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Do animals feel the effects of time-zones to a noticeable degree? If so, what kind of wild animals naturally change time-zones (migration, general movement patterns, etc.) and how long does it take for them to really 'adjust'? | There are tons of migrating animals that don't give a hoot about our time definitions. Domestic animals probably do have issues with jetlag just like they have issues with daylight savings time. They are conditioned to get fed or their owner's arrival at a certain time of day. My dog knows when it is time to get fed and is very vocal about it. DST screws her up for about a week. | Ehh, I think it's probably just another one of those common animal misconceptions, like "bats are blind", "goldfish have no memory", "ostriches stick their head in the ground when frightened" etc. etc. If I leave for 15 minutes and come back, my dog doesn't really react. Just looks at me from wherever she's laying down. If I leave for 5-6 hours and come back, she's way more excited when I come back. And then of course you have all those videos of war veterans returning home to their dog going absolutely apeshit with excitement. I'm fairly certain they do have a sense of time, might be slightly different than ours, but they do seem to be aware of the passage of time in the same way we are. |
What are the differences between nodes, threads, cores, and CPUs? | A thread is a single set of instructions, possibly running in parallel or concurrent with other threads. The concept of 'cores' and 'CPUs' is a bit blurred. By convention, a 'CPU' is a physical device that contains one or more 'cores'. Each CPU core can run one or more threads concurrently. The idea of a 'node' is really application specific, but it's usually recognized as a single configured component in some kind of distributed application system. | CPU (as its name implies) refers to the actual processing unit or thing that does the various computation we want it to do. A CPU core is just referring to a distinct one of these units so when it says “quad core” there are 4 of those units inside. A thread is a theoretical programming concept of a “task” or some thing you want to do. A thread is a task that is being done within a computer program, that is, they share memory. Most of the time when talking about threads you’re talking about an application which runs multiple threads simultaneously: a good example of this is having one thread manage the interface, while another does work for the user. This is different from separate programs which use separate memory. TLDR; a cpu core is something that does things for you and a thread is a task that a program performs, generally separately from its “main execution path” Source: software engineering student Edit: added some clarity to the end |
Spin of an electron. What is it? Why can there be only two electrons with opposite spin in an orbital? What does “opposite spin” even mean? | A spinning magnet produces an electric field. Electrons produce a similar electric field so they were said to 'spin'. We now know electrons are not physical particles that spin but the term has stuck. Electrons produce a magnetic field as if spinning. Some do it as if spinning clockwise and others as if spinning counter clockwise. So we say they have opposite spin. Each electron is paired with one that has the opposite spin. This makes the total spin balanced. When an electron has its spin altered, its paired electron instantly alters its spin to match no matter how far away. We do not know how this can happen but it does. So to sum up: we know electrons exist, have magnetic fields in one of two directions, and are paired. We don't know what they are, how they produce a magnetic field, or how pairs are linked. We use the term 'spin' even though it is inaccurate because we have no better term. | Electrons (like all particles) have a property called spin that represents an intrinsic form of angular momentum and gives some particles, like electrons, an intrinsic magnetic moment. Paired electrons always occupy opposite spin states, so the spin magnetic moment cancels out unless there are unpaired electrons. |
What part of the brain induces feelings of paranoia and anxiety under the influence of psychedelic substances? | THC and other cannabinoids work on CB1 receptors in the brain. These receptors are located presynaptically and inhibit neurotransmitter release in both glutamatergic and GABAergic cells. GABA is the main inhibitory neurotransmitter. If GABA effect is increased, as by benzodiazepines, e.g. Valium, a decrease in anxiety is observed. Depending on many factors, cannabinoids can cause a decrease in GABA release leading to anxiety. This effect is generally opposed by cannabidiol (another component of cannabis), which clears cannabinoids and may have intrinsic anxiolytic effect. To answer the question of what "area" of the brain mediates anxiety, I would say amygdala, but that is an oversimplification. | The endocrine system regulates your flight or fight response, releasing various chemicals that attach to your receptors and make you feel scared. Paranoia is a reaction to fear, such as is anger. If there is no immediate threat, your brain is going to rationalize your fear. It's why we get pissed when someone pulls out in front of us, or laugh when we get a jumpscare. It's our brain rationalizing fear into something we can process consciously. Boo! You could have anxiety or something, but cannabis will also cause random paranoia even when you haven't smoked it in a while. Good luck. |
Why did the Soviet Union invade Afghanistan? | First of all, the pictures you saw are misleading. Afghanistan wasn't some amazing modern country in the 50s and 60s, those pictures were just of the rich elite. As to the Soviet war in Afghanistan: a communist strongman took power in a coup in the 70s, and naturally the Soviets supported him. He was a brutal person, however, and quickly lost the support of much of the country, especially due to his attacks against religion (hence, the birth of the original jihadis, the mujihadeen). When he was about to fall, the Soviets invaded to prop up a Communist government while getting rid of him. They failed as well, in no small part due to the US government giving the mujihadeen weapons, and the Taliban, which was one of the most powerful jihadi groups, was able to take control after a years long civil war. Then the US invaded after 9/11 because the Taliban gave safe haven to Osama bin Laden, and the country is still in a state of war. | *This prompted me to ask another question about events preceding this. I think it is a separate discussion. I'm getting the "you're either a brand new user or your posts have not been doing well" error, neither of which is true, and I have not posted here for 6 months. Could a mod or another user post this question?* > ###How did a communist regime gain control (however briefly and tenuously) in Afghanistan in 1978? > Given what we know of the country today, the idea of bringing atheistic communism to such a old-fashion Islamic people seems absurd and bound to have tragic consequences. There has been a lot of reporting on the aftermath, from the Soviet invasion to the invasion after Sept. 11th. However the most perplexing part is how the Reds gained power in Kabul, regardless of Soviet aid. > How did this movement get as far as it did? |
What is Game Theory? | Game theory is the mathematical study of strategies. If you're playing Monopoly one day and decide you want to work out, mathematically, exactly what the best decisions at every phase of the game would be, then you would be creating a work of game theory. It doesn't have to be a board game, though, just any situation where people are making decisions in pursuit of goals. You study the situation, the odds, the decisions people make, work out which would be optimal, then look at what people actually *do*. So the situations game theory might study include optimal betting strategies in poker, or nuclear weapons deterrance strategies between nations, applying many of the same concepts to both. | It is an example of a complex system that derived from very simple rules. You are right, it is more of a simulation rather than a game as such. |
What is Game Theory? | It is the mathematically study of adversarial decision making. You have some situation, where participants have competing goals and make decisions based on reaching their goals and preventing others from reaching theirs. Game theory allows them to devise an optimal strategy, taking into account the other player's desire to win as well. | It is an example of a complex system that derived from very simple rules. You are right, it is more of a simulation rather than a game as such. |
What is Game Theory? | Game Theory has nothing to do with what you're talking about. Rather, it's about setting up 'games' where there are specific rules and each participant has clearly defined interests - and then analyzing what the best strategies are. The Prisoner's Dilemma is the classic example. You've got two criminals who conspired to commit a crime. The authorities are questioning them independently. If one rats out the other, the rat goes free while the other criminal gets 10 years. If neither rats the other out, they both get 2 years. If both rat each other out, they both get 5 years. (The numbers are arbitrary in the version here) The question becomes: should the prisoners rat each other out? Game Theory attempts to answer that question quantitatively. | It is an example of a complex system that derived from very simple rules. You are right, it is more of a simulation rather than a game as such. |
How do cashback credit cards work? Do you just get money for using the credit card? That doesn't seem very smart | Yes, that's how they work. Credit card companies charge businesses about 2-3% to process transactions, they pay out 1% to customers and the 1-2% is their revenue (plus all those huge interest charges for customers carrying balances). Many card also have annual fees, especially if the rewards are more generous than 1%. And many of the offers are not actually costing them the full 1%, i.e. they can buy airline miles wholesale, or partner with gift card companies and pay a wholesale amount for the gift cards. | in the US, many "debit" cards have the functionality to be run over the credit card's networks. This allows for usage in situations where a merchant does not take [traditional] debit cards To the consumer, there is little difference. Press credit, and you will probably have to sign for it. end of story. Press debit, enter your pin, ask for a "cashout/cashback" if you want to, and thats it. Either way, your money gets deducted from your account. On the other hand, any "rewards programs" usually require being run as "credit". Some banks charge a large fee to the cardholder if a card is run as "debit" For the merchant, its a story of fees. When a customer charges as credit, the credit card networks (visa/mc/etc) will charge their normal fees for credit cards, which is usually percentage-based. Debit transactions are usually a flat, but rather large (often in the $0.20ish range) fee (this is one reason why cashbacks are allowed over debit) |
How exactly do fitness wristbands such as the Jawbone and the Samsung Gear Fit track my amount of time in "deep sleep?" | They are able to track very small movements of your wrist. When you are sleeping deeply, your body doesn't move at all. It's a phenomenon called "sleep paralysis". The tracker software notes that at night you stop moving, then you stop moving at all. It is during those periods of virtually no movement it assumes you're in "deep sleep". | Hope this helps- "In sleep mode, the UP registers more subtle movements. In essence, it acts like an actimetry sensor. These sensors register a person's movements as they rest and sleep. The UP system analyzes the data by processing it through proprietary algorithms. The result is a record of whether you slept like a log or tossed and turned all night long. Sleep and fitness are related -- a good night's sleep can help you reach fitness goals faster." Reference: _URL_0_ |
When will be able to harness the power of lightning? | Probably never! Thunderstorms only occur in a given area a few days out of the year and only last a few hours. In much of the world, months will go by without any lightning striking, and in some populated places of the world there is virtually never a thunderstorm. The unreliable nature of lightning makes it impractical as a source of energy, so the technology will probably never be developed. If your question is actually "could we produce the technology, and if not, when will we be able to?", I'm afraid I can't answer that. | Technically speaking this wouldn't be too difficult, we have the technology to do it today. The problem is that despite looking awesome, there isn't that much energy in lightning. You can see the calculations [here](_URL_0_). For comparison, that's the equivalent of about 1 gallon of fuel. |
At the airport recently I saw a design for the winglet on the end of the wing I'd never seen before - one fin up, and one down. We have had at least 60 years of jet airplane design why hasn't the optimal wing design be found already? | We’ve only had like 20 years with wind tunnels, computer modeling, and expensive enough oil to make the pursuit of the absolute most efficient wing tip design worth the up front cost. Add to that the average fleet age for the Airlines (this varies depending on which specific airline) is like 14 years. So many aircraft flying passengers today are 20+ years old and we just don’t do ground up redesigns on planes that often. The 787 represents some huge leaps in technology and efficiency as the most recently designed operating passenger jet | It took a year to design fighter planes when they were essentially a gun with wings and an engine. The capabilities of modern fighters are so advanced, the designs are so perfect, there's a razor's edge to improve upon in the the current crop of fighters such as Russia's T-50. Essentially you need to design absolute perfection, flight test it, maximize payload while improving maneuverability, all the while designing around the weakest link, which is the human pilot who can withstand far less G forces than the plane itself. It was easy to design a gun with wings when that was the only requirement. |
What is the point of a conductor in an orchestra when everyone knows what they are playing? | In addition to keeping it all together during a performance, most of the hard work a conductor does is during the preperation that leads up to the performance. It is the conductor that usually decides and applies what the musical details are. | 99% of what the conductor does happens outside of the performance. He selects the music, arranges the music, organizes rehearsal, manages the musicians and basically does everything required to put on the performance. The part where he waves his arms around, that's just the culmination of many months of works. That is important too, he set the tempo and cues the musicians, but compared to the rest of what goes into preparation, that part is minor. If the conductor was ill, an reasonably skilled assistant who has been involved in the process could take over baton duties without losing much. |
How do helicopters with coaxial rotors and no pitch control turn? (Like on some rc copters) | Yes, it does. These little helicopters are able to rotate the blades independentally, and rotates by slowing down one while speeding up the other, creating unbalanced torque. Real coax helicopters are a little different. Their blades always rotate in sync, but by changing the collective pitch on the rotors in opposite directions they can produce a torque in either direction. | The angle of the blades of the main rotor can change mid-revolution, so that they can be more flat at the front, and at a higher angle at the back, creating more lift in the back and tilting the entire helicopter forward. Helicopter pilots also have another control available to them: the collective, which changes the average pitch of the rotors, allowing them to control lift. |
How are bouncers allowed to assault the customers they are 'throwing-out'? | They aren't... but they are allowed to defend themselves and to remove you from the private property *which they are hired to remove you from*. 99% of the time that means calmly escorting your drunk ass out of the building... but once in a while that means physically removing you by force. If you're being thrown out, the correct thing to do is to politely leave the establishment in a calm and orderly manner. The minute you start getting belligerent *you* are the one creating a situation. | Part time bouncer here. In my state to be a bouncer, you get licensed as a private security, that coupled with citizens arrest laws provide some level of legal protection. If I use force on someone, it has to be done exactly by the book. Either in defence of person or property, or in the course of a lawful arrest. All that being said I carry half a million dollars worth of insurance to protect me from any civil suits. |
How can scientists accurately measure the populations of insects? | Look up malaise flight traps and pitfall traps. These are two common methods for collecting insects and the data gathered by them can be used to explore the incidence and abundance of the species. I use pitfall traps to estimate the abundance of native ant species in communities that are undergoing invasion by the invasive tawny crazy ant. | In biology, where a species is either widespread, or for some other reason, counting individuals exhaustively is too difficult, numbers are calculated from exhaustively surveying a set area of habitat then extrapolating based on area of known territory. E.g. A bird species has confirmed sightings in 10 different areas that correspond to its known habitat. The combined area of these 10 sites is 1000km^2. Biologists sample 10km^2 and find 20 individuals and so the population is estimated at 2000 individuals. |
Now that science has likely confirmed the existence of the Higgs Boson/Higgs Field, are we any closer to gaining a complete understanding of how gravity works at the quantum level? | No, the Higgs boson doesn't really relate to gravity at all. | It's not that gravity doesn't work on the quantum scale, it's that we don't fully understand it at the quantum scale, and is often not relevant except at extremely high energies (like, things interacting strongly enough to form black holes) that we can't access experimentally. The electrostatic attraction between electrons and protons, for example, is about 10^40 times as strong as the gravitational attraction. Some of the smallest-scale systems where we've been able to probe gravity experimentally include coherent neutron states in Earth's gravitational field, and measuring quantum interference of freefalling atoms. These experiments generally involve quantum particles in a field that can be understood classically (Earth's), rather than a necessarily quantum source of the gravitational field. |
What is the point in professors making tests so hard that you only need a 20 or 30 to pass? | The general idea is that by making the test so hard no one can get all of the questions right, you are able to accuratly assess how much every student knows - getting a 100% on a test only shows you a student knows _at least_ that much. | > you might be studying a lot for something that doesn't show up on the test The goal is not to pass tests: the goal is to acquire knowledge. Tests and exams are just there to prove you've actually studied to the required standard, but you're not supposed to ignore stuff in the course that doesn't come up in the test. At university level, you're trusted to understand this very important point. |
Why does the bottom bun of a cheeseburger get so much smaller than everything else as I eat? | You are most likely angling your burger 'up' into your mouth. Unless the burger is level with your upper jaw, the burger will degrade like this as you eat it: _URL_0_ Edit: The reason most people slant the burger down away from their face is so that if anything slides off, it falls onto the plate instead of on the individual's clothing or face. | I believe this image explains it well. The bran and germ are removed from the grain in white bread. You're giving up more fiber, B vitamins, etc. _URL_1_ |
What were the strong points of supply or strategy for the German army in WWII? | For supply, the german rail system was quite resilient to Allied bombing. They were short on triangular junctions, but were able to repair most traffic blockages in short order. Specialized units were created for such work, and manpower was also requisitioned from local sources. Only at the very end of the war did German train service break down, and this was despite the paltry resources allocated to its defense or expansion. Christian Wolmar covers this in depth in *Engines of War*. | /u/SMIDSY is spot on in his description, but if you are interested in more specifics, there is a 1943 War Department pamphlet that details German squad level infantry tactics titled *The German Squad in Combat*. I found a copy hosted online [here](_URL_0_). |
If species is defined as a group of organisms able to produce offspring with each other, how do biologists classify species that reproduce asexually? | Turns out there are lots of different species concepts and not a single concept that works for every species. You are describing the 'biological species concept', but species concepts exist that define species by their role in the environment, their physical appearance, their evolutionary history, etc. Many of those concepts work well for asexually reproducing species. Ultimately, scientists go by the concept that works best for the group they are studying. | > I understand that the big definition of distinguishing one species from another is that they can't mate. actually it is when they can no longer produce fertile offspring for example a horse and a donkey can produce an infertile offspring |
Did alliances make WWI global? If not, what did? | I would say that alliances made it pan-european; the fact that all of these european countries also had empires stretching around the world made it global. Also, there was plenty of actual fighting around the world, especially naval conflicts. | A world war requires two alliances that are of roughly equal strength. That doesn't exist. The only people who are seriously saying that another world war is around the corner are those who are not at all well versed in history or geopolitics. Seriously, don't worry yourself overly about it. |
How can some one get a bachelor's of science in nursing degree and make 75k to 100k per year, but some one who goes on to get their masters and starts teaching would only make 30k per year. | Because labor is a resource that's subject to the laws of supply and demand. I know a lot of people with teaching degrees, and they're struggling to find jobs, because teaching is something that a lot of people want to do, but the job market can't support them all. From an employer's perspective, this means that for any given job opening there are tons of people willing to fill it, so you don't have to offer a high salary as an incentive for someone to work for you rather than a competitor. | (As someone who is a paramedic, knows more than a few people that did the jump up to RN) Nurses have a lot more A & P and clinical knowledge than paramedics. Also relevant is the relative youth of EMS as a field. There are still people working who were around for when EMT and paramedic training became a standardized thing. Nurses have been doing there thing for a lot longer, so of course it's a more established career path. |
Why do people have different "types"? How are our ideas of attractiveness created? | A lot of the characteristics we are attracted to are from basic instincts in our brain. Hour glass figures on women are representative of a good body for childbirth. An upside down triangle body on a man is representative of a physically strong man, who is resistant to disease. Some people are attracted to different types due to genetic variation i.e. everyone is different, some are more than others. | The only part i have insight for is what makes them attractive and possibly why. We find symmetry attractive and we tend to be attracted towards people of a similar attraction level (10s like 10s, 2s like 2s). Hope this helps. |
Why do sour candies tend to cause tooth aches and infected/inflamed taste buds? In addition, is this a condition or a general phenomenon? | Sourness is the effect of acid. That acid can cause damage in the same way that lab acids like HCl you used in school can. The symptoms you're describing are those of damaged tissue. Basically chemical burns. | Gating. The receptors on your tongue and the neurons in your brain need a moment to "re-charge." It would be a waste of resources to have them continually fire, as you already know that what you're having is sweet. If you have something sour, it will hit the part of your tongue saturated with more sour receptors, etc. When something sweet hits the tip of your tongue it sends a signal to your brain, in the gustatory system. There is a chemical reaction where by potassium ions go inside your neurons and sodium ions exit the neurons. This creates a voltage difference (electrical charge) and that is what causes the "sweet" sensation in your brain. However, if you have something bitter, sour, etc, after something sweet, you will feel a greater sensation, as the difference between active cells is greater. |
Quantum Field Theory - help in understanding spin? | Spin is not really different between regular QM and QFT (=relativistic QM). You have some rotational symmetry, and spin describes objects with rotational symmetry. Adding special relativity adds extra concepts like chirality and the notion of massless particles (plus helicity), but the way massive particles carry spin in relativistic QM is not much different from non-relativistic QM. | Basically it's the idea that for each particle with a given spin (electrons have a half, photons have one, etc), there is another particle with a spin that differs by one half. Some processes might occur differently if, for example, these particles were being created, but there hasn't been any evidence of that thus far in the LHC experiments. |
Why do "No shirt, No shoes, No service" signs not include pants? | If you aren't wearing pants you are getting arrested. It's necessary, of course, so much so that including would be overkill. | A few reasons: 1.) Going commando while wearing denim is pretty damn abrasive on my boy-parts. I can't imagine how bad it would feel for a girl's private bits. 2.) Poop stains. **Everyone** gets them. You know that hot girl that sits next to you in class? I guaran-goddamn-tee you that she gets skid marks in her undies. 3.) Ever have your pants fall down, or be pantsed? Need I say more? I think you get the point. |
Does any other government in the world have publicly funded statues, memorials, etc of any previous governments of that country? | While this isn't limited to the U.K., just using that country as an example you will find many statues & such of nearly every prior ruler who's ruling family was removed from power. You even have Oliver Cromwell, considered a regicidal dictator by many with a statue right outside of the House of Commons. Right next door you have the eventually overthrown Plantagenet's Richard I statue facing the House of Lords entrance. The actually deposed Richard III has a public statue in Leicester. Along with the monarchs, there's Roman statues (Bath for example), Memorials & statues for the various failed Scottish uprisings (the very large Wallace Monument being the most prominent but far from the only one). These are just a few of many examples. | _URL_0_ All world governments are tracked in terms of their relative level of regime autocracy. There are lots and lots of them, unfortunately, that are best classified as 'regimes'. |
Would a U-Shaped coil be viable for inductive charging? | Induction of magnetic fields works on the principle that moving charges (electricity in a wire) cause a magnetic field in the enclosed area of the wire loop, a consequence of [Maxwell's laws](_URL_0_). Thus, to get the best possible magnetic yield out of your electric current, you want the shortest possible wire loop and the largest possible enclosed area. The shape with the highest area-to-circumference ratio is the circle. A U-shaped coil, conversely, is one of the worst ways to make an inductive coil. The enclosed area is tiny, only the area between the wires in the U-shape would have a magnetic field generated inside it but the 'interior' of the U would be void. Thus, this is not a good shape and you will find orders of magnitude worse performance than a circular shape. | If you mean [inductive charging](_URL_1_), then [you can](_URL_0_)! The only downside is that you need an adapter for your cellphone, and it will make it a little bulky. The reason they don't put inductive chargers in cell phones to begin with is that it would make the phone larger and heavier. |
Is there any evidence that second hand smoke is health risk outdoors? | A quick Google revealed this: [Exposure to Secondhand Smoke Outside of a Bar and a Restaurant and Tobacco Exposure Biomarkers in Nonsmokers](_URL_0_) | Second hand smoke is most definitely dangerous. [An enormous in scope study that shows quite definitively how dangerous it can be is here.](_URL_0_) [Proof it can cause tumours to grow and enlarge.](_URL_1_) It is not however empirically, worse, than primary smoking. |
Why do hackers keep attacking Playstation? | You don't mess with people who want to install Linux on their PlayStations. | They don't really do anything noteworthy anymore, and they have been watered down by idiots claiming to be "master hackers." Sure, they might DDOS a website here and release someone's personal info there, but people just stopped caring because it turned into this cringe-worthy movement of neckbeards and kids in masks making threats in a dark room to a video camera. 95% of people affiliating themselves with the movement are either very amateur with hacking techniques or totally unfamiliar with them at all. |
What exactly is that "library smell" that all libraries have? What exactly am I smelling? | I like to smell books and magazines whenever I read them, is it toxic in any way? | I believe you are talking about the smell that rubber has. If you ever smell a rubber tree it smells like that just stronger. |
The difference between a snail and a slug apart from the obvious shell | Snails keep some of their internal organs in their shells, it's not like a hermit crab. That's probably the biggest difference, all of a slug's organs are inside of its body. | The snail's shell is continuous with its body; the shell stays on the same way your muscles and skin stay attached to your bones. The squishy, slug-like part of the snail has an area called the mantle which produces 3 layers of tissue - as new growth pushes these layers away from the snail, one of the layers calcifies, forming a hard shell. |
How did Leicester City win based off of another game? | Because it's a league with no playoffs. Each team plays each other twice, once at home, once away. We have 2 matchdays to go and Leicester have 77 points, while Tottenham who just played have only 70 points, which means they can only get 76 points if they win their 2 remaining games, which means its not possible for them to get 1st place thus making Leicester champions. | It's a large upset, but it's not unprecedented. Manchester United is in a transitional phase, and therefore is going to lose more games that their fans are accustomed. MK Dons is a team from the 3rd division of the English soccer pyramid. However, the competition that this game took place must be considered. The League Cup is widely considered a "2nd rate" competition, and the best teams are often accused of starting lots of backup players. Manchester United certainly didn't field their best 11 players. Additionally, like most other sports, soccer teams will have days where nothing seems to go right. This is precisely what happened today. |
Does 0.99~ really equal 1? Is the algebra shown to school students considered a legitimate mathematical "proof"? | > Wikipedia says that "Proofs of this equality have been formulated with varying degrees of mathematical rigor..." I was wondering if I could get a better explanation in regards to what that means. It means that there are a lot of ways of showing that 0.99...=1 and some are better than others. Here are some others: * Between any two distinct real number there exists another real number. There does not exist a number between 0.9... and 1 different from both of them, thus they are not distinct numbers * Decimal notation is a means for representing numbers. As such, 0.9... and 1 are two different ways of writing the same number since the limit of the sequence (0, 0.9, 0.99, 0.999, ...) is 1. This also serves as a proof that decimal notation is not always a unique representation. | If you want to know how it proves 1+1=2, you have to read the hundreds of pages that came before that. The thing is that "1+1=2" is a weird claim to *start* with. It's not very pretty if your system of arithmetic starts by defining certain arithmetical equations to be true. What mathematicians would prefer to do is start with some basic properties about equality, addition, and numbers, and *derive* arithmetic from that. The identity sign is being used because, contrary to you what you seem to be intuiting, there are lots of different kinds of equality. If we're working with numbers, 1=one. If we're working with strings, 1=/=one. If we're working with drawings, 1=/=[1 as written by a five year old]. |
Why does weed make your eyes go bloodshot and glassy? | THC, the main active ingredient in marijuana, is great at lowering blood pressure. This causes blood vessels and capillaries to dilate. This includes the blood vessels in your eyes, which leads to increased blood flow, which leads to red eyes. :) | Red eyes in marijuana users is a well-documented symptom of its vasodilative effects. But the effects you describe are probably the result of the residual psychoactive effects the drug has even when the high wears off. If you are a daily smoker, you will feel a fog over yourself that you might not even recognize until you quit outright. This fog may manifest in how your eyes present themselves. |
why do people care about the difference between shaken and stirred? | Without getting into personal opinions, which are subjective, there's a difference between shaking and stirring. Shaking agitates the ice in the drink more, which causes it to melt faster. This results in a colder, more diluted drink. It also introduces air into the drink, which can make it frothier or fizzier, especially if there's something in there like dairy or egg. Stirring mixes the ingredients together in a calmer manner, so less ice melts and air isn't introduced. Stirring results in a slightly warmer, but less diluted drink without foam or froth. For most drinks that are just liquor and mixers, you probably want to stir so you don't dilute them (they'll still be pretty cold). For most drinks that involve dairy or egg or are supposed to be light and frothy, you'll want to shake to aerate them. For drinks that you want to be really cold and don't mind if they get diluted some (e.g., a martini for some people), you can also shake. | From all the contextual clues I've gathered from hours of research from a few different genres of music, the throwing of the hands in the air seems to come from a lack of caring. |
If I bought a brand new muffler for a car, put it to my mouth and screamed, would it make any noise? Why/why not? | Mufflers are tuned in such a way to cancel out a specific type of noise. A 9 year old screaming would probably not be "muffled" to the extent that an engine is. [Read more here](_URL_0_). | Remember when you dug into the cabinets in the kitchen, got out the pots and pans and beat them loudly together? Didn't you feel a rush of joy at controlling the noise, at the power from that control? The loud muffler is just a bigger noise, so a bigger audience. |
If the US dollar stopped being backed by gold in the 70s, what has the gold in Fort Knox been used for over the past 50ish years? | Just because currency isn't backed by gold anymore doesn't mean gold isn't valuable by itself. As of 2018, there are 147,341,858.382 ounces of gold in Fort Knox, worth roughly $190 billion at the current price of gold. That's $190 billion that belongs to the federal government. | They don't. The gold standard was abandoned worldwide 40-50 years ago depending on the country. In the past our money was always redeemable for gold but at some point people realized that was stupid and money can now just be redeemed for other money and you have to just trust america itself will continue to exist and that itself is enough to make money worth something. Fort knox is a little weird because they basically sealed a bunch of gold in a room and don't let anyone check if it's really there so it's easy to get some conspiracy theories saying maybe it isn't. |
Is the data collected by the hovers on Mars publicly accessible? | NASA has an open data API that includes data from Mars rover cameras. _URL_0_ | You can't send information that way. By making a measurement on Earth, you can predict the outcome of a measurement on Mars, but you can't choose the outcome. |
Could breeders use In Vitro Fertilization (IVF) to help endangered species repopulate? | They can, and sometimes do. But generally speaking, that's not an approach that will address the real issues. Species aren't endangered because they don't know how to impregnate each other. They're endangered because of lack of habitat, overhunting, or other pressures. In vitro fertilization is expensive, doesn't have a terribly high success rate, and has to be experimentally adapted for each species. It's really only useful once you're down to a very small number of animals that, for whatever reason, don't breed well in captivity. | In theory I would yes, but not all possible offspring may be viable. E.g., a chihuahua and a St. Bernard mix outside of *in vitro* fertilization would likely be a fruitless and downright dangerous experiment in animal husbandry. I'm not a vet but I've have a basic university education in biology and genetics, as well as having lived around farms and talked to dog-breeders. |
In regards to mental illness, how do psychiatrists determine what is "normal" and what is an "illness"? | There is a well-developed set of criteria for mental illnesses listed in the [DSM](_URL_0_) (Diagnostic and Statistical Manual of Mental Disorders) published by the APA and updated periodically. Anyone in the field who is licensed to diagnose mental illness uses this standard. | The short, lame answer: we can't really be sure. Part of the reason is that the way we define "mental illness" is very deeply tied to our current culture and era, and it's nearly impossible to project that definition very far into the past. |
What is the point of a "smart" credit card (with the chip)? | The main benefit is that in order to clone the chip, you need to get access to the private encryption keys on the chip itself. Short of breaking into the bank/credit union's computer systems, you're not getting those. Meanwhile, cloning the magnetic stripe on the back is a simple matter of buying $150 worth of equipment on Amazon and finding some blank hotel keys. Chip cards can also be set up to require a PIN for purchases but the US isn't doing that for the most part for credit cards*. Many other countries have for their cards though which may cause issues when trying to use an American chip card somewhere that isn't capable of accepting a signature (such as a train ticket machine). ^* Some American credit cards do have a PIN but it's only intended for those ticket machines/gas pumps that I referred to above. [A couple of cards](_URL_0_) require PIN for everything but they're fairly difficult to get and are the exception rather than the rule. | It's harder to clone the cards. With a magnetic stripe, the data you read from the stripe is all you need to charge the card. If I swipe your card through my own reader (or hide mine around the reader at a gas station or something), I can create a perfect copy of your credit card and make charges to your account. With a chip, the card is actually a computer. The reader asks it a question and it gives a answer. The reader can verify that the answer is correct, but it can't come up with the answer on its own without access to a secret stored on the chip that's never revealed. So even if someone were to read the card data (or hack Target's payment system again), they wouldn't be able to use the cards because the next time you try to use it, the reader would ask a different question and your fake chip wouldn't know the real answer. |
Why does soda rupture after being shaken and open? If it's sealed, shouldn't the pressure remain constant? | Soft drinks have gas dissolved into a liquid. When you shake a can, it adds a small amount of energy to the drink, and allows the gas to separate which takes up more space in the can and increases the pressure. If you leave it to settle, the gas dissolves back into the liquid and it won't explode on you when opening. | When the soda is pouring out the volume of space that plop used to be in needs to be replaced by an equally sized plop of air. When the soda is filling the entire opening of the bottle there is no place for the air to get in. Eventually the air gets tired of waiting for its turn and it forces its way in. The soda briefly stop, the air goes in, and then another plop of soda can come out. This process repeats until you lower the angle of your soda bottle so that soda can come out of the bottom half of the opening and air can go into the top half of the opening at the same time. |
why do public sector bodies pay tax? | Not sure what you mean? As a CPA I’ve never seen a government agency pay tax, they have exempt status. | It's an actually brilliant form of taxation that only taxes those that consume the service the taxes end up funding. You pay x amount every time you pass a toll booth. That money (usually) goes to upkeep the roads, so funding doesn't need to come completely from other sources such as income tax, sales tax, property tax, etc. As a result, you get less pushback versus say, increasing income or sales tax to pay for roads. Because the people paying for the increased costs are the ones directly benefiting from the increased costs. |
Why does our hair turn grey as we get older? | Hair gets it's color from a pigment produced in the hair follicle. When the cells that produce that pigment stop working, hair grows as grey. The older you get, the more likely those cells are to stop working. | The time at which our hair turns grey is determined by genetics, although smoking, insufficient B vitamins and thyoride conditions are known to speed up the process of greying. But your hair turns grey because of a lack of a pigment known as Melanin. Every hair follicle we have contains pigment cells known as melanocytes, these melanocytes produce 2 different types of Melanin, a dark (black/brown) pigment and a lighter pigment (red/yellowish). Passing the melanin to the cells which produce keratin, which is a protein in hair. When the keratin producing cells (keratinocytes) die, they keep the coloring from the melanin. When you first start to go gray, the melanocytes are still within your hair, but they become less active. Less pigment is deposited into the hair so it appears lighter. As graying progresses, the melanocytes die off until there aren't any cells left to produce the color. |
Why do American schools have sports teams? | Having school sports teams have many reasons. They first started as a way to have physical education activities. People like watching sports so they organized school leagues. They do promote school unity as well. They are also good sources of income for schools. | American sports teams have a location + mascot. It came from college sports, where the colleges had mascots. College sports were basically unique to the US, they were not present in Europe. Professional sports teams followed the same naming conventions as the college teams did. Also in the early days (late 1800s) cities such as NYC had multiple teams, sometimes a lot, in a sport, so it would distinguish between the teams as well. You can't have 4 teams all called New York Baseball club, that's really confusing. |
If two planes fly by one another in opposite directions, each going Mach 0.5, would there be a sonic boom? Or one that only the pilots could hear? | The key thing is your *airspeed* - how fast you are going relative to the speed of sound within medium you are travelling through. A supersonic aircraft causes sound-waves to pile up along the edge of a cone, and if that cone hits you, you hear the sonic boom. This is caused by the interaction between the aircraft and the air, so you need to be going supersonic through the air - the speed relative to the listener isn't so important. | The air flowing around the plane can speed up or slow down, like a river can go from slow and wide to narrow and fast. When the aircraft goes over a certain speed, called the Critical Mach Number, some of the airflow becomes supersonic. This occurs around Mach 0.8, or 80% of the speed of sound. Since the speed of sound at cruising altitude is about 650mph, this is about 520mph. This Transonic region causes a large increase in drag as well as aerodynamic instability, structural damage, and potentially loss of the aircraft if not designed for it. |
Why do so many asian demonyms end with "ese"? (Chinese, Vietnamese, Japanese, Burmese) | From [this source](_URL_0_): > The -an, -ian, and -ese suffixes all stem from the Latin adjectival naming system: > -ian or -an, from Latin, –ianus, meaning "native of", "relating to", or "belonging to" > -ese, from the Latin, -ensis, meaning "originating in" They all save similar meanings, and the assignments seem to be arbitrary, maybe based on what sounds "better." For example, a citizen of Vienna is both Viennese and Austrian. | It's completely cultural. Some languages are tonal, which means that a word's tone is an inherent part of its pronunciation. If you change the tone from a falling one to a rising tone, you've mispronounced it and have likely said a different word entirely. In Mandarin questions are indicated by adding the word "ma" to the end. The tone of the other words is identical when you convert a statement "You have a car" to "Do you have a car?" Edit: "Cultural" may not be the best term to use. It's purely a feature of the specific language in question. |
Does the colour of coffee have any relation to how long it stays hot or it's temperature? | The coffee with two scoops will cool faster, and it has nothing to do with color. Water has higher heat capacity than coffee, which means that the higher relative water content, the more heat it needs to lose for it to decrease in temperature. _URL_0_ | Temperature changes how you perceive taste— your taste buds undergo chemical reactions with the substances in food or drink, and those are slower at lower temperatures. Also, coffee has many aromatic compounds that evaporate over time. This is why it has such a strong smell. It loses some of the substances that give it flavor over time... so the issue is not necessarily that the coffee *is cold*, but that it’s been a while since it was first brewed and it’s aged while it was cooling down. |
How is it possible for a 747-400 weighing over 800,000lbs to be propelled by engines that produce (in total) just under 250,000lbs of thrust? | In aerodynamics there are four main forces. In the x direction there is thrust and drag. In the y direction there is lift and weight. For the plane to be in equilibrium (or level unaccelerating flight) the weight must equal the lift and the drag must equal the thrust. So the reason is simply that thrust doesn't have to equal weight. This begs the question: how is that much lift created by such little thrust? The thrust accelerates the plane in the y direction, the wings generate lift proportional to the speed of the air flowing over them. This can easily be higher than the amount of thrust in the engine due to efficient air foils (or wings). Source: aerospace engineering student. I tried to simplify | Simple answer: compressed air. Yup, any engine is basically just an air pump with fuel thrown in the mix. To get that much metal moving they basically prime the cylinders in a certain order to get the kinect energy flowing. Huge accumulators hold the air that's used for this (and many other) ship functions. Typically ~400psi is what you are talking. Edit: here's a cool article with some awesome stats and pictures: _URL_0_ The fact that next to things like the camshaft and pistons, the people working literally look like they have been hit with a shrink ray due to the massive scale at which these things are built. The stats are what amaze me... like consuming 1600 gallons an hour, or the massive 5.6 million ft-lbs or torque. |
Why is there lightning during a rainstorm, but not during a snowstorm? | Certainly lightning in a summer rainstorm is far more common than [thundersnow](_URL_0_) but it is a real occurrence. | From Wikipedia, a thundersnow is a thunderstorm where snow, instead of rain, [falls](_URL_0_). It can be caused by: * A normal thunderstorm over cold air, which causes the precipitation to fall as snow, * A heavy synoptic (huge) snowstorm that sustains strong vertical mixing which allows for favorable conditions for lightning and thunder to occur. (A snowstorm that becomes a thunderstorm, but the precipitation is still snow) * A lake effect or ocean effect thunderstorm which is produced by cold air passing over relatively warm water. |
Do municipal water towers freeze during the Winter? | No, they're filled at night and drained during the day. The turnover alone should be enough to keep them liquid since the water is always moving. In areas with extremely low temperatures they may be equipped with insulation or even heaters/agitators to ward off extensive freezing. Frozen water expands with incredible force, and this will destroy all the equipment if the tower is allowed to freeze significantly. | The pipes running to your house are under ground, thermally insulated. When they hit your house (and run throughout your home) they aren't insulated as much. So, the cold water running through the pipes is already cold, and when you add the extreme cold temps that might happen in your house (like the basement in my situation) the water that's already close to freezing temperature is easier to freeze and burst the pipe. But to answer your question, water pipes in the city definitely freeze as well. (only from experience living in baltimore city). in the frigid jan/feb months, some of the city's pipes that might be closer to the pavement surface have a higher likely hood to freeze and burst. Hope this clears that up for ya. |
How does milk turn into cream? | Cream is the fattiest part of the milk. It rises to the top in non-homogenized milk, so all you have to do is skim the surface for it and collect it. | Into the skim milk. Butter is made from cream, cream is made by separating milk into cream and skim milk. |
Could we use decommissioned nuclear weapons to fuel nuclear power plants? | You can alter (i.e. de-enrich) weapon's grade uranium for use in civil reactors, in fact this has been done: the Megatons to Megawatts agreement between Russia and the USA. Reactors use about < 5% enriched uranium (5% U-235, 95% U-238) whereas nuclear weapons are > 90% enriched uranium. Since natural uranium is about 99% U-238 you can combine weapon's grade uranium with natural uranium to get a greatly reduced enrichment. Note that only the U-235 actually fissions (significantly) in a reactor. Using weapon's grade uranium directly in nuclear reactors would be unnecessarily risky: it would pose a risk of people stealing the fuel for use in a bomb, and it would (depending on your reactor design) allow for the possibility of a dangerous meltdown occurring. | This is a viable strategy, and lots of people have thought about doing just that. Indeed, certain spacecraft like Dawn and Hayabusa employed ion engines once lofted into orbit by chemical rockets, much like you describe. As for nuclear...some day. Maybe once we as a species learn that we're supposed to be afraid of the *weapons* part of nuclear weapons and not the *nuclear*. |
Since restaurant employers have to make up the difference if servers tips are less than minimum wage, why is it such a big deal if people don't tip? | Basically, if a waiter has to ask the employer to cover the rest of their pay, they will quickly be fired in favor of someone who can get enough tips. | So the vast majority of wait staff in the USA are vastly underpaid for the extremely tedious and stressful tasks of waiting on customers who unfortunately sometimes double as huge assholes. So as a side effect of this, tipping became prevalent as something to "make up" for the huge lack of appreciation (compensation) that restaurants actually have for their wait staff. There's an increasing number of restaurants in the US that competitively pay their staff and provide them with benefits, etc, these places are so rare that they must state that tips are not required. This my friend, is just one epic fuck up in the US. |
Why are things in "mint" condition? | I guess you're asking where that term comes from? It means something is brand new, like a coin fresh from the mint (where coins are made). | I read an explanation from the chef Heston Blumenthal that what happens is chewing gum loses its sugar over the first few minutes. The mint flavour is still there but the flavour becomes harder to detect as the sugar fades. > We all know that chewing-gum loses its flavour after a period of time. But it does not become tasteless as quickly as we might think. When we chew, the sweetening agent in the gum gradually dissolves in the mouth and is then swallowed, reducing the gum's sweetness. The brain tracks the sweetness and as this reduces, so too does the perception of the mint and menthol flavours. In reality, however, it has been proven that these aromas remain in our headspace for several hours. Link to an [article](_URL_0_) |
How does the animal kingdom deal with “mistakes” or accidents where an animal blunders and accidentally harms another animal? Can animals comprehend sorrow or forgiveness in relation to such an event? | When rough play goes too far, cats and dogs that are affectionate will often start licking the one who they hurt. Many people see that as 'apologetic' behavior. | Animals like food. Back then cruelty to animals was usually the point so they'd just bait a cage near where they new the animals were. So like bait a lion with a tied up goat. Cut said goat so it cries and lion hears and smells it. Lion walks into cage, close door. They didn't usually tranquilize them for the most part as it was easier just to capture. |
The Windows 10 final build is 10240, and the previous version was 10166. What happened to all the builds in-between? | The previous _released_ version was 10166. In between there were internal builds that might be either part of daily business (eg. builds for testing purposes) or got rejected for some other reason. In the company I work for, the build number usually counts the number of commits, though I would assume for Windows thats rather not the case (i.e. 10k commits not a very high number). | The sooner Microsoft gets everyone moved over to Windows 10, the sooner they'll have a single platform to support, meaning they don't have to support previous versions anymore, making their development easier. Plus it's their shiny new baby and they think it'll be a better experience for their users. |
Why is it more favorable to breed a dog so that it ends up having multiple health problems later in life? | It is not more favourable to breed a dog so it ends up having issues later on in life. What you are referring to (using Bulldogs specifically) is the breed standard which has changed over the years. If you were to take that same breeds standard going back several years, you'll read some marked differences. While some breeds have had distinct changes, others have not. While not everyone agrees with said changes, it is ultimately that breeds parent club that sanctions the changes made. Normally it also follows what is winning in the confirmation breed ring. There are a few breeds and one of my favourites is among them, that have marked structural differences seen in the dogs over the last 70 years or so. Some, like the Alaskan Malamute, have seen very little and are still considered a natural dog. | Because we chose to breed dogs with traits that we favored. The ones that were overly aggressive were not chosen to breed; this was part of the domestication process. |
How can we hold onto objects if atoms are "never touching"? | like you said, a force is applied. if you hold an object in your hand, the electrons of your skin repel the electrons on the surface of the object with enough force to counteract gravity. | Atoms aren't necessarily empty per se, they just contain a lot of space in comparison to volume occupied by the protons, neutrons, and electrons. The best analogy would be you holding a billiard ball, we will call this an atom. Its about the size of your fist, it repels your hand, and is hard to squish. Now image that the billiard ball's edges were not the edges you thought they once were, but are just forces pushing back on your hand and the actual billiard ball is a million times smaller than what you once perceived it to be. Same as with atoms. |
Why our bodies can fix cuts and broken bones, but can't repair a chipped tooth? | Your body has no way to move "supplies" into the teeth to repair damaged surface enamel and there are no nearby cells to perform the repairs. Once they leave the gums they're on their own. Other body parts are either made of cells that self-replicate or tended to by cells that will repair minor damage. | Because our bodies do not have the necessary stem cells to produce more enamel. Bones, on the other hand, are in a constant state of remineralization and demineralization, and thus have a plentiful source of bone-producing cells to grow and repair damage if need be. |
Why do I get really cold when I play StarCraft? | Zerg player here. My understanding was that the stress and adrenaline that comes with playing cause the blood vessels to constrict, making your hands cold. Until you get a proper answer here, you may find the info you're looking for in this [thread on Team Liquid.] (_URL_0_) Day9 also talks about it in one of his dailies, but I'm not sure which one. | Imagine your body is a phone. Not a Samsung Galaxy S56XL, just a regular one. You go and open 30 apps and the phone suddenly starts slowing down, right? Well, now imagine the common cold is a VERY consuming app for your cellphone, some kind of new Fortnite 2 game or whatever. Your body doesn't work as well when your immune system is fully fighting the virus and it may start having difficulties to do even the most simple tasks. If the app is too heavy, your phone may crash. And that's the moment you faint. So close all your tabs, lay on bed and play Coldnite 2 until you beat the game and finally uninstall it - you can't replace your body like a cellphone, unfortunately. |
The difference between Shampoo, Conditioner, Body-wash and regular soap. | It's all just soap, feel free to read the ingredients. Girls have crazy high standards for not being disgusting, apparently you can't pee down the shower drain either... Of course, they add some extra stuff to the soap depending on the use. Body wash has moisturizers and maybe even those "scrubbing micro beads" or similar. Conditioner has higher acidity, moisturizer, and some random chemicals that make you silky and smooth. Just like a cookie is a cookie whether it's peanut butter, raisin, or chocolate chip, soap is soap whether it's shampoo or body wash. I've showered with dish soap, I've washed cars with TRESemme, I've shampooed with bodywash, it's really just marketing. Heck, if you buy generic liquid soap in bulk, many times it has instructions for body wash, shampoo, cleaning, and laundry. _URL_0_ for an example. | Shampoo and body wash are both surfactants, which means that they reduce the surface tension of water, making it much easier to remove dirt and oil. Effectively, adding a surfactant to water makes the water particles act smaller so they can fit between the dirt and the surface they're on and lift them away. To my knowledge there's no practical difference between shampoo and body wash. Conditioner is effectively an oil that is added to the hair. It's purpose is mostly to replace the natural oils that you're washing away with the shampoo. Mixing the two will gives you a goo that will wash away most of the oil in hair and skin but not all of it. The effectiveness and utility of this is definitely up for debate. |
Why is corruption so difficult to eliminate | Where there is power, there will always be those who seek that power to further their own desires. In that sense, there will always be some level of corruption. And it's difficult to remove, since those who have the power to do something about it are often the ones benefiting from it. | Because being corrupt pays better than it used to, relatively speaking. The developed world was at the top of the food chain, and the only people they could bribe was each other. Now, if you are a powerful official in a developing country, it is not just the people your poor country who can you can get bribes form. People and corporations from the rich, developed countries can bribe you, too, at a much greater scale. |
Can an "inoperable" tumor ever be operated on? Isn't it worth at least trying? | Not always. Usually when a doctor says "it's inoperable" they mean the probability of you surviving the operation is so low that it wouldn't be worth the time you have left. Say a healthy person at your age would live for forty five more years. The tumor in your head will kill you in six months. An operation could give you those forty-five year back, but it has a 99% chance of killing you outright. Do that math. .01 times 45 is less than six months. | Generally, if it is too close to, wrapped around, or entering a vital organ that cannot have pieces removed, or if it is in a location that will cause death if an attempt to remove the tumor is made. |
Why do competitive divers shave their body hair, yet not wear swim caps? | From what I've been told, swim caps are frowned upon by judges in competitive diving. My daughter dives. Some girls wear caps during practice, but only one wears a cap in competition and it's because she has a braid that goes to het butt. | So I was actually wondering this out loud the other day while I was watching the Olympics with my wife, and not 10 seconds later the commentator on the TV actually explained it. He said occasionally you will see some swimmers wear their goggles with the strap on the outside of their swimming cap, but most wear them with the strap on the inside. Some swimmers wear their goggles with the strap in contact with their hair, and then a single swim cap over top, but other swimmers may feel that their hair is too slippery for the goggles' strap to stay in place, so they wear a swim cap, then the goggles with the strap over top of the first swim cap, and then a second swim cap to make sure their goggles can't slip off. He seemed to know what he was talking about, so I trust his explanation. |
The current American immigration problem | The **unbiased** report is that the politicians are still arguing what they think needs to be done. And since they're arguing and arguing and arguing about it, nothing gets done. In the meantime, many poor and desperate people from the impoverished countries of Central America will continue to immigrate illegally to the USA. They will do the jobs which most US-Americans refuse to do, like agricultural work and cleaning jobs. | The US is actually one of the easiest country to immigrate to, some country simply will not let you become a citizen, ever. No country will just let anyone in and there has to be a highly selective process in order to protect the interest of their own citizen workforce. |
- how can you get stretch marks on your bum from sitting down too much? | Your can't. You get stretch marks from rapid weight gain or growth. So if you put on a lot of weight in your hips and butt you can get stretch marks there. Something you can get from sitting down too much are pressure sores commonly called bed sores, or hemorrhoids. | You have two layers of skin: the epidermis, which is the outer most layer, and the dermis that sits below that. Both of these layers can be broken down into even smaller layers. In the lower layer of the dermis lies collagen. Collagen is rubber band like strands of proteins that essentially holds up all the shit above it. Whenever the skin stretches, such as in pregnancy, weight gain, rapid growth in puberty, and the body fails to keep up with this process by not producing enough collagen to hold everything up, the existing collagen tears, and you now have a stretch mark. |
Why are depictions of little kids used so often in horror films? | Cognitive dissonance. It's the unpleasant feeling a person gets when 2 or more thoughts/ideas/perceptions (cognitions) contradict each other. We often perceive children to be a symbol of innocence and generally cute. When presented with a horror scenario where we expect to be scared, our 2 perceptions clash giving us a feeling of discomfort which depending on how well the scenario is presented could amplify the feeling of being scared by making us decide that children are creepy or make us question the movie (ie. Eh, kids aren't so scary. This movie sucks.). | IMO the characters are usually visually stimulating with many different colors and the voices are soothing to children. In addition there are so many different elements such as color, movement, humor displayed on the screen/stage it holds children's attention (for some time at least). |
why do American style electrical outlets have holes in both prongs | "Bumps" inside the outlet fit into the holes and keep the plug in place so it can't be pulled out easily. | UL rules are if you can prove neither prong can accidently electrify anything outside the charger you don't need a polarized plug (a plug that fits one way). Generally that would be devices with an entirely plastic case (so a lose wire can't electrify anything) and full isolation between the wall and the power (basically, prove that the USB side isn't connected to either of the prongs with a conductive path). If you can't do that, you need polarized plugs (which are used because only the "hot" wire is suppose to have voltage, so the neutral should be safe to touch), a polarized plug makes sure it's in the right direction. Practically everything is designed to not need a polarized plug because it's safer. Things that need a polarized plugs (like stuff with a metal case, or an air conditioner, etc) generally require a three prong plug (because neutral is only suppose to be safe to touch, ground actually is considered safe to touch, and ground is suppose to be connected to things you touch) |
To what extent did the entry of the US army in the first world war contribute to Allied victory? | I wrote about the US during the first WWI in response to some earlier questions [here](_URL_1_) and kinda [here](_URL_0_). Basically, my theory is that the Allies would've won even without the US, but thanks to the boost in materials and morale (as well as bodies on the line) and thanks to the pressure this put on Germany to act, they sped up the victory by some degree. | In 1917 Germany began a policy of unrestricted submarine warfare in the Atlantic ocean to cut supplies to Britain - this meant the sinking of American ships and the killing of American citizens. It was in response to this that the US entered the war. Therefore it was the way the U-boats were used - to attack American shipping, that brought the US into WW1. |
why does time move in one direction only ? | The trick is with time is not to think about it as the same kind of physical dimension as height, or length, for examples. Don't think of time only moving in one direction, instead think of time as the dimension in which we constantly move through in the only direction in which time exists. So, time doesn't move in only one direction, but instead we move through time in the only way possible, which is forward. Edit: spelling | Time is the fourth dimension. Your mind can't visualize it, so don't bother trying. But we are moving through time just like we are moving through space. But we can only go one direction. |
Why does the English language have a different word for prepared meat and the animal it comes from? (Eg. Pork and pig, venison and deer, beef and cow) | It comes from when England was invaded and conquered by the Normans from France in 1066. Being from France the Normans spoke French while the rest of the country being English spoke English. The English were mostly poor and did not eat a lot of meat though they did raise the animals. The Normans being the conquerers had more money and ate the meat but did not raise it. So we ended up having English names for the animals like cows and sheep, and French names for the meat like boeuf, and mutton. The French names eventually became the words we use today. | The animal names are Anglo-Saxon / Germanic, while the meat names are from Norman / French names for the animals. The traditional explanation is that the Anglo-Saxon peasants raised the animals, while the Norman nobility got to eat the meat and so their names for the animals stuck as names for the meat. So where's the French word for chicken meat? That would be poultry, which has ended up as a more general word for birds, both as animals and as meat. Presumably chicken was the meat that peasants could afford to eat, so there wasn't the same strong separation of words. |
Japanese mercenaries fighting in Asia during the Tokugawa period. How common was this and were they able to return to Japan? | In 1623, a Japanese mercenary was caught in an act of espionage by officials of the Dutch East India company on Ambon Island. After waterboarding torture, he confessed to be part of a group of 20 mercenaries in the employ of the British East India Company, and were here to assassinate the Dutch director at that base. In the same incident, 9 other Japanese mercenaries were executed, and two were released by pardon for unknown reasons. Japanese mercenaries were among those who helped to enthrone Cambodian Prince Ramathepothei (Ramathipadi I) in 1642. He went on to fight the Dutch in the Cambodian-Dutch War of 1643-1644. Not sure on the particulars of the Japanese Mercenaries involved, or if they were able to return to Japan after their adventures abroad. From... The Dutch East India Company: The History of the World's First Multinational Corporation by Charles River Editors. | I wasn't aware of them being "disbanded" per se. As far as I recall, the Shinsengumi fought with the pro-Shogunate clans in the Boshin War until they were forced to retreat to Hokkaido, where they attempted to establish an independent, Shogun-led, Republic of Ezo. They were defeated by Imperial troops, and most of them fought to the death. A few of the members survived and either lived out their lives quietly or supported the Meiji regime thereon after. One of the more famous of the survivors, Saito Hajime, actually later served as part of the Battotai, a group of special sword policemen that were part of the Meiji army that was sent to crush the Satsuma rebellion. |
To keep liquid inside a tumbler hot for a longer time, leave the outside cool, or heat everything? | Barring some weird expansion of the materials that breaks the insulating properties of the vacuum then the hotter the mug overall the better off you will be. Some heat will be transferred from the inner wall to the outer wall no matter what you do, and increasing the temperature of the outer wall will slow down that heat flow at least a little. However, if the tumbler is constructed well and you normally can't feel any warming of the outside of the vessel even after a long time then you probably won't notice any difference whether you heat the outside or not. Most of the heat lost from the liquid will come off the surface and go into the air, so to keep things hotter for longer you would need to insulate the top for best results. | Presumably, the goal is to keep the food/beverage contents of the cooler cold and not keep the ice from melting. Leave the ice cold water in the cooler as it's increased cold mass will help keep the contents cold for longer. |
Can long chains of triple bonds be created? As in Polyacetylene? or Polyalkyne? | There are compounds called [Allenes](_URL_1_) which have multiple double bonds in a row. So if polyacetylene is -C=C-C=C-C=C- (alternating single/double) then allenes are like H2C=C=CH2 (propadiene). I don't know how long they can be. There are also alternating single/triple bonded structures (-C#C-C#C-) known as [polyynes](_URL_4_). From that page: > The longest reported (synthetic) polyyne to-date contains 22 acetylenic units and is end-capped with triisopropylsilyl groups Again, I'm not sure why you don't get polymers of these - difficult to synthesise, perhaps. edit: [Here is a short article with a good image](_URL_0_) - showing a polyyne in the role of a [rotaxane](_URL_3_). edit2: The page on [Linear acetylenic carbon](_URL_2_) claims a maximum chain length of 300 carbons for an allene-like structure. | If it's chemical structure allows it to make bonds in such a way that you can make out a discreet unit that repeats indefinitely. Organic molecules are good at forming polymers because they involve chains of carbon molecules that have the capacity to make four covalent bonds. YOU can string them together indefinitely. |
European medieval (~1200) - books with picture request. | Visual source documentation of fashion prior to 1300 is very scant: archaeology can't help (clothing degrades), preservation wasn't an apparent concern until late middle ages, and visual resources are thin (manuscript imagery is not in full gear yet, painting hadn't taken off yet). Some also argue that 'fashion' hadn't taken off yet, either - or at least that is the argument of this book: * Sarah-Grace Heller, *Fashion in Medieval France* (Boydell & Brewer, 2007) This book covers the 'start' of fashion in the 13th century and, this is the frustrating part typical of academic work, it lacks illustrations. However, the bibliography is huge and has some very good resources. If you want the bibliography I can scan it for you - just PM me. Again, bear in mind that you will be working with a time period with a lot of guess work. | For background, 'Early Christian Ireland' by T.M. Charles-Edwards is pretty good. It covers from Christianisation to the beginning of the Viking period. I haven't read it myself, but I've also seen 'Early Medieval Ireland' by Dáibhí Ó Cróinín recommended. It's shorter, and covers a longer period (400-1200), but the later bit is probably what you're more interested in anyway. |
Why can't pilots see when a laser hits them? | Lasers spread out the farther they travel. That "tiny dot of light" isn't so tiny after it travels 1000 feet through the air. If it hits the plexiglas cockpit window, it diffuses out even more. The result looks [something like this](_URL_0_). You're right that it only flashes for a split second, but that's all it takes. When people say that it blinds pilots, it doesn't mean that the laser is burning out their retina and causing permanent blindness. They're talking about *flash blindness*, the temporary dazzling effect you get when a bright light flashes in your eye. Like when someone uses a camera flash in a dark room, and you have to blink away the aftereffect for a few seconds? Imagine trying to land a plane during that. | They use very bright IR lasers, which you can't see because they're outside the visible spectrum. The LIDAR can easily see the spot from its laser - it's no different than using a [bright laser pointer](_URL_1_). Combine that with an extremely [aggressive filter](_URL_0_) on the lens and it's not much of a problem. Edit: there are other tricks you can do as well. For example, you can gate the sensor, such that only returns in a certain window are accepted (get back too early or too late and the return is rejected as spurious). Or you could code the laser pulses, so only returns which match the signature of the laser pulses are accepted. Either way, visibility isn't much of an issue. |
how do electrons, protons and neutrons define an element? I'm super dumb on these things what can I watch to help? | Khan Academy might be a good place to start. The number of protons tells you what element it is. As in what makes an atom carbon is that it has 6 protons, nitrogen has 7 protons, etc. In a neutral atom the number of electrons = the number of protons. In an ion, you just need to do some simple ish maths to work out how many electrons there is. Negatively charged ions (anions) have gained electrons equal to the charge, positively charged ions (cations) have lost electrons equal to the charge. The number of neutrons tells you what isotope of a given element it is. Carbon-12 has 6 protons and 6 neutrons which gives you the 12. Carbon-13 has 6 protons and 7 neutrons, carbon-14 has 6 protons and 8 neutrons. | You classify by elements by their protons. It goes in "perfect order" because you're just counting the number of protons to identify the atom. The number of neutrons and electrons vary though. It's like saying all animals with "fur/hair" are mammals. You just use a trait to identify the thing. |
Why do cars not have oil level sensors? | Some do have an actual oil level indicator. I am not sure 100%, but I think it comes with more luxury cars. I know for a fact some Audi's made in the last 4 years have them. | And you're told this by people who sell oil. Maybe that should give you a clue. Certainly in modern cars, that should be unnecessary. Edit: Spelling |
Why do we ride horses and donkeys but not cows or sheep? (Sheep would be comfy, I imagine.) | Two reasons 1- Physiology. Horses are relatively easy to mount and control with the reins. Cows are very wide and while you can mount them for a time (rodeo) they are uncomfortable to ride for extended periods of time. 2 - Social structure. Horses have a hierarchy. You break the lead horse and the rest of the horses see you as the new leader. Cows don't generally have such a defined hierarchy. If you manage to tame the biggest bull, other bulls will just keep challenging you. Not to mention that we most likely domesticated horses first and they are much faster than cows. | Because horses are monogastrics and thus can digest cellulose which is the majority of grass. _URL_0_ |
Is there any religion with no recorded religious-based violence? | I feel like this question is a bit leading, as many historical religious-based conflicts arose from other problems than religion, though religion was used as justification for violence in many cases. It's hard to determine what was actually religious-based violence and what was conflict with religious overtones. | Bloody religious wars are actually somewhat unusual except for the Abrahamic religions, and so it isn't so much that Asia is unusual as the West is. To be clear this is not to say that Western monotheism invented religious violence: wars as far back as Mesopotamia have been framed in terms of divine missions to repay religious insults and more recent events have tragically proven that brutal religious violence is by no means limited to them. However, the imperative to maintain religious orthodoxy through violence is rather unusual. While there are many cases in history of individual sects being targeted, the persecution of all forms of worship besides one is more difficult to find. I'm not entirely certain how to source this but can provide sources regarding individual regions if you would like. |
How some people argue that the Holocaust the was a hoax? | Well, that's your problem. It's a conspiracy theory. There's a lot of evidence available proving that it did happen. These days, Holocaust deniers don't have much ground to stand on, so they're now saying that it did happen, but that historians have exaggerated its scale. | You could argue Holocaust denial I guess. It comes up more often than I'd like, by which I mean it exists. |
The Halting Problem in Computer Science | Can a single computer program determine if any other computer program will run forever? No | It could be a variety of things: Stuck in a loop Waiting on a program or server to respond It's slow and actually calculating something |
How exactly does computer hacking work? | The aim of a lot of hacking is to exploit a weakness in a system, such as buffer overflow. Another example: ever heard of the heartbleed bug in programming? Here's a good comic that explains it: _URL_0_ | Hacking leaves a paper trail kinda like money embezzling does. There’s always a slight trail, but it takes a trained eye or quality developed program to be able to both detect it/hide it. |
What turns a "skin crease" into a "wrinkle" that stays there even when the reason for the crease (smiling, sitting a certain way, etc.) is gone? | Think of it like an elastic waistband. That thing can go a long time retaining its elasticity -- in my experience, ten, fifteen years. But eventually it hits that point where it's stretched too much. You pull to stretch, and it -- stays stretched. Basically it's run out of elasticity to return back to its previous shape. Skin has elasticity in the same way, but as we grow older, that elasticity decreases. Eventually it stops tightening back. | Often times it's the production of [Sebum](_URL_0_) It helps lubricate, waterproof the skin, and protect from bacteria. |
Why is living with your parents seen as taboo in the USA and Britain, but not in most of the world? | Because you're expected to be productive and earn your own way in the world. A big part of that is living in your own place and paying your own bills. If you cannot sustain yourself, what could you possibly produce or contribute to society at large? That's a prevalent attitude in the U.S. anyway. Of course, the U.S. is only now starting to deal with staggering unemployment/underemployment in the 18-30 range. This is something that has existed even in the robust economies of France and Italy for some time, so it has become more normal there (and less stigmatized). All that said, I understand that living with your parents isn't necessarily motivated by economic considerations, but it's perhaps most often the case. In the U.S., people generally don't want to be seen as mooching off their parents if they can help it. We prize self-sufficiency (and the appearance of the same) very highly. Edit: Realized my original answer didn't really address the question. | Actually Anglo families are the notable exception in this respect. Most other cultures are notably more family oriented. I don't know any clear answer as to why this is but generally the Western European tradition has higher degrees of social trust outside of family than is the norm elsewhere. There is a greater reliance on the rule of law, and trustworthiness of public institutions. The tradition at least in my experience with Chinese, Greeks, Indians is that everyone outside your family is to be trusted only with strong caution. |
Are the effects of dark matter and dark energy observable on a smaller scale i.e. here on Earth? | No, they're too weak to be relevant. Dark energy is extremely dilute, while dark matter is very uniform. We possibly hope to be able in the near future to detect dark matter through non gravitational interactions, but these have not been observed yet, and are at the very least ultra-rare. | Yes. The one thing we know about dark matter is that it interacts gravitationally; that is how we detect it. |
How are STDs formed, and what is the earliest case of one? | STDs are not specific to humans; they're almost certainly hundreds of millions, if not billions of years old. The very first humans would have suffered from them. STDs will almost always have evolved from other similar diseases to specialise in sexual transmission. | It began as a pathogen with a hospitable host that was conducive to both development/evolution of long incubation periods, and the ability to jump hosts through exchange of bodily fluid. In theory there could be much worse STD/STIs, but thankfully they damage/kill the host before they can find a new one. |
How come we never witness lightning in open space? Can't there be charge differentials in large nebulas, etc.? | Even if there was long range charge transfer, we wouldn't see it because there is no atmosphere to be ionized like there is for lightning. We do see the effects of rapidly accelerating charge in space though, for example, in x-rays produced in accretion disks. | Lightning is just superheated air (plasma) which gives off photons after being excited. In a pure vacuum, there wouldn't be any atoms to give off photons, so you wouldn't be able to see any lightning. The closest you can get to "space" lightning would be either [Sprites](_URL_0_) or [Aurora](_URL_1_). |
Can someone explain to me what a tax bracket is? | There are four categories of tax brackets in the United States: Single, Married filing jointly, Married filing separately (same bracket as single for each spouse), and head of household. Married filing jointly provides the best tax bracket, and each category will have different dollar amounts for the tax brackets. I'll provide the single tax bracket: * 10% - $0-8,500 * 15% - 8,501- 34,500 * 25% - 34,501 - 83,600 * 28% - 83,601 - 174,400 * 33% - 174,401 - 379,150 * 35% - $379,150+ For example. If you make $50,000 per year, the first $8,500 is taxed at 10%; all income between $8,501 - 34,500 is taxed at 15%; all income between $34,501 - $50,000 will then be taxed at 25%. So if you calculate that, your tax bill (ignoring credits and deductions) will be $8,625. Edit: four categories, not three | Typically they mean a 90% *marginal* rate, not a straight 90% tax rate. The way taxes work is based on tables. The tables go something like this: On the first $10,000 of your income, pay 0% tax For the next $10,000 of your income, pay 10% tax For the next $50,000 of your income, pay 20% tax Above that, pay 30% tax. And so on and so forth. Today, the tax rate tops out at 35%. What that means is, it doesn't matter if you got paid $1 million or $1 billion, the top marginal rate for you is still 35%. Some people think it should be more like 90%. |
How do Laser powered drones work? | You just need some sort of photovoltaic cell (i.e. a solar panel type device) on the drone. Hit that with the laser and power is generated. The efficiency will be hopeless, but it works. The number of lasers you need really depends on how high the drone flies, the laser aperture, how much spare power there is (i.e. how much of the beam energy can you lose before it can't power the drone any more), the weather, etc. I don't know enough about the system to give more precise answers. | Power. Military grade lasers that can destroy objects require batteries the size of trucks. Size. Said lasers are huge, the most compact I have heard about are anti missile lasers that are fitted on our largest jumbo jets and make use of every inch of the craft for storage of the laser and its battery. Cost. Bullets are cheap and effective. |
What happens if you feed an herbivore meat? | Very few 'herbivores' are vegetarians. Most animals will eat carrion if it comes their way. Ruminants like cows would have trouble if they ate too much, because the bacteria in their gut that break down plant fibre would either go haywire, or be outcompeted. | Meat is more energy-rich than plant matter. Herbivores have to essentially eat all day while carnivores don't. |
Why is the Spanish abbreviation of the United States EE.UU? | It's common in Spanish abbreviations to duplicate letters to represent that you're substituting for a plural. For example, the Spanish for Armed Forces is Fuerzas Armadas, and its abbreviation is FF.AA. They don't do it in every case, like ONU (Organización de las Naciones Unidas) is the acronym they use for the UN even though it contains a plural, but like everyone else mentioned, using EU would lead to a lot of confusion. | It may very well be, as /u/Searocksandtrees points out, simply a matter of the different capitalization standards of the time, but I think it probably has something to do with the fact that it wasn't meant to be the name of a country. The United States was exactly that, a union of independent, sovereign political entities (not unlike the modern European Union). Therefore, the "united" was just the adjective describing the relationship between the states. |
How does digestion work in zero gravity? | digestion still takes place even when you are upside down because our digestive system has many muscles that force things to the end. | It would proceed mostly intact through your stomach and into your small intestine. Upon reaching the ileum (the portion of your small intestine that is the farthest downstream from you stomach), they would be degraded into sugars, bases, and phosphates by membrane-bound nucleotidase enzymes in the epithelial cells. Those compounds would then be absorbed into your body, enter your blood stream, and travel to your liver. Some time later, they may be reused to synthesize ATP inside cells. |
How does digestion work in zero gravity? | I would assume it works the same as it does with gravity. Peristalsis is what moves the food through the digestive tract. | It would proceed mostly intact through your stomach and into your small intestine. Upon reaching the ileum (the portion of your small intestine that is the farthest downstream from you stomach), they would be degraded into sugars, bases, and phosphates by membrane-bound nucleotidase enzymes in the epithelial cells. Those compounds would then be absorbed into your body, enter your blood stream, and travel to your liver. Some time later, they may be reused to synthesize ATP inside cells. |
How tightly is DNA coiled? | This depends a little bit on what you are talking about. Are you talking about the helix, and how many base pairs it takes for it to turn? The answer to that is 10-10.5 base pairs per helix turn for B-form DNA, the most common type. The helix is, in this case, around 2 nanometers wide and each helix is around 3.3 nm long. But DNA is coiled in a lot of different ways. In eukaryotic cells, DNA is coiled around histones to make nucleosomes. The DNA gets wrapped around the histones 1.67 times (146 base pairs), and each nucleosome is separated from the others by 20-90 base pairs . These nucleosomes end up looking like ['beads on a string'](_URL_0_), and are about 10 nm in diameter. Anyway, point being, when you talk about DNA coils, people are going to have a lot of interpretations regarding what you mean. | What you're looking for is the tensile strength of DNA compared to the tensile strength of something like, say, nylon. It takes about 1 nN to break a strand of DNA, which at around 2nm wide and roughly circular, gives you a tensile strength of about 318 MPa. This is compared to somewhere in the neighborhood of ~100 MPa for nylon and other common polymers used in ropes. If we assume you can weave DNA strands into a cable, they would be quite strong, barring degradation and the thermodynamic nightmare that would be building such a large DNA structure. Even though DNA is pretty rigid as a double-strand, once you get very long, thermodynamics make it want to curl up on itself, so you've got that working against you. Source: Materials science researcher with a background in DNA nanotechnology |
Why is the coefficient of dynamic friction lower than the coefficient of static friction? | We think of friction as some force that just exists between two objects. But it has a reason behind it. Friction is actually a lot of little forces. Some important examples are the force to break little bonds that form between the molecules of one thing and molecules of the other thing, or the force to break off little nobs or spikes on one thing that are pushed into little holes or ditches on the other thing. When two things are moving not two points are ever together for more than an instant. They don't have time form all kinds bonds because the molecules don't get time to line up into special patterns. Those bonds still slow the movement down but they don't do it as much. When the objects are touching and not moving the two objects can (quickly but not instantly) form some bonds or settle into a more over-lapping shape. It takes more force to break all those bonds at once. | The reason ice has such low friction is actually due to a small layer of water that forms at the interface and acts as a lubricant. While a "rough" ice surface will have more friction than one that isn't rough, it isn't going to be a whole lot more. So the smoothness really plays a very small part in it's coefficient of friction. It's worth noting that if you could keep the interface cold enough, the ice wouldn't melt under the pressure/heating combination and would actually have a decent coefficient of friction. |
Why do voices in sped-up videos always have a higher pitch? | Pitch depends on the frequency of the sound wave. When you play a recording back at a faster speed you have increased the frequency, which raises the pitch. | If they've been sped up slightly, to cut the time wasted on that noise, the pitch will be a bit higher. Think Chipmunks. |
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