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Would a box with a perfectly reflective interior have light inside?
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There is no such thing as a perfectly reflective material. Any apparently reflective material will still absorb a small amount of the light reflecting off of it.
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I'm not an expert but I'm thinking [Diffuse](_URL_1_) vs [Specular](_URL_0_) reflections
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Why can’t small models be scaled up directly?
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[The square cube law.](_URL_0_) When you double the scale, all surfaces are multiplied by 4 and all volumes by 8. Strength is proportional to the surface, mass is proportional to the volume. This means that when you scale something up, your strength to weight ratio (and also heat to cooling) goes down dramatically.
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There is no limit to the scale of an object for the laws of quantum mechanics to be applied to it. So, the question should be at what length scale do the predicted quantum effects become too subtle to be observed with our current technology. This smallness of scale depends on the value of planck constant h (or h bar) which controls the scale of quantum behaviour. However, the macroscopic manifestations can of quantum theory can appear in certain systems like superconductivity and anisotropies of the CMB generated by quantum fluctuations.
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How does a U.S. Destroyer, a vessel equiped with advanced technological systems, that is supposed to engage in tactical naval warfare, collide with a cargo ship?
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Massive and systemic watch-keeping failure on the part of the Naval Vessel's crew. Heads are going to roll here. Court-martials, possibly criminal-negligence charges. There is no excuse for this. None. Navy Ships have multiple people in the pilot house, lookouts all over the ship, people in CIC monitoring surface contacts. State of the art computer processors crunching enough data to take down 10's of targets at mach speeds. Able to scan the environment with different radar systems. The Cargo ship had the right of way : > *Collision Regulations Rule 15: When two power-driven vessels are crossing, the vessel which has the other on the starboard side must give way and avoid crossing ahead of her.* Navy ships also are required to have other vessels standoff outside their respective exclusion zones, to avoid [shit like this](_URL_0_) happening. It's a complete breakdown of every single navigational procedure.
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They're privately owned cargo ships. They move goods around. In wartime they can be asked to assist in the movement of military cargo.
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How does the voice of performers like Michael Buble come across so evenly despite the varying distance between the microphone and his mouth?
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Great vocalists have impeccable mic technique. When he’s pulling the microphone away his voice is louder. And when it is closer his voice is softer.
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The different shape of their vocal cords and projection area (the mouth and throat) combined with different uses. That is to say, the way your "vocal area" is shaped, and how you manipulate it with the muscles in the area greatly effects the sound that comes out.
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Why do many ice-cream trucks use "Turkey in the Straw" as their music?
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Ice cream parlors at the turn of the century used to play minstrel music to keep their customers entertained. A popular song, set to 'Turkey in the Straw', was 'Nigger Love A Watermelon! Ha! Ha! Ha!' - it was very popular in its time. As a way to make a correlation between the pleasant experiences in a ice cream parlor, early ice cream trucks would also play similar music from music boxes. Leading to the wordless jingling rendition that we all know. Source: [Code Switch article, from NPR](_URL_0_)
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I'm American (from New York) and I've never heard of anything called "Turkish Delight" other than Lokum. Could you link a picture or something?
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what anarchism is and why it's labeled as 'evil'?
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Anarchists are often seen as people who _disobey_ the law at all price, but really it's an ideal about a self-regulating society, an aiding human race without higher control or regulation. A 'lawless' society. If they are seen as "evil" as you say, it's because in reality the ideal is hard to attain and you mostly see them in protestation or as a ridiculous thought. Also, it has somewhat common grounds with communism (look at philosophical and political ideologies of the 19th century) which has a strong negative opinion in the occidental societies.
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If you look at it economically, anarchism has strong ties to socialist/communist theory. Anarchists are pretty misunderstood, it's not all about no rules and complete chaos. Early anarchists believed that you should grow food, and whatever extra you had you should give to your neighbours for free, and vice versa. This idea is basically the opposite of capitalism, where you pretty much want to make as much money as you can off of your extra food. That is just one example of policy why it is on the left, rather than the right.
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What is Astigmatism?
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Astigmatism is the effect of a lens not being perfectly round. This can include the lens in your eye, combined with the lensing effect of the fluid in your eye. A lens that is misshapen in this way doesn't focus the entire image in the same plane, so some areas are out of focus when others are in focus.
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It can, it's a treatment option they offer. Astigmatisms are misshapen corneas, the laser eye surgeon reshapes the corneal curve with advanced laser tech to produce a more even and proper curve, eliminating the problem.
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Cymbals are never really in "tune". So why don't they clash with the sound of guitars?
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But they do, and that's often the point. Percussion is less about tone and more about rhythm, and so you want a sound that doesn't harmonize or blend with the rest of the music. A cymbal crash is full of a variety of tones, to the point where you don't associate it with a single note. Think of a cymbal crash while a guitar plays a C. The cymbal crash itself is full of consonance and dissonance, and the two sounds don't harmonize. This doesn't necessarily sound bad, it just keeps the two sounds distinct.
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Because the cymbal takes time to fully make the sound they want it to make. When you hit the cymbal there is the initial crash and then a drawn out noise as it continues to vibrate. If you hit the same cymbal over and over, all you would get is the crash and nothing else.
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When and why did it become taboo to discuss or exhibit nudity in Western culture?
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Taboos regarding nudity seem to date to prehistory. Attitudes toward nudity change all the time. Neither the Greeks nor Romans nor their major Barbarian counterparts were fine with people just walking around naked whenever they felt like. Sure, the Greeks thought the nude male body was a beautiful thing and venerated it and competed nude in sport. Sure, the Romans bathed together. Sure, the Gauls went into battle with no clothes. These were exceptions to the general taboo of public nudity. The modern west similarly has exceptions. Take nudity in daily sauna sessions and for swimming in ponds in 20th century Finland or nudity in locker roomers and YMCA pools in 20th century America. They weren't examples of general societal nudism where you could walk down to the corner store to buy some milk naked; it's much the same with ancient nudity.
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Nudity as a cultural taboo varies wildly between cultures and within cultures, and isn't fixed for any extensive amount of time, either. So, it's hard to generalize, other than to say that everyone's different, and the risks and rewards are unique to each person in every circumstance. Is there some specific behavior/culture you're thinking of?
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The reason behind Colorado county secession vote today
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Many states have tensions between urban areas, which tend to be more liberal, and rural areas, which tend to be more conservative. In Colorado, which in recent years has trended liberal, legalized pot, banned high-capacity magazines, etc, the rural conservatives are particularly distraught. Of course, it's rather superficial. To secede from a state you need approval of that state and the federal government, and that is not going to happen. Basically they are just having a pointless ballot referendum on how annoyed they are at being on the losing side of various elections.
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[In this previous answer](_URL_0_), I address the matter of the ordinances of secession to a good degree.
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Why does such a large portion of the world population live in South-East Asia?
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Because some of the largest fertile areas in the world are in China and India; because consistent civilization has lasted longer in those areas than in any other part of the world; and because there is more place to build in those two countries than in any comparable areas of the world.
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Mongolia cannot support a large population of people, most of the area is made up of the steppe which is not arable. Their main source of food is from their lifestock, atleast until the 20th century
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What happens to gases (eg. nitrous oxide) when you release it into a room or large air filled enclosed space? Does it just float around indefinitely?
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Gases diffuse over time. If you release a volume of gas into a room, the particles will spread out and intermingle with those (i.e. atmospheric gases) already present. In a perfectly airtight, undisturbed container, the new gas will spread out evenly throughout, given enough time. In a normal room, it will eventually spread out under doors, through windows and cracks to surrounding areas, eventually becoming so dilute that no trace remains in the room it was released. If the room is poorly ventilated, this will take a very long time, however.
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Yes, mostly. Gas will naturally settle, like liquids, with the most dense at the bottom. Look up "gas stratification" to read details. This can be very dangerous in certain situations. For instance, a closed off industrial space such as a bridge compartment can have rusting metal. This uses up the oxygen. Or a closed off space that has bacteria at work using up the oxygen. The heavier air molecules left (other gases) such as carbon dioxide will fall to the lower portion of the room. This can asphyxiate someone who walks into that room. However, this does NOT mean that something like carbon dioxide (C02) will break up into carbon falling lower and oxygen settling higher. You have to take the density of the molecules into account, not the separate elements. Stratification can also happen with different temperatures. Look up thermal stratification.
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How can you justify multiplying a wavefunction with a spin vector?
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> Since the wavefunction and spin live in different Hilbert spaces, what allows you to multiply them with each other? It's not a standard multiplication. You might see abuses of notation like Ψ(**r**)χ(s), but it's just shorthand for |Ψ > ⊗|χ > , or < **r**|Ψ > ⊗|χ > in the coordinate basis. The "⊗" symbol is a tensor product. It's an operation that essentially staples together two vector spaces. It takes the infinite-dimensional Hilbert space in which the coordinate-space wavefunction of the particle lives, and staples it to the finite-dimensional Hilbert space in which the spin state of the particle lives. > Also, the total symmetry of the function is the same, as if you would multiply 2 functions of the same space with each other, how can this be? I'm not sure I understand what you're asking.
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Well first of all, this doesn't really work for identical particles. Two electrons are identical fermions, so you have to make the composite state vector antisymmetric with respect to particle exchange. Writing a composite state vector as a simple product works for independent, non-identical particles. Furthermore, this isn't just one function multiplied the other, it's a tensor product. |a > |b > is shorthand for |a > ⊗|b > . If |a > is an element of vector space A and |b > is an element of vector space |B > , |a > |b > is an element of vector space A⊗B. If you have a state vector |Ѱ > |Φ > and you project onto coordinate-space ( < **r***_1_*| < **r***_2_*|)(|Ѱ > |Φ > ), the result is Ѱ(**r***_1_*)Φ(**r***_2_*). Now this *is* just a product of two functions, and it *is* zero when either one of the individual wavefunctions is zero. It's very small when one of the two wavefunctions is small, and it's large where the two wavefunctions overlap significantly.
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How did people wake up to work before the invention of alarm clocks?
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In the UK, we had a [knocker-up](_URL_0_) , who was a guy with a big stick and would tap on your bedroom window when it was time to get up. No idea who woke him up though.
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I'd be interested to know why I feel very awake if I wake up too early, but cannot drag myself out of bed if the alarm clock wakes me.
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Why is it that humans typically need braces to get straight teeth, but other animals (cats, dogs, etc) don't?
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I'm guessing that maybe some animals could use dental work but are extremely unlikely to make an appointment with the local dentist any time soon.
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No, because we don't bite things to hurt them. Animals like dogs have their teeth as their main weapons, so they show them when they're angry to remind other animals that they can fight back. The human equivalent would be flexing your biceps or showing a weapon, because we use blunt force and tools instead of biting.
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During WWII, were there any cases of tail-gunners accidentally shooting off their aircraft's tail?
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If you strictly meant tail gunners, then on most aircraft with tail gun positions, that was impossible, as the gun emplacement was already behind the tail and control surfaces. For example, [B-17's](_URL_3_), [B-29's](_URL_2_), [Lancasters](_URL_4_), and [He-177](_URL_1_). Now, if you meant a dorsal gunner's position, then it depended on the aircraft. Pivot machine-gun mounts, like the [He-111](_URL_0_), typically featured no protections, just a simple machine-gun mount. More complex turrets, such as the B-17's dorsal emplacement, had stops to prevent the weapons from firing into the wings or propeller arcs. Later-war remotely aimed turrets like those on the B-29 and He-177 also had similar stops.
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I'm sure there are more examples, but the most famous one I can think of is the Red Baron. Although the identity of the shooter is still ambiguous, [it's fairly widely accepted that Manfred von Richthofen was killed by a bullet fired from the ground.](_URL_1_) Richthofen's autopsy found that he was shot from below by a .303 caliber bullet, as used in a variety of British small arms, including the Lee Enfield, the Lewis gun, and the Vickers machine gun. ([Source](_URL_0_)) I would imagine that as aircraft design and doctrine improved over the decades, the usefulness of small arms in taking down planes would diminish significantly - however, I am only speculating, and I will leave it to an expert to expand further.
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Why did the sun appear on the North side (on their right as they traveled West) of sailors doing around Africa in Herodotus' Histories?
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I'm not familiar with the story you're talking about. But in the Northern Hemisphere the sun sweeps across the southern part of the sky, and in the Southern Hemisphere it sweeps across the northern part of the sky. Half of Africa is in the Southern Hemisphere, so as you sail around it you're going to see the sun in the north (it still rises in the east and sets in the west, but while it's up it will be north). This would have been of interest to the Greeks since they didn't get that far south very often.
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While there’s always more to say on the subject, there was a good answer to this a while back from u/mythoplokos: * [How accepted is the hypothesis that Phoenician sailors circumnavigated Africa in antiquity?](_URL_2_)
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Why do some predators befriend other animals and others kill them?
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As for the Crocodile/Bird or Shark/Fish "Friendships", those are always a kind of symbiosis (two way dependency). The birds free the crocs from things that get stuck in the crocs teeth. That prevents diseases and inflamatory reactions in the crocs mouth, while the bird gets a free meal. The behaviour is an evolutionary instinct for both. The croc "knows" that it could eat one bird but no other bird would then ever again clean its teeth. For the shark its the nearly the same but the fish feed of parasites that would damage the shark, so the shark leaves them be. When tigers befriend goats, or such the common concept from biologists is that this behaviour is not normal and they do not know where this behaviour stems from. Sorry for bad english, only a secondary language.
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Not to quote an old cliche but it's tasted human blood. Seriously, once an animal is no longer scared of people, enough to attack AND eat them. Then it has to go. It's a different story if it attacked and killed a man defending itself or something but when it eats him, it makes that bear realize human beings are prey. Interestingly, humans tend to kill/drive off animals larger than themselves, unless they domesticate them. The level of animal conservation being attempted world wide is a fairly recent thing coupled with the end of new human settlements.
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What is worse for streets: a bus transporting X weight or several cars transporting the same amount of weight.
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The answer is that buses are much worse in terms of road wear that the same weight in cars. _URL_0_ > For pavement design, but also to determine the pavement wear effect of different tyres, the > pavement wear effects of different axle loads have to be determined. Generally this is described > by a Load Equivalency Factor (LEF), where an axle load is said to be equivalent (producing > equal pavement wear) to a number of applications of a reference (standard) axle load. The most > well-known of such a LEF is the so called “fourth power law” which is expressed mathematically > as follows: > > (N_ref/N_x) = (W_x / W_ ref) ^ 4 > > where W_x and W_ref are axle loads and N_x and N_ref are the corresponding number of load applications. This means that a if a bus weighs 2x as much a car it will produce 16x times the wear. If the bus weights 5x the as much as a car it will produce 625x the wear. This means if you compare five cars to one bus you get 5 'units' of wear to 625 'units' of wear.
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Buses are large vehicles. They have more mass. Thus they are much less likely to get thrown around or tip over if a collision happens.
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Why is it much easier to put a ring on a finger than to take it off?
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Because divorce is a messy process. But really, I think the main issue for most people is that there is more flesh the closer on the finger you get to the palm. When you try to remove the ring it tends to drag flesh toward the knuckle which forces it outwards, expanding to keep the ring in place. Putting it on from the other side of that knuckle there is less flesh available to move, and being narrower less likely to be pulled along.
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Lots of wrong answers here. It’s because of your skin and the shape of your joints. Putting on a ring you are basically pulling your skin tight against your fingertip and pushing it up over the cleft of the joint. It can’t go very far so it doesn’t form folds easily. Pulling off a ring your basically pulling on a lot more skin with no hard anchors nearby and it drops off over the cleft of your knuckle so it folds there and jams under the ring.
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How does the styrofoam cup with coffee brew times on it work?
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It is two cups. The top cup has an arrow pointing down. The lower cup has the clock. Twisting the two cups... or rotating the top cup to make the arrow point at the correct time allows coffee drinkers to see when it was brewed. Edit: I'm not sure if you were looking for more than that? Because there really isn't anything special too it other than it was a nifty idea.
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This should help explain it Your Brain On Coffee: _URL_0_
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Why do Hindu's believe in reincarnation?
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Reincarnation – known as Punarjanma – it is one of the core beliefs of Hinduism that is generally accepted by many of its practitioners. Reincarnation is the natural process of birth, death and rebirth. Hindus believe that the Jiva or Atman (soul) is intrinsically pure. However, because of the layers of I-ness and My-ness, the jiva goes through transmigration in the cycle of births and deaths. Death destroys the physical body, but not the jiva. The jiva is eternal. It takes on another bodywith respect to its karmas. Every karma produces a result which must be experienced either in this or some future life. As long as the jiva is enveloped in ignorance, it remains attached to material desires and subject to the cycles of births and deaths (Samsara). _URL_0_ TL; DR if you give up material things and your ignorance, you escape the cycle of reincarnation. Until then, you will be reborn as something better or worse depending on how close you were.
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Inside the body of every living is a **soul**. The **soul** is like the inside of your head, like when you read to yourself. Hindus believe that this **soul** never dies. It just picks a new **body** when your current body gets too old or you have an accident and pass away. And this new **body** can be any living thing. From another human to bug, or a dog, or a cow. This is why many people who practice Hinduism treat all living things with respect, because one day, it could be you.
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Why was the French Revolution successful?
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I know this may be argued against, but why would you call it successful? After dethroning and executing Louis XVI they went through multiple governments, spent years in war, and ended back up with a monarchy again following Napoleon. They didn't have a stable government through most of the 19th century (constant changes).
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Ontopic question: Why is it even called a Revolution at all? Looking at the French Revolution it seems to me that a Revolution is about redistribution of power from a class perspective and/or changing the system of governance from the bottom up. By this impression, the US independence war seems like little more than a Rebellion for the sake of autonomy to me. It certainly didnt champion Humanism like the French die, given that it was mostly a Rebellion by wealthy landowners, who in the End established a republic which was designed to expand and defend their privileges.
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Where do marimo "moss" balls get nutrients?
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Marimo Moss is extremely, extremely slow-growing. Slow enough that all the nutrients they need can be absorbed directly through the water, and even then they need so little of it and grow so slowly. Most tap water contains trace amounts of nitrates, ammonia, and bacteria that produce waste (if it's not chlorinated.) It's not enough for you to be worried about, of course, but it's enough for the extremely slow metabolism of a marimo. If you kept it in 100% pure water with nothing in it (like from a dehumidifier) it would probably die, albeit very slowly.
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It mostly goes into the CO2 that you exhale into the air. Plants then get most of their mass from that same CO2, not the ground that they’re in.
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How certain are we of the existence of quarks?
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The wikipedia page has quite a good [history](_URL_0_). Overall, we are very certain of the existence of quarks. Protons have been probed in [scattering experiments](_URL_1_) and shown to be made of constituent particles. These particles behave as quark theory would suggest. Separately, the various different quarks have been detected in particle collider experiments. There's actually an interesting historical question here; to many, it was originally unclear whether the quark description was a prediction of how things really worked or merely a description that happened to fit. It was only after the various quark detections that their real existence was accepted.
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As of right now, we don't think quarks are made of anything besides quark. There has to be some "lowest layer", and we think that quarks are that lowest layer for neutrons and protons and the like. All experiments we have conducted seem to show that quarks are fundamental, but it's also possible they're made of something even more fundamental we don't know of yet.
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Why does morning light make everything beautiful?
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Photographers call it the Golden Hour. The sun at the horizon has more atmosphere to pass through and so more blue light is scattered. What gets to the ground is redder and lower in color temperature than the rest of the day. The longer shadows also emphasize more geometry than the direct, flat light of noon. Edit: since you seem to be asking more about the 'why' of the aesthetic appeal, it's quite possible that we have an evolutionary leaning towards morning light. To our ancestors it meant they survived the night, it meant warmth and food was closer at hand, and from a biochemical perspective, your pineal gland has kicked your body into waking mode - with huge shifts in melatonin, cortisol, blood sugar, neurological activity and almost every other system you can think of.
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In the evening, there are far more particles in the air, like dust and pollen. The more particles the air contains, the more light is reflected and the warmer the light looks. During the night, these particles tend to sink to earth, as the air is cooling and more moisture becomes available, which weighs them down. This is why morning air feels so fresh, it is cleaner and more moist.
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What would happen to a small CD player in zero-g?
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Sure, the total angular momentum of the system has to be conserved so, in the absence of other forces, the player would start spinning opposite the CD. In fact you can see exactly that in [this video](_URL_0_). Note that you don't need to be in zero-g to see this effect. The same behavior would occur if you placed a CD player on a table with low enough friction.
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"Blank" CDs (CD-R/RWs) have a special alloy (mixture of metals) that can be in a crystalline state that is reflective or an amorphous state that is not reflective. When writing to the disk, the drive uses the laser to heat spots on the disc to about 700ºC. This changes the alloy to its amorphous (non-reflective) state and it will be read as "0." The reflective areas are read as "1." Heating the areas to a lower temperature of 200ºC melts the alloy, but allows it to reform its crystalline reflective state. So by variously heating the tiny spots on the disc, the laser can write 0s and 1s to the disc. :)
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Why do we wear clothes/Are ashamed to be naked?
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A lot of the answers here seem to address the "shame" issue of why we wear clothing, but they're ignoring the largely practical reasons for clothes. Clothes keep you warm, and they also provide some protection for your junk.
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I have always wondered this. I believe it's just part of the stigma we have been tuned into. Religion has a lot to do with it. I'm pretty sure people used to walk around nude when they wanted, but religion came around and told them that it's not proper and they need to cover up.
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During WW2 how was post made possible between the UK and Germany?
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You go through a neutral 3rd country. For Europe popular choices were Switzerland (usually involving the International Red Cross for sending mail to POWs and civilian internees) and Portugal (for everything else). The British Mail service, in order to avoid appearing to colaborate with the enemy, enlisted the help of Thomas Cook & Son. You would send your letter to a Thomas Cook & Son office in Amsterdam (or later when Amsterdam was occupied Lisbon, Portugal). They would then forward your letter into occupied territories. Strict limits were placed on what could be discussed in the letters (for example, if your mail was going through Lisbon no location other than Lisbon could be mentioned) the length of the letters (two pages), and the way the letters were written ("clearly written", no erasing, only topics of "personal interest", etc.).
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Crash Course on Youtube explains it pretty well. WWI: _URL_0_ WWII: _URL_1_ There are more history subjects as well as other vids that look pretty interesting!
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Why can't scientists reverse the solar system to see the initial conditions?
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Gravity is [non-linear](_URL_1_) The solar system is a [many body problem](_URL_0_) How do you know if just reversing the evolution from the current state is the same as what really happened (we don't know of every impact taken by every object in the solar system) etc.
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Understanding how our Solar System works ranging from things very close to the Sun and things very far from the Sun can provide lots of undiscovered information that may or may not present itself immediately. Many discoveries in science aren't explicitly beneficial to human-kind at first. They don't need to be. Understanding the natural order for the sake of knowledge is the foundation that science is built on. It is up to further generations to take this knowledge and build on it. It's how progress is made. Us studying Pluto may at first seem completely pointless, but who's to say the science we establish regarding "dwarf planets" is not going to be used by future space-faring humans when discovering, analyzing, and colonizing new solar systems?
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Why can food be heated relatively quickly (in microwaves, ovens, toasters, etc.), as opposed to cooling (refrigerator, freezer), which takes longer?
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You’re talking about adding (heating) or removing (freezing) energy. Adding energy is easy. Microwaves vibrate the water within the item producing enormous amounts of energy, and the heating elements in regular ovens are shooting 300-500 degree heat straight at your food. Removing energy on the other hand doesn’t happen on the same level in a home environment. Your stove goes to upwards of 600, which is around 530 degrees above room temperature. Your average home freezer on the other hand is more like 20 degrees, or 60 degrees lower than room temp. To put it simply, Home heating options offer you a fire hose, while Home cooling options are a drinking straw.
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Microwave ovens heat food by jiggling molecular bonds in water and fats. This process tends not to get foods to the elevated temperatures needed for the [Maillard reaction](_URL_0_) to take place and browning to occur.
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Soap: When did people start using it? Who invented it and how? How did people get clean before it?
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The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in ancient Babylon. A formula for soap consisting of water, alkali, and cassia oil was written on a Babylonian clay tablet around 2200 BC. The Ebers papyrus (Egypt, 1550 BC) indicates the ancient Egyptians bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance. We do not know how people cleaned before that, but we can guess it from the way most native tribes clean: they use water.
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When humans grubbed about in the dirt and mud, we got dirty. Often times sticky liquids used to fall on us, like sap or blood. Normal water in the rivers was enough to wash ourselves of dirt and blood, but humans noticed that fats helped in removing these sticky resins from our skin. That was the early precursor to soap and from there humanity basically used it as a way to keep ourselves clean of macroscopic things rather than as antibacterial as its used today (not good imo)
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Why our nose runs when we eat spicy food
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Your body is perceiving the spicy food as a threat and it is using mucus production to flush the offending material out of the system.
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Two reasons. The first talks about flavour types of spicy, and the second about hot types of spicy. First, "flavor" is a mix of your sense of taste and your sense of smell. That delicious steak has salt, sure, but it has that wonderful steak-y flavour that's caused by you smelling the food you eat. This is why you don't taste things as strongly when you have a nose-stuffing cold. So a lot of spices used in ethnic cooking, like you'd find in curries or good kebabs, have strong smells that really impact and pump their flavour as they release while you chew 'em. Now hot spicy. That's actually a chemical irritation of your mouth and tongue, not a flavour. Your tongue and taste buds are getting chemically irritated a tiny bit by the chemical "capsaicin" in hot peppers, as an example, and your brain and nerves interpret that irritation as heat. Capsaicin itself has no taste, but its irritation causes a sensation in the same regions of your mouth as your taste buds, so it seems like it does.
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A friend of mine claims Barbarian immigration is the reason for the fall of the Western Roman Empire, how true is this?
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Not being snarky or anything, but there are a lot of related questions [here in the wiki](_URL_0_). The point you make is technically true. All citizens of the empire were given Roman citizenship with the Edict of Caracalla in 212. A lot of these people were Germanic, so in some ways it's true that the Romans were Germanic at that point. However the theory you talked about really isn't accepted anymore . That comes from Edward Gibbon's *Decline and Fall of the Roman Empire* which is highly influential but outdated at this point. Gibbon was writing that when Great Britain was an Empire, so there's a lot of biases in that work to take with a grain of salt. As for why the WRE fell, the wiki can probably answer that better than I can. But to list off a few points, the Crisis of the Third Century, and the repeated encroachment of Germanic tribes across the Rhine were two big factors.
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can one of you guys go into some detail on how the roman system of delegating their lands in the west to incoming tribes is part of the reason of the downfall?
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If water contains hydrogen and oxygen, both of which are flammable, why does putting water on a fire put the fire out, not spread it?
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Water is Hydrogen *ash*. It's already been burnt. It won't burn again.
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Dexter? Yes this is very plausible, depending slightly on how long the fire has been burning. Water has a very high specific heat capacity, meaning it takes a lot of energy to heat up. Added to this the large volume of water present to carry the energy away, and the low starting temperature of the water. Another point is that the gasoline floats and so the heat source will not penetrate to depth.
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Do extension cords lose power?
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There will be negligible ohmic heating loss in the cords, but it will not affect the charging time. The phone charger uses a switching AC to DC power converter that will draw as much power as it needs to output the correct amount.
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At least for phones/laptops/tablet-type devices... The battery is always running the device. The cord simply charges the battery IF it's plugged in. So there's not really any 'drop' or switching.
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Why can I bite into something lava hot and it doesn't bother my teeth, but if I bite into something freezing my teeth hurt like hell?
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Cold causes your teeth to contract, pinching the nerves inside. Hot causes teeth to expand, no pinching.
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The nerves in your mouth become numbed by the cold like if you put an ice pack on a bruise, but since your teeth are more important than a bruise your body freaks out and thinks that something bad happened because it is no longer receiving a signal from your numbed teeth so it tells you that it hurts so you will figure out what is wrong and fix it.
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When did humans start drinking things that weren't water?
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Since I'm interested in seeing this question get answered as well, might I propose breaking this up into a few sub questions so the answer can be found? -What is currently the earliest evidence for humans distilling something so it contained alcohol? -What is currently the earliest evidence for humans making drinkable remedies that involved mixing things into water or other liquids? -What is currently the earliest evidence for humans squeezing fruits and/or other plants for their juices to drink? While it will probably be harder to answer the second or third questions (I don't know how one would document the first evidence for such things - an archaeologist might know this), the first question I posed is probably a previously asked question somewhere around this subreddit. I think these kind of questions are your best bets for getting an answer to your original question though.
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That's actually mostly a myth. There was plenty of drinkable water and there are surviving texts describing how to tell what water is good and what should be avoided. People still drank a lot though. THat being said, medieval booze was mostly very light and you had to drink a lot to get really drunk.
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Why is there that one spot on a paper where you can't seem to make a mark with a pen?
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Possibly because there's a spot of oil or grease on it. Possibly because it's a random spot that your pen skipped and you spent so much time scribbling without effect that you burnished the spot enough that it's too slick to grab the ball point and make it turn.
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[This is what paper looks like](_URL_0_) under a microscope. When you write on it, your pencil or pen leave crumbs of graphite, or smears of ink goo, on those fibers. [This is what an eraser looks like](_URL_1_) under a microscope. It's typically rubber, with some fine sand particles in it, and acts much like sandpaper; it will scrape away the top fibers of the paper shown above, the ones that are smeared by graphite or ink goo, to expose the "clean" fibers deeper inside the paper, where the graphite or ink haven't reached.
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Why do hunters bother wearing any kind of camo when they have orange vests on?
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The bright orange isn't noticeable to the animals they are hunting. What *is* noticeable is a particularly human-shaped outline, and the camoflauge helps break up that distinctive shape.
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Since most animals are color-blind, the orange doesn't stand out to them, but it stands out to other hunters. Wearing orange prevents you from being mistaken as an animal, something that can absolutely save your life when folks get trigger-happy. Source: I grew up in rural area and wore orange often.
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Why do animals shed fur all their lives, but when you make a fur coat, it doesn't shed?
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Because fur on an animal works like hair on a person - it grows and sheadding is a built in way to keep it clean and maintained. Along with grooming habits like licking. A fur coats fur does not grow, as a fur coat is not alive. And the skin has been treated to retain the fur as much as possible.
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With fur, the animal was killed and skinned. With wool, the hair was just shaved off the living animal.
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Why does root mean squared not equal 0?
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Because when you square positive numbers you get something > 0, *and* when you square negative numbers you also get something > 0. Average a bunch of these together, you're going to see a positive average.
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Why is i^2 = -1? Because that is exactly how we define i! Your second question is more interesting. When your start working with squares, it isn't long before you realize that the square of any number is always a positive number. The question that follows is, then what happens when you take the square root of a negative number? Well nothing happens, the square root of a negative number just doesn't exist. Then some old random greek dude said, imagine, there is some number i whose square is -1.. Now suddenly we have a way to express the square root of every negative number! square root of -25 is 5i . It turns out that the ability to express the square roots of negative numbers has very useful applications in engineering so we adopted i and kept it. But it still remains that i has no clear significance when counting. for instance if I had i apples, what does it even mean?! For a long time, it was considered quite pointless and hence the name imaginary numbers as opposed to the other *real* numbers.
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Why were single shot rifles used in European Armies despite multiple shot rifles being readily available by 1875?
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sure, the repeating rifle was available around even the late 1700s. but, like anything. cost/complexity always becomes the main problem. so while they're available, they were expensive due to more complexity. and they weren't as reliable/easy to use etc. i mean, 100 years from now, ppl will ask why we we're still using projectile weapons instead of energy weapons when the technology is available.
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Firearms existed, but were hard to reload. What you would likely have at the time period you are referring to is a flint lock pistol. It took about 90 seconds to reload, could not hit a person across the length of a ships deck, could not be wet, were not powerful enough to reliably kill someone, might not go off at all and blinded you first with a flash and then with a huge cloud of smoke. So if you were able to get a shot off you would likely be charged and had to find another weapon within seconds. Some people carried multiple pistols which allowed them to fire multiple rounds before reloading. However you would have to rely on close combat weapons that did not have any of the problems of a gun. Even as guns improved soldiers were still using knifes to fight in WWI. However in WWII guns and tactics had changed so soldiers rarely relied on their knife, although they were used in some situations where guns were inferior.
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Why do snail trails just start in random places?
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The trail slowly dries and becomes less viable. Enough time has passed for parts of the trail to disappear, giving the appearance that it just started in a random place
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Worms come on the sidewalk cause the ground is full of water and they'll drown if they stay. Snails and other critters can just stay in plants or trees where they usually are.
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did William Wallace impregnate the Princess of Wales as Braveheart suggests?
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With Isabella? She was around 9 years old when Wallace died, so one would hope not. In addition to that I don't believe she had been to England (or for that matter Scotland) until after her marriage (which took place a few years after Wallace died). More than a bit of artistic liberty on the part of Mel Gibson for that one.
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Given he was still a Danish and Greek prince at this point (both titles he would later renounce to marry) and given that his brothers-in-law were Nazi sympathisers, and especially given that the Princess Elizabeth was 14 years old in 1940, was Philip actually seen as her intended during the war? Or just an impoverished Greek prince with British connections?
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How do flocks of birds or schools of fish know where everybody's going?
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These other answers, while correct, aren't answering your question I think. You're not asking how they know where to go, but how they know where everyone is going in relation to them for direction changes while flocking and whatnot yes? They follow simple directions like "Keep X distance between you and the next animal, and go this speed at all times." With this and perhaps a couple others the flock just naturally sticks together. What's interesting is that it ends up creating a fractal organization that is currently being studied.
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schools of fish, or certain flocking birds don't seem to have a social structure other than follow those around you.
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Why do hot chocolate powder packets have a thin aluminum lining?
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Chocolate has oils in it. The oils would leach out if the packet were pure paper, as well as getting moldy from moisture seeping through. The oils would also react to plastic. The foil also keeps light out better than plastic or paper. Milk proteins react to light over time. It's why milk for schools is in cardboard cartons, and it's why gallon milk bottles are (usually) translucent instead of totally clear.
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Chocolate requires tempering, which is a processes that takes very specific high and low temperatures. When the chocolate has been melted it ruins this tempering. The tempering process evens out the fatty acids and ensures a uniform crystallisation. When this is consistent it requires more energy (heat) to disrupt it.
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How can my face "moisturizer" contain four ingredients that start with the word sodium?
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Sodium is just an extremely common element. It also tends to react with just about anything so you end up with lots of different chemicals with sodium in them. Once sodium is in a larger molecule it doesn't aggressively react with other things anymore. For example sodium lauryl sulfate makes shampoo feel more foamy. There's usually other detergents in the soap/shampoo but people assume if it's not really foamy it isn't cleaning well. It's not really the sodium that matters.
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Salt is actually NaCl (Sodium Chloride). When it dissolves in water it dissociates, meaning the sodium and the chloride separate. As such, a lot of the time when you see sodium as an ingredient that sodium is in the form of salt, but not always. Sodium is important in energy drinks because it helps your body move and use water effectively. When you sweat a lot you lose sodium through your sweat (which is why sweat tastes a bit salty), so energy drinks include sodium to replace this sodium lost. Also it just tastes good.
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Why are tires not solid?
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Rubber is not very flexible, nowhere near enough to absorb bumps in the road, so the air helps cushion the ride (along with the suspension). In addition, a solid rubber tire would be expensive and a waste of rubber. Once the treads wore off you'd have to get new ones, wasting all the rubber underneath.
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NASCAR tires are what are called "slicks" which means that they have no tread at all making them very good for gripping smooth surfaces like race tracks. They are also made of very soft rubber which increases traction further. A downside to this soft rubber is that it wears out very quickly compared to normal tires. The high speeds that they drive at also wears out the tire much more quickly than normal which means that they have to change them frequently or risk a blowout damaging the car or having to get towed.
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Is there any known correlation between smell or flavor (bitter, sweet, etc) and nutritional value?
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Yes, that’s the whole point of taste buds (evolutionarily). Small carbohydrates (sugars) bind to sweet-tastebuds, signalling the brain that ’this must be good nutrition’. The weird thing is that most lipids (fat, oil) don’t taste that good even though they are extremely nutritious. Also, animals have during their evolution learnt to associate bad tastes with toxic compounds. For example, bacterial and fungi toxins taste extremely bad (e.g. milk gone bad or moldy bread).
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Taste breaks down into 5 categories: Sweetness, Saltiness, Bitterness, Sourness and Umami (often described as "Savory"). Genetically, humans are programmed to prefer sweet and salty but dislike bitter and sour. However, as we develop, there will be psychological components of taste: 1.) "neophobia"; that is, rejection of new foods on the premise that they are new (as is often seen in children); 2.) the ability to develop new preferences for food based on experience and higher decision making. As an example of "2.)", consider a food that might be associated with a memory, or a food that is thought to be healthier. Therefore, taste preferences may be changed to reflect experiences/knowledge. Source: Birch, L.L. (1999). Development of food preferences. Annual Review of Nutrition, 19, 41-62.
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Why do we naturally recognize some smells as 'good' and others as 'bad'?
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Two things are at work here: instinct and culture/personal experience. At the base instinctual level, there are certain odors that we are naturally disgusted by (shit, vomit, rotting food, dead bodies, what have you) and perceiving their odor negatively makes us less likely to touch/eat/be near them and get sick from germs or posions. Above that are many layers that aren't instinctual and are learned over the course of a lifetime. Some of these come from the culture or place that you live in (for example, people from the country may be more likely to be disgusted by the smell of car exhaust than people from cities, who are more used to it), but most come from one's own personal experiences (for example, people who get food poisoning will often develop a strong aversion to the smell or taste of whatever it was that they ate, even if they loved it before, an aversion that may last for years or even a lifetime).
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Our sense of smell, known as Olfaction, is controlled by[ a host of sensory cells in our nose](_URL_1_). To put it simply, our sense of smell is just a translation of chemicals that enter our nose and come into contact with the [Olfactory receptor neuron ](_URL_0_)to something our brain can perceive as good or bad. If you smell coffee, it's just your brain trying to give you an idea of whether or not it's a good thing to smell. As for *why* this happens and how it's the same for all of us, it's still being researched and is not completely understood.
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What really are proteins?
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Proteins are made up of amino acids. Our bodies can make some amino acids, but not all of them, and therefore we must get some through diet. These are dubbed "essential amino acids." We can't digest all proteins in the world, you need special little biological contraptions called enzymes to break down proteins, and other biological material. Not all species have the same enzymes, which is why some animals can eat things other animals can't, or why some things are poisonous to some animals, and not others (example, we all eat chocolate, but dogs can't/shouldn't). My point is don't go eating fingernails for protein Proteins, in combination with fats, sugars, minerals, etc. make up all the small parts of the cells. Our cells need them to communicate, to build structures, to allow the passage of other small things through channels, and all around they are used to build stuff the cell needs to do work, which can be inside or outside the cell itself.
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I beleive it has to do with the profile of the protein. Complete protein has all essential amino acids in one hit. Most animal product contains all essentials to be a complete protein. There are vegetable sorces that also provide them too.
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Why do terrorist groups like ISIS publicly announce when one of their leaders has died?
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Many such groups avoid it. Mullah Omar, a big Taliban leader, was dead a couple years before it came out. Still, they can't Weekend at Bernie's a terrorist leader forever and if they spin it right they can make their dead leader into a martyr to inspire their followers.
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Another, lesser, reason is so that the mid to low levels members no longer answer correspondence from that person. So when the VP of Hijackings gets killed, the Director of Suicide Bombings doesn't reply to his email (sent by the CIA) asking about when the C4 supply closet is going to be refreshed.
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Why, if royal baby had been named "James", he would not have two "numbers"
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_URL_0_ From the third paragraph: > In order to avoid controversy, it was suggested by Winston Churchill that, in the future, the higher of the two numerals from the English and Scottish sequences would always be used. So the number used would be the higher number. In your example, it would be James VII, not James III or James III-VII.
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It's really very simple. James was king of both countries at once, but the kingdoms were still separate from each other. He was the 6th James to rule Scotland, but the first James to rule England. The regnal number is based off the title, not the dynasty or lineage.
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Before modern counterfeit measures how could people tell if their currency was counterfeit?
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Well if you go back far enough currency was a specific metal, like gold, silver or copper. These metals had a value in the metal itself that did not matter what country issued them, so there was not any issue of counterfeiting as we know it. However people still found ways to scam you out of money. If you look on the edge of a coin, you will typically see that the edge is not smooth. Thats called "reeding" and is used because people used to shave a small amount of gold or silver off the edge of a coin and melt it down to pocket the difference. The reeding on the edge tells people that this coin has not been shaved down.
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The worse a counterfeit is, the harder it is to pass off as real, and therefore the narrower selection of places you could use it at. So, if you have a semi-convincing bill, you might be able to spend it at a diner, but not deposit it at a bank. You'll still get some amount of value from it, but since it takes more work to spend them, they're not worth as much.
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What about a molecule's structure makes it a good candidate to release a photon? (i.e. Luminol)
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Generally speaking, aromaticity, resonance and pi bonds can aid molecules in photon emission (such as benzil) through mechanisms such as triplet emission (phosphorescence) or singlet emission (fluorescence). Additionally Crystalline material can probe photon emission do to the highly packed nature of the material. Ultimatly it depends on the electronic structure* of the molecule. In the case of Luminol, because it's a reaction that causes the photon emission, instead of having the molecule absorb light, it's called **Chemiluminescence**. So, Luminol gets deprotonated (twice) forming a *resonance stabilized* dianion. Next the dianion becomes oxidized by a peroxide which forms an intermediate compound *already* in the exicted state. After singlet decay a photon is released bringing the molecule to the ground state.
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I've never ever heard about molecules made from photons. do you have a link to the article? I seriously question the validity of this idea
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Why does ice taste bad with milk, even though it is great with every other cold beverage?
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Personally I enjoy ice in my milk, I like it to be ice cold and don't mind if it'd a tad watered down at the end
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Two possible reasons. 1. Ice can absorb odors from your freezer (and attached fridge) which will change the taste. 2. If the water is cold when you drink it then your taste buds will be less responsive to the taste of your mouth and your impression of the aftertaste will differ from that of room temperature water.
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Why is it that if a 15 year old kills someone, she's charged as an adult, but if she sleeps with an adult man, she's a "child" and the man must register as a sex offender?
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You've learnt from an early age that killing is wrong. It's only since you've been 11 that you really start learning about sex. Society's opinion on murder is very clear cut. Don't. Sex is so much more complicated. You need to be older to understand all of it than you need to be to know not to murder.
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This is a situational problem that is decided by the judge and proposed by the ( usually) plaintiff if we take imaginary example 1. a 16 year old has 2 beers with friends, then goes joy riding in his dads car and accidently kills someone. There is no reason to try this teen as an adult, for although it was terrible it was not malicious, there was no premeditation and it was accidental result of bad decision making of a young person. Imaginary example 2: A 16 year old is unhappy and feels victimised. he spends 3 months trying to source weapons and ammunition (not hard is SOME countries) then details a plan to kill the three people in his school that constantly torment him. He kills these people, and perhaps a few others. He shows not only a malicious attitude, but also that the acts were premeditated and he understood the consequences of his actions but did the crime anyway. The defence would press to try him as an adult
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The importance of the Mandelbrot set.
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The Mandelbrot set isn't really important *itself*, it's just a very visually appealing and interesting type of fractal. Fractals are important because they teach us that very complicated results can be obtained from simple systems.
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To make the Mandelbrot set, take a complex number, square it and add it to itself, square the result and add it to the initial complex number, square that result again and add it to the intial number, rinse, repeat... Colour your point black if it doesn't run outside of the circle with radius 2. If it does give it a different color according to how fast it flew out of the circle with radius 2. That's the essence, the rest are technical details which are not ELI5 material.
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Why does coming back from somewhere always seem shorter than the trip there?
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I heard an explanation for this a while ago, I'll try to do it justice but I don't know all the scientific terms behind it So when you're going somewhere brand new your brain is taking in all the details, and forming your picture of the area. It seems longer because your brain is working harder to perceive everything about it. On the way back through it you already have those details, so your brain is recalling them as opposed to forming the memories, which uses less power, and feels like it takes less time
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It's because you don't know when it will end. Same goes for a road trip: when you have been down the same road several times, you already have a picture in your mind of the whole thing. The first time through, it's all new and you don't already know when and how it will end.
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Why do we listen to Music?
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You might find [this article](_URL_2_ interesting. It's from a doctor at Duke University that works in cognative neuroscience. The conclusions are pretty complicated and hard to sum up, but basically it says people gravitate to types of sounds in music that mimic the rythems, tones and patterns in human speech. This supports other reasearch that shows that music [stimulates the speech centers of our brain](_URL_1_). It's also widely used in [speech therapy](_URL_0_) for this very reason. Basically, it seems that our brains have developed this big complex region for recognizing and processing speech, and music stimulates it. Weather that's *why* we like it or not is a little more difficult question to answer, but the correlation between music and development of language is pretty solid.
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Most people listen to the radio in their cars, and most people are only in their cars for short drives a couple of times per day. Playing popular songs ensures the most people will listen to that station, and playing the most popular songs multiple times per day ensures that the most people hear it.
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Why does adding a few chicken nuggets in the microwave increase the time it takes to evenly cook them all?
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Think of it as firing small heat bullets into the microwave. Once a nuget has been hit with 100 bullets, it's warm. If there is 10 nuggets you have to wait until 1000 bullets has been fired. If a bullet miss the nugget it will just bounce around until it hit it (the walls are reflective). However, every time it reflects of the wall it loses some energy, which is why the time taken doesn't increase linearly.
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Microwaving food cooks it unevenly, because things like water heat up much faster than things like fat. Microwaving for a long time on low gives more time for heat to spread by conduction through the piece of food, so you get a more even spread of heat.
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Why does the US have a tax on worldwide income?
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Quite simply, it's to prevent Americans from investing money abroad in tax havens. Rich businessmen in other countries -- the UK, for example -- can take advantage of elaborate schemes whereby they officially get their income from off-shore companies and investments, and so avoid paying taxes.
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Other countries outside the US have tax policies that lower the tax burden. However, it costs money to manage this, so it's only worth it once you cross a threshold. Once you're past that threshold though, it's all gravy. So rich people hire someone to handle their money, they open accounts and companies and route their money/business that way.
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Is there any evidence that video learning is more effective than text based learning when accessing the content for the first time?
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Wouldn't the relative effectiveness depend in large part on the learning style preferences of the target students?
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Programming, for anyone who's never tried it, is a very focus-intensive activity, and can be not strenuous at all. These things make marathon learning very useful, as new information can easily be picked up and utilized. (That is to say, you could learn how to use a function and then be able to use that function proficiently in mere seconds.) Compare that to math, which is hard to understand intuitively at most levels. Learning new math tricks takes time, so marathon learning is not a generally good idea in math. Or compare that to history, which must be learned sequentially and intensively for a student to create generate something worth reading. Or compare that to pottery, which is not a high-focus field and thus is not suitable for long sessions in which students may become bored. Many companies will use hackathons to get programmers or students to learn how to use a specific language, API, hardware, etc. Sometimes, hackathons are just "hey, go work with other people and make something cool."
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Which stimuli reactes the fastest? Visual, auditory or tactile?
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Our hearing is the fastest. There is an excellent radiolab podcast where they tackle this, here is a clip from the episode, "Hearing is our fastest sense. (Who knew?!) Horowitz says that it takes our brain at least one-quarter of a second to process visual recognition. But sound? You can recognize a sound in 0.05 seconds. And our brain is so adept at hearing the differences between sounds, we can sense changes of sound that occur in "less than a millionth of a second," according to Horowitz's book. Why this need for auditory speed? It's our evolutionarily-shaped emergency response system. It let our ancestors hear a twig snap in the woods at night, when all was supposed to be quiet and they couldn't see. Yet, for most of us, we're wired to tune out non-essential sound, so the world doesn't feel like a sensory overload".
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Parallax. A nearby object crosses a wider degree of your field of vision than a distant object, so the *apparent* motion is faster.
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How does sneaking up and knocking someone unconscious from behind really work? Is it at all like in the movies?
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No. A blow to the back of the head/neck can knock someone unconscious(like in the movies) but it is highly likely to lead to some damage or even death(oddly they never show that). It used to be not uncommon for police to carry blackjacks or the like to deal with unruly suspects in this manner but it was fatal far too often and the practice was phased out.
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Knock outs are less about absolute force from the punch and more about the forces acting on different parts of the brain. Specifically, a strike that causes the head to twist either down up or side to side can place sufficient stress on the brain stem leading to loss of consciousness. Not surprisingly, variables associated with loosing consciousness are related to neck length, and neck muscle strength which can absorb some of the twisting forces.
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What is the minimum number of human colonists needed to prevent pathogenic inbreeding?
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There's not a hard cutoff. It's highly dependent on the genetic composition of your colonists and what sort of pathology are you willing to put up with. Pathology from inbreeding isn't a death sentence for a population, it mostly just causes elevated death rates until the bad genes get weeded out (and makes populations more susceptible to diseases) So in short, no idea.
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I believe the smallest population size to prevent inbreeding is ~4000 individuals. If the species is limited to < 1000 individuals then inbreeding will be a serious problem which might cause the species to die out completely. There are methods to slow inbreeding such as planned mating with less-related members, cross-breeding with another compatible species, screening for recessive genes etc. However when the population size is small, genetic mutations occur at a faster rate and cause the species to rapidly adapt. It might be that a new species will emerge or genetic defects will accumulate until the population is no longer viable.
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I don't feel as if I'm using any muscles or doing anything to prevent myself from urinating on myself. What distinguishes me from an infant?
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The baby doesn't know any different (hasn't been "potty trained"). You on the other hand recognize the symptoms of needing to urinate, so before you pee yourself, you use the correct facilities
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The sensation of needing to pee is dependent on how much the bladder stretches. But other things can make the bladder stretch like pressure in the stomach from a large meal, feces in the large intestine and for women a baby. Also the sensation of peeing is dependent on the orientation of the internal structures thats why when you have to pee it feels different when you stand or sit Source: my neurophysiology class
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Why isn't Mexico as multicultural as other countries in the Americas?
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I've argued in the past that Mexico is in fact one of the most diverse countries in the Americas and potentially the world. However, Mexico's diversity is somewhat hidden by broad nationalism and institutionalized class systems. As /u/Heresiarca mentions, the bulk of Mexico's diversity is in its indigenous heritage, with the country containing at least 11 language *families*, making for 68 official indigenous languages within the country. For comparison, that's roughly the number of languages in Europe as a whole, including regional variants. But even this is an an underestimation of Mexico's diversity, as its wealth has historically given it strong access to European and Asian trade networks. Mexico is a cultural mixing pot of cultures. The most famous example of this is the introduction of [Döner](_URL_0_) by Lebanese immigrants. Indeed, go through any street fair in Mexico and you'll see clearly identifiable symbols borrowed from cultures.
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Part of the answer to this has to do with the creation of national identities in the 19th c. In Mexico, intellectuals and elites used the idea of mestizaje and a mestizo (mixed European-indigenous) identity to create a sense of nationhood. The popularity of this identity as it grew in the late 19th c. and exploded after the Mexican revolution. In Mexico, major political figures like Jose Vasconcelos heavily promoted the mestizo as the ideal for Mexico. Consequently, in Mexico there are individuals of wholly European ancestry and wholly indigenous ancestry who identify as mestizo. Remember race is social and cultural not biological. That more Mexicans than Peruvians identify as mestizos says more about the social and cultural past than it does any 'racial' past.
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Why does food stick so strongly to plates or frying pans after its sat out a few hours compared to when it's fresh?
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When food is wet, it tends to be soft and goopy. In this liquidy state it can seep into microscopic cracks and such. As it dries out, it loses moisture and both shrinks and hardens. As it shrinks and hardens, it solidifies its grip on the surface as if it were clenching its fists. Once it's hard, as all hard things are, it becomes difficult to move and thus to clean.
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It's all relative. Good bread is moister than comfortable air. Good chips are drier than nice air. When left open either food's moisture levels move toward that of the surrounding air, thus wetter chips, and drier bread.
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Do magnetic fields affects our brains connections?
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Absolutely. [Transcranial magnetic stimulation](_URL_0_). The law is pretty simple, a changing mangnetic field creates a voltage, which drives current. In this case, current through the brain. The magnetic field must be varying, or you get no voltage, and hence no current, and it's the current that will driving activity in your brain cells.
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There aren't any significant effects from the fields that people have been subjected to, about 10 Tesla (a typical MRI is ~2 T). It's difficult and expensive to make fields that are stronger but still big enough for a human to get inside. [Here](_URL_0_) is a review on the topic that might be a bit out of date.
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What effect would a violation in CPT symmetry have on our current understanding of physics?
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You can derive CPT symmetry from Lorentz invariance (the laws of physics are the same in every reference frame + there is a speed limit) and quantum field theory, which is based on Lorentz invariance. A violation of CPT would mean quantum field theory cannot be right. We know it is at least an excellent approximation, but CPT violation would mean either the universe is not Lorentz invariant (there is a preferred reference frame, or something else weird is going on) or the whole idea of quantum field theory is a dead end. The latter looks very unlikely given its success so far.
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CPT symmetry means that if you flip C, P, and time, all of them, the particle will behave the same. It doesn't behave the same if you flip just C or just P or just T.
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Is it possible for a liquid to be volatile but still have a high specific latent heat of vaporization? Why?
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They're definitely interlinked. A liquid at room temperature will contain molecules with a wide range of energies, and the higher the population of molecules with enough energy to enter the gas phase, the higher the vapor pressure you will measure. Actually, the best example I can think of to answer your question is water. Vapor pressure (at room temp) generally tends to increase with decreasing molecular weight, and if you look at other molecules with similar weights (methane, for example), they always boil at temperatures far lower than water. This is because the hydrogen bonding in water is uniquely strong, which keeps it in the condensed phase more easily. Specific latent heat of vaporization is related to the energy per molecule required to leave the liquid phase (*i.e.* overcome all intermolecular forces). So water takes a lot of energy to vaporize, but still evaporates pretty quickly due to its small size. This is why evaporative cooling with water is so effective.
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No. When two liquids with different boiling points are mixed together the bp of the mix is lowered overall. When you boil the mixture the vapor will be mostly the low BP fluid but will still contain some fraction of the high BP fluid. The same behavior occurs with table evaporation
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Why not use fat for breast implants?
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The body can reabsorb that fat and place it where it wants.
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Fat tissues can hold more heat and fluid than lean muscle tissue, making for a more hospitable environment for decomposing bacteria and fungi, this allows colonization of the tissues to occur faster but the difference will likely only be slight, as far as I am aware.
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Why does NASA digitally colorize photos from the Hubble and the Mars Rovers?
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Images, particularly from the Hubble, are frequently taken in multiple frequency bands in order to obtain more information about the target object by comparing outputs at different frequencies. You can assign a colour to the each frequency band and combine them to see the different bands in a single image. Hubble images can also be colourised based on the emissions spectra of different gases present in the target, which allows you to get information about the distribution of different components by looking at the colour image. The rationale for colourisation of images released as press/publicity material (rather than the versions for scientific consumption) is mostly just that they look pretty, though. Part of NASA's mandate is to increase public engagement with what it does and with science in general, and the pretty images are a lot more eye-catching.
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> Taking color pictures with the Hubble Space Telescope is much more complex than taking color pictures with a traditional camera. For one thing, Hubble doesn't use color film — in fact, it doesn't use film at all. Rather, its cameras record light from the universe with special electronic detectors. These detectors produce images of the cosmos not in color, but in shades of black and white. **Finished color images are actually combinations of two or more black-and-white exposures to which color has been added during image processing.** The colors in Hubble images, which are assigned for various reasons, aren't always what we'd see if we were able to visit the imaged objects in a spacecraft. We often use color as a tool, whether it is to enhance an object's detail or to visualize what ordinarily could never be seen by the human eye. Source and more is [here](_URL_0_)
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Could someone tell me more about the US Navy plans for a British invasion between WWI and WWII? What kind of books would you recommend for the topic?
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It was part of the color coded war plans. The British empire one was war plan red, Germany black, Japan orange etc as well as a bunch of other scenarios like problems in Mexico or Cuba. Basically red found that the British would have an upper hand and use Canada as a staging ground for invasion but eventually the US would win. Plan Red-Orange (Uk and Japan) found that USA was not prepared for a two ocean war and should focus probably on the Atlantic and not the pacific. Which is exactly what the US did in WWII, with the obvious exception of the different enemy.
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"D-Day Through German Eyes" by Holger Eckhertz. It is a series of interviews done by a German military journalist during the war, and spent the postwar years interviewing fellow veterans of the Normandy campaign. The interviews were kept in the family and recently published by the grandson. The interviews show a lot of variety, but some common themes include the shock many defenders felt when they saw the mass of ships and aircraft on the horizon. They had been anticipating an invasion, but the sheer scale was hard for the mind to grasp. They also frequently complained that the western Allies were invading at all, and that the local French treacherously betrayed them through sabotage. Volumes one and two are both widely available, in print and electronic, and sometimes even for free through certain sites shared libraries. So this is maybe the most accessible and engaging source on the subject, without going into archives.
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The true meaning behind Orson Welles' famous quote "We're born alone, we live alone, we die alone."
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Its important to include the next part of the quote: > Only through our love and friendship can we create the illusion for the moment that we're not alone Like any quote, the interpretation is ultimately up to the reader, i would suggest in this case, Orson was illustrating that ultimately, we are truly alone in this universe, from the moment we are born, to the moment we die. We view and experience the world through our own eyes, and we are only privy to our own thoughts and experiences. People can share their thoughts and experiences with others, but ultimately, you can only understand them vicariously, through your own eyes, as it were, we can not TRULY understand what its like to live as someone else. But, through love and friendship, socializing with others, we are capable of creating a momentary illusion that we are not alone, but that is all it is: an illusion, because at the end of the day, you are still stuck within your own mind and see the world through your eyes.
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It means there's a better chance life of some kind developed there. Mankind has always had some sort of 'are we alone in the universe' feeling nagging at us. As long as Earth is the only place where we know life developed, we know we might be unique. If there's a second example of life, even grubby little bacteria, it means life might be everywhere in the universe.
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In Quantum Physics how can simply observing something change the way it reacts?
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You have a magnet hidden under a piece of cardboard. Your only way to find the magnet's location is to move another magnet over the top of the cardboard until you feel the magnet beneath resist. In order to feel the resistance, the magnets have to push on each other; so if you feel the push of the magnet underneath your magnet must have pushed the magnet underneath away. That means your "observation" of the magnet underneath affected the magnet and changed the result. When dealing with tiny quantum things, we have the same problem. The only way we can observe an electron is to push on it with another electron; which means we will change its behavior by "observing" it.
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How do you watch without causing some sort of interference? Think of it like this. Before observing the particle, we are not certain of the particles location. We therefore represent it with a probabilistic function. This probabilistic function basically gives us the probability of finding the particle in a specific location if we conduct an experiment to measure the particle's location. Well, if we conduct that experiment, we will deduce the particle's location. So, the new function representing the particle is just a peak at the point we found the particle. It's not glamorous
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"Red sky in the morning, sailor's warning; red sky at night, sailor's delight."
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I recall seeing a post in askscience about this, but it was a very long time ago and I'm sure I wouldn't be able to find it now. The phrase does actually have some scientific merit. If I remember correctly, it's something like this: we get red sunsets and sunrises because of the way the dust in the air scatters the light. Red sky at night means that there is some dust to the west. Dust in the air is generally a sign of high pressure and good weather - and since weather systems move from west to east in most of the world, that means there's good weather coming. Red sky in the morning means the high pressure is to the east, and there is lower pressure to the west, meaning that poorer weather is on the way. I might have the details slightly wrong, but it's along those lines.
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At sunrise/set you are looking at the sun through a much larger cross section of atmosphere, scattering the light more. This is also the reason the sky is red at those times.
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Why do most babies have blue eyes, but then develop to different colors?
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You can think of blue eyes as the 'default' colour that eyes have just because of their structure (this colour is caused by [rayleigh scattering](_URL_3_)). As soon as you add a pigment - in this case optical [melanin](_URL_0_), the colour of the iris will change to green or brown, when there is lots of pigment. Babies (especially caucasians) are often not producing their final levels of melatonin until up to a year of age. So they often start blue, then get progressively darker with age before acheiving their final melatonin expression levels - usually by around 6 years of age ([ref](_URL_2_)). Males go through a second phase where there eyes become more lighter or more golden coloured during puberty, before they darken again at adulthood ([ref](_URL_1_)). For non-white people there is a whole lot less data, it appears that infants have a much higher expressioon of melatonin much earlier, so they are born with already dark eyes and any further changes are thus pretty hard to detect.
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The default state is blue eyes, that's just the colour caused by the structure of the iris. Brown pigment, melanin, is added to darken he eyes and probably gives some protection from UV and glare (melanin in the skin absorbs UV, people with very light blue yes report trouble seeing in bright light) Anything other than brown eyes is a mutation.
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Why do newer vehicles have cigarette lighter ports but not cigarette lighters? Why don't they just switch to native AC or usb only?
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Cigarette lighter ports are a really shitty connector, but unfortunately they're the standard, and standards are hard to change. 120v sockets are problematic to add, since you need an inverter, which is expensive. USB ports are problematic, since they can only handle about 5 watts, compared to ~120ish for a cigarette lighter port. So I guess we're stuck with the cigarette lighter plugs.
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They are for cigarette lighters. Once upon a time, smoking in the car was common and electronic devices small enough to be powered by a car were science fiction. Cars thus had a device to light your cigarette, so drivers weren't distracted by their Zippo while driving. When electronica came along, the choices were: a) adapt to the cigarette lighter socket; or b) entice car manufacturers to add a different outlet. Making 120VAC house current inside a car is difficult, since cars run on DC, and the cost wasn't optimal. It seems that (a) got the most electronics deployed, so that's what the electronic people did. Over time, too many cigarette lighter to USB gadgets were sold, and cars started having USB ports in them because it's easy to make 5VDC from 12VDC. Some cars have AC outlets, but not anything like the majority.
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How does the heart know to beat faster?
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In a normal, healthy heart, the heart beat is triggered from the sinoatrial node in the right atrium. The sinoatrial node will generate a heartbeat of 60-100bpm all on its own, with no input from anything else. The sinoatrial node is also connected to the sympathetic nervous system (via T1-4 spinal nerves) and the parasympathetic nervous system (via the vagus nerve). The sympathetic system generally 'speeds up' (flight or fight) the body and the parasympathetic slows it down (rest & digest). These two systems are both firing continuously and a balance is formed, when one system increases it's firing rate, that systems effects (i.e. speeding up the heart rate in the case of the sympathetic system) dominates. The sympathetic and parasympathetic nervous systems release neurotransmitters that work on receptor sites in the SA node. The control of the sympathetic and parasympathetic nervous systems is primarilly controlled from the medulla, in the brainstem.
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Your heart is made up of a special kind of muscle called cardiac muscle. This kind of muscle cells are designed to work well in a variety of different stresses. It has more engines than a regular cell, if that helps. The heart can't get tired, per se, as this would be counter to survival. Evolution took care of that problem a long time ago. It can get over worked though. When it beats too fast, the chambers don't have enough time to fill all the way up and it doesn't pump as well. This can, and does kill people. Cardio excersize helps make sure your heart can pump high, but not too high, when you need to do something strenious...
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How are birthmarks made?
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A birthmark is a benign irregularity on the skin which is present at birth or appears shortly after birth, usually in the first month. They can occur anywhere on the skin. They can be things like excess fat, blood vessels, or skin pigment.
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Birthmarks are benign (medically harmless), **not hereditary**, and depending on the color and texture may have been caused by any of several irregularities in development. There's no meaningful pattern to their shape or size. Not your fault, but a lot of ELI5 questions these days are "Huh, just noticed an odd aspect of my physiology. How did this help my ancestors survive on the Serengeti?" The answer is always more or less: "It didn't help, but it didn't hurt enough to kill anyone before they had kids." Evolution doesn't breed paragons of adaptation, where every single trait is a feature -- many traits are just harmless bugs. Evolution only weeds out traits that make it harder for the organism to reproduce successfully.
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How strong is the evidence in favor of brain training games? Obviously we can get better at the games themselves with practice, but do the skills really translate into better overall brain "power"?
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From what I have read the whole brain training thing is well funded hyped up science jargon designed to sell you something you don't need. Effects do not generalize and are temporary. Do yourself a favor and go read a book, go for a walk, and do something new. See this meta analysis: _URL_0_ "The authors conclude that memory training programs appear to produce short-term, specific training effects that do not generalize."
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There is some evidence to suggest electrical stimulation of the motor cortex while doing a task increases the rate at which you learn it. There are some products, like Halo headphones, that claim to do just that. While I know electrical stimulation of the motor cortex is being studied fairly extensively for the purposes of speeding rehabilitation I'm unsure of the amount it has been studied for the purposes of improving athletic performance.
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What happens when two event horizons intersect?
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The event horizons (when suitably defined in this changing and unsymmetric spacetime) merge into a single surface. In simulations the two event horizons in a merger protrude towards eachother and join in a thin tube, then the tube fattens and the joined horizon then quickly settles into the standard shape for the final black hole during the ringdown of the merger. Now, this is to emphasize there is always only one event horizon (possibly disconnected). It cannot intersect. If you fall behind this horizon, by definition you will end up in a singularity some time in your future.
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When two black holes meet each other -- i.e., their event horizons touch -- they merge to form one larger black hole.
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What value to society does investment banking add?
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Investment Banking (very simply) moves money placed into savings back into the economy. A worker gets paid and takes his money to the bank, putting it there for safe-keeping. Without investment banking, that money is - until the owner of the account accesses and spends it - "lost" to the economy. An investment bank will use the money that has been placed in it by workers and then loan that money to other people and businesses who can then spend it, thereby keeping it 'working' in the economy. A very basic reason investment banking has become so lucrative is that banks can loan out far more money than they have, thereby accruing huge amounts of interest.
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Really good anawers here, but I will tell you what my dad told me when I was about 5. The stockmarket and banks moves money from people who have it to people who have use for it.
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how the price of crude oil has plummeted yet gas prices stay above $4/gal and oil companies show record profits.
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Most of the companies' record profits has more to do with the overwhelming demand around the world for oil - it's just that important a commodity. When you break down the price of a gallon of gas, only maybe 10 - 15 cents is "profit." Think about how much of something you need to sell if you only make 15 cents profit per unit of whatever it is that you're selling.
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That the oil price has been increasing is more a function of artificial drops in production by oil producing countries (like OPEC) than it is an actual fall in the supply. The reason the price has fallen recently, is that oil producing countries have increased production in response to competing oil production technologies, like shale oil or fracking. They can force the price below the level where those technologies are economical, ensuring the cartels monopoly on oil production even if they are now making less money as a result.
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if a pure black object absorbs all light and doesn't reflect any, what would it look like?
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If it truly was purely black, you wouldn't be able to discern any of the object's features except its rough shape. It would literally look like a silhouette.
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Black absorbs light, white reflects it and clear allows light to pass through it. Various colors on the spectrum absorb SOME wavelengths of light while reflecting other wavelengths which we perceive as colors within the visual spectrum. On a scale of transparency (clear) vs opacity (color), clear is 0% color with no properties to absorb or reflect light.
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Why do some people freeze when they get Scared?
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The flight or fight response is automatic and sometimes if people can't run they freeze so their minds can figure out what to do. Either that or I'm talking out my ass
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I'd like to extend this with a question as well. If they aren't, why do they feel fear when something attacks them?
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If Whisky Needed a Little Water, Wouldn't the Distilleries Add It?
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Some people like whiskey with a drop of water, some people do not. It is personal taste. However if the whiskey manufactures were to add in the drop of water then there would no longer be a choice. It is easy to add a drop of water at a bar, it is impossible to remove it.
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Adding water to whisky will cause more of the flavors to be released, so most people like it. Chilling whisky makes it taste less, but it also makes it burn less so some people like it (but it's still a crime to do it to a good whisky). Ice chills and adds water at the same time. Now, vodka should be kept in the freezer, since a good martini needs less water than chilling vodka with ice adds.
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What Nazi-sponsored consumer goods existed from 1933 to the end of the Second World War?
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Well ... One comes to my mind : Fanta , the lemonade. It was created by the coca Cola Company in 1940 iin Germany. They couldnt import the coca cola syrup anymore that was needed for the production of coke in Germany but didn't want to let the plants run empty. As such the local production managers invented a new drink with what they could get in Germany at the time. It was originally based on whey but with an orange taste. It came to the us in 1955. So quite a time after the war.
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Hitler really wasn't the economic genius that a lot of people somehow think he was. The German economy was already recovering by the 1933 when he came to power (the previous decade was referred to as the "Golden Twenties" because of the country's economic success). Instead of improving the economy, the Nazis created an economic system that was doomed to fail if a war did not start - any development was a result of massive amounts of borrowing from other countries so Germany was saddled with huge debts. Conditions did not improve for workers either, despite what their propaganda said - hours increased, average wages actually decreased, and unions were banned. Basically, the economic plan was "do what it takes to prepare the country for war. When that's been won wel¡ll be rich in resources and won't have to worry about paying anything back."
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If a limb is amputated, how do the blood vessels regrow so that blood can still be circulated?
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I know that [this](_URL_0_) is meant to be humorous, but it go me thinking (and this seems like a good place to ask) - if you do an amputation as shown above, would the blood automatically start to recirculate, or would you have a problem with blood pooling in the amputated limb?
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they repipe the main veins and arteries into a mechanical pump to pump the blood during the transplant.
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How do animals survive in subzero temperatures without freezing, especially those that are really small?
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They have body fat and fur to keep them warm. They also burrow into the ground so they lose less heat to the surrounding environment while resting or sleeping. They also hole up with other members of their species, and use each other's body heat to stay warm.
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Here's a list of a few common ones. ([Link](_URL_0_)) The thing is, most of these animals are actually quite closely related in evolutionary time, so their proteins are similar and will break down at similar temperatures. That being said, birds are the warmest on that list, which makes sense because they're the most distantly related of the group. They're reptiles and the rest are mammals. There are heat-making insects too, but they don't usually create uniform internal temperatures and aren't super relevant to your question.
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f humans are 95% similar to chimpanzees then why aren't there more chimp-human organ transplants?
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Because organs have to be a lot more similar than that. Even among humans, you can usually only get organ donations from close relatives or strangers who happen to randomly match your cells' markers.
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It depends what your expectations are of such a hybrid. It may be possible to use a chimp egg and transfect in some human DNA then fertilise and implant but this isn't going to lead to a talking human-chimp. Humans and chimps are very genetically similar but we have different chromosome numbers 46 vs 48 respectively so it'd be problematic to go much further.
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Will someone please explain what torque is?
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torque is the rotational analogue of force. torque makes things rotate. things like wheels.
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Torque is the twisting force applied to the crankshaft of the engine. HorsePOWER, is power, which is force (torque), multiplied by engine speed. There's a constant in the formula of 5252, so that's why you always see the HP vs. TQ curves on a dyno graph intersect at 5252 RPMs. So torque is force, e.g. how much the engine can push on the crankshaft, where as horsepower, is how it can apply that force over distance, and over time.
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“The only way to get alcohol out of your system is time”, what about exercise?
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Alcohol is metabolized in what's called pseudo-zero order kinetics. That means at most concentrations, your body is metabolizing it at peak capacity already. The _average_ rate of elimination is around 0.02 % BAC (around one standard drink) per hour.
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Alcohol decreases the body's production of anti-diuretic hormone, which is used by the body to reabsorb water. With less anti-diuretic hormone available, your body loses more fluid than normal through increased urination. [source](_URL_0_)
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How (and where) do different types of painkillers work?
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You basically have two types of over the counter painkillers. Most of them, including ibuprofen (Motrin and Advil), aspirin and naproxen (Aleve), fit into a class of drugs known as NSAIDs which stands for "non-steroidal anti-inflammatory drug". The other is Tylenol, which sort of has it's own mechanism that isn't completely understood. NSAIDs (and possibly tylenol) work on an enzyme called COX. COX is involved in creating various molecules that lead to inflammation. Inflammation is essentially the swelling, redness and pain. NSAIDs prevent COX from creating these molecules and thus reduce the pain, redness and swelling associated with the inflammatory response. Now, this COX enzyme is everywhere in the body, so the action of the medication isn't actually in a specific area. It is all over your body. I hope that was simple enough. I tried to keep it as basic as possible.
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A lot of pain killers reduce pain by reducing inflammation. Inflammation is often the body's response to injury (think swelling after a bump). This inflammation is the cause of a lot of the ongoing pain for some injuries, but has nothing to do with the initial pain of a bump. Having taken (certain) painkillers will do nothing to stop the in-the-moment pain of a sudden injury. There ARE painkillers that will lower or even completely eliminate the feeling of sudden pain. If you've had dental work or minor surgery while conscious you may have had some of these painkillers. These kinds of painkillers affect either the effectiveness of your nervous system at sending pain signals at the site (local anesthetic) or at your brain (general anesthetic). The methods they do this by are varied. So in short, some painkillers just reduce a *cause* of pain (swelling), and some actually stop or slow pain signals all together.
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Why does gaming get a bad rep in the media, and how did it start?
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Gaming has developed a lot of negative stereotypes around it that are simply not associated with other forms of recreational media. The most obvious being that it glorifies violence, but there there are also societal/psychological criticism aimed around the idea that it harms social skills, makes kids lazy/fat, and is supposedly more sexist/male oriented than other forms of entertainment. Such a wide range of critique keeps the negative stereotypes alive, but all started with the sensational headlines about violence in the 90s.
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Well if you're following current video game trends, imagine thousands of early access games being sold as finished products without even the possibility that it will be updated. This quality of game was vastly more common than a finished game, as companies were just trying to jump onto the bandwagon of the video game fad even though they didn't understand it. And because it was before the internet, you couldn't easily tell which game was actual of quality or not until either you or someone you know had already paid for it - you couldn't pirate it, and most places didn't have return policies for video games. So the majority of the gamers (which were mostly doing it because it was a fad) stopped playing video games as they didn't find the gamble worth it. Video games were seen as a waste of time, demand for them fell, and companies stopped developing games.
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Why is first to file a good idea?
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I assume it simplifies things. It's easier to prove someone patented something first than to prove someone thought of something first.
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Hi, I worked on the Windows team at Microsoft back when the Registry was created. The idea was to provide a reliable, secure way to store configuration data for a wide range of programs and operating system features. It had to be accessible during the boot process, so its complexity was somewhat limited. Perhaps the biggest benefit compared to INI files is that each key can have a separate access control list (ACL) so different people might be given permission to edit different keys. Another benefit is resistance to file corruption when making a small update. Data items in the Registry can be as simple as a number, or more complex such as the pathname of a file where the program is supposed to get more information. But they are just data. So for example if you change or delete a file, mentions of it in the Registry are not automatically changed or deleted.
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How come some holidays are based on a certain date while others are based on a certain day of the month?
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Back in the 1970's the US government decided to move some holidays to Mondays so that people could have a 3 day weekend and get more rest and enjoyment from them. Certain ones were not moved, religious ones such as Christmas and Passover since those were not the purview of the government or ones whose significance owed to the date, 11/11 for instance.
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It really is arbitrary. February has 28 days because originally it was the last month of the year. By now changing the length of February will be needlessly complicated and pointless.
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