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6a09ih | Chemistry | Why is spit much better at shining shoes than water? | Saliva has enzymes that break up the wax in the polish better than water can. Water doesn't mix as well with wax. | 1 |
74emn5 | Engineering | Every month there’s a new micro SD card with more space than the last. We’re fitting gigs of data when a decade ago we could only fit megabytes. But what’s the theoretical limit of how much data we can store in a micro SD card? How can we keep fitting more data in smaller spaces? | Not so much every month for space, rather for reliability and bandwidth. For instance I remember only a few years ago when solid state drives were not reliable at all. I'm also a bit different, I would prefer having a 256GiB microSD over a 512GiB regular SD. I thought that whole 200GiB gimmick was silly and ingenious at the same time. SD cards are more arbitrary, so it would probably be better to work in centimeters, I mean you wouldn't mind a 1 cm by 1 cm (square) by 10 mm thick card if it hit the theoretical limit, would you? It would also be easy to relate to the size of an SD card. Even better is they use something called nanometer or nm gauged setups, which you get a million per centimeter. So 1,000,000 * 1,000,000 is 1,000,000,000,000 or a trillion bits. Since we use bytes instead of bits you divide by 8 and round to the nearest computing magnitude yielding 128 GiB. Why not 125? Because in computing the numbers work on doubling rather than incrementing like in decimal. This is called binary, or hexadecimal (meaning 6 and 10, or 16). Anyways, you're probably going to be looking at something like 2^40 or 1,099,511,627,776 bits rather than an even trillion. So wait, we have cards that have 256 GiB that are much smaller than a centimeter and we're not even to a 1 nm process yet? What evil magic is this?! It isn't. It's called layers. I'm sure you don't want a card only a nanometer thick! All that itty bitty (to you and me) yet massive (to the switches) extra space lets you stack these cards! [Notice here it says Samsung's microSD cards are made out of what? **3D** V-NAND]( URL_2 ). They are saying they can make this up to 100 layers thick, and they are using a [19 nanometer process (PDF file)]( URL_1 ) to do it. Yes, that's 20x less capacity than we've been working with here, but it doesn't matter when you have 100x more room. If they ever do get that down to 1 nm you'll have 100 trillion little switches! Not only that but what if that allows them to increase the amount of layers by 20x as well? Then you're looking at quadrillions, or 15 zeroes. Those would be petabytes or PB. [I can't wait until we are working at the DNA scale]( URL_0 ), 10 base pairs at 3.4 nm. If we're that close to DNA already I'm actually quite a bit impressed. | 5 |
gvwdfj | Biology | what really happens when you faint? | Typically, fainting involes blood leaving your head (this could happen for a number of reasons). With the sudden blood loss in your head, your brain starts to not work properly and you momentarily lose consciencess. | 2 |
k0ntf6 | Biology | Is the blood you were born with as baby still in your body as an adult? | No. Extremely oversimplified ... Blood cells live about 120 days then get filtered out by your liver and kidneys, where you pee it out. It’s replaced by more blood cells that grow in your bone marrow. It’s a constant/cyclical process... always making more, always filtering out, always peeing spent blood cells. | 1 |
e01b4e | Other | What do americans mean when they say they have to "do their taxes" what taxes are you doing? What do you mean? | In Ireland and the UK, income tax is taken from your pay before you get it. But that assumes you are not self-employed. Self employed people have to file a tax return every year even in Ireland and the UK. This means filling out a form, telling the government how much you earned over the last year, working out how much tax you therefore owe, and paying it. As you can imagine, from the beginning of the year, if you are self employed, you have to estimate how much you will have to pay in tax at the end of the year and not spend that money. Usually people will save it in a different bank account and then hand it over once a year. & #x200B; In the US, everyone has to go through this process whether they are self employed or not. Tax is still taken from their pay, but its rarely accurate because their tax system is very complicated and other things need to be accounted for. For example, people get tax discounts if they have children but this discount is not worked out in advance, so you overpay your taxes for the whole year, and when you file your taxes, you get a small refund to cover that discount. That's just one example, there are many different reasons why you might get a discount. But it can go the other way too. For example, if you sell your house and make a load of money, you have to declare that at the end of the year and pay tax on the profit. You'd have to actually give that money over to the government. That's just one example, there are many reasons why you might have to pay extra. You can see how this gets complicated! & #x200B; Just to complicate things even further, Americans have to pay two separate pots of tax. They pay taxes to the State in which they live (e.g. New York, or Texas) and one pot of taxes to the federal government. & #x200B; The tax year runs April to April so in the run up to the end of the tax year, everyone has to feverishly sit down and file their taxes which can be a massively complicated and time consuming issue, depending on your individual circumstances. & #x200B; I am British, my wife is American, and even though we live in Britain and she earns no money in the USA, she still has to file her US taxes every year, but the form always amounts to $0! | 4 |
6y827p | Culture | Why green is associated with good and red with bad? Since when is this happening? | Green is the color of nature, red is the color of blood and fire. Associating greens with peace and tranquility and reds with danger or passion has been pretty common since ancient times. | 1 |
ci297c | Chemistry | Why are atoms so much "empty space"? correct me if i'm wrong but I'm under the impression that every atom is 99% "empty space" and that the only real bit of substance is the nucleus? And that if you got rid of this empty space we could all be smaller than grains of sand? Why so much empty space? | Even the protons and neutrons in the nucleus are made of much smaller things still. But the way I understand it is that this ‘space’ around the nucleus is actually taken up by the wave function of the electrons in ‘orbit’ around the nucleus. This probabilistic wave function extends down to the nucleus itself. Been a while since I took physics, though... | 2 |
92hg0c | Technology | Why does it seem that every company that updates their user interface makes it worse? | Because it changes from what you're used to, I'm sure if reddit changed from the new version to the old version there would be a lot more complaints. | 1 |
6asf8i | Other | When was the beginning of time? It is often described as possible the oldest period in history but just HOW old exactly? | We don't know, but at least ~13.7 billion years ago, in a frame of reference in which the cosmic background radiation of the universe is isotropic (the same in all directions). That caveat is important, because there's no such thing as 'absolute' time. So it defines a frame of reference in which the universe is 'most old.' In other frames of reference it can correctly be considered younger (less time has passed). | 3 |
a3b65p | Culture | How do we know what names mean? E.g. Hercules wife was called deinara, which means husband destroyer. In ancient greece was this woman literally called husband-destroyer? | Should also note that Hercules, et al are not real people but characters in myths. This matters because the names would have more actual significance in their meaning than if the names were being used by actual living people. For example: if we are referring to our friends John Smith or Mary Cooper, we aren't connecting the names to ironworker or barrel-maker. But if we are referring to Superman or Iron Man, we are aware when we say them of the qualities they represent. | 28 |
9dmrup | Physics | How does gravity bend light if light is massless? | Because gravity bends space-time itself. The light is still going straight, by its own point of view, but the space-time is curved by the gravity, so something traveling straight through curved space-time alters its direction relative to an observer outside the curved region. Black holes basically curve space-time inward to the point that there's no getting back out of that gravity well. | 11 |
iuznyo | Biology | - What is the weird sensation you feel when you clean your bellybutton? Okay, I hope I explain this well. Every time I clean my bellybutton, I get a really weird, almost painful sensation deep inside my body (not immediately below the below button) but a little lower and deeper inside. What causes that to happen? | I have a bit of a phobia of belly buttons because of this exact feeling. I can look at them fine but if someone starts poking and digging around in theirs in front of me it makes me want to die inside. | 6 |
96zlk8 | Economics | People say that the housing market has collapsed. What does that mean and how did it happen? | If you are referring to the present, the main factors include a long, long period of stagnant wages combined with houses that are much bigger than 40 years ago creating a serious issue of affordability. I'd add that a near non-existant level of job security and very high transaction costs makes it very difficult to feel secure enough to recoup your losses in the case of a job transition. Most people need to be in a home for 7 years to make up those transaction costs. | 30 |
9ez5px | Physics | Why does a nuclear bomb detonation emit an electromagnetic pulse that destroys electrical systems? | There are two main kinds of EMP pulse, and they are generated somewhat differently. For weapons that detonation at or near the surface, you get a short-lived and very localized pulse that tends not to be a big worry because it is not that intense outside of the immediate ground zero region. It is caused by the fact that gamma radiation emitted from the explosion will ionize (strip electrons from) a region of the air around the explosion. So you end up with a separation of charges: one region will be full of more electrons and another will be lacking them. This results in an electric field that "pulses" out a bit. This is not super large from a distance standpoint and generally speaking if you are close enough to care about the EMP in such you have probably already been destroyed by the heat, blast, and/or radiation effects. [Image]( URL_1 ). High-altitude bursts (the altitude can vary but you get "best" results at _very_ high altitudes, like hundreds of miles above the surface of the Earth), the gamma rays from the burst will ionize a vast region of the Earth's upper atmosphere below it, sending out lots of electrons that move along the Earth's magnetic field lines. This ends up accelerating the electrons and creating a rather intense EMP over a vast area near the surface. This is what people tend to worry about when they worry about EMP — a high-altitude burst that otherwise is so far up that it wouldn't affect anything, but generates this pulse. [Image]( URL_0 ). I've simplified a huge amount in the above; some of this stuff is just hard to ELI5 because it relies on fairly advanced physics. It should be emphasized that the exact effects of an EMP are hard to model and that there is a split expert consensus on whether it would be a huge problem, not as much of a huge problem, or something in between. | 2 |
cpe7ea | Other | if sand is eroded rock caused by water then how are deserts made entirely of sand, but still some of the driest places on earth? | Most if not all deserts were at one time under water. | 4 |
8rovr8 | Biology | Why are men attracted to a woman's figure? | Big hips mean good for childbearing. Large breasts means she’ll be able to feed your offspring. | 2 |
ff8gxc | Chemistry | Why does the can of compressed-air dust remover gets so cold if used continually at once? | When you compress a gas, the thermal energy contained in that gas is condensed into a smaller area. This raises the average energy in the gas in relation to volume, and thus the temperature. When you let that gas cool down, and then release the pressure, the energy is then dispersed into the new larger volume, lowering the temperature. This is how refrigerators and air conditioning work | 3 |
nf8h62 | Biology | Do plants have unique DNA like humans? For example, if there were two gardenia bushes and a flower fell to the ground, could it be determined which one it came from like genetic testing etc on humans? | Yes. In fact, flowers are part of how plants have "sex". Pollen can be thought of as a plant's sperm and when it's moved from flower to flower it allows for genes from one plant to mix with another. Even fruits like oranges are from humans selectively breeding trees. | 10 |
5qlqwm | Culture | what is the Canadian Healthcare program and why won't it work for the U.S? | The Canadian healthcare system is administered through the government. Each province (kinda like a state, but bigger) funds their own program, while the nation sets some guidelines. What this means is that they don't pay for healthcare like we do here. Instead, they pay taxes, and then when they go to say, the hospital, the government pays all/most of it. The government also takes care of negotiating drug costs etc with companies. What that means is you don't need private insurance, like you would here (unless you're exceptionally rich). However, the public system doesn't cover everything. For example, dental/eye care works more like it does in the U.S. They do have private insurance, but it's more supplemental. The national healthcare is more basic, while private lets you get some perks that would cost extra. This also means you don't need to worry about being turned down if you can't afford treatment. No one is turned away, and the taxes you pay are proportional to income > why won't it work for the U.S? That isn't really an easy question to answer. There's no real proof that it won't- however, people are scared to try, because they think that government being in healthcare will make it very inefficient, or give people bad care. It's never been tried, so a lot of it is speculation tied to political beliefs on the role of the government. People who think the government should be small and leave stuff like this to the free market, are going to oppose national health care. (and vice versa). It's worth mentioning that Canada (as well as many european countries), tend to pay less for the same level of care that we do in the U.S. That doesn't mean it would for sure work- but it's very suggestive that it might, besides just actually trying it to see. While it is much cheaper, there are potential downsides. Canada is known for having relatively long waiting periods to get procedures done, and they tend not to have as many high end options as the US- in the US, there tends to be better specialized options, if you can afford it. A lot of people also argue that we essentially end up subsidizing R & D costs for the world, and that if we switched, less drugs would be made, but it's hard to prove if that is true or not. edit: You might find this helpful, for more detail (but easy to read!): URL_0 Or previous ELI5s: URL_1 edit2: I should also mention, that the reason it's cheaper, is that the government is a *very* big customer. That means they have a lot of bargaining power. The bigger you are, the cheaper you can get stuff (this works for insurance companies as well, they like being as big as possible for the same reason). So they can negotiate much lower prices with medical suppliers, which make much less money than they do in the U.S. The government also doesn't have to make a profit like a private insurance company, which saves as well. (Although insurance profits are relatively low in the US- it's a very competitive field. Most of the money "wasted" goes to providers, the people who make medical equipment or service, like doctors) | 3 |
mwyfsl | Other | Why do bottles filled with water start smelling after a certain amount of time? | URL_0 Here is a Sci-Show episode just about that. But basically most water is at least partially chlorinated and we are used to the taste, but the chlorine and other gasses release from the water into the room over time | 1 |
dn69e4 | Psychology | Why does listening to instrumental music, classical, drum and bass, or even trance, boosts concentration? | The only thing on which I concentrate when I listen to music is the music. I can't help it. Everything else on which I'm focusing stops cold as I listen to music. I don't know how other people do it. | 1 |
je7086 | Technology | How do fighter jets detect that they've been locked as a target of a missile? | Ever wondered what it meant when fighter pilots announced "Fox 1!", "Fox 2", etec? Theyre refffering to a huge part of your question. A fox 1 is a semi active radar guided missile. Fox 2 is infrared. Fox 3 is active. Fox 1s give the warning you are describing. When these missiles are launched, the plane provides the radar pulse out, while the missile only has a receiver it's like if a person with a knife had his buddy hold the flashlight. Fox 1s, like the Sparrow, need a lot of energy to see the target. So the warning isn't from the launch, it's from the attacking airplanes radar hitting you with constant radar energy. It is safe to assume a missile is on its way but not a given. Because the missile needs the parent aircraft to illuminate the prey, if the parent aircraft turns away and stops lighting up the target, the missle will go blind and sail harmlessly off into oblivion. Fox 2s are infrared. They do not provide the radar warning because they do not use radar to see their target, they just look for your heat signature and try to follow that. Fox 3s are full active radar missiles. They work similar to fox 1s, but they also carry their own illumination equipment (transmitters) so the launching aircraft can turn away. A huge advantage the US had in the 90s and early 2000s was a missile we introduced called the AAMRAM which had the advantage of not giving the warning that you'd been locked up until it was about to hit. Older systems like the Sparrow gave a warning because they required the extra energy of a "lock", the AAMRAM would allow a pilot to notice a victim passively in scan mode, use the radar and comouters to rememeeber about where the prey is, tell the missle about where it needed to go and then launch it without a lock up. On the way the missile and parent would remain passive, and the parent would discreetly relay updates to the missile on changes to the targets position. When the missile was within a certain range of where it knew the target should be, it would kick on its own internal radar and light up the target for itself(if youre following along at this point that makes them fox 3s). You would still get a warning, but had very little time to respond. I've hear convincing arguments that the AAMRAM was more of a factor in our dominance in Desert Storm than the Stealth aircraft. One last thing, there are other warning systems than the "lock up warning". The system you are thinking of and shown in most movies is called an RWR, Radar Warning Reciever. In practice, RWR not only emits a frantic beepbeepbeepbeep but also chirps when your aircraft is pinged by less concerning scan radars. It emits a unique sound depending on the signal it hears. There are also launch detectors that aim to sense when a infrared missile is on its way, which of course don't send a radar warning when fired. These systems look for the flash accompanied by the missle's motors kicking off and politely inform you it has seen evidence that a missile is on the way. | 17 |
afg69c | Physics | What’s so special about an atomic bomb vs. any other bomb? Can someone explain the science to me of what exactly about an atomic bomb makes it so powerful and deadly? And why was it such a breakthrough to build the first nuke? | An atomic bomb is a bomb that produces energy based either on fission (breaking apart heavy atoms) or fusion (binding together light atoms). Fission is the first kind of bomb created and it works by putting a specific kind of uranium close together. This kind of uranium has 235 neutrons in its nucleus rather than the much more common 238 neutrons, meaning the U-235 which makes up about 0.72% of natural uranium needs to be isolated and concentrated together. U-235 is special because if a free-flying neutron runs into the nucleus at the right speed it can stick, creating U-236 which is very unstable. This breaks apart into two atoms, one of krypton and one of barium. It also will release three neutrons flying off at high speed. Notice how that works? One neutron in and it releases three neutrons out, along with a significant release of energy when it splits apart. Put enough U-235 together and it can kick off a chain reaction which increases in speed and strength very quickly. The amount of energy released by a single atom breaking down isn't very much, but there are *a lot* of atoms in even a small amount of material. A bomb then can be created simply by putting enough U-235 close enough together that when the U-235 breaks apart spontaneously (as it is radioactive itself) it kicks off the breakdown of the other nearby U-235. This point is called "critical mass" or "nuclear criticality", and a bomb can achieve this simply by having a chunk of material which is slightly under critical mass with an open plug where more U-235 can be inserted to make it go critical. Other ways are carefully timed and measured shaped explosives to compress a shell of uranium into a dense mass which goes critical. The result is a huge release of energy, far beyond what can be produced by chemical reactions at such weights. A nuclear bomb might weigh 1100 kilograms but be able to release energy equivalent to 1.2 million tons of TNT! A related kind of process is fusion, something which generally speaking is only possible at very high temperatures and pressures. Light elements such as hydrogen are forced together by those conditions hard enough to overcome the nuclear forces which normally prevent the positively charged nucleus from interacting with other nuclei, allowing them to bond and release energy. You might be wondering why breaking apart heavy elements releases energy and binding together light ones does as well, and if it makes it any more clear the crossover point is about at iron where neither fusion or fission of iron will release energy. Because absurdly high temperatures and pressures are required to achieve fusion the only practical method of achieving them in the past was with a nuclear bomb itself. The immense power of the explosive release of energy was carefully shaped such that it would compress and heat the fuel to be fused, in turn releasing even greater amounts of energy. | 4 |
j9pwqd | Other | When a programmer puts the code in for the color red into a computer program, how does the computer know what red even is? What is the origin of colors for computer to reference? | The computer doesn't know what red means. For the computer it's a number just like any other (FF0000 in Hex). It will send that number to the monitor and the monitor will just route the first two numbers to the red LED in the pixel because engineers agreed on using the first two for red. It will light up at maximum intensity on a scale from 0-255 | 5 |
5vi0m3 | Other | Why is the majority of girls handwriting nicer looking than boys? | I haven't been able to find any research stating that they do even in fact have better handwriting. It seems mostly based off of anecdotal evidence and a general acceptance (neither of which are very scientific.) Moreover, taste is subjective. I've found a reference to one study that showed boys tending towards a different style of writing; in which case it's subjective as to which is nicer > In her book "Handwriting in America: A Cultural History," Tamara P. Thornton noted a 1910 handwriting expert's study on identifying sex differences in penmanship, which concluded that confident, original script is interpreted as masculine, whereas neat, conventional and circular are considered feminine. As a result, contemporary studies find that people are pretty good (usually better than 60 percent) at guessing whether a handwriting sample came from a man or a woman. In fact, a 2005 study out of the University of Leicester on sex hormones and handwriting noted that biological sex is the only consistent correlate with handwriting ^^[[link]( URL_0 )] It is impossible to know if this is true, whether it is cultural, only in certain scripts, at what ages, etc. | 42 |
f9rct9 | Biology | What happens to your muscles during and after a massage? | Your muscles can get stuck "on" from overuse or say poor posture, a massage therapist will work to find the off buttons to turn them back "off" again. Going further, your muscles have a layer in between your skin and your muscle that gets bunched up over time, like a bed sheet under a blanket. A good massage therapist will work to smooth this layer back out again allowing muscles to move freely under your skin. | 4 |
gouuin | Engineering | Why is glass the dominant window material, as opposed to higher-grade plastics? I understand why car windows should be glass, given the high speeds, and potential benefits in a crash. For home windows or buildings, I would guess that plastics might be more durable, longer-lasting, and potentially cheaper. I assume I'm wrong and someone must have put far more thought into this than me, so I'm curious to hear what that is. | Glass is cheaper, and doesn't scratch as easily. Plastic is lighter, but considering the weight of things, it is a minimal amount of weight compared to the rest of the load. Glass doesn't deflect near as much under pressure, so when you have double or triple paned windoes with evacuated cavaties between layers the glass doesn't distort. Also, any idiot can scry glass.and replace a panel, much harder to DIY a plastic panel replacement. Hope that helps. | 4 |
e4kpb4 | Engineering | How do bottling companies insert champagne corks into the bottles when they make them? | When the champagne is bottled, the fermentation process hasn't completed yet and the yeast continues to make carbon dioxide. The corks can more or less be pressed in (usually by a machine) like normal wine bottling. The fermentation process continues after bottling and this produces the carbon dioxide that dissolves in the "wine" to make it bubbly when the bottle is uncorked. At least, this is how it worked for my home made bubbly! | 3 |
hs2b62 | Biology | why is it human childbirth is so painful and risky, while other mammals seem to give birth almost effortlessly? | Other animals also need help. They show signs of pain. I have pulled many a calf and goat. Been present for horse, dog, cat, and sheep births. Both of my children were born all natural (not even an IV) it hurts but then the brain just kinda stops the pain. | 17 |
f7ucr5 | Physics | ; Why does running allow us to jump higher? I know this is probably simple, but I was wondering why we can jump higher while running, I can understand why it takes us further, but shouldn’t our height be limited to how much our legs can push off the ground ? How does running improve that? Thanks! | Without running, you are correct that your maximum height is limited to the vertical energy your legs can produce. But, if you start by running, you create a fair amount of kinetic energy, albeit in a horizontal direction. Nevertheless, at the end of the run, when your legs generate vertical force, a fair amount of the horizontal kinetic energy is redirected vertically. This redirected energy is added to the leg-based vertical energy, producing more height. | 2 |
8vakyg | Other | What’s the difference between shalt and shall? | shalt is 2nd person singular of shall, and as you might know, we usually speak in 1st person or 3rd person, so its just quite uncommon to use shalt, while shall is more common | 1 |
d664qm | Economics | what it means to "break up the banks." | a bank getting too large becomes a moral hazard; the bank is more willing to take risks because it knows that should it fail, the larger society will have no choice but to bail it out. Arguably this is what happened in the 2009 credit crash. breaking up the banks would mean splitting the largest banks into separate, smaller firms. This means they would be less likely to engage in risky loaning, because the government would be less likely to bail them out should the loans go bad. | 2 |
6culyq | Other | Why does the U.S. have different state driver's licenses instead of everyone just having a United States drivers license. If you move states and you have a drivers license already, you don't have to take a test again. All the laws are the same. So what's the point in not making it a universal license? | Separation of government. Some laws are governed at the state level, and some at the national level. Driving is on a per state basis. Think of it like this. Would you want to have the same driving laws in Alaska that you have in Texas? Completely different types of roads and weather conditions. | 7 |
clmsm6 | Mathematics | what’s the use of e constant and why is it needed it math | Euler's number (not the only name for it, but I'll use it since this is typed and using "e" might get confusing) is important for a lot of the same reasons pi is important. & #x200B; pi is important because it "just happens" to be the ratio of circumference to diameter. The number pi represents a fundamental ratio in geometry. We could maybe imagine a universe where it had a different value (though that would be...weird), but there would always be a number that has this property. & #x200B; Euler's number is important because it "just happens" to be the number whose exponential function has slope 1 when the exponent is zero. The number e represents a fundamental value in calculus. Again, maybe you could imagine a universe where its value was different, but there would always be a number that has this property. & #x200B; Both of those values turn out to matter in a lot of places because circles and exponential functions are important (in geometry, finance, calculus, etc). A neat fact is that Euler's number and pi are both related to trigonometric functions, and trigonometric functions are related to imaginary numbers, so we can construct the most famous version of Euler's identity: e^(i\*pi) \+ 1 = 0 | 2 |
5rr54i | Other | the controversy surrounding Betsy DeVos' nomination as Education Secretary | Simply put: Betsy DeVos has absolutely no professional experience that would qualify her for the role of Secretary of Education. | 5 |
87s1qf | Technology | Why is it that most things that use AA batteries have only 2 spots for batteries, as do most things with AAA batteries have 3 spots for batteries? Is that number a coincidence? Or do they do this on purpose? | It's done on purpose! 2 AA batteries produce 3V when in series with each other. This voltage is commonly used in low power electronics. Whereas 3 AAA batteries would produce 4.5V in series, this would be more commonly be used to power a motor or light source of some kind. But mainly the difference in number of batteries is moreso to do with the voltage requirements of the device to be powered. AA and AAA batteries both produce 1.5V on their own the difference being the power they hold. AA holds 2400mAh and AAA holds 1000mAh. So bigger number means battery lasts longer. | 2 |
hsui1g | Physics | When you open two windows on opposite sides of a room there will be a draft going through the room. What dictates the direction of that draft? I often open my balcony door and my front door to let fresh air into my apartment. I've noticed that the draft almost always flows from the balcony and out the front door. Shouldn't the direction be random? | Prevailing wind outside is pushing the air in one direction without the window on the opposite side there is nowhere for the pushed air to go so the air only moves when two openings are there. | 2 |
hljvd7 | Physics | Why is it that biking requires a lot less effort than walking, yet when the slope gets steeper, it's easier to get off the bike and push it? | Because when you're cycling uphill you have to constantly push the pedals hard enough (apply enough power) to act against (the slope-parallel component of) gravity and to overcome friction while maintaining a speed that allows you to keep yourself balanced, and if you use a very low gear (which makes it easier to overcome gravity) you need to spin the pedals faster to maintain that minimum speed. When you're walking, instead, you're only pushing forward against gravity for part of the walking movement, with the friction between your feet and the ground doing most of the work in the remainder of the time (there is a bit of energy expenditure to arrest the downward movement towards the end of each step, but it's not much and you're not pushing the bike then), and you can go at slow as you wish (and pretty much always go slower than the slowest you can go on a bike). Edit: typos | 17 |
8khjk4 | Technology | Why do clocks gradually become a minute or two off? I've noticed this phenomenon whenever I sync my bedside clock with the clock on my phone. My phone's clock is synced to the Internet, but my bedside clock isn't, and over time—about a month or so—my bedside clock will end up a minute or two faster or slower than my phone's clock, even without me touching it. Why is that? | Your phone's clock is set using the internet, which gets its time from atomic clocks. Your other clocks use some other form of timekeeping (for example, a quartz crystal oscillator) that is less accurate. Therefore the times will begin to deviate. | 3 |
emlv8h | Chemistry | Why when we stir a cup of coffee with layers of coffee sugar and cream they blended but Jupiter still retain distinct layers of different gasses despite millions of years of rotation. | Jupiter doesn’t have a giant spoon that sloshes the gases around much. If you dumped the sugar and milk in your coffee mug and then only spun the mug around, it would not mix well, either. | 2 |
6jw33w | Technology | how come software companies have to wait for hackers to find weaknesses in their system and not just figure it out themselves before rolling out a software package? | There is a more fundamental problem than others have mentioned. If my business goes offline because Windows had a bug that allowed a hacker to shut me down, I suffer damage, but Microsoft does not. Economically, the people who buy the software are the ones who have the incentive to make it hack-proof, but they have no ability to do so. The developers, who get to choose how much time and effort they spend making their software hack-proof, have very little incentive to do so. Until at least some of the economic harm caused by hackers falls on the companies who write the hacked software, they will always under invest in making their software bullet-proof. I am *not* saying they put no effort in, but ask any senior person in any software QA group in any company, and they will tell you that QA is underfunded in their company. | 8 |
gzz3eo | Other | Why are there so many bible versions? | What we consider the Bible was compiled from a variety of texts written originally in Hebrew and Ancient Greek. Then translated into Latin. Latin acted as a kind of defacto universal language in Europe during the Middle Ages and was spoken by the Priests and the Aristocratic class. This also meant that the average person couldn't read the Bible and had to take what was said to them by the clergy at face value. Once the printing press was invented Bibles were the first books to be mass produced. This included translating them into different languages like English, French, German, etc Each translation is slightly different due to variations in translations and loss of context. Then you have examples like the King James bible which was deliberately edited to reinforce the stances of the Church England. Not to mention the Mormon Bible which adds the book of Mormon at the end. There are several more modern translations as well, which are considered the most accurate in context. IE the were translated by modern speakers of Hebrew and Ancient Greek that had a better understanding of the underlying context. But even then some things are translated far too literally and miss the point entirely. The Number of the Beast for example 666 when read in the original Ancient Hebrew is clearly a tongue-and-cheek reference to Emperor Nero. Greek+Hebrew used letters for numbers like Latin. | 3 |
lnqz1i | Earth Science | How do robots that are outside earth send pictures to the earth? Is it the same system that allows us to send messages or phonecall each other inside the earth? Is it very difficult to send and receive stuff to/from outer space? | The ELI5 answer is yes it is the same system. Radio waves. ELI10: This system you use for messages and phones are all based on different parts of the telecommunications system and they too use different radio wave frequencies to talk to each other. Some wired and others wireless. You can think of the photos sent back from Mars, in theory, similarly to a picture message. The data is broken down and transmitted via radio communication and them reassembled once received here on earth. This difference is distance. Here on earth is takes only seconds to send a picture to a friend, while to and from Mars the data travels at the same speed but takes nearly 22 minutes to be received due to the vast distance between planets. | 2 |
9y5em4 | Engineering | How can the Voyager and other craft go to such extreme distance? How does it have enough fuel? Why can't we send humans like that instead? I'm curious about these pictures that I see all the time. Voyager or some other spacecraft sends pictures of distant planets, being some light years away. Even pictures of Earth looking like a speck of dust. How did it travel so far? How is this possible? For humans, I understand it would take tons of more specialized equipment but surely we can send them a great distance than the Moon. Most of what I say might sound very uninformed and downright wrong. So anything and everything related to this will be very much appreciated. Thank you for your replies! | In addition, at least in the general case, humans expect to return. That by itself doubles the need for energy for propulsion. | 20 |
5yu2ya | Other | Is there anything that says you can't cheat in a US election? If cheating was proven true, would it have any effect on the results? | It is illegal to vote multiple times. Illegal to vote under someone else's name. Illegal to vote in a jurisdiction you do not live in. Illegal to stuff the ballot with false votes. Illegal to take away votes from a competitor. And many other laws regarding voting. So yes there are lots of laws that say you cannot cheat in a US election. Doing so will result in you being arrested and fined, and there may be grounds for there to be a recount. If the person running is the one guilty of such a crime (such as stuffing ballot boxes) then they are removed from office and often arrested. | 2 |
o5bojv | Biology | How adhd affects adults A friend of mine was recently diagnosed with adhd and I’m having a hard time understanding how it works, being a child of the 80s/90s it was always just explained in a very simplified manner and as just kind of an auxiliary problem. Thank you in advance. | (ADHD sufferer here. Diagnosed at 35 at the urging of friends. Medication changed my life). ADHD is at its core a brain chemical deficiency. ADHD brains do not produce enough of the usual "happy juice" - the chemicals that, in short, make you happy. There's a lot of them. Human brains need this happy juice to encourage us towards normal human behaviors. Everything you want - food, fun, self-improvement, social activity, even sex, is driven by happy juice. Additionally, human brains make a low level of happy juice (which you get used to) to mitigate the sudden spikes when it makes a bunch of happy juice at once to encourage you to do something. ADHD sufferers don't make enough of this low-level happy juice. Just imagine the passive contentment that you feel every day plain *gone*, replaced by a nonstop feeling of boredom and pointlessness. This has the side effect of a very high incidence of depression (the comorbidity of ADHD and depression is ridiculous). But it also means that ADHD sufferers get *strongly* encouraged by anything that creates this happy juice. One of the things that generates this happy juice is thinking about interesting things. Boring things don't make much. But boring things are sometimes important. The bad news for ADHD people is that their brains will start rigging their behavior to ignore the boring but important thing to hyper-focus on the interesting but less important thing. There is also a certain continuity to this interest. It's a misconception that ADHD people are easily distracted - they're the opposite. Instead they are hyper-focused on a single train of thought and all the stuff other people think is important is what is trying to "distract" them, to no avail. The happy juice is too strong. This means a lot of impulsiveness. Imagine a starving man who only gets to eat every few days, while you get your regular meals. When food does arrive, the starving man is going to chase that food much harder than you. You're wondering why this fool is so obsessed with a few slices of toast, not realizing he doesn't get to eat the toast you have for breakfast literally every morning. Now we talk medication. Stimulants (we're not sure why entirely) suddenly make the ADHD brain produce happy juice. Stimulants have hours-long durations, so while they are in effect, ADHD sufferers suddenly have their happy juice deficiency eased. For a long-time sufferer, the effect can be quite dramatic. This is not perfect or universal - different people react differently to different drugs. The big two are methylphenidate (Ritalin) and amphetamine (Adderall). About 70% of sufferers will have a major positive reaction to one or the other. Look up there - does amphetamine ring a bell? If you watched Breaking Bad, you will know that this is (same name, different salt) part of the name of a street drug called meth. Meth also eases the deficiency on ADHD sufferers, though abusers tend not to be properly regulating their doses and can go overboard from the (mental) addiction to the happy juice. ADHD sufferers have a VERY high rate of addiction to meth, and this is progressively viewed as a desperate attempt at self-medication. If you're wondering if this might extend to addiction to other things, you're absolutely right. Lots of ADHD sufferers end up addicted to specific things of varying healthiness (sports is generally good, video games not so good, drugs pretty bad). The thing these addictions have in common is a proven source of happy juice that they've gotten used to. ADHD is not a condition I would wish on anyone. Even in the best case scenario it makes your life needlessly more difficult. At the worst it can compound with other disadvantages (poverty for example), making the combination impossible to solve without intervention. Keep in mind that no matter how difficult a life situation is, there's probably someone who has that *and* ADHD. Every time I look back at the difficulties I overcame, I wonder where I would be if I didn't have to deal with ADHD at the same time. A diagnosis and proper prescribed medication can be a literal lifesaver for us. For many of us it's the first time we feel like a normal person - and I mean this in the most primal, fundamental sense. It annoys me to no end that ADHD constantly gets maligned in news and media. There was a very important paper published about how lots of child ADHD diagnoses are wrong - this has had the effect of people suspecting adult ADHD is not real. I happen to be a straight-A student because I was obsessed with science, math and reading. But my professional life was basically so much hell keeping afloat that I tried to kill myself in my late 20s. Am on Ritalin now and things are finally livable. | 41 |
cqtafd | Engineering | For dishwashers, washing machines, etc: why does ECO washing take longer than the normal one (even 4+ hours)? Shouldn't it be quicker? | Heating the water is more expensive than anything in this machines, to save energy they have to run longer but with less warm water | 3 |
efvynh | Engineering | When watches/clocks were first invented, how did we know how quickly the second hand needed to move in order to keep time accurately? A second is a very small, very precise measurement. I take for granted that my devices can keep perfect time, but how did they track a single second prior to actually making the first clock and/or watch? EDIT: Most successful thread ever for me. I’ve been reading everything and got a lot of amazing information. I probably have more questions related to what you guys have said, but I need time to think on it. | The definitive story about this has already been written by several people much smarter than any of us. Over 200 years ago, the navigation of ships was a matter of intense government interest in England. The "latitude" was very easy to calculate. However, the "longitude" was based on time, so a very accurate clock was needed. The longer you were at sea, the more accurate the clock needed to be. Here is a 3-hour movie that explains the issue, and how it was solved. [ URL_0 ]( URL_0 ) | 14 |
6i844r | Other | Does Mars (and any other planets for that matter) have plate tectonics like Earth? I think my understanding of plate tectonics is a bit lacking at best. I always thought it was something unique to earth due to the water. Do other planets act similarly? Mars for instance. I just thought it would be crazy if stuff was moving about on Mars causing earthquakes and what not the way things happen here on Earth. | Having a liquid filling is not enough to cause plate tectonics. Venus, for example, has plenty of volcanoes and molten rock, but doesn't appear to have tectonic plates. A lot is still unknown about the whole process. One theory is that plates are pushed up by magma that rises up through cracks between plates, and slide away as their centre of gravity is tipped out of balance. Compare it to broken sea ice that moves about on the waves. The initial break could have been caused by massive meteor impacts on weak spots in the earths crust. Small cracks become big cracks, and they have been here ever since. Because most water on earth came here by meteor, you could argue that water did play a role. But not in the way you might think. Currently, earth is the only place in the universe with confirmed plate tectonics. | 3 |
8z44t1 | Engineering | Why can’t the Panama Canal just dig a deep canal and remove the locks? | Oceans are in constant motion. This means that they surge up and down. Because the Pacific and Atlantic Ocean aren't connected anywhere *but* the Panama Canal, you're channeling the entire difference in wave height at any given time through the canal. Without the locks, that means you'd mostly get a fast running channel from the Pacific to the Atlantic... that reversed from time to time to run the other way. Navigating that channel would be an enormous effort. Instead, they install locks to prevent the water from flowing unchecked from one end to the other. | 2 |
6okby3 | Other | How jurors on long cases maintain a job and a steady income while the case goes on? I'm currently watching the O.J. Simpson case and in it they talk about the jurors being "locked up" in a hotel for ~280 days. How do they maintain a job or get a money? | Don't know how it is in the states but here (canada) you get paid a little for being a juror and your employer can't fire you for that reason. Plus if you are indispensable for your employer they will sometimes release you from jury duty. | 5 |
cisnon | Physics | how do motorcycles go from being upright to almost completely leaned over to back up again? | Once the motorcycle is moving, the rider pushes on the handlebars to lean the bike and to stand it back up. Push on the right bar to go right, push on the left bar to go left. That leans the motorcycle over. The harder and longer the push, the more it leans. The more it leans, the tighter the turn. Relax on the bar and the motorcycle continues to turn in the direction it's leaning. To stop the turn, push on the opposite bar and the bike stands back up. How much you have to push varies from motorcycle to motorcycle. A well set up motorcycle needs no control inputs on the bars to go in a straight line and once leaned into a turn will continue to turn at that radius until it's stood back up again. | 1 |
cubawf | Biology | can critters with exoskeletons (eg spiders, crabs, insects) feel things touching the exoskeleton? | Very ELI5 answer: Take any elongated item, like a needle, a pencil or such. Scratch the surface of your fingernail. You're feeling it just the same as these creatures do. | 9 |
5lml5v | Biology | Why is it that, during menstruation, the womb lining is broken down, only to be built up again almost immediately? | There are a few hypotheses about why humans do this more so than any other menstruating mammal. It could be to help flush out any miscarriages that may otherwise get stuck inside the uterus (humans appear to have a very high miscarriage rate compared to other animals due to chromosomal abnormalities), or the result of an arms race between the embryo wanting to burrow into the mother's blood vessels to get more nutrients and her body wanting to keep a distance between the two in case something goes wrong with the pregnancy. The thick uterine lining, in that case, would be a protective barrier between the mother and the embryo. [More info]( URL_0 ), though this source is not very layman friendly | 2 |
7urmbh | Technology | How does a mobile phone "try" to find a signal? Most of us have had a phone eat up a ton of battery when we were in an area with bad coverage because the device was working to find a signal. Isn't the antenna on it just passively receiving available cell signal? Could you make a stereo use more power by having it "try" to find a better signal on a radio station? | Battery life, as everyone knows, is extremely important for cell phones, so manufacturers do everything they can to reduce the power consumption. The phone has to 'listen' to the radio to see if a call or text message is coming in. When the phone handset has 'found' a tower, it's synced to a specific frequency and receives a very precise time signal from the tower. The tower (and network) tell the phone there's nothing for it. So, go to sleep for 1/2 second and then wake up and listen for 1/10 second. If there's anything for that phone it will only be sent during that 1/10 second. So the phone can turn its radio off and sleep 8/10 of the time and still receive a call or text within a second. If the phone hasn't 'heard' a tower and isn't synced to a time slot, it has to listen all the time. And it's constantly shifting between multiple frequency bands. So it is 'awake' all the time and can't sleep. Because it can't sleep, it uses the battery all the time, and runs down much faster. Here's a (non-ELI5) Wiki on Time Division Multiplexing: URL_0 | 6 |
b5tn0s | Biology | Can plants get their needed "sunlight" from artificial (e.g. normal LED room lights) source? Whats the difference between artificial light and sunlight from the point of view of the plant? So my house is "north facing" and doesnt get much light in some rooms but I like to have plants around (and be able to keep them healthy). I'd like to understand in simple terms whether they can survive and thrive with normal artificial light most of the time (e.g. there are a few windows but not always much light through them). If I'm at home during the day I would usually have an overhead light on, in order to have enough light to work at my computer (or whatever). Other than in the height of summer. Bonus question, can I use "colour adjustable" (e.g. Philips Hue which allows choosing any colour of light using its 'app') to help the plants? edited to add: I'm primarily asking about normal household lighting with possibly some additional lamps, rather than an "intensive growing" scenario. | Yes, the plant cannot tell the difference, as long as the light includes the colors (wavelengths) that plants most need, basically red light and blue light. | 3 |
86rov7 | Mathematics | the intermediate axis theorem | A rigid body that is not symmetric has three distinct principal moments of inertia. So it will always have a largest one, a smallest one, and a middle one. If you work out the equations of motion for rotations around each of these three axes, you find that rotations along the largest and smallest ones are stable, but rotations around the middle one are unstable. It’s easy to see if you just do the math. | 1 |
8wry29 | Technology | Why does power saving use grayscale? Companies such as Samsung use grayscale but doesn't that use more power than RGB? I thought so as gray is made up of all three elements but blue is just using the blue led? Why is this? | LCD screens have white backlights that are filtered through basically tiny colored foils. If you want red. You shut the blue and the green subpixels. And since the whole light comes from the backlighting, you basically shut out 2/3 of the generated light. With greyscale, all subpixels are „opened“ equally and you get the most of the backlight, alowing to dim it and save power. | 1 |
g48hg5 | Biology | what are the differences between ADHD and ADD? One of my best friends has ADD, I have ADHD. I've been wondering the main differences for a while now, just keep forgetting to ask. Thanks | Yep the three subtypes of ADHD (Attention Deficit Hyperactivity Disorder) based on the DSM-V include ADHD - Inattentive, ADHD - Hyperactive, or ADHD - Combined Type. My whole family is the inattentive type. Daydreamers. Always onto the next project without finishing the first. Our thoughts are more interesting than what’s going on around us. Hyper-focus on things we like but almost complete inability to prioritize, plan, and coordinate (unless it’s about something we and we alone are really into). Like when I take my ADHD meds, I will spend HOURS making spreadsheets, organizing, and making decisions. But I lose my creativity in the process. I’m an idea person OFF my meds, and on them I am a doer but I could really use a manager in either situation to direct me to the right use of time. Also anxiety. Worsening ADHD symptoms highly influence anxiety levels, so you start getting worse at getting things done, your anxiety starts getting worse, inability to make decisions results in paralysis of thought - being overly worried about the what-ifs that you can’t consider just trying something, so you throw yourself into time-wasting, distracting activities (reddit) and get even less done, and the anxiety increases more. Eventually people give up on expecting things from you and the anxiety goes away (but the guilt doesn’t). Oh yeah and you get used to people calling you lazy, distractible, and irresponsible. | 4 |
iu6mti | Other | please: Ayn Rand's Objectivism Philosophy EDIT: Thanks everyone! | Objectivism is as Rand described: "the concept of man as a heroic being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.” Basically this means man should act in his own self interest. Instead of asking “what’s my purpose in life” Objectivism would say, “You.” You are the purpose for your life, and creating is the best thing you can do. | 4 |
l7rxqv | Biology | Why is it safe to inhale noble gases I was watching hamilton's pharmacopeia and he was inhaling xenon and seemed to think it was pretty safe. As a layman, my intuition tells me inhaling anything besides oxygen is not safe. Why can you breath pure gases other than oxygen and be fine? | Air is a mix of gases, it's not just oxygen. Noble gases are almost completely non reactive so there is no toxic or caustic effect from them. Now if you only breath in a noble gas you will eventually suffocate, but a single breath is essentially harmless. | 6 |
hbfps6 | Biology | How can stomach acid be strong enough to dissolve thin razor blades, but stuff like corn and tomato skin can pass through seemingly completely untouched? | Sorry, what is this about dissolving razor thin blades? | 6 |
b73k42 | Biology | Why do all animals have natural animal instincts that allow them to nurture a child but humans need parenting classes and support when raising a child? | Lots and lots of non-human animal babies die due to neglect or straight up cannibalism so not sure what you’re on about | 5 |
80ezzn | Economics | When using a debit card, why do some merchants require me to enter a pin, sign a receipt, or simply swipe? Why is it that places like McDonald's can take your card and swipe for you without requiring you to enter a pin or sign anything but other merchants can require one or both of those tasks? | I can't remember the last time I swiped my card or signed a receipt. In the UK it's pretty much chip and pin or contactless. | 2 |
5xl43i | Culture | Why are so many US veterans homeless? Why are they in this position or how did they get to this point (generally speaking) | Lots of reasons: PTSD ain't no picknick. Some people signed up because they had no other option, turns out service didn't change that. Contrary to popular imagination, most skills learned in the military aren't valuable in civilian life. Polishing your boots, shooting a gun, and taking orders isn't valuable in a society where everyone wears sneakers, settles differences peacefully, and are free to make own decisions. Maybe you're lucky and learn to drive a truck or run a warehouse, but if you don't you're out of luck. After service you're in much the same situation as before, except you're older and have some bad memories. If you didn't have your life together then, odds are you don't have it now, either. | 43 |
7lapdo | Physics | Does the 2nd Law of Thermodynamics mean that with time our ecosystem with be more chaotic? 2) Second law of thermodynamics: In a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases. Equivalently, perpetual motion machines of the second kind (machines that spontaneously convert thermal energy into mechanical work) are impossible. | No. Entropy is something that is commonly misunderstood but it's a molecular phenomenon, it doesn't necessarily apply at higher scales. You can mix up a bunch of people with two colours of shirts in a room and ask them to sort into groups with the same colour shirts and they will be perfectly capable of doing that without violating any fundamental physical laws. Entropy is still increasing - they are converting chemical energy into heat, increasing the entropy of them and their surrounding. Entropy is *not* the same thing as a human interpretation of order. | 4 |
i63vs4 | Physics | About entropy and what we actually see Yes, entropy I observe, as a burning candle not ever being unburned and so forth, but what about all the living things we see on our planet? It is surely a more structured form of matter than before, and although I have heard explanations I haven't grasped the explanation of how in spite of the apparent structuring, entropy still increases. | The total entropy of the universe (or a separate closed system) is still increasing when life exists, which is the only thing that is counted in the law that entropy always increases. The sun spreads huge amounts of energy out which increases entropy, and life simply holds onto some of that energy for a relatively short period of time. Organisms also release heat when they consume food or just exist, which also increases entropy. There is also nothing in the laws of thermodynamics that say you can't slow down entropy to a near halt, just that entropy can never decrease. | 3 |
8z3g7g | Physics | Could the force of a hurricane affect the rate of Earths rotation? … and if so, how strong with that hurricane need to be for it to make a measurable change? | Alright, math time. So an average hurricane's radius is about 500 km and is about 15 mm high. Approximating it as a cylinder, that means that it is moving a total volume of about 11 million cubic km of air. With a density of 1.225 kg/m^3, that is about 1.3×10^16 kg or air. That's a big number! That is, until we consider the fact that the earth's mass is about 6×10^24 kg. Let's just assume that the earth is a uniform sphere (which it isn't, but it makes things easier), it should have angular momentum of about 5.8×10^33 kg m^2/s. So for the hurricane to actually effect the rotation, it should be at least within 1% of that, so let's just be generous to and require it to have an angular momentum of about 10^31 kg m^2/s. With a moment of inertia of about 3×10^27 kg m^2, our hurricane would have to rotate at about 3000 rotations *per second*. That is to the point where we can no longer calculate the wind velocity classically, since we get about 1.5 million km/s for the winds at the outer edge, which is about 5 times the speed of light, and since nothing can travel faster than light, this answer is wrong. So, we would have to use relativity to find the correct velocity. So essentially, for an average sized hurricane to actually affect the rotation of the earth, the wind speed would have to be very close to the speed of light, and that is under the most ideal conditions (that all of the hurricanes angular momentum comes from the angular momentum of the earth rotating). | 1 |
dp5rnw | Culture | Why do people say "quote unquote [the quote]" rather than "quote [the quote] unquote?" | I think it allows the listener to understand that "everything I say next belong in the quote", rather than listening intently just to hear the 'endquote' in order to then process what the quote was. | 1 |
b2505l | Technology | How does the ISS never run out of fresh air to breathe ? Since space has no air in it how can astronauts breathe fresh air inside the ISS? Edit: Thanks anonymous redditor for the gold! | **\[EDIT2\] This got a little more complicated the more I did research. So for a 5 year old:** The space station doesn't run out of air because NASA got really really good at recycling the things they already have on the station. They have some magic machines up there that can turn water into air. So then where do they get the water, you ask? From the astronauts pee, from their showers, from their sweat, from the humidity in the air. They turn that gross, weird water into drinkable / air-making-able water. BUT eventually they'll run out. SO they send up a fun little gas called hydrogen (which is a thing that's in water, but way way lighter than water and therefore cheaper and easier to send up) and they combine that with the stuff the astronauts breathe out (CO2) using yet another magic machine that makes water. **Full explanation:** Electrolysis of water (H2O) is the main method to generate oxygen aboard the ISS. Water is split into oxygen (O2) and hydrogen (H2). The oxygen is vented into the breathable cabin air system, known as the Oxygen Generation System, while the explosive hydrogen is vented externally. \[EDIT1\] Check the edit below, it seems like they don't vent the hydrogen anymore and instead reuse it to make more water. The station’s football-field-sized solar arrays are the power source to electrolyse the water. Each day the OGS continuously provides between 2.3 and 9kg (5 to 20lbs) of oxygen. The OGS is a component of the ISS life support system, known as ECLSS or Environmental Control and Life Support System, located in the US Destiny module. The Elektron system aboard the Russian Zvezda service module performs the same vital electrolysis service for the ISS crew. The Electron system was also used aboard the Russian Mir Space Station. Pressurized oxygen storage tanks replenished by visiting unmanned cargo ships provide a backup to the electrolysis method. Finally, the crew can also generate oxygen chemically by igniting Solid Fuel Oxygen Generation (SFOG) canisters comprised of lithium perchlorate. Each canister provides the oxygen needed to support one crew member for one day. From: [ URL_13 ]( URL_13 ) As for where the water comes from, after reading an article on URL_9 , it's mostly recycled. They have systems that efficiently gather all the water. This includes moisture in the air, sweat, urine, and shower water that was unused. ~~There's also apparently another Russian space station that has a large stock pile.~~ They don't usually ship more water from earth because it's so expensive but they can and do sometimes. The NASA article: [ URL_12 ]( URL_14 ) **\[EDIT1\]** I think the idea is the recycling is hyper optimal and also the water that is recycled is all drinkable. I just read some other article (which I closed out of) which mentioned the water tastes like bottled water, although it came from urine. Also /u/ubik2 just posted a good explanation of how the system kind of feeds into itself and how they can get around needing to ship up heavy water to the space station. > Since 2010, they’ve also been using the Sabatier reaction. That consumes the hydrogen from electrolysis and the CO2 from breathing, producing methane and water (which can then go back into electrolysis). This means you don’t have to keep shipping up a bunch of water. Unfortunately, that reaction needs more H2 than it frees (to make the methane), so we still ship that up. Fortunately, hydrogen is very light. As for "where does the nitrogen come from" which is necessary for the air, it seems like they ship that up there (couldn't find any magic processes that produce it). > One system is to have oxygen delivered from [Earth]( URL_7 ) via spacecraft. This oxygen is stored in external tanks; similarly, these spacecraft deliver [nitrogen]( URL_0 ) gas, which makes the ISS air supply. From [ URL_5 ]( URL_5 ) BUT it seems like you don't actually need that for breathing. Super interesting! > Nitrogen, a gas that makes up 78 percent of breathable air on Earth, is inert and can therefore be safely stored onboard spacecraft. Despite its high concentration within ambient air, nitrogen serves no particular physiological benefit to humans and only serves to keep the Space Station pressure at 1 atmosphere (14.7 psia). Prior to extra vehicular activities (EVA or space walking), astronauts purge nitrogen from their blood supply to prevent decompression sickness (“the bends”). It is neither important nor practical to reclaim this nitrogen. From: [ URL_8 ]( URL_1 ) **\[EDIT3\]** From /u/acorz on how often they fly out the resupplies (unchecked source but they mention that work at the [Johnson Space Center]( URL_6 ) aka NASA). > We fly N2 and O2 tanks 2 or 3 times a year. We fly most of our water once a year on [HTV]( URL_4 ). In 4 years, I've only seen small hydrogen tanks for a science experiments, not resupply. **\[EDIT4\]** /u/sharfpang has a really [awesome comment]( URL_3 ) explaining how the Sabatier process isn't actually *currently* used and that they do actually ship the water up. I'm actually not totally sure this is true but they sounded confident (and [this article]( URL_11 ) suggests Sabatier is used). BUT their comment goes into detail with the potential problems that come out of the Sabatier process and some other cool science stuff, so it's worth checking out. **\[EDIT5\]** Just a funny tidbit in this research is the Russian side of the ISS doesn't actually use their urine in the recycling process, but the US side does. I feel like I read it in a more credible source, but here's just a [random article]( URL_2 ) I Googled that says the same thing. **\[EDIT6\]** Alright back to business. So the plot thickens, /u/sharfpang sourced an [exchange thread]( URL_10 ) comment that makes it sound like Sabatier was a "success" which was actually a failure they silently decommissioned. | 9 |
a4e7ed | Biology | Why does getting a shot in the arm make your arm sore after a couple of hours? Meaning like a flu shot, or any other vaccine. | Obligatory not a doctor: When we get a shot, they are just sticking the needle into the muscle, they’re not worried about hitting a vein or anything like that. Your arm gets sore because your body is reacting to this liquid being in/around arm muscle that “shouldn’t” be there. You will look like an idiot, but try circling your arm around after you get a shot. It may help reduce the soreness by spreading the shot around, not just having a bubble of vaccine in the same pocket of muscle. | 1 |
a420ap | Technology | How do buttons on electronic devices have more than one function based on how long you press them for? Like when you want to completely turn off a smartphone you hold down the power button for five seconds, but pressing the same button for just one second simply locks the screen. The same for an iMac where the length of time you hold the power button changes what happens, and there’s (apparently) multiple outcomes depending on how long you hold the button for. Button, how you do so many different things?! | so it used to be that buttons would be hard-wired to a power source and physically either connect or break the circuit between the power source and the rest of the device. Nowadays, they are more complicated devices with pressure sensitive states that will tell a circuit or piece of software (depending on the design) how long the button is held down for before being released, and that will in turn run through logic that dictates what to do with that kind of key-press. Behind the scenes there is some bit of hardware or software that is programmed to do something like "wait for power button to be pressed, then start timer and wait for power button to be released or for 30 seconds to pass. If released and timer is under 5 seconds, toggle screen on/off. If released and timer is between 5 and 30 seconds, show menu. Else hard shutdown phone." which will either turn off your screen if you tap it quickly, present the on-screen "restart phone, turn off phone" menu if you hold it down for longer than 5 seconds, or hard shutdown the phone if you just keep holding it | 4 |
erqsfy | Other | Is there legal complication in copyright laws if the industry that copied the idea is in a different sales/service sector? I've dwelled in this strange but interesting concept for 2 hours so please bear with me if I sound idiotic haha. For example, if a restaurant copies an advertisement in a shoe company with the same artistic style, font and everything. Would the restaurant be held accountable under copyright laws despite one being a sales sector (shoe company) and the other being a food sales/service sector (the restaurant) | Most simply put, if it's decided the average customer would confuse the brands and/or it could adversely affect the other, it's an infringement. If not, then it will likely not be addressed due to it not affecting the other copyright/trademark (this sounds more like trademark law) holder. Assuming US intellectual property laws. | 1 |
6qomml | Culture | Is there an official IQ test? Also why do many people online seem to know their IQ but in real life I've never heard someone mention it? | There are official IQ tests that you can pay to have done. (Keen parents often have their children take them). People mention it online because they confuse IQ, which commonly tests pattern recognition and speed, with something that affects their logic or inherent knowledge. They believe that a higher number (100 being average) is inherently an indicator that they are more likely to be right, regardless of the situation. People who mention this in real life tend to lack the social awareness to know that the above is not true, and don't socialize as much, making them less common. | 6 |
e6psgp | Biology | if HIV originally came from chimps who got it from eating a smaller monkey and it's not transmitted by air etc like the cold. Why are we having such a hard time eradicating it in human hosts? | Are you asking about preventing transmission, or actually treating it/developing a vaccine, because those are different things. The reason why it's hard to prevent transmission is because people can be HIV positive for years and not know it, and thus inadvertently spread it to other people during that time, and then those people will be infected, not know, and spread to *more* people and so on. It's easy to not know you're HIV+ because there are basically no symptoms until your immune system is seriously compromised, which, as I said before, can take years. In western countries, transmission rates are down because of the availability of cheap, reliable, and accurate tests, public awareness, and easy access to things like condoms or clean needles. In a lot of other countries, HIV tests are hard to come by, and there's little or no access to things that reduce transmission rates and not much money for public awareness. | 4 |
5w6uns | Other | Why are American kids shows are dubbed in the UK? I had to watch Paw Patrol with my friend's little sister one day and I noticed that all of the characters spoke in a British accent. I remember Paw Patrol as being American, (Correct me if I am wrong) so why would Nick Jr. are having the need to dub the show to a British accent? I googled it and can't find an explanation. Also, are British kids shows (like Peppa Pig) dubbed in the US? | This is simply a method of translating geographical differences in syntax and terminology. Even though America and England share a demographic of the English speaking citizens, there are still just different words for identical things. Hypothetically, if a child in the UK is watching a program that uses the word "garbage" it could be captioned with the word "rubbish" to convey the point. The prolonged exposure of different slang causes this disconnect, which renders subtitles efficient, even if the differences are small. | 3 |
cus8iz | Physics | why there is no thunder when it snows but only when it rains? Or at least less thunder during snowing time. | You can also get thunder in the desert, caused by dust clouds generating static in the same way as rain drops do in thunder clouds | 6 |
5wvocj | Repost | Why is W called "double U" when it is clearly "double V"? | In the 7th century, the old English language was starting to be written in the Latin alphabet, but it had a sound that the Latin didn't, the W sound. To get around this, they doubled the U symbol to represent it. The following century, the "uu" digraph was replaced with the Ƿ (wynn) rune. This died out after a while and in the 11th century, the Norman (French) scribes reintroduced the "uu" digraph as a single, though jointed instead of curved, character, the "w." Source: URL_0 | 34 |
8zvcib | Other | Why is MGM Resorts suing the victims of the Las Vegas massacre? | It very much seems like a terrible PR decision. Legally speaking, they're looking for a declaratory judgment, which would be a way to get a court to state that they're not liable, without having to wait to be sued. That's not too uncommon in complex liability cases where there are a lot of parties who might have some stake in things, and people are eager to get things resolved. It could be negotiated instead, but if there are hundreds of possible claimants, this is a lot simpler. So, it makes SENSE, in a world where people are only looking at final legal outcomes. But in one where publicity and appearances matter - and they really do, for a company in a customer service business! - it's a disaster. | 2 |
ec3bea | Biology | How come the human genetic code can fit roughly in ~1.5GB of data yet we turn out such complex organisms? Furthermore, the code that separates us from other mammals can fit on o floppy disk. | The complexity of the universe does not need to conform to *our* understandings of what complexity and simplicity are. In other words, it is irrelevant whether something in the universe is complex or simple *by our standards.* Who cares that it's so complex to us? It is easy to imagine DNA being very *simple* to a far more advanced civilization. | 3 |
apvheg | Physics | In interstellar, when Cooper and Brand go to water planet (where 1 hour = 7 years on Earth) what would the scene look like from Romilly's pov? Assuming he had a zooming mechanism to monitor them in realtime? | One aspect that is often overlooked is that light will oscillate at a slower apparent frequency to. So any light reflected up from the surface will be strongly redshifted. Romilly would have to use a radio telescope just to see them. And light stroking the surface from above will be strongly blueshifted... Rather unhealthily. | 3 |
lhda4b | Economics | How do we know how much a currency cost next to the other? How and when we decided to give and compare the value of money? and, why does local currency have the value it has next to other currencies? E.g € vs $, or ¥ vs £ Does it have to do with resources? | The underlying reasons are complex and people debate that all the time - but the stability of the country, economic development, confidence all play a role. How is the value determined? Go to a bank and ask for an exchange. All the people wanting to exchange one way or the other means there is an exchange market - if more people want to purchase that currency, the value rises. If more people want to sell that currency, the value drops. Since there are people holding all these various currencies - their combined desires set the exchange rate. The exchange rate is like the price of a product, in this case it is the "price" of that currency. The price of a product freely traded is determined by demand and supply. | 2 |
5uks3a | Technology | How does an API work? | If I have a company that monitors how much Halloween candy people get, I can collect that number, save it to a computer in database, and make a website that shows everyone who wants to see that number. URL_0 Let's say I have a friend that wants to know how much candy people get on Halloween and Easter. He'll count Easter candy, but he doesn't want to go to my website each time and search for the number for Halloween each time by himself. I can create an API that gives him that number. As long as he tells the computer which year, he'll get the number of Halloween candy back. URL_0 /2016 So an Application Programming Interface is a way to talk with a computer program across the Internet most likely to see its database. | 2 |
gdfh6h | Psychology | Why do drill instructors at military camps make you scream at them even for a simple response? | It's also good for stress relief. You spend a lot of time in silence in bootcamps, being able to yell gets some of the anxiety out. | 4 |
8z5p6f | Culture | Why do so many languages have similar words for parents (mom and dad)? For instance: mom/mama and dad/papa in English, mama and baba in Swahili, 妈妈 (mama) and 爸爸 (baba) in Chinese, ummah/mama and abee/baba in Arabic etc. | because those sounds are easy for babies to pronounce. It takes awhile for a human child's motor control over their mouth to develop enough to make certain sounds. ma and pa are ones that are easy to make, and parents have an interest in their children being able to say their name. So ma and pa have become very common ways to refer to parents across languages. | 2 |
afv8nz | Biology | Why are diseases such as chickenpox and measles more deadly to adults than they are to children? I can't speak for America, but in the UK children are encouraged to catch chickenpox when they are young as they can recover fairly easily from the disease at that age but would be at much greater risk if they were to contract the disease as adults, but surely our immune systems get stronger with age? | Anyone who suggests "pox party" should be shot on spot. Vaccine exists and is safe and effective. It costs £130 though (for two shots) | 26 |
l3uego | Chemistry | Why does cheese taste salty while having almost no sodium? When I eat avocado toast, I put a lot of salt on it and it really brings out a salty flavor. When I eat a cream cheese bagel, it already has that same salty flavor even though the cream cheese I used doesn't contain almost any salt. Why is that? | Do you know the brand of cream cheese? Low sodium doesn't necessarily mean low salt. Potassium salts taste salty without the Sodium and is pretty common as a substitute. So it's likely there's either this, or something else being used as a salt substitute. | 3 |
8nk4pt | Mathematics | How is 0^0=1? | One way to look at it is through combinatorics: x^y is the number of of ways to pick a list of y items from a set of x items, with repetitions and with order (ie the order you choose matters, and you can choose each item multiple times). If you have to pick a list of 0 items, there's only one way to do it - an empty list - no matter how many items you have in the set. | 2 |
ipeaag | Other | How are business people who bankrupt multiple businesses still able to open businesses? How do they keep getting loans for new businesses to run into the ground? Does it lower their personal credit score? | Many people don't understand that the US Bankruptcy Code is actually intended to serve as a positive and encouraging tool to save a struggling business. In the world of business, taking advantage of its provisions is not an embarrassment. Many Americans seem to think it is, but it is not. A person may never file personal bankruptcy, yet be associated with corporate bankruptcy multiple times. A corporation is a separate legal entity from a person, so a corporation going bankrupt does not automatically impact the personal assets, other than the value of their investment in the company's stock, or credit score of its owners or shareholders. The most important point: A chapter 11 bankruptcy is not the end of a business. It’s a strategy for eliminating or reducing debt, using the courts you work with lenders to show that your company, while in trouble now, still has profit potential in the future. Chapter 7 bankruptcy is different. In a chapter 7 bankruptcy the company's assets are sold to pay of creditors, and the business is closed. If there are not enough assets to pay the creditors, well... tough. However after closing a business, there is no law preventing a person from incorporating and starting a new business. And as long as more of your businesses make money than fail then you can keep going. | 2 |
5zsv39 | Biology | Which doctors and nurses work in the Intensive Care Unit of a hospital? Do they all have to be experts in everything? If the most high risk cases come through the ICU, are there specialists in each area of medicine working there? | No doctor is an expert in everything. A patient will receive care from the most relevant doctors. An ICU will have doctors with a variety of specialties. | 2 |
jn0elo | Biology | Why is excess fat stored in places like the belly and buttocks, as opposed to other parts of the body? | To keep it close to the centre of gravity but not interfere with pregnancy for females. If, for instance, it was stored in the lower legs, it would need more energy to swing them while walking. Similarly for the chest which needs to freedom to move when breathing. | 2 |
63thb7 | Economics | How does inflation actually work? Do we really have 30% less spending power/dollar now than we did in 1970? I read somewhere that today the dollar has 30% less spending power than in 1970. What does that really mean? How is it like that? Why is it like that? | It sort of means that. Your grandparents might have said "back in my day you could buy a loaf of bread for a nickel!" There's truth to that, today a loaf of bread cost $1-$3 or so. However back when the Model T (first mass produced car) was being made they paid their workers $5 a day and that was a very high paying job. Today people get paid $7 an hour due to minimum wage laws. So inflation only gives part of the story and isn't really a bad thing. Inflation is generally under control of the Federal Reserve and they try to keep it around 2% or so. In doing so goods and products rise in price by about 2% and due to that workers ask for a 2% raise to meet that price, which in turn can make prices rise again etc. Really what you need to look at is the median salary and a standard 'economic basket'. The basket is a term that basically means take a bunch of standard stuff people have to buy each year and compare that year over year. If the basket is rising in price faster than the median salary we have a problem. | 4 |
nd2bsn | Engineering | forgive my ignorance but why aren’t all airplanes equipped with parachute or something to slow their decent if something fails? | A parachute large enough to "safely" decelerate a plane would be extremely cumbersome to install, maintain, and carry. Many times when things go wrong with the plane, it can still glide. Catastrophic plane crashes are usually in situations where a parachute won't help either. If a plane loses engines a few seconds after takeoff, there's not enough altitude for the parachute to deploy before the plane hits the ground again. If the plane loses control when landing, it's the same problem. Instrumentation errors means that the pilots don't know they're flying into a mountain/the ocean, so they wouldn't think to deploy the parachutes anyway. A parachute is only really useful if the plane has a catastrophic, structural failure, like a wing falling off. These kinds of things are much less common than other failures, because the strength/structure of the wing is (relatively) simple matter, compared to the control and power systems of the plane and pilot training. | 5 |
gzasqy | Biology | If the female orgasm is much more intense than a male orgasm, then why is the female sex drive less intense compared to the male sex drive? | female sex drive is not less intense than male sex drive, there’s just a bunch of factors that prevent them from acting out on it (like threats of physical violence ahem) | 4 |
5wssv7 | Engineering | What prevents water from flooding houses with chimneys | Chimney caps are the USA norm, think of a metal umbrella. Most cities specify how much larger the cap has to be over the hole. Now in some countries baffles are the norm. Where the water coming down the hole is directed outside but the smoke rising up can maneuver around the baffles to rise out. I'm an American home inspector. | 2 |
a8q2sq | Physics | Why does dragging a scissor along a length of ribbon cause it to curl? Wrapping gifts yesterday and currently watching *Elf*... | This is actually a well studied phenomena and the reason is pretty cool. Basically you are stretching one side of the material more than the other side and that deformation persists after you run the blade down the ribbon. Since one side contracts more than the other side it tends to curl naturally. | 3 |
63gz83 | Repost | Why is it illegal to use chemical weapons during war but it's perfectly okay to bomb, shoot, stab, drone strike and beat someone to death in the same context? | Chemical weapons have other issues associated with them (such as use against civilians), and beating someone to death slowly would be considered cruel and isn't typically allowed unless there was no other reasonable way to deal with the situation. Bombings might sound bad, but many people hit by bombings are killed pretty quickly. Chemical weapons often kill slowly and in am agonizing way. | 3 |
a6x02z | Physics | How does the sun burn in a non oxygenated environment? I don’t know if I’m dumb or something, how does the sun burn with a lack of oxygen? | It doesn’t burn like fire. It’s essentially a giant nuclear reactor. The gravity in the center is so great that it smashes hydrogen atoms into heavier elements... It’s more like a super massive nuclear bomb going off and not like a giant campfire. It’s obviously more complicated than that, but the short answer is that it’s nuclear fusion and not combustion. Good question though 😊 | 4 |
64exf8 | Biology | Why so many people have nut allergies? | URL_0 Studies are showing that the lack of exposure of peanuts at a babies age is looking like the cause of the rise allergies. I also suffer from this. | 2 |
614q6k | Other | Today the Koch brothers offered millions of dollars to every congressman who votes against the new health bill. Why did the FBI not immediately arrest them for bribery? | The American word for bribery is lobbying. It is perfectly legal to bribe politicians in the US, with certain constraints to ensure the money paid is classified as lobbying. | 16 |
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