title sequence | over_18 sequence | post_content stringlengths 0 9.37k ⌀ | C1 sequence | C2 sequence | C3 sequence |
|---|---|---|---|---|---|
[
"Assume you have something that generates heat at N degrees. If this heat source were stuck inside an oven and there was little to no way the heat could escape, would the temperature inside the oven eventually go above N degrees?"
] | [
false
] | null | [
"The second law of thermodynamics says that heat flows from hot to cold. If the system somehow found itself in a state where the temperature of the oven is higher than the temperature of the heat source, then the net flow of energy would be from the oven to the heat source. The oven would cool down and the heat sou... | [
"No, the oven can never reach a temperature higher than its heat source."
] | [
"I believe you but something in my intuition isn't meeting you there yet. I guess I was thinking that if the molecules are moving around (which is where temperature comes from) and the heat source is bleeding heat into the oven then it's creating more movement (or maybe pressure?) inside the oven.",
"And since no... |
[
"Were Curiosity and its transport to Mars sterilised beforehand, and if not, is there a chance that microorganisms brought by it will thrive on Mars?"
] | [
false
] | null | [
"Hi Odenetheus thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the foll... | [
"Biology"
] | [
"'Biology'"
] |
[
"What are the gravitaional forces on the inside of a spinning hollow sphere the size of earth?"
] | [
false
] | null | [
"A solid ball and a hollow shell of the same mass have the same exterior gravitational field. "
] | [
"I'm talking about the interior, obviously all gravitational forces would cancel out, leaving a zero-g environment, but if you spin it, could you create an artificial gravity on the inside of the sphere?"
] | [
"Yes. This is a commonly asked question. The centrifugal force mimics a gravitational force.",
"https://www.reddit.com/r/askscience/search?q=artificial+gravity&restrict_sr=on&sort=relevance&t=all",
"https://www.reddit.com/r/askscience/comments/51xg1l/physics_if_the_earth_wasnt_spinning_would_we_feel/?ref=search... |
[
"Why do images flip in a magnifying glass at a certain point?"
] | [
false
] | So I was looking through a magnifying glass and I noticed that when I looked at an object that was about three feet from the magnifying glass (how close it was to my eye was irrelevant... I think), the image in it completely flipped. | [
"This",
" picture is helpful. The lens actually works the same in both directions. (In this picture an object way off to the left is giving off light.) Normally the glass would magnify things for your eyes because the object will appear larger (the light from the object takes up more of your vision) if your eye i... | [
"It has to do with how far you are from the lens in terms of focal distances. It's best to draw a small object and trace how one point of that object gets translated as an image.",
"Follow as I trace the tip of the arrow head to its image\n",
"http://i.imgur.com/maPpF.png",
"Assume the long line in the middle... | [
"While this explains beautifully how the light coming through the lens is affected, it doesn't explain how/whether the distance from the object being viewed affects whether or not it flips. Does that distance have anything to do with it?"
] |
[
"What do moles do during floods?"
] | [
false
] | null | [
"Though I cannot find what I'd consider to be highly scientific sources (lots of gardeners answering), moles dig their tunnels deep enough and at specific angles to avoid water getting into their nests. The soil saturated with water only goes so deep, and established mole tunnels are deeper than this level. This is... | [
"I don't know, but moles can swim very well and don't need much oxygen. The star-nose mole spends about as much time underwater as underground, and desmonds, a sort of mole (a talpid) is an aquatic animal. There isn't much oxygen in their tunnels anyway, so they are very good at going without much of it. So, all... | [
"So they dig water traps?"
] |
[
"How important are shoes to public health?"
] | [
false
] | [deleted] | [
"In addition to the things already stated, even in developing countries, proper footwear is an issue. ",
"In our country, a huge proportion of people (often african american, underprivileged, etc.) are diabetic. This can cause a condition called peripheral neuropathy, in which peripheral neurons effectively die... | [
"Infection is the main public health risk. ",
"Notably: ",
"Parasites...",
"\n- Hookworm. Can cause anemia, intestinal discomfort, diarrhea, and growth delays. Severe or untreated forms (notably in the developing world) can lead to death. An infected individual also acts as a host for further hookworm spread... | [
"Why is tetanus always mentioned in association with ",
" nails? Isn't the risk of tetanus infection the same regardless of what broke the skin?",
" Thanks everyone for the answer! It's not the rust, it's two factors related to the rust: 1) The nail is rusty because it has been exposed to a moist environment lo... |
[
"Cell Respiration"
] | [
false
] | Alright maybe this should be in biology but it’s a question so I put it here. In school I have to make my own lab for cell respiration. We had done a lab that if you activated yeast and put it with molasses in a test tube with a stopper and "U-tube"? it would release CO2 (I think) and you would see bubbles in the water. So when I created my own lab I decided I would change the molasses with other things and see if the yeast still did cell respiration. So I tried it with yeast and corn syrup, and a yeast-sugar solution. So my question is should the yeast have done cell respiration with those things. I'm asking because this lab is a worth a huge part of my grade and I want to make sure it wasn't human error for not working. If cell respiration shouldn’t have occurred then I’m fine. I have made a quick drawing of what the lab was like to hopefully help you understand what I was describing. Sorry if my grammar is not the greatest. Help would be appreciated thanks! | [
"Well, firstly, yeast will die if it is too warm. I think that room temperature is ideal but i definitely wouldnt go over 40C.",
"Secondly, you need to make sure there was no preservative with the corn syrup. Preservative preserves by killing microbes, such as yeast. Check the label on the side of the bottle.",
... | [
"Pretty much anything with sugar should do it."
] | [
"Check what kind of corn syrup you are using.\nFrom wiki:",
"Corn syrup is distinct from high-fructose corn syrup, created when corn syrup undergoes enzymatic processing that produces a sweeter compound containing higher levels of fructose.",
"This would complicate your reaction: for a very simple explanation "... |
[
"What stops water from continually sinking through the ground? (Primary school science question)"
] | [
false
] | My year 4 class started looking at soil composition today and one of the students asked why water doesn't keep sinking through the ground. I promised them I'd have an answer by tomorrow (Sydney time), so I'm hoping the kind people at can help me help them! Apologies if this isn't the subreddit to ask this question. Feel free to advice of a more appropriate subreddit if there is one. Thanks! | [
"Well, there's a number of things at play here. Pick and choose which bits you want to use in the explanation at their level.",
"Chemical wetting. Soil can have lots of clay minerals in it, and these will hold on to water molecules when they are available.",
"Capillary action. Fine pore spaces within the struct... | [
"The simple answer is that the soil can only absorb so much water, and after that absorbing water is going to be much slower as you get closer and closer to the saturation point. For a 9-year-old, an analogy with salt-water would probably work.",
"You could also explain that quite some water ",
" in fact seep t... | [
"That explanation works against the question. If soil could absorb infinite amounts of water, then all water would always be contained in a very thin layer of soil on top of the ground. But since there is a saturation, water sickers further down just like the salt in a saturated water container will sink to the gro... |
[
"Wavefunction collapse is faster than the speed of light. Doesn't this just mean that they used math to answer the question?"
] | [
false
] | I keep reading about how researchers are measuring the speed of the collapse of the wavefunction by sending entangled particles to two different locations, measuring one, and then checking the other. I have recently had a conversation where it was explained to me that a wave function is not just math. My questions are so: 1. At its most naive, entanglement just means that if I know the identity of one, by the magic of math, I know what the other is. How do we know that the collapse of the second is an actual physical event. My spider sense goes crazy when people tell me that they can only prove a freaky experiment works by using a bunch of random numbers and classical conservation laws, but I know that a lot of people have worked on this that are smarter than me. edit: deep dyslexia sucks. Spiders and bats are not the same thing | [
"You're asking questions at the very heart of Quantum Mechanics. People disagree on how to interpret QM. So when you say ",
"How do we know that the collapse of the second is an actual physical event.",
"the answer is we don't. Some consider the wave function physical 'real'. Some don't. If the wave function is... | [
"Believe me, I have a phD in soft condensed matter, and most of quantum physics still sounds like bull unless I really think about it, which is almost never as I spend all my time pretending to understand biology!",
"But I still failing to see how collapsing the wavefunction is anything but already knowing the a... | [
"Are you asking if there's something special about EPR pairs that's impossible to find in classical physics? If so, the answer is a clear yes. ",
"Bells Theorem",
" says that the outcome of a measurement is not pre-determined (unless the world is non-local). ",
"Super dense coding",
" allows you to communic... |
[
"How do bugs actually stick themselves and walk on walls and ceilings, y'know, like Spider-Man?"
] | [
false
] | null | [
"They’ve usually got little claws on the ends of their legs and they grab onto the texture of the surface. ",
"They’re also extremely light, so it doesn’t take much friction to hold them to a surface. ",
"You’ll note that the larger the insect is, the rougher the surface needs to be for it to climb.",
"Consid... | [
"Certain insects have a ",
"crazy fractal-like design to the fur/material on their legs",
"(this image is from a gecko, but similar principle applies to insects), they have hairs that split into two hairs which split into four hairs etc.. This exponentially increases the theoretical contact patch with the surfa... | [
"Nano technology in short. Basically the same effect of when you hold say, a serving tray or any smooth flat surface. You can tilt it sometimes almost vertically without it sliding or falling off of a flat hand depending on how much it weighs. This is due to the surface area of your hand being in contact with the s... |
[
"What is it about a digital camera's sensor that results in noise artifacts in low light settings?"
] | [
false
] | I understand that stronger lighting means more information to outdo the noise, but why does the noise appear in the first place? | [
"Part of it is thermal noise. The electrons in your sensor have some thermal energy associated with them, and can trip the sensors. When you have a high light intensity, the signal generally outweighs the noise. But in low light conditions, the noise is much greater in comparison to the signal."
] | [
"These guys do an excellent job answering your question: ",
"http://photo.stackexchange.com/questions/11910/what-types-of-noise-can-be-present-in-digital-photographs"
] | [
"This is actually a great introduction to stochastic calculations.",
"Let's say I want to measure the value of pi. So I draw a square on the ground, and inscribe a circle into that. Then, I sit above the whole thing and drop grains of rice. I drop the rice in such a way that the rice has an equal probability o... |
[
"How is a mosquito proboscis physically capable of puncturing human skin?"
] | [
false
] | Human skin should be way too dense and strong for something so small and fragile like a mosquito. How is this possible? | [
"It uses two maxillas to cut its way into the skin so the fascicle can enter while the labium remains on the surface of the skin.",
"Think two little rotary saws that cut their way into you while a syphon gets slowly lowered down. ",
"Its not even a puncture at the scale the mosquito is working at."
] | [
"Video here: ",
"https://www.npr.org/sections/health-shots/2016/06/07/480653821/watch-mosquitoes-use-6-needles-to-suck-your-blood"
] | [
"That link’s staying blue for me thanks."
] |
[
"What happens if a gun is fired inside a pressurized cabin? (Like in an airplane)"
] | [
false
] | Today my military friend was trying to tell me that if a gun was shot at a high altitude in a pressurized airplane, that passengers would die from the force of the blast from the muzzle. (Not the bullet, unless of course it hits someone). He also went on to say that if the cabin is open to the air (depressurized) that the gun would act normally. | [
"I do not think that would be correct. The cabin is not extremely pressurized to allow for major changes (like what you might think of as the exploding safe episode of mythbusters).",
"Airplane cabins are generally kept at pressures similar to high land altitudes. See here from wiki:",
"A typical cabin altitude... | [
"Ok thank you. I tried to explain that to him! He was trying to make a point that force is much more powerful in a pressurized environment, specifically an airplane as we are both aerospace engineers. ",
"Are there any physics equations or a relationship between force from an explosion and a pressurized environme... | [
"I don't quite get where that train of thought came from. \"Pressurized environment\" doesn't automatically mean \"higher pressure\" - in fact, as stated above, the pressure is ",
" - maybe the term is confusing him.",
"I can understand if your friend thought a higher pressure environment can conduct a shockwav... |
[
"How do photons interact with eachother?"
] | [
false
] | null | [
"Generally photons don't interact with each other, but in a non-linear medium it is possible. For example, two photons can combine to excite a molecule to an excited state with an energy difference equal to the sum of both photons (two-photon absorption TPA, a third-order process), or two photons can combine to re... | [
"Thank you for the reply. Will read up on it further. :D"
] | [
"Photons can interfere with each other."
] |
[
"If the gas in a solar nebula is blown away as soon as the star becomes hot enough for hydrogen fusion, why are there different-sized stars?"
] | [
false
] | It's my understanding that all stars, at least ones that weren't formed in the early universe, were born in solar nebulae. The gas cloud spins around, and at the very center a star begins to form from accumulating dust and ices. Eventually this young star becomes so massive that the pressure its weight creates causes its core to begin fusing hydrogen atoms. Once this happens, most of the free-floating particles in the gas cloud get blown away, and most star and planet growth ceases. Since hydrogen fusion begins at a specific temperature, this would imply that all stars formed in this manner would have roughly the same mass, as they stopped growing once they became main sequence stars. However, this is clearly not the case, as main sequence stars can range in mass from a few percent the mass of the sun to ~100 solar masses. What's causing this size difference? The one thing I could think of was chemical composition, because it would cause a difference in density and therefore pressure, meaning a star would need a different mass to achieve H-fusion. However, it doesn't seem likely to me that this would single-handedly account for the vast range of possible star masses. Either there's something else causing the difference, or I simply don't understand how great an impact chemical composition makes. | [
"Once the hydrogen cloud is disturbed, the force of gravity causes different-sized clumps to form. Each of these may become a star. The arbitrarily-sized pocket of the cloud begins to collapse.",
"The hydrogen molecules (",
" atomic hydrogen) which comprise this cloud are all attracted to the center of mass o... | [
"That makes a lot of sense. I figured the \"blowing out\" force would overpower the gas particles, but I guess not.",
"You make it sound like it's happening on a really short timescale if the gas is moving towards the star at such a high velocity. Are there any good estimates on how long it takes for the gas to... | [
"These clouds can be tens or even a hundred lightyears in diameter, so it definitely doesn't happen in a short time, you could say it takes a very long time but most of the events are disproportionately packed towards the end of that time, since it's an accelerating process.",
"Once the molecular cloud loses the ... |
[
"Is there a correlation between 1 cal = 4.184 J and water’s heat capacity of 4.184 J/g°C?"
] | [
false
] | I’m in an online introduction class to chemistry. Today’s lesson covered energy, temperature, heat capacity and such. There was one part of the lesson that said 1 calorie is equal 4.184 joules. Later in the lesson there was a part that said water’s heat capacity is 4.184 J/g°C. I noticed that numbers were the same between the two. No where in the lesson did it address this similarity. So I was wondering if there’s a reason that these numbers are the same or if some there is some kind of correlation out side of having joule as part of the measurement? Or is this just coincidence? | [
"It's not a coincidence at all. The \"calorie\" unit is defined to be the amount of energy required to increase the temperature of 1 gram of water by 1 Kelvin (or °C, which represents the same temperature increment). As such, it is directly linked to the heat capacity of water.",
"The heat capacity of water depen... | [
"Water has some very interesting physical properties. Enjoy your studies.",
"For instance, its density is highest at 4 C. This means that as water approaches the freezing point when below 4 C, it rises as water slightly warmer is denser and sinks.",
"What does this mean? Water freezes top down. Most compounds f... | [
"My lesson didn’t mention this at all. It didn’t even really explain what a calorie was outside of a measurement of energy. So thank you a ton!"
] |
[
"Can you compare torque and horsepower?"
] | [
false
] | I am kind of confused by were one reddit user suggests you can directly compare torque and horsepower, yet another user says you cant. In the discussion only the users you say you can compare them have the upvotes, although my intuition would say you cant. Who is right here? Is this reddit being stupid or is it me just being dumb? | [
"You have to very careful, while they both share similar units, they are expressing different quantities. Horsepower is a unit of power, or energy per time. Torque is a psuedovector with units of energy per radian (degrees in a circle), because it's a psuedovector, it has direction as well as magnitude. You can thi... | [
"This article explains how to read a dyno chart:",
"\n",
"https://www.amsperformance.com/resources/technical-articles/56-hp-tq-dyno-chart",
"\nIt's a real graph that's useful in characterising a vehicle's performance. Since the torque is directly tied to your vehicle's acceleration (remember Torque = r x F an... | [
"The formula for Tq is:",
"Tq = HP * 5252 / RPM",
"Where HP is in lb-ft.",
"Which is why those plots will always meet at 5252 RPM."
] |
[
"What exactly does a scintillation counter measure?"
] | [
false
] | I've done a bit of gamma ray spectroscopy, and I'm trying to interpret my results, but I don't know enough about scintillation counters. So lets say a gamma ray comes in, generates and electron-positron pair, and then undergoes a few compton scattering events. The positron annihilates with an electron. So, what gets measured by the photomultiplier? There are several different things all with different energies. There might be 3 or 4 gamma rays with different energies (traveling in different directions), a few electrons with different energies (also traveling in different directions), and maybe theres some interactions between the compton electrons and the scintillator that gives off some lower energy photons. Can the detector "see" high energy gamma rays that don't undergo any scattering? Can it see the compton electrons? What about gamma rays and electrons that get scattered at some large angle (say, backwards and out of the detector)? Are these partially detected in some way, or are these completely invisible? At first, I thought the scintillation counter was literally counting the number of photons with particular energies, but if that were true I cannot explain my results. | [
"When thinking about radiation detection, I like to start at the end and work backwards. At the end, you have a device that measures an electrical impulse. This impulse represents one detection event - also since you are taking an energy spectrum, the size of the impulse represents how much energy was detected.",... | [
"Exactly.",
"The thing with a detector like this is that you don't measure the absolute energy deposited in each event - just the relative energy. So a 500 keV detection event produces a pulse that has twice the voltage of a 250 keV detection event. That is why you have to calibrate your spectrum with a known s... | [
"Your detector would see a signal equal to the energy of the compton electron",
"So how exactly does it see this energy?",
"The compton electron blazes through, knocking a whole bunch of other electrons loose, and when those eventually fall back into place they give off low energy photons, which the detector th... |
[
"How do we keep track of human genetic change? How much change would need to occur before scientists could say a new species of humans has evolved?"
] | [
false
] | I recently saw an exhibit about the brief period when neanderthals and homo sapiens co-existed, both of which could be classified as humans. I've been fascinated with the prospect of different species of humans coexisting ever since. How much would some homo sapiens have to change before we would classify them as a different species? Do we currently measure this change in any way? Does increased mobility prevent any one group from deviating so substantially that it would become a different species? | [
"This is a good question, and it's one for which you would find a lot of contention among biologists. The problem is that we do not have a single definition for species. As humans, we like to put things into discrete categories, but real organisms don't necessarily obey our rules. Now, for mammals like ourselves, w... | [
"Yes, our current global interconnectedness probably makes it difficult for any group to evolve to the point of speciation. As was already stated, species can be very tricky for scientists to determine, but a good rule of thumb is that the offspring of two separate species tend to be nonviable or sterile. This is N... | [
"The evidence for anatomically moden humans and Neanderthals interbreeding is not as strong as previously thought and is explained by human population structuring. Here is the ",
"PNAS article",
". I agree that it would probably be most appropriate to use the biological species concept to define different human... |
[
"What is the physical significance of a commutator in Quantum Mechanics?"
] | [
false
] | It is my understanding that you can use commutators to determine the uncertainty relationships between some observables but I am still having a hard time understanding what the physical meaning of the expression [A,B] is. Also, in addition to the one application above, what else can they be used for? | [
"Hm. It's a mathematical construct which literally tells you whether two operators commute. IMO, it doesn't have a \"physical\" meaning beyond that on its own, just like there is no particular physical meaning behind the \"+\" or \"-\" operator beyond the literal meaning of \"add\" and \"subtract\". "
] | [
"The commutators can however tell you something about the eigenstates of the operators. If two operators commute, there are states that are eigenstates to both of the operators. If their commutator is nonzero, there exist no such states. This is a very obvious and straightforward result, but usually not the reason ... | [
"This isn't really a 'physical' interpretation, but it kind of shows that there's something deeper and more interesting about commutators.",
"Proper maths students will probably slay me for this, but commutators (by using them as Lie brackets) can tell you about the structure of the operator Lie algebra you're us... |
[
"Why is human beard hair so much coarser than either body hair or head hair?"
] | [
false
] | Is it simply a matter of evolution? As beard hair shields a hunter's face against the elements while hunting, it would obviously be an advantage to have facial hair that is stiff and loose to mitigate wind chill or precipitation. What proteins are in beard hair which aren't found in other types of hair? I would love to have any information you can provide on this topic. | [
"Hair coarseness is a function of the thickness of each individual shaft of hair. Beard hairs are coarser than scalp hairs because they are individually thicker than your head hairs. One of the main things that influences hair thickness is the size of the dermal papilla, the space the root of the hair shaft sits in... | [
"A very thorough and well explained response. Thank you. "
] | [
"Just to clarify, sexual selection is a type of natural selection not a different process."
] |
[
"How were heavy vehicles steered before the popularization of power steering?"
] | [
false
] | Manual steering requires a lot of force even with a moderately heavy vehicle such as a mini-van, but power steering wasn't really around commercially until the 1950s. How did heavy vehicles such as cargo trucks get around this problem? | [
"Many older vehicles used what is called ",
"\"worm and sector\"",
" steering which used a worm gear to turn a meshing section of the Pittman arm, which in turn moved the wheels. Today, this has been replaced with recirculating ball steering which operates on a similar principle, only the worm gear moves metal ... | [
"Two things... First, when the vehicle is moving, steering without power is relatively easy. Before power steering, people just made sure the car was rolling before turning the wheel. On top of that, steering wheels were larger. Having a larger wheel has the same effect on it's ability to turn as using a longer lev... | [
"This. You can also have a higher gear ratio between the steering wheel and the wheels (it takes more rotations of the wheel from lock to lock)"
] |
[
"Can black holes be used as giant space mirrors?"
] | [
false
] | Black holes have strong enough gravity to prevent light from escaping. Could they also have light orbit them, such as how planets orbit stars? If so, would it be possible for black holes to have a slingshot effect on light, essentially sending it back in the direction it came? | [
"I read an article that explained that being next to the black hole the light would bend so much that you would be able to see the back of your head in front of you. I thought that was interesting anyone want to do some scientific poetry on that ?"
] | [
"Black holes do bend light; it's an example of ",
"gravitational lensing",
".",
"This is outside my field, so hopefully someone will double-check my math, but I don't think it's possible for a black hole to deflect light 180 degrees ",
". Light inside the event horizon won't be coming back in the direction... | [
"What about rotation? This drags spacetime in strange ways."
] |
[
"Do babies need to breathe after birth if the umbilical cord is not cut?"
] | [
false
] | Babies clearly breathe after birth since they cry, but if the umbilical chord were left alone, would they to? Does the mother stop supplying the baby with nutrients/oxygen after birth? | [
"There is so much to this, so I’ll try to be brief, but also cover the gist of what occurs. ",
"If placenta is still pumping ",
" attached to baby, baby will continue receiving oxygenated blood for awhile, but that varies on a case-by-case basis. Some of baby’s blood volume gets squeezed back into the placenta ... | [
"This is a very in depth summary, but just to further clarify for others, the placenta does not pump. The baby's heart is what moves the fluid around the fetal/neonatal circulatory system. The umbilical cord will have pulsations in its artery, but this is because it is attached to the heart, like any other artery.... | [
"There is a natural instinct when the baby is born to take the first breath. This first breath leads to an increase in oxygen and when oxygen enters the baby’s body a great deal of things occur. One of primary things is the closer of the parent ductus arteriosus and dilation of arteries in the lungs. Essentially th... |
[
"What happens to bodily waste in people who have very infrequent bowel movements?"
] | [
false
] | [deleted] | [
"My experience here comes from human gross anatomy, so stuff at small scales may be best explained by someone else.",
"There's a pretty wide range in defecation frequency in humans. ",
"Here is one study",
" looking at a limited demographic in a single city that found a lot of variation in bowel movement habi... | [
"It just stays there. Its volume is reduced by recycling the water. Which means the eventual bowel movement is more difficult, because the fecal matter, lacking water, is more stiff."
] | [
"Thanks for the interesting reply. I assume you mean 'small intestine' instead of 'short intestine' though?",
"Currently laid up with a bit of stomach flu/food poisoning, so the water extraction part isn't doing it's thing. Not asking for medical advice, but the graph of transit times made me wonder if it's more ... |
[
"What's the most fun or interesting thing you scientists do with chemistry/your knowledge of chemistry?"
] | [
false
] | Just thought it'd be fun to hear or maybe do. | [
"extracting illegal drugs from readily available and legal plants"
] | [
"Precipitating DNA, making H2(g), and of course making dry ice fog."
] | [
"Not a scientist, but I've had some fun with things during my years. Making liquid nitrogen ice cream is a winner with kids, and throw in a reverse flame blower show for added fun.",
"Also we used to make tennis ball cannons shooting several hundred meters with a mineral that made an explosive gas when immersed i... |
[
"Why did Nordic people evolve to have thin bodyhair and blonde hair while people in hotter regions have thick bodyhair which would be better suited to colder climates?"
] | [
false
] | In terms of heat insulation, why didn't people in colder climates evolve to have thick and dark bodyhair which would help you keep warmer. And on the contrary, shouldn't people in hotter regions have blonde hair which would reflect sun and perhaps no bodyhair to keep cool? Or does the sun have an effect that makes hair darker? | [
"The differences in hair has a negligible effect on your ability to survive northern climates: humans won't survive the winters anyway without clothing, so your hair matters little.",
"What ",
" matter is sunlight. Near the equator the intense sunlight is a problem, causing sunburns and skin cancer, so darker s... | [
"The vitamin D hypothesis is a well-supported notion of how light skin developed, but hair color is only weakly influenced by alleles for skin or eye color. It is more likely that variation in hair and eye color was the result of ",
"strong sexual selection at northern latitudes",
" (link to another comment)."... | [
"The reason that hair color/thickness and skin pigmentation evolved the way it did is not due to thermal insulation, but rather protection of skin from the sun. The reason people in, for example Africa, have such dark skin and thick hair is that it allows their body to be less susceptible to sun damage such as sunb... |
[
"Does it take the same amount of energy to slow down a space craft as it did to get to that speed?"
] | [
false
] | null | [
"That depends. It can take less, more or the equal amount of energy due to gravity assists.",
"But let's imagine there is no matter around you. To move forward you need propulsion, and to stop you need the exact same amount of propulsion in the exactly opposite direction.",
"However, in real life there are seve... | [
"There are multiple layers of reality to that question.",
"1st layer: Yes, it takes the same amount of energy. If you shift your frame of reference to the accelerated space craft, you see that to get to the previous \"null\" velocity, you have to make the same acceleration as to get to that velocity.",
"2nd lay... | [
"Not necessarily. The main determinant of power for a rocket is the delta-v, or the total amount the rocket can change it's velocity by.",
"The Oberth effect says that impulse added when your velocity is higher, ie at the apogee of your orbit near the gravitational body, can result in greater final velocities tha... |
[
"What is in between galaxies?"
] | [
false
] | after seeing this picture ( ) I became curious about what is in between galaxies. I know it's a bit of a silly question but is it just empty space or is there more to it? Any info is greatly appreciated. | [
"The 'intergalactic medium' (IGM) is mostly a rarified plasma. The heating mechanism depends on the particular environment -- the gas between galaxies in clusters tends to be very, very hot indeed (millions of kelvin), and emits in the X-ray. This is generally heated via gravitational shockwaves, as the gas falls i... | [
"Much of it (at least the baryons) was ejected from galaxies from either Supernovae or Active Galactic Nucleii. That stuff tends to be moving fast and since the IGM is so sparse, it's hard for particles to interact and potentially cool."
] | [
"Just ask your questions here. If you can't think of any specific questions the AMA would in fact not be fascinating."
] |
[
"How much Carbon does an acre of trees offset each year?"
] | [
false
] | Specifically, in a rainforest that is fairly well established (roughly 100 years old, some trees older, and found in Northern Australia). | [
"That's the thing though; all trees are collecting carbon from the air and depositing it."
] | [
"Well, of course that is possible, which is why I mentioned it. However, in a well established environment, there is very little net burial. It does not just accumulate forever, but rather reaches a state where as much organic material is released by decay as is sequestered by photosynthesis.",
"The balance an... | [
"Unless the forest is increasing in size, or creating a deposit of buried organic carbon, it releases as much CO2 as it absorbs. It is in dynamic equilibrium."
] |
[
"Why aren’t waterfalls just eroded to slopes?"
] | [
false
] | I can understand that water needs some place to go and sometimes the easiest path is over a ledge. However, I would think that the power of erosion would convert these waterfalls into smoother inclines. Are waterfalls usually just the result of recently redirected water where the forces of erosion haven’t worn it down yet? Are tectonic plates moving faster than the forces of erosion can act? Are the rock found at many waterfalls more resistant to erosion? Thanks! | [
"The most powerful weathering happens in two places in a waterfall system. The critical edge, the place with the least support. And the vertical edge, where falling water has a lot of force and there is not much vertical support.\nThese two places happen to be where the defining features of the waterfall are (edge ... | [
"I looked up Niagara Falls erosion and found this: ",
"\"What is the future of Niagara Falls?\nToday, the falls continue to erode, however, the rate has been greatly reduced due to flow control and diversion for hydro-power generation. Recession for at least the last 560 years has been estimated at 1 to 1.5 metr... | [
"If you explore the woods downstream you can see signs of the previous positions of the falls. Giant boulders, bowls ground out of the stone, etc.",
"Niagara Escarpment"
] |
[
"If electric cars become the norm, is it likely it would be economically feasible to own a gas powered car?"
] | [
false
] | Let's say would it be feasible for a middle class guy? | [
"It takes a while to change production of large scale oil fields. What would happen is that as people started switching to electric cars, the demand for fuel would fall relative to supply, causing a glut of inventory and leading to lower prices. The lower cost of fuel would serve to stem the tide of people switchin... | [
"With #2, at some point in time the cost of gas (and very well maybe electricity depending on our supplier) would go up just due to the difficulty in drilling for it, given traditional drilling methods. At a certain point in time usable oil will become to low yield to be worth drilling for."
] | [
"Do you mean gasoline, or natural gas? "
] |
[
"I'm just a lowly at student, uninitiated in the way of physics. Explain the holographic principle to me in one of those over simplified metaphors."
] | [
false
] | [deleted] | [
"Imagine watching a movie. The screen is flat, but your mind kind of interprets it as three-dimensional! This has nothing to do with the holographic principle."
] | [
"The maximum amount of quantum state information that can be contained within a region of space is equal to the area of a sphere with the same volume as the region, measured in square Planck length units.",
"There's not really a metaphor required, because it's really just that simple. If you try to cram the maxim... | [
"If you're coming at this from the point of view of what I call a \"computer person\" — those admirable and infuriating young people who find computers to be natural and intuitive rather than backwards and infuriating, and who thus tend to see everything in terms of how it could be computed with a computer — then i... |
[
"Why could this PVC I am analyzing have endothermic peaks near the melt point when PVC is an amorphous solid?"
] | [
false
] | null | [
"This is run on a DSC. I think I solved the problem. I looked at the pan my tech have me and there is a brown line around the ridge of it indicating some off gassing has occurred. I'm guessing that was the problem. "
] | [
"Not the right sub for such specific / idiosyncratic questions. Try ",
"/r/askchemistry",
" or ",
"/r/labrats"
] | [
"Solved my own problem anyways. The mini cups were popping open because of the volatiles and the \"endotherm\" was caused by the sensor reading an open cup vs a sealed cup. "
] |
[
"Will running a humidifier in a warm, dry, closed room cool the room?"
] | [
false
] | Specifically, does increasing the humidity of a closed system affect the temperature? What about an open system (window opened in the aforementioned room, for example)? I suppose the humidifier produces some kind of heat while running, but I'm not sure if that's important for this question. | [
"With a usual swamp cooler setup you will have positive pressure inside the residence with a cracked-open window or door in the region where you want cool air to flow through the building. If the humid air can't escape then you will saturate the air which may marginally reduce the temperature at first but then you'... | [
"yes, it's very important. since humidifiers are not 100% efficient, you will be adding excess heat to the room. Similar to why leaving your refrigerator door open won't cool your room, it will in fact heat it."
] | [
"A dehumidifier will always warm a room. Heat is removed from the water molecules upon condensation. Additionally, waste heat is always produced by the motor. ",
"Increasing the humidity has the opposite effect; it cools the room. See ",
"swamp cooler",
". Water molecules absorb heat during the state cha... |
[
"How tonal languages such as Mandarin sung without changing the meaning of the words?"
] | [
false
] | [deleted] | [
"To start, in Mandarin tones are not sung. The tune follows the melody and context is all you need.",
"However, this is ",
" the case with all tonal languages. Cantonese is a good example of a tonal language in which singing preserves some ",
" of phonemic tone, but not the actual original tone from the norma... | [
"This is at best an oversimplification on many many points, and at worst just flat out incorrect.",
"It's actually ",
" entirely up to context in Cantonese, where tones are in fact still represented in song. See my longer response to OP about that.",
"\"Japanese has fewer tones than Chinese\". To say that Jap... | [
"This is at best an oversimplification on many many points, and at worst just flat out incorrect.",
"It's actually ",
" entirely up to context in Cantonese, where tones are in fact still represented in song. See my longer response to OP about that.",
"\"Japanese has fewer tones than Chinese\". To say that Jap... |
[
"What are the differences between multi-core and GPU computing? When would you use each?"
] | [
false
] | [deleted] | [
"With a multi-core CPU, each core can do its own thing. To a programmer, it works exactly like you'd expect a multi-core system to work: you can launch threads on all cores and run completely different, individual tasks on all of them. The biggest multi-core CPUs from AMD have about 16 cores (while I believe the bi... | [
"While this is a decent description of modern ",
", it's a bit misleading.",
"GPUs can be MIMD",
".",
"In reality the difference is simply the multicore vs. manycore argument.",
"In a multicore, you create a processor that's as powerful as you can make it, and then, when you can't make it any better, you ... | [
"Very well explained! I've heard bits and pieces of this before but never seen it all wrapped up so coherently."
] |
[
"Why do we develop tolerance to certain drugs? Why don't we develop a tolerance to others, antidepressants for example?"
] | [
false
] | null | [
"Tolerance is caused when a drug blocks a specific receptor on a cell, we'll use morphine and the mu receptor which is located throughout your body as an example, a cell that has all of its mu receptors blocked for an extended period it will try to compensate by increasing the rate at which it produces more mu rece... | [
"Are you trying to say that reuptake inhibitors don't build tolerance? Because cocaine for example is a reuptake inhibitor and is generally considered to build tolerance.",
"\"Tolerance\" is probably a pretty complex process, though. And dose has a lot to do with it."
] | [
"I'm in pharmacy so cocaine is a bit outside my realm of expertise but I thought the tolerance was more a result of a psychological change, with continuous activation of the mesolimbic reward pathway resulting in the brain in an requirement for even more activation in order for the brain to recognize the activation... |
[
"If our skin cells die and regenerate so much, as well as most of the other cells in our body, why are tattoos still visible after so many decades?"
] | [
false
] | null | [
"Our skin has several layers, the top being composed of the epidermis (keratinized dead layers of cells) and the dermis (where your nerves, blood vessels, and epithelial progenitors are). These layers are held together and the cells are positioned by the extra cellular matrix, which is comprised of carbohydrate fib... | [
"Is that not what the henna style tattoos do? Those due your skin and last a couple weeks"
] | [
"Is that not what the henna style tattoos do? Those due your skin and last a couple weeks"
] |
[
"When touching something without looking at it, why is it difficult to distinguish cold from wet?"
] | [
false
] | I first noticed this the other night while in bed, I reached my hands across my sheets and thought I felt something wet. It turned out to just really cold. It got me thinking and I tried out a few objects blindfolded, such as a cold ceramic dish, a cold glass, and porcelain. Is there anything to this or is it purely anecdotal? | [
"Maybe a better question is, do we have the ability to detect 'wet' directly or is it only through a combination of temperature and texture that we determine that something is 'wet'? "
] | [
"To my knowledge, we have no sensory mechanism to detect 'wet' directly in the short-term."
] | [
"Also, our sense of hot and cold is not actually a sense of temperature, it's a sense of heat flux. We \"feel\" energy out (cold) or energy in (hot), and how cold or hot it feels depends on the rate of transfer. ",
"How \"cold\" something feels depends not only on its actual temperature but also on its thermal co... |
[
"Is it possible that the end of the sunspot cycle could significantly slow down global warming?"
] | [
false
] | Sunspots, the enormous magnetic storms that erupt on the sun's surface as the cycle builds, might disappear entirely for the first time in approximately 400 years. If the reported trends continue—a big if, other researchers note—a hibernating sun would have only a slight cooling effect on climate I'm not entirely so sure about that "slight cooling effect on climate"... We know SO little about the Sun's cycles and solar variability ( over timescales lasting more than several decades, since we barely monitored the Sun before a few decades ago). And assuming that this IF happens, then the last time this happened was the time of the Maunder Minimum, when you had snowfall and freezing temperatures (in both Europe and North America) during SUMMER. I would hardly call that "a slight cooling effect" (see ) - although if it happens again, I don't think it will be as severe as what happened during the Maunder minimum. In fact, my fear is that it would entirely discredit the climate modelling community just because they neglected solar variability. Already, I'm afraid that the climate modelling community (along with the broader scientific community, which has vehemently defended the modelling community) might be discredited (by the popular opinion) in 5-10 years, because there are other cycles that can cause an apparent lapse in global warming for around a decade (it's just that the warming in the 1990s was superimposed upon a warming part of the possible cycle, and we now might be heading towards the cooler phase of that cycle, which explains why the last 10 years haven't really seen much of a strong warming trend): But it might give us a lucky break of several decades. That being said, I'm definitely not counting or betting on that happening, and do not think the argument should be a factor towards laxer policies towards CO2 mitigation. Even if it did happen, I highly doubt it would result in anything similar to the repeat of the Maunder Minimum. I'm just anticipating that this be possible, and that if it is possible, then we must at least prepare for its slight possibility (and that maybe we can't completely be 95% confident that global warming is going to be as catastrophic as the IPCC thinks it is). By the way, I actually work with climate modellers, and am in no way sympathetic to skeptics of anthropogenic global warming (although I do have a fair amount of respect for both Dyson and Lomborg, though I don't like it how Dyson also tries to use some of the more scientifically irresponsible arguments). I am open to alternative sides of the data and interpretations, since I'm still just learning (and haven't gone through the entire IPCC pdf yet). With all that being said, does anyone think that the emerging field of could help us better quantify variations in the solar output (especially in the past?) See for a recent science paper (conducted on stars SIMILAR to the sun) | [
"Considering how low sunspot activity was the last few years (It was a very deep minimum) and yet we still had extremely hot years (indeed the 2000's were a good deal hotter than the 1990's I'd say I wouldn't count on it."
] | [
"You dropped this:",
")"
] | [
"\"The temperature change associated with any reduction in sunspot activity would likely be minimal and may not be enough to offset the impact of greenhouse gases on global warming, according to scientists who have published recent papers on the topic.",
"\"Recent solar 11-year cycles are associated empirically w... |
[
"Are comets constantly shrinking? That is to say, are they losing mass through their dust trail?"
] | [
false
] | That is to say, are comets like Halley's comet going to disappear one day? | [
"Comets are constantly losing mass. There is a finite number of passes a comet can do before it \"turns off\". However, common belief is that the comet won't just disappear but rather change. Comets lose ice more than they lose dust. It is assumed that eventually a comet could develop a surface that is a good enoug... | [
"Indeed, there are such objects that have orbits we expect of comets but have spectra more like an asteroid. We call these \"comet-asteroid transition objects.\" ",
"944 Hidalgo",
" is among the most well-known."
] | [
"Comets lose mass when they're near the sun. They heat up, which sublimates/boils ices, causing gas to stream out (and it will carry rocks and dust along with it). Comets are visible to the naked eye when they're outgassing like this (the comets themselves are too small/dark to see, it's the surrounding gas and d... |
[
"If Thorium is so abundant and cheap, why is it so hard to get a sample of?"
] | [
false
] | video from "Periodic Table of Videos" stresses how hard to get Thorium is, but every proponent of Thorium ever has noted that a major benefit of thorium is that it is so abundant and cheap to mine... So which is it, and if it's both, then how is this inconsistency settled? Are people just throwing away Thorium because it has no use currently? I would still expect there to be SOMEONE selling nice thorium spheres or cubes for classrooms... Edit: I'll clarify that I'm not asking about Thorium reactors or LFTRs or MSRs.... Just why is it so hard for a to get a , and when he does why is that sample so tiny? As far as I understand Thorium emits only alpha particles which are easily stopped by the lightest of shielding and might even be safe to handle with only gloves... I'd assume would be selling chunks of it! | [
"Thorium is abundant and cheap to mine compared to other similar elements, but it is still extremely rare compared to common metals like iron and aluminum. The main problem is that if there's no industrial use, there's no proper market and no economy of scale. A mine isn't going to be profitable if the only demand ... | [
"Im a mineral collector, so i speak from that viewpoint.",
"\nMonazite, the major ore, is traditionally minded as sand. To buy a nice Monazite crystal (like, 1-3 cm) can be a bit pricey. A thorianite crystal (1cm is big) can be REALLY PRICEY. So, specifically, in terms of crystals, the rarity is the cause of t... | [
"To buy a nice Monazite crystal (like, 1-3 cm) can be a bit pricey. A thorianite crystal (1cm is big) can be REALLY PRICEY. ",
"Can you give rough numbers? This can mean anything from few hundred bucks to millions"
] |
[
"A question about redshift"
] | [
false
] | Okay, redshift. The distance between me and a galaxy far, far away increases because the universe is expanding, and this shows up as a redshift. In analogy: if I have a magic box from which an ant shows up every second, i get one ant per second if I put it on my desk. If I glue the box to a balloon, and I blow the balloon up, I get less ants per second. Even though the ant still move at their maximum speed-of-ants, they arrive slower. So, the ant-delay (redshift) is a measure of the speed with which the balloon is inflated (the universe expands). Yes? Now, we know that the speed with which the universe expands is increasing. So, younger objects in the universe exist in a faster-expanding universe, and should have a higher redshift. But instead, the really high-redshift stuff is truly ancient. What am I missing? | [
"I feel you are complicating things:",
"If a light source moves away from you the wave length of light you observe from it gets longer - this is red shift - and if it moves faster it gets more red shifted. The universe is expanding everywhere and all the time thus the more distant objects are more red shifted",
... | [
"Your ant metaphor is apt. What is important to remember is that each ant box emits ants at the same rate locally. The fact that the ants are walking across the balloon as it expands is the reason why the ants show up at your door at a different frequency than when they left the box. The ants from farther galaxies ... | [
"So, younger objects in the universe exist in a faster-expanding universe, and should have a higher redshift. But instead, the really high-redshift stuff is truly ancient.",
"Redshift is a function of two things... the rate of expansion, and the distance to the object.",
"So while the rate of expansion is highe... |
[
"Is it possible that there are stable super-heavy elements (beyond atomic number 100)?"
] | [
false
] | Is there a law against it or is possible just taking a large amount of energy? | [
"Probably not. There is a proposed ",
"island of stability",
". However, this is a relative descriptor, as being able to work with something that might last for minutes to days would allow much greater depth & breadth of study than something which decays in fractions of a second.",
"It might also be of inter... | [
"Mendelevium and nobelium have an atomic number of 101 and 102 and are stable.",
"Um ... no?",
"Mendelevium",
":",
"\"Sixteen isotopes of mendelevium from mass 245 to 260 have been characterized, with the most stable being 258Md with a half-life of 51.5 days, 260Md with a half-life of 31.8 days, and 257Md w... | [
"There are legitimate and reasonable theories about the so-called ",
"Island of Stability",
". However, the hypothesized super-stable elements have not yet been synthesized. It is of course possible that there are fundamental reasons for this, thought it might also just be the technical difficulties (alluded to... |
[
"Why aren't airplane fuselage and/or wing surfaces dimpled?"
] | [
false
] | If dimpling significantly reduces drag on a golf ball, why can't a similar principle be applied to airplanes? If I remember correctly, Mythbusters tested dimpling on cars and concluded that it did improve fuel efficiency. | [
"Before adding some other factors I'd like to add to what ",
"u/cantilene",
" said; turbulence reduces flow separation and thus adverse pressure gradient. BUT, it increases skin friction significantly, the other form of drag along with adverse pressure gradient. With a golf ball you have no choice but to acce... | [
"Just to further add onto the topic of the turbulent boundary layer:",
"At the Reynolds numbers most aircraft operate at, the boundary layer is almost completely turbulent. So adding dimples to that would really only give you more skin drag."
] | [
"A lot of airplanes these days have vortex generators on the wings which do essentially the same thing. As to why all planes don't have them, the answer is that planes are built to be aerodynamic whereas golf ball are just spheres. The dimples on a golf ball help prevent flow separation because turbulent flow stick... |
[
"Are all electrons and protons in the universe a product of beta decay?"
] | [
false
] | null | [
"No. Many of them are left over from the Big Bang."
] | [
"Thanks, what percentage of them would you say are beta particles? "
] | [
"I have no idea."
] |
[
"How is our body able to create the material our nails are made from?"
] | [
false
] | null | [
"Hair and nails are composed of ",
"keratin",
". Keratin is an extremely stable protein that is made as a very long, coiled fiber (sort of like a stretched-out slinky). The subunits of proteins, including keratin, are added piece by piece - imagine linking shower curtain rings together, one-by-one. These sub... | [
"That's called the lunula, it's the visible part of the keratin-making matrix that fingernails protect. Your grandmother might have just lost them with age (aging does weird shit to your body), but fingernails are also a good indicator of overall health, so it might be something worth checking out.",
"Fun fact -... | [
"Maybe, probably just compared to people who don't have enough protein in their diets. The enzymes that propel reactions forward, creating your nails, have a limit to how fast they can work. They can only string together so many amino acids (AA) in a given amount of time. If the concentration of AAs is low, the ... |
[
"Undiscovered Mathematics"
] | [
false
] | So as the legend goes, Newton discovered differential and integral calculus to describe planetary motion. Is it possible that there is more math to discover that is necessary to describe the universe? eg. Algebra, Trig, Calculus, ??? For example, might there be quantum mathematics? | [
"The answer is of course ",
", if history is any indication at all.",
"Physics has always been a (the?) major source of new mathematics, and it is as true today as ever. Roughly what tends to happen is that physics is written down using some mathematics that already exists (more or less), but a deeper study of... | [
"True in what sense? You need to define your terminology better."
] | [
"I think you have to account for our admittedly small capabilities of perception as modern humans.",
"We can't travel that fast, see that well, of a multitude of things. Few of us ever live in circumstances where we experience nuances like shifts in relativity in ways that we can directly and obviously observe. "... |
[
"Do we possess the computational power to simulate the origin of a single celled organism from non-living material?"
] | [
false
] | null | [
"Essentially no. Not in the sense that you are probably asking the question. \nWe almost certainly don't have enough computing power to simulate enough molecules and a large enough environment to go from non-living material all the way to cells.",
"But even if we did have the computing power there are many, many ... | [
"Funnily enough I work on protein folding and the evolution of protein folds. I have to say that in 10 years the field as barely progressed and that's with all the advances around distributed computing, faster computers and gpGPU calculation. The biggest and obvious problem is that the models we use, complex as the... | [
"There's a scientific field called \"Molecular Dynamics\" that deals with computer simulations of molecules.",
"The state of the art is simulating maybe 10",
" molecules over 10",
" seconds. So, it is no where near the level of simulating evolution.",
"Here's an example of a molecular dynamics simulation o... |
[
"Where can I get some Renografin 60? Help me, Reddit Ask Science, you're my only hope."
] | [
false
] | null | [
"I'm not sure about asking for prescription medications, even one that is just a radiopaque substance with no clinical effect, on reddit.",
"Doesn't Bracco make it any more? If not, then I would suggest contacting distributors like Cardinal, McKesson, or Owens & Minor. If you're not using this for human use, but ... | [
"One other suggestion. I don't know where you're located, but you might want to contact hospital pharmacies or radiology/cardiology cath labs in your area for expired ionic contrast agents. They are going to be really paranoid about giving away expired product because they will be concerned it will be used in human... | [
"Also, what about Isopaque from Mallinckrodt? It's essentially similar, but I'm not sure what you're doing for your work."
] |
[
"How would the Earth be different if it had three moons of equal size, equally spaced on the same orbital plane?"
] | [
false
] | null | [
"That's not a stable configuration, it would decay and eventually at least one of the moons would either be kicked out of the system or fall to Earth, and another would either suffer the same fate or have to move to a higher or lower orbit. Having two massive moons on the same orbit doesn't work."
] | [
"Of course not, I knew the first answer would make me feel dumb. And I also realized that trying to evenly distribute mass would make the bulge less prominent since it's due to the gravitational imbalance caused by the moon's presence.",
"Hmm, I'm trying to write a story that somewhat hinges on the sea levels at... | [
"I feel like there are probably some simpler ways to get to the intended goal of un-noticed Antarctic mountains, starting with the currently known mountain ranges and mile-thick ice sheet."
] |
[
"Is sexual anxiety a new human trait or has it been around for centuries?"
] | [
false
] | null | [
"Short answer: Yes (probably). ",
"Science answer: A study on macaques revealed that males had difficulty achieving orgasm (less than 2% of time) if the female didn't make noise during sex. When they did shout, ejaculate rates rose to 86%. Source: (It had to be the Germans) ",
"http://rspb.royalsocietypublishin... | [
"You might want to consider specifying which of the two options in the original question you are saying \"Yes\" to."
] | [
"You may have some success asking this question in ",
"/r/askhistorians",
" if you're looking for historical context in connection to current society (porn use and whatnot). It's not a scientific answer, but it may answer some of your questions. "
] |
[
"Does the method of loci/ memory palace technique really work? Are there any notable examples?"
] | [
false
] | null | [
"http://www.usamemorychampionship.com/"
] | [
"The loci method is relatively well documented and has been shown to work moderately well for new learners. It is interesting to note that older people who may have age-related memory deficits don't benefit as much from it as young and healthy individuals (",
"ref",
").",
"An interesting point to note is that... | [
"Here's an interesting TED talk on the subject: \n",
"http://www.ted.com/talks/lang/en/joshua_foer_feats_of_memory_anyone_can_do.html"
] |
[
"What would happen if you uniformly increased the pressure inside a perfect sphere of perfectly consistent material?"
] | [
false
] | If the material of the sphere was perfectly consistent, such as that there are no areas weaker than others, would the sphere ever break? In what manner would it break? I realise that an argument could be made for air pressure resulting in a rupture at a point where more force is exerted for a moment, so assume that the pressure provides uniform force in all directions. | [
"Well, the sphere will break once the pressure is high enough to push apart the bonds. ",
"As long as the material is not perfectly stretchy or something to that effect.",
"Same as with a chain where all the links have the exact same strength, each link is still breakable."
] | [
"Well, the sphere will break once the pressure is high enough to push apart the bonds. ",
"As long as the material is not perfectly stretchy or something to that effect.",
"Same as with a chain where all the links have the exact same strength, each link is still breakable."
] | [
"Yes, but for anything to break it has to start somewhere. In a real material, this happens at the tiniest imperfection, or even molecular bonds are not perfectly spherical.",
"In OP's imaginary universe where everything is perfectly smooth and spherical and not even composed of atoms, there is no single place fo... |
[
"Can a person get the same strain of Norovirus within a week or two of getting rid of it?"
] | [
false
] | I work in an aged care facility, and we are at the tail end of a disatrous Gastro outbreak. Now we have some residents getting it for the second time supposedly, and I'm a little skeptical regarding the legitimacy of these seconds bouts. I've looked online for an answer to this, and only found conflicting opinions with no sources (yahoo answers etc...) Furthermore, if you can get it twice, can someone please explain what the mechanism is? Does the virus mutate? Can it lay dormant? Thanks! edit: Thanks so much for the thorough answers, everyone! Both I and the RN here found this all fascinating. The nurse in particular (@64yrs old) found 'the reddit' to be amazing... just to touch on some questions: Yes, at the onset of the outbreak a Doctor (whoever it was) tested for and confirmed Norovirus. And there seemed to be some concern regarding why any resident here would be getting gastro twice... unfortunately all I can say about that is there has been an influx of very young and poorly trained new staff making many observable errors... making this outbreak drag on and on... I'm trying hard train them etc, but I'm night staff and barely see any of them! And I certainly know how bad the Norovirus is... I was the first Staff member to get it this time! Anyway, thanks again Science community! | [
"Yes you can. But it's highly unlikely and shouldn't happen but is completely possible.",
"You should be immune to the strain you just cleared for a short period (if you weren't then how would you ever get over it!) but this doesn't last long a few months in very fit and healthy people, the elderly probably have ... | [
"Med Student here",
"Apparently you can ",
"http://www.cdc.gov/mmwr/preview/mmwrhtml/rr6003a1.htm",
"\nScroll down to immunity section, about 1/10th way down",
"Susceptibility seems to have host genetic factors.",
"Take away message: ensure infected patients are isolated and vigorous hand hygiene is insti... | [
"That sounded sketchy. ",
"If you go to the CDC articles original sources it says \"",
" and five of the 10 who remained well had a ",
"What the article is saying is the host-genetic factors could cause you to asymptomatically clear the infection without developing an antibody response. That being said ",
"... |
[
"Can you find the Mona Lisa in a Mandelbrot fractal?"
] | [
false
] | Apparently when one goes deep enough into any arbitrarily coloured Mandelbrot fractal one can find amazing structures. Is it possible to find the Mona Lisa painting in there when given enough time and resources? for reference: | [
"No. Just because something is infinite doesn't mean it will have every possible permutation of values.",
"For example, imagine a pattern like 10100100010000100000...",
"It could go on forever and never repeat. No where in that sequence of numbers will 123 ever appear. In spite of the infinite complexity of the... | [
"It's not random. That's the problem."
] | [
"It's not random. That's the problem."
] |
[
"What other things like seeing our nose and breathing we ignore by default?"
] | [
false
] | null | [
"We do this all the time with things that aren't changing in our environment. For example, when you first put your clothes on in the morning you feel them on your skin, but, very rapidly you stop noticing them. Now that you've read this, you might become aware of your clothing again! The same applies to ambient noi... | [
"Generally speaking it's almost impossible to tickle yourself. Your brain filters the sensation of touching ourself to prevent the response another's might provoke. There are exceptions to this.",
"Someone's going to mention you're schizophrenic if you can, but having an ailment like that is a lot more complicate... | [
"There is actually a hole in your sight. Close one eye and take your thumb and, keeping your open eye facing directly forward and focused on a point in the background, move it across your field of view. Eventually, you will noticed that a portion of your thumb will disappear. This is completely natural and present ... |
[
"Why are the noble metals so unreactive?"
] | [
false
] | From what I have gathered so far it seems that the inner electrons have more energy than the outer electrons. But I don't know how this all ties into it. If you are explaining it could you explain it in the most layman terms as possible so I can grasp the concept. | [
"Because we live on a planet covered in water.",
"The best way to understand this, look at the ",
"electrochemical series",
", and scroll down to 0, which corresponds to Hydrogen. Now, observe the metals below that point - Your \"noble\" metals.",
"Basically, the \"noble\" metals stay in their metallic ele... | [
"Not sure why this got voted down - It counts as the \"right\" answer.",
"If we lived on a planet dominated by free fluorine, we would have ",
" \"noble\" metals. If we lived on a planet with no free hydrogen or oxygen, we'd have \"noble\" sodium and calcium.",
"Although ",
"/u/cosmotravella",
" gave an ... | [
"While the other answers are very correct, I'll try and answer your question as well.",
"I'm assuming what you want to know is 'why are the elements at the bottom right of the transition metal series so much less reactive than those at the top left?'",
"This answer will be no good for a degree level course, if ... |
[
"A question on nuclear decay and the number of nuclei."
] | [
false
] | The number of nuclei of a number of atoms after a time t can be defined with the equation: N = N(0) e The half-life (T) is therefore when N = N(0)/2, and so: N(0)/2 = N(0) e ; ... ; T = ln/λ If we were to represent N(0)/2 vs time on a graph, we would get this graph: As can be witnessed, there's a horizontal asymptote of x = 0. Since the y axis represents the number of nuclei left, this means that there will always be (an ever-decreasing) radioactivity. That is all fairly simple and such, however, if that is right, that means that no matter how long you leave a sample out to decay, you will literally never run out of your sample, and furthermore, it implies that you can even never get to N = 1 because if you can't run out of your sample, you would also suddenly lose the radioactivity. AND IF the sample could ran out so that N = 0, it would mean that there won't be any radioactivity anymore in any case. This has confused me, because obviously this is physically impossible, but the math states this is so. So what is the actual scenario in real life cases? | [
"The maths is statistical, it's describing a totally perfect situation where arbitrary amounts of radioactivity are allowed, including fractions.",
"In real life, this is of course not the case. The mathematical model is a very good match when you have many radioactive nuclei because on average everything works i... | [
"Radioactive decay is modeled on a Poisson distribution. One of the assumptions of a poisson distribution is that there are a large number of \"events\" - or in other words that there are a large number of nuclei to decay. The equations don't hold exactly when you get down to very tiny decay amounts, and the resu... | [
"Right, that actually make sense considering decay is random.",
"So, lets speak hypothetically, that you put a single atom of a radioactive isotope in a perfect quantum vacuum, it would decay right? What if it were directly observed the whole time?"
] |
[
"What is the psychological mechanism that causes things like songs or food to \"get old\"?"
] | [
false
] | If I listen to a song I like a lot, after a while I get bored of it, and eventually I'll start to downright dislike it. The same thing happens to everyone with certain foods, movies, even places and people. I just wonder why something I really enjoy can turn to something I actively avoid simply through being exposed to it too much. What drives this change? | [
"While you wait for the scientists to show up, here is the Wikipedia entry on ",
"The Coolidge Effect",
":",
"In biology and psychology, the Coolidge effect is a phenomenon—seen in nearly every mammalian species in which it has been tested—whereby males (and to a lesser extent females) exhibit renewed sexual ... | [
"This is from a sociological perspective (I have a Soc. degree from UCSB). I am at work right now and don't have access to my old notes/books, so it is from memory. I do recall this very phenomena from my socialization class.",
"Habituation. These are actions we perform, or in this case things we do every day. Yo... | [
"I think you mean the law of diminishing marginal utilities, not returns. And although the law holds true, it only gives a name to what OP was asking, not an explanation. "
] |
[
"Why is there only one species of human?"
] | [
false
] | null | [
"There are a variety of reasons, but here are two: ",
"1: Due to our technology and general intellect, humans around the world have been able to live in far more similar conditions than another, equally distributed species.",
"2: We are a relatively young species . Since the migration from Africa and the genera... | [
"This is a tremendous claim to make as fact without citing supporting evidence. What about the hypothesis that humans and Neanderthals interbred, leading to the eventual genetic swamping of the Neanderthal genome?"
] | [
"Because the other species of human (Neanderthals, ",
", etc.) were eventually driven extinct by competition from ",
"."
] |
[
"What caused the super-continent Pangea to split up in the first place? Is that same force still driving the plates in their movement?"
] | [
false
] | null | [
"Just a wee piece of general mislabeling that really grinds my gears as a student of geology, There is absolutely, categorically, completely, no layer of liquid (or boiling) magma in the mantle. There is a liquid outer core, which is composed of iron and nickel, which is not magma.\nThe mantle may behave as an incr... | [
"Pretty much, and Pangea didnt even come around until pretty late in Earth's life span. There were other supercontinets and little proto continents smashing into each other and breaking apart for millions of years before Pangea. Really interesting stuff "
] | [
"Yes. One major example is the ",
"mid-Atlantic ridge",
" which started as the fault line that created South America's east coast and Africa's west. This is still active and expanding even today.",
"You might ask whether there are any current landmasses which are still together today but will likely split in ... |
[
"How would I determine how long it takes my apartment's stale air to be replaced by fresh air with all the windows open?"
] | [
false
] | Every weekend and some weekdays as well I have an argument with my wife about opening the windows and letting out all the warmth and letting in as much frigid fast flowing wind as possible. She's convinced it's necessary and it is nice to have fresh air but I at least would like not to prolong the torture if possible. What would I need to do to determine how long it takes for the complete volume of air in the apartment to be replaced by the air from outside? I'm guessing it really couldn't take that long because as we're on the third floor up and as soon as the windows are opened, very strong winds come in and blow every object in the house on to the floor and shake the bathroom mirror on it's fixtures. How do I approach this question? | [
"In scientific settings you'd seal up the house and add a tracer to the air. A tracer is inert (no reaction/adsorption), doesn't separate (no condensation/settling), and is originally present at a constant quantity (usually zero). Once you mixed the tracer in, and you were sure it was distributed evenly through out... | [
"This is probably the most scientific approach to it I could think of as well. I would just get a smoke machine, fill my apartment. Open all the windows, start a timer, and stop the timer when you feel everything's cleared out. This isn't as rigorous and accurate as ramk13's idea, but it is fairly easy to do."
] | [
"How do I approach this question?",
"The question is",
"How would I determine how long it takes my apartment's stale air to be replaced by fresh air...",
"My first knee jerk reaction is that you must define a satisfactory working definition of what is meant by this. What specification do you require? How fr... |
[
"Curvature of Earth and its effect on travel."
] | [
false
] | On a trip from India to US recently, I saw the path that my flight took, because they display it on your monitors. In image, the yellow line is the path that it actually took, but from what I understand, red should be the shortest path. So, I told this to a friend and he was like, "Well, it's the curvature of the earth that makes this the shortest path.". I was all like, "Oh OK.", but when I got around to thinking about it, I couldn't actually understand why. Could somebody explain why? OR did my friend not know what he was talking about? | [
"The shortest path between points on the surface are ",
"great circles",
". Due to the way the globe is projected on the map, they appear as curves. This is, of course, barring any other aviation considerations such as jet streams."
] | [
"As otgers have said, it's all about great circles. If you want a more tabgible answer, grab a globe and some steing and place it between India and US."
] | [
"It's because of the \"great-circle distance\"",
"Basically, the yellow arc is the shorter distance when viewed on a sphere, rather than a two-dimensional map.",
"Flat, 2-dimensional maps tend to be greatly distorted at their edges.",
"If you were to take a globe, and place one end of a string at your startin... |
[
"Do humans (or other animal species) give off ultra-violet colors similar to flowers that we can't see?"
] | [
false
] | Is that why bees circle us? Or is it merely our scent? Or is it just a warning for us to get the fuck out? | [
"Apparently, they look like they've been smeared with pitch.",
"Here's a link to two pictures",
"one is taken using a regular RGB camera, and shows a person with sunscreen applied to half his face - this is not visible, and he just looks like a regular joe.",
"the other is taken with a UV-sensitive camera, an... | [
"As a photographer who did some experimentation with Infrared imaging a while back, I can say that the world, including people, looks very different. ",
"Here",
" is a link to the wiki, which includes a portrait done under ambient UV light."
] | [
"The sun emits into the UV frequency range, and some proportion of that light is reflected off of everything that doesn't absorb the UV photons. Humans (and most animals) have ",
"melanin",
" which does absorb some amount of UV light (meaning that it would appear darker to UV sensitive eyes), but even the most ... |
[
"How does radiation cause mutations?"
] | [
false
] | null | [
"Simply put, radiation breaks the strands in your DNA. The DNA can repair itself, and it usually does this quite well. A fraction of the time though, the repair process isn't done properly. This means the DNA is now slightly modified, which can affect the next generation of cells."
] | [
"Technically the same as the other two answers currently up, different phrasing:",
"Certain types of radiation can get inside of your cells and then hit an atom with enough force to cause an electron to bounce out, which changes the charge of the atom and creates an Ion (thus the name, ionizing radiation)",
"Th... | [
"Otherwise, it probably won't do much unless it causes a cell to behave poorly, in which case the cell dies.",
"Or rarely it disables the cell's capability of committing suicide because something went wrong. Then at a later time another mutation comes along and deactivates the regulation of that cell's reproducti... |
[
"Does Hydrogen Peroxide kill bacteria?"
] | [
false
] | Hi, So I got into a debate elsewhere about whether H2O2 can actually kill Bacteria. There was also suggestion of it "promoting healing" etc. of which I am more dubious. Peroxide breaks down into Water and Oxygen free radicals, and my understanding is that this breakdown is catalysed by biological matter, and the free radicals screw up chemical structures in the cell walls. Anyone got any citations they can offer, alongside a TL:DR? Obviously I am referring to the low percentage stuff you can get in brown bottles from a pharmacist. | [
"Neutrophils and macrophages actually make their own H2O2 (really starts as superoxide ion, O2",
" --superoxide dismutase--> H2O2) to kill bacteria as part of their oxygen-dependent killing mechanism. So yes this is a pretty good approach to killing bacteria. ",
"Another enzyme, catalase, is present in our bod... | [
"That's great, thanks!"
] | [
"I think you might be mixing a few things around here. NADPH oxidase makes superoxide ion which is the first step for production of reactive oxygen intermediates (ROIs) that kill bacteria. Without this enzyme a person would develop chronic granulomatous disease. In this disease the phagocytic cells can engulf bacte... |
[
"Are there any methods of recording uncertainties without observing them?"
] | [
false
] | Quantum Mechanics has many particles and functions which are in a state of uncertainty until they are observed, where they collapse into a single state. My question is, are there any methods, theoretical or real, to record such things for future observation? For example, is it possible to freeze a quantum state in time so that it may be observed later on, and the data recorded? And as a further question, in quantum mechanics, what exactly counts as observation? Is it only human observation, or can it also be animal observation? What about mechanical? And does changing the observer create a difference in the observed state? | [
"There's a lot of questions in this post and some things you seem confused on, so I'll try to address each thing one by one. Let's start with the confusion.",
"Quantum Mechanics has many particles and functions which are in a state of uncertainty until they are observed, where they collapse into a single state.",... | [
"My understanding is more like \"use\" of the information (with \"use\" not being anthropomorphic).",
"That is to say any subsequent situation in which it matters what the state was at some point prior will cause the collapse. That would include, but theoretically isn't limited to, a scientist taking a measureme... | [
"My understanding is more like \"use\" of the information (with \"use\" not being anthropomorphic).",
"That is to say any subsequent situation in which it matters what the state was at some point prior will cause the collapse. That would include, but theoretically isn't limited to, a scientist taking a measureme... |
[
"How can gene modification work in a fully mature adult?"
] | [
false
] | I understand how we can change the DNA info in a single cell and all but how does this spread to the rest of the body? It makes sense with a zygote because the single cell will split and become all the cells in the body but how does this work with a living breathing adult organism? How would injecting a shot containing genetic info into my arm cause the cells in my feet to get the same cancer blocking (just an example) genes that go to my scalp and lungs etc? | [
"A key thing to remember is that many tissues such as the intestinal lining, various immune cells, and red blood cells regularly replicate. If you can genetically change the stem cells that then divide and differentiate, you can change those downstream cells.",
"The methods used to induce the genetic modification... | [
"Has this ever been done with humans or other large mammals?"
] | [
"Thank you. Very interesting. Hopeful and also a little scary."
] |
[
"Is it possible for an anion to exist in solution without a cation and vice versa ?"
] | [
false
] | null | [
"Yes, this is actually the basis for bioelectricity used in our nervous systemand muscles. Our cells actively seperate ions to create electric and chemical gradients that can be used to power other reactions (typically transport accros the membrane). The inside and outside of the cell are separate solutions seperat... | [
"I don't believe there is. The electric force is so strong that even if it were possible to separate the ions on a large scale your pure ions would become like a black hole for anything with the opposite charge. Plugging in the values for seperating the positive and negative ions from one mole of sodium chloride sa... | [
"Thank you for the informative reply.",
"In that case how exactly is the anion separated from the cation?",
"EDIT: what i mean by that is how could this process be replicated in a lab"
] |
[
"How is CPU or GPU usage calculated and reported? How does a piece of hardware \"know\" how much of its maximum processing capacity is being utilized?"
] | [
false
] | [deleted] | [
"Every process is given time on the CPU by the kernel. This means that you can 'ask' the kernel how much time each process gets and from that, the usage. Take a look at this code if you want to see the nitty gritty details:",
"https://github.com/hishamhm/htop"
] | [
"Game dev here - while true that this is how it works it can actually result in it being easy to misunderstand usage. For instance, one thread can be deadlocked waiting for another thread, and can report usage even though it is not conceptually busy. So knowing the difference between “actually busy” and “reported u... | [
"Any time-sharing operating system has, in its kernel, a bit of code called the ",
", whose job is to co-ordinate the different programs that want to run. (A single-core computer can only do one thing at once; it switches between tasks rapidly to give the illusion of multiple programs running simultaneously. Mult... |
[
"Do ants (and other small bugs) take fall damage?"
] | [
false
] | null | [
"Technically yes, since they are falling downwards, but their terminal velocity is not nearly high enough for any real damage to occur.",
"Plus, most bugs have strong exoskeletons or squishy bodies that can absorb impacts very well relative to their size."
] | [
"So then if we were able to scale ourselves down 1:1 to the size of an ant, would our exiting skeleton now be able to withstand a very high fall?"
] | [
"Doesn't even need to be as small as an ant. A mouse is (for our purposes) physically very similar to a really, really small human, and they can survive a fall from virtually any height."
] |
[
"Do we have a man-made satellite with a big elliptical orbit around the earth?"
] | [
false
] | And if we do what would be the purpose of this orbit? | [
"Yes! A good example of a very useful large elliptical orbit is a ",
"Molniya orbit",
". It serves the same kind of purpose that a geostationary orbit does, however it's designed so that most of its orbit is spent being directly over a much higher latitude. ",
"This is very useful for countries like Russia wh... | [
"What about in non-simple terms? What about 63.4 degrees prevent disturbance by the second zonal coefficient? What would happen if the inclination was another angle, would we see precession moving the apoapsis away from Russia or what? And what about higher order terms and tesseral coefficients, must they be acc... | [
"From that Wikipedia link for Molniya orbits:",
"\"The reason that the inclination should have the value 63.4° is that then the argument of perigee is not perturbed by the J2 term of the gravitational field of the Earth but stays at −90°.\"",
"Details?"
] |
[
"What do you catabolize first during starvation: muscle, fat, or both in equal measure?"
] | [
false
] | I'm actually a Nutrition Science graduate, so I understand the process, but we never actually covered what the latest science says about which gets catabolized first. I was wondering this while watching , where the contestants frequently starve for 21 days. It's my hunch that the body breaks down both in equal measure, but I'm not sure. EDIT: Apologies for the wording of the question (of course you use the serum glucose and stored glycogen ). What I was really getting at is at what rate muscle/fat loss happens in extended starvation. Happy to see that the answers seem to be addressing that. Thanks for reading between the lines. | [
"Finally something in ",
"r/askscience",
" where my degree can be of use (PhD in muscle biology)",
"Whenever you stop eating, your substrate preference will be about 2/3 fat and 1/3 carbohydrates. Those carbohydrates will come from stored glycogen in your liver and muscles.",
"When those glycogen stores run... | [
"Just going off of this: There was a case of a very obese man who ",
"literally starved himself for a year",
" to lose weight. Granted, the fact that his heart ",
" wasn't damaged by doing this was due to very careful monitoring by a team of qualified doctors. ",
"EDIT: The muscles of your heart need potass... | [
"Just going off of this: There was a case of a very obese man who ",
"literally starved himself for a year",
" to lose weight. Granted, the fact that his heart ",
" wasn't damaged by doing this was due to very careful monitoring by a team of qualified doctors. ",
"EDIT: The muscles of your heart need potass... |
[
"If there's no ultimate frame of reference, how do we know the Universe's age?"
] | [
false
] | Could some other civilization in a different galaxy measure CMBR and derive an age other than 13.7 billion years? | [
"The age of the universe is given as measured in the CMB frame, which is the unique frame in which the CMB appears isotropic. In all other frames, the age of the universe is strictly smaller."
] | [
"I take it you have heard of the Doppler effect, where when you travel towards the source of an EM wave, it appears more energetic, and vice versa.",
"Suppose there are two observers, one sees an isotropic CMB, ie same from every direction. The other observer is moving relative to the first observer, thus he will... | [
"Could you explain this a little more?"
] |
[
"Question about possible containment methods for Japan's Fukushima nuclear plant."
] | [
false
] | Probably stupid, but.... Is it possible to contain the Fukushima nuclear plant with a sort of temporary sheet-like cover using the coordinated efforts of helicopters and/or cranes? I realize the plant is right on the shore which would make it quite difficult as there are many obstacles, but wouldn't it work if there were some sort of a "clamp/brace wall", if you will, built just off shore in order to hold whatever would be used as a cover? Any other possibilities? What, exactly, is even being done/discussed in regards to figuring out how to contain it? | [
"They actually are doing this. They are building outer structures with new overhead cranes and a system for fuel cask transfer to the ground level. They are additionally adding more structural supports and putting in HEPA level or greater air filtering to prevent radioactive particulate from escaping. ",
"Here is... | [
"Unit 1 has already ",
"been covered",
", more pictures ",
"here",
". There is work being done to remove the debris from the upper parts of the other damaged units. If you dig into some of the roadmap documents, they have installed a higher tsunami wall, and are planning on placing barriers to reduce furthe... | [
"Hey, thanks. Even though this is an 11 day old post, I'm still interested. Do you also happen to know the current U.S. radiation exposure? I can't seem to find anything on it."
] |
[
"How do you prove the uncertainty of an observable related to an operator is zero?"
] | [
false
] | So, I'm struggling to prove this identity: ∆α=( < Q >−< Q > ) =0 for an operator Q representing an observable α. I assume it has something to do with expanding < Q > and < Q > as integrals, but I can't quite seem to get it :( | [
"Ah I see, that was much simpler than I thought. Cheers!"
] | [
"The idea is that you are operating in a basis set, where the wavefunction |F> is an eigenfunction of the operator Q with the eigenvalue a:",
"Q|F>=a|F>",
"Next, remember what <Q> represents, it can be written in bra-ket notation as <F|Q|F>. This expression reduces to ",
"<F|a|F>=a<F|F>=a, making the assumpti... | [
"Note that your claim ∆α=( < Q",
" >−< Q >",
" )",
" =0 is not generally true of any observable operator in an arbitrary state. It is only true for an eigenstate of that operator, |F> (such that Q|F> = a|F>).",
"This is clear from the uncertainty principle alone: ∆x ∆p ≥ ћ/2 , where both x and p are observ... |
[
"Can dams be built in series?"
] | [
false
] | [deleted] | [
"The amount of energy you can derive from a dam is proportional to the pressure of the water, which is determined by the height. If you have dams in series, you lose that effective difference in height. That's why dams like the Hoover Dam and Three Gorges are all massive structures - that height allows them to hold... | [
"It is actually rather common! Some examples are:",
"The Colorado River",
"The Columbia River",
"The Tennessee River",
"There's also others, such as ",
"the Upper Mississippi",
" and ",
"the Ohio",
" are also dammed, but more for navigational reasons, I believe."
] | [
"There is a curve though. Massive dams like Grand Coulee and Hoover are simply not built anymore because it is more effective to have smaller (still quite big, just not monumental) dams in sequence.",
"Three Gorges dam in China is a mega-monster. It was not built to be the most efficient, it was built to be the m... |
[
"How close could a manned spaceship get to the sun?"
] | [
false
] | The astronauts must be able to survive and return to Earth, in a ship designed specially for this mission - not just a normal one that for some reason comes into course with the sun. Also, what about an unmanned no returning probe? Could one be built that could even get to the surface before burning up or being crushed by gravity? | [
"First, things do not simply fall to the Sun. Or they do but they constantly miss the Sun. When you leave Earth, you're going about 30 km/s, 90 degrees off of the Sun. If you intend to get to the Sun, you need to cancel most of this speed somehow. So far the probe that has left Earth with the greatest speed is the ... | [
"I know and I can't answer that without taking some wild guesses. However, I have a feeling he thought that getting there was no problem at all when in fact it's probably a bigger problem than the heat shielding, at least unless you go ridiculously close to the Sun."
] | [
"There isn't really an answer to this question, because no ship like this has ever been designed. The way engineering works is, you specify design parameters, and engineers design a device that will operate within those parameters.",
"Now that we've gotten past that, a ship could certainly be designed to operate... |
[
"If I am allegic to house cats, am I also allergic to big cats (lions, tigers, pumas, etc)?"
] | [
false
] | Do all cats carry the protien that makes me unable to be around cats, or is it specific to the domestic house cat? It would sound cooler to say "I'm allegic to panthers and cheetahs" instead of "keep that little cute kitten over there away from me!" | [
"According to ",
"this",
" test of IgE and IgG4 reaction to Fel D 1 from many of the big cats - it looks like your answer is yes...you can say \"Get that Beast away from me! I am allergic to its relative Lions, Pumas & Siberian Tigers!\""
] | [
"Reddit doesn't actually display accurate upvote downvote counts as an anti spam prevention measure. More than likely no one down voted it at all."
] | [
"I wonder what 6 people think when downvoting the correct and cited answer. Maybe they are just angry you ruined their dreams of owning a \"big\" cat."
] |
[
"How does the concentration of sugar affect the fermentation in beer?"
] | [
false
] | Will more alcohol be produced with more sugar? Or less? This is for an EEI I am doing at school, thanks in advance :). | [
"Up until a point, the more sugar there is the more alcohol will be produced. Basically alcohol is a byproduct of the bacteria's respiration, so the more sugar they have to metabolise, the more alcohol they will produce."
] | [
"You are able to fine tune the result of your fermentation by adjusting the sugar levels you start with, as well as the time spent fermenting. If you start with a higher level of sugar (you measure it with a hydrometer), you are able to end with a higher alcohol content. If you stop the fermentation early, you hold... | [
"Consider posting this question in ",
"/r/Homebrewing",
" as well :)"
] |
[
"Graphene surface area."
] | [
false
] | I was reading an article on graphene supercapacitors when I came across this line The resulting graphene electrode is highly porous. A single gram of this stuff has a surface area bigger than a basketball court. It is from this article in the MIT review of technology. The electrode to which they refer is in a "coin shaped cell" so presumable its about the size of a quarter, give or take a bit. How is it possible to have such a large surface area if the coin size electrode is made up of graphene, which I understand to be a hexagonal lattice. What surface are they referring to? The surface of the sheets of graphene themselves? or the surface area of the constituent atoms? Are there as many sheets of graphene in the cell as there are quarters covering a basketball court? Thanks. | [
"When discussing porous materials surface areas, we normally speak of gas-accessible areas. This is the \"real\" surface area, that stuff can actually get to and interact with.",
"More formally, we measure the amount of gas adsorbing to surface of the sample, then back-calculate the area using the size of the gas... | [
"This is a great answer. What we do is we force a gas into the porous substance, so that it sticks to whatever it can. Each molecule of the gas is kind of like a pixel of a certain size. If we know how many pixels we can fit onto the substance, and how big each pixel is, we can work out how much surface area there ... | [
"I actually did my thesis on this exact topic. For a visual understanding, here are some electron micrographs of my electrode material:",
"http://s1359.beta.photobucket.com/user/norsoulnet2/library/Graphene",
"The above answer is 100% correct and the SA is measured by BET with N2 gas. This particular graphene... |
[
"photosynthesis equation tattoo"
] | [
false
] | so i have been thinking about getting the photosynthesis equation as a tattoo for a while now. and just saw a post of all the other awesome science tattoos. but my question is can you use E in the equation and it still be correct? (6CO2 + 6H2O + E --> 6O2 + C6H12O6) instead of writing out energy? i know its light energy but ive never seen a symbol for light. most of the equations i see use the word energy or nothing at all. but its a very important factor in the process and i want to include it just looking for the most scientifically accurate answer i can find. | [
"The correct symbol would be \"hν\"",
"h= Planck's (J.s)",
"ν= Greek letter nu = frequency in Hz",
"hv = J.sXHz = J.sX1/s = Joules = energy"
] | [
"This is correct. (to OP) Also, rather than having it as +hv in your equation, this is generally written above the --->"
] | [
"I would just put the word 'light' over your arrow.",
"Sure, not the most correct way to do it, but anyone who sees it will understand what you mean"
] |
[
"[Astronomy] How close can we get a man made probe to the sun before it becomes inoperable with today's technology?"
] | [
false
] | I understand that Helios I and II are the man made objects that have the distinction of being the closest, but I'm curious as to how close we can get with an unmanned probe using today's technology before it would begin to take enough damage that it'd be rendered inoperable. | [
"Here's",
" a good article that addresses your exact question.",
"For a spacecraft, the ability to fly safely near the sun depends entirely on its material, its design, and its fly-by trajectory.",
"Helios 2's perihelion (closest approach to the sun) was ~42 million km. The perihelion of that proposed probe ... | [
"Nice article, but all of the designs discussed were with longer term survival of the probe (much more scientifically useful from my point of view). However, OP seems to be interested in a possible destructive venture (e.g. the Soviet Венера 7-12 find more info on those in the ",
"Venus wiki",
" ). ",
"You co... | [
"Wow thanks, that was an excellent article."
] |
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