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5uji8t | Why are power line wires exposed and not covered with a coating? | Engineering | explainlikeimfive | {
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"Air is an excellent insulator, so further insulation is not necessary. In addition to addition expense, it would also serve as a heat insulator, which would limit the amount of power that could be transferred. The are designed in a such a way that water will drip off the wires and not cause a short circuit.",
"Only overhead power lines are bare wires, because they need to be light. They're put high enough up that nothing should be able to touch two wires or a wire and the ground or a grounded object. Underground power lines are insulated and sheathed."
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5ul7ql | Why can we not harness lighting as an energy source? | Even if not the most practical or maybe reliable, seems like it's free energy we could put to some use? Do we have the technology to hypothetically charge batteries or convert to thermal? Edit: Trying to add 'flair' on mobile app. Fyi you can't which is convenient. | Engineering | explainlikeimfive | {
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"Lightning is unpredictable and at the same time very powerful. The voltage is extremely high and also the current. This results in the components and power stations need to be really robust and will be much more expensive. Anorther thing with electricity is that it's a fresh produce, and only produced for immidiate consumption. No power plant is producing more power than what is being consumed, that's because there's no effective way of storing energy. So this means that the lightning would have to strike exactlt at the moment people need it. And since it only last for a fraction of a second it can be a problem if you want to watch tv for 2 hours.",
"1. Unpredictable. 2. If you solve the issue with unpredictability (building a lightning rod, for example and placing it somewhere stormy), gathering that energy in batteries would be difficult, as the energy source discharges the energy episodically and in very short periods of time (think what happens to your phone charger when there is spike in electricity). 3. There are plenty of ways to gather energy with the existing technology (cheaper, no need to start from scratch)."
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5um071 | Why do elevators decide to wait at the floors they do? | Engineering | explainlikeimfive | {
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"The simplest solution is to have elevators wait whereever they were called last. Some controllers are smart enough that they can be configured to move empty elevators around to prevent having multiple elevators waiting on one floor, and to minimize the wait time on high-demand origin floors. The exact algorithm varies between manufacturer and individual installation"
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5umj3p | Object Oriented Programming Languages | OOP VS procedural and why everyone says its such an important concept for me to understand; but then cant give a clear description of either or why? Thanks! | Engineering | explainlikeimfive | {
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"I actually had to explain this to my 5 year old. A procedural program is like a recipe. If you want to make a cake you take the recipe and do each step. Sometimes the steps refer to other recipes (like the icing); we call those \"methods\". And there are amounts of things you have (like cups of flour); we call those variables. Now let's say you were baking a 8 course meal. You'd have a ton of recipes (methods) and amounts of stuff (variables) to keep track of. Object Oriented Programming (OOP) is a way of organizing the methods and variables to keep everything together. An object is a thing (a noun) and you attach variables (usually called properties) and methods (verbs). The object keeps all of that stuff together and makes sure that you don't mix up your cake recipe with another one. But one important takeaway is that these are not mutually exclusive. Most (but not all) OOP languages are procedural, and a lot (but not all) procedural languages offer OOP.",
"Note that in the following examples, I'm using pretty standard OOP terminology, but things may vary by language. The basic idea of OOP is that you describe your program as a set of objects, each of which have their own data and behavior. For example, a game might have a Player object containing the data \"health\", \"speed\", and \"strength\", and containing the behaviors \"Move with keyboard input\", \"lose health (and possibly die)\", and \"drink health potion\". Now let's say we want to add AI players, or networked players. Suddenly we need our Player class to be more flexible! The \"Move with keyboard input\" behavior is no longer acceptable. One simple way to solve this is to make Player into something called a \"base\" class: replace \"Move with keyboard input\" with the more generic \"Move with some kind of input\", then create \"child classes\" called HumanPlayer, NetworkedPlayer, and AIPlayer that all handle their \"Move with some kind of input\" in different ways. This is known as \"inheritance\": defining child classes that act like a special version of the base, or \"parent\", class. Alongside inheritance is \"polymorphism\" and \"encapsulation\". Your game could store a list of \"Player\"s, each of which is one of the child Player types, and call each of their \"Move with some kind of input\" without caring which type each Player actually is! If you want a new networked player, just add a new NetworkedPlayer to the list -- the game doesn't care what kind of Player he is; it just runs his behaviors like it would with any other Player. In other words, the responsibility of handling all that player's networking code is \"encapsulated\" in the NetworkedPlayer class, so nobody else has to worry, care, or even *know* about it. This is the main advantage of OOP: a powerful way of grouping code so that other groups of code only have to care about the outward interface it exposes, not everything that might be going on underneath. Edit: typos",
"For context, one of the reasons why explaining these concepts is difficult is that the last few generations of programmers did their entire computer science education within procedural and object-oriented paradigms. Both ideas came out of the [software crisis]( URL_0 ) in the 1960s where the complexity of software development projects was increasing too fast for engineers to keep up. Recent CS students and professionals (myself included) never worked in a world where these things were not the main way people did things. In a procedural programming language, a program consists of instructions describing actions the computer is to take. Pretty much every modern and popular programming language is procedural in some way, and your first CS teachers may have actually defined computer programs as \"instructions for the computer to follow.\" One alternative to procedural programming is functional programming where a program isn't so much a list of actions but a list of expressions that represent the type of data the program is supposed to produce. Lisp and SQL are examples of this model of programming. Object-oriented programming is primarily a method of code organization. Generally, you learn about data (variables) and procedures (functions) as separate things. OOP languages package related data and procedures together. The primary advantage of this is that how a piece of a software system *works* is separated/isolated from how it's *used* by the rest of the software system. This idea is called \"encapsulation\" and allows software teams to work separately on parts of a large project and then easily join them together.",
"These are not really different things. Almost all languages are procedural. Procedural refers to procedures. You can think of your code as being one procedure, with maybe sub-procedures in it. Procedure being one set of instructions that your computer follows. Typical example is a recipe, that's a procedure of sorts. Your CPU, at its core, works like this, so most languages derive procedural nature of theirs from CPU. However, once you start building these complex procedures(think of 1,000 page long recipes with cross-references), you'll notice that it's actually darn difficult to safely change any section of the recipe and still have any sort of prediction about what is gonna happen next. If you change one sub-procedure(sub-recipe that may or may not be referenced from elsewhere), you're gonna have to go through all the 1,000 pages with care to make sure none of those pages suddenly stop making sense as a result of your one change. OOP is a proposed solution to this. It packs sub-procedures with the data they handle into Objects. This means when you make changes into some sub-procedure, you only have to check the pages dealing with this object. You can, by purposefully programming so that you refrain from referencing to data outside selected pages, do Object-Oriented Programming even with programming languages that are purely procedural with no Object-Oriented Programming support. OOP languages exist to help programming this way, packing data and procedures that handle that data together. But the big key thing here is that you will have limited access to all Data, which is managed by objects, so that if data is corrupt, that must be because of the limited number of functions that are allowed to handle that data."
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5uqu9j | How does the PID controller works? | Engineering | explainlikeimfive | {
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"Consider a simple \"proportional\" controller. This device takes an input, determines the error between input and set point, and then generates an output which is proportional to the error. Let's take a thermostat. An oven has a thermostat with a set point of 250 C. The thermostat controls a heater. If the oven temperature is 220 C, then the error is 30 C. The controller multiplies the error by a constant (say 1%) and outputs a signal of 30% to the heater. If the oven temperature falls to 200 C, then the heater power is increased to 50%. If it rises to 250 C or above, the heater is switched off. This is fine, but what happens if something happens and the oven temperature suddenly changes - maybe the door is opened causing a rapid drop in temperature. The classic proportional controller waits until temperature drops before increasing heater power. Wouldn't it be useful if the controller could recognise a door opening, and give the heater a boost? This is where \"derivative\" control comes in - the rate of change of error is measured, and used to adjust the output. So, let's say the oven is at 240 C and the heater is at 10%. The door is opened, and the oven temperature starts decreasing at 1 C/s. The controller multiplies this by a constant (say 10% s/C), and adds this to the ouptut. In this case, the derivative term is 10%, which is added to the proportional term (10%) to give a total output of 20%. So what does \"integral\" control do? One of the problems with proportional control is that if you have an external drag on the system (e.g. heat loss from oven walls), then in order for this to be compensated (e.g. by heater power) you need an error input to the controller (because output = error * k, and therefore error = output / k) So, if your oven has 100 W of heat loss, and a 1 kW heater - then you need 10% heater power just to maintain power, and in the example above, this means you need a 10 C error. This means your oven will stabilize at 240 C, even if your set point is 250 C. Integral control integrates the error over time and adds this into the control. So, in the example above, after 1 minute with a 10 C error, the accumulated error integral is 10 C*minutes. In response to this, the controller multiplies this by a constant (e.g. 0.1% /C/minute), which in this case comes to 1% (for a total power of 11%), and adds it to the power. The oven temperature starts increasing and settles at 241 C. After another minute, the accumulated error integral is around 19 C*minutes, and the controller has increased power to 1.9% for integral control and 9% for proportional control - for a total of 10.9%. After several minutes the system settles down at exactly 250 C, the proportional control is at 0%, and the integral control is exactly balancing the heat loss. So, the proportional control, provides the basic control by negative feedback. Derivative control detects developing rapid anomalies and allows for faster correction than would be possible by proportional control. Integral control, detects long term anomalies, and ensures that the set point isn't affected by them."
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5utt49 | Identifying the criteria in engineering | Engineering | explainlikeimfive | {
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"A constraint is a limitation or condition that must be satisfied by a design. A criterion is a standard or attribute of a design that can be measured. The constraints and criteria are used in subsequent steps of the design process to determine which of many possible designs should be implemented."
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5uu7rq | How does genetic engineering affect food? | Engineering | explainlikeimfive | {
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"Genetic engineering is a wide field in agriculture. It is a combination of selective breeding and genetic alteration to produce a desired result. For example, Monsanto is a major producer of GMO seeds. They sell their seeds to farmers at typically 10x the cost of a regular seed. Their seed, however, has been selectively bred and the DNA modified to contain genetics that are desirable to a farmer. The seeds are typically modified through CRISPR (google it if unsure what that is). Monsanto's best selling and most effective GMO seed to date has been soybeans. Their soybean seed has been modified so that it is unaffected by a chemical called glyphosate (also known to most people as Round Up). They market the seeds as \"Round Up Ready\". They have other GMO seeds as well, some not very effective (for example the GMO cotton seeds don't really work and aren't widely used). Basically a farmer plants Round Up Ready soybeans and they can broadcast spray the field with glyphosate periodically which kills all plants in the field (weeds) but does not kill the soybeans. End result: the farmers yield is significantly increased. Weeds are a major problem for large scale farmers. If you don't use GMO seeds then you have to use some other weed control method and most other methods are either labor intensive, cost prohibitive, or not that effective or even speculative. There is a lot of research (literally billions of dollars) going into new methods to control weeds. Over time, weeds develop resistance to herbicides (much like antibiotics and bacteria). There's other issues around GMO seeds, not health issues like you'll get cancer from GMO seeds, but rather issues of cost and genetic diversity among plants. You have to remember GMO seeds aren't manufactured in a lab. Rather they are developed through modification then selectively bred from plants (the seeds come from a fully grown plant). On a side note, the legislation that would require GMO labels on food products would literally result in 99% of food being labeled with a GMO label. Source: I work in agtech investing"
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5uw474 | Why is store bought mayonnaise white, even though the ingredients are mostly yellow? | Engineering | explainlikeimfive | {
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"Mayonnaise is an emulsion. When it's created the ingredients are whipped together create it. This introduces a lot of air bubbles, which is why mayonnaise is rather fluffy and gelatinous. Aerated substances look white. Think of a cloud or a waterfall. Air bubbles reflect light, and thus lend a white color to mayonnaise.",
"Mayo is an emulsion of fat, flavorings, emulsifiers which help it blend smooth, and air. When you whip air into something you make it less dense, which makes it more transparent (less opaque) and we perceive this as it getting lighter in shade. Mayo has air whipped into it which makes it less dense and lightens the color towards white. It's the same reason that salt water taffy looks bright and silvery compared to rock candy, and ice cream is lighter in color than sorbet. It's also the reason that no matter what color soap is, the foam is almost always white."
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5uxa01 | How do cities with high annual rainfall deal with construction? | Engineering | explainlikeimfive | {
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"Concrete doesn't 'dry', it 'cures'. When it hardens, it's because of a chemical reaction that works just as well underwater. So rain is no problem.",
"They are always under construction. Always. Near Seattle here and if they didn't work in the rain, nothing would get done.",
"The construction crew constantly pumps out water from the soil [with submersible pumps]( URL_0 )."
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5uygnf | How do music-box makers simplify tunes so effectively that the pins on a rotating cylinder can flick a comb and yet create such a full sounding version of normally complex works? | Engineering | explainlikeimfive | {
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"They don't need to simplify the tunes much because a music box can play more than one note at once, in other words it can play chords, because it has a separate tooth for each note. Pianos and guitars can also play chords, but wind and brass instruments cannot and nor can a solo singer. So a single music box can play a tune that would take a whole bunch of wind instruments to play all the same notes."
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5uyq37 | How does FitBit or any step tracker know that you are walking and not in a vehicle? | Engineering | explainlikeimfive | {
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"When you walk, it creates a unique pattern on the fitbit's accelerometer (detects acceleration in 3 dimensions), so they use that to detect what you're doing and count your step. There are different signal processing and pattern recognition techniques to achieve this. If you're in a car, that type is motion is not detected in an accelerometer, furthermore they could also use change in GPS coordinates to realize that you're moving at car speeds (ie not walking)",
"It doesn't. I drive to Tulsa almost daily and if I don't keep it plugged into a charger the whole time it tells me I'm an overachiever. Also, there's no other way to turn it off, because per the Fitbit website, any steps mistakenly added by driving should be negligible."
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5uz3eq | What's the black stuff that comes out of sprinklers when hey break? | Engineering | explainlikeimfive | {
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"How the fuck do you accidentally throw a bowling ball at something above your head?",
"It's a bunch of different stuff, and it's the stuff you'll see inside almost any old pipes. *Rust *\"Biofilm\" (bacterial sludge mostly) *Salts and other minerals depending on the water source In really old pipes, you can actually have them closed off by the accumulation of this crap.",
"That black water is only found in sprinkler systems that use black steel pipe (as opposed to CPVC) in commercial buildings. It results from water standing in the pipe for long periods of time. It contains oil residue from the pipe plus bacterial growth. It has a very distinct funky smell to it and will stain most of what it touches. As soon as it's flushed from the first few feet of pipe, it'll run clear with fresher water."
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5v16v1 | Why has the technique for manufacturing a samurai sword never been replicated by modern engineering? | Engineering | explainlikeimfive | {
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"Modern engineering does not replicate the technique for making samurai swords because the technique for making samurai swords, by definition, requires it to be done by hand. Modern engineering also does not seek to create a samurai sword because samurai swords were kind of crap. They were impressive for the material quality the ancient Japanese had to work with, but it's trivial to make a much better sword nowadays. Even back in old times, Europeans were cranking out much better swords because they had decent iron to make them from. Samurai swords being crap is also why modern things aren't influenced by them. The how it's made section would be pointlessly long, and you would end up with an inferior cutting tool compared to what can be produced from start to finish in a matter of days now. And about Japan holding off western powers: They really didn't. Japan wasn't conquered but their military power had little to do with it. Their weapons were not peerless, but it would have been impractical to go over there and conquer them when they let you trade anyway. The United States rather trivially forced Japan to open its gates to trade and Japan was soon after westernized by western powers. Then the United States went into Japan again and rewrote their constitution after Japan did something dumb. Any western power could have conquered Japan after a moderate fight way back in the colonial era had they wanted to do so. Edit: And you wanna know why Japan did that stupid thing that got the US mad at them? They were conquering areas with decent natural materials because it was still an issue for them in the 1930s and 40s."
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5v1rbh | What effect does the curvature of the Earth have on really large buildings, roads and other infrastructure? | If you had a really really large building would you have to take into account the Earth's spherical shape during design and construction? How do you make sure it's all flat and squared up evenly? Sorry if this is a stupid question. | Engineering | explainlikeimfive | {
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"First of all, yes, of course. They are building it on a spheroid. But second of all, we know or can calculate the average curvature of the earth, so could curve it properly if need be. However, practically, I don't think it matters. The only common structure big enough to even worry about the curve (that I can think of) is transportation like highways or railroads, or the occasional bridge. They just build them on the ground*, which has been moved around as needed with heavy machinery to be within tolerances. You can make sure it's all true with good ol' Euclidean (flat) geometry. I know there's a lot more that goes into roads and railroads than literally \"put them on the ground\" but I'm not a civil engineer and that's not really within the scope of the question.",
"With buildings, practically never. They don't cover enough land area that curvature needs to be taken into account, and their sites will be graded flat prior to construction which will eliminate any residual effect of curvature. Tunnels basically ignore it, short ones are just built straight and longer ones (such as the Channel Tunnel) curve to go through the best rock formations. It only really comes into play with really big bridges. The Verrazano-Narrows, for example, has 693 foot tall towers that are 4,260 feet apart, and in order to take the Earth's curvature into account, the tops of the towers are 1.625 inches farther apart than their bases.",
"Earth's curvature changes its height, on average, 11cm per km. This is far, far less than natural local variations in terrain. Therefore it has no effect on people making buildings.",
"Generally, they almost always don't. The variations are incredibly small. However, one (amusing) exception are some proposed towers in the UK: URL_0 They want to use them for high frequency trading with Europe. Turns out over that distance, the curvature does matter, because they want unobstructed line of sight (HFT is sensitive to even millisecond delays). So they need to build the tower a bit higher than normally."
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5v1rm5 | Why is SpaceX so interested in vertical landings? With all the knowledge we have about Mars and its terrain, wouldn't it be easier to plan a "horizontal" entry to the planet, similar to how astronauts land on Earth? | Engineering | explainlikeimfive | {
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"The issue is landing so you can reuse the rocket. The cheapest way to do that is vertically. You just can't deaccelerate quickly enough horizontally. Think of the old NASA shuttle. It ditched the booster immediately after launch so it didn't have so much mass to deal with and slow down on reentry. The goal of spaceX is to keep that booster.",
"I don't think the whole landing trajectory is vertical, just the last part of it so they have a reusable rocket.",
"Landing rockets is about the reusability and therefore reduced cost of rocket launch in the first place.",
"Taking off from a horizontal landing is harder then a vertical landing. By landing vertically its technically possible to land on mars establish a colony and take off again in the future.",
"The space shuttle lands at like 220mph... lol it requires literally a couple miles of flat runway. No such thing exists on Mars. And mars is capable of very high winds and an unforgiving rocky surface.",
"If you're talking about landing like a plane, it would be very hard to land like that on Mars. Why? Because of the extremely thin atmosphere that wouldn't generate sufficient lift at all. It would also be hard to find stable ground until a proper runway would be built. It is much easier to just land vertically and take off vertically."
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5v4ohw | How did people on the Apollo missions knew the specifics of the moon? | I'm reading a lot about the beginnings of space exploration, and especially the early missions from soviet Russia and USA with the moon landing goal. But what I read from now is that most of the "complicated" things were about launching and space manoeuvers (like the CSM and LM docking process). Most of the missions before Apollo 11 even just circled around the moon without landing, and I can't figure how they knew they would have to adapt to an environment that different from space. How did the engineers from NASA (and also soviet Russia, they must have thought about it too) knew what "being" on the moon would be like? What it would need to descend/ascend, gravity, environment, temperatures... Did they have precise data of it or was it more about safety and redundancy? Also, irrelevant but I don't know how people lost interest that quickly for space exploration (Apollo 12 and 13 weren't even widely followed until the Apollo 13 incident). | Engineering | explainlikeimfive | {
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"By knowing the mass and size of the moon, we can what sort of gravity to expect, whether or not there is enough gravity for an atmosphere (there isn't), and without an atmosphere we can determine the temperature of the moon by observing its spectrum from Earth. And we can determine the mass and size of the moon by observing how objects in space move around the moon, and how the moon moves around the Earth. Think of it this way - if you are in the desert and see a small city in the distance - you might not know if it's small and close, or large and far away. So you move closer to it and make another measurement, and now you can determine whether it's small or far away.",
"A lot of it can be calculated or observed. Just by knowing how big and heavy the Moon is it's easy to work out how much fuel and what kind of engine it takes to land. Observations by Earth-based telescopes and space probes gave us a good idea what the surface terrain was like. And there had been robotic landers such as Surveyor 3 sent before humans got anywhere near the Moon. (Apollo 12 landed right by Surveyor 3, near enough for the astronauts to walk over and check out the space probe.) That said there were still some doubts. Would the lander sink into the lunar soil (or 'regolith') for example. The Apollo program always had some risks."
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5v72wh | When accelerating a car, the sound made by the engine is a typical one (constant working of pistons) . But why does the car make more of a mechanical toy like sound while reversing? | Engineering | explainlikeimfive | {
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"The reverse gear in the gearbox is cut as a straight or spur gear instead of a helical gear. This is cheaper than helical cut. And it's noisier.",
"The basic principal of a car is to move rotational energy from an engine to the wheels. To control this we can control the speed of the engine of the ratio of how fast the wheels turn to the engine speed using a gearbox. This is also used to reverse the rotation of the wheels in relation to the engine output. If you imagine a two wheels pushed together, when one spins it will have friction against the other one causing the second wheel to turn. If one wheel is bigger it will turn slower than the other. Obviously if this is not kept tight together to maintain friction the second wheel won't turn. The other issue is that one wheel can turn past the other. To stop this from happening we force the wheels to mesh, creating gears by cutting identical patterns across each face which interlock. This is more robust than the wheel system as there can be no slip, which is why we use gears in a gear box. The easiest gears to make are straight gears, which means the cuts of material are taken across the face of the wheel, from one side to the other. This makes the teeth interlock squarely when presented to each other, and only at one small point with 1 tooth of overlap. The contact between teeth will rub, eventually making the gear teeth smaller than the opposite detent. This means when the face wears, there will be a very small gap and therefore impact as the next tooth meshes against the other gear. This creates a whirring noise, like reverse gear and some older first gears. The gears are straight cut to reduce cost as they are easy to make. Other gears do not make this noise as they are cut on a diagonal, creating longer gear teeth with multiple teeth meshing at the same time/position on the gear. This allows for less wear to occur on the gears, which lets the gears mesh quietly. The helical cuts also make the gears more durable as the multiple teeth prevent wear and promote good meshing of gears. This is why the second gear and above in most cars are helical: You spend most time in them going forwards, so they need to last longer and wear less. The noise reduction is another benefit added in. This is why older cars are noisier to drive, as the gear faces are more worn in the straight cut gears allowing for more play and hence more noise. Tl;dr: reverse is a cheaper noisier gear because you don't spend enough time in it to warrant the manufacturer doing the work to improve the gear",
"When helical gears mesh, there are multiple teeth in contact regardless of the angular position. Straight gears only have continuous contact in theory, but when worn even only a little it becomes an intermittent contact which is more audible. Straight gears can transmit higher torque though."
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5v9z2k | Why are cruise missiles used if ballistic missiles can reach targets faster? | What advantages do cruise missiles have over ballistic missiles and in what scenarios would you use one over the other? | Engineering | explainlikeimfive | {
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"Why do pistols exist if you can hit a target with a 50 caliber sniper rifle at 1000 yards? It's cheaper, smaller, lighter, easier to deploy, and easier to get up close.",
"Because nobody wants to anyone to think they're launching a nuclear first strike. There is no way to tell what sort of warhead a Ballistic missile carries. Launch one of these and you set off all kinds of armageddon.",
"The Minuteman (the USA's current ICBM of choice) cost $7M each in 1970 - that's about $43M in today's dollars. A Tomahawk costs around $1.5M today. That completely ignores the massive infrastructure associated with maintaining ICBMs. ...and a cruise missile isn't going to scare the Russians into thinking you're starting a nuclear war.",
"Same reason people still drive fords when Ferrari's can get places faster. Sometimes you have to weigh the cost versus how fast you're wanting to get someplace.",
"Cruise missiles can track a target, with the exception of some new Chinese anti-ship ballistic missiles ballistic missiles are limited to fixed targets and even then have limited accuracy. Also they are generally easy to spot on radar and easier to shoot down as they are easy to spot and follow a predictable path--although they can be significantly faster than a cruise missile.",
"Part of it is in the name. Ballistic trajectory means that if you can track where it is, you can tell where it's going to land. It follows an arc based on gravity with some corrections. Contrast that to predicting where an airplane that's cruising around is going to land.",
"A ballistic missile goes very fast, is very large and is incredibly expensive. A cruise missile is essentially a plane drone, pretty cheap. You can put a little warhead on it and target one building or a window or now with facial recognition, a person. Also there is very little chance any of the other nuclear powers mistake a cruise missile strike as an ICBM launch so there is that."
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5vcrgb | What is fracking? | I see a lot of controversy over fracking. In Europe, people are overwhelmingly against fracking. On Reddit, I see a lot of people who support this as a business opportunity. But in the end I don't really know what the fracking method is... I searched here but the answers were not really LI5. An extra question would be: is it safe/mastered today. | Engineering | explainlikeimfive | {
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"Fracking is short for \"hydraulic fracturing\". The process involves drilling a hole down to a layer of earth where there is natural gas, then pumping fluid into the hole at extreme pressures in order to fracture the stone and release the natural gas. It is only useful for particular rock formations that have lots of small pockets of natural gas that isn't easily accessed by other means. The main polution problem is apparently associated with dealing with the waste fluids after it as been used to fracture the rock. If the disposal wells are not properly sealed, they can leak up and into the water table (normally located at a much shallower depth than either the gas wells or waste wells), thus contaminating the drinking water. As with many things, it is safe as long as it is done properly, but not so much if the proper procedures are not followed.",
"Picture oilfields as a sponge. Lots of little pockets of oil, instead of one massive underground 'tank' we can just suck out. To get into these little pockets, we drill a pipe into the formation and use explosive charges (or other more fancy tech) that poke little ~0.5\" holes in the pipe. Then we pump about 5000 gallons/minute through that hole, at crazy high pressure creating an effect like a really focused power washer on your mom's garden. This forces a crack into the formation, connecting all those little sponge holes to the pipe of our oil well. Sometimes this process is aided by Liquid Nitrogen, that expands as it goes down, giving it even more pressure at the bottom. Other times we run a slug of HCL to chemically soften the rock formation, making it easier to crack open. Now, this process is occurring 10,000ft++ below the surface, so the pressure is crazy high. Consider the extreme pressures you hear about at the bottom of the ocean, then remember it's deeper than that, and loaded with granite instead of water. That's the pressure the fracking pumps have to beat just to get the cracks open. If the pressure stops, those cracks will almost immediately seal up. To prevent this, immediately after the cracks have been formed we pump sand carried by gel down into the crack, which forces it to stay open. Since sand is very permeable, oil can flow freely through it to our pipeline. The gel carries a chemical that breaks it down within a few hours, and eventually makes its way up to the surface through the pipeline along with the oil. Most of the time this is Guar gel, and isn't too chemically different from using wheat flour to thicken a beef stew. It just cheaper and performs better at extreme temperatures and pressures. The cracks don't extend more than ~100ft from the pipeline. We know this because we can compare the volume of sand pumped down to the base diameter of the hole we blew open, and conservatively estimate the volume filled by the sand as a cone. Generally speaking, public water tables stop at ~100-200ft of the ground surface. Fracking is 10,000+, giving at least 800ft of solid rock between Fracking and Groundwater. It is incredibly unlikely that the two shall ever meet, and as far as I know they haven't. ~~~ What HAS happened is surface contamination. Small scale 'violations' occur almost every day when crews rig up and rig down, dribbling whatever chemical was in their hoses on the ground. These will fuck a farmer's backyard and grazing fields, but not likely a city's municipal water supply. The most ethical companies line a site with plastic sheeting and vacuum up any drippings, but that adds $1mil in cost, and is only as good as the crew applying it and actually doing what they're supposed to. Larger scale violations are some operations that have blatantly drained their runoff and (hazardous) wastewater tanks into the city sewer system, or some corner of a farm, hoping nobody would notice. This is patently illegal and amoral for so many reasons. Typically it's a \"discount hazardous waste disposal\" firm that's doing it for a bigger company, and usually the bigger company is included in the lawsuits for failing their due-dilligence. Other grey areas are the wastewater lakes for re-used water. See, the water that is pumped down into the formation comes back out a hazardous material and full of varying levels of nastiness. However, it doesn't become hazardous waste until it's actually waste. Most oilfield developers will re-use this water for \"tomorrow's\" fracking job, as it's still plenty good for that. That means the trucking/piping/transporting of that water with minimal spillage must be accounted for as well (read: more money). Also, it leaves you with wastewater that is even more hazardous than it was before. Typically this not-yet-wastewater is stored in engineered tanks or ponds that hold the bad stuff in to a reasonable (EPA certified) level, however, eventually someone will be responsible for draining that literal swamp. Usually that wastewater is pumped INTO an existing well in the center of a formation, which pushes oil OUT of surrounding wells. Once the stuff coming out is more water than oil, it's left 10,000ft underground, and won't be seen for a time measured on the geologic scale. Alternatively, there are ways to actually treat the water back to potable standards. It just requires processes and facilities tailored to the particular hazards of the water that aren't usually found at municipal water treatment plants. Drought-stricken farming areas have been kicking in for upgrades to their local water plants, as it actually can be cheaper to use local not-hazardous-anymore-but-expensively-treated water than trucking it in from elsewhere. ~~~ So, is Fracking safe? When working as-designed, yes. Of course there are things that can go wrong, but that's why local, state, and federal regulations require checks and constant monitoring. Having worked in the industry, I'm actually very pro-regulation, because I know the bosses will always put the business first. Without industry-wide regulation evening the playing field, someone will get over the moral issues of bad environmental practice in the name of cutting costs. The only downside to regulation is that it makes OUR oil more expensive to produce than countries that are less environmentally concerned, but I'm OK with that, because that just means keeping more in our borders. I should also note that Fracking has been tied to increased earthquakes. So far, most of the affected areas are also high-tornado areas, so their buildings are already ruggedized for those types of loads, which is why nothing has collapsed yet that wouldn't have anyway. However, the science isn't in yet on whether or not the more frequent earthquakes could be a good thing. See, we're about 60 years behind schedule for a massive New-Madrid earthquake, and there's now speculation that all of the little quakes could be easing the tension, preventing a massive snap that last made the Mississippi River flow backwards for a bit, and would certainly level most major cities between Louisiana and St. Louis.",
"Its safety can be very controversial. Oil wells were first drilled straight down. After a while they learned to tilt the drill and drill at a slant. They became capable of turning a drill hole parallel to the layer with oil or gas. They learned to drill multiple holes from one drill site radiating out in the productive layer. They also learned to pack drill holes with sand, fluid, explosives, and nasty chemicals. Setting off the explosives resulted in fracturing the productive rocks. The sand slips in to keep the fracture open. The nasty chemicals also keep the cracks open. Because of these techniques it is now possible to get oil and gas from shale formations. More can be extracted. It is an oil and gas boom. Supposedly the well hole is sealed for a few thousand feet in the region which has our drinking water. So water wells should not become polluted. Actually water wells were polluted long before fracking. The roofs of well houses would pop off when the pump motor kicked on because of gas accumulation. There are cracks in the rocks. Anywhere you see quartz there is a crack in the rocks in which water seeped. Only a few thousand feet separate our aquifers and the oil or gas layers. Earthquakes happen all the time. So we may have set up a permanent future where aquifers and water wells are destroyed when the chemicals start leaching out. Drilling companies say they seal the hole. Actually at least 5 % of the seals fail within a number of years. We could say they will all eventually fail. It is just a matter of time.",
"Bedrock is not a dense compact material. However it is more like lots of densely packed rocks. And between these there is cracks and openings for gas and liquids to get in. When you drill a well you get some of these cracks and can get the gases and liquids in them. This will cause material from connected cracks to flow towards your well. However depending on the rock and the cracks in them this can be a very slow process. Or the cracks can even get clogged by silt or other materials. One way to get higher gas or liquid throughput is to drill more wells. This is why you might see lots of wells in close proximity to each other. But drilling wells cost money. A cheaper method is to pump liquid down into the well and actually open up the cracks even more. After some time you get small pieces of sand and gravel that locks the cracks open. So when you pump the liquid back up again the cracks stay open and you can get more gas or liquid from the same well without drilling more. This is a technique which is hard to control and there is a lot of crossed fingers involved. You can not control the cracks in the rocks directly but have to rely on the rock to behave like you want it to. And in some cases you can open up the cracks too much and it can get though to nearby reservoirs that might be linked to the ground water. There is also worries about earthquakes since you are in fact moving bedrock and this can cause things to shift. We do have a lot of experience with this technology but not on the scale that we now see it being used. And it is hard to predict the outcome, it may be without risk one place and then with lots of risk at another site with seemingly identical geology."
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5vjdcn | Why are house in America built so hollow with drywall and light wood, whereas homes in other countries like india, houses tend to be built with cement and brick? Which is stronger? | Engineering | explainlikeimfive | {
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"In states like California, the wooden homes can withstand earthquakes (and is cheaper than the other earthquake code approved material, steel reinforced concrete) because they're flexible and can bend a bit. So what homes are made of is going to depend on where you are. Are you on Long Island in New York? The houses will mostly be brick or cinder block with aluminum siding.",
"Of course a house made of stone and concrete is going to last longer than a house made of wood. Stone houses from over 800 years ago are still standing. But wood and drywall work well enough, and they are less expensive, and most people arent building a house because they want something to span the centuries...its just a house.",
"Cost and adaptability. Imagine you wanted to add an electrical outlet to your kitchen. If the house was made of stone you're going to spend most of the time chipping away at the wall, hoping not to do too much damage. While stone is great for longevity, it really adds to the cost of a house. Framing systems can be bought pre-fabricated from a host of manufacturers and erected in a couple of days. There's a local developer near me that can go from foundations to drywall in about 5 days if they're really trying. That's not including a wholly pre-fabricated house that is just dropped onto a concrete pad by tractor-trailer. So it's not a question of \"stronger\" it's \"strong enough\". If the house is rated for a 50 year lifespan, what's the value in shooting for 500? For most, 25 is good enough.",
"First, the foundations for US homes are generally made out of concrete slabs with re bar emerging from the concrete to form the basis of attaching the rest of the frame to the slab. The base of the home is the most critical aspect in terms of stability and durability. Second, in tropical areas, it is much more common to build with cinder block and mortar. Most homes in Hawaii are built out of cinder block (not brick) because termites and the humidity/salt water/rain make wood a poor building material, prone to rotting and being eaten. It is more expensive to build with cinder block, however, because there is more labor involved and in the US labor is expensive. Building with bricks requires even more labor because the progress is slower, so it is fairly uncommon in new construction (most \"brick\" you see in new construction is ornamental and not structural). Most homes in other coastal areas have some sort of cement siding, such as stucco, to add stability and insulation, and to withstand the harsh sea air. As for the standard wood with drywall construction, as long as water, humidity and temperature are controlled (which almost every modern home does through HVAC systems, insulation, and proper drainage/roofing), the wood frame structure can last indefinitely. Many wood framed homes from the 1600s are still standing. Those home used much thicker wood, but they were also less protected/insulated than modern homes. Also, with a wood frame, you can remodel pretty much every part of the home if necessary relatively easily, including the wood framing (if necessary). Just take some scaffolding.",
"Wood and drywall is more than strong enough to withstand standard weather, those things it will not withstand are storms like hurricanes and tornadoes that will destroy cement and brick nearly as easily as they destroy wood. You have to build a 4 foot thick wall with steel reinforcement that has no windows and only a single steel door to make an above ground tornado bunker. Wood is more vulnerable to fire, but it is far better at withstanding earthquakes. So that is a bit of a toss up. So we are down to price. Wood and drywall are much much cheaper than cement and brick. As much as 1/10 the cost of a cement or brick home. Wood homes are also much more user friendly. It is easier to make modifications, put in electric/plumbing/internet/phone etc, and do all kinds of things.",
"I think one part of the answer is certainly that America still has a great deal of forest so wood products are probably significantly cheaper here than in India and some other parts of the world, like the middle east. Our wood products/timber industry has powerful influence in government too and it's in their interest to keep people building houses from wood. Concrete does a good job of staying (relatively) cool and temperature stable in hotter climates which along with cost, adds to its popularity in certain parts of the world. As was mentioned, Americans often do a modifications to their homes, i.e. open up walls to add power outlets or knock down walls and add rooms to a house. A wood framed house makes that much easier to do. Part of it is also tradition. Historically most homes in America have been built from wood. As someone who has traveled a fair amount around the world, I definitely see the benefits of concrete construction. If I were to build my own house from the ground up I would prefer it be concrete than wood."
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5vlb11 | Why do we use fresh water for our sewage? | Engineering | explainlikeimfive | {
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"It's easier and cheaper to have a single delivery system to all buildings than it is to develop and install a second identical system for non-potable water delivery. You're also avoiding the inevitable mishaps when people confuse the two.",
"Because when indoor plumbing was first developed, we thought there was plenty of fresh water, and that was never questioned Some people are changing that by incorporating grey water in their toilet systems."
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5vr4gg | Why does the same radio station on FM and AM last much further out on AM? | I listen to a sports station in Austin TX and when I leave the city the FM signal dies about 30 miles out of the city but the AM signal lasts for about 100 miles out. | Engineering | explainlikeimfive | {
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"AM radio generally transmits around a frequency of 1 Mhz or less. FM radio generally transmits somewhere between 88 and 108 Mhz. Each FM photon has 100 times more energy than an AM photon (note: this is not the same as suggesting that the FM signals are automatically stronger because the power of the broadcasting tower will establish how many photons are sent out). Basically FM radio is mostly line of sight, the radio signals coming off the broadcasting tower more or less just shoot straight at you (straight at everything they can see from that vantage point) when you receive them they're basically coming in on a line between that broadcasting tower and you. As you get further away the tower passes beyond the horizon and you can't get the signal anymore. AM radio because each photon has less energy can both reach you by direct line-of-site like FM, but also the radio waves going upward into the sky cannot punch through the ionosphere well. The ionosphere is a layer of charged particles in the upper atmosphere, and it will reflect lower frequency radio waves back down to the earth extending their range considerably. With favorable conditions the signal can bounce multiple times off the atmosphere and then bounce off the earth and then the atmosphere again and travel very significant distances."
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5vw1u4 | How do people manage to customize otherwise normal vehicles (and normal engines) to produce hundreds more horsepower than what it was originally designed to produce? | Here's an example of what I mean: URL_0 I looked up the "2JZ" engine and it's supposed to have a " contemporary industry maximum" of 276 hp. How does one make it go from 276 to 1100? | Engineering | explainlikeimfive | {
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"Essentially adding power to any engine all comes down to getting more fuel and oxygen into the engine with each stroke. Their are several ways to do this: You can increase the size of the cylinders to allow more fuel & air in. This can be achieved by boring out the cylinders and increasing the diameter of each. You can can also \"stroke\" the engine, increasing the stroke length of the pistons and therefore the effective volume of the combustion chamber. You can increase the amount of fuel and air being delivered through efficiency boosters. This would be a head and cam swap, new intake manifold, or exhaust system. These mods allow air to move more efficiently into and out of the engine. More air, means you can put more fuel in, equals more power. The most efficient method is to use a power adder. This would be a turbo charger, supercharger, or nitrous oxide. Turbo chargers are essentially air compressors. They suck in air, compress it, and then inject it into the engine. Compressed air has more oxygen per cubic inch, so you can then add even more fuel to the cylinder (remember if there is not enough oxygen, then all of the fuel won't combust). The turbo is driven by the exhaust gases exiting the engine, so as rpm's increase, the turbo spins faster and boost increases. Turbos can get up to 40 or 50 psi of boost. A supercharger has the same effect as a turbo, but is less efficient. The difference being that superchargers are driven by a belt that is connected to the crankshaft. As the motor spins, it drives the compressor. Most superchargers develop 5-10 psi of boost, so by comparison, they are not as good as turbos. The one advantage a supercharger has is that it develops boost instantly. Turbo have to spool up before they start creating boost causing a delay after hitting the throttle; this is called turbo lag. Nitrous oxide is a supplement that can be added to the air/fuel mixture to boost power. NO2 has more oxygen in it than air: air is 21% O2 and NO2 is 33% O2. The extra 12% oxygen allows more fuel to be added. Lowering temperature of the air coming in also boosts power. Again, denser has more oxygen and cold air is denser than hot air. A cold air intake kit moves the air filter away from the hot engine bay and relocates it to an area that will allows colder air to be sucked in. You can also swap out the thermostat in the engine. The engine thermostat is a proportioning valve that controls the flow of coolant in the radiator system. You can swap to a lower temp thermostat that will keep the engine cooler, making the air around it cooler, which is the air being sucked into the engine. For engines with a turbo or supercharger, you can add an inter cooler. It act just like a radiator, but in this case it cools the air before it enters the engine, making it more dense. Most other mods beyond those I mentioned are support modifications designed to increase the strength of the components to withstand the increased stress and heat of adding more power. Most stock motors have a horsepower limit that can handled. Most regular engines might have 200 hp but are actually rated to handle up to 400 hp. In the case of a 2JZ, the stock motor was actually designed to handle way more power than 276 hp and is actually good for about 700 hp. Once you start pushing the limits of the engine components you risk damaging the engine. This is why most high horsepower builds end up swapping out most stock components such as pistons, rods, valves, etc. to uprated parts that can handle the stress and be more reliable.",
"There are a few ways to produce more horsepower than stock: Forced Induction: done by attaching a supercharger or turbocharger that forces more air into the engine, and therefore, creates a more powerful explosion in the cylinders, and thus, more power Upgraded Internals: By upgrading parts such as the camshaft, cylinder heads, valves, and other parts, an engine can become more efficient than stock and be able to run at higher RPM, and therefore, more power. Exhaust: by adding a free-flowing exhaust, more power can be generated by removing back pressure from the cylinders, at the cost of more noise. ECU Tuning: by changing the code in a car's onboard computer, it is possible to influence the timing of the engine firing, the amount of fuel put into the cylinders, and the psi created by any forced induction. If any car is generating 2 or 3 times more than it's stock output, it is quite likely it has had all these things done to its engine and possibly more."
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5vyig7 | Why are rest stops built with one on each side of a highway/interstate rather than one build in the middle? | Engineering | explainlikeimfive | {
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"They are in the median in some places. The left exit and entry is problematic for slower vehicles/drivers. Speaking of slow drivers, if you circle around looking for an open parking spot, eat, pee, and get gas, your internal compass may get confused and you could enter the highway going in the opposite direction I almost did it once and I have a good sense of direction.",
"In many cases, rest stops were built after the highways were and usually the lanes of a highway are too close together to plop a building in the middle. Even with new highways, it might be better to keep the road straight and add buildings on the side since that's what drivers are used to and it keeps the exits on the predicted side."
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5w0n94 | why does your car horn sound differently when you lock it and when you press down on the steering wheel? | Engineering | explainlikeimfive | {
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"Car horns are usually made of two horns that are two notes designed to be slightly off. This makes the car horn very noticeable. When you hit your remote to lock the car, your car only plays one of the two horns, since it is only supposed to be a confirmation to you, not a signal to everyone."
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5w1s6w | How do vibrations work in phones, controllers, and such? | Engineering | explainlikeimfive | {
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"There is a small spinning motor that has an off-balance weight attached to it. Here's a video: URL_0"
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5w4ob6 | why are American toilet pipes bigger? | When traveling abroad, you often are told not to flush toilet paper, but to throw it in a garbage can instead. People have told me it's because the toilet pipes are smaller than in America. Is that true? And if so, why? EDIT: currently in Central America, where I've ran into this a few times in past week | Engineering | explainlikeimfive | {
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"It is true. American sewer pipes are larger, waste more water and can handle larger solids, like wads of toilet paper, than waste pipes in many other, mostly poorer countries, like Greece. Smaller pipes cost less and use less water. That's really all that there is to it."
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5w5rnb | How does refrigeration actually make food last longer? Why does it work? Is it proven that there aren't any harmful effects? | Engineering | explainlikeimfive | {
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"Food spoilage is generally caused by the action of bacteria, fungi, or various chemical reactions. When microorganisms spoil food, they're more or less eating and pooping all over it. Sometimes the poop itself is nasty, sometimes the poop reacts with the rest of the food. Chemicals are changed and added - plus the more a bacteria eats, the sooner it can reproduce and work as a team to metabolise more food into poop. The alcohol in most drinks is yeast excrement - yum! *metabolism* is a $5 word for whatever your body does with food. Humans generally process food at the same rate all the time. Being warm blooded is the best. Bacteria, fortunately, get cold. They aren't warm blooded or even blooded at all. Most organic chemical reactions, like the ones used for metabolising food, work faster when temperatures are warm and slow down or don't work at all when things are colder. Your fridge cools food and bacteria down to the point that most microorganisms cant effectively digest/metabolize food. Depending on the reaction/organism/temperature/food bacteria may starve to death before they are able to eat enough to reproduce, so no bacteria can grow except maybe in short bursts if you leave the food on the counter or something. The same basic concept applies to molds, as well as chemical spoilage - milk IIRC spoils due to denaturation or reaction (breakdown) of milkfat molecules. Something like that. Anyways cold temperatures slow that reaction down too. Other types of spoilage like breads going stale happens when breads lose moisture over time (they come out of the oven moist with water, yeast alcohol, etc. For the most part, stale bread is just dried out. Alcohol evaporates way faster than water, and this is a large part of why genuinely fresh bread is so awesome compared to standard not-stale bread.",
"Biological activity and chemistry is temperature dependent. By cooling things you slow the rate of reactions. That's really all there is to it. Its differently effective to different decay processes. It doesn't stop it completely, and there are potentially dozens if not hundreds of decay processes at work within a food."
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5w61p1 | Why are we strongly advised to keep the window open in an aeroplane? | Engineering | explainlikeimfive | {
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"text": [
"That is mostly for take off and landing, and it's because if something goes wrong (most likely time for accident) and the plane needs to evacuate, more visibility helps access the situation outside and determine which side to evacuate from, any obstacles outside the plane like external fire, dangerous terrain, etc.",
"If there is a crash your eyes have become accustomed to the light level, you are able to see what is happening outside if you need to evacuate and the emergency crew can see inside the cabin."
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5w6bja | The maximum speed that cars in the UK are allowed to travel is 70mph, so why are vehicles given the ability to reach much faster speeds? | Engineering | explainlikeimfive | {
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"de7lrxd",
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"text": [
"1 reason is that cars are sold globally and places have different maximum speed limits. The main reason though is that redlining a car is dangerous. It puts stress on the car for no reason and greatly increases the chance of part failure. Design a car to go 150 and it will last for much longer if you only take it to 75.",
"It would be very dangerous to restrict the maximum speed of vehicles to the legally set speed limit. You couldn't accelerate out of a dangerous situation, emergency services would have to have separately built cars capable of exceeding it and if the speed limit was to change (or temporarily go away, like taking your car abroad or to private land) you would need a whole new car."
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5w6y31 | Why is a tunnel ever preferable to a bridge when crossing water? | Engineering | explainlikeimfive | {
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"In some cases shipyards, which often produce heavy water traffic with quite tall ships, are located near the desired location to build bridge/tunnel. So instead of building a drawbridge, or bridges that are extremely high to let ships pass through, tunnels are just built instead.",
"Bridges have many drawbacks. They obstruct ships. They require strong foundations and some places have bad geology for that. They're exposed to the weather. They're visually intrusive. They often require large elevated approach roads. I'm not saying tunnels don't have drawbacks either. They're generally more expensive than bridges. They can have problems with bad geology too. Fire safety can be a serious issue. They can be difficult to build without damaging foundations of existing buildings. So depending on the exact situation, either a bridge or a tunnel might be chosen. Taking examples from New York City. The Lincoln Tunnel and Holland Tunnel both avoid blocking river traffic. The Queens-Midtown Tunnel might have been a bridge, but a tunnel was chosen; it does mean not much surface space is needed at either end. Had the Brooklyn-Battery tunnel been a bridge instead it would have basically destroyed Battery Park.",
"When a bridge would be impossible, but a tunnel not impossible? Imagine trying to design a bridge over the English Channel. I can't imagine it would be an easy feat. It would probably require advances in materials science, to a science-fiction type level.",
"In general, tunnels require less land area at the approaches/access ways. This is especially true for the very high bridges needed over navigable waters. This is why you see tunnels in large cities with navigable waters. Land is expensive and ship traffic is important to the economy.",
"In addition to the answers given, another reason is that a bridge might interfere with a significant natural, cultural or tourist site. e.g. when Sydney wanted to build a second major harbour crossing, they didn't build a second bridge, they built a tunnel. Why? Because a second above-ground crossing would have cut a swathe through significant parklands and Circular Quay, and effectively severed the Opera House from the city. Plus cut through a whole bunch of expensive housing along the harbour. No way that was going to be practical."
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5w84uy | How does satellite navigation work? | I have a little bit of an understanding of this topic, but the part that still confuses me is since atomic clocks are needed to accurately measure the distance, how is my smart phone's clock accurate enough? And an explanation of why it takes 4 satellites would be appreciated! | Engineering | explainlikeimfive | {
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"If you know the distance between you and one satellite (whose position you know) then you could be anywhere on a sphere centered on that satellite with a radius of that distance. If you know the distances to two satellites then you could be anywhere in a circle: draw a triangle between you and the two satellites and that triangle is free to rotate around the line between the two satellites. If you know the distances to three satellites then you can only be in one of two positions: draw a triangluar pyramid between the three satellites and you and either that pyramid points down to your position on Earth or it points up into space. You can safely assume that you're on the ground. ****** That just uses three satellites and doesn't answer the question about clocks, though. The fourth satellite comes in to answer that question: your phone doesn't have an accurate enough clock to work with just three satellites, so rather than judging time by looking at the incoming time vs the phone's time you look at the incoming times compared to each other. Using this method if you receive one satellite you just know what time it is (with some error, since you don't know how far away that satellite is). With two satellites you know what time it is (again, with error) and how much farther you are from one satellite than the other. When you work out the consequences of this constraint you're left with a hyperbolic surface. The shape isn't important here; the important thing to note is that you get a surface, just like how in the first example one satellite gave the surface of a sphere. With three satellites you know one more piece of information. The result is that you could be anywhere on a line (just like how with the original example two satellites gives you a circle—just a line that's closed in on itself). Finally, with four satellites you get enough information that there's only one point that is consistent with all of the information you receive"
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5w9tay | Why are old tv screens round on the edge. | Why is the corner of my crt tv round so that it cuts off the corners of the screen? | Engineering | explainlikeimfive | {
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"text": [
"In addition to problems of fabricating the glass (remember, there’s a vacuum inside, so it has to hold up against roughly seven pounds per square inch of pressure from the atmosphere), it’s harder to get the electron beam to behave in the corners. For years, color TVs, which had three beams to control, were outright round all up and down the sides. Now, of course, they could simply have put a perfect 4x3 image into the center of the screen, but test after test demonstrated that consumers would rather have a big picture with the corners cut off than a perfect picture that was smaller."
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5waby7 | What's the point of changing gear transmission in manual cars? What actually happens to the car when you do so? | Engineering | explainlikeimfive | {
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"text": [
"Gear ratio is the way to express how many times the engine crankshaft turns around itself for one full turn of the drive wheels. This is what you change when you change gears. The engine has a limited RPM range that you have to work on. If you keep it in first gear all the time, you have a hard top speed limit due to hitting the RPM redline above which your engine is damaged. If you keep it in the highest gear all the time, you cannot get your car to start rolling because it's a lot harder for the engine to turn the wheels in that ratio.",
"If you have ever ridden a bicycle with gears it is the same principle. The lowest gear on a flat road has you turning the pedals many many times to make progress. As you move up the gears you turn the pedals at a slower rate to make the same progress. The difference being the size of the rear cog that the chain is wrapped around."
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5waemd | Why does every car that I've ever heard have a different sound in reverse? | Engineering | explainlikeimfive | {
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"text": [
"It's the reverse gear. Most of the gears in your car are cut with helical teeth because they're much soother and more efficient. No one cares about reverse, though, so they cut that gear with straight teeth, which in turn means it's not very efficient. A part of that efficiency loss is the whining or whirring sound you hear when the car reverses. You can see the difference [here]( URL_0 ). All of the gears have teeth cut at angles, except one on the left side, next to the biggest gear on the left (which is 1st gear), which likely means that particular gear is reverse.",
"You mean different from when you drive forwards? This is due to the construction of the transmission. The forward gears are helical, meaning their cogs are cut not straight, but sort of \"diagonally\". This reduces the noise they make by a lot, but limits the amount of torque they can withstand. The reverse gear, however, is cut straight, which creates more noise, but makes it stronger. As you don't spend a lot of time in reverse, the extra noise is usually of little consequence."
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5wan5p | What is difference between arguments and parameters? | Confused about "Keyword arguments are often used for optional parameters" | Engineering | explainlikeimfive | {
"a_id": [
"de8kl3e",
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"text": [
"The parameter is the variable declaration in the function, while the argument is the actual data passed through to the function. Parameter: public void myFunction(int a){ //code } so in this case, \"int a\" is the parameter --------------------------------- Argument: int asdf = 47; myFunction(asdf); So asdf is the argument passed through to the function(myFunction). Source: URL_0",
"Arguments are the elements you give to the function, and parameters are the elements the function really uses. Sometimes these are the same, but the function can also use the arguments to calculate parameters or multiple parameters. For example an app may use your location as an argument, and use it to derive parameters like time zone, language, etc."
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5wbtpn | Why have elevator door close buttons if they never work in the first place? | Engineering | explainlikeimfive | {
"a_id": [
"de8u7ec",
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"text": [
"They do work, but only to cancel the open buttons. They just don't close the doors early in normal operation. Also they make people feel like they are doing something.",
"The one in the elevator where I work works. It's not that they just don't work, it's that they're often disabled by the people who own the buildings in which they're installed"
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5wbys8 | What are these things in Adelaide and San Francisco? | Engineering | explainlikeimfive | {
"a_id": [
"de8wevv"
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"text": [
"Salt evaporation ponds. They're used for evaporating seawater and concentrating it and allowing it to be harvested. The color is probably from algae or bacteria in the ponds that take advantage of the high salinity of the water."
],
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5wd2iz | How many megawatts power an average house | Engineering | explainlikeimfive | {
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"text": [
"Many homes have 200A service @ 120V. So ohm's law gives us power = voltage X current. power = 120V X 200A = 24,000W or 24kW or 0.024 MW So in theory each home could use up to 0.024MW at the same time. So 1700MW plant could supply enough power for 70834 homes. However the most homes never ever come close to using 200A at one time. So the number of homes a that could typically be supplied by 1700MW is probably higher. However there are lots and lots of factors here. We aren't accounting for the power lost in the transmission lines and all the other parts of the electrical grid between the power plant on the homes. Also there are lots of extra stresses the are put on the power system when devices first turn on, so the actually power capacity needed could be a lot higher. Also commercial buildings use a lot more power and many could easily exceed that 200A level on a regular basis. That's not even talking about small to mid-sized factories. Also don't forget about public infrastructure light stop-lights, street-lights, etc."
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5wd82c | Why does ISS cargo and soyouz take so long for rendezvous? | If the time window is set up right, wouldn't the soyouz meet the ISS a few kilometers away and start maneuvering toward it? The whole process shouldn't take too long (24 hours max) but I recently learned that soyouz rides take up to three days, why is that? | Engineering | explainlikeimfive | {
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"text": [
"The Soyuz can actually rendezvous with the station in 6 hours (4 orbits) and they do that for most manned flights but it requires the station's orbit to be adjusted to just the right phase. For unmanned launches where there aren't 3 people crammed into a sardine can for 2 days, they do it the slow way because there's no reason not to. The 2 day route allows for more systems checks once in orbit, and it also saves propellant because the ISS doesn't have to adjust its orbit to the precise parameters to allow for the 6 hour rendezvous."
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5wkvl4 | why do concept cars almost never depict what the final car product ends up looking like? | Engineering | explainlikeimfive | {
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"deaw0vl"
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"text": [
"A concept car is a one off production. It is supposed to show off new technology and designs coming in the future. These cannot always be reproduced exactly once they go into mass production. Certain parts have to be redesigned to be stronger, safer, more reliable, or more cost effective. If this was not done, the price of the car could skyrocket to hundreds of thousands of dollars, and nobody is going to pay $150,000 for a hand made Honda Civic."
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5wm8wd | In cars, why does oil need changed, rather than just refilled like other fluids? | Engineering | explainlikeimfive | {
"a_id": [
"deb7fb0",
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"text": [
"Engine oil wears out. It also becomes contaminated with byproducts of combustion, dirt and debris. Oil is made from long chains of hyrdocarbon molecules and other compounds. This makes oil thick and allows it to keep moving parts from rubbing directly on each other under pressure and heat. But those moving parts eventually chop up the molecules, making them shorter and less able to keep moving parts from each other. The parts will rub more, increasing wear and friction. Oil is also intended to capture and hold harmful contaminants, like partially burned hydrocarbons, moisture, dirt and tiny pieces of metal from engine wear. Some contaminants are removed from the oil by the oil filter. But others remain suspended. Eventually the contaminants build up so much the oils ability to lubricate and protect is compromised. The contaminants are removed when the oil is drained and fresh oil is added.",
"In cars, oil doesn't run out with normal use (it might run out due to leaks), so the same oil is reused day in, day out, which causes it to pick up dirt over time. Other fluids e.g. petrol are consumed when the car is running and just need to be refilled. Let me compare car oil to fryer oil, and petrol to ketchup. In a fast food restaurant, the fryer oil is reused for multiple batches of fries, up to a day or even a few (ew). The same vat of oil can be reused just like car oil. On the other hand, ketchup is consumed with every order of fries, like how petrol is used for every mile/km you travel."
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5wpjsz | given its superior strength to aluminium, why aren't smartphones made from titanium? | Engineering | explainlikeimfive | {
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"the cost is too high, titanium weighs more, Titanium is also paramagnetic, which might cause issues with some electronic functions.",
"It's expensive, hard to work, has magnetic properties which are undesirable, and it's surplus to requirements. The glass, plastic and electronics in a phone will all give up the ghost long before an aluminium chassis will.",
"Because it's never the aluminium part of the phone that breaks. Titanium would be making something stronger that doesn't need to be stronger.",
"titanium is not only more expensive as a material cost. it's also exponentially more expensive to machine than aluminum. press forming a titanium sheet costs more in tooling than aluminum. cutting titanium costs more than aluminum. polishing titanium costs more than aluminum.",
"The end goal is not always to make something as strong as \"possible\", the goal is to make it as strong as *necessary* for that product.",
"[It's more expensive.]( URL_0 ) They have an incentive to keep the cost as low as possible. Besides, if you break your smartphone you're more likely to buy a new one.",
"Would such a phone, even if more destructible in falls, be less prone to \"touch disease\" or if it were a playstation vita, the thumb-stick drift that occurs?"
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5wrdqk | Why are traffic circles/roundabouts so rare in the United States? | Engineering | explainlikeimfive | {
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"text": [
"It's largely cultural rather than practical. In earlier days when automobile safety standards were still coming into existence and traffic flow-related science was emerging, it was inconvenient for American civil engineers to cross the Atlantic ocean and consult the growing popularity and expertise of European engineers. Roundabouts have many attractive features, but without as much input from proponents earlier on in city planning, American city planners went with the basic, easy and efficient square grid layout of cities, which forced road intersections to use squared up signaled intersections. Change away from this in North America is somewhat slow, and moreso in dense areas because roundabouts can have a larger and oddly shaped footprint on the land around them, making a change expensive. Roundabouts also have different rules than signaled intersections, which will force drivers to think differently about what they're doing. The most important thing for a road to have for a driver to use it easily, is predictability. If they don't understand how a roundabout works, it will cause confusion, which causes accidents. Because plenty of Americans are uncomfortable with roundabouts or don't want to learn how they work, they'll try to avoid them or resist having them built.",
"They take up more space than a standard cross or T intersection without providing sufficient benefit to merit that space. They are not friendly to pedestrians because there is no pause in traffic. Without having a pulse of traffic you make it harder to control traffic farther down the road.",
"It's a vicious circle. They're rare which means drivers are unfamiliar with them which means public unpopularity and possible raised accident rates which means they're less attractive to city planners which means they stay rare. Historically, one problem is that early traffic circles often had different rules. For example, in many cases traffic on the circle was expected to yield to traffic wanting to join. That's a disaster - it lets the circle fill up with gridlocked traffic to the point that often police directions were required to disperse it. Also many circles were built large and meant for high-speed traffic, yet nonetheless not really built large *enough* for the intended speeds. The design of modern roundabouts, including the importance of the rule that traffic that wants to enter must yield, was only properly worked out in the 1960s in the UK. By that date the above problems had already spoiled the reputation of circles in the USA. Another contributing factor may be that US cities usually have strong grid layouts, and their simple right-angle crossroads work well with traffic lights or yield/stop signs. By contrast the older road networks of the UK and Europe often have roads meeting at unusual angles, or have five or more roads coming together into a single point, and roundabouts work especially well in those situations compared to other junction types. (EDIT: For example the roundabout nearest to me has exits at 2 o'clock, 4 o'clock, 7 o'clock, and 10 o'clock. Imagine that as an all-way-stop intersection. But it's no problems as a roundabout.)"
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5ws98q | Why can't we just cover all rooftops with solar panels to provide the world with energy? | Engineering | explainlikeimfive | {
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"text": [
"Several reasons: 1) It would cost a huge amount of money. 2) The Sun only shines 1/2 the time, at best. 3) Sunlight is very low energy per unit area. This is good or we'd be roasted. Some processes take high energy density, and that's very difficult to achieve with rooftop solar. There are better solar solutions for process heat, like [the PS20 tower furnace]( URL_0 ).",
"Solar panels are still expensive to buy and install and maintain. They can also put stress on the roof. Not all houses get the same amounts of sun (see URL_0 to check a specific house). As prices drop, it would become more cost-effective. In addition, most houses that use sunroofs use it for personal consumption, the current grid isn't really set up to collect, share, and store the generated electricity."
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5wssv7 | What prevents water from flooding houses with chimneys | Engineering | explainlikeimfive | {
"a_id": [
"decpr4p",
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"text": [
"Chimneys generally have a [chimney cap]( URL_0 ) that keeps the rain out. Separately, drain vents or \"plumbing stack\" vents (also coming up through the roof) are often open to the air without a cap, but that's ok because they lead vertically down to a sewage drain pipe. Lots more details [here.]( URL_1 )",
"Chimney caps are the USA norm, think of a metal umbrella. Most cities specify how much larger the cap has to be over the hole. Now in some countries baffles are the norm. Where the water coming down the hole is directed outside but the smoke rising up can maneuver around the baffles to rise out. I'm an American home inspector."
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5x2bgh | How do combination locks work? | Like those basic locker locks that you turn three times. How does it know when you get the second number right to remember the first number was right or wrong? And then if you get the second or third number wrong it just resets? CANT FIGURE IT OUT | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"[This ]( URL_0 ) should help you out",
"Just to provide a written answer... There's an axle that begins on your dial and goes through the center of several parallel disks (there's one for each number). But only the last disk is actually attached to this axle, all other disks in-between are loose. Each disk has a cutout notch. The disks' edges are dragging on a movable metal pin or tab (parallel to the axle) being pushed towards the disks by a spring. To defeat the lock, all disks' notches have to be aligned, which makes a straight gap going through the disks, and allows the pin/tab to slip inside said notches. So, when you start turning the dial, only the last disk moves. Somewhere on its surface there's a pin that's supposed to make contact and attach to a small tab on the surface of the next disk. When that happens, this next disk also starts moving. This pin/tab mechanism between each disk is made in a way that allows the attachment to happen in just one direction, this direction being inverted on each subsequent disk. But when one more disk gets \"picked\", all previous pin/tab attachment will stay locked for both directions. That's how the lock controls the alternating rotation. Therefore as you input each correct number on the correct direction, one more disk starts moving alongside your dial and all previously dialed disks are guaranteed to be kept on the right position, rotating as a whole. When you're entering the last number, you're actually rotating all disks as a single cylindrical pack with the notches perfectly aligned. If you move the dial on the wrong direction at any time, any previous pin/tab attachment will detach and you'll be back to moving only the first disk. The whole combination of the lock is given by the position of the pin relative to the notch on each disk."
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5x3m2p | What is a car engine really doing when it is "warming up"? | Engineering | explainlikeimfive | {
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"text": [
"they are \"warming\"! Chemical reactions inside the motors are more efficient when happen in a range of temperatures. this is usually especially true in diesel motors. Moreover there are other fluids (oil for example) which are less viscous when warmer than ambient temperature, and when it happens motors work better.",
"Well, first off you don't need to warm up the engine of a modern car. They are designed and built to such a fine tolerance you can simply turn them on and drive under normal operating conditions year round. As to what they are doing they are literally warming up, or getting hotter. Since the engine is made of metal which expands slightly when heated the parts of the engine will expand a bit, and the main engine components (the block and head, or lower and upper part of the engine) will expand enough to float off each other a bit when they get fully heated. This isn't a worry because the parts have a gasket between them designed to make a proper seal so no oil or radiator fluid leak out. This has been a problem in the past, some engines from the 70's and 80's that leaked notoriously did because newer materials expanded at unpredictable rates. We are well past the days of those exotic (for the time) alloys and early aluminum head/cast iron block hybrids."
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5x3zx4 | How do tanks turn? | Engineering | explainlikeimfive | {
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"text": [
"Rotate one tread faster than the other and the vehicle will turn. They can also turn in place by running one tread forward and one backward. How well this works depends on the terrain, and they can really tear up a road surface doing it.",
"When a car turns on the road the inside wheels will turn slower than the outside (When the car is fitted with a differential). This also applies to tracked vehicles, the inside track will turn slower, stop or even reverse to counter the movement of the outside track."
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5x6hx3 | How are "scratch and sniff" stickers made? | Always wondered how. | Engineering | explainlikeimfive | {
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"text": [
"Scratch-and-sniff stickers are one of those novelty technologies that sound like such a good idea... But they never really caught on except in children's books and the occasional perfume strip in a magazine. Why shouldn't nasal information be just as important audio and visual information? Perhaps because no one has figured out how to encode language in smells. Nonetheless, if you have kids, you probably have a scratch-and-sniff book around the house. And even if the book is 20 years old, it still works! The reason the stickers last so long is because of the microencapsulation technology used to create them. The basic idea behind scratch-and-sniff is to take the aroma-generating chemical and encapsulate it in gelatin or plastic spheres that are incredibly small -- on the order of a few microns in diameter. When you scratch the sticker, you rupture some of these spheres and release the smell. The smell is essentially held in millions of tiny bottles, and you break a few of the bottles every time you scratch the sticker. The tiny bottles preserve the fragrance for years. -howstuffworks"
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5xag7f | Why do eco cycles take longer? | Such as my dish washer takes 1 hour + on eco but the others take 30 mins. Same with some washer machines. Does this really save energy and how? *Edit - not really sure if this flair is correct or not but seemed like the best fit... | Engineering | explainlikeimfive | {
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"Nowadays the most expensive (energy wise) thing at washing is the heating of the water. Not the engine that turns the wash drum. The dish washer or washing machines need more time because the less hot water needs more time to do the same job like the really hot water. No native speaker, I hope my answer is understandable :D"
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5xahr9 | why do most electronics run on 110 or 220 volt systems? Is there something special about 110 and multiples of 110? | Engineering | explainlikeimfive | {
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"Most electronics dont run on that voltage but use an internal (or like laptops or phones in the chargers components) transformer to step it into the actual voltage required. For the US the 110 is just what we decided to convene as the norm. For devices that require more (say an electric oven or range) they are wired into 2 different \"phases\" each receiving 110 so they add to 220. So your power company energizes the lines at a high voltage/low amperage setting to travel miles on the poles. A local transformer changes that into a few phases of 110 volt supplies, regulated by your electrical panel. Each slot in your panel is from one of these phases, alternating each spot. A single breaker pulls from one phase and supplies those wires in your house with 110. A two pole breaker receives one from each phase and supplies 2 lines of 110 for a 220 total. Your standard receptacles supply your standard plug with 110, and an in line transformer (the larger block somewhere in your charging cable) turns this into what your device uses. Devices designed to operate in your region (presuming the US) will either be engineered to run on these standards, or have some transformer in them to go from the 110 ac to the devices preferred voltage. For your standard cellphone as an example turns 110 ac into a near single digit voltage at 1 or 2 amps. Edit for source: Handful of years as electrician, and many more of repairing my home electronics",
"When electricity started, Edison was using 110V/220V DC at homes to light them. The voltage had to be at leas 110V to drive the lamps. When the war of currents ended, America stayed with the 110V but now AC and the rest of the world started using 220V since the higher the current the smaller electricity loses during delivery, thats why power lines are using thousands of volts to deliver electricity over bigger distances. 110V was needed to drive the lightbulbs, 220V came up because Edison was installing 3 cables +110V, 0V, -110V, so u could use 110 or 220 depending on the circuit.",
"You clearly live in the USA. Electrical power in the USA is supplied as 60 cycles per second alternating current from three phase power lines. These lines are out of phase with each other by 120 degrees. That kind of power only gets delivered to industrial sites which require a lot of electrical power. Somewhere near your home is a transformer. There the voltage from the lines is stepped down to the 220 volts. This voltage is relative to the two power lines. Relative to a neutral line the voltages are only 110 volts. These two power lines come to your house along with the neutral and connect to your load center. Your high current devices, stove, clothes dryer, central AC, run on the 220 volts having those wires run to them through circuit breakers. Ordinary devices being powered from your wall sockets run on 110 volts, only one lead from the load box is run to them along with the neutral wire. It can be either one of the power lines. The load box is wired to keep the load roughly balanced between the two power leads. You have 220 to your house but each leg is 110 to the neutral wire. The neutral and one hot wire run to your outlets.",
"It's actually 120/240 or 120/208 in 3 phase applications.. and peak voltage to ground is 171v cycling at 60 cycles/second 50 for the UK. Most electronics have built in transformers and bridge rectifiers. Transmission of power at these voltages is ineffectime that is why the power lines up top of the poles is usually 14.4kv then small transformer's on the poles for local distribution. It's just a standard that was developed like 277/480 in the USA and 347/600 in canada"
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5xazss | How can I tell if my Earphones are the wrong way around just by the music I'm listening to, even when I've never heard the song before. | Engineering | explainlikeimfive | {
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"Sound guy here. If you're listening to a band, it is very common for an engineer to pan the drums from the drummers perspective in the mix. From hi-hat on the left, to the floor tom and ride on the right. Ie a drum roll goes from snare to light tom - middle tom - floor tom, left to right. If it goes from right to left, you have the stereo flipped.",
"So, here's how it works: Mixing engineers pan individual audio tracks left and right all the time. A very large part of the sounds you hear will be panned, albeit subtly so the track as a whole doesn't sound disjointed. Most people cannot tell at all. This is the point, really. After panning, many engineers use digital tools to \"fill out\" the track. Some songs will have more pronounced panning of sounds. An interesting example I can think of is \"I Want Wind To Blow\" by The Microphones URL_0 Or \"On The Run\" by Pink Floyd URL_1 However, if you just wanna know how to tell them apart quickly... Most decent headphones and earbuds have a marking on the inside or outside that tells you which is the left side and/or which is the right side. Many headphones and earbuds only fit snugly one way. You can always test it with your audio mixer in your smart phone or laptop by moving the audio fader all the way to one channel and see which side the audio comes from.",
"If you had been listening to an old recording from the early days of stereo mixes you might have noticed that drums were typically panned right, lead instruments left, and others (including vocals) panned hard left or right. If you've listened to enough you come to expect the drums on the right, so you would quickly notice if they were on the left. However, you said this was a contemporary recording, and few people mix tracks in this style anymore. I listened to the first 10 seconds of the first few songs of that album on my crappy speakers at work (which is all I cared to listen to) and didn't notice anything immediately that would sound off if switched. Drums these days are usually plotted from the drummer's perspective, as /u/amygdaladefekta mentioned, but not always (You've probably heard it from audience perspective enough for it to not be disconcerting). Seems like this album does use drummer perspective, at least from the little I heard, so it's a possibility. My guess is that there is some subtle difference in your earphones that you have grown accustomed to. If they're not reference quality monitors then there's a decent chance the quality control during manufacture isn't *that* high and there could be some physical difference between the drivers that affects the sound slightly, or some wear'n'tear or just some earwax buildup unevenly affecting things. Your brain would grow used to hearing that particular color coming from each ear - you wouldn't notice it normally, but when it's backwards you do.",
"You're probably not listening to classical music, but if you are, 99.9% of the time the violins will be on the left, and the cellos and basses will be on the right."
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5xdcch | What's the purpose of push to start buttons in cars when you still need to have the keys in the ignition in order for them to start the engine? | Engineering | explainlikeimfive | {
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"You don't need the key in the ignition for all of them, just the older ones. Newer push-button starters only need the key fob in range of the sensor in the car.",
"It's a easier motor skill to push a button than turn a key. It's really just a rediculously minor convenience that gives the impression of luxury.",
"I haven't seen a push to start button where you NEEDED to have the keys in the ignition...my mom's volvo does have a slot for the key, but she can still operate the vehicle as long as the fob is somewhere in the car"
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5xepj5 | What are those weird plastic pieces that sometimes show up on soda cans? (not six-pack rings but these weird...blob...things) | Engineering | explainlikeimfive | {
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"Could be a drop of glue from the machines that glue the boxes that hold them. Could be the food grade waxy stuff they coat the aluminum with. Either way, nothing to worry about.",
"Aluminum cans are sealed with an epoxy resin to prevent corrosion. The blob is probably a drip from the applicator that dried on the can."
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5xhrwq | Why do fans usually have 5 blades instead of more? | Engineering | explainlikeimfive | {
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"text": [
"The fewer blades a fan has, the more efficiently it moves air for a given energy expenditure. More blades interfere with each other aerodynamically. However, to get the full effect, those fewer blades have to be longer, which takes up more space. 3-5 blades represent a compromise between space and efficiency."
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5xkxdo | Why can cool drinks stay "cool" longer than hot drinks in the same insulated travel container, for example, an insulated tumbler or thermos. | Many insulated containers advertise around 10-15 hours for something to stay cool, while only 4-6 hours for something to say hot, even if you prep the container by making it the same temperature as the contents before sealing. In an attempt to prolong desired temperature retention. I thought the increased delta of the temperature in the hotter items would equate to longer perceived "hotness" but that's not the case. Thanks in advance to everyone who comments! | Engineering | explainlikeimfive | {
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"My guess would be the difference between ambient and what it is you're trying to keep temperature controlled. A nice, cold drink may be at maybe 35-40°F. Ambient in a temperature-controlled office environment or a nice day might be 60-70°. So that leaves a difference of 20-35° for a cold drink. Compare that to keeping a hot drink at 160-185°F. The delta with ambient in this case would be 90-125°, far greater than the difference in the cold case. The larger difference means temperature of the hot drink will fall faster compared to how fast the cold drink warms up. Of course, being in hotter weather will shift this, but the difference doesn't hit even until you reach over 95°F. Most people don't stay out in that temperature for very long.",
"The rate of heat transfer through a barrier directly relates to the temperature difference across that barrier. Say the outside temperature is 20 C and you have a cold drink at 5 C and a hot drink at 95C, then the temperature differences are 15 and 75 C respectively. That means the hot drink will lose heat five times as fast as the cold drink gains heat, at least to start with.",
"Let's say you have a container of hot water at 180 degrees and another container with cold water at 35 degrees. If the outside air is 75 degrees, that's a difference of 105 degrees between the hot container and the outside and 40 degrees between the cold container and the outside. Since the hot container has a larger gradient of heat between it and the outside air, heat will flow away from the hot container faster than the cold container will absorb heat. Just like if you had a room of hot air, if you open the door to a room of cold air, the heat rushes out very quickly. But if you have a room of warm air, it flows more slowly to the cold room.",
"Add to what others have said, the cold drink usually comes with ice in it which is intended to keep the drink cool longer. On the other hand the hot drink does not come with heated rocks in it to keep it hot longer. Then add condensation to the scenario. Here is a [school lesson]( URL_0 ) about two cold cups of water, one of which is inside a plastic bag: > The cup inside the bag should have very little moisture on it because not much water vapor from the air was able to contact it. The cup exposed to air should have more moisture on the outside because it was exposed to the water vapor in the air, which condensed on the outside of the cup. When condensation takes place, on the cup outer surface the water vapour present in the atmosphere becomes water particles there by releasing its latent heat. This helps to keep the cup cooler. This does not happen with a hot cup of water."
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5xleft | The relationship between the clutch, the accelerator and the brake in a car | I'm currently learning to drive a manual car, and I'm pretty confident now with changing gears, stopping and starting etc. but still occasionally stall and I'm not always sure why. My instructor's explained to me that I should let the clutch up more slowly but I'm not 100% on why that is. I feel like if I had a more concrete picture in my brain on what the three different pedals actually did, and the relationship between them, it would make it easier for me to avoid stalling. | Engineering | explainlikeimfive | {
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"The clutch slips to allow you to apply less than 100% of the engine's torque to the transmission. Depending on the gear selected, the engine might not be able to apply enough torque to propel the car without stalling (exceeding the engine's maximum torque). You can press the accelerator to increase engine speed, which also increases maximum torque. The balancing act of starting a manual car is to apply enough accelerator to keep then engine speed up while not letting the clutch out far enough to stall the car. As the car starts moving you can let the clutch out farther, as momentum will help keep the engine from stalling. You need to learn this as a muscle memory behavior, like shooting a basketball, because when you are driving you also have to look around and steer the car so you don't hit anything.",
"- Accelerator pulls on the throttle and increases the speed of the engine. - Clutch disengages the gear from the engine; putting the car into neutral. - Brakes pushes the brake fluid into the brake pads; clamping the brake disc and as a result slowing the car down. When you're in first gear (with clutch in), the gear is disengaged and if you release it too quickly, your clutch grabs the gear instantly causing a jerk reaction which will cause you to stall because you're at a too low speed. When you're in a higher gear and you do this, your engine is spinning fast enough where the car won't stall; however you will feel the entire car jerk and somewhat pull you back. Novice drivers sometimes panic and hit the brakes which causes them to stall anyway. When you do release the clutch slowly while applying the gas/accerlerator, it gives the clutch a chance to ease into gear while when perfected; is so smooth that you won't even notice the change. ----------------------------- When you brake; it slows down the engine speed to the point where the higher gear spins at a speed where it wasn't designed to drive at (basically too slow for the gear) and so the car shakes voilently as it comes to a near stall speed. Most instructor will want you to stay in 5th/4th and slow down at the moment where it's about to stall before you engage the clutch (disengage the gear) and comes to a standstill and so you might want to practice that to pass your test. When you do drive on your own however, it saves your brake pads if you drop down a gear and let the engine do the braking. - Lower gears delivers more power but at the same time drops power more quicker than the higher gear; so putting a lower gear on and letting go of the accelerator will automatically slow the car down without the brakes. **Personal note**: Downshifting without using the brakes will cause this jerk reaction if the car is at too high of a speed. You can circumvent through this by simply engaging the clutch, blip your accelerator so the revs go higher (2-3k revs depending on the car) before releasing the clutch and doing your clutch accelerator method. **This lets you slow down without even using the brakes, however DO NOT DO THIS ON YOUR TEST!!!!!!!!!!!!**. -edit- **IMPORTANT NOTE:** WHEN I SAY DROP TO A LOWER GEAR; I MEANT 5 > 4 > 3; NOT 5 > 2."
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5xlrcq | Is it possible to write an algorithm that corrects a low-quality speaker to sound good? If so, why is it not done? | I assume the "quality" of a speaker depends on how equally the frequencies are present. You could easily measure how a (loud-)speaker reacts to certain frequencies and push those which are weak. | Engineering | explainlikeimfive | {
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"It's not quite that simple, yes you can fix a nonlinear response with an equalizer, but you also need to deal with distortion. With a cheap speaker you might put in one frequency, and get a whole bunch of weird frequencies out, due to the resonances of the different parts the speaker is made of. There's also the issue of quality control, with cheap speakers you might not have perfectly consistent manufacturing, so you might need individual calibration data for each speaker coming off the line, that can get expensive. If you want to calibrate it after installing it at home, you'd need a microphone that's been well characterized, and the device playing your music needs to be able to do the signal processing required to correct all the speaker's deficiencies. That would probably require some engineering to model the behavior of the speaker, or maybe continuous feedback from a microphone into the signal processor. (say some of your distortion is caused by one of the panels of your enclosure vibrating, you might know the frequency at which it vibrates from the initial calibration, but to dampen it out you need to know the phase, so your correction interferes destructively with that vibration instead of interfering constructively and making the distortion worse) Also, the speaker's characteristics might change as the speaker ages, absorbs moisture from the air, with changes of air pressure, etc. Finally, maybe the people making cheap speakers don't have the motivation or expertise to pull something like this off, while the people making expensive speakers want to keep selling expensive speakers. You're also never going to fix stuff like the panels of a speaker box rattling because it wasn't glued properly."
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5xmoq1 | Why can't you use suction to clean dust out of computer vents but compressed air cans are ok? | Engineering | explainlikeimfive | {
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"It is a myth. Air flowing past electronics does not create enough static electricity to damage anything. The fans in the PC would be unsafe if that was true. The vacuum cleaner is more powerful, but is not ducted like the fans are. The only caution is to not cause the fans to run backwards and not to overspeed them because they can be damaged. I've been cleaning very expensive broadcast video equipment and PCs for 30 years with various vacuums. Some of this stuff costs over $100,000 and the manufacturers recommend vacuuming.",
"Another thing is that the average compressed air can is about 10 Bar whereas atmospheric pressure is 1 Bar. That means that even with a total vacuum the biggest pressure differential you can get is 1 Bar, vs 9 Bar with the can. More pressure = more dust moving ability."
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5xok9g | What's to stop someone from broadcasting a radio frequency that is already taken by a local station? | For example: if a local top hits station uses 92.5 FM, what's to stop Joe-Shmo from broadcasting on the same frequency and disrupting the local stations radio? | Engineering | explainlikeimfive | {
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"He will quickly be located and shut down by the FCC. Plus, he would need some powerful broadcasting equipment to disrupt the radio station over its whole area. That equipment is expensive to get and too big to hide.",
"my high school electronics teacher was fond of answering similar questions with, \"but then they triangulate your signal and the big burly FCC guys show up at your door. \" My buddy likes to broadcast his favorite music, pirate style, but he does it from a truck and gets away with it. probably not enough range to ruffle any government feathers, just a few confused commuters from time to time ..trying to figure out why Rush Limbaugh suddenly dropped the bass.",
"Amateur radio clubs sometimes have a contest called a \"fox hunt\" in which someone will set up a transmitter in a city (on a legally available frequency) and the rest of the club will try to locate it by tracking the signal. If amateurs can do it for weekend fun, a government law enforcement agency is gonna be more than capable.",
"So here is a true story. I was on a military exercise in nirthern california. I am electronics technician and responsible for the operation and maintenance of RF (radio frequency) equipment. We were operating in the VHF portuon of the spectrum and had a single channel plain text (unencrypted) net set up using 89.7 mhz as the transmission frequency. At one point our primary net went down due to equipment failure and switched to the 89.7 mhz frequency. After operating on thatvnet for about 4 hours a helicopter was circling our position and 3 federal agents in government vehicles arrived at the entry control point of our basebin the field. We were told that we were interfering with a public broadcast and needed to cease operations on thay frequency immediately.",
"Isn't there a malcom in the middle episode where hank tries doing that, and some government people chase him, because it's illegal",
"The law. And that's about it. But you'd be surprised just how many legal hoops you have to jump through before the law is fine with you transmitting anything.",
"That is \"pirate radio\". And nothing really stops someone from doing it, other than the fact that you'll get found and get in trouble with the FCC fairly quickly. Well, that and the initial cost of building a transmitter.",
"nothing other than laws. if you did it one time, nothing would stop you. the station would report it to the FCC and they'll log it. if you keep on doing it, FCC will send a team to track you down and when they catch you, they'll toss you in jail for it.",
"There is an old Christian Slater movie called [Pump Up The Volume]( URL_0 ) that explores this very topic. Can't say it's super accurate, but I remember it being a decent 80's \"Teen Angst\" type movie..",
"Someone actually does this on a small scale on the interstate by our house. AM station randomly turns to Bluegrass for a very short distance.",
"Now what's really interesting is if you did this on the 2.4ghz spectrum with a big enough transmitter you'd shutdown wireless networks citywide. They'd probably also charge you with terrorism.",
"Physically, nothing. Nothing at all. That said, there are people who will be upset by it, and will track it down and turn it in. That then leads to five-digit fines and potentially jail time.",
"I assume that's why at night when your station turns into Mexican radio it's because they don't comply with FCC. I don't know why it seems to happen only at night either. Someone needs to ELI5.",
"I once built a portable FM transmitter that runs off of a portable battery used to charge cellular devices. The range was about 100ft. The transmitter could broadcast on the entire FM and AM band, meaning I could set it to any popular station and everyone within 100ft would hear what I was broadcasting if they were on that particular frequency. As long as I'm moving I.e in a car, they will have difficulties tracking since they use the tri-locate method described in the comment section. P.S I made it as a prank to mess with a friend who loves alternative music, or rather, hates popular music. I put magnets on it and attached it underneath his car for a week. I made it play pop music on all of his favorite alternative stations."
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5xpt2h | What makes it so hard for countries to develop nuclear weapons? | It seems to me as if it's always reported that countries like NK, Iran, etc, are still *trying* to develop nuclear weapons. Why are they unable to? Is it a technical issue (can't get hold of required ingredients), a knowledge issue (simply just don't know how to do it), a political issue, or something else? All of the above? | Engineering | explainlikeimfive | {
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"There are a few issues building a nuclear weapon. First is the scientific and engineering know-how. Not just of the weapon itself, but the delivery system. Building reliable rockets and missiles that can be depended on to deliver the nuclear bomb is difficult. See how many times NK has had a missile test failure. Even countries with established rocket/missile programs have occasional failures. Next is, it's easy to build nuclear bomb that will fit in a semi-truck trailer. Shrinking it down to something that will fit in the nose cone of a rocket is difficult. You might hear in the news about \"dual-purpose\" equipment. Stuff that can be used both for peaceful and weapons. For example Iran's centrifuges, and other nuclear material processing equipment. Or stuff that can be pretty much used for one purpose, such as high precision altimeters. Key components that are dual purpose or single purpose are carefully monitored by various government agencies, and the buyers of those components are screened and monitored. The buyers of radioactive materials, the mines and other stuff are always monitored. Finally there's the testing, a lot of pressure is placed on not allowing the testing, so countries cant refine their weapon and optimize the effectiveness and reliability of the weapon."
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5xrprv | How do Formula 1 cars produce such an iconic sound? | Engineering | explainlikeimfive | {
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"A very basic answer: a relatively small engine, producing huge amounts of power, with no sound restriction, and then running at well over 10,000 rpm. Where most engines would be exploding, formula 1 are just getting started, and redline near 20,000 rpm."
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5xxrau | How does wiring in work in electronics, and why are there so many different size and types of wire? | Engineering | explainlikeimfive | {
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"Think of the wires like tubes and the electricity as water. Now imagine you need to fill a swimming pool; would you use a small drinking straw or a large hose? The wire depends on how electricity needs to flow through said wire. More electricity flow = larger wire, Less electricity flow = smaller wire."
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5xy0eg | What is C and how is it different from the other types of programming? | Im taking an intro to engineering course and I've been wanting to take a step into the digital world for a long time. Im doing a project that deals with the introduction to C and when she writes on the board, all I see is letters and random words. Im not sure what any of them mean in the computer world. Can someone help me speak computer?? | Engineering | explainlikeimfive | {
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"Disclaimer: not an expert, I actually have no experience in C but I have a grasp of the concepts. Most common programming languages that you see or hear of today, be it Java, C++, or the web dev trio, HTML/CSS/Javascript, are what's known as 'high level languages' and typically go through several layers of abstraction before they're able to be executed by the machine directly. (For example, Java runs on another program called the JVM, which translates it's code into code for the platform it's running on, which is why it's so portable across operating systems) High-level languages generally abstract away concepts like pointers (which 'point' to a specific position in memory, which is helpful for remembering where you stored a value), and you're left with variable names which essentially do the same thing but don't have a lot of the difficulty associated with pointers. (These probably make up about half of those random letters and words, the other half being functions) C is a significantly lower-level language, but it also gives you more direct control over memory. You can directly manipulate segments of memory rather than having a memory management system do it for you. It's also commonly used in robotics because it's excellent for single-purpose tasks like translating a physical button into turning on a motor. Now, these definitions don't exactly answer your question. Programming is generally very structured and has specific naming patterns, and they can seem confusing or otherwise incomprehensible by the average layman. In low level programming such as C, you're generally going to see two major types of things being named: Pointers/Variables and functions. Functions are like mathematical functions, except that they can be called any time and can obviously do a lot more than just mathematics. Variables, or pointers in lower-level languages, basically store directions to getting a specific value in memory. These values can be simple, like a number or a boolean (true/false value), but they can also be more complex, carefully ordered structs (To people who know C, C has structs, right?) which can contain many values. Now, functions and variables can be named just about anything, and C's standard libraries (the functions which \"come with\" C) often have very confusing naming schemes. It's a matter of having the proper documentation on hand. Learning programming can be a tricky task, but there's many ways to get help and resources. Other redditors, if you would kindly link some, go ahead. I'm too lazy at the moment. Also please correct me if I made some huge mistake, or tiny mistake if you choose."
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5xy4is | How do wooden sea ports not rot and fall apart over time? | Engineering | explainlikeimfive | {
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"Wood doesn't really break down that easily. Wood is waterproof from the sides, so long as it isn't damaged. And even then only part of it is accessible by water. Wood is like a bundle of straws. And the on way to break it down is to enter through the ends or physically break it down. The wood used in peers is pressure treated to be water resistant and anti microbial. So it takes a long by time to degrade."
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5y0jju | What is happening when I change gears in my manual transmission? | Bonus for whoever explains what the differences in mechanics are for different types of transmissions. | Engineering | explainlikeimfive | {
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"The same that happens when you change gears in your bike, my dear 5 year old. You want to pedal a lot and not be tired or pedal a little and with all your strength, climb that hill. That's manual transmission. Automatic transmission makes the choice for you. The motor of the car is coupled to the wheels in such a way that it transmits the rotation of the motor to the rotation of the wheels. The rate at which this happens is the gear. Reverse adds a further cogwheel to the system so that the rotation of the motor gets transmitted backwards to the wheels. Manual transmission requires you to disengage the gear before engaging the next. That's what you do with the clutch. You \"disconnect\" the motor turning cogwheel from the wheel's turning cogwheel. Select appropriate cogwheel (gear) release the clutch so cogwheels are \"connected\" again and motor rotation is transmitted Automatic transmission forces the gears to slip to the next one whenever the motor reaches a certain number of rpm. In manual transmission you have full control of the motor. Look at this [diagram]( URL_0 ). The cogwheel from the engine is green."
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5y0zpd | What happens when astronauts clog the toilet in space? | Engineering | explainlikeimfive | {
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"There's not really anything to get clogged because space toilets don't have plumbing like Earth ones do. For solid waste, the astronaut \"sits\" over the opening which has a plastic bag underneath. There's gentle suction so the waste collects at the bottom of the bag. When he or she is finished, they push the bag through a hatch into a larger conainter that holds all the bags until eventually they get loaded into a cargo spacecraft that burns up in the Earth's atmosphere.",
"One of the astronauts has to put on the suit and go outside the ship. He has to reach up the poop chute and pull out the clog. Sometimes they use a plastic bag to put it in, but usually they just leave it floating in space. Sometimes another ship comes along and runs into it This is why the shuttles have windshield wipers.",
"I feel like astronauts diet's are well regulated enough that they don't have massive pizza/whiskey/beer shits every morning like us real American men."
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5y19zp | How is tap water not full of mold and algae when nobody cleans the inside of the pipes that carry it? | Anything wet that I leave outside accumulates mold, algae, and other gross stuff over time. Given that drinking water pipes are not regularly flushed out with bleach or something, how is it that drinking water is not totally filthy from going through dirty pipes? Edit: thanks for all the responses guys! Especially from the water treatment and plumbing experts. Didn't expect to get such a big reaction! | Engineering | explainlikeimfive | {
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"> drinking water pipes are not regularly flushed out with bleach or something They are, essentially. Drinking water supplies contain a low concentration of chlorine bleach or another disinfectant to prevent germs growing. Also the pipes are sealed, with valves and taps designed to prevent air containing germs being drawn in, and they're opaque so light algae need to grow doesn't get in. EDIT: As many people have mentioned, not all places and countries leave the disinfectant in the water. Ensuring that it's clean when it enters the pipes - either with chemicals that are removed or with UV light - along with the pipes being airtight and dark and unfavourable to life is when done correctly enough to keep the water clean.",
"Public water supplies DO have chemicals added, but for people like me that live in rural areas with private wells, essentially it's just the process of using the water on a regular basis that keeps it fresh. Algea and such come from surface contamination, but well water left in pipes for a few weeks or more may get stagnant or have rust from old steel pipes. Last summer I inadvertantly left my garden hose running all day and ran my well dry. After it finally refilled in a day or two from the surrounding ground water, I had to \"reprime\" the system and let the water run to clear out large contaminants like minerals and rust. The water smelled funny and was brownish for a few days. Even under normal circumstances, I probably ingest small amounts of of microscopic minerals, small celled organisms, rust,etc. Not enough to be harmful, some of the minerals might even be good for me. Remember, humanity has been drinking \"dirty\" water out in nature for most of our existence.",
"To add, modern construction uses copper pipes from the municipal main and throughout the entire house. Copper is self disinfecting, as it's toxic to microbial life. That's not why we use copper, we use it because it's cheap and easy to work with, but it's a convenient consequence. If there were microbes in your plumbing, the surface of the pipes would be a hostile environment for them.",
"As someone who designs municipal water systems, if you have a length of pipe that isn't being used enough and the water sits for more than 48 hours, it is considered stagnant. This is a condition to be avoided. To prevent this, we make sure to connect the water system to itself at many points to increase flow, not use excessive pipe sizes and avoid dead ends in the system.",
"It greatly depends the country you're in. A lot of commenters here mention chlorine as main means of desinfection, combined with copper piping. That certainly is the case in the US and many other countries. In other countries, like the Netherlands where I live, chlorine desinfection isn't common practice. Only 20÷ of households in the Netherlands recieve chlorinated water and in that case chlorine isn't used as a primary desinfectant (as that's not allowed), so the chlorine concentrations are very low. Primary means of desinfection is UV or ozon treatment (at the treatment plant). Growth of biological contaminents in the (mostly PE or PVC) piping is prefented by making sure no contaminents are present in the water before it enters the system, combined with measures to prefent introducing contaminents during transport, such as desinfecting piping with silverperoxide before use and mandatory anti-backflush valves at house connections. Apart from the methods mentioned above, there are many more options that are used around the globe, with fluctuating results; in some countries tap meets drinking water standards, sometimes even of better quality than bottled water (like in the Netherlands), in some countries tap water isn't meant for consumption as drinking water but only for use. While the Dutch take great pride in their drinking water quality, something could also be said for not cleaning the water you use for your washer / dishwasher / shower up to drinking water standards.",
"Plumber here, this is actually a concern for unused pipes, when a house is connected to a municipal water supply it receives treated water. That water treatment includes chlorine which among other things kills bacteria. Water quality varies from house to house and so additional treatment is sometimes necessary to maintain good quality. As long as the water is not stagnant In the pipes the system should be maintained at a satisfactory level. Water quality is a semi complicated subject but that is a very basic explanation.",
"Water Treatment Operator here. In the drinking water plant they add more chlorine to the water than is necessary to deal with any of the bugs that lived in it. This leaves extra floating about ready to deal with any other bugs it might possibly encounter in the pipes under the road or in your own house. On top of that to make sure that there is always water with some of that extra chlorine in it operators will sometimes run taps at the dead ends of the underground pipes. These constantly run water, and make sure that the older water gets pushed out of the dead end pipe by fresher water. Also, operators like me (or people we pay) will routinely go around to fire hydrants and open them up full bore and spray a bunch of water all over the roads or into ditches or whatever. This not only makes sure fresh water gets to all the pipes, it also makes the water run really fast through the pipes and it scours off any bugs, or buildup in which they could live, and spews them out of the hydrants.",
"Quantity Surveyor for a water contractor in the U.K. Here. We operate a service called Trunk Mains Cleaning which basically uses a giant spinning metal brush to clean the insides of large diameter mains. The debris is then flushed out at terminal or inline hydrants. This process will commonly cause small problems later with sand and debris coming out of the supply pipes at customers houses which plumbers then have to flush out for us. When water mains get to old the infrastructure maintenance program that we have uses a method called pipe bursting to replace old ductile iron pipe with new P.E pipe of the same or larger diameter (a machine with a large arrow head smashes through the old pipe while dragging fresh pipe in behind it). Tldr Large mains are cleaned with a big brush, small mains and service pipes are flushed or, if they are to old, burst through and replaced with the same or larger diameter pipe.",
"Those organisms need soluble oxygen and sunlight as an energy source to grow and develop; sealed water mains are considered a zero oxygen environment and does not have any sunlight getting to the water. The water utility I manage does not leave a small amount of chlorine in out distribution system (called precautionary disinfection), we do not chlorinate at all, the water we drink come straight from the ground to our storage tank. We also are required by CalEPA to conduct monthly monitoring of our distribution system for bacterial contamination, positive hits occur rarely. (Source: I am a certified water and wastewater treatment plant operator in California)"
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5y7o6u | why do you need to switch on so many things when starting a helicopter? | What are all those switches controlling? Couldn't it be replaced with a single switch for the whole process? Does it happen that you flight a helicopter without turning on several things? | Engineering | explainlikeimfive | {
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"In not only helicopters but most aircraft there are several systems needed in order to sustain flight, such as hydraulic systems, fuel systems, bleed air systems (air supplied by the jet engine providing lift), air conditioning and oxygen, lights, navigation and communication, and electric systems. There could also be multiple systems for redundancy/emergency. All of these switches are turned off to conserve power, make maintenance easier, and prevent accidents. Edit: words",
"I think this has been answered pretty well, but I wanted to draw a comparison to cars to maybe shed more light on it. I fly airplanes, not helicopters, but a lot of the instrumentation and controls are similar. My car has a push-button to start the engine if the radio key is in your pocket. When you push the button, the car's computer negotiates with the key then turns on an electric fuel pump, primes the engine, turns on the starter motor, and enables the ignition system. Once the computer detects that the engine is running, it shuts off the starter motor and turns on the dashboard lights, the radio, and the daytime running lights. While you're driving, the computer monitors a hundred different sensors to make adjustments to fuel/air mixture, ignition timing, and emissions controls, while also monitoring the electrical and charging system. When you want to turn the turn signals, headlights, tail lights, or fog lights on/off, you probably move a single switch which controls all those lights in different combinations. Here's the catch - that computer is a single point of failure for *every single system on the car*. They seem super reliable; lots of people will drive hundreds of thousands of miles without a hiccup from that system. But not everyone - cars occasionally stop communicating with the key, sensors occasionally fail and confuse the system, and electronics occasionally do unexpected things. If you've owned a newer car and gotten recall notices, you'll see a similar trend. For a car, this is a bit of an inconvenience, and you might get stuck in a bad neighborhood or by the side of the road at night. For an airplane or helicopter, this is not an inconvenience, it's a full-on emergency. You can't pull over because the computer flaked out. Aviation is all about separate systems - no matter how confused the battery charging system gets, there's no way for it to affect the ignition system (in fact, airplanes mostly still use an ignition system called a magneto, which was phased out for more efficient, flexible systems in cars by the mid-1930's, because it's fully self-contained - an aircraft engine can run indefinitely with no electricity or outside control or monitoring, as long as you keep giving it fuel). So instead of having a computer overlord turn on all those systems, each one has its own switch for the pilot to operate: 1. Master battery switch - This does make for a single point of failure for the electrical system, but it's not a cheap switch and it still has no control over the engine. 2. Electric fuel pump - This is a secondary pump to supplement the mechanical pump in the engine during critical phases of flight (more redundancy). 5. Priming pump - not a switch, usually a manual pump with a plunger sticking out of the panel. 4. Ignition switch - probably a key in private aircraft, might be a simple switch in military stuff. Selects either or both magnetos to give the pilot control over how the engine is running. 2. Starter motor - hold until the engine is running, then let go. 2. Master avionics switch - Sends power to the flight instruments. 2. Radio switch - Turns on the communication and navigation radios. 6. Strobe light. 5. Navigation lights - wingtips, etc, maybe also instrument panel lights (same idea as car tail lights). 6. Landing light (same idea as headlight). 0. Pitot tube heat - electric heating element to make sure your speedometer keeps working in bad weather. On top of all that, when the pilot is starting they plane they'll probably be changing radio frequencies to get a weather update or flight clearance, and changing settings on the various instruments to suit that flight. And, there are levers to control the fuel/air mixture and a few other things modern cars adjust for themselves. All told, they have to handle more than a dozen controls on the dashboard, because we can't trust a computer to manage all those things reliably enough. And this is on a simple single-engine prop plane; anything with a jet engine, multiple engines, oxygen systems, pressurization, or autopilot typically adds a couple extra switches for those systems."
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5yeczd | How do submarine-launched missile get to the surface to a point where they can ignite? | Engineering | explainlikeimfive | {
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"- The missile is contained in a special canister - When the missile is launched, the water rushing into the launch tube (combined with some high pressure air), pushes the canister to the surface - When it reaches the surface, the canister bursts open and the missile engine starts up - The missile does its thing"
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5yekcr | How do The train-stoppers at the end of the rail work? | Engineering | explainlikeimfive | {
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"You know the spring door stopper behind many house hold doors. Same concept. It's not made to be slammed into by a train but if the train were to roll to far or be under a little power the train stopper can absorb some of the impact and push the train back and keep it from falling off the tracks so to speak",
"They are like heavy duty springs, If the train is slowly rolling toward it it will push it back the way it came. If the train is going full speed it might as well not even be there.",
"What do you mean by train stop? Can you post a picture?",
"They are sort of like when skydivers wear helmets. If you're going slow and bump into it, it works. If you're going fast and slam into it, it doesn't work."
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5yexhg | The purpose of the turbines you see in the top areas of road tunnels | I've been seeing lots of these in videos. Can anybody explain why they have these? Edit: I mean, those things that look like jet engines that are at each end, and are connected to their twin at the opposite end by a tube. They hang above the traffic. Answered: Thank you all so much. Ill be back with new threads with more questions tomorrow | Engineering | explainlikeimfive | {
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"It's likely an exhaust or intake for ventilation. Road tunnels are full of cars that give off toxic fumes, this can prevent build ups. But without knowing specifically what you're talking about that's my best answer.",
"The large turbine-like fans are there to generate air flow through the tunnel. This is so as to prevent the build-up of toxic gasses in the tunnel. These systems are often combined with emergency extraction fans which can be activated in the event of a fire, so as to reduce the chances of death by smoke inhalation. See: URL_0",
"Heard from engineer in ATL about this once, while sitting in traffic in a tunnel with them -- it has to do some with what was already mentioned, but also with the structural integrity of the tunnels. Heat builds up during static traffic scenarios and compromises tunnel materials. It helps a good bit with the upkeep of tunnel repair.",
"Fires. There have been several bad fires in tunnels where people ended up dying. The huge fans pull out the smoke so trapped drivers don't suffocate. Same reason for side escape tunnels. NFPA 502 code Chapter 11.",
"Just to clarify a bit, the other commenters who have mentioned ventilation are correct, but I'd like to specify that they are indeed fans and not turbines. Fans accelerate air whereas turbines extract work from moving air.",
"They are used to keep the air 'fresh.' They protect from toxic build-up from car exhaust and keep it smelling less.",
"As most people have said its to do with air flow to remove fumes. You'll also see it in basement car parks where natural ventilation isn't possible. It's harder to exchange a volume of stale air/fumes there due to corners as there's not clear path through (ideally air is drawn in near the entrance and out through vents on the other side) so vortex fans are used to direct it/increase flow rate/volume."
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5yj4e0 | I have multiple pairs of Levi's 513s, 33W 30L. Why are every single one of them completely different? | One pair is probably 30W, I can barely get them buttoned. Another pair is probably closer to 36W - I can take those off while they're buttoned. Most of them are way longer than they should be. I picked this style and size (513, 33 30) because of one pair that fit perfectly. Why the fuck can't they make that same pair again? | Engineering | explainlikeimfive | {
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"It's very possible that they were, at least at one point, the exact same size, and they have stretched or shrunk because of normal wear and washing. But in reality, clothes really aren't manufactured that well. My office (economics and statistics consulting firm) did a study of clothing sizes. It's 20 years old now, but the findings were surprising. The normal 'variance' in a given size of clothing was larger than the distance between sizes. In other words, your 33W's are 'usually between a 31 and 35'. And that's normal. Moral of the story: sizes are inaccurate. Try each article of clothing on, and for it's own fit.",
"As others have said, it's just poor quality control. They could make them more uniform, but they would cost more money.",
"Levi's are made in multiple countries, from varying types of material. Every pair is different, regardless of what the model number and label size says."
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5ykxej | Why do cone filters change the engine's sound? | Hi, i always hear around that changing your air filter to a cone filter makes your engine "noisier". But i don't understand why? Shouldn't the sound come out from the 'silencer' in the exhaust? Am I missing something? Thanks in advance | Engineering | explainlikeimfive | {
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"It changes the factory intake harmonics. Engineers spend a lot of time reducing NVH (noise vibration harshness)"
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5ymtek | What are Tesla's "Battery Farms" and how do they work? | Engineering | explainlikeimfive | {
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"Australia has a problem. The ways that they generate electricity are fairly constant from moment to moment, but the demand for electricity is not. While they have lots of resources and abilities to generate electricity, demands are far too spiky. Meaning, during the hottest times of the day everyone is turning on their AC. That uses up LOTS of electricity. Most of South Austrians generation is done through wind power and that's a fairly constant generation, even overnight. So while on average demand is meeting supply, there's a problem of timing. Basically, there's lots of electricity at night time, when no one wants it and not enough at noon when everyone needs it. This causes blackouts, and that's bad. The solution here is to store the electricity for use later. Generate it all day and store it in batteries so that they can draw down during the hot times. That is a battery farm. It's really just a very large amount of batteries all in one place. Tesla recently has been building the world's largest battery factory (called the Gigafactory). Batteries, funny enough, are one of the things in this world that we basically can't make enough of. Batteries are in VERY high demand for everything from laptops, and cell phones, to electric cars. So using them for something like this battery factory was previously kind of a nonoption. It simply took so many that it would be too expensive. So electric utilities would look at other solutions like importing electricity from other districts or turning to non-renewable sources that can be easily turned on and off (like a coal plant). Tesla's very large factory has recently started pumping out batteries and that is what's allowing Tesla to do things like sell battery storage products to the home consumer market (the Tesla power wall), sell inexpensive electric cars (like the Model 3) and do battery farm projects like this.",
"They're basically just a really big battery. When you're using fossil fuels to generate power you can just crank up your generator (give it more fuel) to meet demand, but you can't do that with renewable energy. For example, if it's a really hot day and everyone turns on their AC you need more power, but if you're using wind turbines you can't just turn up the wind to meet the demand. With batteries, you can store energy when you're making more power than you need and use it when you're not making enough.",
"Electricity isn't used consistently through the day. Everyone's at work through the middle of the day so there's not much electricity need in the suburbs, but high demand downtown. In the afternoon and evening everyone comes home and does their laundry, turns on their video game consoles and starts cooking dinner, whereas all the offices and factories cool down for the night. Power demand is weird and keeps moving around. Electric generators would like to keep generating a constant amount of power, but the demand is always changing and complex systems are needed to make sure they're balanced. At night there's very little demand, so what do they do with the generators? With coal plants and nuclear plants, generators are actually connected to enormous and [extremely heavy turbines]( URL_0 ) that work by steam pressure. They keep spinning because there's a lot of momentum, and just let the generator spin while disconnected. This is a way of storing extra power generated as *kinetic energy*. It's a problem for Solar Panels and Wind Turbines that they can generate power at whatever time is convenient, but they have no or few heavy parts to use for storing extra power as kinetic energy. So in order to store the extra power generated, we have to build giant batteries. Battery Farms are like much more efficient ways of connecting a whole bunch of car batteries to each other in a warehouse-like building. The batteries are better than the ones you'd find in your car, but the principle is the same.",
"Imagine power is an apple that you want. I only have 2 hands. so you come to me for 1 apple I hand you 1 apple. You and your friend come to me for 1 apple each, I can hand 1 apple to each of you. 1 with my right hand, 1 with my left. You bring a 3rd friends and I can't hand them an apple at the same time because I only have 2 hands. Tesla batteries are like a tray I can place my apples on. I can still only place 1 apple per hand on the tray at a time, but I can just stock pile them on that tray all day long, even when you aren't there asking me for an apple. Then I can just let people grab their own apples when they need them.",
"It's Analogous to water supply. We have enough water in a reservoir but getting it to you when you need it from the reservoir is difficult because you would need to turn a pump on and off depending on when people need it. To solve this instead of turning on and off the pumps we store the water high in the air. The energy to get it to you is ready there so the ability to get water to you is independent from demand fluctuations. Same thing here. They have the energy but getting it to you when you need it is difficult due to timing and demand fluctuations. So they are trying to store energy in batteries as potential so it can be used whenever. Electricity is more difficult that water, because the batteries are more expensive, and you lose energy when you convert electrical to potential.",
"There's lots of correct answers here, but no one has addressed the \"But, why?\" question -- why do we need to store it in the first place? Electricity flows from one place to the next. There's a source and a sink, a producer and a consumer, a plus and a minus. But, electricity does NOT go anyplace if there's no place for it to go and be used. All those windmills turning at night? They're not generating electricity if there's no place for it to go and be used *at that very instant*. Which is WHY we need battery farms in the first place. Now we CAN generate electricity at night, because now it has a place to go -- and here, the water tower analogy is a good one.",
"The concept of a battery farm is that you set up a building, or several filled with the relatively new \"house batteries\" that Tesla has created or their equivalent/better. What this does is it allows you to store power produced at off-peak hours that can be used to supplement the grid at peak hours. This also makes variable power production like wind or solar more viable for primary power production as you can store power from the day for nigh or cloudy days, or can store power from windy days for calm ones. Building these is also a way to help increase the distance you can transmit power as you can put them at the drop off points and store up a larger charge for the next leg of transmission. This would not be extremely efficient, but it is better than not being able to transmit the long distance at all and could theoretically mean that you need fewer power plants. This means you could in theory build a lot of solar plants in say a desert and supply people far away from said desert.",
"To put it simply, think of it like an external battery/powerpack that you can buy to charge your phone. On an average day, you don't need it. But let's just say, you're on a long flight and want to play games on your phone to pass time. You know your phone wont make it through so you use your power pack to charge it back up. Battery farms work the same way. Your consistent use is met by the usual power sources, but when there are spikes in demand, you can use the battery farm to supplement the higher load. And this battery farm can be charged by your usual power sources when there is surplus load (night time, cooler days etc) or by renewable sources (sun, wind etc.) so that they're charged and can be used as needed.",
"Follow up question, to my understanding all of these large battery packs are built upon the humble 18650 cell; why? Is there a size constraint to battery cells that prevents the building of larger cells? Do they become less efficient or increasingly expensive when you build a cell larger than a few inches?",
"Batteries? A reservoir would be the first though surely? Lots of batteries?",
"Ever see The Matrix when Neo unplugs and flushes himself? It's not like that at all!",
"They are a bunch of batteries that store electricity. Usually electricity from things like solar or wind. Solar and wind energy isn't created on demand. Its created when its created. So you store it in a battery farm. The battery farm then provides energy on demand, like when you turn on your air conditioner or clothes washer. Works like a capacitor in electronics: smooths out the flow of electricity(voltage in the case of capacitors).",
"They are giant batteries because \"renewable\" sources are not consistent (the sun does not always shine and the wind does not always blow) so you need the giant batteries to store the electricity for the times when the sources aren't producing electricity. The problem with them is it makes \"renewable energy\" not renewable because the battery farms are lithium ion batteries and lithium is not renewable and mining it is just as bad if not worse for the environment than fracking."
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5ynms9 | Why does a phone charge faster when the data is switched off? | Engineering | explainlikeimfive | {
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"Imagine a jug of water with a valve at the bottom that can let water out. If you fill up the jug while the valve is open full blast it will fill very slowly, as water is draining out of the bottom at the same time; if you fill up the jug while the valve is almost closed it will fill much faster as the water is draining out much more slowly. Your phone charge follows a similar concept. If you have all of the radios on, the phone is using a good deal of power even while it is charging - this is similar to the jug valve being open full blast. If you turn those radios off, the phone uses less power and thus charges faster - this is similar to the jug valve being almost closed."
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5yvri0 | What prevents Tesla cars that are powered by lithium ion from exploding in a traffic wreck? | Engineering | explainlikeimfive | {
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"The battery is protected by an armor plate made from aluminum and/or titanium (depending on model) and divided into separate compartments. This provides decent protection against damage to the battery that could cause it to catch fire. Battery fire is still a risk, but remember that you aren't comparing it to no risk at all, you're comparing it to a risk of fire from a spilled tank of gas, and compared to that it really isn't bad at all.",
"Also, the batteries are made up of thousands of small lithium ion cells, so in the event of a crash a crash, a few of the small cells might explode as opposed to one or two big cells being ruptured",
"The entire pack is liquid cooled, and is designed for a controlled burn in case of fire. A few Teslas have caught fire since their inception, including ones in very high speed collisions and none have exploded outright. The packs tend to burn hot, and are difficult to put out in their own right. But do have the advantage of not *leaking a flammable liquid that floats on water*.",
"Something I don't worry about driving around in my vehicle filled with a hundred litres of explosive liquid. We're pretty normalised to that now. Lithium battery fire doesn't seem that bad by comparison. They're both a pretty deadly compromise to make for the convenience of personal transport. Now hydrogen fuel cell cars, that's when I'll start worrying!"
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5yxzmf | How was it possible for electric cars to exist 100 years ago when the technology only recently became mature enough to become practical? | And what kinds of batteries did they use? It seems to me that electric cars are becoming popular right now in large part because the necessary technology has advanced enough for it to be practical. With the newest batteries and efficient motors and what not electric cars seem to finally be able to compete with gas-powered cars. How could they possibly have worked a hundred years ago? | Engineering | explainlikeimfive | {
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"125-150 years ago cars were a relatively new technology, and it wasn't at all clear that gasoline-powered internal combustion engines were the way to go. Back then the differences between the two were not as extreme. In particular, it was the introduction of mass production by Henry Ford in 1908 with the Ford Model T (which used a gasoline-powered internal combustion engine) that heavily contributed to tipping the scales in favor of gas-powered cars. So gasoline-powered internal combustion \"won.\" As cars powered by internal combustion engines became cheaper to produce and thus more readily available, investment in furthering the technology of electric-powered vehicles decreased. That said, it's really kind of unfair to characterize electric cars as \"finally\" able to compete with gas cars. Gasoline powered internal-combustion received hundreds of billions of dollars in investment over the last 100 years; electric cars didn't. It wasn't until the gasoline shortages of the 70's and 80's that the industry started thinking about investing in electric vehicle technology again. If both technologies had received equivalent R & D over the last century, electric vehicles would have been competitive long ago. But that's not how technological progress occurs. In the early stages of development of a new technology, there are typically a number of competing options, but eventually an industry gravitates to a smaller number of options -- or even one option -- because of some particular advantages (typically cheaper to produce). Then the lion's share of investment gets committed to _that_ option, and it progresses faster than the other options, cementing it's lead. Eventually, though, as alternative technologies continue to slowly develop or faults in the \"winning\" technology become apparent in the long-term (e.g. with cars, fossil fuels' impact on the climate), another option that in the past might have been more expensive to produce or less efficient or whatever, starts to become cheaper or more efficient and can re-emerge. Partially, this is what's happening with electric vehicles. tl;dr -- If Henry Ford had gone with an electric engine instead of a gasoline-powered internal combustion engine, the history of transportation would have been different.",
"Electric cars of the 1880s were very fragile things with very short range and heavy (for the time) batteries, just like electric cars of 1980s and 1990s. But back in those days, competing petrol cars were no good either. They were a nightmare to maintain, hard to start, hard to drive (controls were nothing like today's cars) and you needed good mechanic skills to drive them. Electric cars, in comparison, were only a little slower but much easier to start, stop, maintain and repair. They were often preferred by women drivers and those who didn't want/afford to hire a driver.",
"The big difference now is new kinds of batteries. Interestingly, when the car was a new idea, running one on steam or electricity was as valid as petrol. In cities, electric may have seemed preferable. The big disadvantage was basically how far the car could go on the batteries it carried. In them says I guess it would have been simple lead acid? New Lithium Iron batteries get you much better range for their weight. If you are ever in stuttgart, you can see one of the first Porsche cars at the museum and that's electric."
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5yyv2a | The differences between the types of welding and their uses. | Engineering | explainlikeimfive | {
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"This is not something easily answered here. The real answer would fill a book. There are many techniques depending on what and where you are welding and what the weld needs to accomplish. The most common techniques for metals are spot, stick and TIG and MIG wire feed. There are also weld techniques for other materials such as plastics. At its heart it is using melted material to bond solid material.",
"I'm no expert at welding but I do know a few things - Shielded metal arc welding (SMAW), basically stick welding, is typically used by home-gamers to make repairs on equipment because of the ease and simplicity of use. It can be used to weld in windy weather since the rod is covered in a layer of flux, but it creates a lot of slag that has to be chipped off of the weld. Pipeline welders typically use an upscaled version of this setup. - Metal inert gas (MIG) is a type of wire welder that uses a gas, such as CO2 or argon, to shield the arc from the atmosphere. It makes pretty and clean welds with no slag, but it cannot be used where the gas can be blown away from the weld. Shop use only. - Torch welding is the oldest of all, it isn't typically used anymore because it's kind of difficult to use and very dangerous. You have to not only hold a torch and separate rod to fill with, but you also have to set up the acetylene and oxygen properly. It's mostly used to patch holes in liquid holding containers nowadays. - Tungsten inert gas (TIG) is like the second iteration of torch welding. It combines the principles of torch and MIG welding to create beautiful and structurally sound welds with no slag. But again it cannot be used where the gas can be blown away from the weld. There are more ways to weld than just these but it can really fill a book. You can't exactly have a system that works in all situations so that necessitates having multiple methods."
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5z0kzm | When writing a really big piece of software, how do the large numbers of programmers involved make sure they don't break everybody else's bits of code every time they change something in their little bit? | Engineering | explainlikeimfive | {
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"Large-team software stuff sucks unless you have a strong leader delegating well-communicated and specific tasks. In software, abstraction is important. In other words, for two parts of a program to work together, they just have to know how to talk to each other - they *don't* have to know how the other part actually works internally. In other words, the two parts have to know how to \"interface\" with each other. Imagine I had a method/function called 'add' that would accept two numbers and add them together. To call the function, id say add(3, 5) and the result would be 8. I have no clue how it adds those two numbers, and quite frankly I don't really care as long as it works. So if I create the basic (theoretical) design of the software, I can design all of the interfaces (the function names, the parameters and their types, and what type of item the function returns as a result) and hand out chunks of the program for people to code. If you write my add() function, you can make it work internally however you want as long as you follow the requirements I gave you (that it accepts two integers, and returns the sum of the two integers). And that way I can assign Tim another part of the code that will constantly use your add() function. He will write his code assuming that your add() function will work. Then, everyone puts the code together and tests it. It won't work because that's how life goes. Fix the errors one by one with tons of testing in between. Of course, this is definitely overly simplified, but hopefully it gives you a small hint. The other important part is extreme communication and frequent meetings. Incremental deadlines are helpful, but are hardly met. Lastly, it's good to have a leader supervise everyone else.",
"Every studio does something different from each other, and so it seems most answers will be slightly different from each other. In general, the most important thing to know is that things will and do get broken. Ideally, those things are then fixed before it impacts others much. I will step through each individual piece that's gone through for at least where I work (which is specifically with Video Games). This will likely be a very very long post, so I'll try to simplify each piece down for the ELI5: > **The Main Steps** 1. **Space.** Room to work in. When there's a lot of code to work with, it's much easier for programmers to work on parts of the code where other programmers aren't touching it as often. If you think of programmers in a large house both building the house and building things in the house, the larger the house is then the easier it is to have a couple rooms to yourself or a small group of people. 2. **Isolation.** Rooms try to stay mostly to themselves. You don't want to have your ceiling staying up because you put a log wedged into the cabinet in the next room. Especially if programmers work only on a single room at a time, they might not realize the random log in *their* room is important and that they shouldn't move the cabinet. It's better to build supports in your room for your ceiling. 3. **Modularity.** You don't always know what the rooms next to your room might be, or if they might need to be replaced. So code makes things modular to deal with this, saying \"there are 3 doors. They are these sizes and at these locations\". Where those doors go to can change. 4. **Compiler** (this one will be more specific and definitely not shared by all codebases). Strangely, this massive house everyone is working on only _describes_ the house. Which is why modularity (3) or isolation (2) is so important. You can't always easily see what your room will actually touch until the whole house comes together. There's this thing called a compiler that actually takes all the descriptions of room and builds a house out of it. The compiler will complain when things don't quite connect where they should, or where the modularity says something is wrong, because the compiler can't finish it's job. (Jargon note: There are actually a few pieces in this - such as the linker or preprocessor - and the compiler is just one of these pieces. Programmers a lot of times just group them all together to save time when talking.) 5. **Unit tests.** There's a lot of pieces that require very very specific things that it must do. To keep running with our house analogy, this may be to say that a specific breaker switch controls the electricity to only a few specific rooms in the house. Or that a faucet always gives the same heat when turned on to the same angle each time. In code, this is usually complicated functions that bare most of this wait. Instead of having to check all of these things that are easy to miss, unit tests are made that checks these things for you. They're just more code that you say \"I expect this to always do these things when this happens to it. Check that for me every time I use the compiler.\" And they do. Thank you unit tests. In my experience though, unit tests can't cover even a tiny bit of the range of inputs a video game has possible, so in our case these aren't good enough. 6. **Personal Check.** After the compiler puts everything together, each programmer can walk through the house themself and just check if everything seems to be in place, and then specifically check out the room they were working on and see if it's hooked up correctly for themselves. A lot of times, programmers will make their own tools to let them cheat around their room to make this type of check faster. For games, let's say you're working on a new way to purchase items, you might give yourself a tool that let's you freely make money. That kind of thing. (There's more code to prevent these tools from going out to everyone) 7. **Functional Tests.** Unit tests (5) like to check very small pieces, but a large part of the house can be checked all at once with something called functional tests. Functional tests look at how something should work in general, rather the specifics. In our house, they could ensure things like... starting from the front door, can you still eventually make it into the attic? This helps for cases where someone might remove a door somewhere, for their own good reasons, but fail to see the big picture somewhere else. These also occur automatically, but in our code base it's usually after the programmer has committed the code - so that the programmer doesn't have to wait on these tests (they can take awhile). 8. **QA - Quality Assurance.** There's a large group of people who are really good are doing all these different types of checks themselves as well, predicting what types of changes might break what, or even being very clever at breaking the code in ways nobody else thought to try. These are QA. Tests (like unit tests and functional tests) are only as good as a programmer can predict the program might work, but breaking something can be more extensive a job than what the programmer might consider. In those cases, QA is specialized in finding out where other problems might lie. 9. **Build Pipeline.** Hinted with the fuctional tests bit, there's computers specially setup to do the compiler (4), unit tests (5), and functional tests (7) all on their own. A lot of people can be changing a large part of the house at once and need to have their changes all at similar times. This can create times where personal checks and running your own compiler doesn't catch problems that might arise from two different changes not liking each other. Build machines do the steps above with everyone's code (who put their code in) to provide their own versions of the checks. a. **Build Pipeline - Multiple Operating Systems.** This is a special note for game dev. Operating systems, like Windows XP, Windows 7, OSX 10.6, etc. can all be quite different from each other. Thing of these like broad locations your house can be built on, with the more different the operating system the more different the location. If you're constantly checking if your house might work in a forest, there might not be something you noticed when your house is on a tall barren mountain. Or underwater. Operating systems get very different. The \"big ones\" should be checked yourself, but build machines and QA (Compatability) can help to fill in the gaps. 10. **CI - Continuous Integration.** (Blah that term sounds technical). CI is something of a philosophy that some studios have and a way of setting up the build pipeline (9). CI is the idea that, two sets of eyes is better than one set, and this can only get better from there. When you put code in the shared place so that a build pipeline can use it, it's *possible* that can be one of many places with many different build pipelines. Historically, this is how a lot of code bases worked, you would have teams with their own build pipelines who would then eventually do a large push of all of the changes they did in the last few months (or years) from their builds to the big central build. This was called \"integration\". CI just says \"Hey everyone, just put all your stuff in the central spot and figure out some other way to hide it.\". This means that while everyone is walking through their spots in the house, they might be more likely to see other problems for someone else more often. More eyes. 11. **Playtests.** (Game dev specific, kinnnnd of. Just called different things elsewhere.) If you're building a fun house, play in that fun house to make sure it's actually fun and working the way it should be - and that no random spike it sticking out under a trampoline. It's better for you to get hurt than your players. Game programmers make sure to play where they build. 12. **Large Testing Environments.** Beta testing. Similar to CI (10)'s mentality of \"the more eyes, the better\", programmers try to get lots of different potential home owners to try out their house for awhile just to get more eyes. And, more importantly, more environments - locations - where the house could be. Again, this provides more opportunity for something bad to occur and for someone to see it and report it.",
"you do it by modularizing your code. your own module takes X input and makes Y output. you can have an automated test that provides various X inputs and validates Y output. run it thru 100's and 1000's of different X's and make sure it comes out to the correct Y's. then your module plugs into my module. my module takes A's inputs and makes B outputs. in order to do so, it takes the A's and uses some parts of it as X to call your module. and when it gets back the Y, my module does something to it and makes a B output. another set of tests run thousands of A inputs and validates that output is correct B. whenever the next time you change your module, we'll rerun all the 1000 tests for your module as well as my module.",
"Just to add a note about Version Control Software. I anticipate I'm not native English so bear with my bad explanation lol. We use this type of software which allows teams to cooperate on the same project files while tracking changes and stuff. When merging your changes with other's (ie \"propagating\" them to the rest of the team) if multiple people have changed the same portion of code you'll get a merge conflict, and you'll know that for example someone did not respect that distribution of tasks. Again, sorry it sounds a \"childish\" explanation",
"It's been said multiple times, but software is built in modules that have contracts. \"I accept this, and I give that back.\" You can change anything so long as the contract remains unchanged. If you change the contract you (potentially) need to update everything that uses that contract. When ordering a pizza you don't need to worry that you might not know how anymore because they changed how their ovens work. So long as the contract remains the same you don't need to relearn how to order a pizza. If they changed the contract, like for example, no longer accepting cash, then you would need to make changes yourself. Code needs to be written in understandable components or it gets very messy very fast. I've worked with code like that and it takes ten times the brain power and time to get anything done. When code is broken down into manageable pieces with a single purpose it's beautiful. It doesn't matter how big the total software is if it's just a bunch of tiny parts. When working on something you should only need to know how that one tiny part has to work. It's as if the software only consists of that tiny part.",
"In we'll run projects they use tests to ensure this. They write test code that validates the way the program works. That way if something changes they can rerun the test suite and see if there is anything amiss. This helps a lot but it isn't perfect. There is still human quality assurance that happens to catch unintended things. Even this isn't perfect, and that's how you get bugs in your program."
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5z1ajo | If we went back in time and gave a computer to someone from the early 1900s, would they be able to reverse engineer it? | Engineering | explainlikeimfive | {
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"They could not reengineer it. The semiconductors that make up the CPU, memory and other logic would be black magic to them.",
"They would definitely be able to reverse engineer it, but it would take them time, and they wouldn't be able to produce something of equivalent sophistication on their first tries. It would teach them a *lot* however, and would be a quantum leap ahead in terms of materials science, and electronics design. Ideas that would take generations of many different people to bring together would be laid out there for them to see, in one piece. You'd also be settling issues that would be debated for decades! On one hand, no, they wouldn't re-create it (right away). On the other hand... it would change everything. Assuming that you didn't trigger a war (or wars) and any catastrophe (i.e. assuming a good outcome) you'd be setting technological progress forward in a way that's hard to imagine. Just the power of settling unanswered questions would be *soooo* valuable. You'd be able to take this device to world leaders and say, \"This obscure shit we do? This is where it goes. Think of implications, now give us funding.\"",
"No. Examining modern computers requires technologies and understanding of physics that didn't exist at the time. For example, without an electron microscope to see the actual transistors, a modern CPU might as well be a thin slice of magic shiny metal.",
"No, not even remotely. A computer is the product of _dozens_ of different industries and technologies that didn't exist in the early 20th century exist. All of which would have to exist for them to re-create. A piece of modern technology is like the end point of a line of dominoes that you can't jump forward in. To get the final domino to topple over (create a computer) you have to first topple over the dozens in front of it (create all the industries and technologies that computing depends on). Knowing what the last domino is might help you guess what some of the other dominoes leading up to it are, but you're not going to have enough visibility to intuit all of it. Hell, the first obstacle to our hypothetical early 1900's engineer would be just powering the damn thing on, because the standard grounded plug that we all use today and the 120V AC electrical outlet that it fits into weren't even *invented* until 1928. Without any juice, they'd not even have a way to figure out what the computer *does*."
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5z3ckp | When off, how does your phone "know" that you've held the power button long enough so that it should turn on? | Engineering | explainlikeimfive | {
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"Its a simple circuit. To break things down, imagine a light switch. there is point A and point B. When the light switch is turned off there is no path for current to flow from point A to point B and therefore no current can make it to the light bulb. When the switch is flipped, the circuit becomes \"closed\" and current can flow. In a phone, we have the same thing, only in addition to there being a \"switch\" (the button being suppressed) in-between A and B there is also what is called a capacitor. What happens when you press the button down is the current flows and instead of making it all the way to B, it starts charging the capacitor. There are a bunch of different equations regarding capacitors and how they respond, but suffice to say that the capacitor charges until it is unable to charge anymore and then the current continues out of the capacitor (because it can't hold anymore, picture a you pouring water into a glass and once the glass is full the water overflows and reaches the table) and onto point B telling the phone to turn on. Now, you may ask, why then when i hold the button for 1 second x 3 it doesn't turn on, but when i hold it once for 3 seconds it does...doesn't the capacitor still get charged? Well the answer is yes, but when you stop charging the capacitor it starts spending its saved energy, but at a lower current level than is what is necessary to activate point B"
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5z4a25 | The recent explosion in AI accomplishments | I keep reading about the threat of AI. Has something fundamental about AI changed recently? Have there been breakthroughs in the science? Is it due to better hardware? New data to mine? Or is it just a news trend? | Engineering | explainlikeimfive | {
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"Most likely a news trend. AI technologies are advancing extremely rapidly, however it's going to be a while until they are integrated into our every day lives such as the media is displaying currently."
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5z6ti4 | How do different shapes of glasses affect the alcoholic beverage taste? | There are different types of wine glasses based on the type of wine and the same with beer. How does the shape of the glass affect the flavor and taste of the drink. | Engineering | explainlikeimfive | {
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"Tulip Shape: Bulb that tapers in before flaring out at the top. Purported Benefits: concentration of aroma, support of the foamy head at the top, and comfortable drinking afforded by flared rim. Chalice Shape: A round bowl on a stem. Purported Benefits: Beautiful presentation, foam support, wide mouth for easy drinkin' (in big sips.) Pilsner Shape: Tall, footed, slender, tapered out from the bottom. Purported Benefits: Displays the beer's clarity, while tapered shape supports head. Weizen Shape: Tall, large, slender at bottom, bowled out a bit at the top. Purported Benefits: Large size accommodates a massive, frothy head associated with highly-carbonated German wheat beers. Slender bottom shows off these beers' famous hazy color and protects its lively carbonation. Nonick Imperial Pint Shape: Large, slightly tapered out with bulge near top. Purported benefits: Designed for the no-nonsense drinker. The bulge facilitates stacking and prevents rim chipping. Shaker Pint Shape: Slight taper outward from bottom. Purported benefits: Cheap and easily stackable. Sturdy ones can be used for stirring and shaking cocktails. Snifter Shape: Stemmed, wide-bowled, tapered in at top. Purported benefits: Designed for maximum concentration of volatile organic compounds—that is, aroma. Tumbler Shape: Short and squat with thick glass and a slight outward taper. Purported Benefits: Tradition generally drives the use of this glass, which is usually reserved for Belgian witbier and lambic.",
"The shape of the glass affects how your mouth and nose (eyes to an extent) interact with the beverage. A very wide glass will allow your whole nose to enter the glass as you sip it, the aroma adds to and complements the taste. A very narrow glass like a champagne flute reduces surface area which keeps the bubbly bubbles from gassing out before you can drink it. Other glasses like a Brandy snifter allow to you swirl the beverage without spilling it, the swirling allows the aroma to release but the narrow lip of the glass traps most of it in the glass, so you can get your nose right in there. Some glasses have stems to keep your body heat out of the beverages while other glasses encourage the handling to warm the drink inside. Certain beer glasses have wider tops which allows the head to form and remain which contributes to aroma and protects the beer below from reacting with the oxygen in the air. Beer stiens have a handle so the beer stays cold. There's are many more examples but this covers some basic reasons for shapes. As an experiment try your favourite drink in various glasses and see if you notice the subtle effects.",
"I'm not sure how it works, but if you pour root beer into a square glass it turns into regular beer.",
"I took a wine class in college and a sommelier came as a guest speaker and his answer to this question was: You're favorite wine will taste best in your favorite type of glass. That there was no right or wrong, suggesting how wine as a whole is just the experience you make it. All \"science\" and snooty sommelier-ness aside. I thought it was pretty cool.",
"Until a better answer comes along: Some glassware has different openings, exposing the beverage to more or less air. Taste is related to smell, so a glass that has room for your nose will allow you to 'experience' more of the drink. In beer glasses, some shapes allow for more foam (or head), and that is often part of the taste of the beer (like Guinness or Boddingtons). Different shapes also have different surface areas. Red wine glasses have more surface area because the wine is meant to be tasted at room temp, white wine has less surface area to help keep the wine chilled. Glassware that has stems (like wine and martini) is so the temperature of your hand doesn't change the temp of the drink.",
"The answer is actually quite simple. They don't. The reason as to why we do it can be explained by [this video]( URL_0 )",
"90% of the mythology is hype, put out by glassmakers to sell more glasses to people who already have too many. I use a plain stemmed Bordeaux wineglass, big enough for me to get my nose into, for whatever wine I'm drinking, or even for beer. I just don't want a 'stemless' glass, where the heat of my hand warms the wine, and the glass gets greasy from food if any finger food is involved. And I don't want a deep curve in the glass, where I have to crack my neck backwards trying to get the last drop.",
"OP, you may be interested in the beer glass that Samuel Adams designed. The shape is to help give it a nice head, while it's thicker around the middle do your hand doesn't warm the beer. At the lip of it there is a small ridge that's supposed to tumble the beer as it enters your mouth, \"activating\" it's flavor. What I think is coolest though, is the laser etched imperfections in the bottom of the glass that cause the bubbles to rise and aerate the beer. The imperfections are in a perfect circle at the bottom middle of the glass.",
"The mouth of the glass and size effects aromatics of the drink creating a more pleasurable flavour when consumed. Size of glass for mixed drinks effects the volume left in the drink to tone down the desired alcohol.",
"The shape of the glass affects where and when the liquid hits your tongue, and so what flavors you'll notice first. Since no one inhales as the sip whether your nose is in there too makes no difference. Every wine benefits from swirling to release aromatics, so under fill your glasses. But don't take my word for it! Gather some friends, and some glasses, and give them a blind tasting of the same wine in a few different glasses. Even better if you can do the same three glasses with two different wines."
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5zczya | Technical Standards | I am the kind of guy who wonders why mechanical pencils only come in 0.5 mm and 0.7 mm but never 0.3 or 0.6 or 0.9, and why can you take a lightbulb from the 1930s and screw it in to a modern house, but we still switched from the serial + parallel pair to USB. Who decides Standards, is it an organization, is it just one makes a good standard and everyone goes "yeah, that is good lets do that". Why are some things standardized to oblivion and others aren't at all. also, what is preventing me from making an android phone with a serial port running all measurements in the FFF system in base 64 with a logarithmic clock? Also, why are companies like a company we all know about that starts with "A" try to run "proprietary" things? Also What is proprietary? (I have a lot of questions). Edit: what about the history? | Engineering | explainlikeimfive | {
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"> Who decides Standards, is it an organization There are, in fact, many standards organizations. Often times writing standards is something done by organizations of professional engineers. The International Standards Organization (ISO) does many standards across many industries. The IEEE does many technological standards, as does its sister organization the ACM. > is it just one makes a good standard and everyone goes \"yeah, that is good lets do that\" Yes. In general there should only be one standard on a given subject. The better ones are available royalty free. > also, what is preventing me from making an android phone with a serial port running all measurements in the FFF system in base 64 with a logarithmic clock Nothing. > Also, why are companies like a company we all know about that starts with a try to run \"proprietary\" things? Because for a profit-making company, it is ideal if you can make everyone use your standard and them charge them for the privilege. A lot of companies play dirty games around standards. Perhaps the worst offender of all time was RAMBUS. They sat on a committee that was writing RAM standards and used information from the committee to quietly start patenting things in the standard. They got caught red-handed and were basically bankrupted in the ensuing drama."
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5zg9v3 | Why are there no high quality videos of planets, or probes crashing into the planet? | If a signal is sent from the probe before it de-orbits to let's say jupiter, can we pick it up and see the full video before the impact point (or the point in which the whole probe burns)? | Engineering | explainlikeimfive | {
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"The bandwidth probes send data over is very limited. That's not a huge problem when you have days or weeks to take and transmit images, but it greatly limits your ability to steam live data."
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5zgloj | Why did they make Method-1's hips so narrow if they wanted to make the mech's gait more stable? | It was my understanding that a wide base leads to a more stable platform, if so why did they give Method-1 so a narrow base? Link to Method-1's walking test demo if anyone is curious: URL_0 | Engineering | explainlikeimfive | {
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"When we walk, each time we lift one leg we have to balance all of our weight on the one leg that remains on the ground. Humans can do this because our legs are close enough together that we can lean towards that leg a bit, and put our center of mass directly above the foot. If we didn't, we would tip over in the direction of the lifted leg. Similarly, for Method-1, if they made the hips wider then the legs would be further apart, which means that every time they walk forward the whole machine has to lean over much further, which is wasted energy and probably makes it more unbalanced on a single foot, because of that brief period during the lean where the center of mass is to the side of the part touching the ground. TL;DR: Wider hips would make it more stable while stationary, but would make it much hard to actually walk, which is the point of a mech."
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5zgtle | Why/how do stone buildings burn down or get damaged by fire? | I'm taking a college course on Ancient Greece and rome and you her about these stone structures that are "burnt down" and I just can't imagine how its possible. I feel silly. | Engineering | explainlikeimfive | {
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"Typically the stone itself does not burn. What happens is everything else burns (furniture, paint, wood, etc) and creates such heat that the stones expands and crack. This then causes the building to collapse at which point bricks and stone are crushed into a powder similar to ash.",
"The stone itself might not burn, but depending on the type of stone, and the intensity of the fire, the stone may crack. That might be sufficient enough damage to cause the structure to collapse. Or maybe weaken enough that people abandon it, and over time it collapses. Remember stone structures have combustible materials inside, wooden stuff, tapestry, textiles, candles and candle wax spills, soot buildup, etc. Finally the stone structure may be held in place by mortar, the heat of the fire might damage the mortar and cause it fail which weakens the joints between the stones.",
"In addition to what people here have already said, often the supports for floors and the roof are wood. If those burn and collapse, especially if they do so asymmetrically the beams can lever portion of the walls down and even if they don't you're left with a shell that has few no no internal supports and is heavily weakened."
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5zmpw2 | How do planes charge electronic devices? | I've seen it more and more regularly that planes have charging sockets for electronic devices. How on earth does a plane in the air non-stop for 12 hours, manage to charge all these electronic devices for all these people? | Engineering | explainlikeimfive | {
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"Planes use a generator driven by the engines to produce electrical power. The load of passengers charging electronic devices is very small compared to the plane's normal demand for electricity, so adding chargers doesn't significantly change anything.",
"The same way your car does. The plane has batteries that are used to start the engines, and also to power the many electronic devices on a plane. The batteries are recharged by an alternator connected to the plane's engines, which use fuel."
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5znw7e | what is in car air fresheners to make them say "avoid contact with all surfaces"? | Engineering | explainlikeimfive | {
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"They contain volatile solvents. The solvents allow the piece of cardboard to capture odor molecules, and then when they evaporate the smell is trapped. Alas, your car is made of things the solvents will dissolve, and that will make you sad.",
"Learned this the hard way after a pine tree melted my dash."
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5zosko | Why aren't washer/dryers (one machine, two uses) more mainstream? | Engineering | explainlikeimfive | {
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"1. In most places, space (at least the kind necessary to have separate machines) is cheap so there isn't an economic driving force 2. 2 in 1 machines are more complicated which drives up cost and lowers effectiveness and potentially shortens lifespan 3. Less efficient from a throughput stand point: with separate machines, once the wash is done I can start a second load without waiting for the dry cycle as well 4. If my washer breaks I don't need to buy a new dryer as well and vice versa",
"Primarily because they do an incredibly poor job at both functions. They also have much shorter lifespans and are far more expensive to fix. Also most places have enough space for two machines.",
"At the most basic level, asking a machine to do multiple tasks makes it more complicated, more likely to break, and more expensive. So there isn't really an obvious and compelling advantage to a dual machine. Plus a lot of people prefer not to use a dryer at all since it damages clothes and uses a lot of power.",
"In apartments in Korea they are oftentimes one single machine. They suck. 4hrs to dry your clothes.",
"In my case I don't really need a dryer at all. All I ask is a good washing machine. We have plenty of sun and too much heat most of the year. Seriously. During summer, my clothes are dry in minutes. But even on the coldest/humidest days, they don't need more than a day."
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5zpl5t | How much damage would a one exaton nuclear bomb do? | Engineering | explainlikeimfive | {
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"That's 4.184e+28 joules. That's roughly the same energy as an asteroid 200km across impacting the Earth at 72km/s. For reference, the asteroid that killed the Dinosaurs was about 10km across."
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5zv9pc | Why did cars become so square and boxy in the 70's & 80's? | Engineering | explainlikeimfive | {
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"Gasoline became expensive, and people started to shift towards smaller, more fuel-efficient vehicles. A boxy design preserves more of the interior passenger and cargo space."
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602lhw | What happens if I were to connect a NAND gate to one of it's inputs, then power the other input? Would it make some sort of clock cycle? | Title. Basically I was wondering, well if you take a NAND gate, then power one input and connect the output (emitter?) to the other input (collector?) will it make a really fast clock cycle? Or will it just explode? | Engineering | explainlikeimfive | {
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"Electrical Engineer here. TL;DR, no. It'll reach some steady state where the output voltage equals the input voltage, but it doesn't represent a 1 or a 0. If you want it to oscillate, you need to chain multiple inverters (your 1-input NAND gate). This is called a ring oscillator, and it works because the delay across multiple inverters prevents any of them from reaching the steady state. NAND gates (and really any electronic device) are ultimately analog components. This is important because the way devices behave are dependent on the voltage of the inputs, and not all voltages translate to a logic value. Let's simplify your scenario a little. Think of an inverter (1- > 0, 0- > 1). In reality, logic 1 is really some voltage, call it 5V, and logic zero is another voltage, 0V (generally a little higher than ground, but it doesn't matter). You can think of the inverter as a device that maps 5V- > 0V, and 0V- > 5V. What about a voltage somewhere in the middle of 5V and 0V? Picture a graph, the x-axis is the input voltage, and the y-axis is the output voltage. You know you have two points, (0, 5) and (5, 0). Now draw a line that connects them. That line represents the inverter (or at least a linear model of one). Vout = 5V - Vin. This is a little simplified, but you'll get the picture. Now, think about what happens as the output swings. Say I start at 5V. The inverter will start to move towards 0V. But this changes the input. Let's say we're now at 4V, the output will want to go to 1V. Now we're at 3V. The output wants to be at 2V. At 2.5V, the output wants to be at 2.5V. The inverter is stuck! The input voltage maps exactly to itself. You might get a little oscillation because there is a delay between the input and output, but each time around it will get closer to 2.5V, and eventually it'll reach a steady state. Now, if you chain multiple inverters, the delay from the output of an inverter, through all the others, and back into its own input will be large, and the inverter can get to the desired voltage output before the input changes. This is what we call a ring oscillator. Each inverter adds a little delay, and if the chain around takes longer than the time it takes for the inverters to swing their output, you'll get permanent oscillations, otherwise it'll die off eventually."
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6078qy | Why do blinkers make the blinking noise? | Is this noise made by the manufacturer, or by the actual blinker itself? | Engineering | explainlikeimfive | {
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"Originally, blinkers were driven by relays. Relays are electromechanical switches where a magnet is powered on to physically connect two pieces of metal - and they 'click' when they're actuated. In the modern day, it's more likely that your blinkers use solid state electronics with an artificial 'click' to match people's expectations.",
"There is usually a clicker of some sorts under the dash... whether electric(usually within a relay) or mechanical. It's only purpose is to remind you that your turn signal is on.",
"Actually, the [mechanism of a blinker]( URL_0 ) consists of a bent piece of metal that gets hot when current passes through it (to light up the signal lights); the metal dilates because of the heat, and thus moves away from the contact and interrupts the circuit to the lights. Without the current, the metal then gets cold and moves back into the initial contact position. Basically, it's a switch that uses the fact that electricity produces heat, and heat can make a metal change its shape/size. So that's how the clicking happens, that piece of metal clicking in and out of contact. That's also why the signal lights on (some) cars blink faster when one of the signal bulbs is burned out (the remaining signal light bulb has a different electrical resistance than 2 bulbs)."
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608qzt | Why do high Volt chargers fry a circuit but high Amps one doesn't seem to affect it? | Engineering | explainlikeimfive | {
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"The voltage rating of the charger is the amount that the charger will put out, regardless of what you attach to it. However current (amps) is drawn by the device. So the current rating on the charger is the max amount that it *can* provide. The device only takes as much as it wants. So if a charger says 5 Volts and 2 Amps, then it will put out 5 volts and the device can draw anywhere from 0 to 2 amps.",
"You can think about voltage and current like water in pipes. The voltage represents the water pressure pushing it forward and the current represents, well, the water's current or flow rate. Now, you can have water moving as fast as you want through those pipes, but when too much pressure builds up the pipe will burst. (This is why we can't run transmission line's at infinitely high voltages. They will arc and give off corona discharge, ionizing the air around them, or they will ionize and fry the insulation.)"
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609e50 | how hairdryers manage to heat up to full temperature almost immediately, yet this technology cannot be applied in other ways | Engineering | explainlikeimfive | {
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"Heat capacity is basically how much heat (think of heat as energy) has to be transferred to a material to increase its temperature. If you heat up water it will take a while because of its high heat capacity, though the metal will be really hot almost immediately (if you have a kettle you can notice how hot the metal part is even after few seconds, -if it's not in contact with water that will cool it down-) air has low heat capacity and will heat up just by passing through the hot hairdryer for less than a second. If you were to do that with water (don't) it wouldn't heat up that much.",
"The motor starts immediately and that gives you the sense of an immediate start. The heating element is just pure resistance and is almost as immediately turned into heat. A toaster is fairly immediate as well, but lacks a fan. Put your hand on top of a toaster and you will remove it almost immediately. Hair dryers are not high tech. What other ways would you expect a heating element to be applied?",
"Before someone asks, automakers have played with the idea of using heating elements for heating in the winter. The issue is they use a fuck ton of power. Power your car would else not be using. A standard 1500w hair drier wouldn't heat your car well but 1500w is 2 horsepower. Instead they pull the heat from water heated by the engine. Heat that would otherwise be rejected into the air outside. It's basically free heat. For reference you can typically say a car passes equal energy into to the cooling system as it produces to the wheels. A 200 kw car dumps roughly 200kw into the cooling system. Same goes for the exhaust, a 200kw car dumps 200kw heat through the exhaust."
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60aow7 | How can it be cheaper for NASA to contract SpaceX instead of running their own missions? | Engineering | explainlikeimfive | {
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"To generalize a fair amount, NASA has always been where the scientists worked while defense contractors were where the engineers worked. So in the glory days of the Apollo missions, you had NASA scientists figuring out the environmental conditions and then companies like Rockwell and Grumman actually designing the vehicles. In the modern day, all of the science necessary to build space vehicles is largely done and all that remains is the engineering. Since the engineering has always been handled by private companies rather than the government and operations isn't a particularly complex task, it makes sense for private companies to take over most of the task.",
"One big advantage Space X has is the ability to fail publically. This allows both quick innovation, but also simply lowers the bar and cost on safety mechanisms. Not saying that Space X wants to blow up rockets. But the public generally is more okay with watching a private company blow up some rockets, and then pay for the successful launches (even if those successful launches build the failures into the tax payer bill) than they are willing to directly see their tax money blow up.",
"Remember: space X took on a lot of debt in order to finance themselves. That debt was used to engineer a new solution to reuse their first stage boosters. That is a huge cost saving. NASA would likely not have done this as it would have required short term increased government funding for a non critical part of the mission. The free market is often much cheaper than government. They are much more agile and can take more risks. Risks can go bad but they can also yield amazing results.",
"Not to take anything away from SpaceX or Blue Origin or the like but I think it is important to remember that these new companies are building upon decades of experience before them. If they were all starting from scratch I doubt the costs would be much different. At least for quite some time. As has been mentioned, one of the big problems with NASA and many other government programs (like much of the DOD) is all the politics involved in trying to spread as many jobs as possible across as many Congressional districts as possible. Keep in mind NASA does not build stuff itself. Subcontractors do and subs need to make a profit themselves. Too often there are few incentives for them to worry too much about the costs/profit equation. Much of that can be dealt with by better contracts but there is always the mostly negative influence of lobbying politicians which can make that difficult. I don’t recall offhand but I’m pretty sure SpaceX and the like also receive tax incentives (aka corporate welfare) when they hunt for and decide to locate a facility somewhere. Those sorts of incentives/subsidies generally run into the tens of millions of dollars and aren’t usually tallied in the total costs of service.",
"Nasa is not a financially efficent organization. As it's a governmental organization, it has priorities other then profitability. For example when deciding where it's going to place a new facility, factors like local unemployment and political agendas are as much a factor if not more, then where the most cost effective location is. because of this everything Nasa does is a lot more expensive then a private company could do it. Of course the country as a whole recieves many benefits as 'spin offs' that they wouldn't get if private corporations did everything.",
"SpaceX does an amazing amount of vertical integration in their assembly process. That is to say, nearly all of the parts that make up a Falcon 9 rocket/ Dragon spacecraft are manufacture \"in house\". This allows for cheaper parts without sacrificing quality. NASA hasn't done this. They contract parts to the cheapest bidder no matter the location of he company. This results in an increase in manufacturing costs. Once SpaceX starts re-flying their Falcon 9 booster rockets, I would expect their prices to drop even further. Already, they've given their customer for the first booster re-flight a 30% discount on the launch price!",
"NASA paid people to make their rockets, and those people paid other people to make smaller parts and so on. Everyone added more to the price to get their profits. SpaceX does it all by themselves. Edit: I have learned that SpaceX only does *most* of it by themselves.",
"The answer has nothing to do with private vs government. In fact private companies contract out projects all the time. Even contractors sub contract. I can also tell you NASA's board takes its budgeting very seriously and tries to cut costs wherever it can. Any money used improperly hinders the organizations goals. The answer is that it is actually cheaper for NASA to contract out these projects than to build all the facilities and obtain the resources to complete them on their own. NASA isn't and can't be a factory that specializes in producing every single component that goes into space. This is especially true, since the science and components change all the time. Rather, when NASA is in need of a particular thing, it makes much more sense to find a company that can build it for them.",
"Really, it comes down to politics. Our politicians all want their states to get a piece of the pie. Back in the heyday, it was still more of \"Make AMERICA the world leader of space\". Now it's one politician screwing over others and the country just so their district might get money from it. I had many relative working at NASA in the 60's-80's and they all left because the politics ruined it. Also, citizens don't want to accept that there are people willing to die to advance space technology. Not saying they plan on dying, but they know it's possible. The average joe can't grasp that anyone would be OK taking that much risk. They think those people must be forced into it. Or that when an accident does happen, it HAD TO BE A MAJOR screw up, not just a \"honestly we thought of everything, but missed that one tiny detail\".",
"There are different kinds of government contracts. One option is called a cost plus type where the government pays the contractor's costs plus a fee. This can be costly to the government as the burden for overruns is borne by them. It's typically used when the scope of the effort is somewhat unknown and subject to changes or unpredictability. Another type, though, is firm fixed price, which as the name suggests, is where the government pays the contractor only a firm fixed price for the work they do. Any overruns in the cost are borne by the contractor. Any underruns become extra profit for the contractor. The government likes this approach the best as it minimizes their cost risk. This could be how the government is paying Tessa.",
"This is a wonder of the market system! It's the classic story of an upstart finding a better way of doing things and thereby getting ahead of competitors (in this case, ULA, not NASA). NASA and other suppliers have decades of set practices from which they do not like to deviate. For instance, they used custom made electronics for their space vehicles. However, those practices were first introduced in the 60s and 70s but electronics have come quite a long way since then. SpaceX realized this and conducted lots of experiments proving to NASA that commercial, off-the-shelf electronic components were precise and reliable enough to be used in spacecraft. Using these parts dramatically lowers the cost to SpaceX, and this lowering of cost is passed to the customer, NASA. I'd recommend reading \"Elon Musk\" by Ashlee Vance, which is Elon's biography. It touches on just how much cheaper SpaceX really is, and why it is so (including the example cited above). The argument you're making (decades of experience in something) can be made in every single field - Walmart has decades of experience in retail, but Amazon still came out ahead, Ford has decades of experience in building cars but Tesla still got to electric cars first, and so on. The beauty of the market system is that in order to succeed against an incumbent with more experience, the competitor **has** to find a better way to do things, thereby improving things for everyone!",
"Not wanting to be too glib about this but I can tell that by asking this question that you have never worked for a government department. The sheer waste that goes on should be criminal.",
"I worked at Cape Canaveral as a range engineer from 2009-2013. For starters NASA is full of government civilians with more strict labor regulations. SpaceX is full of a wave of new, brilliant, passionate *exempt* engineers willing to work over a hundred hours a week, especially with a launch coming up. Not that many of the NASA workers aren't brilliant/passionate etc.",
"In addition to what everybody else said, sometimes in engineering scrapping processes and technology and starting new streamlines everything because hindsight is 20/20. We have no idea what kind of technical infrastructure NASA has to build their systems but maybe the overhead costs of restructuring for a particular objective or updating technical infrastructure is too costly in time or money and SpaceX is just in a better position to do it right now and much faster."
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"Internal combustion engines capture the force of small controlled explosions, and turn that into rotating movement. This is done with pistons. Most engines use conventional pistons which move linearly, back and forth. These can be arranged all in a row, or have the piston cylinders arranged like a star - which is a kind of rotary engine. The downside of linear pistons is they may have to move back and forth more than once for each explosion in order to clear out the exhaust from the previous cycle. Another way of doing it is using a piston that has curved sides but is otherwise designed to wobble around in a mathematically designed path called a trochoid. This makes it so that the piston can fire more continuously, because the gasses of the explosion move around and away from where the fuel is injected. The downside is these engines can have sealing problems, allowing burnt gasses to escape into other parts of the engines. They also don't burn the fuel quite as much, meaning they can pollute more and smell bad. This is what their cycles look like. [Linear piston cylinder cycle]( URL_0 ) [Rotary piston engine]( URL_2 ) [Wankel engine]( URL_1 )"
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