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7jjl9r | How did gold and silver became the currency in ancient civilizations even why they didn't have any practical use? | Repost | explainlikeimfive | {
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"You could hardly find a better metal than gold to serve as a low tech money. * It's rare enough to be valuable in small amounts (so a man can carry enough to facilitate almost any transaction). Also it's almost always found in high purity forms. * It's soft/malleable enough to be easily made into change on the spot. * It's dense enough that it's very hard to counterfeit and easy to verify the density with two vessels, a balance, and some water. * It's almost totally incorruptible, so if you hide away some gold, you can be assured that it will be in the same amount and form when you find it (presuming no one stole it from your hiding place). [This is gold]( URL_0 ) that's been sitting at the bottom of the ocean for thousands of years, while some other stuff has accumulated, the gold is unchanged. It's quite hard to find any other objects that meet all those specifications.",
"No practical use? Gold and silver are noble metals-that is they resist corrosion. Silver does slowly tarnish, but because of the long lasting beauty of these metals, they have always been valued. And since they don't degrade, they make good stores of value over time."
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7jks54 | what makes the sound of my tummy rumbling when I'm hungry? | Repost | explainlikeimfive | {
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"text": [
"Your stomach always rumbles, it's just loader when it's empty. Imagine having a bongo and stuffing it full of towels, it would sound muffled and wouldn't be very loud. Now take them out, and give it a bash, it is now loud and actually makes a sound.",
"Borborygmus (the medical term for that rumbling in your stomach) is caused by peristalsis acting on the contents of your intestinal tract. Peristalsis is a constant series of waves of contraction that move the contents along towards the exit. It's like putting your fingers around one end of a ketchup packet and running them towards the open end to get the ketchup onto your fries. Your gastrointestinal tract always has solids, liquids, and gases in it. As the wave of contraction moves along the tract, this stuff gets mashed together and moved along, making the noises you here."
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7jnnxq | How do mathematicians actually go about calculating the digits of pi or of other infinite, non repeating numbers like e? | Repost | explainlikeimfive | {
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"For most of these numbers there are some equations, series, sums or other 'simple' methods for calculating the number to any desired precision. For instance one of the first definitions of e was e = (1 + 1/n)^n as n approaches infinity. So if you want to approximate e just plug in any number instead of n. The larger number you pick, the closer your calculation will be to e. For Pi there are so many sums that slowly tent towards pi that it's quite ridiculous. [Wolfram Alpha has a very large page explaining the most common formulas]( URL_0 ). They'll tend towards pi at different rates, but they'll eventually get closer and closer. Pi also has a fun algorithm that can be used to calculate any arbitrary digit of pi, which is handy if for some reason you wish to *only* calculate the 50013rd digit of Pi for some reason. And so on and so forth. For most irrational constants that have names and well defined values there are also some methods to approximate those values.",
"They prove that a particular infinite series converges to pi, then simply compute enough terms of that series to get the digits they are looking for out of pi. For example: pi = 4 - 4/3 +4/5 - 4/7 + 4/9 ... All you have to do is keep computing terms and you can get whatever degree of accuracy you wish. That particular series is kind of terrible and converges very slow, but more complicated once converge more quickly."
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7jr7e7 | What causes heat tolerance differences between people? | Repost | explainlikeimfive | {
"a_id": [
"dr8iqbe"
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"text": [
"So many different things. Amount of muscle and fat, overall size, skin density and sensitivity, size and distribution of sweat glands, simple preference. Women tend to get cold faster than men because their network of blood vessels is denser in their core, causing lower blood flow to extremities like fingers and toes."
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7jrrda | Why does repeating a word or phrase over and over make it lose meaning in your brain? | Repost | explainlikeimfive | {
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"text": [
"It’s a phenomenon known as Semantic Satiation. It’s just as you describe; one will say a phrase or word so many times that it eventually temporarily loses its meaning. Interestingly enough, there’s also a phenomenon where if you engage in Semantic Satiation, doing the task at hand will become slightly more difficult. URL_0 Edit: There’s a more so “explain like I’m an adult” explanation on the phenomenon where tasks become more difficult if you verbally repeat them, but I couldn’t find much (on the cellular or neurological level) as to why Semantic Satiation in specific occurs.",
"words only have meaning when you use them with other words... so by using it improperly over and over (repeating it nonsensically), your brain eventually begins to believe it really means nothing."
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7jt3w0 | Why do headphone wires get entangled? | Repost | explainlikeimfive | {
"a_id": [
"dr8zjgt"
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"text": [
"Entropy, there's only one way for them to be untangled but billions of ways for them to be all tangled up. Any change of state, say they get jostled or moved about will statistically lead them to be tangled as opposed to untangled."
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7jy6zy | Why do we get that sharp ringing noise in our ears out of nowhere? | Repost | explainlikeimfive | {
"a_id": [
"dra42ty"
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"text": [
"this is called sudden brief unilateral tapering tinnitus...a temporary loud ringing in one ear that after around a minute or so tapers off into nothing. also known as an sbutt :) not much is known about what causes them, but it seems around 3/4 of everybody has had at least one episode, and that having it in the right ear is about twice as common as in the left. there seems to be a loose correlation with regular tinnitus, with people who have tinnitus being more likely to have sbutts, and people who have a lot of sbutts are likely to have or develop tinnitus. all in all, there doesn't seem to be any hearing loss associated with the occasional sbutt."
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7jymvg | Where does the giant amount of money out of the 21 century fox purchase by Disney go to? | Repost | explainlikeimfive | {
"a_id": [
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"text": [
"It goes to the current owners. Since 21st Century Fox is a publicly listed company, anyone can own shares of the company - you or me, for example. I suspect that most of the company is owned by things like pension funds. Most of the payment will be made in the form of shares, rather than cash. According to the [Financial Times]( URL_0 ), current shareholders will each receive 27.4 cents worth of Disney shares per Fox share they own, and at the end of the transaction they will own 25% of the new, combined company."
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7k0fw2 | Why are perfume ads all uniformly bizarre? | Repost | explainlikeimfive | {
"a_id": [
"drajm11",
"dral0ka"
],
"text": [
"Short answer: because they can't use the TV to show what the stuff smells like. Long answer: because they want to make sure that the brand is cemented into your mind in a slightly positive way, so they flood the senses with imagery related to sexuality, pleasant activity, and intrigue, which gets you to remember their version of toilet water above others.",
"We all know what brand of batteries uses an annoying bunny in their ads, we all know which burger chain has a redhead clown in their ads. The thing is all batteries are pretty much the same package of chemicals and a burger is a burger so the more your product is the same as your competition's the more you have to advertise it and use ads that in some way stand out. All perfumes are solutions of smelly things in alcohol so they have to put a lot of effort into making you remember their brand when you decide to find out what it smells like, which they can't possibly communicate in advertising."
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7k0rau | Why are images in infinite mirrors turning greener after each level? | Repost | explainlikeimfive | {
"a_id": [
"drb0ds4",
"dramtmd",
"dramuhr"
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"text": [
"Even truly tiny amounts of iron will tint glass a greenish color. So the green color in mirrors is a result of the glass itself being not totally colorless. Note that other elements will lend different colors to glass, cobalt produces an unmistakable ocean blue and cadmium sulfide produces yellow. Now, since iron is the fourth most common element in earth's crust, and considering that the basic raw materials for glass are bulk minerals like sand and limestone, getting traces of iron out of glass is exceptionally difficult. Nevertheless for things like optical fibers it's important to get high clarity and for that all traces of impurities need to be removed. This is typically done by converting raw silica sand into silicon tetrachloride (SiCl4) which has a low boiling point, then distilling it several times. Then finally the SiCl4 is reacted with water vapor producing ultrapure silicon dioxide. In cheaper grades of glass, such as those used to make bottles, the greenish tint tends to be more obvious. Extra iron salts may be added to make dark green wine bottles. This helps absorb UV light which can degrade wines.",
"Class is not perfectly clear. Nor is the color of the reflection a perfect reproduction. Over many interations you're seeing the slight color variation from the glass stack up over and over.",
"The glass used in mirrors is greenish. Normally it's too thin to notice, but after a reflection has passed through the glass pane thirty times you're now effectively seeing several inches of glass instead of 1/8\"."
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7k0z7k | Why do we experience brainfreezes when we consume cold drinks too fast? | Repost | explainlikeimfive | {
"a_id": [
"drap78x"
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"text": [
"Brainfreeze is caused by your nerves not being totally connected in obvious paths. The trigeminal nerve serves the forehead as well as the roof of the mouth. The brain processes \"too hot\" signals from the roof of the mouth correctly, if you sip a hot beverage. Alas, \"too cold\" signals get mistaken for \"bumped head\" signals because these nerves are a party line. The real term for brain freeze is sphenopalatine ganglioneuralgia (meaning \"pain of the sphenopalatine ganglion\"), and we're not going to switch to that any day soon."
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7k11rz | Why does tubberware never dry properly in the dishwasher? | Repost | explainlikeimfive | {
"a_id": [
"draoq68",
"draoxsy"
],
"text": [
"Plastic doesn't conduct heat as well as porcelain or glass does, so the water isn't able to evaporate from the plastic due to the lower temperature of the material.",
"Plastic dumps it's heat way faster than glass and ceramic because it's far less dense, thus the water doesn't dry off. and this topic comes up a lot in ELI5."
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7k6a4l | what causes the pins and needles sensation when a body part falls asleep? | Repost | explainlikeimfive | {
"a_id": [
"drbx76i"
],
"text": [
"It's actually usually pressure on the nerve, not blood vessels. Basically, when you press on the nerve, it makes it fire extra signals which confuses your brain. It takes a little bit after the pressure is released for everything to readjust back to normal."
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7k6ayo | Could a person get access to the internet without an ISP? How much money and equipment would it take to connect to the internet by yourself? | Repost | explainlikeimfive | {
"a_id": [
"drbvxxg"
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"text": [
"Your ISP is very much like the post office, it helps you send and receive packages of data (packets) between you and your destination (a server). So, along these lines you are asking the question of “how can a person get mail without a post office?” Well, he would have to create his own post office. You will find very quickly that you end up right back with the same system you were trying to get rid of. In reality you would have to recreate the massive infrastructure that Verizon, Comcast, and the rest have collectively spent trillions on in the past 100 years. It’s just extraordinarily prohibitively expensive."
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7k6mhq | why do some things stick together while other things do not | Repost | explainlikeimfive | {
"a_id": [
"drbyqgr"
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"You are staring at the fact that different substances are, well, different. Water is wet. Dry sand is dry. Wet sand can be shaped. If you carefully shape wet sand with a hollow in it you can pour liquid metal into the hollow. When it cools you have a shaped tool. If you are in a subway car and the next car is full of zombies you can wet newspaper and put it over the windows. In that movie zombies did not try to attack you if they could not see you. They were calmer. Atoms have nuclei, very small regions where protons and neutrons are assembled. It took a lot of energy to get them together. But once together they mostly stayed together if the combinations was stable. Most combinations are not stable and will fly apart. So we see the survivors, the combinations which are much more stable than other combinations. Being stable, that is being able to stay together for a long time, often the length of the universe, means the long range effects of stable nuclei show up. Nuclei have a positive charge. No electrons allowed in. But they are attracted to nuclei until they bump up against the strong force which keeps them away. That is why it took a lot of energy to form the nuclei, the strong force keeping things away. Instead of joining the positive forces in the nuclei the electrons will occupy orbitals around nuclei. Generally the most stable configuration is a number of electrons matching the number of protons in the nucleus. Electrons generally stay away from each other. They have the same charge. But two of them can stay closer if they have an opposite characteristic unfortunately called \"spin.\" This spin is not what pool balls, basketballs, or any other balls do when spinning. But the name was thought up and it stuck. Maybe this quality should be renamed. But it is hard enough to visualize things at an atomic level. Electrons are not really little balls, nor do they actually spin, probably. They do exist. They have properties. One is called spin. That is the way it is. Electrons dance around in the area around nuclei. While they dance they arrange themselves into pairs and singlets. They change energy states giving off or absorbing photons. Electrons at the outer edge of these areas called orbitals interact with the rest of the universe. They may actually be in a position between two or more nuclei. They will be occupying something like an orbital, an orbital far more complex than the simple ones close to nuclei, but they are at an energy state less energetic than a free roaming electron. They gave off a photon. They interact far less with the universe. Theoretically free roaming electrons can respond to other electrons and protons very far away. It can be confusing. But these interactions mean some things are sticky while others are less sticky. It is the electrons in the outer cloud of electrons surrounding the nuclei which determine if something is sticky. If the nuclei have an odd number of protons then and odd number of electrons, a number matching the number of protons, surround the nucleus. The electrons between two or more nuclei will tend to stay there if they help balance the electrical charges. But they can move. So when you move two substances together they either stick, or they do not."
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7k6sxh | Where do we get oxygen from during winter? | Repost | explainlikeimfive | {
"a_id": [
"drbyqkw"
],
"text": [
"Most of the world's oxygen comes from the ocean. About 70% actually. And it isn't winter everywhere at the same time, in fact it's pretty much always winter equally globally. The southern hemisphere is actually in Summer right now. Perks of living on a big wet ball, things are pretty much always balanced out"
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7k70i0 | Why can you become ill from eating chicken that’s undercooked, but you don’t from other meats, like beef? | Repost | explainlikeimfive | {
"a_id": [
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"text": [
"First, you're not quite fully correct. You can easily get sick from eating other undercooked meat. Happens all the time in places where there's not the greatest sanitation or proper handling processes. Different meat animals are raised and handled under different circumstances, and then prepared in different ways. Different types of organisms live in, on and around them before and during their processing as well. A lot of chickens pretty much wallow in their own filth, for example, and so there's all sorts of possible sources of Salmonella bacteria when someone mishandles them. Fully cooking chicken kills the bacteria and removes the problem. And some food poisoning sources like the trichinosis roundworm live more with one type of animals than others, and so you're instructed to cook pork thoroughly to avoid that one. You're still taking a chance when you eat blue or rare beef, but usually it's prepared in a way that minimizes its exposure to surfaces, and people usually sear its outside where the bacteria might accumulate. Not quite as true with ground beef though - grinding it exposes a tremendous new surface area to your appliances... and that's why 'medium' hamburger or \"steak tartare\" are not served in a lot of restaurants as a way to reduce the chances of food poisoning."
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7k8mp1 | How do fishes gills work? | Repost | explainlikeimfive | {
"a_id": [
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"text": [
"Ahoy, matey! Yer not alone in askin', and kind strangers have explained: 1. [ELI5: How do fish gills work? ]( URL_5 ) ^(_6 comments_) 1. [ELI5: How do fish gills actually work? ]( URL_1 ) ^(_11 comments_) 1. [ELI5: How do fish gills work? ]( URL_7 ) ^(_7 comments_) 1. [ELI5: How do gills work, and why can't fish survive on land very long? ]( URL_0 ) ^(_2 comments_) 1. [ELI5: how do the gills on a fish filter out the oxygen from the water? ]( URL_6 ) ^(_40 comments_) 1. [ELI5: Do we know how do gills work? If we do, what is stopping us from designing fake gills that you can simply put into your mouth or up your nostrils? ]( URL_8 ) ^(_4 comments_) 1. [ELI5 What do gills do? Why do fish need oxygen in water but can't breathe air? ]( URL_2 ) ^(_5 comments_) 1. [ELI5: Why fish can pull oxygen from the water yet not from the air. ]( URL_3 ) ^(_11 comments_) 1. [ELI5: How do fish \"breathe\" water? ]( URL_4 ) ^(_6 comments_)"
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"https://www.reddit.com/r/explainlikeimfive/comments/631c3s/eli5_how_do_gills_work_and_why_cant_fish_survive/",
"https://www.reddit.com/r/explainlikeimfive/comments/5cdaul/eli5_how_do_fish_gills_actually_work/",
"https://www.reddit.com/r/explainlikeimfive/comments/1uaym8/eli5_what_do_gills_do_why_do_fish_need_oxygen_in/",
"https://www.reddit.com/r/explainlikeimfive/comments/m0gkq/eli5_why_fish_can_pull_oxygen_from_the_water_yet/",
"https://www.reddit.com/r/explainlikeimfive/comments/3v8xq8/eli5_how_do_fish_breathe_water/",
"https://www.reddit.com/r/explainlikeimfive/comments/63ek5q/eli5_how_do_fish_gills_work/",
"https://www.reddit.com/r/explainlikeimfive/comments/3nowet/eli5_how_do_the_gills_on_a_fish_filter_out_the/",
"https://www.reddit.com/r/explainlikeimfive/comments/1qf7e9/eli5_how_do_fish_gills_work/",
"https://www.reddit.com/r/explainlikeimfive/comments/1rdat5/eli5_do_we_know_how_do_gills_work_if_we_do_what/"
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7k991o | How can some things look worse or better in real life than in a photo/video, for example the saying that 'the camera adds ten pounds'? | Repost | explainlikeimfive | {
"a_id": [
"drchynl",
"drcjuqc",
"drckqsp"
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"text": [
"The specific lens a camera uses distorts light. Likewise, certain lighting can make a major difference, as can the angle at which a photo is taken. All of these factors mean that a photo can make something look much better or worse than it normally does, by manipulating those factors.",
"I think a lens can certainly play a factor but I think there are probably some other things at play even if lens distortion is at a minimum. For example they are seeing themselves at an angle different from what they are used to seeing in the mirror. Their posture could be different and the lighting could be more or less flattering.",
"The process that turns a real life object to a picture is full of distortions. To start with the light's path to the sensor: Each lens distorts the incoming light with in a handfull of ways. This can only be partly corrected by adding more lenses. In digital cameras, light is maped to 3 colors: red green and blue (RGB), which match the corresponding photoreceptor cells in the human eye. Although it is impossible to to build a sensor that matches the exact wavelengths and dynamic range of the human eye which varies between individuals. Corrections can be made with digital image processing. The output is then stored in a file which again uses RGB to represent a color. Which are again displayd with RGB dots on a digital monitor. Given the theory of the CIE 1931color space, 3 colors are unable to cover the entire spectrum of the eye, so a digital picture will never look like its real life counterpart. TV display manufacturers try to improove vibrance by adding a fourth color e.g. yellow."
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7kcbxm | Why is that when something spins fast in one direction, it looks like it's spinning in the other direction? | Repost | explainlikeimfive | {
"a_id": [
"drd8r7b"
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"text": [
"Your brain processes imagery at a certain rate; how fast the rate actually is depends in many things such as whether something moves in the center of your vision or at the edge, the motion in question, the colors and lighting evolved, your choice psychological state, etc. For the sake of argument, let's assume our eyes capture a visual snapshot 100 times per second and send it to the brain for processing. If something like the rotor blades of a helicopter was to spin at 100 revolutions per second, the blades would appear to stand still in mid air, as your eyes catch them in the same position each time. But what if they turned at only 95 revolutions per second? Each time your eyes send a snapshot, the blades would almost have reached their previous position, but not quite. And here's the trick: your mind actually interprets this as the blades having moved backwards as it never got to see the intermediate states. Add this up over many snapshots and a rotating object will appear to spin backwards at certain speeds."
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7kd0hg | Where do ISPs get their 'internet'? | Repost | explainlikeimfive | {
"a_id": [
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"text": [
"Consumer level isp's get their upstream connection from backbone isp's. Backbone isp's lay down wire that connect regional or cross country and international cross ocean. Backbone isp's are like level3, CenturyLink, cogent. If you run a tracert command to somewhere like Europe or Asia, you'll see these names pop up.",
"ISPs are like roads with toll booths. The internet is a network of roads. The stuff you want is the trucks and cars that travel on the roads; the ISPs (roads) don't *make* the content, they only delivery it from point a to point b. If you want your own isp you need to be able to put in the money up front to make a whole bunch of roads, including putting in wires to individual houses and providing the modems & routers they need, and then connect their traffic to the larger backbone infrastructure of networks.",
"At that level it doesnt really work like that, there is no \"central clearinghouse\" ISP's have routers (not dissimilar to your router at home, but way way bigger and with loads more interfaces) They also have cables that connect them to other ISP's instead of one up link these core routers have different links to different networks (other ISP's) and a routing table ( URL_0 ) to make sense of what ip's are reachable, and via what distance sometimes traffic for a single IP will traverse several different \"ISP's\" networks before getting to its destination IP Hosting firms (that own data centers) just count as thier own ISP's in this model",
"> I know that the internet is made up of servers that are inter connected and you can instruct your browser to access certain servers, and that all ISPs do is provide the wiring to connect these servers to your house but where does it all meet up? If I were to start my own ISP, how do I set up my service to be able to connect everywhere else? A wholesale internet for want of a better term. Thanks. Your question is sort of asking where all the roads in your country meet up, which doesn't really make sense, considering how many roads there are. If you were to start your own ISP, you might connect to another Internet service provider, say Level3, which have routers that have connections to other ISPs and whatnot. The road analogy is pretty good here, as it is pretty much the same thing. You just need to connect your road or set of roads to some other set of roads with connections to everywhere else. You may want to look at [this AMA post]( URL_0 ) about someone who set up a rural wireless ISP that launches in January."
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7kemv3 | Why does Coke taste different out of Glass, Plastic or Aluminium? | Repost | explainlikeimfive | {
"a_id": [
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"text": [
"Cans contain lining material that may or may not absorb flavor, plastic bottles have chemicals that can migrate (in very minute amounts) into the soda, glass bottles are inert and only really affected by light contamination and temperature changers. Though I find the difference almost non-existent from an objective standpoint when it's poured into a glass. Drinking directly from a can I can tell the difference though b.c. I can taste the aluminium. That all being said, I do think glass bottle coke is better than canned or plastic bottled. Ha",
"Different environments make the same food taste different. * wine in different glasses. URL_0 * food on an airplane URL_1"
],
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"text_urls": [
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"http://www.sciencedirect.com/science/article/pii/S0195666303000825",
"http://www.bbc.com/future/story/20150112-why-in-flight-food-tastes-weird"
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|
7kh9mg | What are memories? How do they happen? How are they stored? Why do they fade? | Repost | explainlikeimfive | {
"a_id": [
"dredr16"
],
"text": [
"Imagine you're building a tiny robot. It's incredibly primitive. About the size of a marble. With tiny wires, legs, and the smallest of circuits that can only remember very basic commands. Mostly it just sort of wanders aimlessly around until it bumps into energy, which is uses as food. Or perhaps other robots. Which they dissemble for food, if that other robot can't run or fight them off. This tiny robot can make more of itself though (if it finds sufficient materials). But the catch is...every time it does, the new one has minuscule, *almost* random changes AND the robots existing adaptions might be passed down to it's \"offspring\". Before long you have tens of thousands of tiny robots. Most of these changes are entirely neutral. But some of them are actually useful - such as improvements to locomotion, new ways of detecting food, or running away from aggressive robots. Conversely, the adaptions that are less useful start to die off as they make it harder for a robot to exist. Given sufficient time, you'll see an amazing menagerie of fantastic robot designs. Some will remain the size of marbles, but some will gradually become bigger! Some of them will smooth their legs over many generations to become wheels, and zip around speedily and efficiently. Some will get larger, or even armored, to dissuade predator robots. Some might get bigger circuit boards to accommodate more chips and wires. Now, one of these robots has an interesting adaption with it's enlarged circuit board adaption. It is able to *remember* things. It has a very primitive temporary storage system that lets it remember food locations. One location at a time. And this gives it a survival advantage over other robots that are just floating aimlessly. This in turn leads to offspring with this advantage, who expand that storage system further so it can remember two things at a time. And then again. And again. The storage space gets bigger, the circuit gets bigger, but it's still a really primitive system build on an ancient way of remembering where food is. And that system is prone to error, data loss and misinterpretation. No matter how many robot generations you observe, that memory system is never going to be perfect because it's a steady gradient of alterations on a primitive system. With no overarching goal and no intelligence watching over it. The only thing deciding whether or not the adaption is an improvement is whether it works *well-enough to not get you killed* and well enough to get you to breeding age. Perfection isn't important. On the other side of the coin, take hard drives. Where an intelligent designer has gone *\"right, we need this data stored and retrieved perfectly. How do we achieve this\"*. Then selected specific piece of technology to do it (Magnetic Disk), provided all the necessary parts, tested it a thousand times, then manufactured it. The system is designed for it's intended role, right from the get-go. **TL;DR** - Our \"memories\" are just sensations stored by our food locating/survival system contained inside our skulls. And said recollections are stored and retrieved imperfectly because the system that designed it (evolution) did not reward perfection. Only what works \"well enough.\""
],
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|
7kjvhx | How do Phone Scammers Spoof Their Caller ID? | Repost | explainlikeimfive | {
"a_id": [
"dreybv1"
],
"text": [
"Many are using VOIP programs that mimic calls, but use a computer instead of a phone. This bypasses the need for a phone service plan, the number can be changed at any time, and no Caller ID in the world would accurately judge where the call was coming from. These are lovely benefits to someone who wants to make a whole lot of spam calls in a short period of time, because the computer can make many calls simultaneously while a phone can really only do one."
],
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"text_urls": [
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|
7kjyy5 | why are keyboards 'qwerty' and not alphabetical? | Repost | explainlikeimfive | {
"a_id": [
"dreyl6n",
"dreya0k"
],
"text": [
"We don't use all the keys with similar frequency while typing. In English ETA are the most used alphabets so ETA are pressed more times than other letters. In the past age of mechanical keyboards and typewriters, when two keys which are next to each other are pressed it caused typewriters to jam To prevent this the most used letters are placed far and requires one to alternate hands which reduced jamming of the keys and lesser used keys(like X) are placed at tricky positions which are not so easy to reach. Other keyboard layouts also exists like Dvorak and workman which are suitable for typing in other languages than English. **ALSO** Contrary to the popular belief QWERTY layout was not designed to slow the typist but rather to speed up typing by reducing jams and alternating hands(which is a desirable trait for good speed).",
"The arrangement of characters on a QWERTY keyboard was designed in 1868 by Christopher Sholes, the inventor of the typewriter. According to popular myth, Sholes arranged the keys in their odd fashion to prevent jamming on mechanical typewriters by separating commonly used letter combinations."
],
"score": [
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|
7kks14 | Why does pouring salt on snow or ice make it melt? | Repost | explainlikeimfive | {
"a_id": [
"drf32pd"
],
"text": [
"It lowers it's freezing point. So you were right. A 10-percent salt solution freezes at 20 F (-6 C), and a 20-percent solution freezes at 2 F (-16 C). Even in snow there is small amount of liquid water. Salt dissolves there and starts to \"spread\". You can try this yourself with a ice cube and a pinch of salt."
],
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|
7kq461 | How do Anti Virus programs work? | Repost | explainlikeimfive | {
"a_id": [
"drgb7on"
],
"text": [
"Most anti-virus software uses a combination of techniques. One is comparing a file or program on your system to its definitions database, a collection of files/programs that are known to be or install malware. The second is \"heuristics\" - basically algorithms and profiles it applies to files and programs on your computer to determine how likely something is to be malware. If something is a certain percentage of a match, it gets quarantined and flagged for deletion. In the terms of cops 'n' robbers (apologies for the not so politically correct analogy)... The first one would be like taking a suspect's fingerprints and seeing they're wanted for a crime. The second would be like police profiling/stereotyping of suspected drug dealers in certain neighborhoods."
],
"score": [
11
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|
7kqvxa | Why cookies get soft when there is a piece of bread in the container with them | Repost | explainlikeimfive | {
"a_id": [
"drghnbz",
"drgifj8"
],
"text": [
"The cookies absorb the moisture from the bread, so you couldn’t use stale or naturally hard bread to get the same results as you would from a nice fresh slice of soft wheat or white bread. If its an enclosed space its normal for moisture to transfer to dryer substances in this space.",
"Cookies are crunchy because they have little water. Bread is soft because it has a lot of water. If you put the two together, water will evaporate from the bread making it tough and chewy, and will be absorbed into the cookies making them soft."
],
"score": [
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3
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"text_urls": [
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|
7ks2lx | what is blue tooth? | Repost | explainlikeimfive | {
"a_id": [
"drgqm6b",
"drgqym8"
],
"text": [
"Bluetooth is a high frequency radiowave communication system. It is not proven to be harmful.",
"A radio signal is sent from one device to the other. Not that different from ones your FM radio uses. This type of electromagnetic radiation has been extensively studied for any negative health effects, and no link between it and negative health effects has been found. There also isn't any known way it could effect our health. Bluetooth uses similar waves as cell phone uses, but the transmitters are operating at significantly lower power than cell phone transmitters are, so even if you'd be convinced cell phones cause health problems(a proposition which has been studied and found false), using bluetooth devices would reduce the amount of radiation you receive by factor of 1000. So the gist of it is, there aren't many things in this world that have been scientifically proven to be as safe as bluetooth devices radiation. Eating bananas is demonstrably more dangerous for example."
],
"score": [
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"text_urls": [
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|
7ks8vw | The theory of time travel via High Speeds | Repost | explainlikeimfive | {
"a_id": [
"drgroki"
],
"text": [
"Basically, by travelling really fast, time slows down for the traveller. The formula for it is [here]( URL_0 ). As you get closer and closer to the speed of light, time for you slows down faster and faster. Note that it is not a linear relationship, so travelling at 10% of the speed of light does not slow your time down by 10%. Now, for example, if you travel at 80% of the speed of the light, following the formula you see that your time slows down by 40% relative to a stationary person. In other times, the other people are going through time 60% faster than you are. So if you traveled for 1 year at the speed of the light and arrived at another planet, the people on the planet would actually have aged 1.6 years, and you had *traveled* into the future by 0.6 years."
],
"score": [
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"text_urls": [
[
"http://www.walter-fendt.de/ph14e/timedilation.htm"
]
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} | [
"url"
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|
7kvjll | how can the universe be finite? If it has a putter boundary, doesn’t there have to be something (even empty space) beyond it? | Repost | explainlikeimfive | {
"a_id": [
"drhixbi",
"drhi8w6",
"drhifne",
"drhhro4"
],
"text": [
"The universe is not finite. The *observable universe* is finite. Light has a fixed speed. We can only see as far as (light speed) divided by (the amount of time passed). The universe itself is infinite. What does that mean? Imagine traveling in one direction until you get to the edge of what you can see currently. What would you see as you look out in the direction you were traveling? *More universe*. This will happen no matter how many times you travel to the edge of that observable universe, and no matter the direction. (This happens in a flat, open, or closed curvature universe). An analogy would be sitting on a ship in the sea. What you can see from that ship is the *observable universe*. But if you sail to the farthest point that you can see, you'd still just see more sea. You can keep sailing in that direction, and you'll never get to the end. *You might even end up exactly where you started*, but you'd still never reach the \"end\". The sea you are traveling in is infinite, in the mathematical/physical sense. While the area of sailable locations might be finite, the topology of sailable locations is infinite. This is an example of closed topological curvature. Flat or open curvature are similar, except you'll never end up back where you started. You'll just keep getting further and further away from your origin if you continue on one direction (think the difference between an infinite 2d plane [flat] vs a 2d sheet of paper wrapped around a sphere [closed]). Edit: the Universe's expansion is somewhat answered by the infinite nature of it. The Universe is all inclusive. So it is \"expanding\" into *itself*. There's really not an excellent way to describe it, Just a lot of thinking. The Universe's expansion isn't like an explosion, or blowing up a balloon, or a loaf of rising bread. **If** the things that make up the explosion, or the balloon plus things inside, or the bread dough, where a representation of everything that is, was, and ever could be, then using them as an example for the Universe's expansion would be somewhat accurate. The point is - you can never be \"outside\" the universe. It is *everything*, so it's expansion is into *something*, and *something* is apart of *everything*, so it's expansion is into itself.",
"It's not clear what the volume of the universe is, or even if a three-dimensional volume is the correct description. A sphere has a finite area, but no edge. The universe may be similarly bounded and unbounded. It does appear to have finite *matter* though, infinite mass (even at great distances) would cause problems in our current understanding of gravity and universal expansion.",
"Ah the old what's beyond our observable universe question. Simple answer is no one knows if it's finite or infinite or whatever. It's pure speculation.",
"I think when people say finite they mean that if you go a googol light years away, you'll actually be in 'empty space', but there will be a discrete 'finite' universe that may still be expanding into that empty space. An interesting thing to think about though is that the electromagnetic field permeates all of space, and so long as there is a field you'll always have the spontaneous generation of particles and antiparticles. So even if you leave the universe you'll still have stuff popping in and out of existence around you."
],
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|
7kx88x | If air particles are moving around randomly at very high speeds, how does wind occur and what happens to the air particles? | Repost | explainlikeimfive | {
"a_id": [
"drhv54c"
],
"text": [
"They blow my mind! Just kidding. Mostly particles are more vibrating rather than running around crazy. When you get wind it's because of high pressure and low pressure zones in the atmosphere and the wind 'flows' like water 'downhill', or to the area of low pressure. Then the air particles are actually moving."
],
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|
7l6szc | What Mastering is, when music gets Remastered. | Repost | explainlikeimfive | {
"a_id": [
"drjztzb",
"drk0pyj"
],
"text": [
"So let's say we have an old recording of something. Like The Beatles (Sgt. Peppers was just remastered for example). In older music the recording methods were not near the levels of perfection that we currently have. Audio samples might have some interference that was undesirable and couldn't be entirely removed. This is easier with digitization. We can also take old samples and boost different frequencies, change the volume, change the dynamic range. You can pretty much change any property of the sound you want. Another example is mono and stereo. Old records (The White Album for example) was mixed for mono, all the audio plays out on channel. This conformed to older system standards. Eventually people bought stereos that were able to have multiple channels so now you can play the guitars out one and the singers out the other so it sounds clearer. Changing from mono to stereo is another form of remastering. TLDR: You scrub undesired noise from the recording and add effects to create the \"perfect\" sound.",
"A *master* is the original finished copy of a piece of audio or video. Before the 1980s, all masters were analog. Copying it meant playing it, and each time you played, it would wear out a little. Masters were used a little as possible, you'd make 10 copies, then 10 copies of each of those copies, etc., until you had all that you needed. Between occasional copies and just the physical breakdown over time, the quality of the master would degrade. Remaster means two things. First, you convert the master to digital, which does not wear out. Then you carefully process the digital copy to remove and repair an imperfection, resulting in a better version that will never break down."
],
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|
7l6zz2 | Why do our eyes get heavy and blurry when we are sleepy? | Repost | explainlikeimfive | {
"a_id": [
"drk5ndp"
],
"text": [
"Quite simply, you eye muscles are tired. You might have been staring at something for a long time (such as a screen or road) or just might have had a long day. Keeping your eyes open and blinking takes energy, and using a muscle too much can make it sore."
],
"score": [
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|
7l8oi7 | How does binary code operate computers with a series of 1s and 0s? | Repost | explainlikeimfive | {
"a_id": [
"drkcmj6",
"drkdmli",
"drkcq7o"
],
"text": [
"Your computer CPU has lots of transistors and those 1's and 0's tell those transistors to turn on or off. Like a bunch of light switches basically.",
"The best answer I got for this is by u/r00nk which I have saved. Here it is: > Lets dive right into the magical land of data. > Whats the symbol for five? 5. Whats the symbol for ten? 10. But wait, isn't that the symbol for one and zero? Right, so in our numbering system, when we get to the number ten, we write the symbol for one and zero. > There is no symbol for ten, we simply recycle the ones we already have. Because of this, we call our numbering system \"base-ten\", or \"decimal\". > \"Ones and zeros\",\"true and false\", and \"on or off\" are all terms you have probably heard before. What these all are referring to is a different kind of numbering system. For our decimal system, we write a '10' when we get > to ten, but for binary, we write a '10' when we get to two. There is no symbol for two in binary, exactly how there is no symbol for ten in decimal. \"On\" or \"off\" simply refers to '1' or '0' in binary. > Just to make sure that makes sense (as its super important): > 01 = one; > 10 = two; > 11 = three; > Make sense? Cool (if not google \"binary\"). > Ok, now for something completely different, but related. > Theres something in computer theory called a \"logic gate\". It's a device. It has two inputs, and one output. The only input it accepts is \"on\" or \"off\", and the output is the same, \"on\" or \"off\". You might see the relation to > binary. > A logic gates output is based on its input. An example of a logic gate is a \"AND\" gate. When both of the inputs are on, the output is on. Otherwise, the output is off. > You still with me? Don't worry, the cool stuff is coming soon. > Another logic gate is the \"NOT\" gate. The NOT gate has one input. If the input is off, the output is on, and vice versa. The output is not the input. Get it? > Now, if we put the input of a NOT gate on the output of an AND gate, we get a NAND gate. Creative, I know. We nerds don't get out much. Anyways, try to figure out what the output would be for all the four different possible combinations of the two inputs for the NAND gate. > [Anyways, heres what a NAND gate looks like drawn.]( URL_2 ) > Now, you have probably heard of computer memory right? [**ta da!**]( URL_0 ) > It's not going to make total sense at first, but that diagram shows a memory-holder-thingamajig. Look at it for a while and try to figure out what it does. Basically it holds a \"bit\" of memory. You could say that a bit is like > one digit of a binary number. You line a bunch of these in a row, and you can start holding numbers. > But what do you do with those numbers? > This is where it gets cool. You do math with those numbers. This next device is called an \"adder\". > The gate on top is called an XOR gate, its output is on if only one of its inputs is on. If there both on or off, then the output is off. > Now, make it [a little more complex]( URL_1 ) and you can add multiple bits at the same time, by linking the last ones \"Cout\" to the next ones \"Cin\". > Cool, now we have a basic calculator. How can we turn this up to 11 and make a computer? > Code. > Now, you know what data is, and so code is easy to explain. Its just data. Thats all it is. Really. > The reason why its different then other data though, is because the CPU interprets it as instructions. > f we wanted to do math for example, and we got to decide the instruction definitions we could use a system like; > 00000001 = *add* a number to another number; > 00000010 = *subtract* a number from another number; > With this, we can set what logic gates are being used based on data. > Now, real quick, memory is organized on a computer by something called memory addresses, basically they just allow the CPU to ask for memory at a specific location. Generally speaking the addresses are sized by \"bytes\" which is just another word for \"eight bits\". So if we wanted to access memory location five or whatever we could store that as '00000101'. > Lets go back and add some more to our table; > 00000011 = move this data into some location; > Cool, now we can say something like: > \"add the number at location #5 in memory to the other number at location #7 in memory.\" > By breaking it down into: > (add) (memory address #5) (memory address #7) > Which is really just > 00000001 00000101 00000111 > Pretty sweet right? > But hold on, how does the CPU know where to get its instructions? > On the cpu, Theres a tiny amount of memory, it does various things, such as hold something called the \"instruction pointer\". The instruction pointer holds the address of the next instruction, and increments itself after every instruction. So basically, the cpu reads the instruction pointer, fetches the next instruction, does it, adds one to the instruction pointer, and then goes back to step one. > But what happens when it runs out of instructions? > Lets go back to our table. Last time, I promise: > 00000100 = set instruction pointer to address > Basically, all this instruction does is set the instruction pointer to a number. You ever wonder what an infinite loop is on a computer? Thats what happens when an instruction pointer is set to instructions that keep telling the instruction pointer to set itself to that same set of instructions. > Thats computers in a nutshell.",
"I guess I'll tackle this. When dealing with electricity, the easiest way to send a signal is having it on (flowing, or in binary, 1) or off (not flowing, 0). Within a CPU, you will have tons of logic gates. These logic gates have what are called transistors, which are very small switches of sorts. Logic gates take inputs and give an output. There's a ton of them, and you need a lot to get a functioning computer. Having a lot of logic gates working together will let you process all sorts of things. But if you Google logic.gates, the Wikipedia has a TON of useful pictures and stuff to better visualize logic gates as well as all of their functions."
],
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[],
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"https://en.wikipedia.org/wiki/Flip-flop_(electronics)#mediaviewer/File:SR_Flip-flop_Diagram.svg",
"http://i.stack.imgur.com/0rqZz.png",
"https://en.wikipedia.org/wiki/NAND_gate#mediaviewer/File:NAND_ANSI_Labelled.svg"
],
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|
7lck80 | how do people mature things like steaks without them rotting? | Repost | explainlikeimfive | {
"a_id": [
"drl7lcr"
],
"text": [
"Yer not alone in askin', and kind strangers have explained: 1. [ELI5: How dry aging meat doesn't make it dangerous. ]( URL_1 ) ^(_ > 100 comments_) 1. [ELI5: How dry-aging meat does not spoil even after 200 days? ]( URL_2 ) ^(_24 comments_) 1. [ELI5: Why does aging steak not cause it to go bad? ]( URL_11 ) ^(_2 comments_) 1. [ELI5: How are cuts of beef \"aged\"? ]( URL_8 ) ^(_1 comment_) 1. [ELI5:How does aging meats and things like cheese work and not just make them rot and gross? ]( URL_9 ) ^(_17 comments_) 1. [ELI5:When you dry age beef, why doesnt it just rot and spoil? What all is going on? ]( URL_10 ) ^(_3 comments_) 1. [ELI5: How can a butcher \"age\" beef for a large period of time (21 days etc.) yet if you were to take the same cut of meat not aged and leave it in the fridge for a time after its expiry it would turn rancid and have to be thrown out? ]( URL_5 ) ^(_7 comments_) 1. [ELI5: why is it safe to dry age beef, but unsafe to keep supermarket beef in the fridge for more than a few days? ]( URL_4 ) ^(_7 comments_) 1. [How is beef dry aged? ]( URL_6 ) ^(_2 comments_) 1. [ELI5:How do you \"dry age\" beef? Is it safe to eat this dry age, or does it pose serious risks like tar tar? ]( URL_3 ) ^(_5 comments_) 1. [ELI5:Why is some food \"aged\" and still edible while others are rotten and tossed out? ]( URL_7 ) ^(_20 comments_) 1. [ELI5: how can a steak be matured for 28 days, but have an expiration date of 3 days when on the store shelf ]( URL_0 ) ^(_21 comments_)"
],
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[
"https://www.reddit.com/r/explainlikeimfive/comments/355m22/eli5_how_can_a_steak_be_matured_for_28_days_but/",
"https://www.reddit.com/r/explainlikeimfive/comments/2fsz5c/eli5_how_dry_aging_meat_doesnt_make_it_dangerous/",
"https://www.reddit.com/r/explainlikeimfive/comments/6ngkbx/eli5_how_dryaging_meat_does_not_spoil_even_after/",
"https://www.reddit.com/r/explainlikeimfive/comments/2ob914/eli5how_do_you_dry_age_beef_is_it_safe_to_eat/",
"https://www.reddit.com/r/explainlikeimfive/comments/6n5eh6/eli5_why_is_it_safe_to_dry_age_beef_but_unsafe_to/",
"https://www.reddit.com/r/explainlikeimfive/comments/35r2s0/eli5_how_can_a_butcher_age_beef_for_a_large/",
"https://www.reddit.com/r/NoStupidQuestions/comments/42mxj0/how_is_beef_dry_aged/",
"https://www.reddit.com/r/explainlikeimfive/comments/7gamwl/eli5why_is_some_food_aged_and_still_edible_while/",
"https://www.reddit.com/r/explainlikeimfive/comments/2jnft1/eli5_how_are_cuts_of_beef_aged/",
"https://www.reddit.com/r/explainlikeimfive/comments/6992vi/eli5how_does_aging_meats_and_things_like_cheese/",
"https://www.reddit.com/r/explainlikeimfive/comments/38kvl9/eli5when_you_dry_age_beef_why_doesnt_it_just_rot/",
"https://www.reddit.com/r/explainlikeimfive/comments/1si9xe/eli5_why_does_aging_steak_not_cause_it_to_go_bad/"
]
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|
7lcvzo | When breathing humid air, what prevents our lungs from filling with water (like a dehumidifier)? | Repost | explainlikeimfive | {
"a_id": [
"drla9z1"
],
"text": [
"Because you breathe *out* humid air as well. A dehumidifier requires special equipment to extract the water from the air."
],
"score": [
6
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|
7leszf | why do fans collect so much dust | Repost | explainlikeimfive | {
"a_id": [
"drlq2cw"
],
"text": [
"There is a certain amount of dust in the air in a room, and as the fan is circulating the air, it has the chance to collect more of it as compared to something passive like a table top. For the table top - only the dust that happens to float by might have a chance to land. The other thing is the friction of blades churning through air creates static charges which then draw dust particles out of the air and they cling to the charged surface. There are actually air filtration systems that use this idea to pull particles out of the air - by forcing it through an intentionally charged up grid."
],
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7lgc6i | Why do pilots sometimes ask you to turn off all electronic devices when there is poor ground visibility? | Repost | explainlikeimfive | {
"a_id": [
"drm13pv"
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"The instruments that the pilots use, called the *Instrument Landing System*, is a sensitive device. The small interference from cell phones or other radio devices can disrupt the radio signals from the ground to the plane and vice versa. In conditions where there is low ground visibility, pilots go for the safe route and ask that you turn the devices off to be sure that they receive accurate information that is crucial for landing and these devices can interfere with the readings given. In such poor conditions, there are a lot of things that can do wrong, so to be safe they ask you to turn them off."
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7ljk82 | Why do some smells like gas smell so strong and the smells stays for so long but for something like a cup of tea you need to come close to smell it | Repost | explainlikeimfive | {
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"The stuff that makes gas smell \"like gas\" is actually tert-Butylthiol (t-butyl mercaptan). This is a chemical that humans can detect in very small amounts. Ordinary methane is odorless, which is a safety problem when leaks are possible.",
"Part of the answer is \"volatility\" or how easily a substance evaporates and then disperses through the air. This might be what you're looking for. There's also a question of concentration-- gasoline is mostly \"smelly stuff\", while tea is mostly water, with some of that stuff added. And we're more sensitive to some smells than others, for reasons which are insanely complicated (some of it is what you'd expect, though-- smells that are dangerous to us or unusual get our attention because it's useful for us to be aware and cautious around them).",
"The type of gas that runs through your house that you heat and cook with is given a strong smell so it’s easily detectable. Tea is just water with leaves, very neutral."
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7ll2to | How do modern smartphones and devices know what battery percent they’re on? | Repost | explainlikeimfive | {
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"Batteries lose voltage as they drain. So a computer that can read its own battery's voltage and has seen how high/low it goes in a charge cycle can guess how much charge is left, and guess (with less accuracy) how long it'll take to drain."
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7lncrp | What is asbestos and why is it dangerous/lethal? | Repost | explainlikeimfive | {
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"It is a fibrous material (like the hair on a coconut) that can create little bits of dust that are easy to breathe in. These little fibers hang out in your lungs, and if there are too many of them, it gets really hard to breathe.",
"[It's a mineral that has a microscopic structure like fibers.]( URL_2 ) [It makes for a great insulator, and does not burn, so it was made into cloth and wrapped or stuffed into just about everything.]( URL_3 ) [It was so fluffy, it was even used as fake snow on movie sets.]( URL_4 ) [Turns out that the dust can get into your lungs and poke your cells so bad that you get lung cancer.]( URL_1 ) So it was (eventually) banned from being used, but not before it was used in just about everything. [So now, when people want to remove it from an old building or something, they have to jump through all kinds of hoops and wear hazmat suits.]( URL_0 )"
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7lnvv1 | how did clocks stay in sync back in the 1800s? | Repost | explainlikeimfive | {
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"you have one master clock in town, and everyone syncs their clock to that. hopefully you have a competent master clock caretaker. London's Big Ben is literally what that's for.",
"The nearest train station was the best place to set your watch because there was a telegraph system that connected and synched clocks between stations. If I remember correctly they were accurate to within 2-3 minutes. How accurate a watch stayed is anyone's guess and dependent on the quality of the watch. Chances are good that the further someone lived from a train station, the less concerned they were with accurate time."
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7lphla | Who was Henrietta Lacks and why are her HeLa cells so important? | Repost | explainlikeimfive | {
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"The problem with cancer cells is that, among other things, they don't undergo programmed cell death. All of the cells in your body have genes in them coding for when they should die, so they can make room for new cells. Cancerous cells have a mutation or damage to those genes, so they don't die when they're supposed to. Even so, cancer cells still eventually wear out and die. Henrietta Lacks' cancerous tissue didn't. The cells just kept dividing and growing when isolated in the lab. That tissue is, essentially, immortal. Samples from that original tissue are *still* alive and in use today. The immortal tissues allow scientists to study all kinds of things that normally require a human patient (or close enough animal substitute) because they need to study the long-term effects of something on cell growth - something you can't do with a normal tissue sample because the cells will most likely die after dividing around 40 times regardless. It also gives you a perfect control sample, since you know your control will be genetically identical to the sample being tested. The tissue was taken without Henrietta Lacks' consent, which at the time was not unusual. And not only because she was a black woman, but because informed consent wasn't really a concept anyone used then. [Relevant SciShow]( URL_0 )",
"She was a Black woman who got cancer and had a tumor biopsied in the 1950s. Her doctor decided to use the biopsied cells for research without her consent. This is, of course, fucking terrible, but it was normal at the time. I'd like to imagine that we've all grown a lot since then. Anyway, it's easier to order an existing cell culture than to find someone with a tumor that's being biopsied around the time you need to do your research. It also makes results more reproducible: you can tell someone else that this treatment kills HeLa cancer cells but has no effect on some other, non-cancerous cell culture, for instance. They're also used when you just need human cells rather than cancer cells in particular. They're cancerous, which means their behavior doesn't precisely match healthy human cells, but on the plus side, they don't stop reproducing. That means the same line of cells can be used for centuries."
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7lqoo0 | irrational coefficients Pi and e | Im an engineering student, and at times when Pi or e appear in formulas it makes no sense why is it there for first, and then how did it even originate. Okay, I know how the Pi was created. But sometimes I dont understand when in formulas it appears, when there is no apparent connection to circles. ( Could be underlying physics rules though) And the second one is natural number e 2.7.. how in the world was it created and how did someone think its going to be important for.. again.. so many formulas and equations. I use it all the time, but when I think about it. It hardly makes sense | Repost | explainlikeimfive | {
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"Without knowing the specific formulas, it would be impossible to answer why they involve pi or e. Sometimes it even baffles scientists and mathematicians. But, e, that's easy to answer. Imagine a bank that returns 100% of your investment at the end of the year. You put in $1 in at the beginning you get $2 out. Let's take that same bank and compound the interest bi-annually. Instead of getting 100% at the end, you get 50% of your investment 6 months in, then 50% of *that* at the end. You put in $1 in the beginning and get $2.25 out (1 * 1.5 * 1.5) Three times a year you'd get $2.37. (1 * 4/3 * 4/3 * 4/3) n times a year can be calculated by the formula (1 + 1/n)^n As n approaches infinity, your return approaches an irrational number, approximately 2.7182... and given the label *e*. *e* is the amount of money you'd get back each year from a bank that nets 100% return and compounds your interest continually.",
"Pi is related to circles but it's also part of the formula for sine and cosine, which are related to angles, waves, and periodic functions. So anything periodic or involving waves will probably involve pi somewhere.",
"Yer not alone in askin', and kind strangers have explained: 1. [ELI5: What is Pi? Why does it exist? Why was it created? And why is it \"infinite\"? ]( URL_1 ) ^(_ > 100 comments_) 1. [ELI5: How does Pi work, how was it discovered, and why is it so critical in mathematics? ]( URL_0 ) ^(_ > 100 comments_) 1. [ELI5: The number 'e'. ]( URL_9 ) ^(_41 comments_) 1. [ELI5:How were the values of constants such as e and pi historically determined, and why do these constants find themselves in so many formulae? ]( URL_7 ) ^(_7 comments_) 1. [ELI5: What makes the number e so special and why is it used as the base of the natural logarithm? ]( URL_8 ) ^(_90 comments_) 1. [ELI5: The concept of e in mathematics. ]( URL_2 ) ^(_26 comments_) 1. [ELI5:How was Pi discovered? ]( URL_11 ) ^(_ > 100 comments_) 1. [ELI5: What is 'e' in math? ]( URL_3 ) ^(_16 comments_) 1. [ELI5: In simple terms, what does the mathematical constant \"e\" mean? ]( URL_4 ) ^(_21 comments_) 1. [ELI5: Why does e (the number) come up in so many seemingly random applications? ]( URL_6 ) ^(_ > 100 comments_) 1. [ELI5: Why is the number PI such a big deal? ]( URL_10 ) ^(_7 comments_) 1. [ELI5 why the value of pi is very important? ]( URL_5 ) ^(_18 comments_)",
"e^(Pi*i)+1=0 There is a reason these (pi and e) occur so often (efficiency of geometry and the efficiency of compounded growth... respectively), but it is still quite amazing how much we misrepresent how powerful they are.",
"Wherever there's a pi, there's a circle. Generally, it pops up in physics because stuff is radially symmetric, which means everything looks the same when you rotate. This simplifies things, and puts a pi out front because you're doing everything in circles. But pi pops up in statistics and factorials and many more things. All of these have some connection with planar or Euclidean geometry, where pi is sort of the number that describes how it works. For example, pi is in the formula for the Normal Distribution. But this is because you use properties of the circle to find the area under such a curve, and the functions involved turn out to work nicely with circles and planar geometry. So pi pops up."
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7lslav | Why do some materials become brittle when they get cold and others do not? | Repost | explainlikeimfive | {
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"This is more ELI am a teenager. I'm sorry, but it's the best I can do. When a material fails, it can fail in two different ways. One way is for the material to deform which is caused by the atoms in that material moving past one another. This is called plastic flow. The other way, is for a crack in the material to propagate all the way through the material cleaving it into two different pieces. This is called crack propagation. In general, failure of a material is heavily dependent on its atomic structure. In some types of materials their susceptibility to fail from plastic flow is heavily temperature dependent, while its susceptibility to failure through crack propagation is not. When these types of materials get cold they lose their ability to fail due to plastic flow (which is synonymous with their ability to deform), and so crack propagation takes over. When a material fails through crack propagation instead of through plastic flow, we call this a brittle fracture. Materials that show this change in susceptibility to plastically flow are said to go through a [*\"ductile to brittle transition.\"*]( URL_0 ) What this means is that some materials when they are warm fail due to plastic flow but when they get cold they begin to fail in a brittle fashion. As a disclaimer, I will add that almost all materials become more brittle as they get colder, but some materials still stay what we would consider ductile as their temperature drops. This is due to the fact that plastic flow becomes easier when atoms are further apart which is the case when a material is warmer. Atoms are vibrating more quickly, and so on average they are farther apart from one another in a warmer material. Because of this they can slide past one another more easily, which is essential for a material to deform. Conversely, a material that is brittle will fail without deforming much at all... It will simply crack all the way through. Credentials: I am a PhD candidate in mechanical engineering, specializing in Mat. Sci. and I often guest lecture for the Mat. Sci. and Engineering course at my college.",
"Like others have said, it’s more of a question of *when* a material gets brittle, not if. That said, the reason the temperature varies is that the atoms can be arranged in different ways that can then move (dissipate energy) in different ways. The best example I can think of is casserole. Imagine a casserole made of small regularly shaped noodles like penne. Put it in the refrigerator. If you tried to break off a piece with your hands, it’d be pretty easy (brittle). Now imagine making be same dish but using spaghetti...suddenly when you try to break off a piece, it is tangled with the rest of of the casserole and doesn’t break off as easily or cleanly (ductile)! That said, if you put it in the freezer instead of just the fridge, it’d probably break in either case.",
"Y’all need to chill about brittle transitions and glass transitions. You need to take it back to what’s causing all of this in the first place. Energetics and kinetics. Yes bcc metals will often be more ductile than hcp bc of slip planes in the system. Yes metals are more ductile bc of metallic bonding. Yes polymers experience a glass transition that allows for polymer flow to begin. Sure whatever fine. Elit: But the reason materials fail in a brittle fashion in colder temperatures is because it’s more convenient to break bonds than it is to create more disorder in the system. go look at a stress strain curve and take the integral. The area under the curve is the toughness of the material, how much work it can take before failure. Work and heat are the similar, and heat capacity is dependent on temperature. Hotter the material, more work can be done. How much the heat capacity varies in temperature determines how much more brittle it will be as it gets colder. Then compare to what is favorable, adding entropy in forms of dislocation, or break a bond.",
"What doesn't get brittle when it gets cold? It is a matter of your \"cold\" scale. My memory is incomplete, but I believe only Helium won't \"freeze\" to a solid state (and it can under special conditions). I'm sure someone can fill in my gaps here. A common solid you may be thinking of would be a metal. Metals are malleable (depending on metal/alloy) due to metallic bonding. Metallic bonding is like an old school stereotype of a hippie commune. Electrons are shared pretty easily, and the atoms slide between partners easily. When cooled further the atoms tend to form lattice structures, like crystals. For the analogy, the atoms are forming long term partnerships like marriage, children, and perhaps get a little selfish with their atoms (though some brittle materials like superconductors share electrons like madmen). These structure cannot slide or move (much). The colder a material gets, the more lattice forms until CRACK! An analogy marriage ends with a full divorce and they are arguing over who gets to keep the box set of Friends.",
"Just like how some materials boil faster than others some materials freeze faster than others. All materials will become brittle at a certain freezing temperature. This has a lot to do with water content. For those things with little to no water content you will have to go to an extremely low temperature to make them freeZe enough to become sufficiently brittle that you can break them easily. Why do objects become brittle ? Because the bonds between molecules weaker as there is no room for movement.",
"Ok, so everything will break if the rate at which you deform it is high enough. Think about silly puddy, if you pull it really quick it will snap. Let's call this 'brittle yield strength' - how high of a strain rate something can have applied to it before it breaks. It just so happens that some materials have interesting atomic and molecular properties which make then have lower brittle strain rates as they get cold, and others are not as sensitive. A true ELI5 is difficult without a few basic chemical principles.",
"In material science, this phenomenon is known as the ductile to brittle transition temperature (DBTT). Once a material is cooled below a certain temperature, it will exhibit brittle fracture characterized by a lack of plastic deformation before failure (no yield). There are several different mechanisms responsible for this behaviour depending on the material. The best understood mechanisms is in body-centered cubic (BCC) metals. BCC refers to the crystallographic alignment of the atoms (crystal structure), which varies from metal to metal. So to answer your question, the mechanisms responsible for a material's DBTT are not always well understood but in the case of metals it is strongly influenced by the material's crystal structure."
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7luceo | Can someone explain SpaceX contrail pattern to me? | Repost | explainlikeimfive | {
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"Right, I'm an expert because I saw an image explaining it an hour ago and I've read some hard sci-fi. First, It was bright because it was high enough to catch sunlight after the sun had set on ground level. As it climbed it stayed thin, then it stopped. It stopped and started again because this is the first stage stopping and separating and the second stage starting. Then the plume started to expand. This happened for two reasons. First, at higher altitudes the air is thinner and the exhaust gas expands more than it does lower down. This is usually not observed because it would be difficult to see against a daylight backdrop. Secondly, the first stage, still traveling at high speed just behind the now separated and firing second stage, had turned around and fired its main engine to slow down. SpaceX has this nifty trick of bringing the first stage back and using it again. The exhaust from the first stage and second stage were blasting into each other like the wands of harry potter and ol' no-nose. They decided not to land this one to reuse, but wanted to pilot it to a safe place anyway. Good guy SpaceX. Lastly the fairings (thin aerodynamic covers) had poped off (intentionally) and were flipping over in the wake, creating some pulsing dots in the fat exhaust stream. I think I covered it all, make sense?"
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7lux0x | In cartoons, why are objects that are interacted with a different color than static objects? | Repost | explainlikeimfive | {
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"It has to do with saving effort where you can, plus the timing associated with producing cartoons. In the clip you show, Spongebob is interacting with only a couple objects including the board in question, but the rest are entirely still. For everything else, a \"background artist\" has to paint it only once for the entire sequence in the cartoon because it's still and not moving. (That background stays in every shot, and the moving parts are on transparent plastic or digital images placed on top of it, depending on how the cartoon is produced.) Because it will move, that board is actually drawn *on top of* the background part of the image - the hole it sits in - as a different layer, so when it's ripped up (removed), you can see the hole. And because it moves, every frame in the image must deal with that board separately. So not only is it drawn later on top of the background image, there are about 10 frames or so where Spongebob was tugging at it and it was changing in appearance. So that's 1 copied-many-times original board, 10-or-so changing frames of bent board, and 1 copied-many-times image of the half-board left after it snaps. And all drawn later than the original background pic so you know precisely where to put that board. The combination of keeping things simple without perfect shading so it's much faster to produce that sequence in the cartoon, and drawing it later, adds up to the colour difference. P.S. You could often REALLY see this in older cartoons with lots of background interaction. Lots of cases in Scooby Doo and Looney Tunes where you knew some part of the background was going to get changed somehow."
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7m1071 | Calculus and why it’s important to our day to day lives | Repost | explainlikeimfive | {
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"Calculus measures the rate of change of things. So anytime you do the stuff equation: Change in stuff over time = (stuff in) minus (stuff out) plus (stuff generated) minus (stuff consumed) Thats calculus. And thats fundamental to any sort of process design ever. If it changes then you are using calculus. EDIT: time not tome",
"The computer you're using was designed by people for whom calculus was indispensable in developing computer technology. So calculus might not be directly relevant to your life-you may not actually use it every day-it nevertheless is fundamental to modern society if we want to have all the technological innovations that need calculus to come into existence. I personally know nothing about plumbing. But without abundant, clean running water, and without modern sewage disposal systems, and without gas lines that heat my house, my life would not be very comfortable. In fact, without plumbing and people specialized in it, modern civilization is not possible. The same is true with calculus.",
"First off if you want to actually learn calculus, I recommend Khan Academy's video series. I won't go into much mathematical details here. Calculus is the mathematics of change, it is useful because our world is constantly changing. I am not just talking about changes in time, I am also talking about changes of many things with respect to many other things. Here is a very simple example: You hang an object down from the ceiling with a spring. When you stretch the spring, you feel a force trying to restore balance. The more you stretch the spring, the stronger that force becomes. Here we have our first change: The restoring force increases with the stretch. Suppose we want to find out how exactly the end of the spring bobs up and down when it is released, ie we want to find a mathematical function of time, h(t), that predicts the height of the object at any time. Our relation for the first change can be summed up into a nice equation: F=-k*h(t) Where F is the restoring force. The minus sign indicates that the force always opposes the stretch. k is a number that tells you how strong the force is, and h(t) is the UNKNOWN mathematical function of time that we are trying to find. We then apply Newton's Second Law, which states that the force applied on an object causes it to accelerate. ie, the force causes the acceleration, aka the rate of change of velocity, aka the rate of change of the rate of change of height of the object. In mathematical language, it says: F = m*a = m*d^2 /dt^2 h(t) Where F is again the force, m is the mass/inertia of the object, and h(t) is the position of the object(again an unknown function in time). The notation d^2/dt^2 (A THING) means \"rate of change of rate of change of A THING\", in this case the object's height. If we combine the two equations together, we get m*d^2 /dt^2 h(t)=-k*h(t) And if we have the mathematical tools to solve the unknown function h(t), then we can predict exactly how the bob goes up or down. If you know calculus, you can work out that h(t)=A sin(sqrt(k/m)t) + B cos(sqrt(k/m)t). The height of the bob oscillates up and down, just as one expects. That is one of the almost infinite amount of applications of calculus to the real world."
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7m11cl | Why is water odourless? | Repost | explainlikeimfive | {
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"Because it's incredibly pervasive. Water is contained in tremendous amounts in the air already, in the form of water vapour, and with its amount measured as \"humidity\". If our nose had adapted during our evolution to smell it, it'd be smelling it ALL THE TIME. That would be entirely useless information so we didn't adapt to sense it. What we can smell, though is 'rain coming' or 'the salt seashore' or other smells associated with water. This is more because damp moist air carries smell to our scent receptors better than dry air, so other smells that we don't normally detect as easily come across as more intense. Water also causes some additional smells to come out of the environment, like that incredibly fresh smell you sometimes get from the woods after a summer rain. And it can affect temperature too, which is why woodland waterfalls often smell deeper and richer."
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7m4isg | How do artificial neural networks work and how do machines learn? | Repost | explainlikeimfive | {
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"A single neuron in an artificial neural network is just a thing that has some number of inputs and outputs that are either \"on\" or \"off\". The \"weight\" of each input is some number. If the sum of the weights of the inputs exceeds some value, you trigger the outputs. Those outputs can be the inputs to other layers of neurons. Exactly what an input is is entirely up to the person designing the system. They \"learn\" by adjusting all weights and arrangements of those neurons. This is not something the NN knows how to do on its own, it's something done externally. The NN is generally static once you've developed it and put it into work. They're not really all that complex, at least at the local level. Complexity comes in when you start stacking up thousands of nodes together and using complex methods to test & reprogram the weights of all those inputs."
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7m549a | How do documentaries get to film organised crime from within like drug dealing, interviewing kingpins...etc? | Repost | explainlikeimfive | {
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"Police can rarely compel reporters to give up their sources. It's protected. And it's not useful anyway. Who cares where some gang members did an interview months ago. There's no physical evidence of the crime that goes with the story. It's just that, a story, otherwise known as hearsay. It's not admissible in court.",
"I’m a documentarian, though never with that type of crime doc. But I’ve read about and talked with others and am familiar with consenting process. I don’t think there is one specific way, but I think often having one solid person who trusts you enough and you convince you’re doing it from a journalistic standpoint and, probably more than anything else, you say you are putting a human face to crime, getting their point of view. You’re probably not going to get the most badass and worst of the worst criminals, you’re going to get the criminals that are open to a sympathetic filmmaker who is trying to get “the other side” or their side of “the streets”. As for legal, yeah, contracts can spell out how the film is for journalistic purposes... I’m not sure how often courts don’t try to challenge that, but a journalist (and a documentarian) can defend their ability to get a story and not have it be used in court."
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7m5dpp | what makes fire invisible? And why are most fires orange/yellow? | Repost | explainlikeimfive | {
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"The color is based on the energy level. Think of it like a rainbow. The lower energy, you have at the start of the rainbow. Red, orange, yellow. If it gets even higher, you can get green and even blue flames! Now if it gets so high, it can go beyond the visible spectrum. Still emitting light, of course, but you can’t see it. So it’s invisible. Or vice versa, below the visible spectrum. But usually that’s too low energy to burn so it’s rare. This is why you hear “infrared” and “ultraviolet” light. Infrared is below red on the visible spectrum, so you can’t see it, but it’s still light. Ultraviolet is above violet. Also can’t see it. Edit: typo",
"As a general rule, there's a relationship between the total heat of an object and the wavelengths of light it gives off. ([Blackbody radiation.]( URL_0 ) Most of the things which fall into the range of \"much more heat than we'd like in our watery blob bodies but still something we might live to see\" correspond to us as red, orange, yellow and eventually a whitish mix as some blues get added. In the fire, you're seeing high-heat atoms in the wood and some floating upwards. If it were a stronger fire (giving off atoms that have more heat) the color would be different. \"Invisible\" fires are often because it's pure gas combusting without any hot solid flecks which would be brighter and easier to see."
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7m5swl | Why does metal spark in the microwave? | Repost | explainlikeimfive | {
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"Metal objects spark in microwave ovens because those objects have peaks and points where static charge can accumulate and spark out. If you could somehow get something metal in a microwave where the metal thing was both perfectly round and perfectly smooth, there would then be (presumably) nowhere on the outside of the metal thing for charge to accumulate. However, this doesn't mean there would be no accumulation at all. It would simply not be on the surface. (Physics Reddit, please correct me if I'm wrong.)"
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7m630p | Why do plastic water bottles start to smell bad when left for a prolonged period after being opened? | Repost | explainlikeimfive | {
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"2 Main things: 1 standing water breeds bacteria, so water left to sit will get nasty no matter what it is in. 2. cheap plastic bottles will leach plastic into them over time (and quicker if its warm). This is why all those bottles have small print saying not to reuse them. Its not too bad if its a day or 2, but you probably shouldn't reuse a bottle for more than a week (if that).",
"Ahoy, matey! Yer not alone in askin', and kind strangers have explained: 1. [ELI5:Why does water left in bottles start to smell bad after a few days? ]( URL_0 ) ^(_19 comments_) 1. [Why does a plastic bottle start to stink after a while? ]( URL_3 ) ^(_5 comments_) 1. [ELI5: Why do many plastic water bottles cause the water to smell/taste bad after being opened and allowed to sit for a while? ]( URL_1 ) ^(_2 comments_) 1. [ELI5: Why do plastic bottles stink after a couple of days with the same water? ]( URL_2 ) ^(_3 comments_) 1. [Why does my water bottle keep smelling bad? ]( URL_4 ) ^(_9 comments_)"
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7m6wpo | Why does meat get tougher when you cook it through in the pan, yet when you slow cook it the meat is soft? | Repost | explainlikeimfive | {
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"When you cook meat in a pan, all the moisture is removed. This makes the meat tough. When you cook meat in a slow cooker with liquids, it is absorbed into the meat which either breaks down the meat or makes it tender."
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7mb35n | If there is no cellphone signal, how does the "emergency calls only" mode works? | Repost | explainlikeimfive | {
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"Your phone is allowed to use any network its physically capable of using for emergency calls, whereas normally it can only use networks you've paid to use E.G. signals from a Verizon tower. EDIT: Looks like I was partially wrong. Quoting /u/psfilmsbob \"Every carrier has roaming deals with other carriers who use the same signal, meaning your AT+T phone will work on T-Mobile towers, vice-versa. Same with every major carrier.\"",
"My time to shine. I've written software for this -- if I say anything more, I might be identified easily by the people who know this. Edit: Important and useful distinction: At least one carrier needs to have coverage in the location you are trying to make an emergency call from. If none of them do, your cellphone won't be able to connect an emergency call. It's not magic, just engineering :) Edit: Since this got upvoted like crazy, disclaimer time. Do not use anything I've said here to make decisions on how you want to act in an emergency. Assume anything I've said below can be completely wrong. Having said that, I've been as truthful as I can be and as my memory serves me. The physical components for connecting to cell phone towers of various carriers and various tech (2G, 3G, etc) are mostly the same. The difference comes in which cell towers you tune to. A cell phone connects to a tower by \"tuning\" into what are called bands or channels. For something simple as GSM, it is literally frequency bands. For newer tech like CDMA and LTE, it's a bit more complicated because the tower signal jumps frequency bands and is mathematically encoded (stuff that even I don't understand well). When you buy phones from different carriers, they are set to ignore bands or channels that the carrier doesn't use. It serves several purposes - 1) to make sure you can't take to phone to another carrier 2) to make sure your phone doesn't waste time and battery tuning to cell towers that won't accept them (if you have an AT & T service, the T-Mobile tower will reject you even if you can talk to it) 3) Less testing of the phone necessary, etc. There's software that picks the best tower out of all the towers your phone can hear/talk to (you might be able hear/talk to multiple towers from your carrier, you want to pick the closest one or the one that supports the fastest data, etc). When you make an emergency call, the software that's responsible for picking to tower tells the tuning software \"THIS IS A FUCKIN EMERGENCY CALL. FULL SPEED AHEAD! CONNECT TO WHATEVER YOU CAN FIND\". The tuning software also keeps track of the last few bands/channels in which it saw any signal. It'll try them first so that you can connect the call quickly. If it can't find any, it'll do a full sweep of all the bands the physical hardware can possibly tune to. Once it finds a tower, the software for making calls says \"HEY MAN, I KNOW WE MIGHT NOT BE COOL WITH EACH OTHER, BUT THIS IS A FUCKIN EMERGENCY CALL MAN! CAN YOU PLEASE CONNECT THIS?\". The tower goes \"OH FUCK! SHIT! I'll connect you\". If the tower is at full capacity, it'll kick out someone who's not in an emergency call and then connect the incoming emergency call. In fact, you don't even need a SIM card (in some countries) or ever have had service in a cell phone to make an emergency call. That's why when there's no SIM card, the phone will still tune to a tower with good signal and show \"Emergency call mode\". This is to make sure we don't waste time when you actually need to make an emergency call. This is why if you are in an area with no cell service from any carrier, your phone drains the battery soon - because it keeps searching each band asking \"Can any tower hear me?\". So you should put it in airplane mode. And if you are in airplane mode and make an emergency call, it'll automatically get out of airplane mode. Again to save you time. In case your call disconnects, you phone will connect back to the same tower again. This is so that the carrier can try to locate you using the tower signals. If you had connected to another tower, the emergency people might have to connect to the different carrier and start locating you all over again. Disclaimer: don't try the next part in a real emergency unless you really don't have any other options. I'm not sure all phones do, but a significant portion of them will. Each country has a different emergency call number. It's 911 in the US, it's 112 (I think) in Europe, something else in Japan. What if someone goes to a different country and get into an emergency? They won't remember what that country's emergency number is -- so the software in your phone will see you are dialing 911 in Europe and go \"this person just wants to make an emergency call. I'll just connect to 112 instead\". There's a ton of cool stuff that goes on in your phone and the carrier to make sure we do absolutely anything possible to connect an emergency call. Hope this was an interesting read. **Edit:** Wow, this blew up way more than I expected. My most up voted comment by a wide margin. Really happy that so many of you enjoyed it as much as I did writing some of this software. It makes me emotional when I think about this work. And obligatory thanks for the Reddit gold. Edit: Also, so many people assuming that this means it's feasible to hack or asking if it's feasible to hack. No, it's super trivial to avoid hacking this to make free calls. The tower just needs to check the number you are calling is an actual emergency number. Also, I wouldn't be surprised if the emergency calls have special routing behavior to make sure it goes to your nearest call center. So it's even more easy to prevent free phone calls.",
"After being stranded in the middle of the Big Bend backcountry, I can attest that calling 911, even on “emergency calls only” doesn’t always work. Word to the wise, for any outdoorsy people on this thread: buy a satellite phone Edit: Story below in the comments but just thought I’d put it here as well Its just good to have. We honestly couldn’t’ve prevented our situation. Friends foot was bleeding intensely and as a result we were not keeping pace with our water consumption. It was desert weather mid spring and no rivers, so we had to carry all our water the entire trip and it would’ve taken days for my friend to get back, so we would’ve run out. Ended up giving almost all our water to one guy so he can go all the way back himself to his car and go off-road to either come get us or get help. It was weird how valuable water sorta became, made me change my perspectives on life in a few ways. In a sense I knew that we could eat cactus to stay alive, and we knew the way back to the road, but just being put in that situation where things are kinda uncertain was strange. I remember giving that guy almost all our water and thinking that there was no way for me to know what is about to happen until it just sorta happened. Interesting experience 10/10 for life lessons 2/10 would do again The guy came back with his car, we got back within 20 ish hours",
"There might be cellphone signal, it just might not be a signal from your phone carrier. Say you have a contract with company A, but all the cell towers around you can only connect you to company B. obviously you can't use that signal. However all cell phone networks, irregardless of what company they serve, must serve emergency calls by law. If your phone has any signal to any network around it it can make an emergency call, it just might not be able to make a normal call. EDIT: I will stand by my decision to use 'irregardless' despite the fact that it contains a double negative and is a nonstandard word. It is a true and tested word that has been[ causing fierce debates since the late 1800s]( URL_0 ), and I am proud to honor that tradition! ^^^sorry, ^^^won't ^^^do ^^^it ^^^again",
"Emergency calls are attempted to be made no matter what, and on any network the phone can connect to. Normal calls, on the other hand, are not made this way.",
"I had an emergency situation (car wreck in the middle of the night, 5m away from our tent) while backpacking in rural Chile, in the patagonia. The cell phone simply did not work.",
"If I have an American cell phone and travel internationally will it work for local emergency number?",
"Another thing that happens is that service may be limited in special circumstances. I'm not sure of all providers do this though. But in tje event of, say a natural disaster where people will be making a lot of calls they may limit service to only 911. My phone company also did this 2 occasions this summer, once when there was a major storm that cut power to the towers, so they're operating on emergency systems, and they prematurely did it when a wildfire threatened some towers.",
"Let's you access any cell signal available no matter the carrier. Just as an emergency service. But if there is no signal from anyone I guess it would not work. Unless somehow it can connect to a satellite.",
"The other answers about useing other companies towers are correct however most states have a department of natural resources, or US Forrest service, or Bureau of Land Management that maintains radio towers for short range radios. Lots of these have a CDMA and GSM (cell phone for the 5 years olds) converter on them. So while you dial 911 you are actually talking to a Forrest Ranger who's useing a handheld/truck two way radio.",
"If there is no signal...it DOESN'T work If there is no sim card, it can still access the network, and any cell tower will patch through an emergency call, regardless of whether the phone has a sim, or account with anyone.",
"Do emergency calls use the same amount of bandwidth as normal calls?",
"FCC mandates that all phones be able to dial 911 (in the us) even if that phone is roaming or not activated with any carrier.",
"Each cell company operates on only certain frequencies (Sprint: 800, 1900.. Verizon: 600, 1500... You get the idea). Most phones are capable of operating on most of those frequencies, hardware-wise. Emergency calls are able to be made on any band for safety purposes. As long as your phone can ping a tower, you can call 911.",
"US and UK law (probably most other countries, but I can only attest to these) require cell towers, regardless of their networks, allow a device to connect and make emergency calls. So, imagine it like this. You're in a town filled with private clubs, and they all require a membership pass (reference: your sim card). But, if you're bleeding and require emergency medical attention, they're not allowed to turn you away. Regardless of if you're a member of their club, some other club, or no clubs at all. No signal, displayed in the GUI of your phone, doesn't mean there's \"absolutely no signal\", just that there are no cell towers that you are eligible to use. But, if you've got the slightest signal and try to make an emergency call, it will connect to the strongest signalling tower to make the call. If the cell tower is operating legally, they're in a rental contract with the appropriate government which states that they will allow, free of charge, calls to emergency numbers. However, there are places on Earth where you're completely out of signal (e.g. FAR out at sea, since there are sometimes cell towers covering a large distance from the coast for distress calls, and also in mountain regions, anywhere near military bases). In these places, you shouldn't be told you can make emergency calls. Edit: Some other things I forgot to mention... When your phone is running normally, it will have a soft limit as to how much power it's [the antenna] willing to expend to connect to a tower. Usually there's a hard limit of about 1 Watt, but this isn't universal (necessarily). But the soft limit, to preserve battery, will be lower; so if you're seeing \"Emergency Calls Only\", you could actually have a weak signal to your own carrier. The weaker the signal, the more power required to communicate with it effectively. So to preserve the power, it doesn't bother connecting to this eligible tower under normal circumstances, meaning you won't receive SMS messages or calls, and can't make them to non-emergency numbers. Whenever you make an emergency call in any country (in accordance with your phone/sim configuration), your phone's antenna begins using the full hard limit. It will establish and register with the strongest signals it can, and maximum priority is given to responding to the pings which are used to triangulate your location. This allows emergency operators to find you pretty much immediately - unlike in movies where it takes an arbitrary amount of time, it's actually a fraction of a second if you're connected to 3 towers in full accordance.",
"Your cell is calibrated to let's say, Comcast. It will only detect Comcast signals, which if you are out of range, will not detect a Comcast signal. If you need an emergency call, your phone will use Verizon's network.",
"Inside your cell phone there is a list called the PRL or *Programmable Roaming List*. The PRL list contains the list of cell towers you can use normally to make calls, get data, Etc. This list is frequently updated by your carrier. Cell sites in your PRL should recognized and permit your phone to log into it automatically. When a phone is in emergency call mode, it connects through the already connected cell site to complete the call. If it's got no bars and no PRL-listed site handy, it will use the strongest tower nearby it can talk to. If you are in the middle of nowhere with no bars, you will be lucky to be able to make any call - even an emergency one. As long as there's some carrier present though, emergency calls should be possible."
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7mbpxg | Why do people hear their voices differently when they speak vs. when they hear it played back on video or tape? | Repost | explainlikeimfive | {
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"When you speak, the sound is transmitted to your ears both through the air, and through the bones in your skull. When someone else hears you speak, they only hear the vibrations in the air. That's also the only thing a recording hears. Thus a recording accurately represents what you sound like to everyone but yourself."
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7mdnnh | How does a diamond, the hardest substance on earth, still get shattered by a hydraulic press? | Repost | explainlikeimfive | {
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"Because it's just hardest, not toughest. It won't scratch easily, that's true. But hardness won't prevent it from turning into expensive dust once you apply enough pressure to it.",
"Hardness, as an intrinsic property of a material is understandably important but it is also easiest to define (see Mho’s scale of hardness); Other engineering properties however, such as Toughness and Strength, are not. On the Mho’s scale, every subsequently harder type of material will ‘scratch’ all materials that are softer. The second hardest substance for example - Corundum, that sapphires are made of, can only be scratched with a piece of diamond (which makes it an excellent choice for ‘sapphire-crystal’ glass such as on a high end watch). But in most cases, hard materials are almost always ‘Brittle’. Brittleness of a material implies that it is susceptible to shattering - the way that glass shatters. A hard material may be resistant to ‘scratching’ at the surface level, but at the bulk level, instead of deforming when struck with enough force or put under sufficient stress (like under a press) will fracture into smaller pieces. The most appropriate example to demonstrate these properties (in fashion with diamond) would be steel (both are crystalline). Steel is also extremely versatile and can be heat treated to either be Hard & Brittle or Soft & Tough (also see malleability and ductility). As an engineered implementation, Japanese swords make use of both forms of steel because neither is desirable by itself (hard steel can hold a sharp edge but can easily shatter and break while softer steel might be tough and resilient but fails as a sword). TL;DR : Hardness is not the only notable physical aspect of a material. There are only other equally significant attributes like Toughness and Strength. (Titanium shakes head in neglect)",
"Being hard and being *strong* are two very different things. Diamond is incredibly hard, and won't scratch, but it's also fairly brittle, because of how hard it is. It will break or shatter before it will bend or otherwise be able to withstand high pressures."
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7me3ld | How does salt and/or sand “melt” snow? | Repost | explainlikeimfive | {
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"Normal rain water freezes at 0°c. Salty water freezes at a lower temperature. As long as it's not cold enough to freeze salty water the ice melts. It's often laid as grit and or sand because salt is soluble, it melts the ice but then it dissolves and runs down the drains with the water. Grit and sand helps hold the salt in place and dissolve more slowly. Interestingly as the ice melts it ~~looses~~ loses energy and actually gets colder! Thats why it's important to grit before the paths and roads go icy to have the greatest effect *Edit typos*"
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7mesl6 | Why is it difficult to make a fist with your hand when you wake up first thing in the morning? | Repost | explainlikeimfive | {
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"Actually, if you put your mind to it, you can. Breathe a little bit and engage your entire upper body muscle, and you can. This means that the physical strength of your body has not degraded, but the readiness, or the mental reaction, hasn't kicked in yet. You've been asleep for a while so you wouldn't be ready to start running or grip with strength. Or, (not quite like sleep paralysis) your physical state and mental state aren't locked in together quite well yet Same reason why you can't flex your biceps or do pushups, or something. Let me give you an example: when I wake up every day at 7:15, I know that alarm is crucial, and I know that I need to stop the alarm fast ~~to drift to sleep~~to start getting busy. I jump right out of my bed because my muscle memory is triggered, not because of readiness to the environment",
"You knuckles swell slightly over night. I often can't get my ring off first things in the morning either."
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7mf052 | Why are 11 and 12 eleven and twelve and not one-teen and two-teen | Repost | explainlikeimfive | {
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"There's nothing special about the number ten when you're an illiterate peasant in early medieval Europe. Yes the king's tax men use a base ten system, but they're using latin numerals and you can't count any higher than your fingers or knuckles can handle. Because of that, the common speech around numbers evolved somewhat arbitrarily in each language until enough people understood enough math to really start cementing and standardizing it. In English, the switch to systematic naming happens at 13. In Spanish, it's at 16."
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7mg1b3 | What is Dandruff? How do dandruff shampoos try to stop it? | Repost | explainlikeimfive | {
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"Yer not alone in askin', and kind strangers have explained: 1. [ELI5 - Why does anti dandruff shampoo get rid of dandruff while other shampoo doesnt really? ]( URL_0 ) ^(_8 comments_) 1. [ELI5: What does Anti-Dandruff shampoo do that is different from regular shampoo? ]( URL_6 ) ^(_ > 100 comments_) 1. [ELI5: What is dandruff and how does pyrithione zinc (head and shoulders) stop it? ]( URL_4 ) ^(_19 comments_) 1. [ELI5: What makes a shampoo anti-dandruff? ]( URL_1 ) ^(_10 comments_) 1. [ELI5: The difference between dry scalp and dandruff. ]( URL_5 ) ^(_33 comments_) 1. [ELI5: How does anti dandruff shampoo specifically target dandruff? How is it different from regular shampoo? ]( URL_2 ) ^(_5 comments_) 1. [ELI5: Anti-dandruff shampoo ]( URL_3 ) ^(_4 comments_)"
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7mgb93 | how do large companies buy other large companies? Who gets the money? What happens to the employees? Is every company for sale? | Repost | explainlikeimfive | {
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"When a company is buying another company, what they're doing is purchasing the stock of that company. The money goes to whoever owned that stock. So if you owned 10 shares of ABC corp and XYZ corp acquired ABC corp you'd be paid for your 10 shares at a fair price, or alternatively your shares would convert into X shares of XYZ corp. Nothing happens to the employees just because of an acquisition. All it means is that a different set of people own the company. In some cases those people acquired the company because the company was profitable, so they'll not change much in the company because it's working. Other times they acquire the company because it has something valuable (patents, buildings, etc.) but it's otherwise not that useful, so they may fire many of the employees. Companies get acquired when people representing a majority (or more) ownership agree to it. The terms of the agreement decide what happens next. If you own 51% of a company and you refuse to sell for any price then your company is not for sale. The reality is most people get ownership of companies to make money, so there's probably some price that's worth selling. In some cases, very big companies can only reasonably be acquired by other very large companies, and in those cases the government might step in and prevent the sale, since it would be harmful for customers and others if it went through."
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} | [
"url"
] | [
"url"
] |
|
7mkbej | How is antivenom made and why is snake venom beneficial for this process? | Repost | explainlikeimfive | {
"a_id": [
"drun01n"
],
"text": [
"This question gets asked a lot so please do a search next time but: antivenom works basically the same was as vaccines; you give your immune system a \"preview\" of whatever the vaccine is for. Not enough to make you sick, but enough for your body to produce antibodies that are ready to go. For antivenom, they use horses as an intermediary. They inject the horse with a tiny amount of diluted venom \"milked\" from a venomous animal. Not enough to sicken the horse, but enough for the horse's body to produce antibodies to the venom. Then they take a blood sample from the horse and remove everything else so only the antibodies remain, and that's the antivenom. Like vaccines, antivenom only works on the venom from the specific species or closely related species of the animal that it came from. In the same way a flu shot doesn't protect you from the measles, antivenom for a bite from a cobra won't help you against a bite from a venomous spider. That's why a lot of different antivenins exist for different species or groups of species of venomous animals."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7mkgzr | How did language split so drastically to the point that we have the vast amount of languages today? | Repost | explainlikeimfive | {
"a_id": [
"druo1pv",
"druoh8w"
],
"text": [
"Languages naturally drift. If you compare, say, American English today to how it was spoken 100 years ago, you will see noticeable differences in vocabulary, syntax, grammar, and pronunciation. Not so much that it can no longer be understood, but still quite significant. Even in recent years, things like dangling prepositions and using \"they\" as a gender-neutral singular pronoun have become acceptable. These differences were more pronounced it the past, before universal education and literacy, and when people were more isolated. With few central authorities declaring exactly how a language should be used and people rarely straying more than a day's walk from the village they were born in, they was very little to keep communities who spoke a given language synchronized, and in as little as a few centuries they could no longer be mutually understood.",
"Very generally speaking, we do not precisely know. We use somewhat messy tools, like *statistical linguistics*, to sort of reverse-engineer our current languages' ancestors and estimate the geographical paths they took. two general postulates seem to be pretty popular right now, but they are not by any means certain or proven: * unlike biological life - where truly all living things on this globe may be traced back to a single common ancestor, and thus a single original burst of life from lifelessness - it is thought that language came about multiple times and that the \"family tree\" of human language may have multiple trunks. specifically, these trunks are the big language superfamilies like Indo-European (containing almost every language widely spoken between Alaska, Argentina, Greenland, the Urals, Bangladesh, and the Mediterranean, with the prominent exception of Uralic, the wildcard family that links Hungarian (Magyar) and Finnish, along with several others), Sino-Tibetan (a smaller East Asian family which nonetheless contains the world's most spoken first language, Mandarin Chinese), Afro-Asiatic (much of the Maghreb and wider Arabic-speaking world), and [many others]( URL_1 ). * Indo-European has received particular attention in the western world, as it is by far its most dominant and influential language family and cultural bias has granted it a preeminent status in acedemia. We think it maybe came from somewhere around southern Russia and the Caucasus republics, and [Proto-Indo-European]( URL_0 ) is the term for both that real language if it existed and our statistical guesses at what it sounded like, trying to work backward from later languages and our best knowledge of how sounds shift with time (flipped backwards). an interesting aside. Indo-Aryan is a sort of sister family to Indo-European which contains a commanding chunk of the many languages spoken in modern South Asia. this term had a broader, and wronger, meaning in the early 20th century, and it is thought possible that this early fumbling attempt at linguistic taxonomy was a major route for the previously-obscure term \"aryan\" into european languages such as English and German. Adolf Hitler, we know, erroneously conflated ethnicity and language (they are quite different, though interplay with each other) and it is from this series of deliberately poor understandings that a large part of Nazi racial doctrine arose. the moral of the story: the popular consensus is definitely not the proven fact of nature. do not ever kill people because of linguistics. killing people over orthography and grammar is frowned on."
],
"score": [
7,
3
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Proto-Indo-European_language",
"https://en.wikipedia.org/wiki/Language_family#/media/File:Primary_Human_Language_Families_Map.png"
]
]
} | [
"url"
] | [
"url"
] |
|
7mkzcf | what is the difference between a debit card and a credit card? | Repost | explainlikeimfive | {
"a_id": [
"druqm52"
],
"text": [
"A debit card withdraws money out of your account right away. So you have $10, buy something worth $5, you have $5 remaining in your account. A credit card allows you to borrow money with interest to pay at a later time. So you have $10, put $5 on credit, and you still have $10 in your account. But at the end of the month, you'll have to pay back the $5 on credit with interest, so now you pay $5.25."
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7ml8nz | why is it when we stretch our hearing gets muffled? | Repost | explainlikeimfive | {
"a_id": [
"drutdlb"
],
"text": [
"Because most of the time you will open your mouth at the maximum to yawn and tighten a lots of muscles around your eyes. The muscle, tendon and skin will tighten and will slightly increase the tension in your eardrum. That extra tension make the ear drum less sensitive and the sound will feel muffled. If you can successfully stretch yourself without yawning you will see no change in your hearing"
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7mlwx8 | how do refrigerators work. Like how do they make things cold | Repost | explainlikeimfive | {
"a_id": [
"druw9mk"
],
"text": [
"1. The compressor constricts the refrigerant vapor, raising its pressure, and pushes it into the coils on the outside of the refrigerator. 2. When the hot gas in the coils meets the cooler air temperature of the kitchen, it becomes a liquid. 3. Now in liquid form at high pressure, the refrigerant cools down as it flows into the coils inside the freezer and the fridge. 4. The refrigerant absorbs the heat inside the fridge, cooling down the air. 5. Last, the refrigerant evaporates to a gas, then flows back to the compressor, where the cycle starts all over."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7mngch | How does a “citizen’s arrest” work? | Repost | explainlikeimfive | {
"a_id": [
"drv7pvf",
"drv7xfn",
"drv7qlj"
],
"text": [
"> Do different states have different rules regarding when/where/who/why you can do this? Yes, which makes answering your other questions hard since it is going to vary by state. For example, in California, you can perform a citizen's arrest under these circumstances * For a public offense committed or attempted in his/her presence. * When the person arrested has committed a felony, although not in his presence. * When a felony has been in fact committed, and he or she has reasonable cause for believing the person arrested to have committed it.",
"Laws vary by jurisdiction. In Canada, this is known as a section 494 arrest, and while it can technically be effected by anyone, its purpose is really to empower e.g. security personnel who are not actually law enforcement or officers of the court to make arrest and detention prior to transfer of custody. To be valid, you must personally witness someone **in the act** of committing an indictable offense (analogous to US felony: assault, including assault by trespass, theft over $5000, narcotics trafficking, etc.), inform the person that they are being arrested and why, and inform them of their Charter rights (US Miranda warning). An arrest under .494 cannot be made for summary conviction offenses (US misdemeanors), and any use of force applied to effect an arrest and detention must be reasonable and necessary. Security officers may need to be licensed by their province to act in this capacity, and may need to be separately endorsed to use restraints (handcuffs).",
"Chances are, you’re gonna get yourself into trouble if you attempt a citizen’s arrest. You can restrain someone until the police arrive if you are preventing harm to yourself or others. But in almost every other situation, you’re opening yourself up to lawsuits. Not mention scrutiny from the arresting officers."
],
"score": [
21,
11,
7
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
7mnlb0 | Why does boiling water turn to snow when thrown in extreme cold temperatures and cold water doesn't? | Repost | explainlikeimfive | {
"a_id": [
"drva5vj"
],
"text": [
"[This]( URL_0 ) is a pretty decent explanation of it. Basically, the water isn't actually turning into snow, but evaporating and then very quickly condensing into a cloud. Near-boiling water is very near to its evaporation point. When you throw it into the air (any temperature air), some of the water will vaporize due the elimination of cohesive force of adjacent water molecules. For an instant you have a bunch of steam in the air. Now when you do this in very cold air, the steam then cools rapidly and condenses back into water vapor, creating a cloud."
],
"score": [
15
],
"text_urls": [
[
"http://thevane.gawker.com/the-science-behind-turning-boiling-water-into-snow-on-1678181346"
]
]
} | [
"url"
] | [
"url"
] |
|
7mov1x | What happens in a cpu that causes it to generate heat? | Repost | explainlikeimfive | {
"a_id": [
"drvitk9"
],
"text": [
"Computations take electrical energy to work. Energy can't be created or destroyed, it can only be converted from one form to another. The electrical energy gets converted to thermal energy by the processor as a consequence of performing the computation."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7mqqgy | When you have a stuffed nose, why is it that one nostril is always blocked/more blocked | Repost | explainlikeimfive | {
"a_id": [
"drvy9ji"
],
"text": [
"Importantly, the blockage is not \"stuff\" (like mucus/snot) that's clogging up the nostril; it's the lining of the nose swelling up and closing off the airway. There are two important facts to know about blocked noses: 1. There's something called the \"nasal cycle\" that occurs normally, where the mucus membrane in your nostrils swells slightly, alternating between nostrils throughout the day. This happens all the time, every day, but isn't severe enough to really be noticeable. 2. When you have a cold, the mucus membranes in *both* nostrils swell slightly as part of your body's immune response. When you combine the two, the nostril that's normally slightly swollen from the nasal cycle gets even *more* swollen because of the cold, and that nostril swells shut. That's why blowing your nose doesn't fix it (it's not blocked by anything that can be blown out), why it switches nostrils occasionally (the nasal cycles changes which nostril is swollen more than the other), and why nose drops don't completely fix the issue (they can't completely eliminate the extra swelling from having a cold)."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7mrx7o | How does the camouflage skin of Octopi, Squid, and Cuddlefish match their surrounding color and texture so accurately? | Repost | explainlikeimfive | {
"a_id": [
"drwjudz"
],
"text": [
"They have highly specialized cells that get a signal from the brain when it detects a certain surrounding colour and then expand or contract in order to change the pigment in the cells. You can notice that they’re never fully campouphlaged but only partly and being under water helps them become ‘invisible’. Due to lack of time I’ll post a link here: URL_0"
],
"score": [
3
],
"text_urls": [
[
"https://www.google.nl/amp/ocean.si.edu/ocean-news/how-octopuses-and-squids-change-color%3famp"
]
]
} | [
"url"
] | [
"url"
] |
|
7mtcnm | Why does Horizon Organic milk last so much longer than normal milk? | Repost | explainlikeimfive | {
"a_id": [
"drwijbn",
"drwihnl"
],
"text": [
"It has been \"ultra pasteurized\", meaning it has been processed by heating it to a high temperature longer than normal milk. This will increase its shelf life while imparting a somewhat \"burn\" flavor which those unfamiliar with it can find off-putting. It doesn't really have anything to do with it being \"organic\", other than that organic producers are not as common so the milk needs to travel a longer distance before being consumed so the longer shelf life is desirable. So in summary it is because it is old burnt milk.",
"Milk, fresh from the cow, spoils fairly quickly because there's naturally occurring microorganisms that like to \"eat\" it. Normal milk is *pasteurized*. That means it's briefly heated to high temperatures to kill the microorganisms. The downside is that this slightly changes the flavor but nobody notices anymore because nearly all milk is pasteurized. The organic milk you find in the store is often [ultra-high-temperature (UHT) pasteurized]( URL_0 ) to kill off *even more* of the microorganisms and make it last even longer. The downside is that this impacts the flavor even more but since organic milk is a niche product it needs to be done. There are fewer producers of organic milk so it often needs to be shipped further & there are fewer consumers so it often sits on the shelves longer before being sold, so it must have a longer shelf-life to be a feasible product."
],
"score": [
13,
10
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Ultra-high-temperature_processing"
]
]
} | [
"url"
] | [
"url"
] |
|
7mtfo7 | How does Anti-Dandruff Shampoo work? | Repost | explainlikeimfive | {
"a_id": [
"drwj366",
"drwj3rh",
"drwqesj"
],
"text": [
"When i took a class on fungi in college the professor told us that the secret to Head and Shoulders or any similar dandruff shampoo is that it is actually a fungicide. The dead skin flakes from your scalp are acually held together by a fungus and by killing it with the shampoo the dandruff flakes break apart into smaller pieces. So really by using the shampoo you're not eliminating your dandruff all together but making the dead skin flakes small enough so they're not noticeable. Plus I'm sure there are some moisturizers and what not in it also to help hydrate your scalp.",
"If my understanding is correct, dandruff is caused by an imbalance in a yeast production in the skin called seborrheic dermatitis. The active ingredient curbs the yeast production reducing the itchy flaky skin.",
"Pro-tip: Sometimes “anti-dandruff” shampoo doesn’t work. If you’ve only got flakes but not as much of an itchy scalp, then give it a whirl! But, if your head feels dry as a Londoner’s humor with an itch you just can’t scratch, then you should try shampoo specifically for moisturizing dry scalps. The active ingredient in standard Head and Shoulders can cause a person with dry scalp to itch more, resulting in more flakes. (OH THE HUMANITY!) Source: A guy who learned that lesson and never looked back at his shoulders again."
],
"score": [
24,
7,
7
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
7mu3ko | How does the television show “Planet Earth” film without disturbing the wildlife? | Repost | explainlikeimfive | {
"a_id": [
"drwnca5",
"drwnekk"
],
"text": [
"With patience, very high quality cameras with powerful zooms, camouflaged bunkers, and careful shot selection. You don’t see the thousands of hours of completely useless footage they get",
"After finding a group of animals to film, filmmakers will analyze the best places to film from and they may have to wait for days, even weeks, to get the shot they want. This is especially the case for migratory filming where they may have to stay put and wait for a single opportunity to present itself. This is one of the reasons major documentaries like PE take so long to film. The filmmakers are literally in and out of the field for years capturing wild life video."
],
"score": [
11,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
7mue54 | Why is laughter contagious? | Repost | explainlikeimfive | {
"a_id": [
"drwq0ev",
"drwqcv0"
],
"text": [
"Because your brain is wired to react to social cues. These reactions, like joining in a laugh, are survival traits for social animals. To survive as part of a group, empathic behavior is mandatory, it sets in-group/out-group dynamics and group cohesion.",
"There are a few theories about why we laugh. But i don't think there is any general consensus. One theory is that we laugh when we realize a situation isn't what we expected it to be. Especially when we though a situation would be dangerous but its actually not dangerous. I.e. You got scared because you though you saw a snake, but its only a tree branch. Hahaha. So its contagious then to help spread the message. Everything is okay, things are not the way they initially appeared. We also laugh in a lot of social situations. If things get tense between two people in a group, one person laughs, the whole group laughs, things are now less tense. We're saying this is not a serious situation. Take it easy. The general answer is that laughter communicates a socials message, and when the group wants to re-enforce that message, the whole group laughs. Its sometimes not contagious, like when you laugh at the wrong time. Nobody else laughs because they are taking it seriously. Then you feel shitty."
],
"score": [
21,
10
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
7mul7v | How do carnivores like Tigers and Lions get enough nutrient balance by only eating meat? | Repost | explainlikeimfive | {
"a_id": [
"drwr2p5"
],
"text": [
"One, By eating things like blood, skin, organs, bones, etc. Obviously that animal they ate *contains all vitamins and minerals required for that prey animal to live* so consuming all, or most, of a prey animal will include a wider variety of vitamins and nutrients. Humans can do this too, for example fish liver oil, whale blubber etc,. Whale blubber contains high amounts of vitamin C. Two, Different animals have different dietary needs. We primates require Vitamin C in our diets but we can manufacture other vitamins , many other mammals, including cats and dogs, *can actually synthesize their own vitamin C* so it isn't a dietary requirement. Cats require vitamin A from animal sources, they cannot process carotenoids(from plants) into vitamin A. Dogs, and us, can eat a carrot and make vitamin A. Different animals have different needs and different capabilities to manufacture vitamins or to dietary input into essential compounds."
],
"score": [
9
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7muw7j | Occam's Razor | Repost | explainlikeimfive | {
"a_id": [
"drwttr9",
"drwv7qq",
"drwsyx8"
],
"text": [
"You go to your room and find a new large purple stain on your bed. Your sibling is standing next to your bed holding a cup that has the remnants of grape juice in it. However, you now remember that your parents recently painted the basement walls purple. Could some of that paint somehow gotten on to your bed and created the stain? Sure, but the simpler explanation is that your sibling spilled the grape juice. This principle, of going with the simpler explanation, is Occam's Razor.",
"The traditional Occam's Razor example is \"When you hear hoofbeats, think of horses not zebras\" In most places the chances of you encountering a horse are far larger than the chances of encountering a zebra so if you think horse you are far more likely to be correct about the source of the hoofbeats. A choice of zebra implies that someone went, picked up some zebras from Africa, shipped them to whereever you are, and set them loose. That's a lot more steps than a mounted police officer or horse from nearby farm is coming. The answer with the fewest assumptions is most likely to be right and should be the one you pick",
"In essence, Occam's Razor is a kind of rule of thumb to take the simplest explanation when multiple are given."
],
"score": [
45,
14,
12
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
7muygi | The heat death of the universe | Repost | explainlikeimfive | {
"a_id": [
"drwtgx0"
],
"text": [
"The universe is expanding. The volume of the universe is increasing, and the amount of usable energy is decreasing (entropy is increasing). Eventually, the universe will expand so much that no particle will ever interact with any other particle again. The universe will be 0 Kelvin, and completely dead."
],
"score": [
9
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7mvu80 | Why does ice cream not melt when being deep fried? | Repost | explainlikeimfive | {
"a_id": [
"drx2rty"
],
"text": [
"It's only deep-fried for about 10 seconds which isn't enough time for the heat to reach anywhere but the surface."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7mw6j0 | what is entropy? | Repost | explainlikeimfive | {
"a_id": [
"drx7555"
],
"text": [
"You're going to get a lot of people telling you that entropy is like 'disorder', but I think that's a poor analogy. Entropy tends to lead to things breaking into smaller pieces and mixing together. While this can appear disorderly at first, it will ultimately lead to something that looks extremely ordered. So if not disorder, then what? Personally, I like to look at the original engineering definition of entropy for guidance. Such a definition might read: \"Entropy is a measure of the energy in a system that cannot be made to do useful work, normalized by the temperature\". If we look at the temperature as an indicator of the thermal energy, then entropy is a ratio that indicates how easily the energy in a system can be made to do something. So a system with high energy and high entropy can't be made to move things very well, despite having a lot of energy. Similarly, a system with low energy and low entropy can be made to move things fairly easily, but won't move them very much. In a word, this is laziness. Entropy is a measure of the laziness of a system, and the second law of thermodynamics says that a closed system will only become lazier with time. Here's a few examples of how you can visualize this. Children are high energy, low entropy: they often move around a lot no matter how you try to restrain them. Teenagers are high energy, high entropy: they have the energy to accomplish a lot, but you would have a hard time convincing them to move. Retirees are often low energy, low entropy: they seem to be constantly on the move, but they move very slowly, and take frequent naps to recharge. TL;DR: Entropy is laziness."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7mxhgf | How do shows like The Grand Tour get away with obvious speeding on public roads all over the world? | Repost | explainlikeimfive | {
"a_id": [
"drxemfw"
],
"text": [
"You go through a shitload of paperwork and permits to shoot a television show. Meanwhile the \"magic of television\" means that say it's an open public road, but in all likelihood traffic is being controlled in the areas where they're shooting. It's really no different to get a permit to speed, than it is to get a permit to set off massive amounts of explosives for a visual effects shots."
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7mxnsb | When there is heavy snowfall, why does it sound so quiet outside? | Repost | explainlikeimfive | {
"a_id": [
"drxg8lb"
],
"text": [
"Snow is an excellent insulator. So many crags and crannies redirecting sound waves end up nullifying the random ambient sounds."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7myeaj | Hot vs Cold water wash | Repost | explainlikeimfive | {
"a_id": [
"drxs54c"
],
"text": [
"Hot water has more energy to allow compounds to dissolve (and it also increases the rate at which dissolving occurs). The heat can break bonds between the stain and the object it is adhered to (like food on a plate) and the water also has more molecules with enough energy to form the bonds required to dissolve the particles. Proteins are usually easier to clean with cold water (like blood stains on clothing) due to the hot water denaturing the protein and making it adhere to objects (especially clothing) more. Detergents and washing powders that utilise enzymes will not work with hot water, as they are also composed of proteins which will denature and not work."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7mygqq | How are underwater tunnels made without flooding and killing the workers? | Repost | explainlikeimfive | {
"a_id": [
"drxnqiv",
"drxpxhn"
],
"text": [
"They don't build the tunnel through the water, they dig *under* the rock that's under the water. [Here is a diagram]( URL_0 ) so you can see what it looks like.",
"The tunnel is bored into the material (rock/clay/sand/etc) that is below the bottom of the body of water. As the machine digs, 2 things happen. First, the area that is directly being bored through is sealed off from the area behind it (where the machine has been) and is pressurized. You know how an airplane is pressurized? Same sort of thing. In this case, the pressure is high enough to keep the water out of the tunnel...or most of it. As the machine moves ahead, the second thing happens. Large sections of concrete (curved to fit the hole) are attached. This both stops the tunnel from caving in, and holds back the water. The machine then moves ahead and repeats the process. Some machines have the ability to pump material ahead of the cutter to fill the cracks in the rock to stop the water from coming in. Another method involves building the full tunnel section on land. Both ends are sealed, and the section is floated out. When over the right spot, the section is partially flooded with water. It sinks, and then is connected by divers to the previous section. At that point, one end is unsealed, the water is pumped out, and then the process is repeated. This tunnel ends up *on top* of the sea/river/lake floor. It's then covered by fill to protect it."
],
"score": [
9,
4
],
"text_urls": [
[
"https://upload.wikimedia.org/wikipedia/commons/thumb/3/36/Seikan_Tunnel_profile_diagram.svg/800px-Seikan_Tunnel_profile_diagram.svg.png"
],
[]
]
} | [
"url"
] | [
"url"
] |
|
7myob4 | What is the difference between my 5GHz wifi vs. my 2.4GHz wifi? | Repost | explainlikeimfive | {
"a_id": [
"drxoh8k"
],
"text": [
"1. Frequency. One operates at ~5Ghz, one operates at ~2.4Ghz 2. Interference. More non-wifi (802.11b/g to be specific) devices utilize the 2.4ghz spectrum/generate radio waves at this spectrum, such as old portable phones, microwaves, bluetooth, etc. 3. Range, speed, and penetration. 5Ghz (802.11ac and 5Ghz n, to be specific) wifi has superior speed, however the range and ability to penetrate solid matter such as walls is inferior to 2.4Ghz wifi."
],
"score": [
9
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
7n0jdu | what is computation, and how does brain compute? | Repost | explainlikeimfive | {
"a_id": [
"dry41bj"
],
"text": [
"Basically, computational theory of mind is the idea that your brain works like a computer does; information goes in, programs are run on it, and information goes out. In a computer, the stuff going in is strokes on a keyboard or mouse movements. The programs are... programs... and the stuff going out would be what's on the screen or what you print. In a brain, the input is the sight, smell, taste, sounds... everything your senses tell you. The output is your words and actions. The programming between the input and the output is what we're still learning. Because we can't watch a brain working (though fMRIs are making this a bit easier), and we can't read the source code for the brain, we learn what it's doing the same way we can learn what a program does; putting things in and seeing what comes out."
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7n1f43 | Why is it that extremely cold things can feel hot and vice versa? | Repost | explainlikeimfive | {
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"To the molecules in your hands, feeling something cold is like being in a car that's slowing down and feeling something hot is like being in a car that is speeding up. But feeling something really hot is like being hit by a car and feeling something really cold is like hitting parked car. Either way you crash and it feels similar.",
"When you feel something sort of cold or sort of hot, your nerves tell your brain that it's cold or hot. When you feel something way too hot or way too cold, the only thing your nerves tell your brain is, \"Ouch, don't touch that!\" At that point your brain can't tell what temperature it is, only that it's dangerous, so it sort of guesses."
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7n4nwd | How crypto currencies fluctuate in price | Repost | explainlikeimfive | {
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"You can think of crypto currencies just as any other finite good or asset: its price is determined by supply and demand which are also influenced by its scarcity. People buy bitcoins or other crypto currencies for different reasons: some do because they believe its price will rise in the future and they will be able to sell it with a profit, others do because they prefer to use them for financial transactions instead of \"real\" currencies. People sell crypto currencies because they want to have \"real\" money instead or because they exchange it for goods. The more people use a crypto currency for buying real goods (instead of exchanging it for \"real money\"), the higher the value of the currency and the higher the price (in terms of dollar) of the currency (and vice versa). This is because the value of a given currency is determined by how likely it is that someone will accept it as payment. This is the difference to goods: while they are consumed, currencies are used to exchange them again for other goods in the future. So as more and more people accept a given crypto currency, more and more people will also want to own it as they will be able to exchange them for other goods with people who accept the crypto currency. However, the massive fluctuations of crypto currencies (as opposed to general trends over time) are largely caused by speculation, i.e. by traders who buy and sell the currency in order to profit from price differences over time. In this regard a crypto currency can be seen as any other financial asset. However, there is one important difference to other goods and assets: bubbles that are intentionally created by a single actor or a small group of people who spread rumors online that the price of a particular crypto currency is going to rise in the hope that many people will follow the advice and buy that crypto currency. They then sell a lot of that crypto currency which they had acquired before spreading the rumor, thereby making a lot of money. As a consequence the price of the crypto currency falls dramatically (as the one who spread the rumor sold a lot at once)."
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7n7k77 | Internet cookies? | Repost | explainlikeimfive | {
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"Imagine you're reading a book. You're at a specific part of the book, somewhere in the middle. You decide \"that's enough book for today\" and you close the book. Next time you open your book, you're going to have to flip through all those pages again and manually find your page. Rather than having to remember what page you're on, why not just have the book remember for you? So you decide to put a bookmark in the book. You can also write down little notes on this bookmark, like \"This character just did this\" so that next time you open the book you can easily remember what you just read and pick up exactly where you left off. Cookies are essentially bits of data that websites leave in your browser so that they can quickly easily access them next time you visit. For example, if you sign into Facebook and say \"Remember Me\", Facebook leaves a cookie that remembers that you logged in on this machine and that you want to be logged in automatically in the future.",
"Yarr! Yer not alone in askin', and kind strangers have explained: 1. [ELI5: How does internet cookies work, exactly? ]( URL_7 ) ^(_9 comments_) 1. [ELI5 what internet cookies are. ]( URL_4 ) ^(_2 comments_) 1. [ELI5: What are (internet) cookies and why am I supposed to clear them periodically? ]( URL_2 ) ^(_8 comments_) 1. [ELI5: What are internet cookies? ]( URL_1 ) ^(_4 comments_) 1. [ELI5: what actually are internet cookies, what do they do and why are they called 'cookies'? ]( URL_5 ) ^(_2 comments_) 1. [ELI5: What are internet cookies? ]( URL_3 ) ^(_7 comments_) 1. [ELI5: What exactly is a \"cookie/s\" when it comes to the internet? ]( URL_0 ) ^(_7 comments_) 1. [ELI5:Why are cookies (as in the things that track your internet history) called cookies? ]( URL_8 ) ^(_4 comments_) 1. [ELI5: What exactly are \"cookies\" in regards to internet browsing history? ]( URL_6 ) ^(_2 comments_)"
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7n7ncu | why ice in a beverage stays in the same position when the glass is turned. | Repost | explainlikeimfive | {
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"Newton's First Law of Motion states that an object at rest tends to stay at rest unless acted upon by an outside force, and an object in motion tends to stay in motion unless acted upon an outside force. So you have ice floating in a liquid in a glass. Ice has a low coefficient of friction, meaning it's slippery. So when you turn the glass, there is very little rotational force along the interface between the ice/liquid and the glass. So given this lack of force, the ice will tend to stay where it is.",
"Because Ice doesnt care about anything its not touching. A fluid will always arrange itself by density if nothing else acts on it, so the denser part will be on the bottom. The fluid didn’t move so the ice wont either, all they care about is gravity."
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7n7pld | What is the difference between Microprocessors found in Smartphone (Snapdragon, Apple) and in PC/mac (Intel, AMD)? | Repost | explainlikeimfive | {
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"Speed and power consumption. But, at the end of the day it's all about 1's and 0's. Also, I had to edit this because the auto mod said it wasn't sufficiently long enough so hopefully this is long enough now because not everything needs a big explanation. But, just incase... Both computers and smartphones are marketed heavily by their processor, and while the function is the same – both allow the individual devices to work – there are two major differences: When processors run they generate heat. Lots of heat. Because mobile devices are considerably smaller than computers, the heat generated by a running mobile processor is often amplified and can seriously harm components, or even melt them. Therefore, the developers and designers of the devices limit, or throttle, the speed at which a mobile processor can run. This means that if a processor is getting hot, it will limit its speed, which equates to slower performance. Because of this throttling, the processor on many phones will actually run slower than the advertised speed. In fact, the advertised speed of mobile processors is normally the maximum. Compare this to most computer processors, where the advertised speed is usually the average running speed, and you begin to see why computers are more powerful. The second big difference is connected with performance. If you take a computer and compare it to a mobile device with the same speed of processor, the computer will usually be able to do more. This is because the processor is limited in what it can do by the other hardware components, like the RAM, Graphics Processing Unit, etc. Computers have more space, so they can fit more advanced components, and are consequently able to do more. That being said, processor and other mobile technology is advancing at a blistering pace and it is highly likely that mobile hardware will continue to increase in overall power, and eventually be able to compete more effectively with larger computers.",
"Yo ho ho! Yer not alone in askin', and kind strangers have explained: 1. [ELI5: What is the difference between Processor of a mobile phone and Desktop computer? And, how does it bring a change in performance to an end-user? ]( URL_4 ) ^(_11 comments_) 1. [ELI5: Why is it my phones processor is better than my laptops processor, yet my laptop is still faster (details inside)? ]( URL_2 ) ^(_4 comments_) 1. [ELI5: how are the processor of phones compared to PC's? ]( URL_1 ) ^(_5 comments_) 1. [ELI5: Smartphone CPUs, compared to PC ones ]( URL_0 ) ^(_6 comments_) 1. [ELI5: if Samsung make good processors for iPhone, why can't they make good processors for Samsung phones? ]( URL_3 ) ^(_10 comments_)"
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7n7spl | Given the sheer volume of snowflakes, isn't it statistically unlikely that they will be unique, even with all the possible permutations? | Repost | explainlikeimfive | {
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"Ahoy, matey! Yer not alone in askin', and kind strangers have explained: 1. [ELI5: How do we know all snowflakes are unique, maybe there's such a large variety of them that it just seems that way. ]( URL_0 ) ^(_5 comments_) 1. [ELI5:How can EVERY snow flake be unique? ]( URL_2 ) ^(_17 comments_) 1. [ELI5: How do we know that two identical snowflakes have never existed and never will? ]( URL_5 ) ^(_20 comments_) 1. [ELI5: How can every snowflake be unique? And furthermore how do we know? ]( URL_6 ) ^(_2 comments_) 1. [ELI5: How Do We Know That Every Snowflake Is Different? There Are So Many, And They Melt Whenever They Touch Something Remotely Warmer Than Them. ]( URL_1 ) ^(_4 comments_) 1. [ELI5: Why does every snowflake have a different patten? ]( URL_4 ) ^(_2 comments_) 1. [ELI5:Why are snowflakes supposed to be unique? ]( URL_3 ) ^(_6 comments_)"
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7n9v5e | why does the human body go into a "coma" and what is the body doing during this period? | Repost | explainlikeimfive | {
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"At the most basic level the body is prioritizing the immediate tasks needed to stay alive (keeping the heart beating & breathing) at the expense of more advanced stuff like processing stimuli and thinking. Comas can happen for a variety of reasons (trauma & infections being the main ones) and can be induced by medical professionals to keep the body focused on repair when it might not have the resources to both fix itself and fully function. Edit: Medically induced comas are also used to minimize psychological trauma which might result from being semiconscious while intubated (tube down your throat to your lungs to handle breathing); it’s not a pleasant time. Edit: There’s a variety of different awareness states & pain relief goals that can be targeted by a provider, which range from local anesthesia where a patient is conscious with a specific spot numbed to general anesthesia where a patient is fully unconscious & unresponsive to stimulus. The approach is dictated by the patient’s particular presentation, history, & the goal of treatment. If you’re interested in how a “coma” is defined clinically (in treatment like a hospital), you can look at the “Glasgow Coma Scale” which provides gradiations of consciousness depending on patient presentation. There’s a lot that needs to go wrong to put someone into a comatose state as the body is pretty resilient to outside changes. But if stressed, the body is structured to protect heart & brain function, at the expense of other parts of the body. For example, when cold, the body will constrict blood vessels far from the core (fingers, toes, etc) which saves heat and blood for important organs. The body can do this successfully because some tissues are more tolerant of being deprived than others, the use of tourniquets for bleeding is a great example. Tourniquets are used to stop massive blood loss on a limb (leg or arm), and when applied correctly, completely cut off blood flow. If you did this to a brain, it would be begin to take damage and die in a matter of minutes, but the limbs can be cut off from blood completely for several hours without tissue death. A coma is where the body has so few resources that it prioritizes basic functions (heartbeat and maybe breathing if it can be managed) but can’t do anything else. These base functions are typically the last to go before death. The heart runs on an internal pacemaker, so even if the connection between the brain and the heart fails the heart continues to beat. You need signals from your brain to breath, but in a hospital setting that can be managed by a machine if your body won’t do it.",
"Since this is ELI5, there are many factors that can cause coma, but lets simplify: Brain damage, your brain is like a computer, sometimes circuits can be rerouted and that takes time so your brain has to shut down for a while to do this work. Thankfully, most basic functions to stay alive are automatic, things like breathing and heart beating, even digestion despite the fact that you can't feed yourself. This can happen from a seizure, an impact, infection, lack of oxygen, stroke, or other problems. Self preservation, some events can cause so much damage to the body that continued function would lead to death, as a product of evolution designed to survive, your brain can turn you off to take time to perform repairs and try its best to keep you from dying. This can happen from overdoses, chemical imbalances, even poor nutrition causing nervous system malfunction. For adults wanting a little more depth than a five-year-old; Hyponatremia, hypoglycemia, and diabetes are all common causes of coma.",
"I'd like to ask a follow up question on this. Why is it that some comas last for several years, decades or even forever, long after any damage has been fixed? Does the body not have enough control to wake you up again? And why can't we medically wake someone up?"
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5re01q | Why is it that when my internet connection is poor, whatever video/stream I am watching lags terribly, while the advertisements before it are perfect quality? | Repost | explainlikeimfive | {
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"Ads are programmed by your site, often even regardless of what you're watching. Youtube essentially knows you're a techie guy and will start preloading techie ads before you ever get to actually watch any. That way, then it comes to showing you an advert, it will often just play one that it already locally downloaded to your buffer. This is a common technique that anyone who's worked with mobile apps and games is familiar with. Most advertising networks provide preload functions, and ways to check whether your ad has loaded. In short: your video is streamed, but your ads are downloaded before they play.",
"The programming is delivered at a variable bitrate. If your connection is slow, your program stream switches to a lowered quality in an attempt to keep it flowing. Advertisers do not want to pay for their beautiful commercials to be displayed at that crappy quality, so they insist on being displayed at highest quality, regardless of whether it causes a bottleneck or not. Source: commercial producer for a major cable company(sorry...)",
"If you're referring to web commercials, it's because they're highly compressed and tend to be loaded before your video even begins to buffer",
"Adverts are short and don't play until the whole thing is ready. Films are streaming and if your internet is slow it drops the quality in preference to pausing while it buffers.",
"It's the other way around with 70Mbps Virgin Media connection in the UK - ads take an annoyingly long time to load (which means it takes longer until I can skip them) then the video loads straight away. I assume it's because they are big enough to have worked out their own routing and caching with YouTube but don't use it on the adverts."
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5rey1d | How comes the universe is flat? | I read it everywhere lately. 2D universe, holographic world, etcetc... But didn't find any explanation. D: Is this a legit theory at all? I mean like compared to hypertorus, for example. Also how this 2D universe comes together with string theory, or with any other popular theory? Thanks for the answers. | Repost | explainlikeimfive | {
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"You are mixing different concepts here. When cosmologists say \"the universe is flat\", it has nothing to do with the number of dimensions. The surface of Earth is not flat in that context. If you make a triangle on a perfectly flat area, the interior angles add to exactly 180 degrees. If you make a triangle on the surface of Earth, you'll see that the angles add to more than 180 degrees: The surface of Earth is curved. Within the precision of our current measurements, the universe is flat: If you make a triangle, the angles will add up to 180 degrees. Holographic universe: It is the idea that the world might have one dimension less than we think it has, similar to a hologram on a 2-dimensional paper that looks 3-dimensional if you see it (hence the name). We don't know if that is true. A recent study found that both a normal 3-dimensional world and a 2-dimensional world are in agreement with observations, with the 3-dimensional world leading to a slightly better (!) agreement. We don't know yet, and we will need more precise measurements to see what works and what does not. All this is independent of string theory, which is an interesting approach, but cannot make good predictions yet."
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5rf0v2 | What's the benefit of displaying a menu price without tax included? Plenty of countries include the tax in the final price but the U.S adds it separately. | Repost | explainlikeimfive | {
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"If your competition doesn't show the price tax-included, it makes their products seem less expensive (even if they're the exact same price or a little higher). In addition, it allows advertising to be done for prices across boundaries where the tax rates might be different (such as across state borders - or sometimes even within a given state). It also means any changes to the taxes in an area doesn't mean you suddenly have to reprice everything manually. It also lets you easily see exactly how much tax is being paid by looking at your receipt, instead of just assuming that the company is paying the sales taxes properly.",
"Gets people to spend more. Same reason why most prices are not rounded. $4.99 14,995 Strangely enough studies have shown that menu prices in restaurants that just show a whole dollar figure make the diner feel like the restaurant is more luxurious. I.e. 12- vs $11.95.",
"Just taking McDonlads as an example. There are over 14,000 restaurants in the nation. Printing menu signs for each and every one is going to cost a significant amount of time and money. Standardizing the signs across the board allows them to save a lot of money and give a consistent experience. Taxes and laws are different everywhere in the USA, even just across the street. It is to the benefit if the companies to not have to include sales tax so they do not have to individualize each menu. Taxes also change, remember NYs soda tax? Should every restaurant be forced to alter their menu while the law is tested in courts? It would be nice to know the exact dollar amount you are going to pay but if you live in the USA no matter where it is your responsibility to know the local taxes. As an alternative, consider shopping more local as many local places at least around me just do flat fees for food and such, they just worked out the price and tax to equal an even number or close to it.",
"Tax can vary by region, and occasionally day. For countries like that, it's easier to put the initial price."
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5rfbc3 | Why do our arms move back and forth as we walk? | Repost | explainlikeimfive | {
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"You lift your right foot up off the ground and move it forward. You have now shifted the centre of gravity slightly forwards and to the right. If you did nothing to counter this shift in the centre of gravity then you would stumble forwards and walking would be very ungainly. But what you do is swing you left arm backwards (as well as doing other things like contracting certain muscles in your back and other leg) in order to shift the centre of gravity back to the middle and keep your balance.",
"It's something your body has subconsciously developed to help you maintain your sense of balance. If you will watch a child learning to walk they do not do it as much and fall a lot. Once then understand how to walk they also develop the arm swing."
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