts for the remaining 40%. So the Stage 1 blades (front of the engine) act as a very fast propeller, forcing air through a straw, and ejecting it at a fast rate than the air entering the engine. The by-passed air also provides a sound dampening effect for the combustion nozzle. Think of the business-end of the engine as a donut. Containing the pressure change of the blades cutting the air vastly improves the efficiency and power output of a jet engine compared to a propeller.",
"Propeller engines have a limit to how fast they can spin because at high rotation speeds, the tips of the propeller blades can reach supersonic speeds, and this is extremely loud, and can damage the propeller. Jet engines can spin at much higher speeds since the rotating components are smaller, and force more air through them.",
"One big piece of it is how complex the piston engines are compared to jets. I'm going to go back to 1950s examples because that was the pinnacle of aircraft piston engines and beginning of good jet engines The American B-36 bomber was originally designed in WW2, but on the back burner for a bit and flies in in August 1946, just a giant plane Six Pratt & Whitney R-4360-53 \"Wasp Major\" radial engines to power it originally, each engine required a dedicated 100 gal (380 l) oil tank 28 cylinders, a super charger and a turbo charger, and 56 spark plugs - it weighed 3,870 pounds (1,760 kg) In 1947 we have first flight of a US jet bomber, the B-47. Now it wasn't designed to fly as far as B-36, it was a medium range bomber for it's time. While the B-36 would fly from Texas to the Soviet Union, the B-47 would fly from Morocco, Alaska, Greenland or the UK to the Soviet Union. B-47 is powered by six General Electric J47-GE-25 turbojets It weighed 2,554 pounds (1,158 kg) The Wasp Major engines were known for their complexity and failure rates - \"Normal maintenance consisted of tedious measures, such as changing the 56 spark plugs on each of the six engines; the plugs were often fouled by the lead in the 145 octane anti-knock fuel required by the R-4360 engines. Thus, each service required changing 336 spark plugs.\" and the unofficial motto of the type was \"two turning, two burning, two smoking, two choking, and two more unaccounted for...\" because eventually the B-36 had four J47 jet engines added for extra power...10 total engines Jets were much more reliable - the J47-GE-23 was rated to run 225 hours time between overhauls. As installed on the F-86F, it experienced one in-flight shutdown every 33,000 hours in 1955 and 1956"
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9kzuse | Why is the keyboard qwerty instead of abc? | Engineering | explainlikeimfive | {
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"The reason dates back to the time of manual typewriters. When first invented , they had keys arranged in an alphabetical order, but people typed so fast that the mechanical character arms got tangled up. So the keys were randomly positioned to actually slow down typing and prevent key jams. The QWERTY keyboards were made so one could type using keys from the top row of the keyboard. This random arrangement became standard. Source: URL_0",
"I believe it was to slow people down as typewriters used to jam if used too fast so “common” letters (most used) were spaced apart. I don’t have a source for it but that’s what an old man told me in a charity shop when I thought about buying an imperial typewriter. Hope it helps.",
"to prevent typewriters from jamming. in order to type properly, the arms that strike the letters to the page have to all be able to hit the same spot. letters that are adjacent to each other are more likely to hit each other if pressed in quick succession. by separating letters that are commonly used together, these jams were made less common."
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9l96ea | Why does a clock make a tick-tock sound when it’s repeating the same action? Shouldn’t it just make the same sound every time? | Engineering | explainlikeimfive | {
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"The thing that is 'ticking' and 'tocking' is called the 'Escapement'. Generally, there is some kind of toothed wheel, and a lever with two arms that interfere with those teeth. The timing device - a pendulum or wheel bouncing on a spring - moves that lever back and forth. When the lever goes one way, one arm of the lever releases one of the teeth in the cog, and the other arm catches on a different tooth. Then as the lever goes back the other way, the second arm releases the tooth, and the first catches. These two arms are slightly different, so the sounds will be a little different. In addition, the two arms are often not properly centred, so one of the arms will often release sooner or faster than the other."
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9lipsr | Why does the faster Concorde have boxier less aerodynamic shaped engines than a normal airliner | Engineering | explainlikeimfive | {
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"Most modern aircraft use high bypass turbofan engines. Most of the air is just sucked in by the big fan and pushed out the back, not passed through the engine core. They're big but really fuel efficient at low speeds The Concorde used much more compact turbojet engines where all the air it sucks in is used for combustion. They're much smaller engines and allow for high speeds, this also let them be tucked up as close to the body as possible to minimize drag at supersonic speeds The Concorde played with different drag equations than sub-sonic aircraft. Most planes just want to be nice and smooth to minimize drag, the Concorde needed to be narrow with nothing protruding out too far(like engines on pylons) which would create significant drag at Mach 2. At supersonic speeds, air can no longer move out of the way so drag equations change significantly",
"A few people have tried to answer so far but no one has given a very good explanation. The reason the Concorde engines have the shape they do is to accommodate movable ramps. These ramps are used to deflect supersonic shockwaves when the aircraft is flying faster then the speed of sound and keep them from hitting the compressor and damaging the engine. These ramps also slow the air down to roughly [Mach 0.5]( URL_0 ) (Page 485) in order to allow the engine to be more efficient. However there's more two the story, planes such as the SR-71 have similar systems but have cylindrical engine nacelles, unlike the Concorde. The reason the Concorde has rectangular rather then cylindrical is because cylindrical engines have an issue where in it's far easier for the engine to experience \"Noise, Violent Engine surge and flame-out [Engine turning off]\" (Aerospatiale Concorde Owners Workshop Manual) which isn't something you want a commercial airliner experiencing. I can't tell you why this is the case, and even a look in The Complete Book of the SR-71 Blackbird doesn't have an answer, but I think this snippet from it says all you need to know about cylindrical intakes. \"An unstart is characterized by a loud BANG noise, accompanied by the aircraft rolling, yawing, and pitching. The J58 engine [SR-71's engine] itself continues to run, although the afterburner may blow itself out during an unstart. Unstarts were generally unpredictable. The aircraft yawed violently toward the unstarted inlet because of the tremendous amount of drag induced, creating both a rolling and pitch-up motion of the aircraft.\" Like I said, not a good thing to have.",
"One reason would be the Concorde flies at Mach 2. The engines have a ramp that is adjustable to adjust how the shockwave interacts with the inlet. The F-15 has a similar inlet. A square shape simplifies the ramp. The airflow needs to be slowed down to a subsonic flow before it reaches the engine and the ramp creates an oblique shock wave. The cones on the inlet of the SR-71 function in a similar way. They are adjustable forward and aft to tune how the shockwave interacts with the inlet. Basically all supersonic aircraft will have some sort of feature to create an oblique shock wave."
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9ll5nr | Torque Vs Horsepower | I still struggle to easily define the difference between the two, any help appreciated! EDIT: Thanks for all the answers! | Engineering | explainlikeimfive | {
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"Imagine you're roofing a house and you need to get 100 bundles of shingles up a ladder and on the roof. Torque is how many bundles you can carry at a time, while horsepower is how quickly you can get all the bundles on the roof. If one person can carry one bundle up in a minute and another person can carry two bundles at a time but it takes him two minutes, they have the same horsepower but the second guy has more torque. The first guy has to move twice as fast to accomplish the same thing.",
"Torque is rotational force. You might be familiar with the unit of measurement, *foot-pound* (ft-lb). Imagine you're using a 1 foot long wrench to remove a wheel from your car. If you align the wrench horizontally (parallel to the ground) and set a 50 lb weight on the end of the wrench, you're putting 50 foot-pounds of twisting force on the lug nut. This helps quantify how much force a vehicle can put to the road, or how hard the vehicle can pull. However, having high torque doesn't mean high speed. Construction vehicles have enormous torque to be able to move heavy loads, but don't move quickly. Horsepower takes this a step further by measuring torque *multiplied by engine speed*. This gives a somewhat more useful measure for cars, because it represents an engine's ability to apply its torque over time. Two cars might have the same horsepower, but one achieves it through higher engine speed with lower torque, while the other achieves it through high torque with lower speed. Generally, smaller engines have less torque but can rev higher, while large engines have more torque but cannot reach such high speeds.",
"Okay, lots of wrong answers in this thread. tl;dr at bottom. Torque is how much twisting (technical term: angular) force something exerts. In the case of a car engine, it's basically how hard the engine is trying to speed the car up (or, specifically, how hard the engine is trying to twist the axles, which is what makes the car move). In the case of brakes, it's how hard the brakes are trying to slow the car down. If you know Newton's Second Law, \\*force = mass × acceleration\\*, then the rotational equivalent of force is torque. The reason that we talk about torque rather than force is because when you want to spin something, where you apply force to it relative to the axis makes a big difference. For instance, with a lever, the farther away from the fulcrum you apply force, the easier it is to make it move, but the slower it goes. Torque accounts for this by saying that something that makes something spin the same amount is the same torque. So the closer you are to the axis (the center you're rotating around, like the fulcrum of a lever), the more force you need to produce the same amount of torque. It's similar to how we measure the speed that a wheel is spinning in rpm (or another similar unit) rather than in how fast any individual part of the wheel is moving. Forces only exist when they cause or prevent change of speed, and the same is true of torque. More force is required to accelerate something from a standstill, because you have to give it all the inertia of motion. But once it's moving, you only need to apply enough force to counter drag and friction to keep it moving at the same speed. So a car that's cruising at speed is not actually applying all that much torque; the engine would put in the most torque if you press the pedal down all the way from a standstill, or if you slam the brakes. Horsepower is a measure of power, which is difficult to explain fully without first explaining work. Work is \\*force × distance\\*, and measures how much energy is transferred from the source of the force into whatever is moving. The faster something accelerates, the higher the force, so over the same distance, it will do more work. This works out, because the resulting speed is higher, so the moving object has higher energy. Work is really unintuitive at first, because of how muscles work. Muscles consume chemical energy to exert any force, even just to hold something up. So you shouldn't think of work as how hard you have to strain for something. A better example is a building: a building stays up because, even though gravity tries to pull it down, the forces that hold it together counteract gravity. They don't need to keep spending energy to do so. And since nothing is moving, the total work done by gravity on the building is 0. Power is a measure of how quickly energy is transferred. The SI unit of power is the watt, which is the same thing we measure electricity with, and that helps understand it. For instance, if you use an electric heater, then the wattage determines how much electrical energy can be transferred into heat per second. More wattage means you use up more energy in a given amount of time, but get more heat out. Horsepower is a different unit of power, but measures the same thing (the exact definition varies, but is usually around 745 W unless you're measuring steam engines in which case it's about 9800 W for some reason I can't explain). When applied to motion, we already have \\*work = force × distance\\*, and then we have \\*power = work / time\\*. But \\*distance / time = speed\\* (ignoring the technical distinction between speed and velocity), so \\*power = force × speed\\*. In the case of a car, the power is the speed at which the car is moving, times its speed. In order to exert the same force on two objects, you have to transfer \\*more\\* energy on the one that is moving faster. Remember that the transfer of energy and the force are not the same thing. If we want to talk about torque instead, the same thing comes out once we account for rotational speed (which, again, we measure in units like rpm), we get \\*power = torque × rotational speed\\*. This might seem a bit weird, but the reason is fundamentally because of the fact that kinetic energy (that is, the energy of something moving) is not linear. If you have two objects of the same mass, with the first traveling twice as fast as the first, then the first object actually has four times the kinetic energy than the second. The reason that this has to be true can ultimately be traced down to relativity and to the fact that the laws of physics don't change over time (as far as we know, anyway). But it's also why something traveling twice as fast hitting you can hurt more than twice as much. This means that the power output of the engine limits the top rotational speed of the drift shaft coming out of the engine, because at some point it is already spinning so fast that the engine can't output enough torque to do anything more than overcome resistance. From there, the drive train and wheels (most importantly the gear ratio, but wheel radius plays an important role as well) affect the conversion of torque into forward force. There is a tradeoff between force and speed. In a low gear, you get high torque but a low top speed, which is perfect for accelerating at lower speeds. In high gear, you get lower torque, so the engine has a hard time accelerating the car, but in exchange it can keep it up at much higher speeds. tl;dr Torque is how much force is applied to accelerate or decelerate something spinning. We rate car engines with torque, not force, because car engines work by spinning an axle (or multiple axles). Horsepower is how quickly the engine can transfer energy into moving the car. While it depends on other factors, and the drive train is super important, the horsepower is the ultimate limiter on the top speed of the car. Torque affects how fast the engine can accelerate the car, more torque is faster. For two engines of the same power but different torque, the one with lower torque will have a higher top speed but lower acceleration. The gearbox lets us convert between torque and top speed, though, so then a lot of the distinction comes into the kind of gears needed. EDIT: Talked about drive trains and the role of gears and cleared up the summary, thanks to u/constantino1's reply.",
"Torque is your how hard you're spinning something. A quarter takes less torque than a table to spin around, and a table takes less torque than a large rock to spin around.. Horsepower is how fast you're spinning that thing. Rotating a quarter 10 times per second means more horsepower than rotating a quarter 1 time per second. But having a large rock spin 10 times per second is more horsepower than that same quarter spinning 10 times per second because the rock requires a larger torque to spin. Contextually in vehicles, a lot of engines produces approximately the same amount of torque. But certain engines due to design can get up to higher RPMS, and therefor have much larger peak horsepower values. Take for example a V twin chopper vs. a 4 cylinder sport bike. The V twin probably will often produce more torque within it's range, which maxes out around 5-6k RPM. A 4 cylinder sport bike may produce less torque and thus accelerate slower, but because the engine can get up to 10k RPM, it has higher horsepower on paper.",
"Just think about a game of Streetfighter. Zangief = high torque, low horsepower Chun-Li = low torque, high horsepower. Both can get the job done, lower torque needs applied more often to get there. Edit: more words.",
"Do not listen to alle the people claiming torque is important in engines pulling a huge load. The only thing that matters is the horsepower curve, and thanks to the modern invention of the \"gearbox\", you can choose the torque at the wheels with the gearing.",
"I guess because you've used the word \"horsepower\", you're only getting answers about cars. Horsepower is a unit of power output that can be used to describe any source of work over time - it is not limited to cars. That is to say that power describes a force applied to move an object over a given distance and time. Power can be measured in horsepower or a number of other units. Torque is a twisting force, or a force applied at a distance from a rotation point. They differ in that power is related to time, whereas torque is not.",
"Horsepower is power, ideally measured in Watts. I assume you are talking about a car or something similar, so in this case we are talking about mechanical power, but it is the same as electrical power. It is a measure of the rate at which energy is exchanged. Torque is measured in Nm, and it is the force that is acting on a rotating object, in this case the axle of the car. By definition the horsepower is the product of the Torque and the rotating speed(rpm) of the object. It is important to note that you can achieve the same horsepower with different torques as long as you have different rpm. That is what the gearbox of a car does. The engine provides a constant amount of power(horsepower) by rotating the shaft at a certain speed (rpm1) with a certain force (torque1). When you need to go uphill, you need addtional force, so the gearbox use gears of different radii to lower the rotating speed of the wheels (rpm2) and so obtain an higher force (torque2)."
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9lravi | why do industrial engines (e.g. buses, semi, tractors, generators) use diesel instead of gasoline? | Engineering | explainlikeimfive | {
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"Diesels generate more torque per unit of displacement than gasoline engines, and when you're moving something big torque is what you want. Diesels are also simpler, more robust, and general less maintenance intensive. All of which makes them less expensive to operate.",
"Most heavy duty Diesel engines have a life expectancy of about 1 million miles with less maintenance.",
"Diesel is a very heavy fuel, it's a large hydrocarbon; you can think of it as a very light oil. When it gets cold enough, it turns to jelly - so diesel fuel systems are insulated and have heaters for winter use. & #x200B; This large hydrocarbon burns really hot - and really slow. The whole point of heat engines like sterling engines, steam engines, and internal combustion engines - which include jet engines, are hot expansive gasses provide pressure to perform work. & #x200B; So since diesel is a lot of chemical energy stored, it produces a lot of cylinder pressure for a long time. To take advantage of the slow burn, diesel engines have a long piston stroke. This means these engines produce torque, force rotating about an axis, for a long time compared to a gasoline engine which both burns faster and has a shorter stroke. & #x200B; How slow does diesel burn? The fastest diesel engines rotate at 5,000 RPM. Any faster, and you'll be dumping still-burning diesel down the exhaust manifold. That's destructive, wasted energy. By comparison, F1 engines burn gasoline, and the fastest ever built was a prototype for Ferrari by Cosworth with top engine speed of 25,000 RPM. It never made it to competition due to league regulations. & #x200B; Due to the massive forces a diesel undergoes, and heat, they're built heavy duty and with looser tolerances - to make room for hot, expanding metal components. These things have very favorable durability characteristics. I won't bother getting into the technical nuances, but diesel engines found in trucks, trains, earth moving equipment, generators, ships, etc, have continuous operating lifetimes of years. Gasoline engines aren't built to these tolerances because the vehicles aren't expected to perform such heavy work (they're not as efficient at it) or last that long. In industry, if a truck starts rusting apart, they just replace the body on the frame, and the rest keeps going.",
"There are many good reasons listed in the other posts here. One more reason is that...gasoline will only ignite in a very narrow fuel-to-air ratio, regardless of the load (heavy acceleration vs idling). Diesels can operate at VERY lean ratios, and air is free. This means when they are idling or under a steady cruise state, they only need just enough fuel to handle the load they are under. Of course if you add too much air, the hot air that is uncombusted can produce nitrides of oxygen (NOx) in the exhaust, which is considered a pollutant. If you purposely or accidentally run a gasoline engine too lean, it will stop running. Since internal combustion engines are capable of injecting more fuel than they can possibly burn, the maximum power an engine can produce is directly related to how much air can be moved through it. Hot rodders call it an air-pump that needs a little fuel. Most gasoline engines do not use a turbocharger, but a turbo is such a good fit for diesels, that almost all commercial diesels use a turbo. Since a turbo is a variable displacement impeller, it moves almost no extra air at cruise RPM's, and it is only after higher RPMs are chosen that it will pressurize and pump a significant amount of extra air. This also means that diesels have a very wide operating range in which it provides usable torque. High-power from a fittable size of motor when it is needed, and then very good fuel mileage when a low load is applied.",
"Price. Diesel is roughly the same price as gasoline on a per BTU basis. Right now in NY it's $2.83 for gas and $3.29 for diesel. Per BTU that works out to $2.89 per gasoline equivalent gallon of diesel. Second, diesels have a higher thermodynamic efficiency, this is mostly because they don't have a theoretically compression limit, and higher compression allows higher temperatures which allows you to extract more energy from the fuel. The result is that diesels, after accounting for the more expensive fuel, are generally 30-40% less to fuel, for an equivalent engine (for smaller consumer cars, the gasoline engines tend to be more advanced, but if they put that effort into diesels, they'd do much better). And finally, diesels typically operate at lower RPMs, the high compression ratios demand heavy engines that run slow, and this in general means that maintenance is less frequent. The result is that if you're spending $1k/day on fuel, it pays to spend a little extra for the more efficient engine. Torque is a nice extra, but really it doesn't matter as much as people think, you'd just need different gear ratios to get similar performance with a gas engine.",
"Automotive Engineering student here. Industrial vehicles aim for 2 things, economical to operate over long distance and time, and performance in terms of load carrying ability. & #x200B; To start with, we have to know that Engine Power = RPM x Torque, more RPM = less Torque, and torque is what we want here to pull our heavy goods. Typical petrol engines perform most efficiently at around 3000 RPM, combined with a suitable gearbox it provides a comfortable and reactive drive at both low and high speeds for a people carrier. However, diesel takes more time to burn off than petrol, and generally performs better at lower RPMs, meaning that for the same amount of energy released you get more torque at the wheels to move the goods. Once the vehicle starts moving, the amount of force required to accelerate and cruise would be much lower, that's where the complex gear boxes come in. Goods vehicles have really high gear ratios at low gears to provide maximum torque at low speed to start moving, and toned down to a more practical ratio at higher speed for cruising, and that's why they have up to 18 speeds and why truckers absolutely hate people forcing them to slow down! & #x200B; The next point is that diesel engines run lean and they recycle exhaust fumes, that means diesel engines operate closer to complete combustion to petrol engines. As much as we'd like to, there's always some fuel or hydrocarbon molecules remaining and wasted in the exhaust. Diesel also provides more chemical energy than petrol per unit volume, which, in human language, means that your tank will last longer coz it goes down slower, again very useful perk for long distance goods vehicles. & #x200B; At the moment, the automotive industry is actually trying to downsize the engines in road vehicles especially people carriers and maximise performance of diesel engines with turbocharger technologies. Diesel used to be looked down upon as they usually generate less horses in smaller engines and they make a grunting noise instead of the steady high pitched \"vroom\" noise, but times are changing and emission standards are getting pretty extreme when Euro 6 rolls out. JCB is trying to produce the first ever hybrid powered heavy duty construction vehicle these couple years. Electric systems are getting better by the year and hopefully they get powerful enough to enter the heavy duty market. Unless people carriers, goods vehicles and heavy duty vehicles tend to have centralised depots which charging points can be set up, so it would be much more efficient than the Tesla on the road having to find a petrol station that has a specialised plug.",
"For the people debating hours vs miles... My dash display on my semi shows miles driven AND hours idled. So there.",
"In addition to the higher torque produced for engine size, diesels are more reliable and suited to heavy punishment. A petrol engine requires air, fuel and spark. A diesel requires only air and fuel as ignition is from the high compression ratio. So less electronic parts to foul, fail or vibrate loose. A diesel can also run underwater as long as it is fitted with intake and exhaust snorkels (if the engine ingests water it will seize and catastrophically fail)"
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9lt3na | How do car exterior thermometers ignore wind-chill, humidity etc? | Engineering | explainlikeimfive | {
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"We can ignore the fact that the thermometer is on a car and just consider thermometers in general. Wind chill is the effect of wind feeling cooler than the temperature truly is. This is due the wind wicking the heat off of our bodies quicker that it would in still air, so we perceive the temp to be colder than it really is. This doesn’t affect a thermometer because the thermometer is the temperature of the surrounding air, so wind or no wind there is no temperature differential to be exacerbated by the moving air. In other words it just measures the true temperature of the air with no concern for how fast it’s moving or how effective it is at cooling hot objects down. Humidity is same deal. Our bodies feel humidity because it affects our ability to dispel heat, thermometers don’t have any internal heat they are trying to get rid of and therefore aren’t affected by humidity.",
"They are dry. Only a wet bulb thermometer can measure wind-chill or be effected by humidity. They are actually inside the air intake ducting, and they are there because the engine computer needs the temperature to know how dense the air is. Showing you is a no-cost bonus."
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9lw172 | How do modern computer clocks oscillate so fast? | I see clock speeds of 2 or 3 GHz - how does the computer actually generate these clock speeds internally? | Engineering | explainlikeimfive | {
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"Clock references in modern computers are generated from quartz crystals. Quartz has a special crystal structure which allows it to be piezoelectric, meaning small physical stress on the crystal will be converted to electricity (charge) and visa versa. We exploit this by designing quartz crystals to have a resonance at a precise frequency, then apply a small amount of electricity to stress the crystal, which will then output an oscillating electrical clock frequency at its resonance. Quartz is extremely accurate over time and temperature and very cheap, making it an ideal reference. Many other technologies have been researched over the years to generate clocks, but quartz remains a \"miracle\" material for this application because of its incredible accuracy and low cost. Quartz is a fixed clock however, so a phased locked loop (PLL) circuit takes the extremely ideal reference from the quartz to generate an arbitrary clock frequency, the 2-3 GHz one you described. This also is the circuit that adjusts when you \"overclock\" your PC. Assuming a very well designed PLL (not necessarily trivial), you are only limited by your reference accuracy, making the accurate quartz clock the key to high frequencies.",
"Oscillating fast is not hard to do. You can connect 3 inverters in a circle and create a [Ring oscillator]( URL_0 ). You need 6 transistor to that. A inverted convert a 1 to a 0 and a 0 to a 1. If you connect 3 in a row you can start with the output as 101. The third is connected to the input of the firs and they change to 010 and the back to 101. You have not created a oscillator. They work because it take some time for each inviter to switch when the output of the previous change so you get a signal that change value around the loop. So the high speed is not a problem. The problem is that the time delay is depend on the temperature, voltage, and random variation in the manufacturing process. So the problem is to have a oscillator with the correct frequency that is stable. A common way to do that is a [phase lock loop (PLL)]( URL_1 ). You have a voltage controlled oscillator that you can build with a two operational amplifier. They done have a fixed frequency as the ring oscillator but you can control them with the input voltage. The PLL design uses a external reference that can be a crystal oscillator. You have a Phase detector that ouput a signal when the reference and generated clod is different. That in combination with a low pass filter can be the input to the voltage controlled oscillator with the result that the generate frequency is the same as the reference. To make a higher frequency clock you put a counter on the loop back. If the counter need tow clock tick before the output change the result is voltage will be set so the voltage controlled oscillator generate a signal of twice the frequency of the reference. The clock signal of a computer is generated like that with a crystal oscillator as a external reference and multiply the frequency with a phase lock loop and a counter."
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9m023j | What does 'rod knock' mean? | Engineering | explainlikeimfive | {
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"It's the sound an engine makes when the rod bearings have failed and it's about to die. When the bearings fail the connecting rod its onto the crankshaft much more loosely and rattles around. Once that happens it's only a matter of time before the engine completely fails so it needs to be taken apart and rebuilt.",
"Look at all these mechanics trying to strut their stuff, with their big fancy words... Pfft. Breaking it down barney style for ya, On one hand make a circle with your pointer finger and thumb... You're doing great! On the other hand point... You're so good! Okay, gonna get complicated, put the point finger inside the circle... you're liking where this is going, you dirty bird! The circle is the bottom of the piston the pointer is the crankshaft, the circle can ONLY MOVE, if the pointer moves it, so now for learning sake draw a 1 foot X 1foot square in the air with the pointer. That split second when you feel the pointer leave the circle then touch the otherside is the knock you are hearing.... TL:DR the part of the piston that connects to the crank shaft wears out and you hear the crank shaft knocking about as it rotates Edit for bad cell phone usage and spelling errors",
"In addition to being related to a bad bearing, as others have said, it can be caused by a bent connecting rod. The tolerance between the rods and their counterweights on the crankshaft are typically very small, so a small bend can cause them to rub up against each other, making a really loud clunking or scraping sound each time they pass each other Why would a rod bend? That can be caused by having water in the cylinder during a compression stroke (liquids dont compress, so somethings gotta give). Rods can also bend from pushing too much power through rods not designed for it What if a rod bends a bit further than just barely interfering with the counterweight? Rod will snap and suddenly you have chunks of metal going everywhere, which will typically blow the motor, either by mulching everything to death, blowing out the side of the block, or in a spectacular explosion",
"In a reciprocating internal combustion engine with plain bearings there is a oil film maintained in the clearance between the bearing shell in the lower end of the connecting rod and the crank journal. If there is a loss of oil pressure this film is not maintained and the bearing is damaged or destroyed. The excessive clearance resulting form this damage allows the big end of the rod to \"knock about\" loosely on the rotating crankshaft.",
"One or more cylinders on the main rod connecting all the postons was starved of oil and has rubbed so much it over heated and deformed, this means the engine as a whole is destroyed. This can be caused by low oil, unchanged sludge oil, over heating from lack of coolant, blocked oil passage or a bunch of other reasons. The only option is to rebuild the motor, put in a crate (brand new) motor or the most common option as it's the cheapest and easiest put in a junk yard used motor. Or scrap the car and get something else. If this is a hyundai gdi motor look into the recall current in place.",
"Down on the engine crank, the piston rods connect to the pistons overhead that sit in their well (aka the cylinders). Take for example a four-cylinder engine: four rods are attached to the spinning crankshaft below at 45 degree angles. The crankshaft kinda looks like a bent pipe, but is engineered to spin with perfect balance.The other end of the rods each attach to one of the pistons. If a car is run with oil below the recommended level, or even dirty oil for long enough, the rods can become damaged by losing a bearing or by heating to the point of warping through wear or heat damage. At high rpm on low oil, an engine can have a variety of issues. When a rod is no longer seated on its crank correctly, it does not spin snugly and freely as the crank rotates, it instead slams back and forth on the crank as the crank spins, from one extreme to another. This causes an imbalance in the engine, and causes further wear to surrounding parts. This can damage the cylinder wall around the piston as the piston now flops or with time can damage the crank bearings or cause the rod to fly out of the top of the engine. If caught early, wear on the crankshaft itself can be minimized by replacing the rod or milling the rod to perfect roundness and installing slightly larger bearings. If the wear is too great the entire rod must be replaced, and maybe even the crank. An engine is like any other system, defects or deficiencies in one system will affect other systems over time."
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9m7maa | How do those camera stabilisers work? Like the hand-held one YouTubers use? | Engineering | explainlikeimfive | {
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"Usually gyroscopic mount with a counterweight. Weight holds camera from doing hard movements. And then it is usually zoomed in a bit and edited to be smoother in post. Both Sony Vegas and After Effects have stock or 3rd party plugins for further stabalization."
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9meupv | How do night vision goggles work and do they work like in movies? | Engineering | explainlikeimfive | {
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"Night vision goggles have a few tricks up their sleeves. First of all, they use infrared light - infrared light are like colors of light that your eyes can't see - but they're around us all the time. This helps to see in the dark because there can be more infrared light around than visible, especially at night. Then they use extremely sensitive to light cameras - these cameras can take very little incoming light and make it very bright to the person wearing the goggles. And finally, if there isn't enough light available, you can actually turn on an infrared flashlight on your goggles. This infrared flashlight is invisible to the naked eye, but to your goggles, they're lighting up the room like a big bright flashlight. Now, if you have nightvision goggles and are spying on somebody, and they also have nightvision goggles, you don't want to turn on that flashlight, because then they'll see you."
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9mg9l2 | - How does electricity travel through wire? | In college we were told that its the electrons that travel through the outer part of a wire ... but with current research, how does it really travel through the wire? edit: change electronics to electrons. | Engineering | explainlikeimfive | {
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"Electricity is a stream of electrons. To ELI5, electrons bond weakly with metal, and can move along the metal from atom to atom much more freely than they can in many other substances. If you add a bunch of electrons on one side of the metal, it will push electrons along the metal until they get to the other end, kind of like how pouring water into one end of a hose makes water come out the other end of the hose. It's pretty much like those games you see in midwestern gas stations where you try to knock a bunch of quarters off a ledge by dropping other quarters in front of them and pushing.",
"In conductors, the outer electrons are loosely bound and largely free to jump to neighboring atoms. Normally, the direction of this jumping is random and nets to no overall change, but when an electric potential is applied, electrons jump in one direction more than another, resulting in current. In DC applications, current flows through the entire wire. With AC, you have what is called the skin effect, where the changing current and its magnetic fields cause eddies that create greater resistance in the core of the wire. For 60 Hz, the skin depth of copper wire is about 8.5 mm, and decreases with frequency and conductivity."
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9mgkjp | Why do most car's speed meters go up to 200+ km/hr when the speed limit is only ever between 90-120km/hr at most? | Engineering | explainlikeimfive | {
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"Some vehicles are built for racetracks and similar locations that allow the drivers to reach such speeds. It's a hobby many rich people with expendable income participate in. Other vehicles are built to look like they can do that even though they can't, because if the customer thinks his car can go faster than it can the dealer can charge more for it, and it can be used as a status symbol."
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9mhmv2 | How do hot air balloons navigate? | Engineering | explainlikeimfive | {
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"I’m gonna be lazy and paste in an answer I typed up about a year ago. (Please don’t mock me further for typing all of that and failing to spell balloon correctly, despite numerous attempts.) URL_0",
"The only way to control the direction of flight is to change elevations, works only if one has information about the wind directions at various elevations. In most cases, there won't be much difference unless you are in a mountainous region."
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9mho35 | What makes the SpaceX rockets form the huge plume in the sky when they launch and why don’t other rockets make something similar? | Following last nights launch there’s tons of pictures and videos of Falcon 9 launching over California and I was wondering about the light show of sorts it makes. Is it from the rockets fuel system or how this rocket separates stages? Or could I just be that Elon wanted to make a big show to reignite People’s passion for space travel? | Engineering | explainlikeimfive | {
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"It's just down to the timing of the launch. Launches during the day you won't see it because the sky is already bright, and launches very late at night you won't, because the whole sky, horizon to horizon, is dark. It has to be that time of day where once the rocket gets up to a decent height, it's back in sunlight again, so the plume is lit up like, quite literally, a cloud in daylight. The reason it gets so wide and spread out is because as the rocket gets higher up, the atmosphere it's in gets thinner and thinner and lower pressure, so the high pressure exhaust from the rocket spreads out that much wider and farther."
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9mhxy1 | How do refrigerators work? I understand making hot air- but how do you make cold air? | Engineering | explainlikeimfive | {
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"Gas cools down when you release pressure on it and let it expand. So you compress a gas, get rid of the heat that compressing it caused, then let it expand again. The tubes it expands in get cold. Then you take it and compress it again, and around and around it goes.",
"A refrigerator actually does make hot air, just that heated air is in the radiator in the back of the appliance. Tubes of gas are designed so the gas to expands when inside the fridge, causing its temperature to drop and absorbing heat from the inside. That gas is then piped out to the back of the fridge where it is compressed, heating it. The atmospheric air absorbs the heat, cooling the compressed gas which is then cycled back to the expansion stage again.",
"Stuff called refrigerant (commonly know by the brand name Freon) has special properties that allow it to become really hot when vaporized, and really cold when compressed/condensed, air conditioners and refrigerators all use this to make cold air. The refrigerant first comes into a compressor as a low pressure gas then through a radiator called a condenser to cool and condense it into a liquid, which makes the condenser hot (hence why ac's and refrigerators have hot air blow out of them too) the high pressure liquid refrigerant then goes through an expansion or capillary valve to relieve excess pressure then the liquid goes into another radiator called an evaporator which, well evapoates the refrigerant which makes it cold, a fan pushes air through this to produce the cold air output. The refrigerant after this point is a low pressure gas that is sucked back into the compressor to start the cycle all over again. P.S. Refrigerant is nothing to be played around with, 1 single molecule of a refrigerant type with an open chlorine atom can break down 100,000 O-zone atoms. A common air conditioning system can hold 6lbs of liquid refrigerant, it is hell for the O-zone, dispose of AC's properly please."
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9mixn5 | What is six sigma? | Engineering | explainlikeimfive | {
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"Sigma is the notation for a standard deviation from a normal distribution. The original Six Sigma was a set of techniques and tools used to improve processes used to make things, and was enacted by Motorolla to ensure that 6 standard deviations worth of product off of its' assembly lines (or 99.99966%, or 3.4 per million) were free of defects. Nowadays it has been adopted as typical corporate buzzwords, much like AGILE coding doctrine has been, to mean some parts (but probably not all) of what the original meant, and so it is very likely going to be tricky to really define what they mean at your workplace, other than that they want to make things more efficient.",
"Officially it's a methodology to improve a process by reducing the defects. First you define then problem. Once it's defined then you measure it. After you've narrowed the focus of the project by measuring it you analyze to understand why the defect is happening. Once you've found a root cause or potential root cause you improve the process and then you put controls in place. The acronym for all of that is DMAIC. It's definitely a buzzword for many companies but some do a good job of using the method and tools."
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9mjuy9 | Why are flying wing aircraft so uncommon? | Engineering | explainlikeimfive | {
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"Flying wing aircraft are intrinsically unstable and have limited cargo space due to their shape (larger internal volume requires a thicker wing and resulting drag). There also isn't any space for windows so even if commercial passengers could be stowed somehow they wouldn't be able to see out, or efficiently escape in an emergency. Basically the only benefit is that they have a low cross-section and this makes them naturally difficult to see or detect via radar. But that isn't something a commercial aircraft cares about.",
"Woohoo one that I know about. They are good for military applications and you see aspects of the \"flying wing\" in a lot of military aircraft, even the horizontal profiles of the 5th gen fighters like the F-22 and F-35 you can see the aspects of it in their design. But on fighters you need more maneuverability and vertical control surfaces as well as horizontal control surfaces add to the quick response to control inputs. As to your point about almost no civilian interest, I believe Boeing pursued a concept for a short time that they called a blended wing body (BWB) but development of an entirely new airframe is expensive and there is a good deal of risk involved in doing something that has never been done before. Some other reasons it is probably not practical in a civilian airline design are: 1. The 90 second evacuation requirement 2. People like window seats 3. Maintenance costs go up due to more restrictive access to things like engines and major components. 4. Circles are much easier to pressurize than ovals,even if you put a tube inside, you have lost space that adds weight and surface area (drag)."
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9mmjom | How does castor angle in automobiles help return the steering wheel to normal position after a turn? | Engineering | explainlikeimfive | {
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"Edit: Look at [this]( URL_0 ) picture. This is a front right side wheel hub with the wheel removed. You notice how all the gubbins that holds it to the car, everything above the brake disc, is leaning *ever* so slightly backwards? That's relevant below, read on. The front wheels in a car don't steer around a completely straight up vertical axis point, the point around which they steer is angled slightly backwards. If you imagine this point drawn through the wheel, it will meet the road slightly in front of the point where the tire touches the road. What this means is the point where the tire touches the ground is behind the point of rotation, much like the wheel on a shopping trolley touches the ground behind the point it can rotate. That results in the wheel being dragged straight, if you're travelling forward. Not that I'm recommending you try this, but if you go backwards and don't hold the wheel, the wheel will try and turn, because it's now trying to castor around the other way, the way a shopping trolley wheel spins round to face the other way if you pull it instead of pushing it. Only in a car, it can't go all the way around obviously.",
"Ok I tried for a good 10 minutes to type this out in a way that makes sense in basic terms. And I failed. Waiting to see how others can phrase it though."
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9mnptx | How does HEAT rounds work? | I have read numerous explanations on it and i still don't understand. I'm talking about high explosive anti-tank rounds in case you are wondering. | Engineering | explainlikeimfive | {
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"So, you want to penetrate / do damage to something that could be miles away, how do you do that? In general, there are common several tank rounds- AP - Armor Piercing - The most basic type of shell. It's a hunk of material material that uses its kinetic energy to attempt to penetrate armor. It's was cheap, was 'effective', and got the job done when tank designs were basic and were more similar to heavily-armored cars than they were tanks. Early tanks had armor thicknesses as thin as 7mm, compared to later tank designs such as the Tiger 1 that had 100mm. HE - High Explosive - Not normally used against tanks, but the shell was used against infantry, reinforcements, or buildings. It's a standard shell that explodes once it contacts a surface, it generally doesn't penetrate, and hitting another tank with it would certain daze the crew, but likely not knock them out. [APCBC]( URL_2 ) (and other similar shells) - Armor Piercing Capped, Ballistic Capped Shell - These rounds came about because the angle at which a shell comes in determines if it will deflect (or bounce) off the armor, or impact it. With standard AP, it was found that by creating armor that was sloped (called sloped armor), you could cause an incoming shell to \"bounce off\" and deflect, rather than penetrate the tank. This slopped design is seen to great extent with the famous Russian T-34 tank. This caused the rounds to ricochet instead of penetrating. To remedy this, they designed a shell which would be able to \"[grip]( URL_6 )\" the tank upon impact. Think of it like giving an armor piercing more of a grip to impact at a better angle, and lower the chances of ricocheting. [APCBC-HE]( URL_14 ) - Armor Piercing Capped, Ballistic Capped, High Explosive- This round features the outside design of the APCBC shell, but was considered to be extra lethal, due to the High Explosive part of it. So you design an armor piercing shell that can penetrate a tank, but what happens after it does? Well, you have hot toxic fumes enter the tank, scraps and chunks of metal flying inside, but it would not necessarily knock the crew out. So how do we make it more lethal? Let's make it **explode** after it penetrates, of course. After penetrating, this shell would detonate after traveling a certain short distance. This would create a dangerous pressure-explosion inside the crew cabin, and would likely kill most of the crew if the explosion itself doesn't outright. One shot kills were common, as was setting off the ammunition inside the tank, which would cause the tank to explode. [HESH]( URL_11 )- High Explosive Squash-Head - A very interesting type of explosive, in general, it works by \"squashing\" a high explosive compound on the surface, and then detonating it. The goal is not to necessairly penetrate, but to rather cause an effect called [spalling]( URL_0 ). It would cause the other side of the armor to blast outsides towards the crew, and create many small tiny pieces of steel throughout the crew space, penetrating the crew itself. It functions similar to HEAT, in that the velocity of the round doesn't affect it's killing potential, but rather the angle and if it makes contact well enough for it to stick that matters most. [APFSDS]( URL_12 )- Armor-Piercing-Fin Stabilized-Discarding Sabot - This is the latest design. A dense kinetic energy penetrator round is used to defeat composite armor from a great distance away. Speed kills armor, and if you concentrate enough kinetic energy into a single point you'll be able to go through thicker armor (This is also the principle behind HEAT rounds, discussed below). The fins are used to prevent the round from tumbling in air, and the sabot is used to ensure the round fires as straight of a path as possible once fired out the barrel, but once its traveling it's discarded to prevent drag from slowing it down. [HEAT]( URL_8 ) - High Explosive, Anti Tank - This round came about as more and more tanks began using thicker armor. Creating larger shells to penetrate thicker armor wasn't scaling well, because the larger the gun, the larger the tank needed to be, and the heavier it had to be. Instead, we can concentrate all that energy into a single point, because that is all we need. HEAT rounds are shaped charges, which focuses kinetic energy (it doesn't \"melt the armor\") towards a single point. It's the kinetic speed of this jet that penetrates the armor. A good thing to remember is that speed negates armor. The faster something is traveling, the greater the armor-penetrating effect will be. A metal ball traveling at 5 miles an hour won't break through 100 mm of armor, but a metal ball traveling at 33000 miles per hour will break through it like it wasn't even there. That is how HEAT rounds penetrate, it uses a shaped charge that creates a jet stream of liquid metal that is traveling at ~25k miles an hour. At that speed, it \"slices\" through the armor and into the cabin, creating a stream of molten metal that travels into the crew cabin, potentially knocking them out. It's not the temperature of the HEAT round that causes it to penetrate, it's the **speed** that molten stream of metal that causes it to. Counter-measures- Tanks employ several measures to counteract new shell designs. It's fascinating learning about a new shell design that came around, and how armor changed as a result. [Sloped Armor]( URL_5 ) At first it was sloped armor, they found that 90° armor designs (such as the famous Tiger 1 tank) were ineffective given the fact that it used 100mm of steel, and provided 100mm of protection. But if you were to angle that armor 45 degrees, then the amount of protection increased (correct me if I'm wrong, but I believe it would be sqrt(2)x100, giving us 141mm of **effective** armor). Rounds that would normally penetrate a flat 100mm plate of armor would not penetrate, and the likelihood that a 140mm steel penetrating round would penetrate either, because of the fact that it's at an angle of 45° instead of flat 90°, which may cause it to bounce. The downside of this is that you need more armor total to cover your tank, so it's not just a straight up benefit. If your armor was 45°, then you would need sqrt(2) more armor to cover the same distance if it was flat. [Extra armor]( URL_4 ) - You'll notice in the [Tiger 1 tank]( URL_3 ), that there seem to be things sticking out from the front bottom of the tank. This is actually a piece of tank track, which was put there for two reasons. The first is to provide a backup of a section of tank track in case they become damaged. The second (and the reason why it's actually there and not elsewhere), is because it increased the distance that a shell would have to penetrate the tank. That section might be many millimeters thick, which meant that even though it wasn't designed to stop rounds, a round that had an explosive cap would detonate on that instead of the surface of the armor, meaning the likelihood of success of it penetrating to inside the tank greatly decreased. Nearly every single element of a tank design is for functional, rather than stylistic reason. Tigers [Anti-Spalling]( URL_13 )- As said before, spalling creates tiny fragments of metal that travel throughout the crew space, potentially killing crew members. To counteract this, you can install Spall-liners which would \"catch\" the metal spalling, and is placed in between the steel armor and the crew space. Kevlar can be used for this for example, and it used for body-armor as well. [Spaced Armor]( URL_7 )- Note the metal sheets on the sides of the tank. Spaced armor is useful in creating a gap between the penetrating shell, and the steel armor. The gap may detonate the ballast cap of the shell, and may cause the armor piercing shell to tumble before it hits the armor, greatly reducing the penetrating effect. It also causes HEAT rounds to detonate their shaped charge early, which greatly reduces that concentrating effect of liquid metal against the armor. [RPG's]( URL_9 ) are basically mobile HEAT rounds (note the distintive cone shape of the head). [Reactive Armor]( URL_1 )- So you have an incoming round that is likely to penetrate, and you want a last-minute ditch effort to try and slow it down. This is the thinking design behind reactive armor. If a paper airplane is coming towards your face and you have nothing but your mouth to prevent it from directly hitting you, what could you do? Well, you could try to dodge, but if you can't, the next best thing is to blow against it, that is what reactive armor does, it \"blows away\" an incoming shell by creating a secondary explosion that causes the incoming shell to lose energy. If I have a force of say 5 units, and the reactive armor pushes back with a force of 3 units, the total force against the armor would only be 2 units, which is far better than having 5 units of force, and at that point, my composite armor will likely protect me. [TROPHY/Arena countermeasure system]( URL_10 ) - This is a high-tech system designed to detect incoming rounds, and \"shoot\" them out of the sky before they have a chance of hitting the tank. Currently, Israel has the Trophy System, and Russia has the Arena system, but both work in the same principle. They intercept incoming rounds with either a \"shotgun\" blast to deflect/blow up the missile, or a mini-rocket to intercept and blow up the incoming projectile. And that's the post limit. Hope this helped and you learned something.",
"Iirc HEAT uses shaped charge copper penetrators. These work by setting off a high explosive behind a metal (in this case copper) dish. The shape of the dish as well as the properties of the explosion combines to convert the solid or powdered metal into a stream of liquid or vaporized metal moving forward at many times the speed of sound. At that speed, tank armour stops acting as a solid as, simply put, solids only stick together at the speed of sound (in that material), so when an impact happens faster than that the impacted atoms have no time to convey that impact to their neighbours, and thus they're moved aside with relatively little energy required. This allows the molten copper, and possibly a secondary charge, to enter the interior of the tank and mess stuff up. Obviously any human hit by it will be grievously wounded or killed, while hitting a tank shell can set it off (killing everyone), and as mentioned some anti tank rounds have a secondary charge (I think I heard somewhere though I could be completely wrong) which is basically a small explosive that flies/falls through the hole the penetrator just made and then blows up (killing everyone). Edit: The Slow Mo Guys did a [video]( URL_0 ) using shaped charges recently (along with quite a lot of det cord and other explosives). Worth a watch just to visualize how fast shaped charges fling copper, as well as the holes they make.",
"HEAT rounds work similar to an EFP. I'll compare HEAT to AP to help explain. An AP round is just a specialy designed projectile. It relies on the velocity of the round when it leaves the barrel to penatrate armor. In its simplest form it is like throwing a rock through a piece of paper. HEAT does not rely on the velocity of the round when it leaves the barrel instead the round has an explosive charge behind a metal liner. When it hits the target the charge explodes turning the metal liner into a jet of molten metal and projecting it through the armor. To put it in a super simple way. It's kind of like the HEAT is a tiny gun that you load into a bigger gun. You shoot the tiny gun out of the big gun and when the tiny gun hits the target it fires its little bullet at point blank range into the armor."
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9mojv0 | Why are men's bathroom urinals not universally the same height? | Engineering | explainlikeimfive | {
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"Small ones are ADA (handicap) use and as a secondary byproduct, good height for kids. Taller ones are just standard size... this height is based on average user height to help eliminate splash and ease of use",
"Men are basically incompetent at using urinals. If they were all at the lower height, 90% of the pee would be on the floor. Especially in a bar.",
"The real question is that it’s like $50 max to put a divider up between urinals, stop making me pee with some dude peripherally looking at my dick.",
"Cause tall people don't like pissing on their feet?"
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9mrgwc | Why the SpaceX rocket trails look like this? | Engineering | explainlikeimfive | {
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"Those pulses are from thrusters periodically readjusting the alignment of the rocket. They use what spacex calls cold gas thrusters which use compressed nitrogen gas to nudge the rocket into the desired orientation. They are used along with the fins to keep the booster so that it doesn't spin uncontrollably or burn up in the atmosphere as well as keep it on track for landing at the designated location."
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9mtitf | Why are Australia's vast empty planes simply not covered in Solar Panels to help with their power productions crisis? | Engineering | explainlikeimfive | {
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"A couple of reasons: * it's expensive as fuck * you lose a lot of the power having to transfer it across lines to where it is useful. * despite it being fairly inhospitable to people, there's still a great deal of wildlife there that would be impacted by such a huge construction project. I mean yeah put a solar plant or two as close as you can to civilization, but don't cover the land with them.",
"The same reason they're not spinning up new gas plants - Money and maintenance. It's not like you just stick solar panels out in the middle of a dusty wasteland and that's that. They need to be continuously cleaned to deliver anything close to their rated output."
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