question stringlengths 3 301 | answer stringlengths 9 26.1k | context list |
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When fish take out oxygen from water, do they leave behind hydrogen? Or how does that work? | Fish take oxygen (O2) that is *[dissolved in the water](_URL_1_)*, not the oxygen from the water (H2O) molecule.
Further, taking out oxygen from water is a chemical reaction, not a nuclear one. While it takes a lot more energy than filtering out oxygen gas from water, [you can do it with a battery](_URL_0_) instead of... | [
"Laboratory tests conducted by fish culturists in recent years have demonstrated that common household hydrogen peroxide can be used safely to provide oxygen for small fish. The hydrogen peroxide releases oxygen by decomposition when it is exposed to catalysts such as manganese dioxide.\n",
"Dissolved oxygen (DO)... |
Why did soldiers in the Civil War assume aliases? | I haven't read much about the use of aliases during the American Civil War, but something called "bounty jumping" was indeed a practice people engaged in, and this would likely involve the use of an alias. So during the war, one could earn a bonus for voluntarily enlisting in the army (the idea being that you might get... | [
"Although it is unknown what led Lanning to use an alias, aliases were common in the Civil War, often used to prevent people's families from finding them. Lanning was additionally estranged from a number of people in his family; in his widow's pension file, Lanning remarks to his aunt about his deceased parents in ... |
how do they get bottles to break over people's heads so easily in movies? | It's usually sugar glass. Here's [the wiki for it](_URL_1_)
IndyMogul also [has a good how-to video](_URL_0_) if you want to make your own. | [
"The vast majority of bottle cages consist of a single hoop of metal tubing or rod bent to hold the bottle snugly and engage the top, or an indentation in the case of larger bottles, to prevent it from bouncing out.\n",
"To shotgun a beverage, a small hole is punched in the side of the can, close to the bottom. I... |
why are we more attracted to a person when they're tan? | Are we? This seems much more like a personal preference than a universal truth. I searched for your question and found an answer [here](_URL_0_). | [
"Improving appearance is the most-cited reason. Studies show that tanned skin has semiotic power, signifying health, beauty, youth and the ability to seduce. Women, in particular, say not only that they prefer their appearance with tanned skin, but that they receive the same message from friends and family, especia... |
The Emperor of China was believed to be the ruler of all under heaven. If so, what were their opinions of foreign rulers? | Your understanding is exactly right. Even until the late 1800s the majority of the Chinese literati felt outraged as the notion that their Emperor is addressed as an equal by foreign entities. I will give you a few examples:
1) The rivalry of China and Japan could be traced to the point where Japanese rulers were proc... | [
"The center of this world view was not exclusionary in nature, and outer groups, such as ethnic minorities and foreign people, who accepted the mandate of the Chinese Emperor were themselves received and included into the Chinese \"tianxia\". In classical Chinese political thought, the \"Son of Heaven\" (Emperor of... |
when a large animal at a zoo dies, what is done with its body? | according to a roommate who worked at a zoo, they are often fed to other animals. | [
"The zoo witnessed a series of animal deaths in 2004 and 2005. In August 2004, a Lion-tailed macaque was found mysteriously dead. An emu and a tiger were also reported to have died mysteriously. On 4 September 2004, an elephant died, reportedly of acute hemorrhagic enteritis and respiratory distress. It was reporte... |
What are the rarest cells in the human body that have an important function? | Long-Term Hematopoetic stem cells - These are hematopoetic stem cells that single-handedly have the power to recreate your entire bone marrow and hematopoetic system; we do not know exactly how many of them are there in each human individual, but in mice, for example they just constitute 0.00019% of the cells in just t... | [
"Due to the different array of markers expressed in these cells, it is difficult to specify their exact cell-type and function. Newer findings propose that pituitary FS cells are made up of groups of cells with disparate immunophenotypes and are not a homogeneous population; however, it still isn't clear if these g... |
why do phone calls consume the most battery on a cell phone? | The answer to both questions is related.
Transmitting a reasonable facsimile of your voice through radio waves is data-intensive. Compare, for example, the size of a digitally-compressed music file (~5 megabytes) to the size of the transcript of its lyrics (1 kilobyte, less than 1/5000 the size). You could send 5000... | [
"The 999 phone charging myth is an urban myth which claims that if a mobile phone has low battery then dialing 999 (or any regional emergency number) charges the phone so it has more power. This was confirmed as a myth by several British police forces who publicly cited the dangers of making such calls.\n",
"The ... |
What are the effects of the smoke generated by the fires in Australia? | Hi! Atmospheric chemistry PhD here. I researched wildfire smoke composition and health effects in graduate school. I'm currently doing postdoctoral research in medicine trying to understand the finer details of air pollution toxicity.
Here's a few quick things about wildfire smoke!
**What's in the smoke?**
A complex... | [
"Haze is caused by \"hotspots\" (zones with high temperature levels as seen via satellite imagery) in Malaysia and Indonesia. Lingering smoke from forest fires on the Indonesian island of Sumatra are identified as the primary cause. Farmers regularly burn scrub and forest to clear land during the dry season for agr... |
scary movie decisions | Understanding this is as simple/complicated as understanding the nature of art and catharsis itself.
If the end goal is to stimulate a psychosomatic response in the viewer, certain tropes prove effective towards that end goal. They're not painting rational life portraits--they're just storytellers, executing their cra... | [
"On working with feature movies: \"You need to be honest, because this way your audience will be able to identify with the topic and the hero. My role, as an artist, is to prepare a text with open questions and hide the fact that I have an answer key. Questions will provoke audience to discuss the film and seek new... |
What happens when a bee or wasp hitches a ride in your car, then gets out of the car a long distance from home? | According to a study by the Australian National University, bees are very good at finding their way home, even over long dustances, and often rely on the position of the sun, the polarisation of light in the sky, the panorama view of the horizon and landmarks including towers, mountains or lakes.
From that article: “I... | [
"If you slowly approach a perched individual during hot weather then it may repeatedly fly up and grab any mosquitoes or freeloader flies circling around you, often returning to its original perch to feed for several minutes after each catch.\n",
"In 2010 the Australian Civil Aviation Safety Authority (CASA) issu... |
Why is it not yet economically viable to genetically engineer an organism to produce motor fuel from waste materials? | There are certainly gas-producing organisms that generate methane from garbage, and in fact there are efforts to commercialize this kind of technology (look up 'biogas').
The problem is these processes are not very efficient. The molecules you are talking about have an extremely high energy density, and it's difficult... | [
"With the potential future creation of man-made unicellular organisms, some are beginning to consider the effect that these organisms will have on biomass already present. Scientists estimate that within the next few decades, organism design will be sophisticated enough to accomplish tasks such as creating biofuels... |
Why can't phone chargers/ charging ports have a higher voltage, thus charging faster? | They do. Various "QuickCharge" technologies use higher voltage output (compared to the default 5V) on the charger to allow for faster charging.
Since almost all phones (and other mobile devices) use a USB port (micro-USB or USB-C) for charging, most manufacturers tended to stick to the USB specifications to prevent co... | [
"Since these currents are larger than in the original standard, the extra voltage drop in the cable reduces noise margins, causing problems with High Speed signaling. Battery Charging Specification 1.1 specifies that charging devices must dynamically limit bus power current draw during High Speed signaling; 1.2 spe... |
What are some historians' opinions on Jan Gross' book Golden Harvest which is about Polish collaboration with Nazi atrocities against Jews? | I'm not a historian, nor have I read the book, but.. Fear makes otherwise decent people do terrible, terrible things, like collaborating with Nazis. You could point fingers at basically any country that was controlled by the Reich for a period of time and find collaborators, even among the Jews themselves. That's not e... | [
"Historian Grzegorz Rossoliński-Liebe, writing in \"H-Soz-Kult\", reviewed three books: \"Judenjagd\" by Grabowski, \"It Was Such a Beautiful Sunny Day\" by Barbara Engelking, and \"Golden Harvest\" by Jan T. Gross. He wrote that all three studies are noteworthy explorations of the Polish participation in the Holoc... |
how come a sound gets longer the more of it there is? | Sounds dont get longer the more there is, if you look at the video you can see that the videos arent all playing at the same time, there's a delay in some which can be seen by the wave like motion of the videos in the later parts of the video. | [
"Duration is perceived as how \"long\" or \"short\" a sound is and relates to onset and offset signals created by nerve responses to sounds. The duration of a sound usually lasts from the time the sound is first noticed until the sound is identified as having changed or ceased. Sometimes this is not directly relate... |
what would happen if the federal reserve/congress placed a forever permanent "cap" on the amount of dollar bills in circulation? | Just based on a supply and demand logic, I imagine that money would get more valuable...a dollar bill would be equal to a greater amount of commodities. As more "things" were produced but the amount of money remained the same, it would seem to me that one unit of money ($1) would be worth an increasing share of produc... | [
"The United States Government Accountability Office (GAO) has stated that discontinuing the dollar bill in favor of the dollar coin would save the U.S. government approximately $5.5 billion over thirty years primarily through seigniorage. The Federal Reserve has refused to order the coin from the mint for distribut... |
how do record players and records work? they constantly spin, but if you lift the needle off and put it back down it knows where it left off, right? or am i way off there and it does actually skip ahead if that happens | It goes down near where it went up but not precisely, the rotation is variable, but the arm is normally still in the position across the record (from the edge to the centre). Basically the needle follows the grove on the record which is a tight spiral moving in towards the centre, with the bumps in the grooves being wh... | [
"The mechanism causes the lower portion of the spindle to rotate clockwise like an ordinary record player, while the top half of the spindle rotates counterclockwise to permit the bottom of the record to be played in the correct direction. The spindle contains three sets of retractable claws which hold the records ... |
What's worse for your body: a bottle of soda, or a bottle of beer | A little bit of alcohol might actually be good for you. | [
"However, the most striking feature of \"Beer Bad\" is the twin moral: Beer and casual sex are bad. In a BBC interview, Petrie states: \"Well, very young people get unlimited access to alcohol and become horrible! We all do it — or most of us do it — and live to regret it, and we wanted to explore that.\"\n",
"Be... |
why do people put gold on food, other than the purpose of showing off how rich they are? | Flaunting wealth is often one reason. However, if you consider food to be an art form, putting gold on the plate could be completely a creative expression of the chef. We eat first with our eyes, gorgeous plating goes a long way towards creating a multisensual dining experience. | [
"Gold has worked to evaluate the hypothesis that hedonistic overeating is a pathological attachment to food like any other addiction. Gold is a co-editor of the 2012 textbook, \"Food and Addiction\", published by Oxford Press. More recently, Gold also co-authored: Why are we consuming so much sugar despite knowing ... |
What happened to people in jail during the Great Depression? If the public could barely afford to live how could prisoners? Did any of them die from starvation or were they all adequately fed? | I have an add-on question. How true was it that the average person 'could barely afford to live'? I've heard anecdotal stories from older relatives of small southern towns being basically unaffected by the depression. | [
"Overcrowding soon became a big concern, as well as poor sanitation. The jails turned into breeding houses of illness. Furthermore, the jails were even unable to fulfill their basic purpose of containing offenders within its walls. Escapes were very frequent. The prisons held not only those who were awaiting trial ... |
Does Earth experience a tidal force from Sun? | Yes, we experience a tidal force from everything, it's just question of magnitude.
[The tidal force from the Sun is about ~~3%~~ 44% as strong as from the Moon](_URL_0_), because unlike the basic gravitational force, the tidal force drops like 1/r^3
Edit: 44% | [
"The tidal force on Earth due to a perturbing body (Sun, Moon or planet) is expressed by Newton's law of universal gravitation, whereby the gravitational force of the perturbing body on the side of Earth nearest is said to be greater than the gravitational force on the far side by an amount proportional to the diff... |
single variable calculus, specifically the differentiation of elementary functions. | Do you mean taking derivatives using the definition, or using the tricks and rules you can memorize to make it easier/faster? | [
"Elementary calculus is the calculus of real-valued functions of one real variable, and the principal ideas of differentiation and integration of such functions can be extended to functions of more than one real variable; this extension is multivariable calculus.\n",
"Elementary Functions- a study of the elementa... |
why after a good long cry can't we take a big deep breath without that huh-huh-huh tracheal contraction? | Intense crying can cause less oxygen to enter the brain, therefore the contractions are like yawning, it’s supposed to allow more oxygen to enter.
Source: I’ve cried once. And took an anatomy class once. | [
"This happens due to elastic properties of the lungs, as well as the internal intercostal muscles which lower the rib cage and decrease thoracic volume. As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air. During... |
why is it ok for generic brands to blatantly rip off brand name companies for their own profit? | Its not, I cant call my cereal frosted flakes. I cant use the image of tony the tiger. But There is nothing to stop me from making "Frosted cereal shards" putting them in a blue box and having my mascot be a lion, why would there be? | [
"Some generic products may try to leverage their existing cost advantage (due to lack of promotion) further by using inferior ingredients for production. This can damage the reputation and lead to customers avoiding future purchase. Prevalence of such acts necessitates the customer crosschecking the crimp for list ... |
Who are some of the better known Chinese artists? | The answer is that we know quite a lot about many of the great Chinese masters. However, the history of art in China goes back a deal further than europe. So provenance becomes a major issue. This is particularly the case with the monumental landscape masters of the 10th and 11th centuries. I will mention a few of them... | [
"Zhang Daqian or Chang Dai-chien (; 10 May 1899 – 2 April 1983) was one of the best-known and most prodigious Chinese artists of the twentieth century. Originally known as a \"guohua\" (traditionalist) painter, by the 1960s he was also renowned as a modern impressionist and expressionist painter. In addition, he is... |
magnet torrent links. what are they? | A magnet torrent link is a unique set of numbers and letters that describe a specific file, like a fingerprint. Torrent clients can use this fingerprint to ask other clients if they have a file with the same fingerprint. If they do, they can send it from them (peer) to you (peer). | [
"the original research are implemented. Other file sharing networks, such as the Kad network, use distributed hash tables to index files and for keyword searches. BitTorrent creates individual overlay networks for sharing individual files (or archives). Searches are \"performed\" by other mechanisms, such as locati... |
How did it come to be that all of the genes relating to sex are on the same chromosome? | They aren't: the genes that **trigger** (specifically, SRY) the male phenotype are on the Y chromosome, but males also have a complete set of female DNA, and ~~many~~ almost all of the distinctly male characteristics are side effects of this trigger alone. And even this is a little bit of a misnomer, as SRY (or lack of... | [
"Many species have so-called sex chromosomes that determine the gender of each organism. In humans and many other animals, the Y chromosome contains the gene that triggers the development of the specifically male characteristics. In evolution, this chromosome has lost most of its content and also most of its genes,... |
Do bra-less women have lower rates of breast cancer? | _URL_0_
*Factors not likely related to risk*
*Although not as well-studied as the factors described above, based on the research to date, the factors below are not likely related to breast cancer risk.*
*Bras/underwire bras*
*Scientific evidence does not support a link between wearing an underwire bra (or any type ... | [
"HRT has been more strongly associated with risk of breast cancer in women with a lower range body mass indices (BMIs). No breast cancer association has been found with BMIs of over 25. It has been suggested by some that the absence of significant effect in some of these studies could be due to selective prescripti... |
why some metals glow brightly when hot (i.e., steel or iron) when others just look like liquid metal (i.e., aluminum or mercury)? | Aluminum and mercury will glow too if you get them hot enough. Pretty much everything glows (incandesces) at the same temperature, aluminum and mercury just happen to melt before that temperature whereas steel melts at a higher temperature. | [
"Iron or steel, when heated to above 900 °F (460 °C), glows with a red color. The color of any heated object changes predictably (due to black-body radiation) from dull red through orange and yellow to white, and can be a useful indicator of its temperature. Good quality iron or steel at and above this temperature ... |
how do wammy bars (on guitars) work? | Basically you use the bar to add extra tension to the strings to shift the pitch as you play. | [
"The \"barbat\" is held similar to a guitar, but care must be taken to have the face vertical so that it is not visible to the player, and to support the weight with the thigh and right arm so that the left hand is free to move around the fingerboard. Note the idiosyncratic manner of holding the \"mizrab\" (Turkish... |
why do some people have no sense of rhythm whatsoever? | As an audio engineer, I've broken this down a few times. There are two types of people: 1. People who dance to the beat (kick drum and snare) 2. People who dance to the vocal melody/lyrics.
| [
"An individual with this condition has an especially difficult time maintaining a steady beat, and even has difficulty following along to a steady rhythm. Before it was a known disorder, it was thought that these individuals were just severely uncoordinated, and therefore were unable to follow along with the music.... |
Does the Cambrian Explosion coincide with the move from ocean-based to land-based life forms? | In general it is presumed that the Cambrian Explosion happened essentially in the ocean and maybe to some degree in lakes and rivers. According to wikipedia (_URL_0_) land plants began spreading 490 mya ago and I am quite sure that multicellular animals on land needed those for nutrition.
Anyways, your theory would not... | [
"The \"Cambrian explosion\" can be viewed as two waves of metazoan expansion into empty niches: first, a coevolutionary rise in diversity as animals explored niches on the Ediacaran sea floor, followed by a second expansion in the early Cambrian as they became established in the water column. The rate of diversific... |
how can rocket boosters push things foreward and navigate in space when there is no atmosphere to use? | You would need an atmosphere for things like paddles and propellers. Because they have to push air to work.
Rocket thrust is different. Equal and opposite reaction, right? The rocket fuel or exhaust goes out the back *and pushes the rocket forward*. The force only has to act on the rocket, not against another medium. | [
"Rocket propellant may be expelled through an expansion nozzle as a cold gas, that is, without energetic mixing and combustion, to provide small changes in velocity to spacecraft by the use of cold gas thrusters.\n",
"The rocket booster would place the vehicle onto a suborbital, but exoatmospheric, trajectory, re... |
Does evolution ever stop? | Correct, since Evolution is a slow process in which the traits of a given generation are passed on (due to their survival), as the Environment changes, so too would the requisites of survival change.
Consider an organism that exists in an ecosystem that is devoid of outside influences:
As the organism evolves thro... | [
"Bateson suggested that all evolution is driven by the double bind, whenever circumstances change: If any environment becomes toxic to any species, that species will die out unless it transforms into another species, in which case, the species becomes extinct anyway.\n",
"According to Thomas S. Ray and others, th... |
What was the average day like for an allied soldier in post WWII Germany before the rise of the Soviet threat? | I've not done research in the matter, but my grandfather volunteered to stay on occupation duty with the Canadian Army.
From what he said the days were fairly boring. He was around Baden, so not a Nazi stronghold like Bavaria. The people were broken, trying to rebuild some semblance of life after the war. He was ... | [
"During World War II, between 1941 and 1944, the german Wehrmacht ran a prisoner-of-war camp (Stalag 333) there for Soviet soldiers. More than 30,000 of them died from harsh treatment and malnutrition.\n",
"During 1945 it was estimated that the average German civilian in the U.S. and the United Kingdom occupation... |
why are some men able to grow a beard and others not? is growing a beard a sign of of wellness? | some of it is diet but more of it is gentics. Asians for example tend to have a lot harder time and are less likely to grow a full on beard as you see it other races
fun fact it was seen as very special if you could in many asian cultures | [
"Many men in Western cultures shave their facial hair, so only a minority of men have a beard, even though fast-growing facial hair must be shaved daily to achieve a clean-shaven or hairless look. Some men shave because they cannot grow a \"full\" beard (generally defined as an even density from cheeks to neck) bec... |
What sort of tactics did the Muslim armies use during the Crusades? How different were they to the Crusaders? | While moving through Asia Minor the First Crusade was confronted with armies composed almost entirely of cavalry. These Turkic armies consisted largely of light cavalry who fought with bow and arrow from horseback much like their nomadic brethren/ancestors. They used mobility to exhaust and demoralize their opponents i... | [
"The Muslims lay in a semicircle east of the city facing inwards towards Acre. The Crusader army lay in between, with lightly armed crossbowmen in the first line and the heavy cavalry in second. At the later Battle of Arsuf the Christians fought coherently; here the battle began with a disjointed combat between the... |
[Physics] Where does the mass come from in fusion or fission? | The mass difference comes from the binding energy of the nuclei, via E=mc^(2). | [
"Due to spontaneous fission a supercritical mass will undergo a chain reaction. For example, a spherical critical mass of pure uranium-235 will have a mass of 52 kg and will experience around 15 spontaneous fission events per second. The probability that one such event will cause a chain reaction depends on how muc... |
why does boiling contaminated water make it drinkable? | The heat kills bacteria and other potentially icky things in the water. It's not fool proof but it's better than nothing. | [
"Water must be purified of harmful living organisms and chemicals. Some commercial filters can remove most organisms and some harmful chemicals, but they are not 100% effective. Distillation filters, purifies, and removes some harmful chemicals. Chemicals with a lower or about equal boiling point of water are not e... |
how do they fix power lines when a tree falls on them? | They shut off power to the line and then rebuild it. Power lines are kind of like tinker toys. You just replace the parts that need replaced. Everything from the wire to transformers. If a pole is broken, they cut it off and plant another one. | [
"Areas with large trees and branches falling on lines are a problem for aerial bundled cables as the line degrades over time. Due to the very large strain forces cracking and breaking insulation can lead to short circuit failures which can then lead to ground fires due to dripping of molten insulation.\n",
"Trees... |
Where does rust go? | This depends on the metal! When iron combines with oxygen in the atmosphere, the resulting iron oxide compounds take up much more space than just the metal did, but more importantly they don't have much structural strength. This means that the growing layer of rust on the outside cracks and flakes, creating gaps that l... | [
"Rust is a mixture of iron(III) oxide and oxide-hydroxide that usually forms when iron metal is exposed to humid air. Unlike the passivating oxide layers that are formed by other metals, like chromium and aluminum, rust flakes off, because it is bulkier than the metal that formed it. Therefore, unprotected iron obj... |
Can gravitational lenses (or a series of them) turn a light source back on itself? | This can happen near black holes, where the path of light can be bent so much that it passes the event horizon. However, to modify the path of a distant star back to its direction of origin would require the perfect setup of perfectly placed black holes which is so unlikely as to never happen. | [
"A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer, that is capable of bending the light from the source as the light travels towards the observer. This effect is known as gravitational lensing, and the amount of bending is one of the pre... |
how american football divisions and pre games work (not the rules of the sport) | Pregame, are just exhibition games. They are sometimed used to help determine who gets the last few spots on a team's roster. Divisions are groups of 4 teams. There are 4 divisions per conference. Every team in a division plays eachother twice, as well as 8 teams outside of their division. This is how you get big divis... | [
"Brackets are commonly found in major North American professional sports leagues and in U.S. college sports. Often, at the end of the regular season, the league holds a post-season tournament (most commonly called a playoff) to determine which team is the best out of all of the teams in the league. This is done bec... |
Am I seeing the history of the sun? | Yes but using that logic you are seeing the history of everything. because there is a delay between the object you are looking at and the light hitting that object, reflecting off, and hitting your eye. Similarly there is a delay between when your nerves endings in your eye or skin are triggered and your brain processe... | [
"\"The Sun\" first gained notice for its central role in the Great Moon Hoax of 1835, a fabricated story of life and civilization on the Moon which the paper falsely attributed to British astronomer John Herschel and never retracted. On April 13, 1844, \"The Sun\" published as factual a story by Edgar Allan Poe now... |
why does putting clear (scotch/packing) tape on a frosted window let you see through it? | Frosted glass is simply glass with a (chemically) roughened surface which causes the light passing through the pane to diffuse in all directions, instead of letting straight through.
(Scotch) tape is essentially a clear plastic surface coated with a thin layer of transparent adhesive. When you stick it to frosted glas... | [
"brwhy this tape sounds the way it does.bralthough it could be argued that the tape sounds this way because I'm dumb, I would prefer you think it's because rooms, recording tape and tape machines are not invisible.br-- Al.\n",
"To prevent the recording on the tape from being erased, there is a small write-protect... |
During the American Revolutionary War, 42,000 English Redcoats deserted. Where did they go? What happened to such deserters stranded in foreign territory? | Can you please link this because I can not find that 42,000 English redcoats deserted from an army that averaged about 39,000 soldiers in the colonies during the war? | [
"During the French and Indian War (the North American theatre of the Seven Years' War), the Acadians were expelled from Grand-Pré during the Bay of Fundy Campaign (1755). There were various British soldiers who kept a journal of the deportation from Grand-Pré such as Lt. Col. John Winslow and Jeremiah Bancroft. The... |
What happened to the indo-greek states? | [/u/Daeres](_URL_1_) posted a great answer to a similar question yesterday on [/r/badhistory](_URL_0_). I've quoted it here for those who haven't read it yet:
> Some necessary background- Alexander III of Macedon's conquests (or Alexander the Great if you prefer) in what is now Pakistan and Central Asia were not witho... | [
"After the death of Menander (c. 130 BC), the Kingdom appears to have fragmented, with several 'kings' attested contemporaneously in different regions. This inevitably weakened the Greek position, and territory seems to have been lost progressively. Around 70 BC, the western regions of Arachosia and Paropamisadae w... |
what, if any, consensus is there on michael jackson's multiple charges of alleged child molestation? | The evidence is really much the same as it was before, which is to say that there is not enough evidence to convict someone beyond a reasonable doubt. | [
"In 2005, Jackson was criminally tried for several counts of child molestation charges following concerns raised in the 2003 documentary \"Living with Michael Jackson\". He was seen holding hands in the documentary with 12-year-old Gavin Arvizo and talked about sharing a bed. Jackson was acquitted of all charges. I... |
what causes the "helicopter blades" sound effect when i'm driving down the freeway at a certain speed with a window open a certain amount? | Pressure oscillations. The incoming air compresses the air inside the cab. But because of inertia of the moving air, it compresses it more than the air in the cab can handle, so the inside air rebounds like a spring.
This happens over and over and you get the whup-whup-whup-whup of the oscillation.
| [
"HSI noise is caused by transonic flow shock formation on the advancing rotor blade, and is distinct from loading noise. The source of HSI noise is the flow volume around the advancing blade tip, hence it cannot be captured by examining only the acoustic sources on the surface of the blade, HSI noise is typically d... |
How do we determine the habitable zone of a star that is lightyears away? | We can calculate the average temperature of a planet given its size, [albedo](_URL_0_), distance from the star and the star's luminosity. The habitable zone is simply defined as the range of radii in which water would be liquid at this temperature. | [
"The habitable zone for this star, defined as the locations where liquid water could be present on an Earth-like planet, is at a radius of 0.26–0.56 AU, where 1 AU is the average distance from the Earth to the Sun.\n",
"The habitable zone for this star, defined as the locations where liquid water could be present... |
When and how came humans to the concept of right and left? | There are actually cultures, because of their language, that do not use left, right, etc. and only use cardinal directions, like North, South, etc.
One of these is an aboriginal tribe that speak,"Guugu Yimithirr".
A bunch of deaf kids in Nicaragua invented their own sign language that didn't include terms for left and ... | [
"The terms \"left\" and \"right\" were not used to refer to political ideology per se, but only to seating in the legislature. After 1848, the main opposing camps were the \"democratic socialists\" and the \"reactionaries\" who used red and white flags to identify their party affiliation. With the establishment of ... |
Has a childless hereditary ruler ever died while his wife was pregnant? | Succession laws [were not uniform across medieval Europe](_URL_0_).
Disclaimer: not a historian. | [
"If the King were to die without a male Heir his wife not being pregnant, or if she were pregnant but the pregnancy was not to result in an Heir to the Throne, then the Crown would be retained by His Royal Highness Prince Al-Hassan Al-Rida who would become the origin of future successions to continue through His li... |
where exactly is dna? | So DNA it's in the nucleus of a cell, all of the Eukaryotic organisms, that's all of the animals, plants, fungi, have their DNA stored in the nucleus, think of DNA as a really long wire, actually 3 football fields kind of big (if my genetics professor is to be believed) and it's super thin, all of that encodes the prot... | [
"Natural DNA is a molecule carrying the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses. DNA and ribonucleic acid (RNA) are nucleic acids; alongside proteins, lipids and complex carbohydrates (polysaccharides), nucleic acids are one ... |
why does someone get cold right after turning off the shower, but can be out in real cold weather when out of a jacuzzi? | As someone who spent part of a winter vacation in an outdoor hot tub in Garmisch, Germany... it's still ridiculously cold when you get out. | [
"Water left stagnant in the pipes of showers can be contaminated with pathogens that become airborne when the shower is turned on. If a shower has not been used for some time, it should be left to run at a hot temperature for a few minutes before use.\n",
"If, for example, someone flushes a toilet while the showe... |
how is it so many poor countries are expensive. | I'm pretty sure it's not normal to "eat out" outside the US. It's for rich people and tourists. | [
"BULLET::::- Probably the main economic benefit that workers in rich countries obtain directly from poor countries is cheap consumer goods, but in fact the monetary value of these goods is statistically only a small part of their \"total\" budget. The big ticket foreign-made items in working class budgets are forei... |
Why do dispersion affects differents colours in different ways? | Frequency cannot change at an interface, that would mean you have a discontinuity in energy flow. See for example an animation like this:
_URL_1_
If frequency changed at an interface then the black lines, representing a maximum of the electric field and thus a maximum in the energy of the wave, would be discontinuou... | [
"The most commonly seen consequence of dispersion in optics is the separation of white light into a color spectrum by a prism. From Snell's law it can be seen that the angle of refraction of light in a prism depends on the refractive index of the prism material. Since that refractive index varies with wavelength, i... |
What did Pre-Columbian Native America trade routes look like? Where were they, what goods did they carry, how far were goods traded, and who did the traveling along with the goods? | While you wait for an answer you might be interested in the ["Pre-Columbian Trade and Contact"](_URL_1_) section of our [FAQ on Native American History](_URL_3_).
In particular, you may be interested in [this answer](_URL_2_) by myself, /u/Mictlantecuhtli and /u/retarredroof, [this answer](_URL_4_) by /u/Cozijo, and ... | [
"There is common academic agreement that significant systems of trading existed between the cultures of Mesoamerica, Aridoamerica and the American Southwest, and the architectural remains and artifacts share a commonality of knowledge attributed to this trade network. The routes stretched far into Mesoamerica and r... |
can a rigid blimp only be inflated with hydrogen, or will helium work too? | Both will work. Hydrogen will work better because it can fill the same volume with less weight, but it will also be worse because it is prone to explosions when exposed to oxygen and sources of ignition (see: Hindenburg).
Helium is preferred when available, but in the Hindenburg's case the Germans were not able to se... | [
"Methane (density 0.716 g/L at STP, average molecular mass 16.04 g/mol), the main component of natural gas, is sometimes used as a lift gas when hydrogen and helium are not available. It has the advantage of not leaking through balloon walls as rapidly as the smaller molecules of hydrogen and helium. Many lighter-t... |
why do so many public drinking fountains just dribble water out? | low water pressure. the lower fountain works better because the pipe supplying the water is shorter, so it has less distance to travel. | [
"Drinking fountains are used especially during the summer, yet a lot of people are reluctant to drink the water due to fear of disease. According to the Public Health Office of Slovakia (), all drinking water fountains supply the same tap water as residents have in their homes and the water is safe to drink. Drinki... |
what is the purpose of the "circular net" in front of microphones of recording studios? | Pop filter. Stops bilabial sounds like "b" or "p" from sounding like loud pops. If you've ever heard a low quality youtube video, you know the pop I mean. Basically it smooths out the audio. | [
"A microphone splitter is a device with an input from a microphone and multiple outputs. It is also known as a \"rathouse\" due to the large amount of cabling involved. A splitter is often used at larger venues to provide feeds from microphones or other sources to both a front of house mixing desk and a monitor des... |
why is ireland not united? and do most irish want it to be? | There has been about 100 years of fighting over this very question.
Very simplified history here:
Northern Ireland was created in 1921 after an uprising of Irish Republicans lead to a peace treaty between Ireland and the UK which partitioned the country between the Irish Free State (later the Republic of Ireland) wh... | [
"United Ireland (also referred to as Irish reunification) is the proposition that all of Ireland should be a single sovereign state. At present, the island is divided politically; the sovereign Republic of Ireland has jurisdiction over the majority of Ireland, while Northern Ireland is part of the United Kingdom. A... |
Who was enslaving and who was trading 6th century Anglo-Saxons? | So while the exact veracity of this anecdote is impossible to verify, I can talk a little bit about the slave trade in Northern Europe at this time in history.
Slavery was an integral part of the Anglo-Saxon world, as well as other cultures and groups in the North Sea world. Scandinavians, Saxons, Frisians, the Iri... | [
"As German rulers of Saxon dynasties took over the enslavement (and slave trade) of Slavs in the 10th century, Jewish merchants bought slaves at the Elbe, sending caravans into the valley of the Rhine. Many of these slaves were taken to Verdun, which had close trade relations with Spain. Many would be castrated and... |
Why do we freeze for a split second when something startles us or makes us jump? | The freezing response is mediated by a circuit involving the amygdala and a part of the brainstem, the periaqueductal gray. This circuit can coordinate the typical motor output: freezing, jumping, yelping, etc.
Anyone can come up with plausible-sounding evolutionary "explanations," but this can easily spiral into just... | [
"Freezing behavior or the freeze response is a reaction to specific stimuli, most commonly observed in prey animals. When a prey animal has been caught and completely overcome by the predator, it may respond by \"freezing up\" of in other words by staying complety still. Studies typically assess a conditioned freez... |
How did the people of England respond to the Declaration of Independence? | I read a paper a while ago from Stephen Conway that deals with changing perceptions of the relationship between Britain and the Thirteen Colonies during and after the War of Independence. Bear in mind that while his perspective is useful in answering your question, it may not represent the full picture.
_URL_0_
Esse... | [
"The United States Declaration of Independence was approved there on July 4, 1776, and the Declaration was read aloud to the public in the area now known as Independence Square. This document unified the colonies in North America who declared themselves independent of the Kingdom of Great Britain and explained thei... |
why do snail shells grow with them, but hermit crabs have to keep trading up? | Snail shells are actually a part of the snail. The more calcium they eat, the quicker they grow. Hermit crabs aren’t born with a shell, so they have to move into a new one as they grow | [
"As the hermit crabs grow, they must exchange their shell for a larger one. Since intact gastropod shells are not an unlimited resource, there is frequently strong competition for the available shells, with hermit crabs fighting over shells. The availability of empty shells depends on the abundance of the gastropod... |
I was once watching a TV documentary about Rome with my dad. One of the experts started to talk about the orderly way Romans did combat, my dad turn to me & said it reminded him of how the riot police used to operate back when he was one in the 1980s. Is it just a confidence the two are similar? | I'm not really sure what you are asking. Are you asking if modern riot tactics can be traced back to the idea of a body of infantry moving as a tight group? Or are you asking if modern riot tactics are deliberately modeled after Roman formations, as in someone sat down and said "let's emulate Roman heavy infantry on pu... | [
"The film focuses on the life of a group of riot control force policemen, the \"Celerini\", and their life in Rome \"cleansing\" stadiums of Ultras, public demonstrations, evictions and everyday family life.\n",
"BULLET::::- \"Rome\": A historical drama set in Ancient Rome that primarily chronicles the lives and ... |
How thick does a layer of gold need to be to be fully opaque? | Gold has a resistivity of about 2.44 x 10^-8 ohm-meters. Visible light has frequencies between about 400 and 700 THz. So, using a [skin depth calculator](_URL_0_) the skin depth is only a few nm. For "fully opaque" you probably want somewhere between 3 and 5 skin depths.
So 100 nm is probably overkill. They might have... | [
"Very thin crystals of MoTe can be made using sticky tape. When they are thin around 500 nm thick red light can be transmitted. Even thinner layers can be orange or transparent. An absorption edge occurs in the spectrum with wavelengths longer than 6720 Å transmitted and shorter wavelengths heavily attenuated. At 7... |
how small is an atom? | There are more atoms in a grain of sand than there are grains of sand on every beach on earth.
I feel using anything but an analogy makes it very hard to understand | [
"Atomic dimensions are thousands of times smaller than the wavelengths of light (400–700 nm) so they cannot be viewed using an optical microscope. However, individual atoms can be observed using a scanning tunneling microscope. To visualize the minuteness of the atom, consider that a typical human hair is about 1 m... |
How did wrestling become staged? | Wrestling has a long history in Europe, going back to Ancient Greece where wrestling was a pretty popular sport in the Olympiads and it continued on throughout history Early Modern Era, Modern Era, etc. Although very different wrestling from what we think of when we think "wrestling", and I mean in both the staged vers... | [
"Professional wrestling, in the sense of traveling performers paid for mass entertainment in staged matches, began in the post-Civil War period in the late 1860s and 1870s. During this time, wrestlers were often athletes with amateur wrestling experience who competed at traveling carnivals with carnies working as t... |
what has caused such a divide between u.s. citizens and their police force? | An uneducated public who only reads 144 character tweets for the entire story. A lack of understanding that a few officers fucking up doesn't make us all evil, heartless, bastards with a God complex.
The medias refusal to show POSITIVE stories and constant push to make every single story negative or "juicy" or racia... | [
"Concerns about the militarization of police have been raised by both ends of the political spectrum in the United States, with both the right-of-center/libertarian Cato Institute and the left-of-center American Civil Liberties Union voicing criticisms of the practice. The Fraternal Order of Police has spoken out i... |
why do humans hear a musical "beat" in repetitive sounds? | The human brain is highly adapted to pattern recognition. Our neurons like to overlay “filters” over things to see patterns from random noise. Do a repetitive sound will sound like a beat and rows of different colours look like stripes. | [
"Music is the only form of communication that saves us from an overwhelming amount of small talk. This is not only a human phenomenon, but happens throughout the animal world. Thomas makes examples of animals from termites and earthworms to gorillas and alligators that perform some sort of rhythmic noise making tha... |
how come the human genetic code can fit roughly in ~1.5gb of data yet we turn out such complex organisms? furthermore, the code that separates us from other mammals can fit on o floppy disk. | A few key differences between the genetic sequence and a computer sequence:
1. Computers run in binary. Genes run in quaternary (4 types of nucleic acids). That immediately increases the amount of data you can store exponentially. One step further, gene sequences build amino acids. There are 21 total amino acids that c... | [
"In many species, only a small fraction of the total sequence of the genome encodes protein. For example, only about 1.5% of the human genome consists of protein-coding exons, with over 50% of human DNA consisting of non-coding repetitive sequences. The reasons for the presence of so much noncoding DNA in eukaryoti... |
why didn't evolution make females just as 'horny' as men. | as far as i know women are just as horny as men. evolution is great, isnt it? | [
"Male animals are typically more elaborately ornamented than females. The classic sexual selection theory notes that because sperm are cheaper to produce than eggs, and because males generally compete more intensely for reproductive opportunities and invest less in parental care than females, males can obtain great... |
the difference between pixel- and vector-based images | Raster images (those made up of pixels) have a fixed size. It's like taking a piece of graph paper and coloring in the squares. If you want to make a picture bigger, you only have as much information as was in the original pixels. This makes the image blocky or fuzzy when you zoom in or try to blow it up.
Vector im... | [
"As opposed to the raster image formats above (where the data describes the characteristics of each individual pixel), vector image formats contain a geometric description which can be rendered smoothly at any desired display size.\n",
"Vector graphics formats are complementary to raster graphics. Raster graphics... |
how does an artist “go platinum” in today’s world of spotify/apple music? | They changed the rules for platinum, so now a certain number of digital track purchases, or a larger number of digital on-demand plays, counts as equal to 1 album sale. | [
"In a June interview with Hypebot, Wallach reported that $180 million of royalties was paid out in 2011 and 70% of Spotify's revenue consisted of royalty payments. Spotify's growth meant that the per-stream royalty rate doubled between the service's inception and mid-2012. He said that, at the time, compared to iTu... |
why does everyone believe everything snowden leaks as truth? | When Snowden started releasing information, the US government got very upset. You know how sometimes you get upset, even though you don't mean to? Usually it's because there is some truth there. If somebody said something ridiculous, like your brother is a raptor, you wouldn't be mad because you can prove it's not ... | [
"In the aftermath of Snowden's revelations, The Pentagon concluded that Snowden committed the biggest theft of U.S. secrets in the history of the United States. In Australia, the coalition government described the leaks as the most damaging blow dealt to Australian intelligence in history. Sir David Omand, a former... |
What were Nazi Germany's plans post-WWII in the case of an (unlikely) Axis victory? | Territories in the east were to be governed as something like German colonial provinces called *Reichkommissariaten*, whose inhabitants would be mostly killed off by an engineered famine called the [Hunger Plan](_URL_0_), with the survivors being used as slave labour on German farms or forcibly relocated.
The Nazis p... | [
"With the signing of the Tripartite Pact on September 27, 1940, creating the Axis of Germany, Japan, and Italy, Decoux had new grounds for worry: the Germans could pressure the homeland to support their ally, Japan.\n",
"In February 1942, Raeder presented Hitler with the \"Great Plan\", a grand strategic design f... |
fast fourier transform (fft), and/or discrete fourier transform | Not sure if you're after an explanation of what it does or how it works - I don't think I quite get the maths enough to explain the latter....
I always think about an orchestra. If you have never heard any of the instruments before when you listen to the orchestra you will still hear the sound they make but they're al... | [
"A fast Fourier transform (FFT) is an algorithm that computes the discrete Fourier transform (DFT) of a sequence, or its inverse (IDFT). Fourier analysis converts a signal from its original domain (often time or space) to a representation in the frequency domain and vice versa. The DFT is obtained by decomposing a ... |
the reason and use of the serial numbers on cash bills/currencies and why coins do not have such | The printers on currency use the numbers to keep track of how much is printed, so workers can't wander off with some of the product. Coins are heavy, and the amount that could be pocketed wouldn't be worth nearly as much. | [
"In contracts and other documents, the numbers written were not actual numbers of the coins, but their value in a standard system: for example, the standard often used the gold system, but the payments were done with the local silver coins. \n",
"The first U.S. currency with a series year was printed on United St... |
how/why do migraines make your eyes extremely sensitive to light? | Migraine sufferers have a problem with a specific part of the nervous system the opthalmic division of the trigeminal nerve that causes pain around the eye.
Eli5 translation: The brain has 12 major wires. And one specific wire(trigeminal) which also has small wires connected to it: opthalmic(around the eye), mandibula... | [
"Some studies attribute migraine headaches to overly intense light, while others linked it with certain spectral distributions. In one survey bright light was the number two trigger (affecting 47% of respondents) for causing a migraine episode. \n",
"These cause permanent obstruction of aqueous outflow. In some c... |
Was the Holocaust rational enlightenment carried out to its most twisted ends? | > I feel as though the Holocaust has its roots in something other than antipathy towards Jewish people.
Why do you feel this way? What's your justification for this idea?
> I can elaborate on this more,
You should - as it is, it doesn't really follow at all.
> but placing more blame on the enlightenment helps... | [
"In their analysis of contemporary western society, \"Dialectic of Enlightenment\" (1944, revised 1947), Theodor Adorno and Max Horkheimer developed a wide and pessimistic concept of enlightenment. In their analysis, enlightenment had its dark side: while trying to abolish superstition and myths by 'foundationalist... |
What's the earliest recorded condemnation of racism anywhere in the world? | From Muhammad's final sermon, March 9th 632
**"Indeed, there is no superiority of an Arab over a non-Arab, nor of a non-Arab over an Arab, nor of a white over a black, nor a black over a white, except by taqwa (piety). "**
Tirmidhi Hadith, Hadith #159
It is a fairly concise sermon, focused on giving advice to the M... | [
"Francisco Bethencourt is Charles Boxer professor at King's College London. Bethencourt's research centres on the history of racism, Portuguese and European expansion from the 15th to the 19th centuries, missions and religious history in the Catholic world, and identities and cultural exchange in Iberia. Bethencour... |
With advances in many fields of Medicine including the transplant of synthetic hearts and 3d printing of various body parts making cheap prosthetics possible, why haven't we seen significant advances in prosthetic cartilage for damaged joints and herniated disks? | Ok, first things first :
The synthethic hearts are not too good. In most cases they are used as "bridge-to-transplant" solution, not as an endgame. People don't survive too long on them. Also 3d printing body parts is highly experimental and pretty far from being a standard.
Now, yes we do use mechanical heart valves... | [
"3D printing for the manufacturing of artificial organs has been a major topic of study in biological engineering. As the rapid manufacturing techniques entailed by 3D printing become increasingly efficient, their applicability in artificial organ synthesis has grown more evident. Some of the primary benefits of 3D... |
why/how one can hear the voices of the actors on a tv show/movie so clearly without any extraneous noises in the background. can it really all be edited out? | The actors have mics following them everywhere on the set. The mics pick up the dialogue and from the tape made, the sound man can edit out background noises and modify the actor's voice. The recordings are made in multiple tracks and fixing the voices is not much different than how artists record songs.
When you see... | [
"In film, the filmmaker places the sound of a human voice (or voices) over images shown on the screen that may or may not be related to the words that are being spoken. Consequently, voiceovers are sometimes used to create ironic counterpoint. Also, sometimes they can be random voices not directly connected to the ... |
What would it look like if I constructed a cube made of one-way mirrors, so a person could see into the cube but the inner walls were reflective? | The way one-way mirrors works is that the glass reflects part of the light, while transmitting some. This work _both ways_. The reason it _acts_ as a one-way mirror is because the side that looks like a mirror is much brighter than the other side. (For example, the interrogation room is brightly lit, while the observat... | [
"There are also two pairs of mirrors in the museum, that are placed at an angle of 90 degrees in such a way that one cannot see one's own face but others can see. It was used by the Nawab to prevent predators from harming him, and was kept at a place so that the predator cannot see his face and think a mirror to be... |
What calendar is used for older dates? |
Practicing historian here. (Moving a lower level comment up and expanding some)
I work in the period both before and after the Gregorian calendar was adopted in the Spanish Empire (1582). Yes you could adjust dates for events occurring under the Julian calendar but then you would be using different dates than thos... | [
"A calendar era is the year numbering system used by a calendar. For example, the Gregorian calendar numbers its years in the Western Christian era (the Coptic Orthodox and Ethiopian Orthodox churches have their own Christian eras). The instant, date, or year from which time is marked is called the \"epoch\" of the... |
Where can I find a truly complete history of the British Isles? | The task is certainly massive. Just one comment, as you say there are many and based on my experience I find myself better off with a good generic history that typically would awake my interest in certain periods worth going deeper.
To start with? BBC has a good history program.
_URL_0_
Others may contribute somethin... | [
"British Isles – A Natural History is an eight-part documentary series produced by the BBC Natural History Unit and presented by Alan Titchmarsh. Originally broadcast in the UK on BBC1 from September to November 2004, it took viewers on a journey from the formation of what is now the British Isles some 3 billion ye... |
Why do my leftovers stick if I don't wash my plate soon after eating? | The moisture in the leftovers kept them from adhering to the plate. When you leave it out, they dry up and stick to the surface.
Basically, on a very small scale your plate is not a smooth surface, it has peaks and valleys and such. With moist things like sauce, the food particles flow all over these peaks and valleys... | [
"Regionally, the tradition varies from not wasting food on one's plate, to only eating what one feels like and leaving the rest. However, in some regions, leaving food as an offering is common; some consider this as a method of only wishing to consume pure spirits of the food and the discarded food will represent t... |
why 720p hd is 1280x720 but hdtvs are 1366x768 | 1024x768 panels already exist. It's cheaper to just cut them longer at 1366 than to make 720 ones. Most 720 screens seem to actually be 768. | [
"BULLET::::- First, the HDTV-standard 1280720 (otherwise commonly described as \"720p\"), which offers an exact 16:9 aspect with square pixels; naturally, it displays standard 720p HD video material without stretching or letterboxing and 1080i/1080p with a simple 2:3 downscale. This resolution has found some use in... |
how do major airports recover from mass flight cancellations? | It's not the airport that has to recover, it's the airlines. That makes a big difference and aids in explaining the issue.
Let's say Delta has one flight per day between two cities. On Monday, they cancel the flight, stranding 250 passengers. Tuesday's flight has 15 open seats, so they re-book 15 people. Their partn... | [
"Flights that have not departed their airport of origin will be delayed or cancelled. Airlines are required to manage their aircraft at all airports to minimize the impact to passengers affected by the ground stop.\n",
"The airport was supposed to be demolished to make way for a housing estate, but that plan was ... |
how does metadata work and what is written behind files? | Metadata depends on the file. For recordings, such as pictures and video, metadata will typically include things like date, time, and camera settings. Metadata in other files such as application ZIP files and movie files will often contain copyright, licensing, and distribution information.
Cameras, for instance, may... | [
"Metadata can be found in many types of files such as documents, spreadsheets, presentations, images, and audio files. They can include information such as details on the file authors, file creation and modification dates, location (GPS), document revision history, thumbnail images and comments.\n",
"Sometimes, m... |
what are the differences between the xbox one and ps4? | Sony is a hardware company.
Microsoft is a software company.
| [
"The PlayStation 4 (or PS4) is a video game console from Sony Computer Entertainment. Billed as the successor to the PlayStation 3, the PlayStation 4 was officially announced at a press conference on February 20, 2013. The fourth home console in Sony's PlayStation series, it was launched on November 15, 2013 in Nor... |
how solar power works, from the pv to the inverter and the lightbulb lighting up! | A PV cell converts light energy into DC electrical energy.
An inverter converts DC to AC, by switching the DC off and on 60 (or 50) times /second. It usually uses a transformer to convert the chopped AC to 120 (or 240) volts.
If you are using only DC you may not need an inverter, but most situations have one to con... | [
"Solar power is the conversion of sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP). CSP systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. PV converts light into electric current using the pho... |
what is fantasy football and how is it different from video games and gambling? | Fantasy football is not like a video game mainly because you don't physically play. It is a lot like betting on horse races. In the beginning of the season you join a league. With friends or with random people. There may be a buy in or some other kind of ante or there might not. You then draft football players. There ... | [
"Fantasy football is a genre of board game or wargame which normally involves two teams of fantasy races (such as elves, dwarves or orcs) competing in an extremely violent variant of gridiron football. Often the only resemblance to gridiron football for many fantasy football games is to get the ball into an end zon... |
how can we listen to the sound of two black holes colliding if there is no sound in space? | That sound was generated based on other emissions, and is an artificial approximation. Think "how it could be heard if that was sound waves" kind of thing. | [
"A sonic black hole, sometimes called a dumb hole, is a phenomenon in which phonons (sound perturbations) are unable to escape from a fluid that is flowing more quickly than the local speed of sound. They are called sonic, or acoustic, black holes because these trapped phonons are analogous to light in astrophysica... |
What happens at the limit of a laser pointer's reach? | The '2 mile reach' is very arbitrary. I would imagine they define 'reach' as the largest distance without appreciable divergence of the beam. Beyond 2 miles the photons will still continue their journey at the same angles they left the pointer at.
I guess there will be a small amount of scattering and absorption by th... | [
"A Class 2 laser is considered to be safe because the blink reflex (glare aversion response to bright lights) will limit the exposure to no more than 0.25 seconds. It only applies to visible-light lasers (400–700 nm). Class-2 lasers are limited to 1 mW continuous wave, or more if the emission time is less than 0.25... |
how come d-day came as a surprise to the nazis? | Deception on a scale never before seen. Double agents. False radio transmissions. Fake armies. And even then, the Germans still knew an invasion was coming. But they were greatly misled as to when it would be, where it would be, and how many troops would be a part of it.
[Operation Bodyguard](_URL_0_) is the term... | [
"Planning for the operation began in 1943. In the months leading up to the invasion, the Allies conducted a substantial military deception, codenamed Operation Bodyguard, to mislead the Germans as to the date and location of the main Allied landings. The weather on D-Day was far from ideal, and the operation had to... |
When and why did karate become a popular thing to teach children in the west? | I hope this is OK, I'm not a professional historian, but I was a karate-ka for about 20 years. And part of that was reading. So I hope I can provide an in depth answer that satisfies requirements. A lot of my reading comes from Randall Hassell's "Shotokan Karate: Its History and Evolution" and Gichin Funakoshi's "Ka... | [
"\"The Karate Kid\" is a semi-autobiographical story based on the life of its screenwriter, Robert Mark Kamen. At age 12, after the 1964 New York World's Fair, Kaman was beaten up by a gang of bullies. He thus began to study martial arts in order to defend himself. Kamen was unhappy with his first teacher who taugh... |
If oxygen can bond with 2 other atoms, how can ozone exist? | What you are thinking of is a very simplified picture of lewis-dot structure type bonding, where O has 2 unpaired electrons. Lewis structures are only really a simple tool to get a handle on more complicated concepts. Using the idea of resonance you can help explain ozone. See here: _URL_0_
But again, as stated before... | [
"Three forms (or allotropes) of oxygen are involved in the ozone-oxygen cycle: oxygen atoms (O or atomic oxygen), oxygen gas ( or diatomic oxygen), and ozone gas ( or triatomic oxygen). Ozone is formed in the stratosphere when oxygen molecules photodissociate after absorbing ultraviolet photons. This converts a sin... |
Is it impossible for a planet the size of Jupiter to not be a gas planet? | Yes, a large enough planet will be a gas giant. All planets are made out of star-stuff which is mostly hydrogen (~90%) and helium (~9%) (the same stuff in gas giants). Rocky (terrestrial) planets will lose a large fraction of hydrogen and helium, as the light elements move faster at a given temperature and [have a la... | [
"Given the planet's high mass, it is likely that 47 Ursae Majoris b is a gas giant with no solid surface. Because the planet has only been detected indirectly, properties such as its radius, composition, and temperature are unknown. Due to its mass it is likely to have a surface gravity 6–8 times that of Earth. Ass... |
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