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[ "What I believe you're describing is technically called a mirage. If you've ever seen something incredibly hot, such as a jet engine, against a detailed background, you can see that the air around the hot object ripples. This comes from the immense heat of the object warming the air around it. This air becomes less dense, and rises. This means that hot air and colder air are swirling past eachother in a turbulent dance, and the place you're looking switches between more and less dense air. This difference in density bends light, which you see as a sort of shimmering or rippling. The same, more or less, happens in transparent (or near-transparent) oils on a hot burner." ]

[ "This isn't a \"story.\" It is a well-documented interaction. The drug reduces inflammation in the body but has a common side effect which is increased risk of ulcers in the stomach because it prevents the formation of mucus (which protects the stomach from the acids in it).\n\nPair this with alcohol, which thins the blood, and you have a situation where you have higher risk for developing bleeding ulcers in the stomach and blood which clots less readily. Upper GI bleeds are no joke.", "There isn’t “sides to the story” as you say. It does work as a painkiller to get rid of your headache but also increases risk of stomach ulcers. \n\nOther painkillers like paracetamol would be better" ]

[ "The word deutsch (and dutch) originaly included both Dutch and german and the differences between german dialects were comparable to the difference between Dutch and german back then. Since England had more trade and contact with the Netherlands and flanders these were the Dutch they knew. When the german language started unifying they called that language (and eventually the country) by another name.", "Originally Belgium, the Netherlands, and large parts of modern Germany formed a single realm. The common language was Dietsch. Later on, the people occupying the lands of the modern Netherlands + Belgium and modern Germany started forming two more independent communities and languages. These languages were Neder-Dietsch (the Netherlands and Belgium) and Hoch-Dietsch (Germany).\n\nActual Dutch and German only really started to develop a few decades before Shakespeare’s birth, so for the English people, those of both Dutch and German descent were known to speak Dutch (Dietsch).\n\nSince England has always had better relationships with the Belgian and Dutch people, it makes sense that they would keep on calling the Dietsch (and later languages) of the Netherlands and Belgium Dutch." ]

[ "Metal expands and contracts with temperature. That's just hot parts cooling off, they make that sound as they settle back to their cold size and position.", "It's the sound of metal parts in the engine cooling and contracting." ]

[ "Walt Disney used shell companies to buy up land for Walt Disney World in central Florida. Nobody really wanted that swamp land, so they knew they could buy it cheap as long as nobody knew Disney wanted it. If someone thought that one rich company wanted it all they could have got land in the middle of everything and charged a lot more. However, the different shell companies started buying up the land and it took a while before people realized who it was and jacked up prices.", "Import companies are typically still run by (either directly or indirectly) by the companies where the product is made. \n\nSmirnoff for example, is a \"different\" company in the USA than it is in the UK (where it's owned) and Russia (where it's produced). But in practice all three of those different companies are the same company. In the USA it's absolutely a shell company for the purpose of making the operation legal, as the company must be US based to be allowed to import. Most spirit companies do this. So while Smirnoff of America is it's own \"stand alone\" company on paper, in practice it's functionally operated by another company.\n\nSo import businesses are a legitimate use for shell companies." ]

[ "Given how long the dates are and now quickly they turn over stock and stores get new shipments, and the production cycles of such products, it’s easy enough to simply reduce or pause a delivery so as to prevent overstock and items approaching their expiration date. There are always channels like dollar stores as ways to dump close to expiration products as deep discounts.", "One method: a lot stores offer a discounted section where goods at or near their expiration are marked down to a fraction of their original price. Actual perishable items like produce are simply thrown away as they reach the end of their marketability." ]

[ "The sauna isn’t set to 300 degrees, that would kill you. Instead they built a sauna in a location that was extremely cold, so it was a 300-degree temperature differential between the outside temp and the sauna temp" ]

[ "Movie studios make it very difficult to find out exactly who is spending what and who is getting paid, it's called 'Hollywood Accounting'. Studios want to hide how profitable their movies are because if they made a deal with the actors or the writer to give them a share of the profits, you want to make it look like the movie didn't profit very much so that you don't have to pay anyone but yourself. It'll also effect how much you pay in taxes so it's better to say that of the $150 million dollars you profited, $70 million went to the marketing company (which you own) and another $50 million went to repaying your investors making the 'actual' profit of the film something like $30 million.", "The producer of the film is the group that funds the film. There is usually also marketing/distribution costs that are not counted as a \"movie cost\". This can be as high as the production cost. \n\nTheatre revenues are split between the distributors and the producer. I believe the producer receives a large share of the revenue. Also note that big name actors and directors/screenwriters all may have a \"cut\" of the revenue as part of their contract in making the movie." ]

[ "The saliva on your tongue is a much better conductor than the dead skin cells on your finger; even if you make them wet, dead skin cells. The tongue also has more sense cells per unit area than almost any other part of the body." ]

[ "Yawning affects your eustachian tubes, which regulate pressure in your ear. The change in pressure hampers the passage of sound because it lessens your eardrums ability to vibrate while \"hearing\"" ]

[ "Apparently the phones create a lot of \"noise\" for the plane's system and airplane mode \"silences\"your phone as it's not searching for a network and stuff" ]

[ "The \"why\" for genetic mutations isn't going to make you happy, they are mostly random. The term \"funnel breast\" isn't a very scientific one, but here's one alternative.\n\nPectus excavatum is the formal name for a chest deformity in which the sternum and rib cage are shaped abnormally. This produces a caved-in or sunken appearance of the chest. It can either be present at birth or develop after puberty.\n\nIt's a serious medical problem can impair cardiac and respiratory function and cause pain in the chest and back.\n\nPeople with the condition may also experience severe negative psychosocial effects and avoid activities that expose the chest." ]

[ "Pretty sure this was disproven a long time ago, and it was the fact that, at one point, babies who were exposed to classical music had attentive, educated parents and the class advantage that derives from coming from an educated and affluent family in western society. It’s all just cultural bias. \n\nJust spend time with babies, talk to them a lot, and provide for them a stimulating environment (an aspect of which is just about any form of music). The time invested into babies and making them feel wanted, stimulated, and secure is what matters at that age,", "Propaganda. Brain power is certainly not running short in places like India and China where their native classical music is very different than European/Western classical." ]

[ "Because some foods have high water content like bread that dries up when it gets stale and therefore hard while others we prefer with low ater content and absorb humidity from the air and get soft when they are stale like cereal.", "What happens when you put a cup of cold lemonade and a cup of hot coffee on your kitchen counter? One gets hotter and the other gets colder. Why? Because they're both approaching room temperature. When they reach room temperature, you have \"warm\" lemonade and \"cold\" coffee.\n\nIt's the same with bread and crackers, but instead of temperature, it's moisture content. The bread starts off with a high moisture content and loses some to the air in the room. The cracker starts off with very low moisture content and absorbs some from the air in the room. If you leave them both sit, they will end up with similar moisture content and it will be \"dry\" for bread and \"soggy\" for cracker." ]

[ "Roads do get eroded by tires eventually (especially if used frequently or by heavy vehicles), you just don't notice it as much since you are traveling over them at high speeds. Roads are repaved due to erosion pretty frequently in some places. Also, your tires erode quicker than the driving surface (I assume because they are normally softer)." ]

[ "Sometimes the company buys regional companies and they consolidate ownership but keep the existing regional brands due to their local customer loyalty.\n\nSometimes companies have one name and aquire another company and combine names. Like GlaxoSmithKline.\nWhich where three different brand names.", "I will say that GM is a different sort of story.\n\nGM is a parent company, they have multiple brands appealing to different actual markets:\n\nChevrolet (Chevy), Cadillac, GMC, Pontiac (now defunct), Saturn (now defunct), Buick, Geo (now defunct), Oldsmobile (now defunct), Opel (now defunct), Saab (spun off), Hummer (now defunct), and other defunct brands I never heard of.\n\nSimilar with other US car companies:\n\nFiat Chrysler owns (or has owned) Chrysler and Fiat (obviously), as well as Dodge and Ram (formerly a type of Dodge), Jeep, Eagle (now defunct), Plymouth (now defunct), Maserati, and Alfa Romeo. They had considered buying Saab off of GM, but didn't for some reason, which is why Saab was just spun off of GM (I think it was actually bought by an investment group).\n\nFor a brief period before they merged with Fiat, they had been merged with Mercedes (Daimler) and were known as Daimler-Chrysler, but they eventually split up as it wasn't working out and they mutually decided to see other car brands.\n\nFord owns (or has owned) Ford, Lincoln, Mercury (defunct), Jaguar and Land Rover (both sold to Tata Motors), Volvo (sold to Geely?), and Aston Martin (spun off)\n\nThen there's \nToyota + Lexus + Scion (defunct) \nNissan + Infinity + Datsun (defunct?), \nVW + Audi + Porsche + Bentley + Bugatti + Lamborghini \nHyundai + Kia + Genesis. \nHonda + Acura. \n\nThe main difference between these internal brands is that people can like one brand and dislike another. People who buy Bentleys probably aren't looking to buy a VW. Some high-end car buyers wouldn't be caught dead in the cheaper brands (too much emphasis on what others think of them).\n\nNot a lot of Cadillac owners would have been driving Saturns, after all." ]

[ "For combustion, you need oxygen. There is no oxygen inside a lighter. When the butane inside a lighter is released, it reacts with oxygen in the air to make fire. Because there's a much higher pressure inside the lighter than outside it, oxygen can't get in while the trigger is flipped \"on\" since butane gas wants to get out into the lower pressure and oxygen doesn't want to go into the higher pressure zone. Even if oxygen wanted to get into the higher pressure zone, it's being consumed too quickly to get in.", "I literally came in this subreddit to ask this question and you just posted it, wow, amazing", "Butane in liquid form, like other liquid gases, doesn’t burn. What burns is the vapor. It has to have a very specific ratio of vapor to O2 to be flammable. \n\nI know propane because that’s what I work with so that’s what I will use. For propane to burn it has to have 2.4%-9.5% vapor to O2. More or less and it won’t burn. Gasoline, butane, natural gas, all work the same way. You can put a lit match out in a bucket of liquid gasoline if it makes it past the vapor. \n\nSo when you light a lighter the spark is igniting the vapor that is being released. The vapor comes out with a good deal of force behind it and does not allow back flow. Once the hatch is closed the vapor is stopped the fire dies.", "There is a valve controlling the amount of gas. For ligthers like zippo's it has to do with the way the fluid is pulled through the cotton. Same way a stove doesn't explode when lighting it." ]

[ "Nowadays, it's mostly kept on computers, ideally in a large, properly equipped server setup with redundant backups and good security. \n\nIn the past, film production companies typically had physical storage areas available for film reels, both to keep them prior to mass production and also to serve as an archive. Today, Disney talks about bringing movies \"out of the vault\" in a purely metaphorical sense when returning them to circulation, but it used to be an actual archival vault they were kept in until needed/wanted. If something happened to that vault (fire, accident, ceiling leak that went unnoticed for a few months because no one ever went back there), it could result in the physical loss of the original/master copies, which in turn could result in a film being completely lost if a digital copy hadn't been made." ]

[ "Stars \"live\" for a characteristic *approximate* lifespan based on their mass, composition, and luminosity (how brightly they burn). We can pretty accurately estimate all three of these, by splitting the incoming light from a star and examining it. Different elements absorb light at different frequencies, so by studying the gaps in the spectrum of light we can tell what the star is (mostly) made of. Because stars all start off as balls of mostly-hydrogen, this also gives you some information as to how old it is. \n\nLuminosity is a matter of figuring out how far away the star is from us, and how bright it appears to be. Mass is a little more tricky, but can be inferred to some extent with a number of methods. Put it all together and you compare this star to the many others we've observed and classify it. Once you've done that, you have a pretty good idea based on its composition and luminosity just how long its lived, and how long it's likely to live." ]

[ "Burning causes things to expand, heat up and release gases. if its in an enclosed space such as a pipe, grenade casing, gas can, etc... then the pressure from these reactions builds up causing the big bada boom.", "Whether a mixture of air and gas is combustible depends on the air-to-fuel ratio. For each fuel, ignition occurs only within the explosive range (i.e., the lower and upper explosive limits). For example, for methane and gasoline vapor, the explosive range is 5-15% and 1.4-7.6% gas to air, respectively.\n\nSo a sealed or partially sealed can of liquid gasoline wouldn’t actually explode. The top layer would burn and consume oxygen, but it can’t burn faster than it consumes oxygen. However, a can of gas vapor at the appropriate concentration would explode.\n\nSame goes for wood. A block of wood will burn steadily, because the exposed surface area is limited. However, if sawdust is thrown into the air it can combust rapidly because the individual grains of sawdust have more exposed surface area and more available oxygen. This is why sawmills and grain silos blow up every now and then.", "chemical reactions often create gases. gases want to expand. If they are confined into a casing they instead build up pressure. Usually the pressure rises till the casing breaks under the pressure, and the high pressure is released very fast. that is an explosion. If your casing is stronger, you get a bigger explosion.\n\nOpen flames also create gases, but they don't build up pressure, as the gas can easily expand into the open air. The only way to get an explosion with an open flame, when the flame spreads faster than the pressure can relax into the air (which happens at the speed of sound)." ]

[ "Light gets scattered when it moves across a boundary, from water to air, or from air to water. If you have \"pure\" ice, with no tiny air bubbles, it is perfectly clear. The more air mixed into the ice, the more white and opaque the ice is, because light gets more and more scattered every time it crosses the edge of an air bubble.\n\nWhen you make ice in an ice tray, you fill it with water and freeze it all at once. Very little air, mostly clear ice.\n\nNatural ice formed from layer upon layer of compacted tiny ice particles will contain more air.", "Icebergs are going to contain flaws and other things that aren't pure water. These flaws make it harder to see through the ice. Also, the more ice you're trying to see through, the more flaws will get in the way. A thin sheet of ice will look transparent. A thick iceberg will look opaque.", "Icebergs come from snow that's fallen inland that has been compacted for thousands of years and slowly migrated towards the ocean. There is a lot of air and things that aren't water trapped in them making them appear opaque." ]

[ "Cold is nothing, but the absence of heat and not a distinct entity that can be created and has a mind of its own. So, it should be viewed as a baseline state that changes with addition or removal of thermal energy. Said removal happens automatically in nature with rapid dispersion of heat to the environment via infrared radiation mainly and convection and conduction to an extent (gravity tethers us onto other objects to which we will lose heat to if they are colder than us). \n\n\nPlaces like CERN has to remove the heat manually which is done according to refrigeration/air conditioning principles with a liquid medium being used to transfer heat energy from place A to place B. This is achieved by slowing down of the molecules of air when they “collide” with the slower spinning molecules of the coolant medium (as heat is simply the energy that spins particles of matter faster). In return, the coolant’s particles spin faster following these collisions. If you pump these particles to somewhere else, then the net effect is cooling down of the place that they were removed from.\n\n\nSo, there is no “freeze gun” that spews freezing cold magically onto objects, and sci-fi writers would be more scientifically accurate if they replaced it with a “heat removal gun”.\n\n\nHope this helps.", "There are two basic kinds of chemical reactions, exothermic and endothermic. Exothermic reactions liberate heat. Endothermic reactions require heat, and therefore can be thought of as \"creating cold\". (Cold is just the absence of heat, it's not really a thing in itself.)\n \nSo yes, there are such reactions." ]

[ "The gills are a series of very thin membranes through which blood can flow. The membrane is so thin that gasses can cross through via osmosis. Basically, if oxygen is higher on one side, it will cross the barrier until the concentration is equal on both sides. The same thing will happen with carbon dioxide, ammonia, water - anything that can cross the cell membranes.\n\nIt should be noted that all of this happens in the alveoli in lungs. The main difference is that since the alveoli need to say moist and you are not underwater, the alveoli are kept inside big sacks that are more or less climate controlled.\n\nGill don't work well outside of water because they also need to stay wet and when they dry out they start to stick together. When the membranes stick together, the sides touching each other *aren't* touching water or air, so they can't dissolve anything into or out of them.", "They run the water over a large surface area and extract the small amount of oxygen dissolved in the water - _URL_0_" ]

[ "We haven't. In fact Nasa plans on putting a man on the moon in 2024. Planning missions like these takes a long time in advaced, because literally every contingency needs to be planned for. Not to mention we plan to use it as a test for a new rocket design. These things have to be built, people need to be trained to fly them, Experiments need to be decided for the launch, etc. These things take time.", "We’ve learned a thing or two about space travel in 50 years, so you’d hope to include some improvements. Also, unless they were required to deliver design documents and procedures, NASA likely has no idea precisely how most of the stuff was built by the many contractors involved in the original Apollo missions. And manned space flight designs must be *exact*, or they must be requalified through test.\n\nSo you might as well just redesign and retest everything, and build in all the advancements we’ve learned in the last 50 years.\n\nThe problem these days is space isn’t sexy anymore. It’s hard to get sustained funding, because it’s easy to ask “why are we spending all this money on space when I could spend it on XYZ project which is *clearly* more important” (whatever it is). So projects start and stop and it’s difficult to get momentum going." ]

[ "It’s called the gate control theory of pain. Pain signals enter the spinal cord at a certain level. If you rub the area, you send many non-painful sensations of touch and pressure to the spinal cord that enter at that same level, basically flooding the input and preventing so many pain signals from getting through and up to the brain.\n\nImagine someone was shouting insults at you (the pain). Then imagine that 50 of your friends were shouting compliments at the same time. It doesn’t hurt so much now." ]

[ "French bread has only four ingredients: flour, salt, yeast, and water. No fats. Other breads can contain fats like dairy, oil. It’s the lack of fat that makes French bread get hard and stale faster." ]

[ "Babies are not talkative, but you can very well observe a babies reaction to various eye sight tests. An example are the Heidi tests which have various smily faces on differently contrasting backgrounds. Even a baby will react to facial expressions and this way you can conclude things about how well the baby can see. It takes more time obviously, but there are plenty true and tested methods.", "The real answer is - they struggle, a lot.\n\nYou can use lots of aides such as their reaction, but until they're a little older - you simply don't know if the prescription is correct" ]

[ "You generally don't taste things as well when they are cold, so cold alcohol is a bit easier to take that warm. You actually taste it just a bit less. This is the same reason why melted ice cream at the bottom of the bowl is just so darn yummy. One of the theories behind this is:\n\nYour tongue sends signals to your brain. Warm food actually changes the way your tongue sends those signals at the level of the individual cells, so the signal is actually stronger with warmer foods!", "There's an immediate numbing to your taste buds that take place when something cold is put on them, and thus they are less active. For strong alcohol, like grain alcohols, this makes the terrible taste of the large amounts of ethanol in them less apparent, while letting the other flavors come to the forefront." ]

[ "The way I understand it is that paper isn't completely flat, it has jagged edges so it's almost like a cut from a jagged knife." ]

[ "Interesting question. Most physical properties are defined by time. Ex: Velocity is distance per an amount of time, acceleration is a change in velocity per an amount of time. As such, you could say that time \"turns acceleration into velocity\", or time \"turns velocity into distance\". Thank you for making me think, and lmk if you have any further q's. It sounds to me like you'd enjoy a rundown of relativity, but I don't give those out unless people ask for them. || Edit: If you want to get into really deep physics, time could be described as the only force that actually exists due to relativity. Mass is drawn towards regions of slowest time. This means that gravity is merely objects moving towards places where time is slower for them, as well as electromagnetics and the strong and weak nuclear force. Ultimately this is just a thought experiment and has no real applications in physics tho.", "Essentially light often is considered to be \"time\".\n\nLight doesn't have mass, but it follows a so called \"null geodesic\". You probably have seen images of a black hole on some sort of grid or fabric, where the fabric or grid is going \"down\" and bends because of the black hole. This \"grid\" is the null geodesic, which would be why black holes can attract something without matter.\n\nAnd as light would be time, time slows down around a black hole.\n\nBut time as people normally understand it is generally a \"simplified\" construct made easier to put in perspective for us humans, because we (normal people) have a hard time wrapping our head around the concept, including the higher dimensions, and so on." ]

[ "Light reflecting off the back of the eye (the retina)\n\nFun fact: doctors actually test for this in kids. It's called the 'red light reflex,' and not having it is a sign of a tumor that can happen in kids or cataracts.", "It's the flash reflecting off of our retinas. A lot of cameras these days have \"red eye\" mode which will pop off a small flash to constrict the pupils, and then the regular flash when the picture is taken, and mostly prevents the issue.", "My son's pediatrician asked us to take a photo with an old camera (not our phones) to check for some sort of genetic thing." ]

[ "The Marines as the British Empire used the term were originally the soldiers on a ship. They were the ones that boarded an enemy vessel, or went ashore to claim a beachhead. In the US they had the same role. Over time they grew large enough that they were separated from the Navy but they still have close ties with it operating as security on Naval vessels and the like. \n\nIn modernity they are the \"Tip of the spear\". This means that they are essentially shock troops. They are trained to be among the first wave of an attack and take control of a piece of territory. In particular they \"specialize\" in water to land attacks. From the Spanish-American war onward, and in particular WWI every Marine was a trained sharp shooter so they were among the first to develop the modern concept of sniper in the US military.", "From a strategic point of view, Marines are a force projection tool. They are used outside your own borders to employ military force where one is needed. \n\nMarines are the spearhead that gets inserted to claim ground which can then be controlled by the Army once a secure beachhead has been established. They are carried and supported by the Navy which has all the tools to make sure that the Marines succeed in their mission. The Navy will clear the waters and landing areas with ships, submarines and Navy aircraft. The marines will then start claiming land. Once the land is secure you can utilize an existing airfield or build a temporary one which will be used to bring in the Army including Engineers. \n\nThe Army will then create semi-permanent facilities which can be used to bring in the Air Force if required. That's usually only the case if you're planning on staying for a while or if the land battle gets too remote from the sea and the Air Craft Carriers. Or if you want to disengage / re-position your naval assets. \n\nMarines are often thought of as the \"first ones in\" but in reality they are the second set of soldiers you have on the ground. \nThe first ones are spec ops operatives that will work with local friendly forces, gather intelligence, take out defenses and mark targets for smart bombs.", "Ive heard it described to me like this. The air Force brings the army to the battle and the Navy brings the Marines to the battle. That said, the Marines are like the tip of the spear in every conflict, they are trained to be capable of going from water to land, essentially being the first to attack.", "Hah! Good question. I can't give you a precise answer, but... As I understand it, the marines act much more in tandem with the navy, and tend to be the \"first responders\" to combat. Meanwhile, the army is organized to sustain long-term warfare on foreign soil, and has the technical capability to do so. There is actually an ongoing rivalry between the two departments due to their similarity, especially in terms of publicity." ]

[ "Are adults supposed to be light sleepers? I have to set like 15 alarms to wake up and have slept through a gas explosion right down the street lol", "Don't have a scientific answer but I think it's just because kids trust the adults around them to keep them safe. Both my kids sleep like the dead, I can move them and everything and it never occurs to their Spidey sense to go off and investigate why they're suddenly being carried off. I couldn't do it, if I was sawing logs then suddenly being carted off somewhere in the dark I'd freak but when you're 6 it's just like \"sweet, room service! I didn't even have to walk to my bed or tuck myself in!\"", "There's a host of factors, but you seem to be asking more towards the development side than physical things. When you are six, your brain isn't fully developed, so a lot of trained reactions aren't there yet. As a result, its easier to fall asleep and stay asleep.\n\nFor example, you hear strange footsteps in the hallway. You as an adult are now extremely alert. The six year old down the hall? Doesn't recognize this as an issue. These things add stress, which makes it harder for you to fall asleep. This is why if you have a ton of stress either from work or w/e, it encourages us to not sleep deeply.", "I became a much lighter sleeper after having a family, I've put this down to stress and instincts." ]

[ "Hard disks are composed of spinning disks that can be magnetized or de-magnetized in order to store data. To read or write on a certain part of the disk, the target region of the disk must sit below the read-write head. This part of the disk is then either re-magnetized or measured by a magnetometer. To achieve this, the disk spins, and the head moves closer/farther from the center of the disk. This means that memory access speed is limited by how quickly the disk spins and how quickly the head moves. Solid state systems, meanwhile, store data in special transistors. These transistors are arranged in such a way that a few electrons get trapped inside or outside of a part of them, and these electrons can be detected by the special transistor. These electrons are moved by other transistors in a network that decides which particular bit of the drive is to be read. The speed of these drives, if fully optimized, is primarily limited by how quickly data can be squeezed through the wire and terminals that connect them to the processor/RAM. In reality, (I think) these drives are limited by how quickly they can detect and communicate the presence of this excess/lack of electrons.", "In SSDs, you’re basically storing your bits of data in special transistors called floating gate. Electrons can get trapped in an area and stay there for a long time, even without any power. The SSDs have circuits that detect if there’s any electrons trapped or not in these floating gates. Obviously you need a ton of these transistors to be able to store som descent amount of data." ]

[ "The Earth is a big 'ol magnet. In space, there is a constant onslaught of charged particles (often electrons and protons) coming from the sun, other stars, and pretty much everything in space. These particles are deflected by the Earth's magnetic field, and due to some weird physics stuff, often find themselves bouncing between the north and south poles at high speeds. This means that they travel in these huge arcs over most of the Earth, and are lowest at the poles. Sometimes, these particles are low enough to hit the atmosphere. When they do this, they generate light due to the immense energy that is released in the impact. This light is the aurora.", "As other have mentioned Earth is basically a gigantic magnet. Earths magnetic field looks a bit like this-\n\n __ __ \n / \\/ \\ \n [ / \\ ] \n [ \\ / ] \n \\ __ /\\ __ / \n\n < edit1: dang it Reddits autoformating is destroying my ascii art > \n < edit2: Yay! fixed it i think. > \n\nMagnetic Field lines emerge out of the pole, arc out into space, and loop back in, returning to earth at the opposite pole. Charged particles from the sun upon entering the field get channelled along these field lines (the direction depending on the charge they have) and due to the shape of the field, get funnelled down towards one of the earths poles. When they strike molecules in the upper atmosphere, it's a high energy collision that produces light which we call the Aurora" ]

[ "I absolutely hate fake cherry flavor... I didn't eat cherries for 21 years of my life because I thought they all tasted like cherry candy..." ]

[ "Team A has a $50m budget because they have a rich donor. \n\nTeam B has a $10m budget. \n\nTeam A can afford to lure multiple top tier players and therefore always walk all over Team B. Salary caps help to stop teams buying their way to the top of the ladder and even up the playing field.", "The majority of American sports (NFL NHL NBA) have a salary cap, but NBA has what they call a soft cap. \n\nEssentially the cap is determined by a % of the revenue the whole NBA brings in. This revenue includes ticket sales, tv rights, merchandising etc. \n\nSay for this year the cap might be $100m. NBA teams cannot sign players that will push them over this cap. There are a lot of exceptions to this rule, that I won’t expand on, but they basically relate to keeping your own player (bird rights), certain yearly exceptions, rookie contracts, mid level exception, minimum salary exception and you can trade players that will put you over the cap too. There are more exceptions that I’m not even too familiar with. \n\nThen there is a luxury cap threshold, say for example it’s $120m, owners will have to pay the league a penalty for everY dollar over this luxury cap (this can get ridiculous because it can go to 4-5x the amount you go over the cap. If you go over the cap by $20m, you could pay $40 in taxes). Lastly, there is this tax apron level, it’s about $6m higher than the luxury cap threshold and if you exceed this, you get limited to what exceptions you can use (eg mid level exception)\n\nIn terms of how much players get paid, it generally depends on how long they have been with the league. If you have been 0-6 years in the league, max is 25% of cap, if you have been 7-9 year, you get 30% etc. Again, there are a bunch of exceptions like rookie contracts from draft picks, team loyalty type exceptions (designated player/ Derrick Rose rule), and super max. \n\nIt’s actually quite confusing and I don’t even fully understand it. Hope this helps" ]

[ "Gelatin works by creating a medium-loose bond between water molecules using collagen which is a type of protein. When you freeze prepared gelatin, the water molecules break the bonds with the collagen. These do not reform properly when it is thawed. I have not tried completely melting the gelatin again to see if it would re-set, but it seems unlikely.\n\nAs far as why it is dissolving when submerged, gelatin does that when left submerged even at room temperature as far as I have experienced. I think the water dissolves the collagen bonds as it tries to form a homogeneous mixture." ]

[ "[Turing](_URL_0_) is a microarchitecture (a type of chip) from Nvidia. It's used to build GPUs (chips specialised for graphics) with support for more general purpose parallel programming (GPGPU) as well. Turing shaders are programs written for this type of chip." ]

[ "An even number of rotors makes it easy to prevent unwanted spinning. Each rotor spinning clockwise has a twin rotor spinning counterclockwise, which allows the drone body to sit still without rotating. Now, in order to tilt forward, backward, left, and right, the drone needs three or more blades. Four is the smallest even number greater than three, so it is usually chosen. There are, however, drones with more rotors. I've seen six and eight rotor drones, and there are probably even bigger ones. Usually, for small and simple systems, four works best. Edit, since you lot keep asking it: HELICOPTERS USE COMPLEX ANGLE-SWITCHING ROTOR BLADES AND VERTICAL TAIL ROTORS THAT AVOID THE ISSUE", "Am I allowed to post a follow-up? Why don't modern manned helicopters use 4 rotors? Cost, design efficiency, don't fix what isn't broken? Do we know of any modern manned designs that take inspiration from UAVs or are there are plans for up-scaled and manned quadcopters?", "Ooh, ooh! I know a really good answer to this one!\n\nFirst of all, when people tell you \"an even number of rotors is good for preventing unwanted spinning\" etc, etc, this is, frankly, only a half truth.\n\nThe bottom line of the matter is that the mathematics involved in keeping a multicopter in flight is hella complicated, and the problem of handling an odd number of propellers is trivial by comparison to the problem of reacting successfully to random fluctuations, slight differences in rotor behavior, and discrepancies between control and response. In fact, even the act of a quad-copter turning involves all the math necessary to overcome an odd number of rotors.\n\nWant proof? Here you go:\n\n[Pentacopter](_URL_0_)\n\nIt's uncommon, but it is possible and has been done.\n\n***That being stated,*** it is very much true that the ***amount*** of correction needed is significantly reduced if you have an even number of rotors.\n\n# The real reason you want at least four rotors is actually straight out of linear algebra!\n\nThere is a concept called ***Degrees of Freedom.*** In a single sentence, it basically says that if you want to be able to control N aspects of your kinematic state, you need N independently controllable force/torque appliers.\n\nThe reason this comes from linear algebra is that you can think of the total torque and force at any given moment on your multicopter as a vector in 6D space. To be able to achieve any torque/force combination, you need to have force appliers that, when combined in different ratios, let you access the entire 6d space.\n\nIf you only have three rotors, you are restricted to a 3D slice of the 6D space.\n\nTo make this less math, and more practical, think of it this way: Each additional rotor gives you, essentially, control over one additional aspect of your multicopter's kinematic state.\n\nA quadcopter has four rotors, and hence (with typical configurations) has control over the following aspects:\nAcceleration Forward/Back, Acceleration Left/Right, Acceleration Up/Down, and Yaw.\n\nThat's four. With four rotors, once you pick those four, you have no control over the remaining two torques: Pitch and Roll. That is why quadcopters ***always*** tilt the at the same rate for any given side-to-side acceleration. They don't have a choice in the matter.\n\n\nNow, you can see the problem with only three rotors. You can control your position in 3D space, but to do so you must sacrifice control over your yaw torque. The exact math works out that to maintain stable position, a tricopter would have to sit there spinning violently. (***This is where the notion that an even number is required for torque balancing comes from -- but in reality, you just need a number greater than 3*** That makes them \"unusable\" for most purposes.\n\nNow, this seems odd, because there do exist a few tricopters out there. But, if you [look closer](_URL_1_) these copters have a hidden servo which achieves a fourth Degree Of Freedom by tilting one of the rotors.\n\n# TL;DR It's not true that you need an even number of rotors. It is only true that you need at least 4, because you need 4 degrees of freedom to be able to move around and turn with stability.", "It's the smallest number that makes control really easy, because you can change direction forward, backward, left, and right, simply by changing the amount of power each rotor gets.", "Lots of great answers here about \"fixed pitch\" blades vs a traditional helicopter rotor head design.\n\nWith small electric motors you have instant access to 100% of the tourqe that electric motors supply. Being that there is no spool up or spool down time, a fixed pitch blade is the lightest design for electric motors.", "You need an even number. If you don't have the same number of motors going clockwize as there are ones going anticlockwize, or the drone will just end up spinning.\n\nAnd with two, you could only tilt forward or back, but not side to side.\n\nBut when you need a fairly large drone, you can ad pairs of rotors for extra lift. Professional camera drones are often hexacopters, with 6 rotors. You could do 8 rotors or more, but once things get bigger than a certain level, you can be better off ditching the electric motors and fixed blades, and building a real helicopter.", "There's an economical side to it too. This is regarding general drones on the market, not military or high spec.\n\n4 rotors is typical because it's cheaper. Its the lowest and easiest quantity to work with, for the reasons others have said (stability, maneuverability etc). Generally speaking, 4 rotors is the most common because it's decent stability and control without too much manufacturing or cost involved. It's also lightweight which makes them more agile (ideal for drone racer), and saves on manufacturing costs. \n\nIf you go up to 6 or 8 rotors, the stability would be a lot better. But it also draws more power, meaning less flight time and higher expense.\n\nIf it was designed PROPERLY with an 8 rotor, it could still be efficient and have a decent flight time. Each rotor would only need to produce a small amount of thrust, so each rotor would operate more efficiently, therefore resulting in a more efficient system. \n\nBuuuuut the world runs on money so the cheaper option is always taken for generic rotors. The whole system would have to be custom, each individual rotor and motor. Highly doubt the ones you find on the shelves are custom designed. \n\nEconomically speaking it's cheaper to take 4 off-the-shelf rotors to make the zipzip go zoomzoom.\n\nI hope this makes sense I'm really high and my aerospace engineer boyfriend confuses me. Also this is his personal educated views on it as he does not work in the specific market (his work is on jet engines/turbine engines, not drones).", "4 rotors give you control with fixed rotors and no servos. 3 rotors and you need 1 servo.\n\n5+ rotors give you redundancy and increased max lift at the cost of efficiency. An octocopter can lose motors and not fall put of the sky but is less efficient.", "There's an interesting way at arriving at 4 rotors that ignores virtually all of the physics of how they fly: looking at degrees of freedom.\n\nDegrees of freedom is a way of considering how something moves. Take a car, for example. It can go forward and backwards and it can turn left and right. It can't (normally) roll on its side or pull its nose up. It can't go up or down (not like hills, but flying). It can't slide sideways. Since cars can move in two ways we say they have two degrees of freedom.\n\nIn order to control that they need two control inputs. For a car those inputs are the steering wheel and the combined effect of throttle and brake.\n\nNote that *any* attempt at giving car-like motion to a vehicle will need two control inputs. If you only have one then that kind of control is impossible. If you have more then you can't actually get a meaningful effect out of some of your control (we see that with throttle and brake on cars, where holding both pedals gives the same effect as pressing neither—at least in terms of motion). A tank, for example, has the ability to go forward and backwards and to turn left and right, but its two control inputs are the speed of the left track and the speed of the right track.\n\nWith this means of analysis in our back pocket we can look at drones. We want the ability for them to fly up and down. They should be ale to turn left and right. Then we look at moving around left/right and forward/backwards. We don't actually need to have those two degrees of freedom because we can instead make them able to tilt nose down which makes any upward thrust also push the drone forward. This means our last two degrees of freedom are tilting nose up/down and rolling left/right. Note that full-sized helicopters need the same four degrees of freedom.\n\nWith these four degrees of freedom we need to start finding our control inputs to allow for that motion. Helicopters get their control inputs by having the ability to alter the pitch on the blades rapidly, as they move in a circle. That makes for a very complicated mechanism. On a drone the goal is for the control input to be speeding up and slowing down the motors, so we need to arrange as many rotors as we have degrees of freedom: four.\n\nNot just any arrangement would work here—stacking four rotors on top of one another doesn't actually give four meaningfully different control inputs—but luckily there's a simple arrangement that does work. We arrange all four rotors on a plane and make them alternate the direction they spin. To go up/down you increase/decrease all of their speeds. To turn left/right you increase the speed of the clockwise-spinning rotors and decrease the CCW rotors, or vice versa. To roll left/right or tilt nose-up/down you increase the speed on the side that's going up and decrease the speed on the side that's going down. It winds up being a pretty simple control approach to design and operate at high frequency.\n\nYou can make a drone with more rotors easily, though you generally want to stick to even numbers so that half of the rotors can spin one direction and the other half spin the other direction. 6- and 8-rotor drones are common for drones that need to carry a heavier payload. You can make a drone with 3 rotors but then you need to have another control input. I've seen this done by adding the ability to tilt one of the three rotors in its entirety. You can also make a drone with only two rotors, but then you need two additional control inputs. That's a helicopter.\n\n4-rotor designs are common because that's the minimum number of rotors (and, more importantly to cost, motors) needed to give the control you want without needing some extra method for enacting control on the drone.", "It was quite interesting following multi rotor experiments in the R/C helicopter forums back in the day.\n\nA R/C helicopter generally has a 3 (every 120°) or 4 (every 90°) servo setup to control the swash plate. The swashplate controls the pitch of the blade as it makes 1 full rotation. \n\nFor example to induce forward flight the swashplate will induce more pitch as the blade travels to the rear and less at the front of the circumference of its travel resulting in the helicopter pitching forward.\n\nMixing inputs to all the servo's from the control sticks makes it possible to move in any direction. \n\nThe tail rotor (rudder) pitch is controlled by another servo and is pretty much impossible to control without aid. You have to compensate the torque from the main rotor as well as giving the right amount of output to change the direction you wish the helicopter to face.\n\nA gyroscope is used to keep the tail in control and keeps the nose pointing in its current direction when there is no input from the pilot.\n\nPeople started adding gyroscopes to the servo's controlling the swashplate in an endeavour to create a stable easier to fly helicopter with success.\n\nThen replacing the swashplate servo's with motors that drive an individual rotor leads us to the familiar drone look.\n\nIt can be looked at like a flying swashplate which removes all the extra complicated mechanisms required to make a helicopter.", "As the other posts have shown, this is quite a complicated subject.\n\nFirst, let’s look at a modern helicopter. They have a single rotor on top that provides their lift and thrust, with a small rotor on the rear for stabilization. This second rotor is required because of Newton’s 3rd Law of Motion, “Every action has an equal and opposite reaction.”\n\nSimilar to how, floating in a pool, if you push your arms to the left, your body will spin to the right, this means that once the helicopter is off the ground (and therefore has no friction holding it straight), the rotation of the upper rotor causes the body of the helicopter to rotate in the opposite direction. The rear rotor on most helicopters is designed to prevent this rotation, and also to speed up or slow down to force the body to rotate in either direction. Most retail drone designs use a multiple of two rotors spinning in opposite directions, because the spins offset each other and prevent rotation of the drone body during stationary flight.\n\nTo fly forward, most helicopters have their upper rotors on an actuated joint (it can be angled forward or backwards, usually using pneumatics or hydraulics), and when angled forward the upward thrust goes up at an angle, pulling the body of the helicopter forward. These types of joints are rather complicated, and drone makers don’t end up needing them, because they have a different way to angle their rotors.\n\nInstead, they (typically) use four rotors. This is the simplest way to address the complications of 3D flight. With four rotors arranged in a square, and each rotor traveling the opposite direction of its neighbor (so the rotor on opposite corners spin the same direction), the drone will not rotate in the air normally. To rotate the drone clockwise, you spin up the counter-clockwise rotors, because then the clockwise rotors won’t completely offset the rotation; and vice versa.\n\nFor lateral movement (forwards, backwards, and side to side), you spin up the motors opposite the direction you want. To go forward, the rear 2 rotors spin up, and the added upward thrust tilts the back of the drone up, which angles all the rotors so that they’re slightly forward. This creates the same forward angle as the helicopter, without the need for the extra joints, and the thrust then pulls the drone forward.\n\nThe reason 4 rotors are used is because it’s the fewest rotors to be effective without complicated math. With 2 rotors, you can only rotate and go forwards and backwards; no side to side. With any odd number of rotors (like 3), you need to carefully balance the total force of all clockwise motors against the counter-clockwise ones to prevent unwanted rotation, and that mostly prevents using the same type of motor for each rotor. And more than 4 is functional, but more rotors = more power. That’s why the ones you see at the store have 4.\n\nThere are hobbyists who use more rotors, however, and it can offer advantages. More rotors means more fine control of directional travel, for example. It’s not hard to take a 4 rotor drone and make it fly at an angle (forward+right), but a 6 or 8 rotor drone will do it more smoothly. Also, with more rotors, if one motor goes out, you can have the onboard computer shut off the opposite rotor to stabilize, and you still have at least 4 rotors for 3D movement. This is particularly handy if you are drone racing or doing aerial acrobatics with an expensive drone, so at least you can get it down relatively safely for repairs.\n\nTL;DR - 4 rotors is just the cheapest way to build retail drones, so it’s most common. Depending on the drone’s purpose, and how important stability is when a motor fails, more rotors can be used, but it will increase power consumption and require a more complex computer, making it inefficient for beginning hobbyists who just want to fly a cool drone around.", "A search of the first 200 comments didn't touch on it so I'll just bring up the reason that real helicopters don't use the same configuration as drones, weight. Ideally 4 rotors is a great setup but as an item gets bigger it's mass increases exponentially, specifically the [inverse square law](_URL_2_). As a result, scaling everything makes multiple rotors insufficient to lift a full size helo. Small electric motors are good enough for a drone, but batteries are super heavy so a full electric manned helicopter is just not feasible with today's technology. Add in the weight of the extra rotor and gearboxes/motors and it's easy to see why single main rotors are the standard with just a few specialized designs opting for 2 rotors. Even drones suffer from this, larger ones often have 6 or 8 rotors but each time you add another rotor you get fewer and fewer gains for the same motor being added; as size increases mass just increases faster. Eventually you hit the point where the complexity of making a single main rotor work far outweighs the downsides of adding a half dozen more rotors.", "Six is best for resilience. If a motor or rotor fails, its partner on the other end can also be stopped.", "These drones have a total of 4 moving parts which makes them mechanically extremely simple machines.", "_URL_3_\n\nThis guy experiments with different types of rc vehicles if you were interested", "Mostly it comes down to stability.\nYou have 3 general directions to move about in space\nForward and backward (pitch)\nLeft and right (roll)\nAnd rotation (yaw)\nThen there’s thrust to change altitude\nPitch roll and yaw movements spin up, or slow down rotors in order to move the drone how you want it to.\nThe more rotors the more stable the drone becomes by mitigating things like vibrations or prop wash. You’re high end cinema quality drones will use 6 or 8 large rotors to increase stability for a better shot.\nThere are videos on YouTube from Rotor Riot that have tested all kinds of drones from 2 rotors to 8 that you can watch and they break down the nuances a lot better than some of us can", "drones don't have to have 4 rotors, its just generally the best all-round setup. \n\nbicopters: require careful balancing and need two servos to tilt the the two rotors for a yaw axis.\n\ntricopters: less picky about the balance but still needs a servo to tilt one of the rotors to gain a yaw axis.\n\nquadcopter: all axies can be controlled by changing the speed of the motors, also controls the same in any direction.\n\nhexa/octo-copters: controls like a quad but with more power and redundancy, but at the cost of efficiency", "you need 2 at minimum to counter torque like helicopter with single rotor and tail rotor or like tandem heli \n\nany number after that works as well but with less then 3 you need rotors that have more mechanical controls on them with 3 or more you can control pitch roll and way with just speed changes \n\nreally these drones are inefficient has all hell your better off with single or tandem rotor helicopter layout for payload and endurance", "To add into higher comments, it depends on what you want to use your drone for. For package carrying 4-8. Heavy packages 6-8. Etc. You can customize it immensely so its possible with pretty much any number. It's just that 4 is often used b/c it gives a good balance of all the different numbers of rotors: pretty stable, can provide decent lift, decent speed, responsive handling, etc.", "Probably more interesting us how they went from being called quadcopters to every remote controlled flying thing being called a drone. A weird combination of media misunderstanding and politics somehow took a word only being applied to large, remote controlled aircraft that fire guided missiles and applied it to RC hobby crafts. This both accelerated the vilification of quadcopters and played down seriousness of military remote aircraft.", "4 motors have no redundancy (cheaper), 6, 8 etc have redundancy. Kinda like airliners having more than 1 engine for safety compared to small private planes. Airliners have to meet minimum performance capabilities if an engine fails were as the single engine planes ‘glide’ and hope for the best", "This is because 4 rotors are the minimum required to tilt the drone in all directions, without any servos (aka moving hinges, etc).\n\nAlso, 4 larger propellers are more efficient than smaller 5,6,8 propellers.\n\nFor more information, google 'Flight dynamics of quadcopters'." ]

[ "If a company or individual sets up a company or purchases assets or a significant share of an existing company in a foreign country, that is considered FDI. The assets purchased are located and in use in that foreign country.\n\nDay to day or small trades in shares of a foreign company does not constitute FDI. These typically only reflect in changing in equity ownership (no controlling interest) and does not inject new capital into the firm.\n\nBuying assets and exporting them to another country for use or sale (say capital equipment or products like phones, cars etc) does not constitute FDI. It is considered international trade. \n\nForeign currency trading or speculation is not considered FDI.\n\nFDI is an important statistic because it implies a long term commitment to operate in the country. These investments are less subject to capital flight risk unlike, for example, trading in company shares/stocks or foreign currency purchases. If a country attracts a lot of FDI, it is a signal that foreign investors have confidence in the economy and, to a certain extent, the governance of that country. Many factors go into building foreign investor confidence - rule of law, manageable corruption, a good track record of fiscal and monetary policy management, stable government, ease of capital inflow/outflow, fewer rules discriminating against foreign ownership etc etc. In more recent times, issues like human rights, environmental policy, labor laws also play an increasing role in the attractiveness of a country for FDI." ]

[ "Once the motorcycle is moving, the rider pushes on the handlebars to lean the bike and to stand it back up. \n\nPush on the right bar to go right, push on the left bar to go left. That leans the motorcycle over. The harder and longer the push, the more it leans. The more it leans, the tighter the turn. Relax on the bar and the motorcycle continues to turn in the direction it's leaning. To stop the turn, push on the opposite bar and the bike stands back up. How much you have to push varies from motorcycle to motorcycle. A well set up motorcycle needs no control inputs on the bars to go in a straight line and once leaned into a turn will continue to turn at that radius until it's stood back up again." ]

[ "The path the tires follow works with inertia to adjust the bike's angle. Starting a turn, you actually have to steer *opposite* the direction of the turn to get the lean going. From there it's a combination of steering and slight shifts in body weight to maintain course. When you want to straighten out again, you steer a little more sharply to, in a sense, \"put the bike back under yourself.\"\n\nReally it works the same way as on a bicycle, but with a lot stronger forces involved." ]

[ "A benchmark interest rate is set by independent financial institutions to show how expensive (i.e. at what rate) banks or funds can get money from the market (bank to bank transactions of borrowing money). The independent financial institution collects estimates from a panel of various banks on what they ecpect the rate to be at which they can borrow money. This is then used to calculate the benchmark rate. \n\nOne way a bank makes money is borrowing money to companies at the benchmark rate +x% where their profit is basically the x%. \n\nA prime rate is the interest rate a commercial bank (a bank you and I use) will offer to its best customer for borrowing money. The prime rate partly depends on the benchmark rate and is also calculated as benchmark rate +x%. \n\nSorry if its not ELI5 enough, i tried my best." ]

[ "There are various methods, such as using computer models of stellar life cycles, but the most tangible way is simply that we know that other things that probably formed around the same time as the Sun were formed around 5 billion years ago.\n\nIt's likely that the entire solar system (the Sun and the planets) formed at roughly the same time, so to approximate the age of the Sun, we can take a look at the age of objects in our solar system. The oldest meteorites we've found are approximately 4.6 billion years old, according to radiometric dating; round that up to 5 billion and there you have it.", "Dating rocks, specifically Lead: \n [_URL_2_](_URL_0_) \n\n\nEarth rocks tell us the age of the Earth, finding the oldest meteorites tells us the age of the Sun, as those meteorites were formed at the same time as the Sun. When using the scale of hundreds of millions or billions of years, knowing that this took place around 5 billion is possible to estimate by comparing what we observe elsewhere in the universe as well.\n\n [_URL_1_](_URL_1_)", "Sun and Jupiter formed from the same disk of matter. Sun uses itself as fuel. Differences between Jupiter and Sun show how long Sun has been burning.\n\n\nELI20:\nWe can type composition variances between the Sun and objects made from the same interstellar disk. Jupiter is a fair example as it is far enough away that solar radiation has not caused large variations, and what variations exist can be accounted for through parameterization.", "We know the pattern of a stars make up as it ages, like wrinkles on a person, but much more accurately. The amounts of certain elements can be seen over time by observing the colour of a star. Our Sun has about half the amount of a chemical (sodium) in its outer layers than similar stars closer to death. We know that stars the size of our Sun last 10by, so know it must be about half way through its life.", "Im no documented science thing figurer outer but:\n\nWe know what the sun is made up of (probably very accurately).\nWe know what the sun does with the stuff we probably very accurately know it's made up of.\n\nWorking backwards using math that is probably only made up of letters and hieroglyphics, documented science thing figurer outers can provide us with a best guess of when it all happened.\n\nThere is room for error but on that scale 1% is the difference between dinosaurs walking the earth and the end of ww2.\n\nThere are various space goggles that have seen and are watching these things unfold to help these documented guys make \"corrections\" to or \"support\" the current math equation.\n\nBut again, this is just my guess of how it's done. Correct me if I'm wrong.", "The most common isotope of uranium has a half life of 4.6 billion years. When it's trapped in a crystal lattice it can't just pick up new materials. By knowing the total amount of material that's trapped and how much of it is uranium and how much is lead we can get a number. Now expand that sample size and you have a number you can trust, especially when that experiment gets repeated by others and their data backs up the method. This tells us how long the rocks have been around in the cloud that would make the sun, so it's fair to say the sun is pretty close to that value since the time scales are huge (a few million years really doesn't mean much)." ]

[ "If you mean like the Dyson fanless fans, they have one big fan hidden in the base, that sucks in air from the holes, then pushes it all out of the 'fanless' section via a slot that runs along the edge" ]

[ "Languages show the connection. Indogerman languages are spoken in Europe and the western of asia, the anchestors of German, English and many other languages. You see the relationship in word like \"mother\" or \"Mutter\" (German), \"knee\" and \"Knie\". They didn't imitate each other, they are both \"a dialect\" of Indogerman. (Beside them - with no relationship - there are Finno urgic \"Families\" with Hungary and Finnish.)" ]

[ "The economy is all about people spending money and money changing hands, which is affected by inflation. \n\nImagine you have £100 or $100 in your hand.\n\nWith that £100 you want to buy a load of things. Due to steady inflation, that same amount of money is less powerful the longer you hold on to it.\n\nIf you know the things will slightly increase in cost over time, then it means you have a reason to spend the money now, benefitting businesses, rather than later. Money changes hands and the economy keeps working.\n\nIf you know the things will get cheaper over time (deflation, negative inflation) then you may wish to hold on to your money and wait until you can buy more things with that money. If everyone did this, money would stop changing hands and the economy would break, putting lots of people out of business and out of jobs.", "Say you want to make a cup of coffee. You need ground coffee beans and water (plus equipment). If you have 1 bag of coffee, you can make 10 cups. If you have half a bag, you can make 5 cups.\n\nCoffee beans are expensive so it makes sense that the limit on how many cups should be based on how much you spend on beans. It doesn't make sense for water to be the limiting factor. Water is extremely cheap. You just turn your tap and you have a near limitless supply. You shouldn't have enough beans to make 10 cups, but be limited because you don't have enough water.\n\nThe same thing applies to the economy. Oil, steel, rice, etc. are all limited resources on Earth. It makes sense that we don't have enough of these things. But money is not a limited resource. The government can just print it out whenever it wants. There should never be a transaction that is limited because even though there is enough rice, there isn't enough cash.\n\nSo central banks aim to have exactly the right amount of cash for all transactions. They might build in a slight margin of error too so the supply of money is slightly greater than what is needed to avoid any risk of limitation. Plus, the economy is constantly growing. The money supply needs to grow to match. So if the economy grows at 2-3%, then it makes sense to have the money supply also grow at 2-3%\n\nThere are also risks of too much inflation. But since you specifically asked about the risks of deflation, I just focused on that.", "The problem is that you can then get deflation, where prices actually decrease in value while this does initially seem like a good thing it can have some really serious consequences for an economy as spending on goods and services slows down - _URL_0_", "In the ideal world, we would have a target inflation of zero. The problem is that it is impossible to get exactly on target, so we aim for 2%, to avoid accidentally going into negative inflation—I.e. deflation. \nDeflation is bad because it will make people postpone purchases since they know the price will go down. Postponed purchase lead to decreased gdp which leads to recession." ]

[ "Container vs Codec:\n\nEvery video consists essentially of still images played at a frame rate. Each image consists of pixels. Each pixel consists of 3 colors. Each color takes up a byte at least. \n\nThis is a lot of data. File sizes for videos would normally be massive if not for a little trick we knew, compression.\n\nCompression takes a file and just applies various tricks to shrink its size. For instance if it sees that two frames are the same, rather than storing both, it will store one and have the place where the other one is say \"this is a duplicate of frame x.\" But in practice things get more complicated than that, we have developed a **lot** of math tricks to bring file sizes down. \n\nThese compression algorithms are known as codecs. Software that would play video that uses them has to have the decoding algorithm for that codec to figure out what the pixel colors and what not are.\n\nThis differs from a container, which holds the video compressed by the codec, along with a lot of other things, like audio, subtitles, ect. MP4 denotes container, not codec. Its just a way of organization." ]

[ "Light travels at a known speed, by reflecting the laser back , it can time it and give you a read out on distance based on the time it took to come back to the source." ]

[ "It probably has something to do with aour blood pressure, and that when we stretch, ouor muscles contract increasing that pressure, making as more \"alive\", and \"rested\", which helps us be active.\n\nNot sure, tho.", "Blood flow out of your legs (called venous return) is largely dependent on the use of your muscles. Your leg muscles are in close proximity to your veins, and veins don't have their own muscle like arteries do, so when your leg muscles squeeze when you walk, they also squeeze the veins a bit. Thus pushing the blood up. Your blood supplies oxygen and carries out all of the waste junk your body doesn't need (waste removal is most affected by poor venous return), so it is super important for a happy, healthy body. Getting up and moving a bit after being sedentary for a while helps get things moving better. Your muscle tissue can go for a good long while in this state, so it isn't like your muscles are damaged by sitting for a bit. But it feels good to restore that full blood flow. \n\nThere is a similar reason why you should get up and spend some time walking the aisle when you are on a long flight. Static blood likes to clot, so sitting for too long without moving your leg muscles at all raises your risk of a blood clot in your legs. \n\nCredentials: Medical student.", "Educated guess here but I imagine it's because blood flow to the lower extremities is more restricted when sitting. When you get up and and stretch you're increasing blood flow to oxygen-deprived muscles, which feels good." ]

[ "\"Better\" is subjective.\n\nHas anybody ever been biologically male, and then biologically female, and compared the two? I don't think so. So we can't ever actually compare them.", "Because men are virtually guaranteed an orgasm and women are not. If you had an orgasm every time you did something, you’d be highly motivated. If you had an orgasm only sometimes, you’d be less motivated. Most women do not achieve orgasm during intercourse. Statistics vary, but the story is consistent: _URL_0_", "Every woman is different regarding whether they thoroughly enjoy sex or not with a lot of various factors (i.e. confidence, beliefs, respect, if the focus is always on the man or also on the female) but I think a major factor is their man - if he knows their body and how to do the job it’ll be a big difference. I think society’s association with being a slut if a female likes sex is also part of it. That cliche saying about it not just being about the end, but also the journey also applies to sex. It’s good to please your man and he should also please you. Ultimately, it is different for every female." ]

[ "When an EU visitor buys stuff, he pays the store for the item as well for the sales tax. The store will transfer the sales tax to the state.\n\nWhen an non-EU visitor buys stuff, the initial cashflow is the same. The non-EU visitor can claim the sales tax back when leaving the EU with the item. Usually the store will pay them back at a later point, and then not have to pay the sales tax to the state.\n\nProfit for the store will be the same. For stores located near EU borders, it is a minor act in paperwork, but a huge incentive for non-EU customers to come and buy there. Basically free advertisement.\n\nSource: did this multiple times when living in non-EU.", "Notably, that buyer will have to pay taxes on imports to their own country. We have harmonised in Europe to make it not a thing between us, but someone from outside doesn't get taxed twice *if the goods are exported* (you have to show evidence at the airport)." ]

[ "The vagina is formed from two different bits of the back end of the embryo, the hymen is considered to be the boundary between the two where it has failed to break down" ]

[ "It's a warhead strapped on a rocket. Rockets go fast.\n\nIf you can identify and properly track the rocket, sure. You'll need a rocket that can go faster than your enemy's.", "Because an ICBM is a just a rocket and rockets go really fast. Rockets that reach orbit are traveling at least 7.8 km/s. ICBMs are only a little bit short of that speed. The very first rockets that sent satellites and even humans into space were literally ICMBs but with a satellite or capsule instead of a nuclear warhead.\n\nCan they be intercepted? Technically yes, but it's really hard even under ideal circumstances. It's like trying to shoot a bullet out of the air with another bullet.", "An ICBM is really just a single state rocket booster with a warhead slapped on top. They can go extremely fast at altitude as a rocket engine that carries its oxidizer with it does not lose thrust with altitude, where the air gets thinner means it can go much faster only being limited by heat friction. And yes they are possible to intercept with other missiles. But it is an untested system. As far as i know there are no aircraft that can get to ICBM altitude and launch an AAM at it before its out of firing range making interception very unlikely.", "An ICBM is a multistage rocket. The first two stages will get the payload up a few thousands kilometers in about 5 minutes, the third stage will then propel it towards its target at a 6-7 km/s letting it arrive anywhere on the world in 30 minutes of launch.\n\nThis timing may seem really short, but remember the ISS orbits the Earth every 90 minutes and it doesn't have a big rocket strapped to its back to hurry it along. They also go up far enough that the Earth does orbit under them as their orbital circumference is now 50% longer than the Earth's circumference.\n\nOnce they're headed back in, it will deploy the MIRVs(Multiple Independent Reentry Vehicles) of which some are decoys and some hold nukes that will take out a city. The Sub launched Trident II has 8-14 MIRVs on it.\n\nInterception during the Boost phase(initial launch) is easiest from a technical stand point as you've got this big missile that you need to hit and it isn't moving very fast yet. The problem is that they tend to be launched from deep inside a country's territory to protect them while makes this feasibly the hardest stage to intercept them in.\n\nThe other most likely stage for intercept is the Terminal stage when the reentry vehicle with a warhead or a decoy is headed straight at you. Its moving at Mach 10 towards you so you don't have long to hit it. Its now down to about 0.3 meters in diameter and 1 meter long which makes it a pretty small target, and if you miss millions die. Good luck!\n\nThere are also efforts to make the MIRV steerable. When you hear concerns about a Hypersonic Reentry Vehicle this is what it refers to. Its hard enough to hit a 0.3 x 1 meter cone that is flying in a perfectly straight line, it will be even harder if it is taking evasive maneuvers on its way in.", "ICBM's go super fast and super high. They use massive rockets to propel themselves at speeds that boggle the mind, and use this speed to traverse vast distances. They use gravity to ensure that they come down where they are supposed to. Can they be intercepted? Yes. Easily? No. Because of their speed, radar can have trouble picking them up, and missiles can have trouble tracking them and keeping up to them. Also, due to their height, you need your own massive rocket to reach them during most of their journey, and once they are nearing the ground, you need an even *faster* missile to intercept them before they reach their target. Currently, no functional anti-missile system is publicly described, due to the fact that their functions are top-secret. AFAIK, one of the U.S.'s current systems involves intercepting missiles right as they launch, which is when they are moving their slowest. This requires ships armed with the weapon to patrol most of the world to ensure that they are within range of any enemy missile sites." ]

[ "Statistics is a branch of mathematics that addresses questions like this. Put simply, if you choose a representative sample from a much larger population, the opinions on the sample group align tightly with the opinions of the entire population. It comes down to two things. The first is that none of us is special or unique - there are literally millions and millions of people who think about any given issue the way you do. So if you are part of a sample group, you speak for a big piece of the entire population. Second, the polling company needs to make sure the sample group isn't homogeneous - in other words, there needs to be differences in the sample that reflect the population you want to draw conclusions about. If the larger population is 55% women, then your sample should be 55% women. If the population is 20% between 18 and 29 years old, your sample should be 20% be between 18 and 29. Etc. Good polling firms interested in reliable and meaningful results know how to craft a representative sample.\n\n/edited to correct typo", "When you take a sample that can be subdivided the same way as the larger population (let's say, X% of each race, gender split, lgbt representation, income brackets, etc), there is a mathematical model for how confident you are in your statistics based on the ratio of your sample size to the population size.\n\nLet's say you had 95% confidence. That means if you repeated the survey 19 more times, with the same representation, only 1 of those would have significantly different results.\n\nSo if you have something with 95% confidence, that actually means nothing, because it can be the one study out of 20 that is way off. However, once people start replicating the study, you can validate the data." ]

[ "For US specifically, nickles contain once contined a decent amount of nickle. Whereas older dimes had silver content. The sizing of the coin may very well be related to the volume and type of precious metal that used to be in the US coinage.", "I will preface with that I don't know the exact answer.\nHowever, what I do know is that dimes originate from back when people used silver dollars - a dollar, a coin which contained enough silver to be worth approximately one dollar. \n\nIt's important for a coin of any denomination that the value of your coin be equal or greater than the value of the material its made of, or people would melt them down in large quantities for profit. Thus, your 5-cent nickel would have to be half the size again of an already-small dime. Your coin would grow so tiny so as to be unpleasantly difficult to keep track of. \nSo in the end, people moved away from the use of actual precious metals for their coins, and nickels could be made larger than dimes - designed to be easily recognisable, and not hard to keep track of. \n\nThe case with the Euro is somewhat different since all Euro coins were introduced simultaneously. Again, I don't know the full and complete answer here, but we know the 10 eurocent coin is made out of copper, whereas the 5 eurocent coin is made out of copper-covered steel. It wouldn't be a long shot to assume that the size difference is simply to prevent the value of copper metal from mandating coins become too tiny to handle effectively.", "Euro Coins are sorted into three groups:\n\nBi-Color: 2 Euro and 1 Euro \nNordic Gold: 50 cent, 20 cent and 10 cent \nCoppered Steel: 5 cent, 2 cent and 1 cent\n\nThey were designed to be distinguishable by touch, tiering them all by size would however cause some to be rather large or some to be rather small or them all being too close in size to tell apart by touch. Instead they are distinguishable by the pattern on the edge, the thickness and weight. The 50 cent coin also is heavier and larger than the 1 Euro coin, with a striated edge just like the 10 cent coin, telling it apart from the bi-colored coins of similar size. The 10 cent coins striated edge tells it apart from the 20 cent and 5 cent coin, so the 5 cent coin can be slightly larger and thus easier to handle.", "Just as a side note. My first thought when I read this question was the practical application of coin sizes. In order to make any amount of change with the fewest coins you'll never need more than one nickel, while you might need 2-4 dimes depending on the amount. I wonder if that was considered when the relative size, value and material for each coin were first established." ]

[ "Basically its the idea that Darwinism (natural selection and self pruning of undesirable traits through low suvivability) applies to brain neurons. \n\nKey part of it is that when you are born, your brain develops in a ton of diverse ways, just because. As you age, the brain goes \"This part's not needed\" and prunes that part off, so that things that are needed develop more.\n\nThis is important because it differs from the view that we are born with a blank slate, and as we do things growing up, our brains build things in response to those ideas. Similar end result, different process." ]

[ "You nose contains the same spongy tissue as a penis! It's true! [Here's an article about why the nose does what you're asking about. ](_URL_0_" ]

[ "All burns do this. Lots of blood flow to the area causes more obvious heat radiation than from other areas.", "Sunburn means that there's widespread tissue damage which results in inflammation as your body pumps blood and white blood cells to the site to fix it. That also make it warmer than the rest of your skin which typically is much cooler than your core temperature." ]

[ "You can shift position while still asleep subconsciously, or wake up. The only times I've heard of damage is when sleeping in a position that seriously cuts off blood flow while sleeping significantly drunk.", "you can move somewhat without becoming conscious and yes you can be woken by all manner of sensations. but it's worth pointing out that your limb being asleep isn't from loss of blood flow. it takes a rather significant event to significantly impede blood flow to a limb.\n\nyour limb \"falling asleep\" is called \"paresthesia\" and is usually caused by pressure on the nerve bundle. we have a few places on the body where the nerves come together to move through some bit of anatomy like a joint and these can be stretched or pinched. \n\nin a healthy human being, this isn't a concern. as mentioned previously, your sleeping body does have some ability to right itself and any position you could remain asleep in wouldn't exert enough pressure to cause damage. \n\nthis *can* be a problem for those who are unconscious due to drugs or injury, as they have no ability to right themselves nor will they necessarily wake up as it progresses toward injury." ]

[ "Most products go through a lot of design steps before they are put into public\n\nIt usually start with concept artwork, schematics & CAD design then once that is refined a prototype is made\n\nPrototypes can be expensive to manufacture so you usually want to limit the quantity & once you have the prototype you can beta test it & tweak the design, aesthetics & materials for better functionality, appearance, ease & cost of manufacturing etc\n\nThen you would put it out to tender with manufacturers capable of mass production & get costs - they will usually provide a sample for an agreed cost & then you choose the mass producer you want to manufacture the product\n\nIf you going to manufacture it yourself you need to factor in the cost of the setup & operation of that into your product & or amortize it over a number of products\n\nEssentially who decides what design & materials the product have is up to the individual or company who will be selling it & usually based on consumer feedback during beta testing & focus groups", "The start of every design is a requirements analysis. What is the product used for and what implications does that have? \n\nFirst come the functional requirements like weight, strength, flexibility etc. Next are the non-functional requirements like aesthetics, additional features, cost, ... Both functional and non-functional requirements are set by both engineers and marketing departments. They aim to translate the customer's requests into a technical spec-sheet. \n\nThis all leads to an initial design idea, material selection and production process. All three are influenced by each other: 3D printing, molding, milling, ... all have some limitations on what materials and shapes you can use. \n\nWhen these questions are answered, you can start drawing an actual model. Then it gets put into a CAD model, simulations of forces or aerodynamics or ... are done on the model, then a prototype is built on which physical tests are done, and then a final product is built.", "As I understand it, a lot of product design has to do with how it is manufactured, which is in turn decided by how expensive it is and how it works. If possible, ergonomics and aesthetics are taken into consideration as well. Different products all face different design requirements - for instance we try to make TVs big and thin, we try to make drills drill-shaped, and we make beds to hold mattresses of standard sizes.", "There’s also heaps of research into the product before conception even begins. Is there a market, how do people use it, what are the competitions differentiating advantages and disadvantages, the list goes on. Rapid prototyping / manufacturing with the obvious advantages afforded by digital design in the aughts has made the process much different than before as well." ]

[ "Rotator cuff muscles are a group of 4 muscles that stabilize the shoulder. They all attach to the humerus (arm bone) and the scapula ( two flat things on your back) at varous places. The shoulder joint is a highly mobile joint, its literally a ball in a socket so it can rotate 360 degrees. With this type of range comes instability, which is why you have muscles dedicated to stabilizing it. Biggest issue with the shoulder is that the ball comes out of its socket, a dislocated shoulder. The muscles in the shoulder work together to keep this from hapening." ]

[ "I'm not really sure, because this is very situation-specific (for instance, iPhone batteries have some special features).\n\nHowever, many batteries will also be very hot when they run out of life. When cooled, the charges flow better, so you might be able to squeeze just a little more life out of them.\n\nSome batteries (esp. computers and phones) turn off before they're fully empty to stop you from physically damaging the hardware. Sometimes you can trick them into turning back on after that.\n\nEnergizer batteries and such will randomly start and stop working near the end of their lifespan as the chemicals stop reacting. There's no correlation between what you do and how well they work; you're just drawing a conclusion because your brain dislikes randomness.\n\nsrc: astrophysicist, this is basically a summary of what I know, but may not be 100%", "The answer is that they aren't dead. It's the same reason why if a battery is dying you can roll the battery or take it out and put it back in and it starts working again.\n\nPart of it is as the battery reacts it will cause the contacts in the terminals to oxidize which can disconnect the battery (the terminals can also start to oxidize), another thing is that batteries have 2 parts, a liquid electrolyte and solid electrodes... If the active electrolyte all goes to one side of the battery then you will have some of your battery not reacting making it seem like it's dead but when you remix the electrolyte solution (by moving it as its some material dissolved and suspended in a solvent, the solute can either partially precipitate or if it has a higher/lower density it might sink/float on the remaining solvent... Shaking it can mix it back to equilibrium).\n\nOther times it could be that, depending on the use, some functionality of the device was trying to draw a higher current than the battery could supply causing the device to shut off but after a later attempt it was trying to draw a lower power and as such was not dead... Basically dead batteries are almost never actually dead, as they die their voltage decreases and most devices operate at a specific voltage so when the voltage of the battery drops too much the device will act as if the battery is dead (not intentionally... Basically if the voltage isn't high enough then the device won't even register the batteries as being there as the batteries won't be capable of even powering the device)", "It depends on what type it is.\n\nThe simple answer is voltage recovery.\n\nImagine going for a run. You run until you can't anymore so you stop. Even if you wait for only 5 minutes, you start to recover your energy and can run for a bit longer.\n\nI can go into the different battery chemistry types if you want?" ]

[ "I think the other people have missed the critical element here.\n\nThe critical element was the shift from disposable to reusable rockets. Now, to their great credit, NASA did make that move in the 70s with the space shuttle, but it was a bit too early, and the whole shuttle project was a bit of a logistical and political shitshow. \n\nBy the time SpaceX came along, technology had advanced considerably. Here's a great talk by Raffaello D’Andrea explaining it [_URL_0_](_URL_0_)\n\nIn short, between the Space Shuttle and the Falcon 9, feedback control got good enough, and cheap enough, that the idea of landing an otherwise traditional rocket vertically was very feasible. By this point, the Shuttle was seen as a failure - technologically impressive, but economically unviable, and increasingly outdated. So NASAs focus was off of reusability and onto cheap disposability. In that environment, dumping money into R & D is a bit pointless if you have designs from the 60s that are reliable and well understood. They'll only fly once, and the cost of space flight is really in the minimization of failures. So, advances in engines and control systems largely stopped. \n\nSpaceX saw things differently. Believing they could take what looked like a conventional rocket and land and refly it, meant they could change the economic model. Launches were rare because the cost of disposing a rocket each time was high, and because the cadence was low - there was no incentive to build out production lines that could spit out a rocket every two weeks. But if you could reuse the rocket, even just one more time, you'd need half as many of them. Refly it 4 times, and you need to build only 20% as many. So, SpaceX went for a commodity strategy - build one really really good motor to serve first and second stage, rely on modern control electronics to regulate 9 motors operating together in the first stage, and engineer for reusability, and get your reliability that way, and dramatically cut costs to fly the rocket and use that money to pay for the new R & D. Digital feedback control wasn't the only thing that had dramatically advanced since the 70s, so had manufacturing techniques and materials engineering. So SpaceX could build simpler rockets that performed better than was possible in the 70s. \n\nNASA didn't want these rockets, believing in their tried and true approach, but private companies did want them and with time SpaceX won them over. Bezos saw the same opportunities, as did others. Existing companies didn't see the opportunity because their value was in their tried and true methods, their decades of engineering experience at this, their detailed knowledge of how these old system worked, which made them reliable. \n\nThis is also a story of why established companies rarely pivot their business model to adapt to changes, and why startups and other new entrants are key to advancing industries. They can take these risks, they can invest in the new technology and not invest in the legacy technology. Had SpaceX failed, we wouldn't even be talking about them - so there's some survivors bias baked in here too.", "They haven't really. \n\n1) They utilized all of the science that NASA learned thus they \"had\" the same experience level as NASA. \n\n2) NASA has never had a massive budget. Even during the Space Race their budget was relatively small. Companies like Space X's budgets are comparable in size. \n\n3) NASA stopped designing new Rockets for a time when they were operating the shuttle. When they retired the shuttle they started designing new Rockets again and will be constructing them for the upcoming missions.", "To build a new rocket, lots of design and testing is needed. Problems will be found, so how quickly these are found and fixed decides how quickly a new rocket can be completed.\nBecause of restrictions due to it being run by the state, Nasa can't adapt anywhere near as quick as spacex; for example, when spacex realised carbon fibre wasn't the way to go for the BFR, they fired all the workers working on carbon fibre designs. This was necessary, but would not be possible in Nasa.\n\nThe fact that they have to be acting in the best interests of the country means that designs from Nasa are dictated by created jobs, and less by the actual advantages of the design, leading to many issues that are delaying many programs.\n\nThey also have major direction changes with each election, meaning that they work towards one goal for 5 years, then a new leadership tells them they want a different project doing, so they cancel the first one, and end up getting nowhere.", "Aside from using known published resources from NASA and likely the old Soviet era, technology has changed dramatically since the 60s. \n\nThey’re able to run many simulations in a short time period that would have been impossible for NASA back in the day. \n\nThere’s likely less politics involved too. \n\nComputer technology I’d guess been the key difference that has allowed them to do things like reusable components. I’d assume material science has had a big change since the 60s too. \n\nIn all fairness, NASA built the shuttle which was a pretty damn impressive bit of tech. Not without it’s issues but it was cutting edge.", "NASA is heavily regulated, risk avoiding, and making decisions by committee.\n\nSpaceX has been able to build on all of NASA's experience, as well as take advantage of more modern underlying technology. The other big innovator in this field is Elektron, in my opinion.\n\nI think the elephant in the room is nothing to do with NASA, but rather ULA. Why is SpaceX able to build such a better business model than ULA, who has the years of experience and the resources?", "SpaceX has a few advantages, but I'd say the core thing here comes down to two main factors. \n\nFirst, big NASA rocket projects (and by this I mean something like the Shuttle or SLS), which are not exactly made by NASA but are designed and built by them in cooperation with oldspace companies like Boeing and Rockwell, have to answer to a large number of competing interests. The companies of course want to make a profit and NASA wants their science, but also congressmen want some of the contracts for building these rockets to go to their states, and sometimes the military wants specific capabilities, and sometimes the system needs to be designed to use a specific set of preexisting resources or expertise, etc. And since all this stuff is subject to funding bills, etc, it can't be easily or cheaply changed. SpaceX, in contrast, is more or less answerable only to themselves (except when fulfilling a specific contract). If they need to switch an approach or try a new thing or whatever, they can just decide to do it. This gives them a lot more flexibility and helps them do things for a lower price.\n\nThe second is the drive of necessity/lack of money/lack of being established. Oldspace companies (who are a better comparison here than NASA, which doesn't really build Falcon style rockets) have been launching rockets for ages and were dominant in the market. Sure, their rockets were expensive, but they got the job done effectively and all their customers were willing to pay the price and no one was undercutting them. Spending a lot of research money to make it possible to build rockets for cheaper and maybe even reuse them just didn't make sense to them. Why take the risk and expense when life was already good? But SpaceX didn't have that option. If they wanted to survive at all, they had to be able to figure out a way to undercut the competition and win their contracts. That means taking risks and working hard to make rockets for cheap, using more cost efficient manufacturing. That was the first revolution of SpaceX, and more important to their past success than reusable landings (though that will be more important going forward). There have been other new rocket companies that tried this and failed..it is a risky approach, but SpaceX made it work. Worth noting that this is not limited to the rocket industry, many industries have had established players get overturned by new upstarts who were better because only a better company could break into the market in the first place. It's not even limited to industry for that matter.\n\nA factor I _don't_ think is as important: technology...the stuff SpaceX is doing is impressive but not due to any particular unique technological breakthrough on their part. It was within the capacity of NASA or ULA or Boeing or whoever to do the same thing if they chose to put in the engineering work. They couldn't have done it in the 60's (and SpaceX probably couldn't have existed at all back then) but they could have done it when SpaceX was doing it.", "A point I do not see mentioned yet is that SpaceX does not need to please any governors in different states, so they can have their production wherever they want, and basically SpaceX can do whatever they want in that regard. In comparison, Nasa has widespread production and facilities, and is a much older organization.\n\nIf Nasa were to be completely wiped and restarted, I doubt that they would not be able to do similar things to what SpaceX has done." ]

[ "Night terrors happen when the waking-up process gets out of sequence.\n\nDuring REM sleep, the dreaming stage, our brains shut down signals to our muscles, effectively paralyzing us. This helps prevent sleepwalking.\n\nA night terror occurs when you regain consciousness before your brain has restored muscle control. You start becoming aware of the real world before the dreaming has fully terminated. You can see your bedroom walls, but you can't move to sit up. Your still-kinda-dreaming brain panics and instantly starts fantasizing explanations of why you can't move, and may create visions that seem very realistic for a moment until that dream state finally switches off." ]

[ "People usually pay significantly more due to interest than a loan is originally worth. This allows the relatively minor loss of money to be offset by the deceased's prior interest, as well as the interest of other debtors. It's not like the majority of the population dies with 100k debts on their shoulders. Also, when people die in debt, this debt is often paid for in part by selling everything they owned.", "Sometimes just the way the loan is structured, sometimes compound interest, especially on any missed or late payments. An unpaid debt accrues interest, and that interest accrues additional interest, etc. If an interest rate is high to begin with, it's not hard to repay an amount that exceeds the total amount lent but still owe plenty more due to the impact of interest. Start missing a few payments, and the penalties and interest upon interest really starts to add up. Keep missing payments, or make sporadic payments, and growth of the debt accelerates.\n\nAn example:\n\n$1,000 borrowed at 15% interest assessed once per year, with a 10 year even repayment term (this is super simplified and not at all how this would actually be calculated - the actual calculations generally favor the lender far more than this simple example).\n\nSo, at the end of year one - $150 interest + $100 principal is owed - $250 paid, remaining debt is $900\n\nEnd of year two, $135 interest + $100 principal is owed - $235 paid now, $485 paid total, remaining debt is $800\n\nEnd of year three, $120 interest + $100 principal is owed - $220 paid now, $705 paid total, remaining debt is $700\n\nEnd of year four, $105 interest + $100 principal owed - $205 paid now, $910 paid total, remaining debt is $600\n\nEnd of year five, $90 interest + $100 principal owned - $190 paid now, $1,100 paid total, remaining debt is $500\n\nStopping here - there's still $500 in principal owed even though the borrower has timely paid $1,100. So if the borrower dies, the estate still owes $500 even though the lender has received more than the amount loaned. Further, if any payments were missed along the way (or were late or short), penalties and an increased interest rate likely kicked in, greatly adding to the amount owed." ]

[ "Magazines are typically done on offset presses, using standard sheet sizes. The type of paper printed on is specified by the customer, generally proofed before a full production run. Matte vs. Glossy is often a varnish applied on top after printing is done, before it goes to binding. There are usually multiple machines that go into making the finished product. I work for an OEM that makes/designs/services these types of machines, it's a huge industry.", "[Sheet sizes explained.](_URL_0_) The ISO sizes at the bottom are typically what's used. If you're a graphic artist, I will add that most print shops employ graphic artists to tweak customer design requests into things that can be used to make print plates/ die plates. If using Adobe, you'll notice you can separate into CMYK layers, and add spot colors. A newer thing is 7 color (CMYKOGV) process; larger gamut = less spot colors. Pre-press work (IE- graphic design) is only going to grow in demand. If this interests you, you can absolutely make a good paying career out of it." ]

[ "There is almost always a bigger need for downloading information than there is for uploading it, and the cables that cable internet travels over are more limited than fiber optic. So, cable and DSL companies prioritize download speeds by using more channels for downloading than for uploading.", "As others have said it’s due to most residential customers are surfing the web, essentially downloading each page they view. Hardline coaxial cable (the cables on the poles) are only capable of Carrying so much data in each direction. Due to this cable companies prioritize download over upload. This is a generalization of your question because there can be a lot of other factors like node capacity (maximum number of people who can be plugged in in a given area) and CMTS limitations (CMTS is the brain of your cable companies internet) also keep in mind that the industry evolves with demand and 99% of people are not uploading massive amounts of files over the Internet, so there is no real problem to address. I’m sorry if I don’t explain it in simpler terms I just wanted to give validity to what others are saying\n\nSource: Broadband Technician for the past 4 years\n\nEdit: almost all cable companies use fiber optic but recently they have been bringing the fiber to the home and almost all new build outs for cable companies are strictly fiber optic." ]

[ "They act as a reseller for tickets via a centralised database for them. Since they can determine their own profit, higher volume (relative to them) allows them to discount. This makes filling planes a surer thing, and many people (rightfully so), still drift direct carrier to buy.\n\nThey never work with all the airlines, and I had a long haul flight that was a bit lower than the standard price but I had near 50% luggage allowance and a couple of additional minor benefits." ]

[ "The map is stitched together from many different observations, so expanding it would be done by adding more observations near the edges.\n\n\"Orientation\" is a bit vague a question, but the field is within the constellation Fornax, in the southern hemisphere southwest of Orion." ]

[ "In general cars are much smaller in Europe than in the US because of narrower streets and less space in general. For example what is considered a humongous SUV over here (Audi Q7, BMW X5) would't be a particularly large car in the US. \n\nTherefore there's no market for US cars. I see Honda being named as a very small and fuel efficient car by americans a lot (at least on reddit) but compared to other European and Japanese manufacturers its really not that great. \n\nFor example you can get super efficient french diesel cars for a great price (Citroen, Renault) or if you like the \"prestige\" you can go for a german car. When it comes to japanese vehicles you see quite some Toyotas and more recently also korean cars like Hyundai and Kia which have ridiculously long warranty periods and really affordable hybrid drive trains.\n\nIf you see all that Honda is just one manufacturer among others and (in my opinion) their deisgn is quite weird as well. They look straight out of transformers movie nowadays which is weird.\n\nRegarding Ford you see a lot of the smaller models like the fiesta or Ka which are made in Germany or the UK and none of the monstrous american trucks for which you woulnt't find a parking spot and at 6.5$ per gallon for basic gasoline in some countries you don't want to fuel one either.", "Some Ford models are made in EU,so no import taxes and parts are cheaper and easier to find.", "One of the big issues is that car margins in Europe tend to be pretty small, if you're not selling tons of cars, its not a good place to be. Honda has (though they officially don't acknowledge it) put very little resources in growing their business in Europe, and instead focusing on US and Japanese markets where they perform very well and margins are higher, and basically just being \"present\" in Europe but not trying too hard.\n\nThey never made much of a name for themselves in Europe and haven't been up with European car trends, and since the margins there are so low, they really aren't interested in investing more into Europe right now.\n\nOther Japanese manufacturers are doing OK there, but Honda specifically isn't investing much in European operations.\n\nIt sorta seems odd as Honda certainly could make cars to appeal to Europe, and they have a European production facility, but they seem very reluctant to actually invest into the market." ]

[ "The detergent is composed of molecules with one end that is attracted to water and one end which is attracted to oils. Oils and water normally don't want to mix, but the detergent acts like an intermediary and forms tiny bubble membranes around the oils, allowing them to be washed away by the water.", "Soap molecules have a polar head and a non polar tail. The non polar tail end will be attracted to, and wrap around, other non polar substances, like grease, oil, and fat. The polar end is attracted to water and other polar substances.\n\nSo basically, the tails of soap molecules surround the gunk, and the heads carry it away with the running water." ]

[ "Animals usually dont have similar facial expressions to humans, the exeption being our closest genetic realetives like chimps and such. Even then the facial expressions mean very different things to them. And animal with it head and ears up scanning its surrounding is looking for a potential threat so it can run the opposite way usually." ]

[ "Grab a paper towel tube and hold it up to your eye like it's a spyglass and you're a pirate. Declare \"yarrr!!\"\n\nNow use your new cardboard spyglass to look close to a light, but not quite. The line from your eye to the light is blocked by the wall of the tube, so the light doesn't reach your eye. If you turn your head just a little bit then the tube aligns and you can see the light. Now you know that the tube is aligned between your eye and the light.\n\nEratosthenes did much the same, but with wells. These wells are long tubes that were bored straight down, where \"straight down\" is a direction that changes as you move from place to place.\n\nMost of the time sunlight won't directly shine on the bottom of a well, since the sun isn't directly overhead. However, at 12:00 noon on certain days of the year the well and the sun align. Someone leaning over the edge of the well will see the shadow of their head against the water at the bottom of the well.\n\nOn that same day at the same time someone some distance away could try the same thing, but they find that the sun isn't aligned. It's a little bit to the north or south, depending on whether the second location is north or south of the place where the aligned well is. (Aside: if the second location is East or West then that also messes things up, but we'll assume here that either the second location was due north or due south or that the second observer makes their observation at their own local noon).\n\nAt that location the observer can erect a tall, vertical pole of known height and look where the shadow of the top of that pole lands. Based on the length of the shadow and the length of the pole they know the angle of the sun.\n\nThe final piece of the puzzle is the distance between the two locations. This allows the observer to set up a ratio: \"If I walk XXX miles (or stadia, as the case may be) then the sun changes angle by YYY degrees. Therefore, to make the sun change in angle by a full 360 degrees I'd have to walk < circumference of Earth > miles.\"", "It’s also worth noting that Erastosthenes didn’t discover that the Earth is round...people had recognized the curvature of the Earth for a very long time. Ships disappear bottom first when going beyond the horizon, which wouldn’t happen if the Earth were flat...they’d simply continue shrinking until they are too small to make out with the human eye.", "Erastosthenes measured the shadow cast by two Obelisks on the same day, both at high noon. One was in Alexandria, and (with help from an assistant) the other was in Southern Egypt. If the Earth was flat, the shadows would be the same length, due to having the same angle relative to the sun. Instead, the lengths were different, and because the distance between the two cities were known, Erastosthenes could use geometry to estimate the difference in angles between the two obelisks, relative to each other. From there, he could use geometry to calculate the distance necessary to achieve 360 degrees, a circle." ]

[ "The small amount of powdered gelatin disperses into a kind of large, cross-linked web structure throughout the liquid, holding it together. Since the fibers of gelatin are very thin and widely spread, the block of jello is pretty fragile and jiggly and not very physically strong." ]

[ "When James Watt was touring the country selling his steam engine, it was easier to tell people how many horses they could replace than how many joules of work his engine could accomplish per minute... or how many pounds of force it could apply a given distance in a given time. So he came up with a unit of measurement that people could relate to - horsepower. So a 1 horsepower steam engine would be able to supply the power that a single horse could continuously exert.", "Others have answered why the horsepower first got used -- because it made for good marketing to say \"this steam engine is worth 12 horses\" than it was to say \"this steam engine can lift 6600 pounds at 1 ft/second\"\n\nFor legacy reasons, horsepower still makes a lot of sense. People are good at understanding smaller numbers, and most modern economy cars are between 100-200 cars. A more sporty car might go to the 400 horsepower range, and a supercar up to 1000. That's a really easy to understand scale.\n\nThe closest equivalent I can think of is the kilowatt, with one horsepower being about three quarters of a kilowatt, but no one wants to be the first person to switch over and make the comparison harder.", "Horsepower (hp) is the common unit of measurement of mechanical power in the English system. Horses were first used for most major tasks which needed a lot of power, and were later replaced by the steam engine. To (presumably) make things easier for people to understand, steam engines were rated as having the power of a certain number of horses. This formula for calculating power in units of horsepower (hp = (ft 1 b/min)/33,000) does not become mathematically unsound due to the change in engine type, even though we are far removed from the period in time where we needed things compared to the work that horses are able to do in order to understand it. Soooo... it's mathematically sound and it sounds cooler" ]

[ "Bacteria does not \"find\" a target. Instead, you have so much bacteria just going everywhere that some inevitably finds some food it can live on. The bacteria that does not find food reproduces and makes more bacteria which goes out hoping to land on even more food." ]

[ "The issue with contamination is that you cannot separate or sort it. Recyclable material get contaminated if they get into contact with un-recyclable materials that you cannot easily separate. For example, although a cardboard box is recyclable, a pizza box isn't recyclable because the grease from the pizza cannot be separated from the cardboard, hence the pizza box is \"contaminated\". It's way too expensive to try to remove the grease from the cardboard, so the entire cardboard is thrown into a landfill. Also, the grease from the box can leak from the box and contaminate other objects in the lot, meaning that the entire lot must be discarded.\n\nIf you left a receipt into a plastic bag, it's a different story. The receipt could get manually removed quite easily from the bag, and the bag could proceed to be recycled correctly." ]

[ "Per a quick google search, they are often lawsuits for this. However, I’d hazard a guess that court costs and lawyer fees are factored in before moving forward. Generic copy at Walmart maybe only profits 40k$, but the lawsuit would cost 200k for both sides. It’s now a loss to sue and not worth moving forward. Adidas sued Walmart for infringing on their 3 stripe design a while back and won. Those shoes now have 4 stripes.\n\nEdit:changed a letter" ]

[ "Oh I actually think I might know this one!\nHumans are really good at recognizing patterns. We see faces in everything- toast, clouds, stone, etc. We just automatically look for patterns in things, so when we see a spot in some leaves that seems to have a separate pattern, or doesn’t quite line up, we’re likely to notice it. At least, I think that’s the reason!", "If you are the target of an animal, you likely won't see it if it's stalking you in its native environment until it is very close to you. A big cat's coloration and markings are perfectly suited in its natural habitat to render it effectively invisible even to humans. You might pick up on its movements, and a sharper look will expose it, but humans have no special or heightened awareness when it comes to noticing predators. Camouflage isn't designed to allow the predator to walk up to you and tap you on the shoulder, it's just designed to give it as much of an edge as possible when stalking prey, so it can get as close as possible before relying on an all-out assault take the prey down.", "Colour vision, most animals can't see the ranges of colours that humans can, colour vision is really important in omnivores and deciding which fruit is ripe, it is less important in pure carnivores.", "Can we? There's a bunch of confirmation bias, you only recognize the ones you spot and never realize the ones you don't see (because how would we know we didn't see it). Camouflage is extremely effective.\n\nThat being said, there are some things going on. camouflage is a designed to work more at a distance and works best with nonmoving objects. Most of the things we see are very close up or moving. Then there's a matter of what your camouflaging against. Different animals have different senses, ever notice how hunting vests are orange? Deer don't see orange so it doesn't matter if a hunting vest is orange. We might have different senses that allow us to easily pierce camouflage.\n\nFinally human brains are the most complex and powerful computers in existence. It can abstract patterns and make connections like nothing else. It can recognize a part of an animal and knowing what that animal looks like, it can reclassify what it previously thought to be background.", "It works plenty well on humans - it doesn't work if you're looking at a picture that you're told has a tiger in it, but that's not the point. Most pictures don't have a tiger in them (or, as relevant here, most glances at the forest's edge. \n\nThe question for the camouflaged animal isn't whether you can see it if you look closely, but whether its presence will trigger than suspicion to look closely in the first place, especially if most of its body is obscured and you're at a distance. Until it's too late." ]

[ "Computers run on sets of instructions telling it how to run all the parts of the computer and build an interface so you can use those parts. \n\nSay you're following a recipe for a cake. Then you finish the cake and someone comes along with a better way to make a cake by adding another ingredient and changing how much salt is used. You can't unbake your cake at this point to try it out. You have to start over from scratch and remake the cake. \n\nSo when an update happens, you have to restart the program or even the whole computer to before you were using those instructions that changed. So the computer can follow the newer, better instructions when it builds you your interface.", "Some files maybe in use by the OS or Application and can’t be uttered updated so a reboot allows that to happen as they are not in use", "You know how you can't open a file when another application has it open? Well some of the files on your hard drive are opened by the operating system (windows, linux, macos etc) and the operating system keeps them open right up until you switch the computer off. When you install an update, you might need to replace one of these files that the os has open. Since the os has it open, your installer can't also open it.\n\nThe solution is to tell the os to update that file next time the computer starts before the os opens the file. So until you do a restart, the update isn't fully complete.", "Consider a car. While the car is running, you can load or unload passengers, or plug and unplug your phone, but you can't change the oil or replace a tire. There are moving parts that can't practically be replaced while they're in motion.\n\nA computer program is the same. There are “moving parts” that can't practically be replaced while they're moving. But it's easy to replace parts that are stopped." ]

[ "So Russian oligarchs are fucking scary. One of the best stories to come out of the death of Stalin was about the guards on duty outside his bedroom. Reportedly, they heard him hit the ground when he died, but refused to enter the room for the next 8 hours because he might be angry at being disturbed and kill them." ]

[ "It is called chromatic aberration and it is from the lens of the camera used to take the picture. You now how a prism used to split light will bend light different angles depending on its wavelength? The lens does that too, just the effect is attempted to be minimized." ]

[ "It depends on the amount of melanin you have in your body. Darker skinned people tend to have more melanin and are therefore more resistant to sunburn. Usually you can determine the amount of melanin you have in your body by you skin, eye and hair colour. For example, a red headed person with blue eyes and freckles probably has very little melanin, while a person with brown eyes and an olive complexion would have more.\n\nEither way, wear suncream. The sun is dangerous regardless." ]

[ "Magnetic strips can be much more easily duplicated than the chips.\n\nThe strip can be duplicated just by reading the swipe, since the data it gives *is* the data it has.\n\nThe chip, instead, gives an encrypted code based on what you ask it by combining the value you gave it with a secret one it has, and even if you ask it hundreds of times, you won't be able to figure out the secret number it stores inside it. When the reader says to it \"what value do you get when I give you Value Y?\" the chip responds with what it gets, and then that is checked by the institution that issued the card (who know the secret number too so can do the same calculation and see if the results match).", "The magnetic strip is like a secret code that lets you buy things. I can copy your secret code and use it to buy things.\n\nThe chip is like a little man who makes secret codes that can each be used to buy one thing. I can copy the secret code but not the little man. Because the secret code only works once and for a limited time, and in one situation, stealing the secret code isn’t useful. You can’t steal the little man without doing a lot of work.", "Others have already explained how it works, so I will go to the practical side a bit more. \n\n\nYou know how in the news, big companies sometimes have hackers steal credit card information? If they steal information from a magnetic strip, then they have your credit card number and can now buy things on YOUR credit. \n\n\nIf they steal the information from a chip it's useless to them. They can't use it to commit fraud because the numbers the chips makes can only ever be used once. \n\n\nSo using the chip makes you hacker proof in any places you use the chip. \n\n\nNote that it does really protect you much if you've ever used both at the same place or if you use the actual card number online. So it helps a lot, but it's not foolproof.", "If only in the USA we'd go the next step to \"chip and PIN\", I wouldn't feel like a caveman when I go to other countries and they have to find a pen for me to sign a receipt. \n\nOr we could just go totally backwards and I could carry a special individual seal with me, and they'd scramble to find me some wax.", "The chip is actually a tiny computer that is powered by the reader. \n\nIt has a secret number inside of it that cannot be read. Only the bank knows the number. There's no way to ask it the secret number. Instead, you can only give it another number, and it will do some math on that number and its secret number and tell you another number. That's what happens when you read the card. The bank picks a number and asks the card to respond. The bank does the same math, and if your card has the same secret number it must be legit.\n\nNow, you're probably thinking someone could figure out the secret number by just getting it to do the math enough times. But the numbers involved are so big, this will take too long to be practical, more than 10 years to get enough numbers to have a shred of making a guess. Even with very modern computers. That's longer than your card's expiration date so it's fine.\n\nAnd if computers get fast enough the math fails, the banks can simply change the chips to use new algorithms and new, bigger numbers that take even longer to crack.", "The chip causes the terminal to generate a random number sequence which is then checked against your card issuer. It's safer than a magstripe because you can't simply clone the chip like you can the numbers on the magstripe.\n\nOf course, as long as cards still have the magnetic stripe, they're still vulnerable because there are terminals that don't accept the chip, but it's a start.", "A *really* ELI5 explanation is that the chip effectively produces one-time card numbers that are only valid for single transactions, whereas a magstrip always produces the same card number. It's not quite that simple, but that's sort of the idea. Since the data produced by the chip card is only valid for a single transaction, a seller or middleman (card skimmer, hacker, etc) has no incentive to store or reuse the data, unlike in a magstrip transaction, in which the actual card number is used and can thus be reused to, eg, drain the account or make fraudulent purchases.", "In theory they were supposed to be. Until they had to create fallback in case the chip couldn't read. \n\nYes, fallback to mag strip. \n\nSo now fraudsters just put a bad chip in a stolen mag strip card. 3 trys on chip...\n\nthen you are back in business stealing other people's money via mag strip data.", "One thing to note that wasn't mentioned yet, is that outside the US it is a \"chip and PIN\" system. If someone steals the physical card, they still can't use it at a terminal without knowing the PIN. The PIN wasn't implemented in the US, so in that sense the card is just as vulnerable as it was before. Countries outside the US have had this implemented properly for years. Major retailers in the US still haven't enabled chip capability for some reason.", "People are forgetting the number of your card is ON YOUR CARD.\n\nI am guessing many people dont know cards used to be manually imprinted on a piece of paper.\n\nNothing is stopping a dishonest waiter or cashier from taking a photo of your card or writing down/skimming the pin number, cloning the card and using it as a credit card ANYWHERE IN THE WORLD.\n\nThey dont even need the PIN to use it as a clone.\n\nThese cards are so incredibly vulnerable its mind boggling.", "I'm not sure if this has been mentioned, but from what I understand, who ever has the subpar tech is liable (I'm guessing this depends on state/ county jurisdiction). You have a chip reader but the gas station only accepts swiping? Gas station is responsible. \n\nThe chip tech alleviates skimmers. It's easy to read a swipe with your card, but now they have to break through the encryption. Always trying to stay a step ahead.", "ELI5 Answer\n\nMag Swipe Card\n\nTerminal: Hi who are you?\n\nCard: I'm Number 5538...\n\nTerminal: My system says your card is valid; Are you a copy?\n\nCard: I'm Number 5538...; with an expiry of 02/21\n\nTerminal: OK Great\n\n\nChip Card\n\nTerminal: Hi who are you\n\nCard: I'm encrypted code XyM2...\n\nTerminal: I connected with my external resources and they say you are valid; Are you a copy?\n\nCard: I am encrypted code version 283\n\nTerminal: Sorry my resources say the next available encryption is version 287 I think you are a copy and will decline this transaction. \n\nThe system is much safer from replication not from physical\n thief. That is where the signature or PIN adds value when used correctly.", "Say you've got a door that can only be opened with a password (your bank account) but you don't want to say the password, because you know there are people listening (whoever owns the card reader). It is actually possible to prove to your bank that you have the password without saying it out loud. What you do is you ask them to create a puzzle that can only be solved by the person with your password. Then you solve the puzzle (this is what the chip can do). Your bank knows you have the correct password because you solved the puzzle, but you don't ever have to say your password out loud.\n\nSwiping just tells the machine your password.", "mag strip can be copied easily while the chip keeps its secrets to itself. also the chip is smart and generates a unique digital signature for each transaction while the mag strip is just dumb data storage.", "Magstripe was developed in the 1960s. Basically the first one was made with cardboard, recording tape, and a clothes iron. \nThis is a great article -\n\n_URL_0_\n\nThe data on the magstripe is static. The EMV chip (and EMV Contactless) is dynamic.", "Because the fact that you had to insert it 30 times before being recognized ensures that you were indeed at that establishment.", "Suppose there's a bridge guarded by a troll. A magnetic strip is like a password written in troll language that any troll can read. So to get across the bridge you show him your troll scroll and he lets you in. But now he knows your password so he can write down your password on another scroll and use it to get into your castle which is guarded by a different troll. \n\nThe chip is like a tiny magical pass fairy. So when you get to the bridge the troll can ask it a random question like, what's your fairy mom's name and the fairy will know the answer. But if that troll goes to your castle that troll will probably ask a different question and the bridge troll won't be able to use his answer to get in to steal your gold.", "Basically, the strip does nothing more than give the CC number and the stuff on the front of your card. No more secure than just calling a pizza place and reading your cc # to them. The chip is a secondary bit of info that is more complicated than that, and both need to be present for chip machines.", "Imagine your parents gave you a secret password you could use to get a cookie. Let's say the password was \"47\". You say \"47\" to your parents, and they automatically give you a cookie. Say it again, another cookie. Pretty cool, right? Now, when your friends are over visiting, one of them sees you saying \"47\" to your parents and getting a cookie, so he gets the bright idea that he's going to say \"47\" to them, and they give him a cookie, too. \"Right on!\", your friend says, as he says \"47\" over and over again, getting all the cookies from your parents. So when it comes time that you want a cookie, you go to your parents and say \"47\" and they don't give you anything, because there aren't any more cookies because your friend ate them all.\n\nNow, imagine your cookie word was \"1 – 7 – 3 – 4 – 6 – 7 – 3 – 2 – 1 – 4 – 7 – 6 – Charlie – 3 – 2 – 7 – 8 – 9 – 7 – 7 – 7 – 6 – 4 – 3 – Tango – 7 – 3 – 2 – Victor – 7 – 3 – 1 – 1 – 7 – 8 – 8 – 8 – 7 – 3 – 2 – 4 – 7 – 6 – 7 – 8 – 9 – 7 – 6 – 4 – 3 – 7 – 6 – Lock.\" There's no way your scheming little friend can remember all that, but as long as you do, your cookie supply is secure. Now, that's a lot of numbers to remember, but if you had a little chip in you, you could store all that easy.", "The chip is encrypted and the data is non-static. The mag stripe is plain text and static. Easy to dupe with a mag stripe writer. Chip costs more to duplicate and must be reverse engineered/un-encrypted to do so.", "The simple answer is that magnetic strips cannot \"compute\" . \n\nA chip can perform a computation. At a shopping counter, a magnetic strip can only be read. So you read it and get a \"number\" that you can verify. This means that anyone (including the shopping counter) that has read your magnetic strip \"knows\" the number. It is upto the shopping counter to safeguard your security by making sure the number stays secret.\n\nA chip does something else - it generates something like a hash. IT does the verification. I am simplifying this, but it stores a secret number say \"42\" . Your bank also knows this number and the pin. The chip and bank also have a preencoded \"calculation\" that they do for your number and pin. Say the calculation is \" pin\\*78 + 199992\\*secret number\" . \n\nLets say your pin is 1234. So when you access the counter, the chip makes a calculation \"1234\\*78 + 19992\\*42\" gives out the number \" 935916 \". This number is sent to the bank. The bank does the same calculation and checks the answer. If it matches, the card is approved.\n\nThe upshot is that at no point, did anyone except the chip and the bank actually see the secret number. This makes the chip secure.\n\nNow in reality, the calculation I provided is a simplified fake analogy. In reality, the computation is very very complex and the chosen secret numbers are very very large prime numbers. They are not easy to guess and would require millions of years to check one by one at the current speed of computers. The idea is that it is so hard to find out the number and calculation that it is simply not feasible to do so.", "I work at a payment network. Within a certain data element of a transaction message the chip collects particular details about the transaction and uses a mixture of hashing and cryptography to make that transaction extremely unique and challenging to duplicate. \n\nMag stripe doesn't utilize this technology. On top of this, many cards are now tokenized. Whether, cardholders are aware or not. Tokenization, in this case, is where the bank presents a 16 digit dummy number and the main payment networks Visa/Mastercard will replace the dummy number with the actual number so the merchant doesn't actually get your real card number, but the stream of how the purchase is authorized, cleared, and settled doesn't change. After breaches at merchant locations, yeah looking at you target, home depot, etc., many lack infrastructure to manage PCI software around the card details. Thus a combination of tokenization for merchant compromises and chip for transaction duplication, it is considered safer than traditional mag stripe. The US market was always extremely behind most of other developed countries because many large merchants had to spend enormous amounts of replacing their card readers. Imagine Walmart having to replace millions at around $237 / reader. US regulation forced merchants, now by law, to migrate to chip readers over a 3 to 5 year period.", "A lot of these answers are referring to a \"secret number\" the chip has hidden inside it, and it may be tough to differentiate this from the \"secret data\" hidden in a magnetic stripe.\n\nWhat's really happening is the chip contains a very complex electrical circuit which only you and your bank know the layout of. The reader then tests multiple inputs to the circuit and checks that the results your chip give are the same as what the bank says it should give. There is, however, no easy way to look at and replicate the electrical circuit on the chip, because (1) it is so small and complex, and (2) the circuit has been designed in such a way that reverse engineering it by looking at many inputs and outputs would take lifetimes of computing hours.\n\nA magstrip, on the other hand, simply has the data encoded right on the stripe, easy to read, view, and copy. It's basically equivalent to just handing someone a piece of paper with your credit card number on it.", "Here in Estonia our entire lives exist via Chip. My health care, information, job, permissions for banking and contracts, prescription, everything exists on a card. We have two levels of numbers that decide the permissions our cards grant to the business, government agency, school, whatever requiring it. There is an entire generation who has never known or seen a cheque in their lives as Estonia no longer uses such ancient methods of banking. We rarely if ever use cash. I can rent a car, board a bus and get a ticket from a police officer all via Chip. It seems ridiculous to be any other way. I thought it was great when I lived in Canada but now? Omg so much better.", "When credit card companies switched from swipe to chip readers, they changed the terms of who gets stuck out of money in cases of fraud.\n\nBefore, if there was fraud, it was the credit card company's problem to pay the merchant. Merchant swiped, and merchant got paid.\n\nNow, if there merchant swipes the card instead of using the chip, the merchant is responsible for charge backs. Those chips only last so long, and most people don't care to get them fixed. This pushes more responsibility for bad charges to the merchant and not the card provider.", "An important detail is that the chip (or RFID, if you live somewhere where that's standard as well) will often return the actual credit card number, which can easily be cloned onto a plastic stripe card. The power comes when an entire society switches to the chip+pin system from the magnetic stripe, because the magnetic stripes cannot be used anymore. \n\nAlso, with chip came PIN's, where even if the physical card is stolen, large purchases cannot be made.", "Mag stripes on credit cards are nothing more than a bar code. You can view it by brushing some iron filings onto it. Chips, on cards, can do a challenge and response with the bank to verify the card and that it's legitimate. This is why it some times takes so long to approve the transaction. They are harder to clone but not impossible.", "A lot of people already said that magnetic strips reveal their \"secret\" when swiping. A chip is able to keep a secret and still prove that it has it - without telling. There is an actual ELI5-themed paper, called [\"How to Explain Zero-Knowledge Protocols to Your Children\"](_URL_1_), which has a wonderful story explaining it.", "We should also be aware of the difference between chip-and-PIN, common overseas, and chip-and-signature, the US model. Chip-and-signature provides no security whatsoever. When was the last time some clerk checked your signature against that on your card?", "Fun fact: The american economic infrastructure is so old that the added security from the chip doesn't work on our systems. So we went through the entire change over for nothing.", "What about the tapping kind of payment?? Where you just tap your card onto the screen to pay, what happens then/where is that on the safety scale?", "The chip was invented because people had scanners that could steal information in someone's pocket, the chip prevents the scanner from working properly", "I was busted four times before I figured out the term \"swipe your card\" didn't mean to swipe(steal) a card from someone else.", "Sorry to piggyback but what if it’s Apple/Google pay? Is that more/less secure than chip?", "In the US it is just a false sense of security.\n\n_URL_2_" ]

[ "some pills do that. See: the gummy one a days.\n\nbut generally, it's easier for people to understand to take one pill once a day than two once a day, even if it's little uncomfortable.", "Because most people would see 2 tablets once per day and then tell the retailer \" do you have one where I can just take one tablet?\"\n\nIf someone wants a smaller pill it's easier to tell them to use a pill cutter or a liquid(btw never use a liquid multivitamin if you can avoid it, the good ones taste like shit and the good tasting ones have little to no vitamins/minerals in them) opt for capsules!\n\nPeople are VERY PICKY!" ]

[ "Typewriters are complex mechanical contraptions, so having commonly used keys next to each other makes them jam easily if you're using an alphabetically ordered keyboard.\n\nQWERTY has the keys more or less evenly spread so that typewriters could write at high speeds without jamming, and once the convention set it became nearly impossible to sell alternatives.\n\nDvorak is one relatively popular (and supposedly faster) layout, but since learning different layouts takes a lot of effort, QWERTY is the norm." ]

[ "Once we left we would immediately then have to do a trade deal with Europe as its such a big and important trade block.\n\nThe term no deal is not accurate. We would still need to do a deal but we'd be in an even weaker position." ]

[ "We track their movement through the sky. There is actually a lot of interesting history behind this.\n\nThe effects of gravity and the math of orbits were always well understood. Kepler and Newton figured out how gravity and orbits worked (which is interesting since Kepler somehow figured out his three laws decades before Newton figured out how gravity worked, nonetheless it was quickly found that Newton's law of gravity produced Kepler's laws as a consequence). \n\nFor instance Kepler's third law states that \"The square of the period (time of a year) of any planet is proportional to the cube of the semimajor axis (distance from the sun) of its orbit.\"\n\nThe interesting thing about this was this led to the existence of the astronomical unit. We knew that the period of Earth's orbit is 365 days, we could observe the orbits of other planets to see how long they orbit, this means we could calculate how far a planet was from the sun based on how far the sun was from the Earth.\n\nBut finding out the distance from the Earth to the sun was a vastly trickier undertaking, which is why many early measurements are expressed in astronomical units, the distance from the Earth to the sun which we just didn't know at the time. The best way we knew of measuring it was using parallax but that itself was pretty difficult due to the sheer scales of the distances we used, and often the best measurements would only happen by observing transits of Venus from different points on Earth which is why there was a bit of a scramble during this time to send out explorers all over the world to observe this. The basic logic was that we worked backwards from here, using parallax geometry we could calculate the distance to Venus, thus knowing the distance from Venus to earth in terms of AU, we could figure out the distance from the sun to earth. \n\n\n\nWe got pretty good estimates from these, with accuracy to a few percent. We continued to refine our estimates by taking more measurements but the big breaks only happened in the 20th century, when we used radar technology to send a lot of microwaves to near earth objects like venus where the microwaves would bounce off and hopefully be detectable by antennas here on the ground after a while, using this time and the speed of light we could calculate distance to these things.", "The quick answer is RADAR. The distance to Venus was first measured in this way in 1961.\n\nDistances in the solar system could be worked out very accurately relative to the size of the earth's orbit using the theory of gravity. The average distance from the earth to the sun is called the AU, the Astronomical Unit. For example, we knew Venus was 0.722 & #8239;AU from the sun but we didn't know exactly how may kilometres there were in an AU. The reason James Cook sailed to Hawaii in 1769 was to get a better estimate, essentially by observing Venus during a transit from both sides of the earth.\n\nCheck out the [history of the AU](_URL_0_). Once we could work out an earth-Venus distance accurately with RADAR, that allowed us to work out the AU much more accurately than before, which in turn gave us more accurate distances for the whole solar system.", "We can estimate their distance through parallax (measuring the angle between them and the sun, and using geometry to find their positions). We can also measure the time they take to orbit, and use this to predict their positions based on gravitational equations." ]

[ "Caffeine is a vasoconstrictor, so if the migraine has a vascular component, caffeine may have an effect on blood flow.", "Headaches are caused by dilated blood vessels. Caffeine is a vasoconstrictor. \n\nIt also could be side effects of caffeine withdrawal. (Caffeine is a drug) And getting the caffeine helps with the withdrawal.", "Older theories suggested that migraines occurred due to fluctuations in blood flow to the brain. While there may be an influx of blood to the brain new ideas have come out that it's actually not what's causing the pain. Newer theories believe that it has to do with hormonal balances like serotonin and estrogen to name a few. So back to the question at hand, caffeine by itself can cause vasoconstriction, and just basing off the present day research if it is a hormonal problem drinking caffeine can limit the amount of blood (and hormones) to your brain.\n\nFun Fact: Coffee is considered to be a vasoconstrictor, i'm seeing some people wondering if it's one or the other; where the confusion comes in is when you stop drinking coffee (let's say between afternoon and the next morning) your blood vessels will actually dilate a bit and cause headaches/irritability/where all those morning coffee memes come from. It is a fairly complicated topic to talk about the receptors here but suffice to say that your body almost \"forgets\" that it needs to regulate its constriction/dilation but eventually catches on or if you drink that cup of coffee that'll set you straight. \n\n\nEDIT: Didn't really take much time to study hormones or neurology, most of my knowledge comes from what i learned in school and supplementation. Here's an article or 2 that i used if you guys want more reading\n\n [_URL_0_](_URL_0_) \n\n [_URL_1_](_URL_1_) \n\nplease note that both are somewhat dated, i generally don't like to use studies older than 4-5 years but i'm not writing a thesis so i think i'll be okay." ]

[ "The car has cameras in the front, rear, and in the two side mirrors. Those images are stitched together (kind of the same way that your phone creates a panorama) to give a kind of 360° view of the car's surroundings. That image is then displayed in such a way that it looks sort of like a bird's-eye view instead of like the 360° panorama that it actually is." ]

[ "Alcohol dilates your capillaries (the smallest blood vessels closest to the outside), increasing the flow of blood through them. More warm blood flowing through capillaries makes you feel warmer, but that blood is being cooled down from being exposed to the cold, and that brings down your body temperature.", "Alcohol acts as a vasodilator, which means it makes your blood vessels relax and open. This means they carry more blood which carries warmth. The problem is, alcohol isn't generating ant warmth, it's just making the warmth you already have more noticeable.\n\nA faster transfer of heat, which temporarily feels warmer, means you lose heat faster. This is why it \"cools you down, \" it just brings the heat from your core to the surface of your skin faster where it radiates into the environment.", "Alcohol dialates blood vessels, makes them bigger.\n\nBlood is warm from your body heat.\n\nBlood vessels close to the skin are where your temperature sensors are located. You dont have many temp sensors in the center of your body.\n\nThat rush of blood to the skin makes you feel warmer, but that heat is being transferred away from the center of your body, where vital organs are and is being transferred outside the body to the surrounding air.\n\nSo while you feel warmer your internal core temperature is decreasing due to the loss of body heat." ]

[ "Step 1: Submerge wetsuited body in water.\nStep 2: Wetsuit fills with water.\nStep 3: Body heats up water now trapped in wetsuit.\nStep 4: Body stays warmer than the water outside of the wetsuit. \n\nAddednum: Wetsuits typically range from 3mm to 7mm thick. Thicker wetsuits provide more protection against the cold of surrounding water.", "they're basically insulation. they prevent water that your body gets in contact with from flowing away and being replaced with cold water. after a few minutes the water that's being insulated will eventually settle at some temp and the wetsuit keeps out as much of the colder water as possible from contacting your skin." ]

[ "It would be tantamount to what Thomas Kuhn termed a ‘paradigm shift.’ Basically, it would revolutionize the most basic conclusions scientists have had about the origins of life for hundreds of years.", "it basically means that all forms of life that we're familiar with isn't the only form of life that's possible. which opens up the possibility of life on other planets/environments that we would probably not survive in.", "We have built the basis of life on things like water and oxygen. A non-carbon based life form would throw all of these rules out the window" ]

[ "Most large aircraft are actually modular. Wings, tail, etc only require a few bolts and some cable disconnects to unship them. Then, they can be loaded onto trucks ( or trains, I’ve seen that once) for long haul shipping.", "If possible, they are repaired wherever they are, so the are good enough to fly, then the fly somewhere and are repaired properly. Air Canada Flight 143 was repaired at Gimli and flew out two days later.\n\nTACA Flight 110 landed on a levee. It had it's engines replaced and took off from a nearby road.\n\nIf they are near water, they may be barged out. Otherwise they are getting cut up for scrap." ]

[ "Its a condition that only affects some people (me included) its to do with the nerve endings in your face getting crosswired. The eyes and the nose are very close to each other so some people have this problem." ]

[ "You are all lunatics. Cranes don't build the structure around themselves, the crane will be either free standing next to the building or sitting on the current top floor. When they build a new floor they move it up another level.\n\nSo your question has no answer because it isn't a problem that exists." ]

[ "Certificates are typically awarded for a short term study in a specific field. Diplomas are awarded for completing (typically) a multiyear study at a non university level. Degrees are awarded by universities for the completion of a multiyear course of study. The first level of degree is a Bachelor's. Graduate degrees are Masters or Doctorate level.", "Sort of a cheap explanation, but broadly speaking you could say the difference is time needed to acquire each.\n\nLeast time -- > Certificates, diplomas, degree-undergrad, degree-masters, degree-doctorate -- > Most time\n\nIf you take a forklift operators course for 8 hours, you'd likely get a certificate at the end. If you spend 8 years studying the portrayal of forklifts in Western media, you'd likely get a doctorate at the end.", "A certificate is a piece of paper that says you accomplished something. It may be a three hour CPR course or two weeks of swimming lessons. It may or may not be issued by an accredited institution.\n\nA degree is a \"title\" that you've earned for attending a course of study. The degree says that u/itsmygam12 has taken a series of courses, typically at an accredited University, and that you've passed those courses that lead to a \"Bachelor of Science in Mathematics\" for example. \n\nThe diploma is the piece of paper that says you've earned a degree. When you graduate from Medical School and earn the title of \"Doctor of Medicine\" you get a diploma to hang on the wall to show everyone that you earned that title.", "Certificates and diplomas are both pieces of paper that certify that you have undertaken some form of training or education. Typically certificates are awarded for skills based training or education, while diplomas are awarded for knowledge based training or education.\n\nA degree is actually a title. The idea derives from the hierarchical social order that is still somewhat prevalent in Europe to this day. For example, a blacksmith's son who earned the title \"doctor of laws\" would be treated as a better person (and given better opportunities) than a blacksmith's son who simply became a blacksmith.\n\nIn the modern world, universities and schools award just a diploma to graduates of their lowest level knowledge based programs. For the higher level programs they award both a diploma (piece of paper) and a degree (a title with a bump to your social rank). It's actually kind of a weird tradition when you think about it, but it hangs around because universities and colleges are nothing if not conservative.", "In addition to the excellent answers, certificates are sometimes add-on items to a degree. My field is music. You can earn a Masters Degree, and at some schools also ear a performer's certificate. It just is basically a pat on the back for doing extra work in a certain area." ]

[ "The Game Genie and Game Shark peripherals were special cartridges that sat between the system and the game cartridge. This lets it read and modify memory in any way it wants.\n\nThe special codes you put into it contain the memory address and the action to perform. It can be as simple as \"Set this value to X and don't let it change\" or something more complex like \"When the 'A' button is pressed, add 4 to this value\"." ]