title list | over_18 list | post_content stringlengths 0 9.37k ⌀ | C1 list | C2 list | C3 list |
|---|---|---|---|---|---|
[
"If I drive to a point that has a lot of dynamic elevation change, and I then drive back to the starting point - will my gas mileage be roughly the same as if the road were completely flat?"
] | [
false
] | Especially in a truck, going up hills requires a lot more gas, yet coasting down seems to save a huge amount as well. Does the drive average to almost flat, given that you'd spend as much time coasting as you would climbing the hills? Or is one more/less efficient than the other? | [
"On a level road at constant speed, the engine must replace the energy lost due to friction with the road and air drag. The energy that must be replaced is the work done by these combined drag forces, which is the net force times the total distance traveled. ",
"On a hilly road, you must travel a greater total di... | [
"Awesome, thanks you. If you were to have a very lucky/perfect scenario - say, no braking needed, and no stops at the end of the hill, allowing you to coast for a good while, would it then be the same?"
] | [
"Not likely. If you were driving at a constant speed on the flat road you would experience constant drag (ignoring wind). If you are however coasting down a hill without braking then you're speed will increase and the drag will increase even more so as drag is proportional to the square of velocity. Think about if ... |
[
"Does the size of a (dust)-particle determine the wavelength of the light it scatters?"
] | [
false
] | null | [
"Maybe the best explanation for 'why is the sky blue' I've read."
] | [
"Yes, it does. When the particles are much smaller than the wavelength, one can use ",
"Rayleigh's model",
", which is proportional to the frequency raised to the fourth power and the diameter of particle to the sixth. On the other hand, when the particle size becomes comparable to the wavelength, one must use ... | [
"Your explanation is correct though in reference to the question it doesn't decide what wavelength it scatters; it just determines the probability of the scattering."
] |
[
"Why do some solutes become less soluble as they are heated up?"
] | [
false
] | [deleted] | [
"Inverse solubility is more common than you would think, the most common one is calcium salts in drinking water, and it's a big problem if you have a hot water heater in an area that has particularly hard water.",
"I'm sure you did a google search, and probably found a bunch of chemical engineering pages that des... | [
"This is a pretty good explanation. Also, if the OP is interested, he/she should look up UCST (upper critical solution temperature) and LCST (lower critical solution temperature). The thermodynamics of mixing is interesting stuff especially for large molecules (polymers)."
] | [
"The solubility is another way to describe the equilibrium between the solid phase and it's soluble constituents. That equilibrium is described the same relationship as all other reactions like [A][B]/[AB] = K. As defined here (and usual convention) higher solubility corresponds to a higher K. The temperature depen... |
[
"Is it possible to \"magnetize\" non-metallic objects? If I aligned the poles of a piece of plastic, could it stick to my fridge?"
] | [
false
] | Is magnetism solely a property of ferromagnetic materials, or is it possible to induce magnetism in otherwise non-magnetized objects? | [
"Ferromagnetism is a result of ",
" electrons. Something like plastic doesn't have unpaired electrons, thus it won't have a permanent magnetic moment for you to align.",
"As OanaMitrache mentioned, you can make an electromagnet with a conductor. There are other phenomena, such as paramagnetism and diamagnetism,... | [
"Yes, but in a sense, ",
". In a sense, the electrons will orient in a way that opposes the applied magnetics field, also known as Lenz's Law. This is a property of materials called diamagnetism, and EVERYTHING is diamagnetic. ",
"The problem is the diamagnetism is SUCH A SMALL EFFECT that it is usually complet... | [
"Then has the ",
"discovered magnetic polymer",
" been refuted? "
] |
[
"Does the temperature change in a can of pop when it's opened? Can you show me the proof one way or the other?"
] | [
false
] | Need help settling a bet and I'm having a hard time finding anything through Google that seems to answer this question satisfactorily. For some reason I'm convinced that opening a soda can actually causes the temperature to drop slightly, but I can't remember why I think this or why it would be true. | [
"Yes, there would be a slight temperature drop. When the can is closed, there is a lot of CO2 dissolved in the soda. When its opened, the gas will expand as it forms bubbles. This expansion is happening against the atmospheric pressure outside the can, which requires that the gas do some work. As long as the bu... | [
"If we ignore the liquid and concentrate on the gas (dissolved carbon dioxide), ",
"ideal gas law",
" states:",
"PV = NkT",
"where P = pressure, V = volume, N = number of particles, k = Boltzmann's constant and T = temperature.",
"So when you decrease the pressure by opening the can, to reach equilibrium ... | [
"Because the liquid remains at constant volume and the gas experiences a pressure drop that will drop the temperature of the gas, if the gas escapes quickly it wont have time to absorb heat from the liquid.",
"The ability of a gas to reduce (or increase) it's temperature comes from the relationship PV=nRT, Pressu... |
[
"Are any of Einstein's predictions yet unproven, and if so, which would be the most groundbreaking if proven correct?"
] | [
false
] | Over 100 years after they were predicted by General Relativity, gravitational waves were observed by LIGO last year. Are there any more of his predictions floating out there? | [
"Gravitational waves were only recently detected directly; we've had pretty good indirect evidence for many years.",
"I would nominate hidden variable theory. Einstein never really accepted quantum mechanics as a fundamental theory of the world, and said that there must be something deeper going on, something whi... | [
"Another interesting prediction from Einsteins equations are white holes. The same equations that say black holes can exist can also be reversed to show that white holes can exist. They work the opposite of black holes. Light and matter can escape from them but can't enter, they have a reverse event horizon. A ... | [
"Bell's theorem only rules out ",
" hidden variable theories. It still allows for non-local theories, such as de Broglie-Bohm pilot wave theory."
] |
[
"How do animals know which animal to fear and which to not?"
] | [
false
] | [deleted] | [
"The basic mechanism at work here is that prey species need certain fears in order to react appropriately to predators. If they don't have these fears, they die and don't get a chance to reproduce. As such, there's selective pressure on prey species to react to certain stimuli with fear--smells, shapes, sounds, etc... | [
"Interesting side note to your point on snakes: even monkeys raised in captivity (with no exposure to snakes) will react strongly to an image or model of a snake. It's just built in. (For the record, I do not recommend showing a research monkey a toy snake. They will not be a happy camper.)"
] | [
"Rottweilers started out as a herding breed so there's the human factor. Total fearlessness around cattle would have been a required trait.",
"How do they actually tell the difference? Dogs have a really good sense of smell and really good hearing but very limited vision. They can almost certainly tell that a cow... |
[
"In science, is it possible for a measured/calculated quantity to have SI units equivalent to a fundamental concept, but not actually be that? [X-Post from /r/answers]"
] | [
false
] | Note: I originally posted the question in , and someone suggested to post in . . Sorry for the mix-up, still getting the hang of reddit. Thanks! In undergraduate physics I remembered reading in a book something along the lines of "Although [XYZ] has units of [abc], it is not actually [force,momentum,etc.]" I thought th... | [
"The Hubble Constant, which measures the rate that the Universe is expanding, has units of km/s/Mpc -- which actually works out as units of inverse time. This doesn't really mean anything, as even when you invert it, the so-called \"Hubble Time' doesn't necessarily have to apply to anything real in the Universe.",
... | [
"Well, first off there are things that don't ",
" have the same units. For instance, both energy and torque have dimensions of force * distance, but one is a ",
" force * distance and one is a scalar.",
"But you can compute an arbitrary number of physical quantities with the units you want. For instance, if y... | [
"The stress tensor, a very important concept in fluid mechanics, has terms with units of pressure, but they're not actually pressures."
] |
[
"Thorium reactors"
] | [
false
] | I've heard a lot of buzz lately about Thorium reactors (like front page post). But when I read into it and asked a couple nuke-e's at my college (UCB, I'm mech-e) they said that mat-sci just wasn't there to handle the ridiculous amounts of corrosion from the chemicals handled and it would be too expensive to constantly... | [
"Materials issues are being worked around right now. Hastelloy N was made, which worked very well, and experience minimal corrosion. We can't use Hast-N, so were testing out other alloys under strict chemical control. Also, the guys at UCB aren't working on the materials side, so I don't think they have the full... | [
"So you would say it's feasible with traditional alloys? Please elaborate."
] | [
"http://www.energyfromthorium.com/pdf/ORNL-TM-5782.pdf",
"Yes"
] |
[
"I live 80 miles north of Atlanta. If there were a nuclear attack on American cities, I've always assumed that I would never be affected. Is this likely?"
] | [
false
] | null | [
"80 miles away there would be no effect from the blast itself, although radiation could still be an issue, depending on wind patterns. Radiation can travel hundreds of miles in the downwind direction."
] | [
"Now I know. Thanks."
] | [
"[deleted]"
] |
[
"How does your body handle the extra vitamin dosing in energy drinks?"
] | [
false
] | I am wondering, energy drinks advertise vitamins and other such natural ingredients. I know our bodies can only handle so much of a dose of each vitamin then expels what is not needed. Is this true or does our body try to consume it in another way? | [
"Most of the extra vitamins that are added are water soluble vitamins, such as vitamin B and vitamin C. These vitamins have no real storage areas in the body, and are simply secreted out in your urine. ",
"Have you ever noticed that after taking a multivitamin your urine is dark yellow or even green? That is all ... | [
"Yep - vitamins A, D, E, and K ('adek') are fat-soluble, and you can experience ",
"vitamin poisoning",
" if you take far too much. It's not common, and it would be pretty much impossible for most adults to get to that point taking 1-2 vitamins a day. IIRC there are some rare diseases, mostly congenital, that... | [
"It depends on the vitamin. You can overdose on some fat soluble vitamins. "
] |
[
"what make thing see though?"
] | [
false
] | glass,crystals, some gems. but why are they transparent? are the atom just lined up right or something | [
"Quoting Griffiths' footnote on his Introduction to Electrodynamics book with some amendments ",
"As the electromagnetic wave passes through, the fields busily polarise and magnetise all the molecules, and the resulting (oscillating) dipoles create their own electric and magnetic fields. These combine with the or... | [
"The homogeneity is a property of the material. In this case it means that the electric permittivity and magnetic permeability are constant throughout the medium.",
"If you have a material where the density, or structure, or some other irregularity varies with position then the permittivity and permeability might... | [
"So when we say \"homogeneous\", does that only apply as far as the wavelength of light in question? So it's only a good approximation if the light wavelength is wider than the average irregularity?"
] |
[
"When using f=ma for a punch, what is inputted for mass?"
] | [
false
] | Is it the mass of the arm? Or all the muscles involved in a punch? How does this work if someone is using a blunt weapon? | [
"A punch is fundamentally a collision. For collisions, it is more useful to view them in the context of conservation of energy and conservation of momentum than from a force perspective. A punch before the collision has kinetic and rotational energy. In the case of a hook, we could consider the torso and arm a f... | [
"This is not quite right. The 'm' in 'F=ma' is the mass of the point particle (or something that we can treat as a point particle) ",
" by the force 'F'. You do not have to consider the type of punch at all to get 'm'!"
] | [
"You can definitely apply F=ma to every choice of system. However the answer you get when you solve the differential equation for 'a' will ",
" give you the dynamics of the center of mass of that system ",
". Since the equation only gives the dynamics of that particular point, F=ma really is a point particle eq... |
[
"Mechanical-potential energy mismatch! Please discuss what I am misinterpreting."
] | [
false
] | I am analyzing the gravitational potential of a water droplet resting on a surface and comparing it to the total surface energy of the water. My hypothesis is that the total surface energy of the water, which causes the mass to sit above the 0-height position, will be equal to the (mass)x(gravity)x(centroid of mass), w... | [
"Understood thanks. I didn't consider that there may be an initial height."
] | [
"Understood thanks. I didn't consider that there may be an initial height."
] | [
"You may find ",
"http://en.wikipedia.org/wiki/Contact_angle",
" to be of interest."
] |
[
"How is specific information (e.g. Speaker configuration) transmitted via. radio waves?"
] | [
false
] | Yesterday I was listening to the radio in my car and heard an ad which was a conversation between two people. Instead of the sound playing equally across both speakers, the male voice was in the left speaker and the female voice in the right. How is that kind of information transmitted via. radio? I can't stop ponderi... | [
"Essentially, the radio transmission contains two pieces of information: the sum of the left+right audio streams, and a sideband channel producing difference information (left - right). The stereo system uses the second channel to modify the audio being transmitted to the left/right speakers.",
"If you're using ... | [
"This is correct.",
"The clever thing about doing it that way for analog FM radio (as opposed to separate left and right channels), is that even if you don't have enough signal to receive the stereo signal, you can pick up the primary (L+R sum) information and still listen to the mono audio signal."
] | [
"The following ",
" how it happens, but it's a way for you to imagine how it could be made a reality. The purpose is to make your imagination-tool more able.",
"Imagine that there's a radio sender which just sends energy to the receiver. The receiver can detect if there's radio energy. (By the way, radio waves ... |
[
"Is Laser Toner (specifically yellow) classified as a liquid or solid?"
] | [
false
] | Second part what properties are looked for, for this classification? | [
"Yes, it is a solid because it is a powder. The powder is made up of carbon and polymers, so it's kind of like a wax or plastic powder. (This explains why heating it makes the particles bond to each other and then to the paper. It's just like melting wax or plastic and fusing it a piece of paper.)",
"Each particl... | [
"Toner is a powder, made up of mostly carbon. Laserjet printers work by placing a negative electric charge on the paper, which then attracts positively charged toner in such a way that the powder will form the desired image. The paper is then heated, fusing the powder permanently to the paper.",
"(Inkjet printers... | [
"Thank you very much."
] |
[
"Why do we use \"baby talk?\" Have there been studies conducted proving that babies and pets are more responsive to \"baby talk?\""
] | [
false
] | null | [
"So, \"baby talk\" or motherese, is a really well studied area in language development. There are a lot of negative connotations with \"baby talk\", with people thinking it's so dumbed down that it must hurt babies' understanding. There always seem to be anecdotal stories about how somebody's aunt talks to their 12... | [
"There have actually been multiple studies that show that absent mindedly chatting with your baby while working actually promotes more brain development than \"baby talk.\" I'm on mobile but I'll source when I get to a computer if no one else does it by that time. "
] | [
"I had an anthropology teacher several years back tell me that the idea behind baby talk is really just to slow things down so that children can even differentiate the sounds in the first place. Saying \"goo-goo-gaa-gaa\" within a second doesn't do much, but when said slowly had a huge effect on mimicking behavior.... |
[
"How do scientists know that people evolved the ability to digest animal milk recently?"
] | [
false
] | I've heard that the ability to digest animal milk was evolved recently in human history, and earlier humans couldn't digest it. I'm curious about how we know this? Given we only have fossils of earlier humans and no remains of their organs, how do we know that they couldn't digest milk? | [
"Lactase persistence is the \"official\" title given to our ability to continually produce lactase (the enzyme responsible for the breakdown of lactose), and this persistence appears to be unique to humans. Right off the bat, this suggests that our long ago ancestors did not have this trait, as no other mammalian s... | [
"Genetic mutations occur at a relatively predictable rate. By comparing the individual DNA sequences of lactose tolerant and lactose intolerant individuals, the minimum number of mutations required to go from one to the other can be estimated, and converted into a measure of time. ",
"Sources:\n",
"http://www.n... | [
"See (Bersaglieri et al. Am J Hum Genet 74:1111-1120, 2004) for one of the first papers to come up with the 5k-10k ya figure.",
"It's just math. Population-level genetic events like this are analyzed with statistics that detect how \"coalesced\" (or similar) a population is, how frequent the allele is across a fe... |
[
"Is it possible to harvest wood from trees without killing them?"
] | [
false
] | Is it possible to harvest wood from trees without killing them and destroying a forest? I feel like if logging companies could harvest trees without destroying whole forest or simply still growing trees. | [
"More useful is to think of the forest as the organism to be protected. Trees have a relatively short lifespan in comparison, and removing them selectively can lead to long - term increase in the health of the forest. ",
"http://www.tandfonline.com/doi/abs/10.1080/02827581.2014.938110#/doi/abs/10.1080/02827581.... | [
"Coppicing used to be very common in the UK to make charcoal for heating. Not sure to what extent the practice is still common. "
] | [
"Coppicing used to be very common in the UK to make charcoal for heating. Not sure to what extent the practice is still common. "
] |
[
"exercise increases growth hormone in the blood stream. If this is true, does that mean people who exercised more often in their formative years are taller?"
] | [
false
] | I remember reading growth hormone production increases after exercise. Not sure if this influences anything other than recovery I guess. But do kids/teens who exercise during periods of growth end up taller than kids/teens who do not? | [
"I found this summary. ",
"https://academic.oup.com/ajcn/article/72/2/521S/4729572",
"",
"It didn't talk about HGH, but it did summarize a great deal of studies that specifically look at height compared to physical activity during puberty. For women it appears that extreme exercise such as gymnastics makes y... | [
"while wrestlers (known for extreme dieting) are generally shorter than average",
"What about bias? Highschool wrestling coaches seem to favor shorter wrestlers since they excel in the area. Just as football coaches favor stride/height and speed. This could then become a \"thing\" in the family and the love of th... | [
"They talk about that as a source of bias in the summary, but there is evidence that begins to discount it. Wrestlers during the season have lower mass growth rates, but during off-season they typically jump to the top 99% in mass growth. It wasn't clear if this extrapolates to height growth as well, but there is a... |
[
"Broken contrail in the sky, engine flameout or...?"
] | [
false
] | Sorry in advance for the poor quality, I snapped while driving. I've often seen jet contrails and they've almost always shared certain characteristics. Usually they're in a more or less straight line, and they're usually consistent. This one, on the other hand, shows the plane having made a rather abrupt turn, and seem... | [
"The condensation trails appear because the exhaust from the plane causes water droplets to form in the moist upper atmosphere. The term for this is nucleation. The exhaust gives something for the water to glom onto. ",
"The moisture in the atmosphere is not constant with altitude. The plane of constant moisture... | [
"Thanks!"
] | [
"dude, you must have been really bored. "
] |
[
"Is there any historic evidence that the residence of a scientist was ever overrun by the iconic \"Angry Mob\"? Like the one we see in the Frankenstein movies and others of its genre? Or is Mary Shelley solely responsible for that imagery?"
] | [
false
] | We see the "Angry Mob" in just about every genre of movie or television program. Does it perhaps hark back to the witch hunts of the late Middle Ages? | [
"Hypatia of Alexandria",
" was a mathematician and was murdered by a mob."
] | [
"Angry mobs you say? Over running homes of scientist? ",
"Only event close to this I can remember is the Catholic Church's dealing with Galileo.",
"I guess if religious leaders of the past wanted to whip people up into a riot over science it could have easily happened. "
] | [
"This doesn't have to do with the science of your question (or history, I suppose), but in the original Frankenstein novel written by Mary Shelley, there is no angry mob that overruns a scientist's house, or that of the monster. That was probably more exciting for a movie."
] |
[
"Do any other species have pets like humans do?"
] | [
false
] | null | [
"Here is a video of Saudi Arabian Baboons kidnapping puppies and raising them.",
" Although the kidnappings look rather rough, the dogs are assimilated into the family groups almost 100%."
] | [
"The closest thing to other species having pets is ants 'farming' aphids. Somewhat similar to us farming cows for milk (they dont eat the aphids, just the honeydew which the aphids secrete). The aphids in return recieve protection and are herded to optimal 'pastures'.",
"http://en.wikipedia.org/wiki/Aphid#Ant_mut... | [
"The main reason these baboons capture puppies at a young age is so that they can raise them as one of their own, essentially raising another family member. The family groups of baboons at these garbage dumps are extremely territorial, as food is restricted to a relatively small area. The dogs offer protection from... |
[
"What happens if we tried to add another proton to the last element on the periodic table? (Currently called Ununoctium.)"
] | [
false
] | That may not be exactly how you form elements but what happens if you were to try and make it? Would it be too massive to form an atom? Can there ever be more to the periodic table or have we already completed it? | [
"No, if it were possible, you'd just get ununnonium and it'd decay and you'd be left with its fission products.",
"What you appear to be asking is why the table ends where it does. The reason why it does is simply because Uuo is the element with the greatest number of protons that has been discovered. ",
"The I... | [
"I don't think the answer provided here is a good one (sorry computerdl) but stating that there are no more elements is simply wrong.",
"from a theoretical standpoint there is an unlimited number of elements (as you can always just 1 up the previous one).",
"just because element number 119 hasn't been created y... | [
"Also, a history of the periodic table."
] |
[
"I'm a little stumped about an aspect of natural selection..."
] | [
false
] | Natural selection shows that random genetic changes organisms get can benefit or harm their chance of living long enough to reproduce and continue to pass that gene on. I have a decent understanding of how this works in terms of a bird having a slightly larger beak or something simple like that, but what about things l... | [
"It occurs gradually. The ones that are just a little better at hiding have a slightly better chance at reproducing. And so they do. If a slightly more seaweed look helps you survive, you have more babies than your smoother breathren.",
"This example is how evolution was explained to me in grade school",
"http:... | [
"It's the same pattern of incremental changes. Say the ancestor of that seahorse was brown, like most seahorses. There is going to be some variation within the population of that seahorse species, but those that stand out against the red coral are going to get eaten while the more reddish-brown ones will be safe... | [
"It seems like there's some sort of sharing of genes between the organism and the plants they live on/near.",
"No, there isn't. You're mistake is assuming the process happens in one step or that several advantages happened at the same time.",
"It can't be that a random genetic mutation just happened to match th... |
[
"Why are all digital watches not as accurate as an atomic clock? Can they not be programmed with that level of accuracy?"
] | [
false
] | null | [
"Digital watches usually keep time with a crystal oscillator, which often is quite literally a small quartz tuning fork that's been laser trimmed (or otherwise manufactured) to have a precise resonant frequency; let's say it's 32,768 Hz (because that's often what manufacturers choose). Quartz is piezoelectric, mean... | [
"You provide a good and complete explanation. I'd add that the mechanism for an atomic clock is also too large to sit on a wrist whereas a crystal can be made very tiny.",
"I have a watch (a Citizen) which adjusts itself to the atomic clock reference signal every evening. Because crystal drift is generally less t... | [
"Speaking of cesium oscillator size, ",
"I am reminded of this.",
"It's not just the size either; it's also the power. Rubidium oscillators (another type of atomic oscillator) have been getting smaller and smaller. The smallest ones are smaller than 3.5\" hard drives for desktop computers. ",
"Case-in-poin... |
[
"How can I remove the copper coating from a penny without harming the zinc?"
] | [
false
] | My friend didn't know that pennies only have a copper coating, and I'd like to show him the zinc inside; is there something I can soak the penny in to erode the copper (but not the zinc) so I would have a penny that looks like ? Thanks. | [
"If you don't care about the surface details, you can just grab a dremel (or something similar) and grind off your surface. Or to be fancy, a google search brought up this reaction:\n",
"http://www.youtube.com/watch?v=jRiBYMv6Tz4"
] | [
"That YouTube link has the answer for which the OP is looking."
] | [
"No, Gray did it using cyanide and several other nasty chemicals. See ",
"here",
"."
] |
[
"How do we know the \"real\" colour of a star with the doppler shift in effect?"
] | [
false
] | So, I read somewhere that we look at which wavelenghts of light are absorbed and deduce the atoms in a stars atosphere, but how do we know which ones are absorbed? Also, that some scientist figured that other galaxies are getting further from us because of redshift. How did he know their true colour in the first place? | [
"When a photon passes through a cloud of gasses, it will occasionally be absorbed by an electron. This will \"bump\" the electron up to a different orbital, and each possible movement requires a fixed amount of energy, as a result, it can only be achieved by a precise wavelength of light. When you look at the light... | [
"Thanks a lot! I was worried that I couldn't word my question well, but that explains exactly what I had in mind.",
"Bonus question, where does the heat of a star come into effect. If the colder ones are red and hotter ones are blue-white, do the atoms in their atmospheres affect their heat?"
] | [
"The overall apparent color of the star comes from black-body radiation (ignoring red/blue shifting and other external phenomena). Objects emitting light because of heat (like a star) emit a wide range of frequencies of light, but their peak emission frequency is dependent on their temperature. Their temperature is... |
[
"\"In general relativity, the effects of gravitation are ascribed to spacetime curvature instead of a force.\" Why do we need a force-mediating graviton if gravity is not a force?"
] | [
false
] | ...is this really the case? I've read too much Wikipedia today and got all confused, I guess. | [
"There are two things to bear in mind here: what does it mean, mathematically, for spacetime to have curvature, and what does it mean (again mathematically) for a force to be mediated by a particle?",
"The curvature of spacetime is described by a matrix called the ",
" which has different values at each point i... | [
"A theory of quantum gravity ;)."
] | [
"No, a working theory of quantum gravity doesn't have to converge at high energies. That would be nice but it isn't necessary.",
"EDIT: Maybe I should clarify.",
"Looking for the patch that clears this incongruity up is a big part of what is sometimes called the search for the Grand Unification Theory.",
"Thi... |
[
"Mars masses 1/10 of Earth. Why is gravity 38/100ths of Earth's instead of 1/10th?"
] | [
false
] | null | [
"They have different radii."
] | [
"So the surface gravity of a planet depends on its mass and its radius."
] | [
"So the surface gravity of a planet depends on its mass and its radius."
] |
[
"What's it called when someone says something to you and you don't hear it at first but then your brain plays it back to you?"
] | [
false
] | I thought it was called a phonic loop but I can't seem to get any results for that on google | [
"Echoic memory, the auditory version of sensory memory, refers to the phenomenon in which there is a brief mental echo that continues to sound after an auditory stimulus has been heard. I know that this isn't actually a 'process'; however, I feel that it best accounts for the initially passive experience that you a... | [
"Condition yourself so that your immediate reaction is to pause and throw a look of contemplation while you wait for it to repeat in your head.",
"It will also build up suspense and might enhance the conversation in some cases."
] | [
"all this after you've asked them to repeat themselves of course..."
] |
[
"Thermally generated reverse current and the second law of thermodynamics."
] | [
false
] | In the last lecture of my solid state physics class, my professor mentioned that there will be a small "thermally generated reverse current" in a P-N junction because a small number of electron-hole pairs are steadily created in the depletion region by thermal energy. These flow in the junction field. This current is... | [
"Yeah, your definition of entropy is at best too vague. Also, the current stops after a short while, so you can't get free current.",
"You're talking about a diode, I believe. The current is set up because there are positive charge carriers on one side and negative carriers on the other. In addition, both the P a... | [
"Thanks for the reply, corvidae. But, the current that I'm measuring doesn't stop, I can keep measuring it as long as I leave the detector connected. ",
"In the text books that I'm looking at, the equation describing the current in a pn junction is:",
"I = I0 (exp(eV/kT -1)",
"(sorry, it would be nice if Re... | [
"Phenomenon-wise, it seems like the electron-hole pair generated by thermal excitation is equivalent to the pair generated by the photoelectric effect. So if we completely ignore the thermodynamics of that process, we can focus on the thermodynamics of thermal excitation.",
"The beauty of entropy is that it reall... |
[
"What variables are at work to cause these different colours?"
] | [
false
] | I took this during some heavy rain fall last night. Why do some drops appear red and others blue or green etc? Is it the size of the drop? The distance from the flash/camera? All of the above? | [
"Was the flash the only source of light?"
] | [
"Yes, just the flash.",
"0.005 sec (1/200)",
"f/4.0",
"3200iso",
"-2 EV",
"lens EF35-70mm f/3.5-4.5"
] | [
"Can you describe the physical arrangement for taking the picture? Were you inside takinig the picture through a window with raindrops on it, or were you outside taking pictures of the rain directly?"
] |
[
"I aim a laser beam at a mirror and reflect it back to me. Is there a point in time when the velocity of the beam of light is zero? A point (maybe only in theory) when the beam has struck the mirror but has not yet been reflected back?"
] | [
false
] | In other words, does the velocity of the beam of light go from , to zero, to ; or does it remain at throughout the process of reflection? I honestly don't know if this is a stupid question or not. If it is a stupid question, I apologize. | [
"Really interesting question, and definitely not stupid! I can think of two answers.",
"First answer: In a ",
"ray model of light",
", the velocity at the point in time of reflection doesn't exist. The function of position as a function of time of a beam element is not differentiable at that point, so there i... | [
"In vacuum the speed of the wave is c, the speed of light, and the reflected wave will travel at this speed. Any electromagnetic disturbance will travel at this speed in vacuum. ",
"However, near the surface of the reflector, there are two electromagnetic waves counter-propagating with the same velocity c. If the... | [
"You could argue it's not \"the same\" wave that came in and out of the mirror, but that might or might not be a useful way of thinking about it. There is only one electromagnetic field, and it has waves -- where a wave stops and starts and what counts as \"one\" wave or \"multiple\" waves is blurry, because of the... |
[
"How is superposition possible if gravity exists?"
] | [
false
] | Sorry, not entirely sure how to word this, but if some particle is in quantum superposition, wouldn't gravity immediately make it collapse into one position? Or am I misunderstanding something? My knowledge of science is very limited, but I look forward to any answers you may have. Thanks! | [
"This is actually a pretty deep question and honestly one that isn't actually solved. In standard quantum mechanics, the other forces like electromagnetism are so strong compared to gravity (conversely you can say the masses of the particles are so tiny) that we generally ignore gravity because we get essentially t... | [
"The answer isn't thoroughly known, but no matter what the ultimate answer is going to be, we'll have some state which includes its superposition WITH gravity. I.E. We have a coulomb potential that binds an electron to a hydrogen atom. We'll find that that quantum gravity correction will just be a state that includ... | [
"If the particles are electrically charged, the photons don't immediately make it collapse into one position because they just become entangled with the particles. However, gravity isn't the same as electromagnetism. Gravity is a fictitious force. It's just warped space time. How that works with quantum physics is ... |
[
"Does playing sports when you are sick with a cold prolong or illness?"
] | [
false
] | Edit: title should read "prolong illness". Basically I always play hockey when I'm moderately sick, and I've always wondered if it (1) made the illness worse or (2) prolonged the illness? I've had people who seem to know what they are talking about claim it both ways. So med students and doctors, let me know. | [
"Thanks for the information. This is good to know but I wonder if it applies when you already have a cold as well. That's really what I'm trying to answer."
] | [
"There's been a few papers using mice to look at this question and the best evidence seems to suggests a moderate workout is the best option. There's a good ",
"NY Times article",
" on the relevant research:"
] | [
"Hi. I did a (quick) search for information on this topic/find sources. Also, I have education in exercise physiology and medicine. Firstly you should define what you mean when you say \"sick/illness\". The common medical term for a cold/flu would be an upper respiratory tract infections (URTI). The effects of exer... |
[
"Is it possible for a pathogen to gain a mutation that alters its mutation rate?"
] | [
false
] | If so, what's the mechanism? | [
"Yes. There are multiple mechanisms for mutagenesis but each one is typically an error in the way DNA is supposed to be copied. The most straightforward example is mispairing mutations that occur during DNA replication. During normal replication the two complimentary strands of DNA are unwound, and each strand serv... | [
"A typical good polymerase makes a mistake in ~1e-10 base pair additions. Considering that the human genome for example contains 4e9 base pairs, you still get roughly one mutation at every cell division.",
"Should be 1e10, then?"
] | [
"yes, edited to correct. mutation rates are typically reported as # of mutations per number of bases copied, hence 1e-10"
] |
[
"What would the visual experience of flying through a gas giants atmosphere be like? Would it be opaque constantly? Like flying through a cloud? Would you be able to see for a distance?"
] | [
false
] | Of course this is assuming physically surviving the experience isn't an issue. | [
"I am not an astronomer but I can give it a shot. Gas giants are thought to be built in \"layers\" of gases, with the least dense on top and the more dense lower down. So, it is possible you may hit a layer with a translucent gas, which would allow to see around for miles and miles. Of course, as you kept going dow... | [
"Opacity can vary. It is penetrable by light in terms of different amounts of 'cloudiness'. I imagine some layers of the gas giants to look like your in a somewhat thick fog with maybe a different hue to it."
] | [
"I wrote that based on this:",
"o·paque (-pk)\nadj.\n1.\na. Impenetrable by light; neither transparent nor translucent."
] |
[
"Does the body process nutrition differently if you eat over the course of the day rather than at three meals?"
] | [
false
] | null | [
"Here's some of the more recent literature: ",
"http://www.jissn.com/content/8/1/4",
"The TL;DR version is: ",
"Yes there are subtle differences between different meal frequencies, however it won't fundamentally change your energy expenditure and won't have significant impact on your weight. However, higher m... | [
"This is a reminder that anecdotes (e.g., \"I do this\" or \"this is how my wife eats\") is not allowed in ",
"/r/askscience",
"."
] | [
"From the link:",
"Increasing meal frequency appears to help decrease hunger and improve appetite control."
] |
[
"Two unrelated questions on gravity and temperature."
] | [
false
] | Firstly, at least classically the electric field is very similar to the gravitational field, they both have sources of point masses/charges, similar governing laws coloumb/newtons laws and gauss's laws. But one of the glaring differences is the fact when the source is moving for the electric field, a new field comes in... | [
"That's a very interesting question that I have never thought about before. I believe there should indeed be a gravito-magnetic force, because the argument for why the Lorenz force must exist by switching frames of reference and observing Lorentz contraction on the line charge still holds. So you must have some sor... | [
"About point 1: I always thought that ",
"gravitational waves",
" were predicted because you would get them from a lorentz invariate theory of gravity.",
"About point 2: The concept of a temperature makes only sense for systems in equilibrium. The reason that you can nevertheless give a temperature field for ... | [
"I always thought that gravitational waves were predicted because you would get them from a lorentz invariate theory of gravity.",
"That's new to me. As far as I know, they were predicted because they form a solution of the linearized Einstein equations in vacuum."
] |
[
"How common were dinosaurs?"
] | [
false
] | It sounds dumb but hear me out. In movies, we always see dinosaurs in a mass quantity, squished together and nearly on top of each other. But if we were to go back right now, how often would you see dinosaurs? What would be the density of dinosaur life? What modern day animal sightings could you compare dinosaurs with?... | [
"The basic functions of life hasn't changed from prehistoric eras to today. Things need calories, water, oxygen (generally) to live. They need to live long enough to procreate. Species that are not efficient at procreation die. There was a \"food web\" with a hierarchy. Lots and lots of smaller critters (predators ... | [
"So that means that there likely were areas that had massive amalgamations of various herds of different species, kind of like we see in some movies or documentaries? I'm thinking of the giant herds of zebra, water buffalo, antelope and other herbivores with predators circling the outside looking in... Just the din... | [
"Likely. There's still a lot of debate in this department. We've found evidence of herding behavior, and found collections of nests, that seem to imply group rearing.",
"But it seems likely that, especially herbivorous dinosaurs, traveled in herds.",
"That said, it's not like there's a ton of evidence in this d... |
[
"Why is the term \"law\" used in physics, but in every other field \"theory\" is the most definitive term that is used?"
] | [
false
] | null | [
"Laws are used to describe specific relationships in data. Hooke's law describes the relationship of the amount a spring is compressed is linearly proportional to the force pressing on the spring. Snell's law tells us that the index of refraction times the sin of the angle incident to the surface is equal on both s... | [
"No no no. No no no no.",
"There is no such thing as a \"law,\" even in physics.",
"Pretty much everything which is called a \"law\" in physics a) dates back to the 19",
" century and b) is broken under certain conditions. It's an archaic misuse of language, not something which signifies anything meaningful a... | [
"Yes yes yes. Yes yes yes yes. This.",
"Except for some such as the conservation laws of energy, momentum, and angular momentum. I'll allow you the point that nothing can be ",
" proven based on observations, but some laws describe observations so well and so ",
" that they may as well be the binding word of ... |
[
"What are the effects of being close to a Neutron Star/Pulsar?"
] | [
false
] | I know they probably can kill you. I just want to know the damage cause by them. To humans and machinery like spacecraft. Let’s use the Crab Pulsar as an example. What damage would the Crab Pulsar’s magnetic field do to electronics? What are the effects of being in a stable orbit around a the Crab Pulsar? What are the ... | [
"There's a lot of stuff going on here, some of which I've never really thought about, so I'm going to put a few thoughts out there. I'm happy to clarify on the math in various spots.",
"We always like to say as a fun fact that if a ",
"magnetar came within half the distance to the Moon",
" it would wipe all c... | [
"If you stood up in such a spaceship, the tidal force between your head and toes would be several million Newton. You would be a very thin red paste on the wall of your spaceship, assuming it was made of some exotic material that could withstand the immense stresses."
] | [
"Thank you for being the first, and probably only, person to provide an answer for my post. ",
"By stable orbit, I meant an orbit similar to the Earth and Sol. A near circular orbit. ",
"Let’s say for instance, a spacecraft orbits at an average of 120 km from the Crab Pulsar in an orbital plane in line with the... |
[
"What are the negative effects on the body due to the \"flight-or-fight\" response?"
] | [
false
] | [deleted] | [
"Deceased bloodflow to your gi tract and skin. Inability to maintain an erection. You may also poop and/or pee your pants."
] | [
"Increased activation of the sympathetic nervous system will raise stress hormones called glucocorticoids. Increased levels of glucocordicoids over long periods of time have been shown to cause actual brain damage in the hippocampus, the part of your brain responsible for memory and learning. The size of the hippoc... | [
"Those are long-term problems associated with repeated arousal. One stressful response isn't bad for you."
] |
[
"Can a flammable gas ignite merely by increasing its temperature (without a flame)?"
] | [
false
] | Let's say we have a room full of flammable gas (such as natural gas). If we heat up the room gradually, like an oven, would it suddenly ignite at some level of temperature. Or, is ignition a chemical process caused by the burning flame. | [
"Short answer Yes. If you look up a MSDS for solvents, in particular, you will find they have an auto ignition temperature. If you heated the solvent to that temperature, in air, it would ignite w/o an external flame source (presuming it didn't ignite already).",
"Who does these experiments? Guys without eyebrows... | [
"You can simply look up \"how a Diesel engine works.\" It's entirely based on compression raising temperature to ignition, rather than introducing a spark. Speaking of which, if a mechanic tells you to replace the spark plugs on your diesel, the mechanic is trying to scam you."
] | [
"Diesels do actually have a sort of spark plug, except it's a ",
"glow plug",
". It's not there to provide combustion once it's running, but rather to ",
" the engine running."
] |
[
"Before mining happened on earth, which natural resources would be visible from the surface?"
] | [
false
] | I imagine the easiest bits were mined first. Would there have been mountains literally glistening with gold and diamonds just 10,000 years ago? | [
"The answer will really depend on time, and on what you mean by « visible from the surface” ",
"Why time? Because the definition of what is or isn’t a resource changes over time, with technological change and the interplay of offer & demand. 500 000 years ago, Flint and Ocher were pretty hot commodities. These da... | [
"And here I was imagining actual veins of gold in prehistoric rock faces. ",
"Well, I'm not saying it ",
" happens, but it is a very rare occurrence. In several years of prospecting in gold districts in the Canadian Shield, I may have found one of two native gold occurences at the very most. And flecks at that.... | [
"to add onto the great explanation by ",
"/u/Gargatua13013",
" solid veins or chunks of metal are occasionally viewable from the surface, like in his example of the copper in the Keweenaw peninsula. I have seen parts of that area where chunks of copper were pulled from rock by Natives way back when, but you are... |
[
"Is there any real science suggesting that the Moon has any affect on human behavior?"
] | [
false
] | It doesn't seem like it would be the most unusual thing considering the affect the Moon's gravity has on the ocean and the fact that humans are largely water-based. But, it also seems pretty out there... | [
"Of course. We send probes to it and even went there six times. That's affecting human behaviour ;)"
] | [
"The moon affects the ocean because of the distances from the Moon to both sides of the Earth. Since the difference between these distances is relatively big (in relation to the distance from the Moon to the Earth), the difference in the forces due to gravity on either side of the Earth is big enough to makes waves... | [
"The gravitational force from the Moon acting on something on Earth is about 3.3 × 10",
" ms",
" × ",
", where ",
" is the mass of the object. This is about ",
" of the gravitational force from the Earth. So I'd say it's negligible."
] |
[
"Does the speed that we are traveling through space effect our perception of time?"
] | [
false
] | null | [
"No. Time passes at the same rate for you, always."
] | [
"So, then it's a perspective thing?"
] | [
"No. Elapsed times between the same two events can be different depending on the path taken (c.f., twin paradox). But 1 second feels the same to you no matter what."
] |
[
"What is this frying-pan sorcery?"
] | [
false
] | So when I heat up oil in my non-stick pan and add seasonings (ground dried garlic,garlic salt, pepper, sage, and I believe thyme), this honeycomb pattern starts to form. I've noticed it with a number different seasoning combos, most of them similar to the one described above. I haven't noticed if it doesn't occur in ce... | [
"These would appear to me to be convection cell edges - you strongly heat the bottom layer of a uniform fluid and convection has to take place to transfer heat, as the hot buoyant fluid will rise. In a low aspect ratio layer (i.e. much wider/longer than it is thick) the convection breaks up into many discrete cells... | [
"Why hexagonal? It makes intuitive sense because hex can tessellate well (and lots of lattice structures are hex tiles) but is there a particular reason its hex and not triangular tessellation instead?"
] | [
"tl;dr\nhot oil is rising up and pushing the seasoning to the side, forming this pattern."
] |
[
"Can we count/quantize photons of low/ultra low frequency EM waves?"
] | [
false
] | And how do the properties of a high frequency photon differ from those of a low frequency photon? | [
"The only thing that makes two photons different is their frequencies. All photons of the same frequency are identical.",
"Now, if you want to change the number of photons you're seeing at any given time, you don't change the ",
" of the electromagnetic radiation, you change the ",
". It is possible to turn... | [
"I had forgotten about radio telescopes. Do they really just use CCDs for detection? With lower energy photons, it must become more difficult to design a detector responsive enough to sense the photons. Do you know whereabouts the lowest frequency we can detect is? "
] | [
"IANA radio astronomer, so I don't know a whole lot about it. I know that optical and near optical (UV, IR) telescopes use CCDs similar, but much bigger and much more sensitive, to the ones in digital cameras. I can also tell you that the issue with observing very low frequency sources is not that the sources are... |
[
"Females complete oocytogenesis before birth while males undergo full spermatogenesis throughout life. Why? (benefits / reasons?)"
] | [
false
] | I haven't been able to find much in terms of an explanation for why this might be the case. Why would the process through which we create haploid cells diverge so significantly? Is there a benefit for males producing sperm essentially ready-to-order while females let their mature-eggs-to-be sit around for 14 or so year... | [
"Evolutionary biology is not my area of expertise, but three things came to mind.",
" EDIT: upon further consideration, the age of childbearing has little to do with the question.",
"The second is mitochondrial inheritance. We know that both maternal and paternal age are associated with birth defects. The cri... | [
"OK, I'm going to work your brain here. You have some good ideas, now I want you to explain them a little more because I feel like I'm missing something and might learn something from this. I don't intend for any of this to sound negative, so forgive me if it does:",
"Your first thing doesn't make much sense to m... | [
"I'd say because females are capable of storing the eggs in halted mitosis where as the males would have to store a LOT of sperm to last them their entire life. ",
"Also, the deterioration of females oocytes (they'll never use them all, by the by) isn't as rapid as that of spermatozoa. There's already millions ... |
[
"What is the difference between Convective Condensation Level and Level of Free Convection?"
] | [
false
] | What is the difference between Convective Condensation Level and Level of Free Convection? Are they the same, just different titles? | [
"CCL is the level to which a parcel of air, raised from the ground due to heating from below to its convective temperature (and then cooled adiabatically as it rises) would reach the dewpoint (also changing with altitude). This is the height that you would find the base of convective clouds.",
"LFC is the level a... | [
"I have another question, The only difference between the lifted condensation level and CCL is how the air was lifted?",
"Thanks for answering too :)"
] | [
"Basically that. CCL is what is relevant for calculating the base of summertime convective / thunderstorm cloud bases. LCL is relevant for calculating the base of cloud lifted in other ways.",
"I would emphasize that the CCL is based on air that has been ",
" until it starts to rise on its own. I think that is ... |
[
"What are the geometric patterns at the beginning of this simulation?"
] | [
false
] | null | [
"It actually looks like something called grid imprinting, which you get when you try to simulate spherical things on square lattices, and not something physical.",
"All the information I can find about grid imprinting is extremely technical, unfortunately: ",
"http://www.newton.ac.uk/preprints/NI12086.pdf"
] | [
"No, I'm with Iorg here. They look exactly like the kind of grid or boundary effects you might expect when performing a simulation on a square lattice. The fact they are isolated to the early part of the simulation (i.e. where smoothing algorithms are least effective, and where numerical instability is greatest) su... | [
"That's not actually a surface. These simulations are of the core of the star only, so the star itself extends well outside the frame of the video. The well-defined shape is created by imposing some sort of cutoff, likely a minimum density, and only rendering the areas that meet this cutoff. Because there is a shoc... |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] | [
false
] | Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! ... | [
"Over 20 years ago there was a product called \"oxyglobin,\" basically synthetic hemoglobin that gave a short term boost to blood's oxygen carrying capacity (2-3 days max).",
"I'm not sure what ever happened to it, be right back after I look it up.",
"E:",
"https://en.wikipedia.org/wiki/Biopure",
"Tl;dr: th... | [
"Vegetables, grains, meat, all normal mostly whole foods work as prebiotics, yogurt and fermented foods are probiotic. Basically eating regular healthy foods will all contribute to healthy gut flora"
] | [
"Vegetables, grains, meat, all normal mostly whole foods work as prebiotics, yogurt and fermented foods are probiotic. Basically eating regular healthy foods will all contribute to healthy gut flora"
] |
[
"Could you apply enough pressure to water that it wouldn't move?"
] | [
false
] | So I'm probably mixing up different concepts but here's my train of thought: If you fill a bottle half-full with sand and shake the bottle the sand shakes. However, if you press down on the top of the sand and keep pressing while you shake the bottle, none of the sand will move separately. All the grains of sand will m... | [
"That's Ice!",
"Ok so it's a bit different as sand is multiple small jagged solids being jammed against each other and the water would form a more continuous solid... but yes, if you apply enough pressure, the water will cease to act as a liquid. However, the pressure needed to do this at room temperature is pret... | [
"Nope! One of the fundamental definitions of a liquid is that it flows. That is, if you apply a shear force (parallel to the surface) to the liquid, the \"layers\" will move at different speeds. Shaking a bottle like in your post is an example of applying a shear force. ",
"Solids do not behave this way. If you a... | [
"The definitions become a bit, uh, muddy, when the substances are exotic. Colloidal suspensions can still be reasonably classified as liquids, like milk for instance. Perhaps peanut butter was a bad example, but I wanted to choose something relatable and viscous enough so the mind's eye can \"see\" what makes it fl... |
[
"Is there one major goal for the large hadron collider?"
] | [
false
] | I know there is a huge potential in the field of physics but I'm wondering is there something that would benefit everyone else beside a scientist in my lifetime? | [
"Copying my post from another thread.",
"X-rays: Roentgen, an experimental physicist, trying to figure out how cathode rays work. Didn't give a shit about medical imaging at the time.",
"MRI: Isadore Rabi, an experimental physicist, realized that nuclei resonate in magnetic fields. Didn't give a shit about medi... | [
"I know this is not really the place and doesn't add to the topic but: ",
"Relevant"
] | [
"I don't think we will know untill it happens. Think of electricity. When it was first discovered I highly doubt anyone could have envisioned it's future potential. "
] |
[
"How does adding texture to a surface reduce drag?"
] | [
false
] | I saw that Airbus is trying to mimic shark skin’s denticles to decrease drag, but I don’t understand how something rough creates less drag than something smooth. How does this work? Is it similar to why a golf ball has dimples? | [
"Actually, it is not like golf balls. The mechanism used by golf balls and other turbulent trips are designed to increase the pressure recovery around a body and thus reduce its profile drag (what people generally refer to when talking about how different shapes have different drag like ",
"this overview",
").... | [
"Not really. ",
"The microscopic rough patches hold a thin layer of air against the material. It creates a boundary layer that has almost no flow with regard to the metal. Then you don’t have the friction of air flowing over metal, but the friction of air flowing over boundary layer. ",
"That air-air boundary w... | [
"A lot of the fuel efficiencies cited in the Boeing 737 Max was due to the reduction of drag by going with a composite single piece construction for the wings and fuselage, removing the need for rivet fasteners. I'm sure even more could be gained through the use of advanced coatings."
] |
[
"Why is polyploidization more common in plants than in animals?"
] | [
false
] | null | [
"Hmmm...This got stuck in our spam filter. I know a panelist who might be able to answer it, too. Would you mind resubmitting? Then we'll let ",
"/u/WRCousCous",
" take a crack at it (no guarantees though). "
] | [
"I think I would like to take a crack at answering this, but I can't find it in the modqueue. Is there a way to put the question into circulation?"
] | [
"Did you resubmit it? Just make a new post. "
] |
[
"Would a planet near the centre of a galaxy be effected by the light and heat from stars other than the one it orbits around?"
] | [
false
] | Looking at the recent Andromeda photo it's got me wondering just how close the stars near the centre of a galaxy are to one another. | [
"According to ",
"this source",
", the night sky would be 200 times brighter than the full moon. The amount of starlight would be easily enough to walk around or read in the deepest night. Although this sounds alot, it would still be many times dimmer than the light of the home star itself. The same goes for i... | [
"Wow. It sounds really cool actually. Imagine the kind of life that would exist on the right planet. Thanks for that. "
] | [
"You have to look at the big picture, the distance between suns is huge. Image standing in football stadium with a candle on the other side. Also the heat, although almost so miniscule it is negligible, is still there. "
] |
[
"Is it possible for thermohaline circulation to stop?"
] | [
false
] | With rapidly changing ocean temperatures and salinity is it atually possible for the earths thermohaline circulation to stop? Thanks for the responses everyone. Happy Holidays :D | [
"For this to happen, the oceans would need to be in an equilibrium state, that is, the temperature of the oceans is constant at all depths and all longitudes/latitudes. I would be astounded if this was ever achieved because sunlight heats the oceans unevenly. Near the poles there is significantly less sunlight than... | [
"We alread had almost that state during the creatious era. That was also the epoche were most of todays oil reserves were formed, because of low water column mixing, the deeper sea was anaerobic and the falling organic substances (plancton) couldn't break down properly. ",
"Most of this effect is dependant of gla... | [
"to completely stop, no",
"There are also a few incorrect statements posted by others. ",
"The Gulf Stream will not stop flowing if the thermohaline circulation stops; the thermocline circulation is only one component of the Gulf Stream transport. The Gulf Stream is a western boundary current that exists to th... |
[
"Predisposition towards a Universal Template."
] | [
false
] | [deleted] | [
"What you are seeing is mostly due to common ancestry. Evolution adapts from the genetic building blocks available, reshaping them to mean environmental needs.",
"Mammals, birds and reptiles evolved from a common ancestor, a fish like creature with fins adapted for brief journeys on land. Its genes had the blue... | [
"This is the correct answer! ",
"DNA, found in amoeba, starfish, trees, and humans with vastly different body plans, has no intrinsic quality that favors one of those plans. However, once a working plan has evolved, it is elaborated on by nature quite extensively."
] | [
"I'll try to get to the rest of the question when I'm less intoxicated (if I remember), but I got about halfway and found a glaring problem.",
"nearly everything is bilateral in nature",
"is not true at all - it ",
" true for vertebrates and arthropods, but not for pretty much anything else, including plants.... |
[
"How do vaccine manufactures plan to test new COVID vaccines such as ones designed for the Delta variant now that a large portion of the population is vaccinated and those that aren't are hesitant to take approved vaccines?"
] | [
false
] | null | [
"If its a vaccine to say, target a new variant, they just use it on those willing to take it. If its a completely new vaccine, then there are countries around the world that have yet to get vaccinations, so they typically look there. Previous vaccine use shouldnt really skew the outcome if the the majority of the p... | [
"I help design and complete clinical trials for a living.",
"There are CONSTANTLY new trials going on all the time. Currently 6,885 trials have been listed related to COVID19. That includes completed and new or on-going trials. The below link takes you to a government run database to submit clinical trials in the... | [
"If its a completely new vaccine, then there are countries around the world that have yet to get vaccinations, so they typically look there. ",
"This is the right answer. Places like India where there are millions of unvaccinated people in areas amenable to doing trials are perfect places to test.",
"And studi... |
[
"What can happen with a second language if you develop disorders like dementia?"
] | [
false
] | [deleted] | [
"The same thing you would expect to happen with a dementia that is impacting language. Often individuals will show problems with word finding, naming, etc. in both languages. Something interesting I've observed (and probably more along the line of what I think you are asking about) is that patients will show declin... | [
"This may seem... Oddly off topic, but I've got to try to share my strange experience.",
"Some friends and I used to care for and elderly gentlemen who's wife paid us to watch him during the day. We were young and crazy, smoked/grew weed, so it was always around. Said gentleman used to be a drug runner (marihuana... | [
"As informal as your format is (I loved the story,) this may have clinical significance."
] |
[
"At what point does a short term memory become a long term memory?"
] | [
false
] | I'd love to know the answer to this simply because as far as I'm aware they are two separate parts/mechanisms of the brain | [
"There is a process called \"Memory Consolidation\" that is essentially the transfer of STM --> LTM.",
"The first part of it involves encoding the memories in neural circuits in the hippocampus, and takes minutes to a few hours. The second part of it involves transferring the memory from the hippocampus into the ... | [
"When I am studying for an exam, am I essentially trying to speed up this Memory Consolidation process?"
] | [
"Is there something we can do after a traumatic event to prevent the memory from forming?"
] |
[
"What is the difference between the six types of quarks?"
] | [
false
] | I know that there are 6 different types of quarks (up, down, charm, etc.) But what exactly is the difference between them? How was it determined which combinations make up protons, neutrons, and so on? On a side note, are they small enough to be considered on the Planck scale? By throwing h = E in Einstein's E=mc m=2.2... | [
"There are three \"generations\" of increasing size, and in each generation there is a quark with 2/3 the charge of a proton and another with 1/3 the charge of an electron. The first generation is up/down, the second is strange/charm, the third is top/bottom.",
"Starting in the 1950s, more and more particles were... | [
"On an interesting note further to the other comment, you will notice if you look online for the mass of the quarks across the generations, the values quoted vary depending on what interpretation of the mass is being considered. We are unable to liberate the quark constituents of a subatomic particle from the confi... | [
"The first experiment that appeared to directly observe quarks was the ",
"deep inelastic scattering",
" experiment at SLAC. Electrons are fired at hadrons at relativistic speeds, such that they are not strongly deflected by the very dense hadron, but are still scattered by the even denser collections of charge... |
[
"What would happen to someone who got chemically addicted to a substance without knowing it?"
] | [
false
] | What would happen if (hypothetically) someone's food was laced with a highly addictive substance like cocaine without their knowledge? The chemical addiction would set in, but they wouldn't know what to do to feed the addiction. Normally addiction of this type leads to all sorts of harmful behaviour in order to feed th... | [
"The people involved might develop some kind of ",
"superstitious behavior",
" that they believe will lead to the reinforcing effects they are experiencing. ",
"If they kind of food is served consistently, the person might begin to seek out that food because they are associating it with the pleasurable effect... | [
"There are a lot of misconceptions around the concepts of ",
" and ",
".",
"Addiction involves continued use of a substance despite the fact that doing so is leading to problems with one's health and social and legal predicaments.",
"Dependence is a state in which, if the substance is not continually used, ... | [
"I remember video of an experiment where subjects were given amphetamine with and without knowing - those given it with the knowledge had a good time, those without were indeed terrified and found it highly unpleasant. ",
"I'd imagine if there was a continuous imperceptible ramp up in dose you ... |
[
"When using a length of wire for a joule heating component, what resistance should be aimed for to attain the maximum energy transfer?"
] | [
false
] | I'm seeking a formula that can be applied to this situation? Too high of resistance (eg. really long wire) will no create enough current flow to produce heat. While too low of a resistance (too short a wire) will not produce as much heat as well. Thanks a lot for your help in advance. | [
"I'm using a constant voltage from a power supply, however the potenial difference will still change each time I change the wire (correct?)? Because the power dissipated from the wire will also change. And yes I am working with a changing current."
] | [
"I'm using a constant voltage from a power supply, however the potenial difference will still change each time I change the wire (correct?)? Because the power dissipated from the wire will also change. And yes I am working with a changing current."
] | [
"The maximum energy transfer to the load happens when the load resistance (within the thermodynamic boundary in question) is equal to the total source resistance (outside of the thermodynamic boundary in question). ",
"Assuming that you are using a voltage source the source resistance includes the impedance of t... |
[
"Is it true or not that we're \"running out\" of water?"
] | [
false
] | I asked this before, not sure if it was here or not. I do remember the replies however. They were along the lines that because it always rains water will always be deposited. But im hearing about a water shortage. I know this is 'drinking water' issue. Do these articles mean third world countries have no water or is th... | [
"The earth is covered in water but only a small portion of it is drinkable and usable by humans. We can't drink salt water and we can't drink polluted water, so the usable amount is very small. ",
"Water is purified naturally through the soil and accumulates in underground reservoirs which we tap into to get well... | [
"Yes, the world is running out of drinking water. While its true that the water cycle naturally replenishes source of drinking water, some sources are running a deficit because water is being pumped faster than it is restored. Sometimes even rivers can run dry from too much pumping/irrigration."
] | [
"So we are not really running out, but demand exceeds supply (in some areas)?"
] |
[
"Why am I able to hear a demodulated commercial FM radio signal through my computer speakers?"
] | [
false
] | [deleted] | [
"EE here, a rf low pass filter followed by a Rf detector forms a crude fm demodulator. In this case the wiring and passive components form the filter, and nonlinearity in the audio amp causes it to act like a rf detector. "
] | [
"The filter attenuates the radio signal based on frequency, turning the FM into a signal more like AM with the encoded signal varying the RF amplitude as well as frequency. This allows the detector-like behavior in the audio amp to demodulate the signal.",
"The audio amp applies a non-linear function to the signa... | [
"So the lower frequency parts of the signal are attenuated more than the high frequency parts, and this is enough to cause an audible sound signal? Can you explain more what an rf detector is?"
] |
[
"What is the limit for human athleticism?"
] | [
false
] | Will anybody ever run a 4 second 100 meter dash? | [
"That depends on what you define human."
] | [
"this answer makes my imagination go crazy :3"
] | [
"This will be a very close approximation. ",
"http://www.london2012.com/"
] |
[
"If our body odour is influenced by microbes on our skin, can our own body odour change and evolve as a result of spread of different microbes from another person?"
] | [
false
] | null | [
"You share and eventually equilibrate to some degree all your microbtiota (skin, mouth, gut microbes) with folk you are cohabiting or intimate with. This happens fastest for intimate partners and family members but if you live with room mates for long enough you'll share one another's microbes eventually.",
"Skin... | [
"Some infections do change your scent. For example, if you have malaria then you smell differently. One theory is that mosquitoes can detect the smell of an animal with malaria and the mosquito will preferentially bite the infected. Thus malaria is likely to be spread by scent.",
"In general, your skin is cove... | [
"One theory is that mosquitoes can detect the smell of an animal with malaria and the mosquito will preferentially bite the infected. ",
"This doesn't sound right... but maybe it is. Malaria is detrimental to the mosquito as well. It harms both the human and the mosquito. If anything Mosquitos would want to ",
... |
[
"Can a wind turbine on a moving vehicle ever produce a net gain of energy?"
] | [
false
] | [deleted] | [
"The best you could get with theoretically perfect bearings, generators, etc, is no loss of energy. But since all components lose energy (as heat, sound, etc) the system will lose energy. A net gain is impossible because ",
". You can't make energy. Only transform it and move it around."
] | [
"That would be a perpetual motion machine, whis is impossible due to the second law of thermodynamics. A similar example but easier to understand imo would be a boat with a wind mill that spins its propeller."
] | [
"Also gotta include having increased drag because of the turbines. "
] |
[
"I just read about 'superionic ice' being added to its over a dozen forms. Is ice/water unique to having all these variations?"
] | [
false
] | null | [
"On the contrary, many if not all solids can exist in several crystalline forms depending on the external pressure and temperature. Wikipedia has a nice, clean ",
"phase diagram",
" for iron, as an example. Maybe water has more solid phases than your average substance, but the phenomenon is hardly uncommon.",
... | [
"To add to this, more complex materials i.e. molecules instead of elements, will have more possible structures. Since water has been studied far more than most compounds, a large number of solid phases are known."
] | [
"Cool, thank you!"
] |
[
"if I just rinse my fruit and vegetables before eating them, does it actually do anything to clean it of pesticides and chemicals?"
] | [
false
] | People always say wash your fruit and veggies before eating them. I usually take that to mean quickly rinsing it under the tap for a few seconds, maybe rub it a bit if it's an apple or something then consume. If I eat a lot of fruit this way am I taking in a lot of unwanted pesticides and chemicals? Or am I actually w... | [
"While pesticides/agrochemicals are generally much more soluble in organic solvents, rinsing with water and rubbing the vegetables will still help quite a bit. ",
"This is because most of the pesticides will be absorbed by the dirt/dust on the outside of the vegetable, and if you get this physically removable mat... | [
"Some people do wash some vegetables with soap, although this is problematic because many fruits and vegetables are somewhat porous and the soap then gets into the food. If you are going to eat non-organic produce, I would recommend lukewarm water and rubbing the food as much as possible, clean hands would be fine ... | [
"Iodine is generally used to kill bio organisms, not to destroy or solubalize industrial chemicals like pesticides. If you are worried, there are some gentle soaps made for washing fruits/veggies. I can't speak to their efficacy, though, but in theory they might help by having non-polar chains that will help to ret... |
[
"Can a helicopter fly upside down?"
] | [
false
] | You know, like how some planes can fly upside down. | [
"The full sized AH-64 can do loops.",
"http://www.youtube.com/watch?v=vd6Q5G1v0PI"
] | [
"RC Helicopters have the ability to invert the ",
"pitch of their rotors",
". In other words, where you'd normally have downward thrust you can generate upward thrust instead. ",
"Video here.",
"The problem when you scale this up is that there isn't a material strong enough (yet?) to sustain these kinds of ... | [
"I think you posted the wrong video link. "
] |
[
"What are \"natural flavors\"? Are they harmful?"
] | [
false
] | null | [
"The difference (In the US) between natural and artificial flavors are whether or not it has a non synthetic base. They can chemically alter it all they want, but if it came from a plant its \"natural\"."
] | [
"Note that the ",
" can be listed as a \"natural\" or \"artificial\" flavor, depending on whether it was extracted from a plant, or synthesized in the lab."
] | [
"The U.S. Code of Federal Regulations describes a \"natural flavorant\" as:\nthe essential oil, oleoresin, essence or extractive, protein hydrolysate, distillate, or any product of roasting, heating or enzymolysis, which contains the flavoring constituents derived from a spice, fruit or fruit juice, vegetable or ve... |
[
"How can bones last so long outside the body (such as a skeleton after the person/animal dies) yet become brittle and weak with age during a shorter period in the body (e.g. dogs in 15 years)?"
] | [
false
] | Update: this blew up more than I thought!! Thank you so much for everyone providing explanations! | [
"I can only give a shallow intro to this, but hopeful others can add more.",
"Inside a living body, bones are also alive. The functions of the body interact with them constantly. The body breaks down older materials, and rebuilds them in a cycle.",
"This means that if something malfunctions due to old age or di... | [
"Osteoclasts are a trip. Your bones continuously accumulate microfractures, and these little fuckers basically ziplock seal the microfractures with their ruffled border, melt it with acid, then regrow it. Just continuous remodeling ans growth."
] | [
"The bones last so long because they are just lying underground. If you put a human bodies worth of force into them they would break. ",
"The day to day stresses of a hipjoint in an elderly lady is much more than a bone lying in a Cairn for 600 years"
] |
[
"CP Symmetry Breaking and how it applies to Bases"
] | [
false
] | A question to the particle physicists out there: What are the physical interpretations that can help me understand what happens when CP symmetry is broken on a bases inversion? I am having trouble understanding why merely choosing a different set of bases (looking at the experiment from a different position) can affect... | [
"CP violation comes from the fact that the mass basis of the quarks is different than the interaction basis of the weak interaction. This is the idea behind mixing angles introduced by ",
"Cabibbo",
". There's a nice picture of it on that page.",
"When we shoot particles at each other, or wait for them to dec... | [
"I don't really know about the Cabibbo thing... I mean, it would have been nice if he was given a share of the prize as well, but K&M really built on the work of the Glashow-Iliopoulos-Maiani paper, which gave an origin for Cabibbo's mixing angle, and showed it came naturally from the assumption of 4 quarks. ",
... | [
"I'm sorry, but I don't quite understand your question well enough to answer it. Sorry. I'd really like to help tough, can you be more specific as to whether you are interested in the theoretical picture of what CP violation is, or what signatures of it we look for in our experiment?"
] |
[
"Is hydrogen radioactive? And if Yes why?"
] | [
false
] | For what i have heard a fusion reactor does not generate any radioaktive waste | [
"Hydrogen has seven known isotopes. Two of them are stable (hydrogen-1 and deuterium). One of them (tritium) has a half-life of 12 years. The rest decay in a matter of zeptoseconds.",
"Only the first three are relevant for fusion reactors."
] | [
"A fusion reactor does produce radioactive waste - but it is much better than fission reactors. The product of fusion (the most promising reaction at least) is helium-4. It is not radioactive. The products of fission reactors are various radioactive isotopes that make up most of the waste. While fusion reactors wou... | [
"The vast majority of hydrogen in the universe is hydrogen+1 consisting of a bare proton and an electron. This hydrogen was produced in the Big Bang and has remained unchanged since then.",
"Protons are, by all evidence so far collected, stable by themselves. ",
"A small percentage of the hydrogen in the univer... |
[
"Why doesn't the sugar in my tea crash out of solution when chilled despite the tea needing to be warm to dissolve it in the first place?"
] | [
false
] | null | [
"It doesn't need to be warm to dissolve it in the first place, it just takes more aggitation and time to dissolve it in a cold liquid.",
"The way sugar \"dissolves\" is based on hydration of the sugar molecules (compared with dissolving salts, which is based around ionic interactions). In theory, you can have sug... | [
"Salts like NaCl are ionic solids, meaning they are an extended network of alternating positively- and negatively-charged ions packed into a regular pattern. You can imagine this like a brick wall containing alternating blue and red bricks. When an ionic solid like NaCl is dissolved in a polar solvent like water,... | [
"Sugar dissolves more quickly in a hot medium then a cold. Because the atoms have more energy. More energy, more interactions/collisions a second so faster in solution. ",
"But also something weird is if you would dissolve that much sugar that no sugar dissolves anymore. You reached the saturation point of the li... |
[
"Can you eat something that causes you to gain more weight than the weight of the food you just ate?"
] | [
false
] | [deleted] | [
"Not sure exactly what type of answer you are looking for. From a strict mass balance point of view, the answer is no.",
"If you allow for secondary effects, you could easily 'eat' a pill that causes you to ",
"retain more water",
" and your weight would likely increase by more than the weight of the pill. Th... | [
"Yea isn't that a Law of something (blanking on the name, I think thermodynamic) that energy cannot be created or destroyed? So if you ate something of a certain mass or calroic content you could gain up to only that content mass wise because you can't create energy out of nothing?"
] | [
"I wasn't approaching the question from the point of view of energy since OP asked about weight, which is effectively mass."
] |
[
"Does childhood participation in lotteries have any impact on whether or not a person is likely to develop a gambling problem (then or later in life)?"
] | [
false
] | Current controversy about loot-boxes is computer games is that they are wrong because they prey on children and they are often characterized as a form of gambling (usually when real money is involved). But is there any scientific knowledge on whether participation in lotteries change gambling tendencies amongst childre... | [
"Interesting question, I did some digging. ",
"This study: ",
"https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0206767",
" finds a correlation between loot box \"abuse\" and gambling problems, but the study did not conclude any causal relationships. I would guess we would need some longitud... | [
"Since loot boxes are somewhat new, maybe it will take a while to see if there is a corresponding uptick in gambling addicts once they come of age."
] | [
"Yes, if there is a causal relationship between loot box use and gambling addiction. I don't know enough about gambling addiction to know if the availability of such stimuli creates an addiction, or if there are any other underlying causes feeding this behavior unrelated to the act of gambling itself."
] |
[
"Question on freezing water?"
] | [
false
] | So today when I got in my car I had two water bottles that had been sitting in the car both more than half way full. One was a poland springs and the other was my essentials ( a shaws brand). The shaws brand was completly frozen but the poland springs was not frozen at all. When I picked up the poland springs to look a... | [
"The water is probably fairly pure and as a result there were no good nucleation sites for ice crystals to begin to form. The water was subsequently cooled below freezing while having nothing to latch onto and freeze. ",
"When you picked up the bottle you disturbed it enough for an ice crystal to find a place to ... | [
"Thanks, yeah that first link you posted is exactly what I saw."
] | [
"I imagine that would be very difficult to actually pull off. Super cooled water is very sensitive and freezes very easily. I doubt you could get it into your mouth before it froze."
] |
[
"ok so energy doesn't decrease it simply changes state, please expand how this is possible."
] | [
false
] | [deleted] | [
"You're mostly right. When you drop the brick, you will hear sound (which dissipates). After all of these collisions/conversions energy ends up as heat death. This is why we hear about the heat death of the universe- as eventually all usable energy becomes heat, equally dissipated throughout the universe. "
] | [
"Energy isn't real. It's a mathematical tool that we noticed is \"conserved\" for all purposes. The mathematical relationships between movement and position in a potential are consistent enough so that we can create a term called \"energy.\" ",
"Sound isn't a magical flowing ether either. Sound is particles movin... | [
"It's not, it's the same answer, but I chose to direct you away from the understanding of \"chunks of energy\" and energy as some independent entity.",
"Energy is not real. It's a mathematical coincidence that we manipulate. Forces are the only thing thats real; for some reason, this accelerates that. The way tha... |
[
"Is it really ever possible to \"see\" a galaxy, nebula, etc. as it appears in photographs?"
] | [
false
] | My question's a bit verbose so bear with me... I'm asking about the angle/scope of view of those photos, not the false-color aspect of it. Because its scale is so grand, am I right in assuming that a galaxy only looks like a spiral when it's a single point of light that we artificially "zoom in" on, as we see in telesc... | [
"I think the question is more like if we were a planet orbiting a star which has been ejected from a galaxy and is say a 100,000 ly above that galaxy, would someone on the planet see something like ",
"this",
" in the night sky?",
"*edit: ",
"Carl Sagan quote",
":",
"...But from a planet orbiting a star... | [
"There are several issues here. One of them is resolution. The size of an aperture places fundamental limits on what can be resolved through it. The angular resolution scales linearly with aperture size. So the human eye is unable to see anything below a certain size (I can't recall the value at the moment) as any... | [
"The answer is yes, but it would be fainter than those photos. At best it could look like the milky way seen from the earth."
] |
[
"At what speed do electric fields propagate?"
] | [
false
] | null | [
"Changes in electric fields propagate at c in vacuum."
] | [
"Thank you! Is there a proof or a link to a proof that you could provide for me? "
] | [
"There is a great text by Landau and Lifshitz about treating electrodynamics as a relativistically covariant field theory. It's available online ",
"here",
"."
] |
[
"Why does the driver hit the golf ball the farthest?"
] | [
false
] | null | [
"The biggest factor is probably a more simple one than you were expecting: it's the angle of the face, known as loft. The drivers have a face that is more close to vertical at the moment of impact, as opposed to irons which have higher angles designed to send the ball higher, but with less forward velocity.",
"Th... | [
"Is there a point where less loft actually makes the ball travel less? I imagine that if the club had 0 loft, the ball wouldn't get very high off the ground. ",
"And wouldn't the ball essentially be a projectile, so a 45 degree loft should actually make the ball travel further?"
] | [
"Without wind resistance (aerodynamic drag) the optimal angle is 45°. With drag it's a lower angle. So yes, some loft is needed to clear the ground and too much loft results in a high ball that does not fly as far."
] |
[
"What's the physics behind walking?"
] | [
false
] | When we walk, we take a step so we exert a force onto the ground and receive a forward force pushing us forward. However, what about the static friction? Because static friction is equal to the force applied onto the feet (until a certain applied force then it goes into kinetic friction) will it cancel out the reaction... | [
"Biomechanics of Human Gait (walking) is incredibly complex. It involves a lot of different forces and moments exerted by the skeleton and muscles which can dynamically adapt by shifting centers of pressure and exerting mechanical advantage through different skeletal configurations. I'm going to be making a lot of... | [
"Oh so the static friction and the ground reaction force are speedster forces. The static friction would be in the backwards direction while the ground reaction force in the forward direction right?",
"Also, shouldn't the static friction be equal to the ground reaction force at all times because the foot planted ... | [
"Your answer to the first question is correct in terms of directionality.",
"You are correct in your second assumption, however the surface interactions are not always this ideal (Think dust on the surface, ice, or other things that would reduce its coefficient of friction). This would lead to slipping and an in... |
[
"Why do female dogs mount/hump other dogs/things?"
] | [
false
] | explanatory. Different genders with humans have different sex drives, I know for sure that animals like wolverines have different sex roles...why then do some female dogs hump things? What's the evolutionary point of that? | [
"Dominance. It's got little to do with sex."
] | [
"\"I'm a female, and I'm still making you my bitch!\" ",
"-- Female Dog"
] | [
"I've seen human women hump other people. You can imagine it's pretty much for the same purpose."
] |
[
"Can anyone explain how the Mars Reconnaissance Orbiter moves around Mars? (details inside)"
] | [
false
] | I'm not an astronomer or rocket scientist, but I'm a fan of the MRO and trying to understand how it gets around the planet. To be more clear, my question has two parts: (1) Does the spacecraft simply twirl around the planet, in a constant westward-walking helical orbit? (did I say that right) or does it use its thrust... | [
"The animation on the right ",
"here",
" is a good example of how a satellite can obtain full coverage without using thrusters. "
] | [
"The animation on the right is okay (it's from NASA), but the animation on the left is ",
". A geostationary orbit is always over the equator. A satellite cannot remain \"directly above 30°N, 45°E at all times\". Every satellite's orbit must be in a plane that contains the Earth's center. In fact, the orbit is an... | [
"The orbiter is just that, orbiting. As you said over time its orbit allows it to see the entire planet as the planet moves beneath it. Thus, they do have to wait for features of interest to be beneath the cameras. AFAIK it only used its thrusters to make orbital corrections (change the periapsis of its orbit) and ... |
[
"how do we know what the milkyway actually looks like?"
] | [
false
] | null | [
"By mapping the stars. We've gotten pretty good at measuring distances between us and other stars, and by putting those into some modeling software, we can then look at them from different angles. Kind of like how cartographers were able to make accurate maps before satellites or even aircraft were a thing.",
"ht... | [
"I would add mapping the clouds of dust and gas, as well. You can measure the distance of these constituents of our galaxy and see their direction in our sky, so you can map out their location in three-dimensional space. For objects in our quadrant of the galaxy, these data are reasonably complete and accurate. For... | [
"I feel spoiled and lucky to have spent my summers at a cabin in the middle of a forest 2 hours from a major city. ",
"The northern lights and comets and Milky Way and constellations as clear as day was so cool. Laying at the end of the dock counting shooting stars listening to the water lap the shore are some of... |
[
"Question about formula 1 air intake (fluid dynamics)"
] | [
false
] | Can someone please explain why the pressure would increase as it spreads out before it reaches the manifold? I feel like the increase in volume would cancel out the decrease in velocity. "Inside the air intake is an expansion chamber (diffuser) that slows the air down and thus increases its pressure ready for its passa... | [
"You may want to read ",
"this entry on Bernoulli's principle",
" if you truly want to get to the bottom of this.",
"The result follows from simultaneously applying conservation of mass and conservation of energy principles to a system at equilibrium (yes, clear as mud, I know).",
"You could think of it thi... | [
"The path of causation between the size of the chamber and the volume of the gas would go something like this: Increased cross-sectional area => lower average velocity => higher pressure => slightly higher density (since air is compressible) => slightly lower volume for a given amount of gas",
"It sounds to me li... | [
"So that explains why a decrease in velocity means an increase in pressure, but it doesn't explain why a decrease in volume wouldn't lead to a decrease in pressure that would counter the increase from slowing down. Is the change in velocity just greater than the change in volume? (More volume with the same number o... |
[
"Could you say that a regular polygnom with an infinite number of sides is a circle?"
] | [
false
] | Title says the most, could you count it as a circle or does it simply look exactly as one? (Edit: mabye I should state it as the number of sides going towards infinite, as in number of sides lim>infinite) | [
"Yes (essentially). ",
"An aside: One of the ways of calculating pi is to take an equation that relates distance across the polygon as a function of side length, and take the limit of that function as the side length approaches 0 (i.e. the number of sides approaches infinity.)"
] | [
"That's exactly it; you're being very technical. I said \"essentially\" because I know circles aren't polygons. As a polygon approaches infinite sides, it approaches a circle. ",
"Kind of like limits in calculus. When you say \"What's the limit of 1/x as x approaches infinity?\" The limit is 0. But when you ask w... | [
"That's not what I'm saying at all. By ",
" reasoning, I'm willing to say that there are rational numbers that can be used to represent sqrt(2) and pi sufficiently for a desired level of accuracy.",
"Edit: Small typo :) (my instead of by)"
] |
[
"How did all the water on earth come to be, and is the process that resulted in its existence still happening?"
] | [
false
] | I realize that there are multiple theories surrounding this question but I was wondering if one is more reputable or likely than the others. Also, are there any special conditions for water to form on a planet and if so what? | [
"Some was formed from burning hydrogen.",
"Some was brought via comet(s).",
"Some was created by life (water is a byproduct in a boatload of biological reactions).",
"Some was produced from hydrous minerals (e.g. copper sulfate) eventually lost their water over time.",
"The majority was created from burning... | [
"An interesting follow up question is how did the water in space form so it could come to Earth. On Earth we can burn O2 and H2 to make water, but in space, the gases are so diffuse it is not efficient.",
"The major source appears to be from interstellar dust grains. O and H atoms absorb onto the surface and ev... | [
"Sounds like this could lead to clouds and raindrops (though frozen) in space. "
] |
[
"Science of Knife Sharpening"
] | [
false
] | Everybody says/thinks a steel does not sharpen a blade, yet my knives have never seen a stone in 15 years of work and are razor sharp do only to me stroking a steel with them before they get very dull. My most used blade has visible shrinking due to years of stroking steel. How can I explain to the doubters/haters how ... | [
"Its going to depend on steel grade as to whether steel will be able to sharpen your blade.",
"Theres sharpening and honing. Honing will buy you a lot of milage, but eventually you'll probably need to remove material in order to get a sharp blade. That second process is called sharpening.",
"If, for example, yo... | [
"This depends on your definition of sharp. Let me explain...\nFor example a honed blade (after an oil stone) will shave your arm nicely but a blade that has been used on a steel won't, yet it will slice a tomato like a champion...\nThe reason for this is that a steel creates micro-serrations or burs on the blade g... | [
"To clarify, ive used these knives in professional kitchen for over 15 years. They used to get the steel four times a day. They have never seen a stone. When I am done with them a steel they will most certainly shave a patch off your arm. "
] |
[
"why is speed of light a limit?"
] | [
false
] | Is there a simple way, what vulgarisation could help to explain why the speed of light is a limit? | [
"A rigorous answer to your exact question would be «no one knows, and physics isn't meant to answer that», because it's a «why» question.",
"Now, you can get a better grasp at the notion of a limit if you ask «how is c a limit ?».",
"It's a surprising idea at first because in our day to day life, everything loo... | [
"The fact that ligth speed is a limit is a mathematically derived conclusion. ",
"When you derive kinematic expressions you can take in account different things, mostly the thing that you take in account is that some phyisical quantity remains constant for the different systems of reference. In classical kinemati... | [
"Thanks! It helps me a lot. The Michelson - Morley experiment makes it easier to understand and explain (for me at least). "
] |
[
"What's underneath the sand at the beach? How far does the sand go and what is beneath that?"
] | [
false
] | null | [
"It depends on the sand and geology of the area. Essentially the deeper you go the more compact the sand becomes and eventually you would run into sand stone. Under that there would be a layer of limestone. This pattern would alternate for the riseing and falling of sea levels. Thicknesses depend on how long sea le... | [
"The Los Angeles basin in particular is a deep bowl that's been opening up and filling up with sediment from the nearby mountains for millions of years. ",
"This site",
" includes a shallow drill core made near Long Beach: under the sand, it's all compressed and solidified shoreline sediments (old remnants of ... | [
"(33.7545522,-118.1318353) This is where I was when I asked."
] |
[
"If you are on Mars would the constellations and star maps be similar to earth?"
] | [
false
] | null | [
"Yes, because the distance to the stars is so enormous. Mars is 170,000,000 miles from the earth. But the nearest star is more than 100,000 times further away. As a result, any angular differences will be very small. ",
"Anything farther than ~4 light years (about 23,462,800,000,000 miles) shifts by less than 1/3... | [
"There is, however, one major difference: You can't see a certain red dot, but a certain blue-white-ish double dot that travels through your sky on a different path."
] | [
"The one major difference is that Mars's and Earth's rotational axes are not aligned, so the immobile northernmost and southernmost points of the sky would be different, and there would be a somewhat different split of northern hemisphere/southern hemisphere constellations, and summer/winter constellations within e... |
[
"If you ate a poisonous spider, would you die?"
] | [
false
] | Let's say it died in your mouth the second you bit down. Would the poison just seep out of the spider's body and kill you? | [
"Yes, if you ate a poisonous spider. But you said poisonous when I think you mean venomous.",
"There is a slight distinction between venom and poison. Venom is most effective delivered directly (e.g. stinger or fang). Poison can mean it's deadly when processed through the digestion system. Venom is a poison but i... | [
"AFAIK most snake, spider and platypus venoms are proteins. As such, they're destroyed in your stomach before they can be absorbed, and so can't hurt you (unless you have open wounds in your mouth or esophagus)."
] | [
"I used to think this was true, and it would create neat answers for a lot of nutrition and health questions. But empirically, lots of proteins and biologically active peptide fragments make it to the intestines intact. It's one of those long-held assumptions that is being shattered in the fight against complex chr... |
[
"What caused Mars to be as arid as it is now?"
] | [
false
] | I've just seen this that shows how possibly Mars was 4 billion years ago, and it made me wonder what could have happened that caused Mars to be so arid now. I've read somewhere that Mars atmosphere desintegrated. If that is true, why did it happen and could that happen to Earth? | [
"Heat the Earth, and you'll see an increase in evaporation, which means an increase in cloud cover",
"That isn't necessarily true, it's a lot more complicated than that."
] | [
"You also have to consider the fact that Mars is only about half the mass of Earth with a much weaker gravitational field. During the Heavy bombardment period of our solar system it would have received very few impacts as compared to earth. Being smaller Mars would not have been able to hold the heat from these imp... | [
"You might be interested in ",
"this AMA going on right now",
". The MAVEN satellite is designed to figure out basically what you are asking, and the AMA is with one of the lead scientists working on the project."
] |
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