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[
"Why do some people see this dress as Black and Blue, while other people see it as Gold and white?"
] |
[
false
] | null |
[
"This is the only question about the dress that will be on askscience today! All other dress questions will be removed! ",
"Please do not make top-level posts in this thread unless you have relevant expertise.",
"Do not speculate, or post about what colour you see it as.",
"If the thread becomes out of control we will have to start being jerks."
] |
[
"Hi! me and some other grad students have been discussing this for the last half hour. It's likely due to some kind of ",
" illusion, where some people are perceiving the context to be something like \"lit by blueish daylight\" and others are perceiving it to be something like \"under yellow department store lights.\" In the former case, your brain will try and get the objective (if such a thing can be said) colour by subtracting out the blue as a shadow, and in the latter case it will do the same thing for the filigree by subtracting out the yellow as a reflection. This is a common illusion in psych : ",
"See here.",
" but it's not seen that often 'in the wild,' even though your brain does this constantly. "
] |
[
"Hey, so this post turned into about 50 anecdotes and your comment. We've opted to make a ",
"post using our moderator account",
" so we can moderate it more easily/sticky it/paste the expert explanations into the body of the post. I'm letting you know in case you want to repost your comment in that other thread. ",
"For what it's worth, we've had our panelists discussing this behind the scenes and this is their explanation as well. Oh, and if you like answering questions here I'd recommend ",
"applying to become a panelist",
". :) "
] |
[
"For every pound of excess fat, how much vascularization and innervation needs to be created to support that this adipose tissue?"
] |
[
false
] |
I am really curious about the capillaries and nerves that are undoubtedly created when excess fat is stored in the thighs, butt and abdominal region. If one is fat enough and the blood has to circulate through so many more meters of blood vessels, does that put an extra strain on the heart?
|
[
"does that put an extra strain on the heart?",
"Precisely. The more vascularization there is, the more the heart has to work to pump blood. That is precisely one if the major concerns regarding obesity - the weight puts an enormous strain on the heart, which can damage the organ if it its stressed for a sufficiently long time.",
"I'm uncertain if this is a related point, but extremely muscular people develop very thick \"ropes\" of veins. With wider veins, the heart can pump blood at a lower pressure and faster rate. ",
"(If i'm incorrect, sometime fix it, please.)"
] |
[
"This is also why excess fat ends up having areas of necrosis (dead cells and debris): angiogenesis can't keep up with fat deposition in the obese setting, and so once cells get outside the range of diffusable oxygen, they die. Because vascular and lymphatic networks also deliver circulating cells responsible for clearing cellular debris, you have all sorts of necrotic junk hanging around too."
] |
[
"I see. Is this why obese people who also happen to be diabetics run the risk of peripheral vascular disease (and eventually an amputation if an infection persists)? Why does the diabetes make the circulation so much worse? "
] |
[
"Do we know whether Covid is actually seasonal?"
] |
[
false
] |
It seems we are told by some to brace for an epically bad fall. However, this thing slammed the Northeast in spring and ravaged the “hot states” in the middle of summer. It just seems that politics and vested interests are so intertwined here now that it is hard to work out what is going on. I thought I would ask some actual experts if they can spare a few minutes. Thank you.
|
[
"Emergency Physician here: It’s not because we expect ",
" to be worse, it’s because of all the other Acute Febrile Respiratory Illnesses (AFRI) that ARE seasonal will also occur. Flu pushes US hospitals to brink of capacity most years without any additional new pandemic. And because the symptoms of most are overlapping (and NOT mutually exclusive - people get flu and COVID), disguising between them is expected to be awful. This is why rapid testing (like 1 hour) is so important, but also why we are basically going to be locked down until there is a widely available vaccine."
] |
[
"It's not seasonal because the disease is obviously still ravaging us in peak summer like you say. ",
"However fall and winter are still of particular concern because of a few things: ",
"1) even though the virus does survive in the heat and it should be even more stable (and thus more infectious) in the cold ",
"2)human respiratory systems are vulnerable to infection in fall and winter because of the dry air. ",
"3) if it's cold outside people are more likely to be inside spreading those sweet droplets around with inadequate ventilation ",
"So even though the disease isn't seasonal there's still plenty reason to think things will get worse in the winter ",
"Edit: those ain't the the only reasons either! Lots of good other responses like complications flu season will introduce"
] |
[
"Shouldn't there be less seasonal infections than in previous years due to people wearing masks/washing hands?"
] |
[
"My friend found what He thinks is a meteorite from space in his neighbor's yard. Anyone who can chime in on identifying the mystery object?"
] |
[
false
] | null |
[
"It's a big marble",
"http://www.rainbowturtle.com/meteor-50mm-marble-p-434.html",
"\n",
"http://www.rainbowturtle.com/chrome-steel-marbles-p-5584.html",
" ",
"This has got to be the most unusual website I've cited for AskScience since LOTRwiki"
] |
[
"Or someone dropped it. It may have been there for a while."
] |
[
"Which would mean either he's lying or someone is firing marbles out of a cannon somewhere. thanks for input."
] |
[
"Could a satellite gather molecular gases from orbit to maintain its orbit?"
] |
[
false
] |
[deleted]
|
[
"It's an active area of R&D. The European Space Agency test fired such an engine in a vacuum chamber earlier this year.",
"https://en.m.wikipedia.org/wiki/Air-breathing_electric_propulsion",
"Conservation of energy is not broken because the engine would take in gas and then use solar (or nuclear) power to expel it faster.",
"It's only necessary for low orbits. Satellites in medium, geostationary, and high orbits already experience so little drag that orbital decay would take thousands of years."
] |
[
"Xenon easy to ionize compared to other noble gases. Atomic oxygen and nitrogen are pretty close. And it gets more complicated when considering molecular gases. The lower molar mass shifts thing toward a higher Isp and lower thrust to power ratio but it's not necessarily a deal breaker. ",
"My point is that it's not necessarily more complex than regular electric propulsion systems and in some cases can present advantages. This is why people in the field of plasma propulsion have been toying with that idea for decades. But by all mean if you think that's a stupid idea I will pass on the message."
] |
[
"The ESA study is essentially an ion thruster that uses ambiant gas as propellant. The issue with xenon is that it's a pain to store. You need to get it to 150 to 200 bar to get in the supercritical range and that results in bad mass fraction. Some people believe that the inlet/collection device can be lighter than traditional tanks."
] |
[
"During a solar eclipse if you followed the path of totality how fast would you need to be moving to stay in darkness?"
] |
[
false
] | null |
[
"It comes out to basically the speed of the Moon's orbit, which is about 1 km/s or 3600 km/h.",
"As the Moon orbits the Earth, it moves relative to the Sun, and that makes its shadow move relative to Earth. If the Moon moves 1° relative to the Earth-Sun line, then its shadow moves 1° from that line. So the angular speed in degrees/second of the Moon's motion relative to the Earth-Sun line is the same as the angular speed in degrees/second of the Moon's shadow.",
"To convert angular speed to linear speed in km/s, we convert the angular speed to radians/second, and multiply by the distance to the object. As the angular speed of the shadow (at some fixed distance, i.e. the Earth's surface) and the Moon are the same, this means that the difference in linear speed is just the ratio of the distances.",
"The distance from the shadow on Earth to the Sun is 1 AU. The distance from the Moon to the Sun during a solar eclipse is (1AU - 384,400km), where 384,400 km is the distance to the Moon. 1 AU is about 150 million km. So the speed of the shadow is about (moon's orbital speed)*(150,000,000km + 384,400 km)/(150,000,000km). As 1 AU is much much bigger than the distance to the Moon, (150,000,000km + 384,400 km)/(150,000,000km) comes out to basically 1 - it's like 1.002. So the shadow on Earth moves like 0.2% faster than the Moon. The Moon goes at about 1 km/s, so the shadow goes at basically 1 km/s."
] |
[
"On the 30th June 1973 Concorde did this, experiencing totality for 74 minutes. This was already quite a 'long' eclipse with totality from the ground of just over 7 minutes, which makes the aircraft tracking an easier task. Concorde was capable of flying at 600 m/s or Mach 2."
] |
[
"Right - this is the speed relative to the centre-of-mass of the Earth. If you're actually, you get some speed for \"free\" because you're already rotating with the Earth. The Moon is orbiting in the same way the Earth rotates - west-to-east - so in practice its relative speed is a bit lower than that.",
"At the equator, you actually get like 0.46 km/s of boost, which gets you almost half way. However, that's only if the eclipse is right on the equator, and going directly west->east. In practice, the alignment isn't perfect and the Moon goes a bit north/south too, so you won't get that ideal boost."
] |
[
"Could the principles behind the dyson bladeless fan be applied to airplane wings?"
] |
[
false
] |
This isn't just layman's speculation, I'm genuinely curious about this phenomenon and would greatly appreciate it if anyone knows more about it. I always thought it was interesting how the dyson bladless fan works. By using an impeller at the base, drawing air in and forcing it out through narrow slits along wing shaped disc, it creates a flow of moving air from an otherwise motionless surface. But this got me thinking, could airplane wings use the same feature? I'm under the impression that lift is created by air moving at different velocities as it passes under and over a wing. I imagine that an aircraft might be able to direct some of its thrust specifically over the wing, even by narrow slits all across the leading surface such as in the dyson fan. The design implications could be profound, such as an ability to maintain very slow flight. Despite a low airspeed that would normally cause a stall, the actual speed of the air moving over the wing would be much higher. I imagine it would operate something like the custer channel wing, (link: ) but much more compact. I swear I once saw a wikipedia page about a Navy aircraft that operated on a similar principle, but I can't seem to find it. EDIT: I am aware that many airplanes use the Coandă effect by the placement of their engines, but I'm more interested in knowing whether this application has been taken to the extreme I also wonder what the potential drawbacks to such a design would be, as it clearly isn't a popularly implemented feature of modern day aircraft...but then again maybe most designers haven't put much thought into it.
|
[
"I actually worked as a research assistant on something very similar to this for a summer during college. ",
"Here's a paper",
" that describes some of the basic ideas behind the research. I specifically worked on testing different configurations of jet geometries for a standard NACA airfoil (forget which one) and testing and optimization of a conceptual high efficiency vehicle design that took 2nd place in a NASA competition ",
"here",
". The conceptual vehicle tested a bit poorly due to some unforeseen detrimental flow characteristics, however the basic airfoil saw increases in the L/D ratio of between 200-500% depending on the air speed, AOA, jet geometry, etc. ",
"The main areas that this would likely be used is for low speed flight, such as take off and landing, loitering, and other low speed applications. It could drastically decrease TO and landing distances, which could help airports cut down on runway space, or help get exceptionally underpowered planes off the ground in a reasonable distance. Also, it could reduce fuel usage during takeoff as most planes need to use max throttle to lift off before the end of the runway, which burns fuel much more quickly (planes will often use ~3.5% of their total fuel just during takeoff). ",
"The tech is really impressive in the lab setting, but like anything else, what will make or break the technology will be how successfully it can be integrated with an air vehicle system. It adds complexity (read weight), and presents significant design challenges. ",
"Here",
" is the website of professor I worked with, you can read some of the results, see some cool flow visualization pictures of the tech, and look into it further if you would like. "
] |
[
"Taking this to the extreme would mean that the engine exhausts in a thin slit over the entire wing, and the wing directs this jet downward for additional thrust. Routing exhaust this way would be very lossy (inefficient) and would be worse than useless at high speeds, where efficiency, rather than lift, is the primary concern. There has, however been a lot of research into using small jets to control the airflow around a wing.",
"Just in case you don't this, the boundary layer is a thin (typically <1mm) layer of air around the skin of an aircraft in which viscous forces are important. In the frame of the aircraft, the fluid in the boundary layer is slowed down by viscosity over the entire chord of the wing. Pressure gradients push the boundary layer faster over the front part of the wing, then slow it down over the back part. At a certain point of the back side of the wing, the boundary layer can not keep going in face of viscosity and the unfavorable pressure gradient, so the boundary separates from the wing. When this separation occurs a significant distance from the trailing edge, a large, turbulent region forms behind the separation point, reducing lift and increasing drag. This is called stall.",
"A lot of current research is focused on how to use small jets (because small jet=small energy cost) to control boundary layer behavior, with a goal of being able to achieve a higher lift coefficient with a given airfoil than is possible without the jets. If you want more information, try googling \"synthetic jet\" \"flow control\", and \"boundary layer separation.\" Also, ",
"this wiki article",
" has some references at the bottom you should check out. ",
"maybe most designers haven't put much thought into it.",
"Believe me, designers have put lifetimes of thought into each aspect of each commercial or military plane that has ever entered service. Flow control faces the problem of being largely poorly-understood and of being new. New things take a while to get onto aircraft because of safety/regulatory concerns (and rightly so)."
] |
[
"There is a fan with blades in the base of the Dyson unit."
] |
[
"If one's optic nerve were severed, but the occipital lobe wasn't damaged, what function would neuroplasticity give this useless heap of tissue?"
] |
[
false
] |
I was wondering what happens here with blind people. I hear their other senses are heightened and some can even echo-locate. Is this a result of neuro-plasticity?
|
[
"First, its important to mention that there are other destinations for visual information in the brain, not just the occipital lobe. I'll trace out the pathway below, hopefully making it easier to understand.",
"When light enters the eye, it is transduced by the rods and cones in the outer layer of the neural retina, and the resulting information travels through the deeper layers, ending up in the retinal ganglion cells. The central processes of the retinal ganglion cells (which are bipolar; the peripheral process is very short and synapses in the retina) group together to form the optic nerve, or cranial nerve II. When CNII reaches the optic chiasm, the information from the nasal retinal fields crosses over to the other side, while the information from the temporal visual fields remains ipsilateral. At this point, the bundle of axons traveling from the chiasm to the brain is actually called the optic tract, not the optic nerve.",
"So, here's where your question comes in. From the optic tract, visual information goes to one of four destinations:",
"It's also important to mention that, as far as current research has shown, neurogenesis in the adult mammalian brain is limited to the subventricular zone of the lateral ventricles and the subgranular zone of the dentate gyrus, neither of which are involved in the visual pathways.",
"So. All this being said if one were to sever the optic nerve, theoretically, all four destinations of visual information would be deprived of input. If, however, only one optic nerve were severed and the other remained intact, one would still have full sight in the unaffected side (the lesion being distal to the optic chiasm). If both optic nerves were severed, then all visual input would be cut off and the individual would indeed be blind.",
"As far as neuroplasticity goes, since there is no evidence of neurogenesis in or around the optic nerves, theoretically, once that nerve is severed, one would be totally blind forever. You mentioned heightened senses and echo-location, some of which can be attributed to a very interesting phenomenon called \"blindsight\".\nEDIT: Also, neuroplasticity has more to do with damage to cortical areas of the brain. When the input mechanism is undamaged, new pathways can sometimes be made to other cortical areas to pick up the slack, but in this particular case, the input mechanism is cut off, meaning that no cortical area can receive it.",
"I am certainly not an expert in blindsight, however, as far as I understand, it is a rare phenomenon in which visual information from the lateral geniculate nucleus is cut off, resulting in blindness, but the other three destinations of the optic tract remain. This results in the ability to sense objects without actually perceiving them visually. If there are any experts in this phenomenon out there lurking, please feel free to school me on this. I am not worthy of your expertise.",
"Anyway, ",
"here",
" is a really cool video of a patient experiencing blindsight, if you're interested.",
"Sorry for the long-winded answer, I hope it helps!"
] |
[
"it is a rare phenomenon in which visual information from the lateral geniculate nucleus is cut off",
"Blindsight is broadly any disorder where visual perception is disrupted, but some low-level visual processing still occurs. For example, a stroke that takes out the visual cortex renders someone perceptually blind. They are unable to ",
" things, but processing outside of the visual cortex continues to occur, so they are able to react to some information (for example, they can orient to a sudden change in contrast)."
] |
[
"You may find ",
"this article",
" of interest. It talks about what happens in the brain after damage to a lot of different parts of the visual system. Figure 1 is pretty good, it shows you what happens to someone's visual field if you damage different parts of the visual pathway.",
"One thing that may occur is cross-modal plasticity. That is, visual regions may change their responding away from visual stimuli to, say, auditory stimuli. For a long time this was thought to only occur in young brains, but ",
"this paper",
", for example, presents evidence that this sort of change is possible in an adult brain.",
"You may also be interested in ",
"Charles Bonnet syndrome",
" which is a disorder that may develop following the loss of visual input due to macular degeneration, or due to loss of the optic nerve. In this syndrome, patients experience often very complex hallucinations within the blind parts of their visual field. While the precise nature of the disorder is not known, it is thought to be a result of the blind visual cortex becoming hyperexcitable."
] |
[
"Why do some parts of the eyes not need blood vessels?"
] |
[
false
] | null |
[
"The cornea and lens both lack blood vessels, since they need to be clear for good vision.",
"The cornea (front window of your eye) is only about 0.5 mm thick, enabling it to get the oxygen it needs via diffusion (the front half gets oxygen from the outside air, and dissolved O2 in the tear film. The back half gets its O2 from dissolved O2 in the aqueous humor).",
"The lens is not nearly as metabolically active as the cornea, so its oxygen needs are much lower. The oxygen it needs, it gets via diffusion from the aqueous humor (eye fluid)."
] |
[
"Nuclear Caddy pretty much nailed it.",
"The fact that your cornea does not need or have blood vessels in it, also means the body's immune system also has much more limited access to the cornea. This explains why a corneal transplant from person to person in 1905 was (more or less) the first successful transplant, since the host's immune system didn't recognize the graft as foreign and kill it.",
"",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1857444/"
] |
[
"Yep!",
"That said, it can last a lot longer on a little bit of oxygen.",
"The scary one is Contact Lenses. This is part of the reason why you have to change your contacts, since wearing them too long can damage the cornea easily."
] |
[
"Tap water looks a bit grey on 11th floor. One roommate says its the chemicals, the other says its the building pipes pressure that makes small bubbles. Who is right? (We are in Santiago, Chile)"
] |
[
false
] | null |
[
"That high up, the water is pressurized by auxiliary pumps. It may very well be small bubbles, or it could be sediments in the pipes being disturbed by the higher pressure."
] |
[
"most likely from the booster pumps used to push it that high. "
] |
[
"Fill a glass and let it sit for a bit. If it clears up, BUBBLES! If it doesn't TIME TO MOVE!"
] |
[
"If we just connected Europe and America with a wire, would electric current flow through it?"
] |
[
false
] |
By connecting continents with a wire I mean just plugging it into the ground. I read somewhere that electric potential in the ground is not the same everywhere on Earth - in fact, it varies greatly. Is this true? If so, why don't we harvest energy this way?
|
[
"The OP is talking about static charge in the crust of the earth and not electricity grids."
] |
[
"Depends on the wire. Here's a handy table to look up the resistance of various gauges and lengths of copper wire.",
"http://www.cirris.com/testing/resistance/wire.html"
] |
[
"There are already optical fiber wires across oceans. Sounds like it's doable. Why doesn't it make sense? If the current is very strong, perhaps it is cost effective. I'm really curious."
] |
[
"In snowy mountain areas, avalanches occur, we all know this, but does the same happen in the desert on high dunes?"
] |
[
false
] | null |
[
"Yes, avalanches ",
"are common and are a fundamental part of how dunes behave/evolve",
". Basically, grains roll and bounce along the windward, more gentle side of a dune and are deposited at the top of the leeward, steeper side of the dune (i.e. the slip face). These grains build up until they destabilize the slip face and avalanche down towards the base of the dune. This is a fundamental part of how a dune migrates."
] |
[
"Its misleading to think of those avalanches in the same way snow avalanches occur however. Sand \"avalanches\" are never* large enough to be dangerous. Snow can form different layers with different densities and cohesions that can build up to a dangerous instability, whereas sand will slide almost immediately after reaching its angle of repose."
] |
[
"Yes, they do. They move pretty quickly (at least compared to other geologic processes), so we can actually measure their migration, ",
"e.g. this paper",
". "
] |
[
"How much man-made space debris is there?"
] |
[
false
] |
Pictures I see on the internet show space debris covering most of the surface. Obviously, the actual debris isn't that large or we'd be seeing it in the sky everyday. So, how much is actually there? What happens to it? How do we avoid the debris hitting spacecraft?
|
[
"Yes, there is that much stuff and most of it isn't that large. Space is huge compared to space debris. I'm not sure how much debris and obsolete spacecraft there are, but it's a lot, and it's mostly by chance that spacecraft aren't converted into space debris constantly. Save for the International Space Station and probably a few other craft, nothing is able to alter its course.",
"However, there is also some \"air\" in space. Not much, or else it wouldn't really be space, but enough to make a difference over time. I forget who's developing it, but it's basically a \"sail\" that is deployed from satellites after a certain amount of time that works just like a parachute does here on Earth. Once the satellite has slowed down enough, it'll be dragged into the atmosphere and burn up (or be recovered if it's designed to do that)",
"To put the danger of space debris in perspective, a fleck of paint cracked a window on the ISS!"
] |
[
"I think the other way to visualise the danger of debris is to consider the damage that ten grams of metal flying at a kilometre a second does to a person. (Hint: I'm talking about bullets).",
"Objects in orbit are traveling at around nine times that speed. Getting hit by one fucks anything up."
] |
[
"A paragraph I got off of someone a while back, don't have time to crop it but it's about a space elevator + debris.",
"\"If I were at FAA or NTSB I would be vocally worrying about the implications of the SoaceX plan to launch 4000 internet satellites in the 1200 to 1500 mile orbit range, possbly to be expanded to 7000, while another company us discussing launching another 4000 for the same purpose. These satellites will all be some 700 miles above the ISS and other items in LEO (assuming everything proceeds as planned), but that is still doubling or tripling the number of active units in orbit, and it greatly complicates routing of anything past LEO to avoid being within the risk zone formed by the geodesic orbits, which cover the earth.\nTo get a little more detailed about the SE, it's not just space junk. There are roughly 36,000 objects larger than 10cm presently being tracked, including active and defunct satellites, various launch vehicles, junk, and rocks. There are believed to be about 300,000 smaller bits that are too small to track.\nJust keeping the trackable items in mind, that amounts to 72,000 equatorial crossings per collective orbit. Orbits vary from around 90 minutes (the ISS) to geostationary (one orbit per day, synced with Earth's revolutionary period). The locations and timing of these crossings represent a chaotic (like random) distribution, that constantly varies. Any space elevator would be required to maneuver its cable system to avoid those collisions to prevent its destruction. Assuming a level distribution around the equator and averaging the orbital period linearly, roughly 3000 will occur every 60 minutes or 24 times per day = 72000, 3000 every 120 minutes or 12 times per day = 36000, and so forth for a total of very roughly 3000 * ( 24 + 12 + 8 + 6 + 4.8 + 4 + 3.4 + 3 + 2.67 + 2.4 + 2.2 + 2 + 1) = 117 * 3000 = 350,000 equatorial crossings per day. If we spread those around the equator evenly, that's about 14 per mile of equator at ground level, distributed up the length of the elevator to GEO. That's a potential impact with a softball sized object at a relative speed of Mach 10 every few seconds.\nA posting on here yesterday showed the damage created by impact of a 1/4 inch (6+ mm) ball bearing into a thick metal sheet in a simulation of an actual spacevimpact.\""
] |
[
"Why are most of the world's oldest trees found in North America?"
] |
[
false
] |
After looking at this on wikipedia, I realized that nearly all of the world's oldest trees come from North America. It is so definitive that there must be a reason backing this up. Could anyone give an explanation?
|
[
"Last continent colonised? "
] |
[
"Probably this. We humans have changed the environment around us so much that anything living on a huge timescale is likely to be negatively effected. Look at the California redwoods, now mostly gone in a single century.",
"Also, you may have noticed many of the oldest trees are pines and grow in high, dry areas where there isn't as much competition or pressure to become a huge tree which then eventually collapses. A lot of these ancient trees are still tiny!",
"Edit: I went on to see ",
"this post",
" which seemed relevant."
] |
[
"This would be my first thought as well."
] |
[
"Will chewing gum make your stomach secrete acid and enzymes?"
] |
[
false
] |
I was reading something from a natural foods book about when you chew gum that you'll release stomach acid and enzymes. Apparently when you actually eat you may be low on stomach acid and enzymes which will lead to gas and bloating. Is any of this true?
|
[
"When the acidic content from the stomach enters the first part of the small intestine, feedback mechanisms are activated that reduce the further excretion of stomach acid, and that neutralize the acidity of the partially digested food as it travels further down. Imagine it as if the small intestine tells the stomach 'okay dude, your job's done, we'll take it from here'."
] |
[
"Yes. Gastric secretion, that is secretion of acid and enzymes (pepsinogen) in the stomach, occurs or is regulated in three phases: the cephalic, gastric and intestinal phases. In the cephalic phase (cephalic comes from the Greek word for brain, ",
") which is stimulated by factors in the head and pharynx, thinking about, seeing, smelling, tasting, chewing and swallowing food will increase gastric secretion. This reflex is mediated by the vagus nerve, or ",
" in the original Latin. The point of this, physiologically speaking, is to prepare the stomach for the incoming meal.",
"I don't know specifically if being low on acid or enzymes would cause gas and bloating, but I hardly think you would be able to run low on either one: due to the cephalic phase of secretion the stomach will prepare for the incoming meal well ahead of time. And the secretion isn't really inhibited by anything other than the small intestine. Food in the stomach actually increases the release of both acid and pepsinogen. I'm not sure however, and welcome anyone who knows more to chime in :)"
] |
[
"And the secretion isn't really inhibited by anything other than the small intestine.",
"Thanks for the answer! Glad to see this sub-reddit has great comments (first time here). ",
"The only thing I didn't understand is when you said... \" And the secretion isn't really inhibited by anything other than the small intestine.\" Can you rephrase that? I must be reading it wrong or something."
] |
[
"Our Sun and Andromeda"
] |
[
false
] |
[deleted]
|
[
"First, our sun isn't going to undergo a supernova event. It's too small for that.",
"Second, while the sun's orbit about the galactic core could certainly be affected, it's unlikely that the orbits of the planets about the sun would be altered much, if at all. "
] |
[
"There will, if I remember correctly, be about 6 (six) collisions between stars when the galaxies meet. I don't think we need to be too worried."
] |
[
"Heh i'm not worried. What happens is gonna happen."
] |
[
"Do we know of some species with more than two sexes?"
] |
[
false
] |
Wouldn't having more than two sexes some evolutionary advantage like two sexes reproduction has over one? (in terms of variations,etc.) Even if that is not true why aren't species with three (or more) sexes not common?
|
[
"There are sparrows with 4 sexes",
"Fungi: Well... ",
"it is complicated",
". ",
"Really complicated"
] |
[
"Thanks for the links about the sparrows. It was a really interesting read."
] |
[
"“This bird acts like it has four sexes,” says Christopher Balakrishnan, an evolutionary biologist at East Carolina University in Greenville, North Carolina. ",
"Acts like. There are still two distinct sexes, but a chance mutation led a further differentiation due to a problem with chromosome two, leading to compatibility between a certain % of the population. "
] |
[
"Does pasta have to be boiled in order to cook properly?"
] |
[
false
] | null |
[
"Boiling increases diffusion, so it can speed up the process.",
"\nAlthough it's not essential, you can try by pouring boiling water over pasta and leave it, it'll get soft as well."
] |
[
"Water diffusion into the pasta.",
"\nAlso - heat diffusion - water is 100 C but pasta is not."
] |
[
"Diffusion of what? Heat? The water can't gain any more heat, that's why it's boiling."
] |
[
"How would an earth size planet following our exact orbital path and speed on the other side of the sun affect us?"
] |
[
false
] |
Would there even be any noticeable difference on Earth? Would it have any affect on tides, the lunar orbit, how seasons changed, or what the pull of gravity is on earth? How would it affect other planets in the solar system?
|
[
"This plot would be symmetrical if there were an Earth opposite in the L3 position. "
] |
[
"Planetary orbits are known with precision, and a body that size would perturb the orbits of other bodies.",
"Earth Two would have shown up in photos taken of Earth from the deep solar system.",
"If the Earth's orbit was more eccentric it would surely be visible from here, because of the properties of an elliptical orbit."
] |
[
"I think it couldn't be in the same orbit instead it would have to be in the earth sun L3 point. ",
"http://en.m.wikipedia.org/wiki/Lagrangian_point"
] |
[
"Are \"zero calorie\" sodas really zero calories?"
] |
[
false
] |
I find it hard to believe that the ingredients in soda will not release any heat when the body breaks it down. And if this is so, then if calories are just a measure of heat/energy, wouldn't the soda have calories? Or maybe I am just completely wrong and the ingredients don't release heat/energy when the body breaks it down. Could anyone explain it please?
|
[
"According to the ",
"FDA",
", foods with between 0 and 5 Calories are considered \"Zero Calorie.\" Keep in mind that your body is not capable of breaking down every molecule you consume. Regular pop contains a lot of sugar which you can metabolize and is thus a source of Calories. Diet pop contains artificial sweeteners that are designed to taste extremely sweet, only be present in small amounts, and not be readily digestible. So, they are not a significant source of calories."
] |
[
"The only significant contributor of calories in sodas is the sugar. Diet sodas use sweeteners that trigger sweet sensations, but do not yield any meaningful usable energy when broken down.",
"Source"
] |
[
"Yup. I acutally never thought of it like this before and my original answer was \"HELL NO!\" But then I did the math (below) and can't seem to find a reason why you would be wrong. Heck it has been a while since I have been in undergrad (for heaven's sake I was a double major bio and chem major but am not in dental school...)",
"Anywho...",
"So if we have 1 kg water, and we know that 1 kCal is present, how much of a temperature change do we see",
"Where Qwater is the heat captured in calories (1 kCal = 1000 cal)",
"Rearrange and solve for ΔT... ",
"So for 2,000 kCal/day diet",
"Please someone correct this if it is wrong"
] |
[
"In the human body, does being in (great) pain = damage?"
] |
[
false
] |
[deleted]
|
[
"No. Your sensory system can be mistaken. (e.g. ",
"allodynia",
")"
] |
[
"Yes it does. Living in chronic pain causes physiological changes to the body. This article describes the effects of pain that are experienced from all of the body's systems: ",
"http://www.nursingtimes.net/nursing-practice-clinical-research/understanding-the-physiological-effects-of-unrelieved-pain/205262.article",
"Also, autonomic dysreflexia is an example of where the body is in pain, but the nervous system is unable to process it. It can cause very serious side effects, including heart attacks. I would consider this to be an example of pain = damage.\n",
"http://en.wikipedia.org/wiki/Autonomic_dysreflexia"
] |
[
"A more interesting question is: does ",
" horrible pain alter any pathways in the brain. Any alteration of brain chemistry due to the experience itself could be called \"damage.\""
] |
[
"If lightning was fired into a vacuum, would it appear straight?"
] |
[
false
] |
Wondering why lightning is always a jagged shape
|
[
"You could not fire lightning into a vacuum. Lightning isn't a physical thing, it is the process of an electric current discharging through the air. When the sky and earth build up a difference in charge to a sufficient degree, the electrical resistance of the atmosphere is overcome and electrons flow between the earth and sky or vice versa. The glow of lightning is the air being super-heated. The forking and \"jagged\"ness of lightning is due to perturbations in the air and because the path between the sky and the earth is formed randomly. As the difference in charge builds, the electrons are constantly looking for a path to discharge through. When one of those paths connects with the ground, the sky or ground is able to discharge along that path.",
"In a vacuum, there are no atoms or molecules which the electrons can travel through. It might be possible to force the electrons to directly jump the gap, but you wouldn't be able to see this. In partial vacuums, you can form vacuum arcs, but I'm assuming you want as close to a perfect vacuum as you can get.",
"As the lightning propagates, the air is being ionized (electrons being stripped from the molecules), forming a plasma."
] |
[
"I think this is 90% right, but it might be even more clear if you mention that as the lightning propagates, the air is being ionized (electrons being stripped from the molecules), forming a plasma.",
"In a vacuum, there's no molecules that can be ionized to form plasma, therefore, no lightning."
] |
[
"Thank you, yes."
] |
[
"Carbon dating method requiring \"best guess\" before measurement?"
] |
[
false
] |
This question just came up in my Facebook feed and is most likely some sort of creationist pablum, but I checked talkorigins.org and did my best to sift thru a couple other sites but could not find info on this. Here is the original post: I work with a young Earth creationist contractor who swears carbon dating is nothing but a hoax. He mentioned that if you request an item to be carbon dated the application requires you to estimate the age of the object. It surprised me so I went to verify and he was correct that it asked, but I did not see anything saying it was required at least for the 3 sites I searched. I am awaiting a response back from the sites as to why they ask for this but was curious if anybody else had heard that. I've asked OP for clarity since it's definitely lacking, but has anyone heard of this? Is this a thing? Edit: Here's the site he's talking about:
|
[
"My guess is that an older sample will require more precise instrumentation to get an accurate measurement. If the sample is getting close to the limits of what radiocarbon dating can be used for, there will be very little C-14 left, which means that great precision will be necessary to establish the correct age, because a slight change in the amount measured will translate into a significantly different extrapolated age."
] |
[
"Well, I haven't done anything with radiocarbon dating yet, but I have a few thoughts. You do have to be able to account for the atmospheric concentration of Nitrogen-14 (I think it's N-14, it may be C-14), I believe, during deposition. Since N-14 varies, it can skew results. But we have pretty good estimates for how N-14 has varied over the past 50k years, so that's not a big deal anymore. Worst case, this variation can produce a 10% (",
") error in results. The error involved with radiocarbon dating itself has a range of .1% or .01%... I forget. Somewhere in there. Knowing an approximate age of the object probably helps a lot with letting the lab know which tests to preform (expensive accurate tests, or if quick and cheap tests will work).",
"More importantly, there are literally hundreds of dating methods besides radiocarbon dating, some of which are much, much more accurate in certain settings, and many of which lack the few flaws that radiocarbon dating has. ",
" radiocarbon dating was ",
" worthless, we still have mountains of evidence for the history of the Earth (enough to make denying it absurd). Notably, radiocarbon dating is worthless beyond 40-60 k years (depending on who you ask). It's very convenient in many situations, but it is not responsible for our understanding of geologic time."
] |
[
"It's almost certainly to do with trying to fit to the correct place on the C14 curve. The amount of C14 int he atmosphere varies with time. Without this information, you'll get a ballpark figure with a larger error on it than you would with an estimated age, which would allow more precise calibration to the curve. Of course, once an intial age has been calculated you can go back and recalculate. It's just a lot easier if the the archaeologist has a ballpark age to do that in the first place. \n",
"http://en.wikipedia.org/wiki/Radiocarbon_dating#The_need_for_calibration"
] |
[
"With the recent discovery of at least one planet around Alpha Centauri, do we have the technology to directly observe the planet to any significant degree? If not, what would it take?"
] |
[
false
] |
Say a planet just like Earth is orbiting Alpha Centauri, would we be able to observe it well enough to distinguish continents and oceans? Even more? If not, how likely are we to develop the technology within this lifetime?
|
[
"Directly observing with visible light is limited by two things:",
"The angular resolution of your telescope",
"Capturing enough light.",
"These are both improved by building a bigger telescope. I don't know the size of this planet, but let's say it's Earth-sized, and 4.37 light years away. I'll call \"observing to a significant degree\" having an angular resolution 1/100",
" the diameter of the planet. This is ",
" like taking a picture in which the planet is 100 pixels across. I said \"sort of\" because it isn't really like that at all, but we'll go with it.",
"Diameter of earth: 12756 km",
"Required spatial resolution: 127560 m",
"Distance from earth: 4.13425 x 10",
" m",
"Angular resolution: 1.768 x 10",
" degrees. Oh boy...",
"I'll give you a fighting chance and say we're using infrared rather than visible light, which has a longer wavelength. Really long wavelength infrared, like 100 μm.",
"sin(angular resolution) = 1.22 x wavelength / aperture. Your telescope needs to be 3,954 kilometers in diameter. I don't think you'd have any problem collecting enough light.",
"You don't need to have a single mirror 3,954 km across, however. You can use an array of telescopes spread out across the distance, and construct the image in post-processing. The problem is you need to know the position of each of your array elements to much better than one wavelength. This is commonly done in acoustics, with wavelengths in the millimeter to meter range, but extremely difficult in the sub-micrometer range. If you were to build such an interferometric telescope, you would be limited only by the amount of light you could capture. If you have maybe $50 billion to spare, I think you should go for it."
] |
[
"Aren't there arrays of radio telescopes all across the earth that do this same thing? So if they all pointed to Alpha Centauri, they could theoretically observe the planet?"
] |
[
"I think if you combined these you would have enough angular resolution to study the planet, but I'm not sure if radio telescopes can be configured to produce images (or if radio images are even useful)."
] |
[
"If the human eye could record video, how much space would one minute take up? (x-post from /r/AskReddit)"
] |
[
false
] |
Assuming it was being recorded at "full quality" and the highest "framerate" (for lack of better words)
|
[
"The human eye does not have a frame rate. The amount of data would be very dependent on how you sampled the signal. "
] |
[
"The eye itself uses pre-processing and compression strategies before sending the image to the brain. ",
"This article",
" estimated the bandwidth of the optic nerve to be about 8.75 megabits per second, which is around 1 megabyte per second.",
"So a minute would put you right around 60 MB. Note that the 60 MB value is compressed video for one eye only."
] |
[
"I was thinking more along the lines of a raw video feed, but this was really helpful"
] |
[
"How does obesity physiologically increase one’s cancer risk?"
] |
[
false
] | null |
[
"I can explain for some cancers.",
"Body fat which contains cholesterol can provide ground substance for producing steroid hormones one of which is oestrogen. Excess fat - > excess oestogen. In females, oestrogen has stimulator effect on breast and uterine lining-endometrium. Stimulation - > increased multiplication - > increased chances of errors in DNA. Apart from which added factors like PCOD in obesity means is unopposed oestrogen action without progesterone. Therefore obesity could lead to increased chances of breast as well as uterine cancer.",
"Obesity could also mean underlying poor eating habits. Low fibre diet, high red/smoked meat and constipation could mean the potentially carcinogenic agents remain in colon for longer, allowing more time for cancerous change. Hence, higher risk of colorectal cancer."
] |
[
"Yes they can but obese people are more likely to have larger amounts of visceral fat. ",
"Your points were sweeping generalisations which I felt mislead the person who asked the question so I thought I’d put a counter point. If you still think what you said was more accurate then it’s up to them to do their own research and come to their own conclusions based on the two sides of information we provided."
] |
[
"Yes they can but obese people are more likely to have larger amounts of visceral fat. ",
"Your points were sweeping generalisations which I felt mislead the person who asked the question so I thought I’d put a counter point. If you still think what you said was more accurate then it’s up to them to do their own research and come to their own conclusions based on the two sides of information we provided."
] |
[
"Can someone explain Faraday's Law and Lenz's Law to me please?"
] |
[
false
] |
Any explanation would be awesome, I just need a better understanding of it. Examples/Diagrams would be helpful.
|
[
"What kind of understanding of calculus do you have?"
] |
[
"A pretty good one I'd say.\nI've taken up to calculus 3 at my university and now I'm in linear algebra and differential equations"
] |
[
"What is your current level of understanding of Faraday's law? What is it that you're having trouble understanding? Did you look at some YouTube videos and Wikipedia?"
] |
[
"How can the Higgs boson be everywhere? How come we don't see it if so?"
] |
[
false
] |
I know we feel its effect, but if it's everywhere surely we should be able to see it - and anyways, how is there enough energy to make higgs bosons for the whole of the observable universe?
|
[
"Nah, the Higgs boson isn't everywhere. Higgs bosons are pretty rare.",
"The Higgs' vacuum expectation value (VEV) is everywhere and it's pretty big. We don't see it because it doesn't couple to photons, which is why photons are massless. It gives mass to the other fermions and bosons, and that's all it does at low energy.",
"Btw, you need ",
" energy to have the VEV turned \"on\" than switched off, which is why it's on in the first place."
] |
[
"sort of, it's the value that the Higgs field has in the ground state. For most fields, that's zero, not so for the Higgs field."
] |
[
"Sorry, what's a Vacuum expectation value? Is it like the default state of the Higgs field?"
] |
[
"How does a magnifying lens concentrate heat from sunlight along with the light, and do so without getting hot itself?"
] |
[
false
] |
i've been playing around with this fresnel lens i took from an old projection tv and i started wondering how the heat from sunlight could be condensed.
|
[
"Lenses don't concentrate heat, they only concentrate light. The effect you're noticing is that the light gets converted to heat when it strikes a material. "
] |
[
"It's easier to talk about a round glass lens than a fresnel lens, so I will. But first some theory.",
"Light heats a material because the electron cloud of a material will absorb some particles of light and the energy they carry (I mean they're moving pretty fast, there's a lot of energy to dissipate). Materials which absorb a lot of light heat up more; I always buy white cell phones because I live in California and the black ones overheat when I go outside. (Depending on your knowledge of light, \"black\" is the perception of all the light particles being absorbed and \"white\" is the perception of reflection.)",
"A transparent material is one which does not absorb many light particles (or any, if it's good). However, the light is still passing through ",
" and depending on the material its course will be altered. In glass, particularly if the surface is smooth, the path of light is not altered much; so little you can still make out an image on the other side. Milk jug plastic (low density polyethylene I think) is a different story; it's rough and scatters the particles so you can't see a detailed image.",
"So while a glass lens doesn't really absorb light, it does redirect it. A well carved lens points the particles inward toward a central point (which is three dimensional, it's not only at the center of the lense but a certain distance from the lens which is pretty easy to calculate). If you put something at that focal point, a shit lot of particles strike it all in the same place, many are absorbed, and things get hot.",
"Think of it like a gravitational deflection. Imagine there's an interplanetary war between the Jovians and the Venutians, and it just so happens that Earth is sitting between the two. The Jovians could launch a ring of missiles around Earth and they would all curve inward due to our gravity and destroy the shit out of one spot on Venus. Interestingly this actually happens to light; you can occasionally see stars which are behind the Sun because it curves the light they emit inward toward Earth. This is of course pretty difficult to observe without a really good telescope. See: gravitational lensing."
] |
[
"As gammalbjorn alluded to, some of the energy in the sunlight is actually absorbed and converted to thermal energy in most lenses. Not all the visible light is transmitted - maybe 15% is absorbed. Also, depending on the type of glass or plastic, much of the infrared and UV wavelengths are absorbed in the lens. (Here's a ",
"plot",
" of light transmitted vs wavelength for one type of glass.)",
"But this absorption is spread over such a large area that the lens loses energy fast enough (by heating up the air around it and through thermal radiation) to not increase its temperature by a large amount. If you left it outside for a few hours on a hot, sunny day, though, I'm sure it would be noticeably warmer.",
"If you want a great layman's explanation of how lenses work, I'd recommend reading Feynman's book QED."
] |
[
"If warm water has energy that can be used, does frozen water also have energy?"
] |
[
false
] | null |
[
"A heat engine requires two reservoirs at two different temperatures to extract work. A heat pump is a heat engine in reverse. You are expending work, not extracting any."
] |
[
"A heat engine requires two reservoirs at two different temperatures to extract work. A heat pump is a heat engine in reverse. You are expending work, not extracting any."
] |
[
"Warm water doesn't have energy that can be used unless you have something colder as well. You can only get energy out of a temperature ",
". Transferring heat from a hot thing to a cold thing gives you usable energy. But a system where everything is at the same temperature has no usable thermal energy regardless of what that temperature is."
] |
[
"Why does time have a direction?"
] |
[
false
] |
really, I'm just curious about time in general. Please don't refer me to a particular book for information, I don't really have time to research in depth. Condensed answers are good enough
|
[
"Because not all processes are invariant under time reversal. On human scales entropy increase is the most noticeable example, but there are others too.",
"Or do you mean some kind of philosophical why? We can't really help you there."
] |
[
"Further to your comment, the 2nd law of thermodynamics is an axiom. We have no way to prove that entropy is an intrinsic law of nature other than it is a feature we continue to see over and over again. ",
"Philosophy of science seems like an interesting thing to argue, but at the end of the day it usually gets you nowhere.",
"*damn spelling"
] |
[
"Well considering that all systems increase entropy, it is no suprise that we perceive the arrow of time in the direction we do. Human beings need to increase entropy to function, therefore the more chatoic path is the \"down stream\" side of time for us. If there was a being that ran off a decrease in entropy then the arrow of time would point the other the other direction (our past would be its future) for that being. Thankfully, the second law banishes this alien being to philosophical discussions like this... well except for Benjamin Button and Merrlin of course."
] |
[
"What's past the cosmological horizon?"
] |
[
false
] |
Do we know what's past the cosmological horizon in the un observable areas of the universe?
|
[
"By definition, no; the observable universe encompasses all that we can have any information about. But there's no particular reason to imagine it would be much different from the local area--it's just impossible to confirm."
] |
[
"As the universe is the same everywhere we can look it should be the same in places a bit farther out as well. But this is purely inference, we can't observe it by definition."
] |
[
"The definition of the cosmological horizon has it that it is the furthest we can have information from; there's no way of knowing about anything further. The ",
" is that it's just more space, the same of here, nothing of interest. From there you can speculate on things such as the ",
"shape of the universe",
", but so far there has been no experiment to suggest that the universe is anything but boring and flat."
] |
[
"Is string theory relativistic?"
] |
[
false
] |
Is string theory Lorentz invariant or is someone going to have to reconcile that later after they better understand what it is?
|
[
"String Theory obeys relativity and concepts like Lorentz invariance."
] |
[
"String theory is meant combine quantum field theory and general relativity. Both require Lorentz invariance, so string theory would naturally have it as well.",
"I can't imagine any unified theory not incorporating it as well."
] |
[
"The reason I wonder is that I have read that string theory is not background free and remains a purturbative theory. Not understanding that very well I wondered if it implied that string theory, as currently formulated, is not Lorentz invariant.",
"OTOH, as you say, if it successfully becomes a theory of gravity it will have to encompass general relativity which has special relativity with its Lorentz invariance as a limited case in regions where gravity is extremely weak."
] |
[
"When turtles pull their heads into their shells, do their spines buckle or contract?"
] |
[
false
] |
I was reading Cat's Cradle and I stumbled upon this fascinating question. Unfortunately, it was left unanswered. If they neither buckle nor contract, then how do they get it all to fit?
|
[
"Good question. There are actually two answers to it. Two main suborders of turtles exist - Cryptodira...most turtles and tortoises that you encounter including freshwater turtles, snapping turtles, tortoises, soft shell turtles, and sea turtles actually lower their head and contracting their vertebrae to allow the head to go beneath their spine, completely hiding the neck. Pleurodira is the other suborder which are more commonly known as side-necked turtles that fold their head sideways along their body and into one of their leg compartments, leaving part of the neck exposed. "
] |
[
"Nice answer - just to add a clarification, in cryptodires the vertebrae don't \"contract\" exactly; the neck just deepens its bend in the vertical plane (as opposed to side-necks in which the neck bends in the horizontal plane). When a cryptodire pulls its head in, the neck basically goes from ",
"this position",
" to ",
"this position",
" - and the neck can actually go a bit further back than shown in the 2nd diagram. PS the 2nd link is from a blog with a great summary of recent fossil turtle discoveries & the evolution of the turtle shell."
] |
[
"All vertebrates have spines. In turtles its ",
" the shell, but it's still there."
] |
[
"I do not understand the nature of light... I do not know what I do not understand about it either..."
] |
[
false
] |
So, I'm looking at a star -- say the North Star. Now, I understand that there is a stream of particles (waves?) flowing from the surface of the North Star straight into my eyeball... Also, the light emanating from Polaris is moving out in all directions from the surface of the star. ( I imagine a sort of shell of light [composed of trillions of photons] pulsating from the star, the thickness of a photon, over and over again.) How is it that I can look in the sky and see the North Star as a of light... I assume it has to do with the surface area of the star (how many photons are being emitted) and the size of a photon and in relation to the size of my eye -- But, I really don't get it...
|
[
"Imagine that the surface of the North Star is spherical. Now, pick any point on the surface of that sphere, and draw a line from the very center of the sphere, through that point on the surface, and continuing outward. Now, imagine that there are lines like that coming out of every possible point on the surface of the sphere. If the lines go on forever until they hit something, some of them will be pointing directly into your eye if you look in the right direction. Now, imagine that the lines are photons. I'm not sure how many photons are in the \"point\" of light that constitutes the view of a star from earth, but I fairly certain that it's greater than 1 and less than what you would see during the day. I'm also fairly certain that multiple photons are emitted from the same point on the surface many times, so rather than the pulse of a shell of light you imagine, it's more of an enormous number of extremely tiny pieces of a shell flying out over and over.",
"So, some relatively small (compared to daylight) but still greater than 1 number of photons hits a spot on your eye. Your eye has nerve cells that are able to detect if a photon hits a certain molecule called an opsin. When the photon hits the opsin, the molecule changes shape. Sufficient opsins changing shape in a single nerve cell will cause it to signal to other nerves in the eye that it detects light. If enough cells in a certain area detect light (and the cells next to the detecting cells DO NOT detect any light), they will relay the signal onward and tell the brain that there is light in one area of your field of view. Because the nerve cells in the eye relay which are detecting light and which are not, the brain can detect edges between light and dark (also I think that's how colors work, not positive). There are only so many opsins on only so many nerve cells in your eye, and the number of photons coming from the North Star is only so many to what the eye normally deals with, so only a very very small proportion of nerves detect light. I think that this keeps us from discerning an \"edge\" on the starlight and makes us see it at a \"point.\""
] |
[
"How is it that I can look in the sky and see the North Star as a point of light…",
"Because your eyes have lenses in them that focus the light that intersects them, forming an image.",
"It's the same basic idea as exposing a piece of photographic film to light, versus putting it behind a lens. In the first case, you get a more-or-less uniform blur; in the second case, you get an image."
] |
[
"That still doesn't make sense to me... I think it has something to do with the <refresh rate> or whatever you would call it biologically... For instance, if you do a long-exposure you get light trails... Those light trails seem to be a more reasonable depiction of reality than what we actually perceive. ",
"There is a solid stream of photons flowing in 360",
" from any visible object, yet we see a consolidated point that is the object. This is confusing to me... "
] |
[
"Why do I feel better after vomiting even when what caused the nausea has long since been digested?"
] |
[
false
] |
I meant to ask this question this morning, but decided to go back to bed instead.
|
[
"I know we aren't supposed to make off topic comments but it makes me smile that your title includes complex fluid engineering and you're commenting on vomiting. I'm also easily amused and it's been a long day."
] |
[
"When you vomit, ",
"endorphins",
" flood your bloodstream, making you feel much better. It's a weird kind of natural high, I suppose you could say.",
"As for citations, ",
"wikipedia",
" mentions this, as does that endorphins article I linked, but I can't find much material more scientific than that. This effect has also been ",
"linked to bulimia",
" (maybe that counts)."
] |
[
"Anecdotally, about twice a year I will get severe migraines that last for >6 hours. The only relief comes when I eventually vomit. ",
"And when it happens, I feel GREAT afterward from a combo of pain relief and apparently the endorphins that are released. I also develop a raging appetite and elevated mood. ",
"Great links and thanks!"
] |
[
"Do paper toilet seat covers really work?"
] |
[
false
] |
You know, the ones you find in the better public bathrooms. They're made basically out of toilet paper and they're shaped like a toilet seat, and you put it over there. How effective are they for shielding you from bacteria and the like? Or is it just there to make me feel good?
|
[
"Interesting fact for you but the typical toilet seat is cleaner than the typical computer keyboard or the typical paper bill, or really anything else you handle with your hands alot. Hands are one of the big ways that we pick up and transmit bacteria. Toilet seats just don't get touched alot not to mention the material they are made of isn't really an ideal living area for stuff.",
"Also as someone with janitorial experience I can tell you right now that that flimsy little piece of paper isn't doing crap to stop any piss on the seat from getting on your skin. They aren't exactly waterproof and they tear if you so much as look at them wrong. Not to mention they usually sit right next to the toilet which has been spraying microscopic urine and fecal particles all over them each time that toilet was flushed.",
"On the plus side getting urine or feces on your ass probably won't do you much harm, your skin is a pretty good barrier against keeping stuff like that outside your body where you can just wipe it off. Really the only thing those covers do is give you an unneeded false sense of security."
] |
[
"[citation needed]"
] |
[
"[citation needed]"
] |
[
"What is the aluminum-foil-looking material on spaceships, and what does it do?"
] |
[
false
] |
[deleted]
|
[
"I think you are referring to Multi-layer insulation (MLI).",
"\nIt consists of several layers of thin opaque foils which are kept separate by layers of webbing or by letting the outer layers crinkle, thereby reducing the thermal conduction significantly.",
"\nTherefore the only way of heat transportation left in space (since there is also no convection) is heat radiation. Radiation is a relatively bad transportation method, and each two separate layers of MLI provide a huge hurdle for the transported heat.",
"\nThereby, MLI insulated the spacecraft against loss of heat into space or overheating due to solar radiation.",
"\n",
"https://en.wikipedia.org/wiki/Multi-layer_insulation"
] |
[
"I don't know that brand of bottles, but normally for everyday applications other types of insulation is used, e.g. just a foam material to hinder conduction and a reflective surface to reduce absorption. Expensive and sometimes sensitive materials like MLI are not needed there.",
"\nMLI has the advantage of being very light weight for a given insulation requirement especially if the temperature gradient is large. It looses a lot of its insulation when it is not in a vacuum, since then conduction through the air in the layer spacing can again be dominant over radiation effects.",
"\nThe MLI variants which just crinkle the reflective layers to reduce the conduction instead of using extra spacing layer are also sensitive to compression, as then you just press all the metal reflective layers together and therefore create a very good conductive path for the heat. "
] |
[
"So my CamelBak insulated water bottles have space technology in them?"
] |
[
"What is multiplication ?"
] |
[
false
] | null |
[
"From a purely computational standpoint, this in a sense boils down to how one explains multiplication by fractions, such as 0.7 * 2. Clearly that is 0.7 + 0.7, but it is also 7 * 0.2 = 0.2 + 0.2 + 0.2 + 0.2 + 0.2 + 0.2 + 0.2, where all we're really doing is playing around with powers of ten. Once you understand how to represent a fraction in terms of powers of ten, multiplication by fractions is very similar to integer multiplication. I'll show below how we can use this to retain the interpretation that multiplication is repeat addition:",
"e ~ 2.72, π ~ 3.14",
"e x π = 2.72 x 3.14",
"2*(3 + 0.1 + 0.04) +",
"7*(3 + 0.1 + 0.04)/10 +",
"2*(3 + 0.1 + 0.04)/100 = ",
"3 + 3 + 0.1 + 0.1 + 0.04 + 0.04 +",
"0.3 + 0.3 + 0.3 + 0.3 + 0.3 + 0.3 + 0.3 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.004 + 0.004 + 0.004 + 0.004 + 0.004 + 0.004 + 0.004 + ",
"0.03 + 0.03 + 0.001 + 0.001 + 0.0004 + 0.0004 = 8.54",
"Edit: I should say that this is just an explicit example which shows that multiplication as repeat addition makes sense for fractions. I'm sure there is some other explanation as well, which more directly answers your question, ",
"."
] |
[
"Sounds like you want to take a class in real analysis. The really quick answer is that your definition works for rational numbers, and we extend that to irrational numbers by defining them as limits of sequences of rationals.",
"Here's a bit longer answer, but you'd likely need at least the first few chapters of a real analysis book to make sense of it. You construct the real numbers from Cauchy sequences of rational numbers. (Equivalence classes of Cauchy sequences with the same limits, to be precise.) For multiplication, you just create a new sequence by multiplying the elements (pairwise) of the two multiplicands. Proving that this is also a Cauchy sequence is easy. ",
"In general terms, think of it as writing e and π to ",
" decimal places. Then your repeated addition definition works fine. Now do it for ",
"+1 digits. Show that as we add more digits to the multiplicands, the product doesn't change until (say) ",
"-1 digits. So we can compute the product to arbitrary precision just by starting with enough precision in the multiplicands. "
] |
[
"It is easy to understand a multiplication as the area created by the factors of the multiplications. For example, e x π would be like the area of a rectangle that has a side e and a side π",
"....e.....",
"| e x π | π",
"|..........|",
"There are a lot of super nice videos in ",
"this youtube channel",
" that helps to visualize and understand mathematics in a way you will be fascinated :)",
": ",
"This",
" is the relevant video that tackles this problem!"
] |
[
"Was I smallpox vaccinated in eastern europe in the late 90s? If not, what are these scars?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed.",
"We do not offer ",
"medical advice",
" on ",
"/r/AskScience",
". Please see our ",
"guidelines.",
" If you have concerns about your or someone else's health, you need to speak to a medical professional.\nWe also cannot evaluate the safety of commercial products or how healthy a specific practice is.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Probably BCG"
] |
[
"confirmed, asked fellow eastern european who did not get it due to allergy"
] |
[
"Is the sleep you get after being really drunk (i.e. passing out) the same as a regular night’s sleep?"
] |
[
false
] |
Do you go through the same stages? Do you stay in a certain stage longer?
|
[
"No, it isn't. Alcohol causes problems with the placement and duration of REM stages, causes disruptions in sleep maintenance, as well as problems with SWS stages. It isn't the same for everyone, and it actually depends on how much alcohol a person has had.",
"EDIT:",
"For those asking about ",
"cannabis and sleep."
] |
[
"The point isn't whether you pass out or whether you fall asleep intentionally; alcohol, regardless of the quantity, changes sleep architecture. The problem is that there is a lot of disagreement about what the effects are and at what dosing. Having one drink, and then going to bed 3 hours later should have very minimal impact on sleep, although some research shows that it can actually alter total sleep time. There are too many variables to completely describe here, but it also matters if the person is a chronic drinker or not. Consecutive nights of sleep after drinking will be different than a single night of sleep after drinking. "
] |
[
"Guess I'll put on the \"Mod Hat\" as well. ",
"This is ",
"/r/askscience",
". ",
" Thanks!"
] |
[
"What would the perspective an observer going near-light speed look like?"
] |
[
false
] |
I understand that, according to Einstein's Relativity, the closer one gets to the speed of light, the slower time moves for them (relative to our perspective here on Earth, for example). If we were to theoretically look at them, we would see them move extremely slowly because they experience time at a much different rate than us. But let's say we were the travelers. What would we see if we were theoretically able to stably observe the world moving past us? If we were able to observe Earth? Would it look like Earth, and everything on it, was moving in fast motion?
|
[
"They would play \"catch up\" and see a bunch of photons they had almost been outrunning catch up to them and light coming from Earth would go in fast-forward (well, at least compared to the way it looked on the way out) until they got back to Earth, resolving the paradox.",
"That's not what resolves the paradox (not that there is one, really, to resolve).",
"If you ignore the light travel delay of photons, then the ship would still see (as in calculate) that clocks on Earth are running slow on the trip back.",
"What resolves things is that, during the mid-point of the journey when the ship turns around, clocks on Earth run faster (literally) - what the ship considers to be \"now\" on Earth swings into the future. Once they stop turning around and are now coasting again, clocks on Earth go back to running slow, but that slowness isn't enough to undo the speed-up during turnaround.",
"What Earth calculates to be happening is that the ship's clock runs slow on the way out, comes back (momentarily) to normal at turnaround, then runs slow again on the way back."
] |
[
"You're thinking of the two clocks as ticking like this:",
"|---|---|---|---|---|\n|----|----|----|----|\n",
"Both in the same \"direction\", with one ticking slow, and, therefore, necessarily, one ticking fast.",
"But relatively-moving clocks in special relativity don't tick like that. They tick along different \"directions,\" and when you project (i.e., consider what is \"now\") from timeline to another, then each timeline sees the other as running slower. It's like two people both being able to stand on each other's left, if they face different directions.",
"This diagram sort of explains it (but is not quite true to reality, because reality is more complicated than this):",
"http://i.imgur.com/MUsAtRa.png",
"It shows how, from their own perspectives, both the Earth and a muon flying through Earth's atmosphere see the other reference frame as running slow."
] |
[
"Paradoxically the traveller would also see Earth going in slow-mo. It breaks intuition, but that's what GR says would happen. Both frames of reference perceive the other as being slow.",
"Now if the traveller were to stop and turn around and come towards Earth, then it gets interesting. They would play \"catch up\" and see a bunch of photons they had almost been outrunning catch up to them and light coming from Earth would go in fast-forward (well, at least compared to the way it looked on the way out) until they got back to Earth, resolving the paradox.",
"Interestingly, Earth would also perceive them as going slow on the way out, and then time speeding up on the traveller's journey back to Earth, just not enough to compensate for the \"time lost\" by the traveller due to their relativistic motion.",
"The traveler and the people on Earth would agree that the traveller had aged less than the Earthlings.",
"I hope this helps. "
] |
[
"Are two individual carbon atoms identical in every way or are they each unique?"
] |
[
false
] | null |
[
"Adding to what others have been saying here, assuming you are talking about two atoms of the same isotope with the same charge, they have to be indistinguishable to resolve the ",
"Gibbs Paradox",
". If they were different, you could come up with a system that violates the Second Law of Thermodynamics."
] |
[
"There are different isotopes of carbon, but I don't think that's your question. Two C atoms of the same isotope are going to behave like each other chemically, and if you take carbon-14 atoms, each is just as likely to decay as the next, in a given amount of time.",
"Does it really matter if they're unique, if they're close enough to identical that we can't distinguish them based on behavior? "
] |
[
"From my understanding, yes.",
"All atoms of the same type are completely identical in terms of structure. There is only one real way that atoms could ever be 'classified' and that is by their probability to radioactively decay. But the beautiful thing about radioactive decay is - it's like flipping a coin. It doesn't matter how many times you flip the coin, the odds are always 50/50. So even if you had an atom of tritium that was created 50 years ago (half life of tritium is ~12yr), and an atom of tritium that was created 10 seconds ago, they both have the exact same chance of decaying into a He(3) atom and a beta particle in the next 10 seconds. ",
"That's why you can radio carbon date a GROUP of carbon atoms, but you cannot radio date a SINGLE atom because the result would be meaningless. "
] |
[
"Is it likely that a monocyclic HCN-pentamer could form adenine in interstellar space?"
] |
[
false
] |
My textbook describes Aminoimidazolecarbonitrile as a precursor to adenine. I see here there was a study done by Glaser,R in a 2007 article called "astrobiology 7:455-470" Is there anyway I can look up this mechanism? Ive tried google and nothing is showing.
|
[
"So in grad school we actually looked into this. Its really a bitch of a problem. ",
"Linked here is a paper we wrote.",
"The problem with complex molecules is they have to survive a lot of improbable situations. This makes predicting the chemistry extremely difficult. Even the best calculations for the dynamics of what can be produced in the ISM at the moment are flat out bad (they are getting better but they are still based off too many parameters that are just assumptions and end up orders of magnitude off).",
"We were able to detect the HCN dimer which leads one to believe that the possibility of higher order systems can and will be formed. The downside is the likely mechanism doesnt start off the way we did.",
"Edit: there are several different synthetic routes. The difficult part, for astrochem, is getting rid of that excess energy when a bond is formed. Thus often there has to be something that falls off to carry away a lot of the energy or the process must occur on grains (ignoring gas phase IVR)."
] |
[
"Strange, because I found ",
"a pdf",
" of that article very quickly with google.",
"It's a theoretical study (of the kind I do, really). To answer your question, I don't think it's very likely with the mechanism given. It involves very energetic intermediates to the extent that it'd simply never ever happen purely thermally. They're arguing that maybe it could happen through photoexcitation, but that both involves a whole bunch of additional assumptions, and is less likely to happen even if it can.",
"(I might also add that I generally feel that raising the possibility of reactions occurring through photoexcitations and in interstellar space is more of a thing theoretical chemists do to justify their work when it turns out the mechanism they studied just wouldn't happen under ordinary conditions. I can't say I'm entirely guiltless of doing that myself)"
] |
[
"To expand on your high energy comment. The general rule of thumb is that any reaction that happens in space is going to have to have barrier of around 0 or <0 kcal. The reaction pathway in the paper has one barrier at 75kcal which is way way way way below the available thermal energy .",
"The annoying thing is you can throw in reactions in ices which have local heating, photon bombardment, cosmic ray bombardment and etc so that you can get around some of these things but that barrier is still even extremely high for those processes to be efficient.",
"If you want math then you can break out the Arrhenius equation and ignore the exponential prefactor for now (for astrochem the prefactor is roughly the collisional rate or ~1/1000000 1/s). Here its e",
" KT at 100K (typical hot core temp) is ~70cm",
" or 0.2Kcal/mol and the barier of 70kcal is roughly 24500cm",
" . That gives us the equation of e",
" which comes out to 9*10",
" This means that everytime a molecule collides it has that probability of reacting, in this case that number is essentially 0. ",
"At that rate it would take 10",
" or 10",
" years (longer than the age of the universe) for a single molecule to react past that stage."
] |
[
"If light is red-shifted due to the expansion of the universe, does that mean that its energy is not conserved?"
] |
[
false
] |
As space expands, photons travelling through it increase in wavelength. But isn't an increase in the wavelength of light the same as a decrease in its energy? Does that mean the universe is losing energy as it gets bigger? And if not, where does that energy go?
|
[
"Energy is not conserved in expanding universe models. It's my understanding that the energy lost from redshift is just lost. The reason is that Noether's theorem tells us that conservation of energy is derived from a time translation symmetry. ",
"The standard model of cosmology",
" is not invariant under time translations, so we wouldn't expect it to conserve energy. "
] |
[
"simplistically it's an issue of energy v. energy density... but it's actually complicated to the point of unasking the question. very zen actually.",
"http://preposterousuniverse.com/writings/cosmologyprimer/faq.html#energy",
"http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html"
] |
[
"First answer: From a Newtonian perspective energy is conserved. Photons lose energy, but since they have a pressure, they do PdV work in expanding the universe. These two factors exactly cancel out.",
"Second answer: From a GR perspective, there is no such thing as a conserved quantity called energy, because the FRW metric doesn't have a timelike Killing vector. (Same thing jimmycorpse said)."
] |
[
"Why does an electric toothbrush need to operate in such high RPM?"
] |
[
false
] |
What is the reason that electric toothbrush operate at so high rpm? What is the science behind it?
|
[
"The reason for a fast rate is simple inertia. If it was slow, the bristles would not \"flick\" the food particles off as well."
] |
[
"I don't think the toothbrush head itself is actually spinning, it's only going back and forth extremely quickly without actually completing a whole turn.",
"Although there is a motor inside of the toothbrush and it's the ",
"cam and gear unit",
" that converts the high-speed spinning motion of the brush's electric motor into a back and forth brushing motion which is what cleans your teeth more efficiently. "
] |
[
"If you're talking about ultrasonic toothbrushes, this higher speed increases the frequency of vibrations needed for breaking up biofilms made by plaque bacteria and the calcified deposits of tartar they leave behind."
] |
[
"How much \"gravity\" is there around the Earth's core?"
] |
[
false
] |
Ok, so I got this idea from watching "The Core" - not one of the most scientifically accurate films, I'm well aware - during a scene in which our heroes are trying to handle some very heavy equipment inside a ship that's floating in the Earth's outer core. The ship bucks, and the equipment falls and breaks someone's leg. And that got me thinking - how heavy would the equipment actually be at those depths? Let's assume that you managed to get an airtight capsule that was strong enough to withstand the crushing pressure at that depth, and pressurized so that the air inside wouldn't kill whoever was in it, and place that capsule somewhere inside the Earth's liquid outer core, and placed, say, a 1kg weight on a measuring scale inside it. How different would 1kg weigh at the Earth's outer core compared to the Earth's surface? In a sealed environment that allows anything inside to ignore the force of the pressure around it, does gravity get stronger as you get closer to the core (since it gets weaker the farther you get from the Earth), or does it get weaker because you're only being drawn towards the core, which, while hugely dense, is still a smaller amount of the mass that accounts for the gravitational pull of the Earth? Again, I know "The Core" isn't really the film to be pitching any type of serious physics question at, but it struck me as an interesting thought experiment. Has already tackled this issue before?
|
[
"As mentioned in a different answer, inside a hollow uniform spherical shell you feel no net force from the shell, no matter where inside it you are. It perfectly balances.",
"Outside a uniform hollow spherical shell, it behaves exactly like a point mass at its own centre with the same mass.",
"Therefore, as you tunnel down inside the Earth, you feel a force only from the volume of Earth at a greater depth than you. Since the gravitational force from a point scales with 1/r",
" and the volume, and therefore mass, below you scales with r",
" the force felt scales with r.",
"This means that below the surface of the Earth, assuming it's uniform (it's not quite, but it's close), the force of gravity drops linearly from its maximum value at the surface to 0 at the centre."
] |
[
"Oddly enough due to the high density of the Earth's core, if you could walk around the Earth's outer core you'd experience an actual maximum in your acceleration due to gravity of ~10.7 m/s",
" . ",
"(Dziewonski & Anderson, 1981)",
" This is known as the Preliminary Reference Earth Model (PREM).",
"calculated"
] |
[
"does it get weaker because you're only being drawn towards the core, which, while hugely dense, is still a smaller amount of the mass that accounts for the gravitational pull of the Earth?",
"Pretty much. Check out the ",
"shell theorem",
": A solid, spherically symmetric body can be modelled as an infinite number of concentric, infinitesimally thin spherical shells. If one of these shells can be treated as a point mass, then a system of shells (i.e. the sphere) can also be treated as a point mass.",
"Earth is only an approximation of this, since it's not a perfect sphere of non-constant density, but the concept is the same. The gravitational pull from the mass closer to the surface cancels that from the other side of the Earth, so you're only attracted by what's below you."
] |
[
"Why do these biotite crystals have blurred edges in thin section?"
] |
[
false
] |
[deleted]
|
[
"You would probably get more traction over at ",
"/r/geology",
" (where you can post images). Without knowing exactly what you're describing, my guess would be it's simply a product of the orientation of the biotite grain with respect to how the thin section was cut and/or an effect of \"seeing through\" a less opaque portion of another mineral that overlaps or underlaps (remember that thin sections do have thickness). In terms of cleavage, basal sections will have no cleavage, looking up examples of biotite in thin section might be helpful e.g., ",
"this page",
"."
] |
[
"By blurry do you mean rounded? Like if the crystal habit looked like a “rounded rectangle” instead of perfect sharp corners? That could actually just fall out of the Wulff construction for crystal habits but I’m not sure what it actually means for the conditions in which the crystals were grown except the surface energy (crystallography-dependent interfacial energy between the crystal and the surroundings) had some extra term messing with it making planes less favored."
] |
[
"Thank you for your reply, really helpful! The biotite does overlap quartz, so could it possibly just be the way the section is cut, that it’s just slightly see through around the edges, and not actually anything characteristic of the Crystal itself? Thanks again!"
] |
[
"Whats going on in your body when you get the irrational \"I feel like something is behind me\" feeling?"
] |
[
false
] |
I'm sure everyone has gotten this at some point. Its the uncomfortable feeling you get maybe if its late at night, where it feels like someone is behind you. Its an urge that can only be satisfied by turning around and checking. What is going on internally when this happens and what causes it?
|
[
"Humans evolved in the wild. We were not always so completely safe from other predators. People who developed a good response to the possible threat of a predator typically survived long enough to reproduce and pass on those traits. What you consider as irrational now may have been a perfectly justified response when our ancestors roamed and foraged. Having an instinctual response to a possible risk of predation is commonly seen in other animals ranging from fairly basic animals right up to primates. It's a fairly basic response, except in humans it has developed as a complex state of alarm and corresponding changes to things like adrenaline release, feelings of anxiety and paranoia, goosebumps which (were we to have hair like apes) would make us look bigger and more threatening, also blood in your body is redirected from your gut and viscera to your limbs and brain to allow fight or flight. This is your sympathetic nervous system engaging."
] |
[
"There are two main functions for goosebumps. By making your hair stand on end, you trap a layer of air between the individual hairs (if you were a hairy ape) and so it acts as additional insulation. That's why we get them when we're cold. The other reason is to make yourself bigger and more threatening. This behaviour is found in most mammals and other animals as well; some will puff up, others like cobras have flaps on their flank etc."
] |
[
"It's an involuntary response that's associated with the activation of your sympathetic nervous system. Deriving pleasure from music, activates the reward pathway in the brain and in turn leads to activation of the system. But this is just something I covered briefly in one of my modules at Uni so I'm probably not the best person to give you a detailed answer. I'm sure it has been asked on here before, so you can try searching."
] |
[
"How accurate are the fuel pump meters at gas stations?"
] |
[
false
] | null |
[
"Most states in the US require the fuel dispensing pumps (and any scales used for commerce, under generally the same regulations) to be inspected annually or so. You'll usually see a rather prominent inspection sticker. ",
"Here's a Car & Driver article on it: ",
"http://www.caranddriver.com/features/the-pump-police-feature",
" -- in Michigan anyway the standard is 0.5%"
] |
[
"Every pump I've ever seen has had a sticker on it labeling when it was last inspected. I'm pretty sure that if even one was to be found significantly off, a politician's opponent would lambast him in the next election.",
"Therefore, logically, I predict they are at least somewhat accurate. It isn't like it's difficult to make very accurate liquid flow rate meters these days."
] |
[
"I think this question is better suited to ",
"/r/askengineers",
" or even just ",
"/r/answers",
" "
] |
[
"Hey, Reddit! If an explosion happens in a cloud, how is the cloud effected?"
] |
[
false
] |
Title about sums it up. Does the explosion propel the matter of the cloud outwards, therefore dispersing the entire cloud, or what?
|
[
"Does the explosion propel the matter of the cloud outwards, therefore dispersing the entire cloud, or what?",
"The explosion creates a pressure wave through the cloud. It does get pushed outward a bit, but generally there isn't enough gas released to really cause the vapor to be significantly displaced. Depending on the strength and speed of the explosion the pressure wave might force water vapor to condense into droplets, but that would probably be confined to a relatively small portion of the cloud.",
"Overall the cloud probably wouldn't be significantly affected."
] |
[
"I lose all of my photos and most of my music"
] |
[
"The cloud will just ripple like water."
] |
[
"Why do LCD readouts, such as digital clocks, appear to \"bounce\" when you view them and chew at the same time?"
] |
[
false
] |
I hope that others have also experienced this phenomenon. I could understand that the force of our jaw is enough to cause our eyes to vibrate somehow, but why is it so pronounced in these circumstances?
|
[
"Here's the key; only one segment of the display is on at a time. This is because only a fixed amount of power is available to the display, so the number 8 (made up of 7 segments) would otherwise be dimmer than a number 1 (made up of 2).",
"They cycle through so fast that they appear to be continuous... but when your eyes are moving at a relatively high speed, the segments are in relatively different places. Since they're intense and separate, they appear to jiggle more than the surroundings.",
"If the display were moving in a straight line very fast, you would see the effect there as well."
] |
[
"Oh okay good. I thought you were sitting on the couch watching the evening news with a vibrator on your head."
] |
[
"CRTs work in a similar way, and you can recreate the above example of the display moving in a straight line very fast with an oscilloscope. This actually messes with me often at work when I think I see erratic movements on my scope, but it was just me clearing my throat."
] |
[
"Question about determining the expected activity and dose rate from a sample of fissile material (U-235 or Pu-239 in this case) exposed to a flux of thermal neutrons?"
] |
[
false
] | null |
[
"I figure that the best way to do this would be to sum through the entire list of fission products, weighted by their fission yields, using the standard neutron activation equation to determine the activity at EOI.",
"As far as I know, this is the only way to do it.",
"But you should try a more specialized nuclear engineering sub."
] |
[
"Ah, I figured. Do you have any recommendations of subs that might be able to help? I've tried ",
"r/nuclear",
" as well so far."
] |
[
"/r/nuclear",
", ",
"/r/AskEngineers",
", maybe ",
"/r/AskPhysics",
"."
] |
[
"What technology will cell phones of the future undoubtedly possess, but currently cannot due to size (or other) constraints?"
] |
[
false
] | null |
[
"Such hypothetical / speculative / open-ended questions are better suited for our new-ish sister sub ",
"/r/asksciencediscussion",
". Please consider reposting there instead."
] |
[
"While there may be some speculation, I definitely think my question is grounded in reality and may warrant some great answers by people who work for telecommunications companies or technology companies that are developing future mobile technologies. If you insist, I'll repost, but for these reasons, I ask you reconsider."
] |
[
"All people who have flair here have flair there as well."
] |
[
"What did Earth look like from Space at the dawn of life?"
] |
[
false
] |
It must have looked very different. For one, the atmosphere had a completely different composition. Also, the geography must have been very different as well. What can we infer from the geologic record about the appearance of the Earth so many billions of years ago?
|
[
"Single cell life came about ~3.8 billion years ago or so, but our grasp of geography during those time is a bit shaky. This is \"just before\" the formation of the first (theoretical) ",
"super continent, Vaalbara",
", which started forming around 3.6 billion years ago (completed at around 3.1 billion, and broke up around 2.5 billion years ago).",
"Not sure if the scientists can say with much certainty what Vaalbara looked like, though, much less what Earth's land masses' distribution before Vaalbara."
] |
[
"I am curious about the atmosphere. What colour would the sky have been? What about cloud cover?"
] |
[
"I am not an expert but I do take interest in these topics. Considering Earth had a reducing atmosphere at the time, it would've been filled with volatile chemicals, mostly methane, CO2, and nitrogen, possibly ammonia, with some other trace compounds so the sky was possibly an orange color like a permanent sunset. The oceans also were filled with iron, I've heard the color either being blood red, or dark blue/green/brown depending on whether the iron was partially oxidized or not. "
] |
[
"Considering the winter storm in the Midwestern U.S. currently, at what temperature would wildlife start dying?"
] |
[
false
] |
How cold does it need to be for the region's wildlife - foxes, deer, owls, coyotes, wild cats - to just not outlast it? Also, could it ever get so cold that trees or other plants are killed?
|
[
"Conservation Biologist here. Cold spells are like any abiotic factor which will cause changes to survival rates. Think about it like other natural disasters - e.g. hurricanes, floods, fires, etc. etc. etc. Most of the creatures that live in these regions have already evolved over thousands of years to be somewhat prepared for the cold. That said, of course more will die when the conditions are tougher. All I know is that I am glad to be a human right now because there is certainly a difference between surviving, and surviving comfortably. In regards to the second question, if the temperature becomes cold enough to cause the water to freeze within a plant, the water will expand as it changes to ice and will cause the chambers holding the water to break and thus kill the plant. "
] |
[
"Conservation Biologist",
"Interesting field of work. What's your typical day at work like?"
] |
[
"The temperature that an animal dies at depends on how desperate the animal is. ",
"A well fed animal with available natural shelter will probably survive the coldest weather in a century. But most of the animals might die.",
"Wild animals are rarely well fed. They are often at the edge of starvation especially late in the winter because if there were enough food to feed the current population well then there would be enough food to feed a larger population badly. There are obviously many more factors but you can think of the population size as growing until a cold winter and then a sharp drop. ",
"The colder the winter the larger the drop. "
] |
[
"If there is a stationary source of sound, and I am moving away from it, will I experience a Doppler shift?"
] |
[
false
] |
If so, will it be different from the Doppler shift that would be experienced if the source was moving and I was stationary?
|
[
"Yes. There may be differences based on the relative speed of the source, the air and you. Otherwise no, it will be the same."
] |
[
"I can understand why you can downshift all the way to 0 Hz when moving away from the source (when you begin to travel faster than the waves propagate through the medium), but why is there a theoretical limit to how far the signal can be downshifted when the source is moving? It would seem that as the source moves faster and faster, the observed frequency would go to 0. "
] |
[
"I was a derp. No theoretical maximum, but the magnitude of the shift is different. If you're moving away from the source at the speed of sound, the sound is shifted to 0 Hz. You can imagine this as just riding next to a pressure wave, without the wave causing any vibration of your eardrum.",
"If the source is moving away from you at the speed of sound, it's still sending waves toward you at the speed of sound, and they still reach you and vibrate your eardrums. Even though your relative speed is the same in both cases, you have a much smaller shift when the source is moving away than when you are moving away.",
"Even though the shift is smaller, the source will still be shifted to 0 Hz at very high source speeds."
] |
[
"Does fog form over the deep ocean?"
] |
[
false
] |
I've had a brainworm on the ocean and I've not been able to find an answer. I've asked a military subreddit and then also Navy servicemembers and they weren't able to say one way or the other. On the deep ocean, hundreds of miles from land, does fog form? If so, is it known if it is a common event? Lastly, and assuming it is within the purview of AskScience, if it is common, how do ships deal with it? Thank you!
|
[
"Yes it does. However, you won't get it forming in the lowest meter or two over the water, due to the curvature effect (water vapour will condense onto the ocean surface rather than into droplets). Also, there are fewer nucleation particles for fog to condense onto. Finally you won't have as much radiation fog because the heat capacity of the ocean is higher than that of land so it doesn't usually cool enough for radiation fog to form. So not as common as over land but still possible.",
"Sorry for the technical answer, happy to clarify any of these terms if you want."
] |
[
"Thank you so much for finding this post and answering it! ",
"I'm writing a story that at one point focuses on a fishing boat deep in the Pacific at a point when Earth is suddenly covered in fog. I wanted to depict the crew's reaction as realistically as possible. ",
"So to be clear, fog does form, but it would probably not drop so low to completely surround a boat, but a boat that is higher over the water would experience it? Do you know if this is a common phenomenon? At least enough that deep sea fishermen have probably encountered it? ",
"Thank you again!"
] |
[
"Yup, so the main takeaway is that fog can form, but less commonly than over/around land. It won't form at the lowest metre or so close to the water, which is lower than most deep ocean boats, I want to say?",
"I can't say exactly how common it is, except that it does happen but is less common than in coastal/land areas. (It is uncommon for me to get a request to forecast for the middle of the ocean!) Once you leave the coast areas it really does drop in frequency, but there are probably \"hotspots\" of fog that follow the ocean currents. Keep in mind that sailors have definitely encountered fog before; coastal areas are very prone to fog.",
"If you're really dedicated to this detail in your story, you can look for fog currently occuring. A trained eye can spot fog from visible satellite images (",
"https://www.ssd.noaa.gov/goes/west/weus/h5-loop-vis.html",
"). Unfortunately it is quite difficult for someone who's not experienced to spot fog.",
"Just a side note, has nothing to do with your question, but an interesting fact is that marine fog/cloud drops are larger than those over land! This is because there are less \"nucleation\" sites (ie aerosols/particulates) in the air for water droplets to form around."
] |
[
"Splenda and other artificial sweeteners are \"hundreds\" or \"thousands\" of times sweeter. How do they measure this? They taste the same to me."
] |
[
false
] |
Artificial sweeteners like Splenda are said to be hundreds or thousands of times sweeter than real sugar. How do they measure this? And why is it that a teaspoon of splenda in one of those little packets tastes exactly as sweet as a teaspoon of sugar? Shouldn't my mind be absolutely blown by how sweet it is?
|
[
"Because it's also diluted thousands of times so that in the packet it's about a 1:1 analog of sugar. ",
"That way when you are used to putting one packet of sugar in your coffee, you use one packet of Splenda. Otherwise your mind would be blown. Plus, it's hard to put only a couple of grains of Splenda in your coffee. "
] |
[
"You can purchase pure Neotame on eBay (also called newtame), which is 8,000 times sweeter than sugar and actually tastes pretty good. I purchased some years ago and like to dip a toothpick in the powder and then tap off the excess and have people lick it. Your mouth is overcome with sweetness from the smallest amount, and you can sometimes taste it in the air after opening the container."
] |
[
"That's not how it works. Pure sucralose is 300-1000 times sweeter than sucrose. 1:1 volume substitutes with sucralose is included with a lot of filler.\nJust because something is \"derived\" from something else does not necessarily give them similar properties."
] |
[
"Are SpaceX rockets susceptible to inclement weather on landing? What means do they have for delaying landing in such cases?"
] |
[
false
] | null |
[
"First stage never achieves orbit, it's on a more or less ballistic trajectory and can't really wait for the conditions to improve.",
"\nSomething they ",
"did recently",
" was move the droneship on which it lands to a different position due to storms."
] |
[
"They have precisely 1 means of delaying the landing in case of unacceptable weather at the landing site: Postponing the launch. What goes up but doesn't reach orbit, must come down rather immediately.",
"The Space Shuttle had similar requirements at launch for weather conditions at its abort landing sites in Africa and Europe. At least 1 shuttle launch was delayed for that reason."
] |
[
"There's landing weather criteria, ",
"here's a pic",
" showing wave and wind conditions required. Not sure if it has been revised since.",
"\nThey have delayed a launch at least ",
"once",
" due to unfavorable landing conditions."
] |
[
"Why do COVID-19 deaths go up and down on a weekly cycle?"
] |
[
false
] |
[deleted]
|
[
"Reporting differences on weekends are quoted as a reason, but would deaths really go unreported for days?",
"It can take a couple of days for a death to be formally reported and logged.",
"The paperwork is likely done pretty quickly but it will take some time for the paperwork to be processed. This is why it can take a couple of days for a death to hit the daily reporting stats.",
"Less people work at the weekends so there are less people to process the death notifications which is why you get less deaths reported at the weekend. The backlog gets processed during the working week which is why the reported deaths go up then."
] |
[
"For example, in several countries, like the UK, if you've ever had Covid -even if you have completely recovered- and die for any reason, for example run down by a car, then your death is recorded as a Covid death.",
"I've heard this conspiracy nonsense since the early days of Covid, but I have yet to see even a shred of evidence. I don't suppose you have any?"
] |
[
"It is what was stated in the press briefings by the authorities in the UK."
] |
[
"If we could anchor an object into space itself, how would it appear to us on Earth?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"I'm super confused. I can't ask a question about something I don't understand because I don't understand. What's the point of this sub? "
] |
[
"I am sorry but that question just doesn't make sense. You cannot \"anchor a object to space\". There is no absolute reference frame so you can't define a fixed point in space. To make it simple everything moves relative to everything else so you can't define something as immobile."
] |
[
"If you're under a mountain, would the slight increase in gravity from being closer to the core be negated by the mass of the mountain above you?"
] |
[
false
] |
Had a student ask be this today.
|
[
"At the most general level (and not specific to the particular scenario), if we consider a simplified version of the density structure of the Earth (e.g., ",
"PREM",
"), because generally density increases with depth (with some large step-changes across specific transitions) we would expect gravitational acceleration to increase as a function of depth until somewhere near the core-mantle boundary (e.g., the blue line in this ",
"figure",
"). Embedded within this are the implications of ",
"Gauss's law",
" (or alternatively, the ",
"shell theorem",
"), specifically that if we imagine a solid sphere that we discretize into a series of shells (and assuming any individual shell is a homogeneous density) as we move to smaller radii (i.e., go down in depth), we do not experience any gravitational acceleration from the shells above us (i.e., between our position and the surface of the sphere), only those below us (i.e., between us and the center of the sphere). From this \"we'll consider the Earth as a perfect sphere with only symmetric radial changes in density\" perspective, we can effectively ignore the mass of the mountain above us and say that the strength of gravity only depends on the mass and radius of the sphere below us. So, gravitational acceleration (g) is dictated by the basic equation, g=GM/r",
", where G is the gravitational constant, M is the mass of the sphere below us, and r is the radius of the sphere below us. Because of the increase in density with depth, the decrease in M as the sphere radius decreases is generally decreasing much slower than the decrease in r, so g increases up until a point. ",
"Now, obviously, at some relatively shallow depth below a mountain, say at mean sea level, we can't really say that we're below a uniform shell, so things get a bit more complicated. We also have to consider that there are a variety of density variations we can expect in the crust of the Earth, e.g., the contrast in density between ",
"continental",
" and ",
"oceanic",
" crust. In mountainous regions, one of the primary things we need to consider is that if our mountains formed from collision (like the Himalaya), they most likely have a thick 'crustal root', e.g., ",
"this diagram",
" (don't worry about the various panels in this, just look at the top one). This crustal root, which is typically made of continental crust, effectively displaces higher density material from the mantle, meaning that for a comparable location at sea level (e.g. sea level in the center of the mountain vs sea level in a nearby flat, low elevation area) there is less integrated mass below you (and thus less gravitational acceleration) when you're in the center of the mountain. This is the most easily visualized by considering ",
"gravity anomalies",
", where we calculated deviations in measured gravity from idealized expected gravitational acceleration. The most relevant for us would be the ",
"Bouguer anomaly",
", which is the deviation from expected gravitational acceleration after correcting for elevation (i.e., the ",
"free air correction",
") and the acceleration expected because of the rocks between the measurement point (e.g., the top a mountain) and the ",
"geoid",
", which for our purpose we can consider sea level. Thus, the Bouguer anomaly can kind of be thought of as how different would gravity be at sea level within our mountain compared to sea level in some idealized section of the Earth where the elevation is equal to mean sea level and the integrated mass/density below is \"normal\". Typically, in mountains regions with significant crustal roots, the Bouguer anomaly is ",
"negative",
" meaning that gravitational acceleration would be less (by an imperceptible, but measurable, amount) in our mountain, at least if we were at sea level. Now, the answer depends a lot on the details (e.g., how deep are you? what is the integrated mass beneath you? etc) and all of the above is still a pretty large set of simplifications (and I'm sure a geophysicist will pop in to tell me how I screwed up my explanation of gravity anomalies, I have to basically reteach myself what they mean everytime I have to deal with them).",
" the critical detail is what is the integrated mass/density beneath you and your depth. Compared to a generic location at a similar depth/elevation, you might expect there to be less gravitational acceleration because typically mountains (at least ones formed through collision) have thick, low density crustal roots. This means that the integrated mass beneath you for the same radius is less, meaning gravitational acceleration is less compared to a reference. This is superimposed though on a general expectation that gravitational acceleration would increase with depth because even though both the mass and radius are decreasing as a function of depth (i.e., the shell theorem), because density increases (generally) with depth, the decrease in radius is more significant than the decrease in mass until you're near the core-mantle boundary."
] |
[
"I'm a geophysicist, and your explanation of the nature of the bouguer anomaly is one of the clearest ones I ever saw."
] |
[
"If this was the short clear version, I’d hate to see what an in-depth analysis and explanation would be. (⚆_⚆)"
] |
[
"Can dark energy tear apart black holes?"
] |
[
false
] | null |
[
"Hi Sp1hund thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"'Astronomy'"
] |
[
"'Astronomy'"
] |
[
"What kind(s) of motion does an air bubble trapped in an acoustic standing wave (propagating through water) have?"
] |
[
false
] |
I'm working on a project involving sonoluminescence and need some help with the hydrodynamics. We've trapped air bubbles in an acoustic wave traveling in water and saw a pattern in our readings which I don't think can be explained by the pulsating of the bubble's radius. Our measurements are made from a piezo-electric crystal at the bottom of a water tank which will read the pressure fluctuations over time from the movement of the trapped bubble and display these readings on an oscilloscope. We get what looks like a sinusoidal function in a saw-tooth waveform envelope. This saw-tooth envelope is in phase with the acoustic frequency in the water. Could this be explained by the bubble's radius collapsing and expanding over time or is there some other form of motion that we're not considering?
|
[
"What is the radius of the bubble and what is the frequency of the wave? For an air bubble in water, the resonance frequency and radius multiply to about 3 m/s (e.g. a 3 mm radius bubble would have a resonance frequency of 1 kHz). You could try ramping the frequency and seeing if there's a resonance peak around this point. What is the pressure of the wave? If it's large compared to the equilibrium pressure, it's quite possible that the bubble's radius is undergoing nonlinear oscillations."
] |
[
"If you could put up an image of the signal you are seing that would help quite a bit in trying to decipher the behavior. "
] |
[
"well as far as a sonoluminescing bubble goes, there actually tends to be more light at colder water temperatures"
] |
[
"Does pushing on an object propagate through the object at its speed of sound?"
] |
[
false
] |
If I hit one end of a long rod for instance, the sound wave travels down the rod at its speed of sound, caused by the electromagnetic force affecting successive molecules pushing against one another. If I instead slide to the rod forward, the pressure applied to one end of the rod sends a wave through the material via those same forces. So does the far end of the stick respond to a push at the speed of sound?
|
[
"Yes, it does. Any disturbance at one end of a body will not be instantly noticeable at the other end, but travel through it at the speed of sound. It is important that the speed of sound can be pretty fast in solids, up to 12'000 m/s in diamonds. ",
"Here is a useful list"
] |
[
"I'm not 100% sure because this isn't my field, but isn't the speed of sound synonymous with the velocity factor for a mechanical signal?"
] |
[
"Nope, it depends on the \"speed of signal propagation\" in the material. The speed of sound also depends on the material.",
"EDIT: apparently I was wrong, as explained in other comments :)"
] |
[
"Is it highly probable that aliens would evolve sexes, or are our male/female sexes a freak of nature and the norm is no sexes or gender?"
] |
[
false
] | null |
[
"http://www.sciencemag.org/content/333/6039/216",
"\nGood evidence it's strongly selected for hence likely."
] |
[
"Thanks very much!"
] |
[
"Since by aliens, you likely mean aliens with a comparable intelligence to humans, I would agree that a male-female gender pattern would likely emerge. However, this does not hold true for all potential alien species.",
"On our planet, most if not all mushrooms have evolved to not use a male-female gender pattern. Instead, every individual mushroom produces spores of different mating types. There are multiple mating types per species, and the only rule is that two spores of the same mating type are incompatible.",
"I can envision alien \"plant\" species that follow these rules. If there are 5 \"mating types\" that are evenly distributed, one member of the species can reproduce with 80% of the other members. There is no reason to believe this is impossible."
] |
[
"Why does my AM clock radio depend on it's orientation while my car receives clearly in all directions?"
] |
[
false
] | null |
[
"Directional antennas are less likely to pick up erroneous side-band noise and harmonics from other signals, but require to be aimed in the direction of the transmitting signal. Omni-directional antennas require no aiming, but need a stronger signal for clear audio. The manufacturer of the clock radio assumed you'd take the time up front to enjoy a clearer sound.",
"What's really fun is when the transmitting source changes from their primary antenna to an auxiliary source. This could happen for a number of reasons (antenna testing, line distortion, maintenance on the tower, etc.). Then you are sometimes required to move your directional antenna for the best quality sound only to require it be moved back when they change their source once again.",
"In a perfect world, multiple antennas aimed directly at every potential source with a power divider would be optimum, but unrealistic."
] |
[
"Don't forget the obvious. One antenna is huge and open to the air, the other is tiny and inside 4 walls and a roof."
] |
[
"The size of the antenna has less to do with the result than the gain of the antenna. But the walls and roof will affect the signal. Not as much as higher frequencies (FM, TV, ect.), but it will affect it. That being said, even outdoors you're likely receiving an AM signal after it has reflected off walls or the ground. Otherwise you'd not be able to receive the signal in a downtown surrounded by buildings. "
] |
[
"What would happen if gravity was \"turned off\"?"
] |
[
false
] | null |
[
"It's impossible, but if it did happen, the Earth and its atmosphere would fly apart from the massive pressure that exists at the core."
] |
[
"Wow! I didnt even think of that! So the entire earth, from crust to mantle and core would seemingly explode? That's awesome."
] |
[
"You should read Larry Niven's \"The Integral Trees\". Like a lot of Niven's stuff, it's a really brilliant concept, artfully imagined then rendered into a pretty puerile teenage novel with stilted dialogue and lots of sex (most of which happens by allusion only). But it's worth wading through the schlock for the awesome vision of what life would be like in a place with atmosphere and no gravity.",
"Of course, like other Niven ideas (e.g. Ringworld) there are some problems with the physics if you carry it beyond the back-of-the-envelope stuff he used to set up the story. But if you can suspend disbelief and allow his world to exist, he's physically consistent within it."
] |
[
"How did the first RNA/DNA strains not break down from hydrolysis?"
] |
[
false
] |
Correct me if I am wrong, but don't the amino acids that build RNA, which is thought to be the start of life on our planet, break down when introduced to water? (hydrolysis) How did it avoid this?
|
[
"The RNA world hypothesis (",
"Wiki",
") is what I think you are referencing. It is thought that RNA came together with help of random chemical processes. RNA is somewhat special in that it can take on many conformations in a single strand (or even double strand state), these RNAs are able to actually catalyze reactions, which was the genesis of this theory. While hydrolysis is a real problem, especially with RNA, if the molecule was self replicating, it could overcome this by making many copies of itself (or in early history, just make more random RNA, mutations at this stage were probably rather neutral, but could be advantageous later on!) There is a very recent article that has put togther all the data on this theory, which should be freely available ",
"here",
"."
] |
[
"under neutral conditions, the phosphodiester bond in RNA and DNA is very stable. also, amino acids make up ",
", not DNA/RNA. what makes up DNA/RNA are ribonucleotides."
] |
[
"I am not a scientist but I do read lots of science magazines, etc.",
"The conditions at the start of life on earth were VERY different than they are now and there is always exotic places where life could have started such as geothermal vents. I recall these two life origin theories I read about somewhere along the way.",
"origin of life metal theory: where metals act as catalysts to connect the mollecules of life\n",
"http://en.wikipedia.org/wiki/Iron%E2%80%93sulfur_world_theory",
"\n",
"http://www.sciencedaily.com/releases/2010/09/100903210416.htm",
"origin of life clay theory: where a drying clay lake bed would have been a good place for accumulation and concentration of various molecules and under the clay they would have been protected from the UV radiation\n",
"http://en.wikipedia.org/wiki/Abiogenesis#Clay_theory"
] |
[
"Questions about Metatharians..."
] |
[
false
] |
Are there any extant species of Metatharians that are not marsupials? I'm aware of extinct marsupial ancestors that were Metatherian, but not of any living ones. Are Prototherians (i.e. monotremes) the ancestors to Eutherians and Metatherians? Further, are Metatherians the ancestors of Eutheria? Am I correct in my assumption that all Eutherians are more closely related to one another than any of us are to Metatherians? That is, humans, wolves, whales, elephants, armadillos and bats are all more closely related to one another than any of them are to kangaroos and bandicoots?
|
[
"Well, a thorough read-through of ",
"this",
" would probably get you most of what you want to know (and far far more). However, I'll do my best to give condensed answers to your specific questions.",
" As far as I can tell, no. I'm by no means a specialist on taxonomic stuff like this, but the ",
"section on metatheria",
" from that wikipedia article I linked to before states that ",
"The living Metatheria are all marsupials.",
"so that's probably your answer.",
" First off, \"",
"prototherian",
"\" and \"",
"monotreme",
"\" are distinct, while overlapping, categories. When referring to extant species, it probably doesn't matter that much, as all living prototherians appear to be monotremes (as best I can tell), but I just like to be careful with terminology.",
"Anyways, no, prototherians are not ancestors of eutherians and metatherians. And metatherians are not ancestors of eutherians. This represents an (unfortunately) extremely common misconception about evolution. All three of these groups share a common ancenstor. You can see that if you look at ",
"this tree",
", where the monotremes are represented by the platypus; the metatherians by the possums, marsupial mole, wombat, kangaroo, and kaola; and the eutherians by everything else. You can see that none of these three groups are ancestors of the other (",
"). The common ancestor can be thought of as existing on that tiny little line all the way over to the left.",
" Yes. This is correct."
] |
[
"The following link should answer your second and third questions. Basically, these three groups aren't monophyletic, there are extinct groups of mammals that existed alongside the extant groups. ",
"http://tolweb.org/Mammalia/15040"
] |
[
"In the same way that modern reptiles are not the ancestors of humans, but our common ancestor would have been classified as a Reptile",
"This is incorrect. The common ancestor we share with reptiles would have been more \"reptile-like\", but it would not formally be classified as a reptile. I should also note that, phylogenetically speaking, reptile is a rather meaningless term, as it includes all descendants of the inferred historical \"proto-reptile\", except for birds. In essence, birds share a last common ancestor with all other reptiles which they do not share with any other group of organisms. As such, any phylogenetically coherent classification that includes all reptiles should also include birds.",
"Anyways, to address your question: The answer is still no. This is because of the way that we define categories like prototherian, metatherian and eutherian. It is important to keep in mind that these categories are arbitrary ones that we make up in order to help us understand evolutionary history. They are defined specifically such that they are mutually exclusive. ",
"The common ancestor of all mammals may have been more \"monotreme-like\" as they seem to share more traits with reptiles, but it's tough to say for sure with my level of knowledge about them (a phylogeneticist may know more than I). Many of the traits of a metatherian, or at least the ones we're thinking of (i.e. pouches) are derived traits (i.e. they evolved after they split from eutherians) so I don't know that the metatherian/eutherian common ancestor would likely have been \"metatherian-like\". If anything, I would think it was probably more \"eutherian-like\", but I'm just sort of speculating at this point. The most that you could say definitively about the common ancestor of all three groups is that it was a mammal.",
"I always find this concept difficult to explain, so let me know if I did a poor job and I'll try to clarify."
] |
[
"How much longer will Venus be visible in the night sky?"
] |
[
false
] |
Venus and Jupiter were visible throughout March. Jupiter seems to have disappeared at this point, but Venus still shines brightly every night. Will it last for a few more weeks? (I hope that bright point of light I see IS in fact still Venus, otherwise I've just made a fool of myself.)
|
[
"Yes, that's Venus up there.",
"One good way to answer this would be for you to download some planetarium software and see for yourself :) I really enjoy ",
"this one",
". Set it to your location and set the time and date to tonight, then skip forwards days and hours until it pops behind the sun."
] |
[
"As a rule of thumb, it's visible a few months at sunset in the west, then disappears, then it's visible a few months at sunrise in the east, then disappears, repeat."
] |
[
"As others have mentioned, yes its Venus.",
"It should stick around until the end of may at which point it will be too close to the sun to really observe well.",
"mars and saturn are also up right now not too long after dark.",
"and yes, stellarium is an awesome free planetarium program."
] |
[
"When we measure an object's mass using scales, are we actually measuring the *mass* of the object, or just inferring it (more inside)?"
] |
[
false
] |
Hello, science people, My question is quite simple, really. When we use scales (say, for instance, the electrically powered ones you stand on) to measure an object's mass (in our example, a human's mass) in KG, aren't we actually measuring the object's weight, and converting the result from Neutons into KG, using the assumption that we're working in an environment of 1G? If so, then would these devices need to be calibrated when used in environments of lower or higher natural gravity? Could they even be calibrated without a reference mass object, like the ACPO's Silicone sphere?
|
[
"It depends on the scale. If it uses force (like your bathroom scale) the result would indeed be different depending on you location in space (even differs on earth quite a bit). However, if you were to use a balance, it wouldn't change, since it compares the weight of both sides (even though the actual weight in your environment would be different).",
"If you know the gravitational factor of your location, you can just change the calculation."
] |
[
"the result would indeed be different depending on you location in space (even differs on earth quite a bit)",
"For anyone curious, cool science folk have mapped this pretty well; it's called the ",
"geoid",
". It's a lookup table of how much gravity you'll experience at any given point on earth.",
"It looks like ",
"this",
" (blue=less gravity, red=more gravity).",
"In fact, GPS uses a ",
"model",
" of the gravity changes around different parts of earth in order to better estimate above/below sea level altitudes. Yay GPS and gravity!"
] |
[
"No, the balance idea is genius. If you have a reference object that you know has a mass of 1kg, and the object on the other side of the scale balances it perfectly, than it doesn't matter what gravity is, you know they are the same weight and therefore the same mass."
] |
[
"Why are the mods ignoring their own rules to accumulate karma?"
] |
[
false
] | null |
[
"It isn't about accumulating karma. The mods are actively discussing whether it was appropriate to include that joke in a distinguished post. We understand that a lot of people in the community are upset by the decision and are certainly taking that under advisement. Thank you."
] |
[
"I'll be honest. It bothered me because I am literally, as I discovered this question, studying for my physiology test in which that is a major point of discussion. My answer is correct, but now nobody will see it because they're all pissed I tried to call out a mod. If this truly is not a scientific community, I am fine with that, I will continue on my way. If it claims to be, it should be held to a particular standard. Did I mean to come off as a bitch? No. Did I? Probably."
] |
[
"right now your answer is sitting at 5 up and 1 down. I don't think people are rejecting your ",
" in addition to your \"calling out\" of a moderator. Granted even if they did, that's still something that I would ",
" with, but have no power to stop. That's kind of one of the problems of the reddit voting system. I can't prevent people from burying good comments just because they don't like who said it. ",
"I agree that the community is right in pointing out that they disagree with the action a moderator is taking. (regardless of my own personal opinion of the matter) I think, and I'm not entirely sure, but when moderators started deleting responses to that comment, it wasn't an attempt to \"silence\" anyone, it was more that we wanted everything to be focused on scientific answers to the question at hand. The several pun threads that were started could have snowballed out of control, and it was probably assumed that a few deletes would discourage people from continuing to try.",
"I think that messaging the moderators of askscience may be a more fruitful path of expressing discontent rather than this post (which was caught by our spam filter, and violates our meta-post rules none the less)"
] |
[
"During fertilization the sperm mitochondria are marked with ubiquitin and destroyed and the human embryo only receives the mother's mitochondria. Why?"
] |
[
false
] |
Wouldn't it be better to receive two copies of mitochondria in case the mother's version was faulty? Also wouldn't it help natural selection to have mitochondrial DNA and genes participate in sexual reproduction as well instead of the asexual cloning process that our mitochondria experience?
|
[
"Last time I've heard this topic come up, I believe it was still being debated, so there isn't a clear answer yet.",
"First off, yes, there is evidence that sperm mitochondria are targeted for degradation. It is not a simple matter of sperm mitochondria dilution. The sperm tail is not excluded from the embryo upon fertilization. ",
"There is a good sobering review on misconceptions in this area",
" that I was happy I skimmed again. ",
"It is hypothesized that the reason may be an evolved protection from inheritance of damaged sperm mitochondrial DNA (mtDNA). Sperm require heavy usage of their mitochondria, so they generally are exposed to reactive oxygen species (by product of electron transport chain metabolism) during sperm creation and throughout the fertilization process. This can, in theory, ",
"have deleterious effect on their mtDNA",
". The female egg mitochondria are relatively quiescent, perhaps maintaing mtDNA integrity. ",
"Another hypothesis that comes up and one protective mechanism that may serve in addition to the one above is to avoid ",
"intragenomic conflict",
" and problems that may arise from having two competing genomes. Though this topic is a little outside the scope of my knowledge as it pertains to human mitochondrial genetics, but there is some info about it on ",
"WikiPedia",
". ",
"I did some checking to make sure this is accurate and it seems as if it still represents the current thinking of the field. Here are some reviews on the specific topic you can take a look at that backup what I wrote and can be used to find further reading. They should be freely available",
"Fertilization and elimination of the paternal mitochondrial genome",
"Ubiquitinated sperm mitochondria, selective proteolysis, and the regulation of mitochondrial inheritance in mammalian embryos."
] |
[
"The amount of mitochondria in a sperm cell is so little (50-100 mitochondria) compared to the one in an egg (100.000-200.000) so mtDNA is inherited through the female. ",
"That probably happens to prevent lethal cytoplasmic gene competition and to prevent the inheritance of sperm mitochondrial DNA which is degraded by free radicals. ",
"But, generally, organisms are intolerant of mitochondrial heteroplasmy which causes metabolic and neurological disorders. "
] |
[
"The reason we only have maternal mitochondrial DNA is because only the head of the sperm (which contains the parental DNA) enters the egg and combines with the maternal DNA to create an embryo. All the paternal mitochondria is in the tail of the sperm which propels the sperm (its the only part of the sperm that needs an energy supply), so that part of the sperm never enters the embryo therefore we have no paternal mitochondria. Then the useless tail of the sperm just breaks down/",
"\nThats why metabolic disorders of the mitochondria pass down the maternal line.",
"\nLook up the wikipedia on sperm, all the diagrams and information show what I've said. "
] |
[
"What makes stainless steel resistant to corrosion?"
] |
[
false
] |
I know its a passivating layer of chromium oxide that protects from corrosion, but why does a layer of chromium oxide not allow for further oxidation while iron oxide fails to do the same thing
|
[
"Most metals when they oxidize produce a relatively strong layer that protects metal underneath form further oxidation, however iron is a little different because iron oxide reacts with water, increases it’s volume and just falls off exposing more metal",
"If you have a metal that creates a protective oxide layer and oxides before iron you effectively prevent the iron from rusting"
] |
[
"Stainless is about 3 times as expensive as regular steel, it also has different mechanical priorities, and it’s harder to work with weld and form, so it’s not quite that simple ",
"Most of the time it’s not worth it for structural stuff, iron really doesn’t corrode all that fast in regular conditions anyways"
] |
[
"OK thanks again :-)"
] |
[
"Does the Universe have a center of gravity?"
] |
[
false
] | null |
[
"No.",
"There are two possibilities:",
"Space is flat and simply connected. This implies that it is in fact Euclidean space, and is infinite. Then you cannot average the position of masses in the Universe because the sum diverges. The mass distribution is uniform on very large scales, and this goes on forever.",
"Space is curved and/or not simply connected. This means that positions cannot be thought of as vectors and they cannot be summed, therefore they cannot be averaged."
] |
[
"there isn't a concept of centre of gravity or centre of mass in GR."
] |
[
"nah, that's a pretty local feature in the grand scheme of things. It's just a large clump of mass some 50-70 Mpc away. Over much larger distances the distribution becomes uniform."
] |
[
"How is energy going to be harvested from nuclear fusion reactors?"
] |
[
false
] |
So there will be glowing hot ball of plasma 10x hotter than the core of a star inside of an enormous magnetic field. How is energy going to be harvested from the reactor?
|
[
"Each fusion of deuterium and tritium nuclei yields neutrons of kinetic energy 14 MeV (about 22 millionths of an erg). These fast neutrons are electrically neutral and can easily escape the plasma and its confining magnetic field. Their kinetic energy could then be converted to heat--for instance, by depositing their energy in water, heating the water and spinning a turbine. ",
"Alternatively, as with the ",
"LIFE concept",
", fusion neutrons could be used to induce fission reactions in a fissionable \"blanket\" (e.g., of U238) surrounding the reactor. Each fission releases around 200 MeV of energy (about 320 millionths of an erg) and is a way to increase the net nuclear energy release per fusion reaction. This fission energy could then be harvested much like in a conventional fission reactor. "
] |
[
"Very interesting. Concerning the neutrons of kinetic energy, however, is there any chance that these could damage the reactor as they leave the core? It seems like a lot of energy moving out of the core."
] |
[
"Indeed, fast neutrons can do all kinds of bad things to reactor materials by introducing dislocations, defects, and the introduction of nuclear reactions in the nuclei, which can lead to alpha decay and pockets of helium within the matter. All this tends to make metals and other matter brittle. ",
"Developing materials that remain strong when subjected to large neutron fluxes is an active area of materials research. "
] |
[
"When you solve quadratic or cubic equations one or two results may make no physical sense to us. Do they play an important role in some other area of physics/math?"
] |
[
false
] |
As the title says, if I'm solving for Volume, and my equation ends up having two answers that satisfy the equation. one result being 5 and the other being -5, by our understanding a negative volume does not make sense. Does that -5 value play a role in some other type of physics that can be applied in our understanding?
|
[
"This is sort of how the idea for the positron was conceived. Dirac realized that his equations could be solved with either a negatively or a positively charged electron."
] |
[
"The Schroedinger equation is built on the total energy equation from Newtonian mechanics:",
"H = p",
"/2m + V",
"Which is known as the Hamiltonian. The Schroedinger equation comes from the substitution p->-iћ(d/dx), E->iћ(d/dt), which can be derived from the de Broglie and Planck relations.",
"The relativistic Hamiltonian is",
"H = sqrt[(pc)",
" + (mc",
")",
"]",
"Which is difficult to \"quantize.\" We can make the same substitutions for p and E, but the square root of a derivative is weird, and there's an mc",
" hanging around inside the square root too. Dirac's idea was to say",
"E",
" = (pc)",
" + (mc",
")",
" = [a(pc)",
" + b(mc",
")",
"][a(pc)",
" + b(mc",
")",
"]",
"Which is true iff",
"ab + ba = 0",
"a",
" = b",
" = 1",
"Numbers won't do this, so a and b need to be unitary matrices called the ",
"Dirac matrices",
" in order for this equation to be satisfied. We thus have",
"Eψ = [a(pc)",
" + b(mc",
")",
"]ψ",
"But E is a scalar and a and b are 4x4 matrices, so for the sides to line up, ψ must be a 4-dimensional vector. Given the construction of the Dirac matrices based on the Pauli spin matrices, what we will find is that the first two indices of ψ are the spin-up and spin-down solutions, respectively, and the third and fourth indices of ψ are... well, something else. They correspond to the values when E is a negative number (E",
" admits both positive and negative E!), so we call them \"antiparticle\" solutions.",
"Mathematical artifact? Nope! This is how antiparticles were predicted, and they're definitely real."
] |
[
"Positron emission tomography"
] |
[
"If infrared is just another \"place\" on the spectrum that includes visible light, can something be painted infrared? Or is the \"visible light spectrum\" different in some way apart from the fact that we can only see that?"
] |
[
false
] |
Also, if something had the "color" infrared, or ultraviolet, would it be invisible to us?
|
[
"Yes. Although when you say \"painted\" you're defining the spectrum as what you can see. A blue object reflects blue light and absorbs light from all other colors in the visible spectrum. But a what you call a blue object may also reflect infrared light. So to an animal that has the ability to see some of the infrared spectrum, it's more of a blue-infrared color. We don't really have a name for that color because it's not particularly useful or convenient for us to discuss things in those terms. I can give you a common example, though: X-rays are also part of the light spectrum. Lead has the property of absorbing X-rays, your skin is X-ray invisible (clear), and your bones reflect X-rays. So in a way, to a hypothetical animal that only sees in the X-ray spectrum, your skin is like glass, your bones are black, and lead is like a bright X-ray screen. This is why X-rays cameras can see your bones against a lead screen.",
"Edit: as TsuDoNihmh alluded to, this also assumes you're shining a light source that produces all wavelengths of ",
" light equally. Just as if you shined a blue light on a white object it would appear blue, you'd have to shine an X-ray light to see X-ray colors. ",
"Also, I think I may have reversed lead/bone colors. Someone can correct me. "
] |
[
"Also, I think I may have reversed lead/bone colors. Someone can correct me.",
"Yes, you have. Things look black if they absorb of all visible wavelengths or white if they reflect all of them. Hence lead would look black to this hypothetical creature, and our bones would look white (or \"X-ray colour\", for want of a better phrase)."
] |
[
"You can certainly paint something infrared. ",
"This",
" youtube video shows a special type of coating that is opaque in the visible but reflective in the infrared. You can think of it as a type of infrared paint.",
"Similarly, it's possible for a material to be opaque in most frequencies but reflective in the UV. ",
"This",
" company seems to make a whole range of uv reflective coatings for optical experiments and industrial applications. These coatings would have an ultraviolet color."
] |
[
"How much fructose do we need to consume before our liver starts to produce triglycerides?"
] |
[
false
] | null |
[
"The general answer you're looking for, if you're talking about the synthesis of triglycerides, is immediately - insulin production brought on by the consumption of sugars activates FA synthase. Like all biochemical processes in our bodies, it works by feedback - how much insulin there is present affects how much FA synthase is activated."
] |
[
"sorry I am not sure I understand. I was under the impression that fructose which unlike glucose is processed by the liver and it can only handle a certain amount. Once we hit this limit instead of turning it into glycogen it turns it straight into a fatty acid ah la triglycerides? "
] |
[
"Wikipedia seems to agree with you \"High fructose consumption can lead to excess pyruvate production, causing a buildup of Krebs cycle intermediates.[34]Accumulated citrate can be transported from the mitochondria into the cytosol of hepatocytes, converted to acetyl CoA by citrate lyase and directed toward fatty acid synthesis.[34][36]Additionally, DHAP can be converted to glycerol 3-phosphate as previously mentioned, providing the glycerol backbone for the triglyceride molecule.[36]\"",
"source:wikipedia",
"reference [34] is to Biochemical, physiological, & molecular aspects of human nutrition / (c) 2006 Saunders Elsevier [edited by] Martha H. Stipanuk. ISBN 141600209X",
"I don't have a copy of this book, and I don't see more specific numbers anywhere yet. What exactly is \"high\" in this context? Three apples in a day? Four bushels of apples in an hour?",
"[36] is Metabolism of Fatty Acids, Acylglycerols, and Sphingolipids. Missouri: (c) 2006 Saunders, Elsevier. ISBN 141600209X",
"Sounds like we should ask this Saunders individual. ",
"edit: more involved article, provides more specifics on how fructose is interacting w/the liver and glucose, though doesn't provide an exact range of fructose per pound of human when increased FA production starts occurring (unless I missed it).\n",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3032722/"
] |
[
"Why do some vaccines leave scars?"
] |
[
false
] |
I recently got my BCG vaccine as I work in a lab but when they informed me of the blistering and scaring phase I was a little perplexed. What makes the site blister and scar only after several weeks/months? I know it’s to do with your immune system reacting but what is specifically involved / what’s the processes involved and why does sometimes it cause such a prolonged severe reaction at the site of injection? ( How come its only with live vaccines too?)
|
[
"For the smallpox vaccination, \"leaving a mark\" is the sign that the vaccine worked. The vaccine requires multiple punctures giving multiple infection start sites, so it becomes very inflammatory - leaving behind the scar tissue. The TB vaccine is different, in that it is a single injection, but BCG is extremely immunogenic and causes severe local inflammation, which can cause a long-lasting scar."
] |
[
"Thanks. I never knew that was the reason why. I haven’t really thought about it in the 23 (or so) years since I had my BCG, but I just checked for the scar...yep, still there."
] |
[
"It appears to genuinely be a carryover from Jenner’s initial testing back at the end of the 1700s. This is an interesting study (albeit with a minuscule sample size) suggesting the inner arm might actually be a better location: ",
"https://academic.oup.com/cid/article/42/4/e16/385953"
] |
[
"If an object falls into a still body of water, can the water that is thrown into the air exceed the initial height of the object?"
] |
[
false
] |
[deleted]
|
[
"Yes. Can we agree that a turd at the moment of release is lower than your balloon knot? I say yes. The fact that the water can still make a brown bullseye proves that it achieved a height higher than the turd. The object would probably have to be big enough to displace some water so the water claps back into place. Another good example is a can opener at the pool. Splashes frequently go higher than the jumper."
] |
[
"It only applies if the exit velocity is equivalent to free fall. Otherwise assume a slow pinch off on a suspended turd."
] |
[
"I believe it's caused by the water being lifted up as it's forced out of the path of the turd, while at the same time the turd creates a depression in the water. As the water falls back into the depression, all the force is compressed into the epicenter where the turd fell. The water cannot be forced down and so all the force sends a jet of liquid directly back to where the original potential energy was.",
"It's conservation of energy/momentum. if a 2kg turd is dropped from a 1meter very tall person, then it's possible for a fraction of the turd to get rocketed back up you at greater than initial velocity."
] |
[
"What would it be like to swim in a pool on the moon?"
] |
[
false
] |
Assuming it was inside a pressurized, breathable environment. In terms of the lower gravity, how would the viscosity and buoyancy of the water play a role? Would it be like swimming through syrup? Would we be able to swim more efficiently?
|
[
"Actually, and surprisingly, there wouldn't really be any difference at all. First, water is (nearly) incompressible, meaning it would be at the same density on the Earth or on the Moon, and buoyancy is not a function of gravity so you would have to swim just as hard to stay afloat in both locations. The only real difference would be since gravity is pulling you down less on the moon, you would sink slower if you did nothing to keep afloat, or after cannonballing in. "
] |
[
"buoyancy is not a function of gravity so you would have to swim just as hard to stay afloat in both locations.",
"I'm not sure this is accurate. You would float at the same level, but the effort required to keep you upright with your head above water should be less. If you push down with your hands at the water, you will be be pushed up out of the water more than you would on earth. So it ",
" be easier to tread water."
] |
[
"Wait, wait, so if we go swimming on the moon we can swim upwards and out of the water while doing crazy aerobatics like dolphins?"
] |
[
"What is the smallest sized objet we would be able to see on Mars from Earth using current technology?"
] |
[
false
] |
This question came about when I was reading The Martian. Is there any chance that we could use land or space-based telescopes to see a human on Mars?
|
[
"For Earth based telescopes, the largest aperture belongs to Gran Telescopio Canarias (GTC) at 10.4m. Assuming (incorrectly) that this telescope is ",
"diffraction limited",
", and that Earth was at aphelion, Mars at perihelion and opposition (closest possible approach), GTC would theoretically be able to resolve objects down to about 3.2 kilometers across (~2 miles). I wouldn't care to guess what its actual limit would be due to being seeing limited, better ask an astronomer. (Note that these numbers were calculated for green light with a wavelength of 500nm).",
"If the Earth and Mars were on opposite sides of the sun (with a viable viewing path between them) this number would change to ~23.5km (~14.6 miles) for GTC.",
"For Hubble with its 2.4m optics, these numbers would be ~13.9km (8.6 miles) and ~101.9km (~63.4 miles) respectively. "
] |
[
"Did you read the words that immediately followed that statement, or did you just stop there?"
] |
[
"The HiRISE camera (",
"official site",
", ",
"Wikipedia page",
") on the ",
"Mars Reconnaissance Orbiter",
" has a resolution of ~0.3 m/pixel (~1 foot/pixel). An average human standing on Mars would be just over one pixel wide if viewed from straight overhead."
] |
[
"What is the practical significance of ENTHALPY? (Both in chemistry and physics)"
] |
[
false
] |
For e.g, 1. When we say Internal Energy, we mean the sum total of the energy of a system (U) which is the function of temperature. When we say Gibbs free energy (G), we mean the amount of energy in a system which can be converted into useful work. When we say Entropy (S), we mean the energy which cannot be converted into useful work anymore because it has been used to increase the entropy of the system. When we say Heat(Q), we talk about heat exchanged b/w the system and the surrounding So what do we mean when we talk about enthalpy? Why did scientists feel that there was a need to introduce the term enthalpy ? And why was Internal Energy not enough?
|
[
"Enthalpy is an incredibly useful quantity in thermodynamics. It is given by",
"H = U + PV ",
"Where U is internal energy, P is pressure, and V is volume. Since U, P, and V are state functions, H is also a state function. Enthalpy takes into account the energy used for expansion.",
"One of the more useful properties of enthalpy is that the heat transferred into a system at constant pressure is the same as the change in enthalpy. This is useful because constant pressure is much more common than constant volume in most situations. Due to the atmosphere, it is much easier to engineer in constant pressure as well. ",
"Also, entropy is not energy. It is an entirely different concept."
] |
[
"So while talking about U, we are talking bout a system at constant volume? Without any exceptions?",
"And about entropy... Most of the books define it as \"randomness of a system\". I know it's beyond the scope of a Reddit thread so can you suggest any text which talks about entropy?",
"And one last ques, do all spontaneous process have +ive entropy?",
"Thanks for your time sir."
] |
[
"Spontaneous processes will have a negative Gibbs energy vs the previous state (assuming constant T, P, etc).",
"I generally think of enthalpy in solids. A way to then frame it is the energy of the bonds. Attractive bonds have a large negative enthalpy and repulsive bonds are positive (through convention). So, if you have a system where you're cooling you can go from a disordered mix of bonds (some bonds +, some -, and a large S) to an ordered solution where all bonds are -, you now have a much lower S, but a lower total energy system."
] |
[
"Why don't the edges of gas giant planets appear as a gradient? What defines the limits of their spheres?"
] |
[
false
] | null |
[
"I know more about Earth's atmosphere than gas giants, but I assume it would be similar. On Earth, the atmosphere is very much a gradient... the air gets thinner and thinner and some of it just keeps escaping into space. In fact, a lot of satellites (and the ISS) have to contend with atmospheric drag, which is why they sometimes need a boost to a higher orbit.",
"The most likely explanation is that planets in general, and gas ",
" in particular, are ",
", so the gradient is such a narrow band that it's invisible from the distance required to see the whole planet, or even just a significant portion of the planet. Also, the outermost layers may be gases that are mostly invisible to the human eye as hydrogen, helium, nitrogen, oxygen, etc are on Earth."
] |
[
"Light scattering gasses add up quickly too. Think of seeing a little smoke from a smoke machine and it not obstructing view much - now add just several more feet and it looks like a dense fog that is solid. The gas on those planets is very dense and after looking through a fractional amount of thickness the gas appears solid. "
] |
[
"There is a gradient. But the diameter of the star is usually much, much bigger, so the fading edge appears razor-sharp by comparison.",
"E.g., here are images of the Sun I've captured during the transit of Venus in 2012.",
"http://florin.myip.org/pictures/index.php/2012-06-06-transit-of-Venus",
"The diameter of the Sun in reality is 1,300,000 km. The apparent diameter in one of those images is ~ 1,300 pixels. That means 1 pixel is 1,000 km. For the \"fading\" to be visible, it would have to extend gradually for many thousands of kilometers, which is not what happens.",
"Things might be a bit different with very large stars, close to the end of their evolution. E.g., here's the density of Betelgeuse, as seen in 7 mm microwave:",
"http://i.imgur.com/yz6EhfG.jpg",
"We don't exactly know yet how it really looks from up close in visible light, but it's spewing out so much material, its \"edge\" might be less regular and less sharp. The \"optical disk\" drawn on that image is more of a conventional representation (and largely a guess)."
] |
[
"Excluding the Sun, if all of the remaining mass that exists in our solar system were combined, would it be enough to collapse into another star?"
] |
[
false
] |
I'm sure my question is worded poorly. I am also sure that I e heard that the Sun has more mass than all other objects in the system combined. I'm wondering if even a small star could form, given the above scenario. Thanks!
|
[
"No. ",
"The graphs here",
" show why pretty nicely.",
"Also, brown dwarfs, the least massive stars, are ~100 Jupiter masses."
] |
[
"Yup! Almost all the mass in the solar system is in the sun, but almost all the angular momentum is in the planets. That was totally unrelated, but I just think it's a cool fact."
] |
[
"Very illustrative. When I was thinking about this, I thought how all the planets combined would only be such a small fraction compared to the sun. However, I (intuitively) didn't think it was such a landslide. Dito for the fact that Jupiter basically has 70% of the mass of all planets. A true giant. Even though Saturn is only slightly smaller, it's much less massive (lower density)."
] |
[
"If you stimulate your brain during a heavy workout session, will you brain adapt to become more efficient in the future due to less oxygen in the brain?"
] |
[
false
] |
My reasoning is that the central nervous system adapts to chemical imbalances, making things like physical addiction to substances and withdrawal symptoms possible. Would reduced oxygen in the brain force the CNS to burn oxygen more efficiently, and when the brain is regularly and consistently stimulated during periods of reduced oxygen, does the brain/CNS adapt to this imbalance?
|
[
"I'm not sure what you mean by burning oxygen \"more efficiently.\" Burning oxygen is only done one way and that is through cellular respiration. Your body can't make the consumption of oxygen more efficient.",
"The other thing is the fact that the brain, in general, is very very bad at adapting to lower oxygen levels. The risk of hypoxia is too great, so the body always makes sure that the brain is supplied adequately. You shouldn't get a decrease in oxygen to the brain when you work out. That would just be extremely risky and a flawed design. In fact, you tend to get increased oxygen to the brain because of the increased blood flow."
] |
[
"Thank you for the insight. I didn't realize that oxygen is prioritized to the brain anyway. Does more oxygen even mean more cognitive function? That was just an assumption I made as well."
] |
[
"Why is it fairly common for brain function to become significantly impaired during a strenuous workout? Is this actually doing any damage?"
] |
[
"Do you save more energy if you dim your house lights to half, rather than having them all up to full?"
] |
[
false
] |
Granted not all house have dimmer switches, but I was just interested to know if it saves you more money to have your lights dimmed lower.
|
[
"Old dimmers, used a variable resister to dim the light. Lets look at a simple example.",
"example",
"We can find total resistance (RT), by adding up all the resistance.",
"RT = R1 + R2 = 0 Ohms + 144 Ohms = 144 Ohms",
"Then we can find the total current (IT).",
"IT = ET / RT = 120V / 144 Ohms = .83A",
"We'll then calculate the voltage across each resistive load.",
"E1 = IT * R1 = .83A * 0 Ohms = 0V",
"E2 = IT * R2 = .83A * 144 Ohms = 120V",
"Finally, we'll calculate the total wattage (WT)",
"WT = V",
" = 120V ",
" / 144 Ohms = 100 Watts",
"Lets see what happens when we increase the resistance of R1",
"Increased resistance",
"RT = 200 Ohms + 144 Ohms = 344 Ohms",
"IT = 120V / 344 Ohms = .349A",
"E1 = .349A * 200 Ohms = 69.77V",
"E2 = .349A * 144 Ohms = 50.23V",
"WT = 120V ",
" / 344 = 41.86 Watts",
"As you can see, we've increased the resistance of R1 and effectively reduced the voltage across R2. And now we have a dim light.",
"Thyristor dimmer",
"Modern dimmers use a TRIAC, to reduce the amount of time the light is on. However, because of the circuitry in the dimmer, there is not a direct 1:1 energy savings. Dimming the light to 50%, will not equate to a 50% savings in electricity.",
"A typical waveform in an AC system would look like this.",
"AC System",
"A TRIAC prevents electricity from flowing every time voltage reaches 0, something like this.",
"example of prevention",
"So you end up with a waveform that looks like this.",
"Waveform TRIAC",
" \nWith the TRIAC, the light is actually turning off and on 120 times per second. With every cycle, you're saving a small amount of power. Is it enough to actually see on your electric bill? I guess it would depend on how long the lights are on, and what percentage they are dimmed."
] |
[
"Old dimmers, used a variable resister to dim the light. Lets look at a simple example.",
"I've never seen such a dimmer. Even going back 40 years or so, all I've ever seen are semiconductor dimmers. The variable resistor in your example would be dissipating 24 watts, which would make the whole fixture hot to the touch in a very short time. I've seen variacs used for dimming high-powered lighting circuits, but never a rheostat.",
"How far back do you need to go to find a rheostat dimmer in a residential installation, I wonder?"
] |
[
"Yeah, that sounds more like a variable resistor setup than a TRIAC. If it's actually getting hot to the touch rather than just warm, though, it might be worth replacing the dimmer and/or the wiring."
] |
[
"Why do so many animals have yellow eyes? Does the color of an animal's eye indicate anything about the eye's structure?"
] |
[
false
] | null |
[
"Yes. Eye color is a combination of structural (reflects some colors away, and some directly back) and absorbent (reflects some directly back).",
"In humans the structure of the iris reflects as blue, and melanin absorbs to reflect as brown. All other colors of the iris are on a spectrum between the two. That is, except for albinos, which have red eyes as they lack the structure in their irises to hold pigment and so light reflects off of the retina."
] |
[
"This article might give you a good starting point (Negro et al. 2017). The short answer seems to be we don't know. As the authors write: ",
"\"To our knowledge, however, no study has identified all selection factors conducive to light or dark eye coloration\".",
"Most species have invariant eye colours i.e. all the same. The species where we see intraspecific variation are humans, and human domesticated species. This suggests that eye colour does have a function constrained by selection, until human domestication overrides that constraint.",
"I know that in owls, nocturnal species have dark eyes, crepuscular species orange eyes, and diurnal species bright eyes, probably for camouflage purposes. No idea if that is general across other species though.",
"Negro, J. J., Carmen Blázquez, M., & Galván, I. (2017). Intraspecific eye color variability in birds and mammals: a recent evolutionary event exclusive to humans and domestic animals. Frontiers in zoology, 14(1), 1-6.",
"https://frontiersinzoology.biomedcentral.com/articles/10.1186/s12983-017-0243-8"
] |
[
"Can you explain the human brown and blue eyes a little more? Does it actually reflect the ability to reflect and absorb?"
] |
[
"AskScience AMA Series: We invented a better version of CRISPR. Ask us anything!"
] |
[
false
] |
We are CRISP-HR Therapeutics, Inc., an early stage biotech company which has developed a dramatically improved CRISPR-based genetic engineering platform, Cas9-HR. The improvements include increased editing efficiency enabling previously unfeasible large edits (1000s of base pairs) at a clinically viable level, in addition to lower cellular toxicity. Our Cas9-HR Platform represents an exciting step for gene editing. We plan to use our Cas9-HR Platform to develop therapeutics, specifically treatments for genetic diseases that are caused by a diverse number of mutations. Since existing high-efficiency CRISPR technologies are limited to small edits (1-50 base pairs), we believe this is an area where we can make a significant impact. Answering questions today are the two co-founders: We'll start answering questions at 19:00 UTC (8pm BST, 3pm EDT, 12pm PDT) on Friday, July 30th. We're looking forward to hearing from you! The guests have finished for today. Thanks for all the great questions!
|
[
"I'm a molecular biologist, I use CRISPR on the daily. What is it you've done that's different, exactly? You haven't really explained. CRISPR combined with homology-directed repair is very well established at this point. I'm literally using it right now to insert a 2000-base pair gene into primary cells. There are many many mutated/modified cas enzymes with greater efficiency/lower off-targets. What's your USP?"
] |
[
"Really missed an opportunity to call it “CRISPIER”"
] |
[
"Can you please provide links to your papers so we can read more ourselves?"
] |
[
"Could a double orbit between a binary star exist for a planet?"
] |
[
false
] |
I have been thinking about this a lot. My guess is no but I wanted to see what others think. Could a planet orbit two stars (aka a binary star) in a figure eight style? I would think not, because if the planet would be going very fast, when it comes within the gravitational pull of the second star it wouldn't properly transfer orbits, it would just stretch the current one. Then again if the stars and planet were all very far away from each other to the point where the orbit is very slow then maybe it would be possible. Then again, we would have to take into account Star B having a gravitational pull on the planet the whole time it is orbiting Star A. What do you guys think?
|
[
"Yes, this is the Arenstorf orbit, discovered in 1963 and used (in part) for the Apollo missions. ",
"This question",
" discusses the orbit and contains some interesting links (unfortunately, the link to the technical paper is broken). Arenstorf orbits are actually a family of solutions to the restricted three-body problem (where the gravity of the tertiary body has a negligible effect on the other two).",
"You might also be interested in ",
"Moore's figure-eight family",
", where three equal-mass bodies chase each other around a figure of eight path. ",
"Addendum: actually, Arenstorf orbits are not stable: ",
"http://books.google.co.uk/books?id=4Y-ownk6ilsC&pg=PA697&lpg=PA697&dq=arenstorf+orbit+stability&source=bl&ots=KHeaelx_WQ&sig=btLzI5qNmeck3Y_btsJyJAYfHgE&hl=en&sa=X&ei=ngsZUsLUJMSf7gbl94C4DA&ved=0CEwQ6AEwCA",
" I guess that means they can't occur in nature, except temporarily, and they wouldn't be much use for permanent artificial satellites (too much station keeping required)."
] |
[
"The problem with this being possible is that binary stars orbit each other in addition to the planet orbiting the system. It wouldn't be possible (mathematically speaking) for a stable orbit to hold that shape with the stars also in motion. Additionally, binary stars are typically much closer to each other than planets would be in such a system. The most probably stable orbit for planets in binary systems is that the planets orbit the center of mass of the two stars in fairly normal ellipses."
] |
[
"It wouldn't be possible (mathematically speaking) for a stable orbit to hold that shape with the stars also in motion.",
"I once wrote a gravitation simulator with a planet going around a binary star system and found it would be stable if the planet were in a RETROGRADE orbit.",
"If the stars rotated clockwise and the planet counterclockwise the system was surprisingly stable for a very wide range of relative masses between the three bodies.",
"It was stable even for three bodies with the same mass orbiting at the same radius from the center of mass, provided that one of the bodies turned in the opposite direction from the other two."
] |
[
"How big of a nuclear bomb would be needed to disrupt or destroy a massive wedge Tornado?"
] |
[
false
] |
I had a trippy dream about this last night, thus the reason I am asking. In other words, lets say someone wanted to run an experiment to see how big a blast would be needed to destroy a tornado, and prevent that particular supercell from spawning another, how big of a yield would a bomb need? I'd imagine it would be in the megaton range, but could someone here give an estimate as to many megatons? Ignore the small problems like fallout and 3rd degree burns.
|
[
"Well yes, you could obliterate the storm. Let's look at the energies involved, shall we?",
"In order to disrupt a tornadic storm, let's assume you would need to blast it with roughly the same order of magnitude of energy. Supercells (and all \"convective\" storms) are fueled by latent heat released by the condensation of water vapor into cloud and rain droplets. Assuming our supercell is a 10-km cube (most are actually quite larger, but this is a good rough guess) a supercell has condensed ",
"4 billion kilograms of water",
". Water's latent heat of vaporization, or the amount of energy released when it condenses from a vapor to a liquid, is ",
"2257 kJ/kg",
", which means that the amount of energy released by a single thunderstorm is around ",
", or 10,000 TJ. Now let's look at the energy released by a nuclear weapon: One ton of TNT is equivalent to ",
"0.004184 TJ",
", so a quick calculation tells us that ",
". This would represent a ",
"slightly small nuclear fusion device",
". So there's your ",
" answer, but remember it's a lot of assumptions that went into the calculation.",
"No, there have been no supercells spawned by nuclear tests. But this is because no one in their right mind would conduct a nuclear test under large-scale weather patterns that were favorable for tornadoes! ",
"Pyrocumulonimbus",
" storms (cumulonimbus clouds induced by fire) are quite common, and there have even been ",
"wildfire-induced supercells and tornadoes",
". And these are from simple wildfires, which are ",
" orders of magnitude less energetic than a nuclear explosion. Sure, you may have disrupted the individual storm, but you have introduced a huge amount of heat energy to an environment which already has the right large-scale ingredients (instability and shear) to produce tornadoes. There's nothing stopping the atmosphere from putting that new extra energy to violent use.",
"If the large-scale environment is favorable tornadoes, setting off a nuke would be a dumb idea for just about every imaginable reason."
] |
[
"That is one of the coolest questions I've ever seen."
] |
[
"Seems like a good idea to me, radioactive hypertornados."
] |
[
"Can someone explain the current atomic model/orbital theory?"
] |
[
false
] |
My understanding of physics is probably above average but certainly nowhere near doctorate level. All through school you're taught about the Bohr model (good teachers will say it's not an accurate representation of reality, bad teachers will just hope nobody asks too many questions). I understand why as it's a good way to visualize and study atoms without overwhelming young students. Later on you learn more accurate valence shell atomic representation, which to my understanding means there's different quantum numbers instead of simple energy levels, and there is probability of finding electrons at certain levels but they can be other places. So here comes my questions: I hope none of my questions appear foolish because I am genuinely wondering about these things. As Einstein once said "I have no special talents. I am only passionately curious.".
|
[
"Is it still correct that electrons travel in orbit around a nucleus? Do they all travel in the same direction?",
"No, electrons are quantum particles and thinking of them as orbiting around the nucleus the way planets orbit around the sun is incorrect.",
"Is it correct to say that electrons are negatively charged and the nucleus is positively charged?",
"Yes.",
"I understand that an electron with a certain quantum number is much more likely to appear in certain regions around the atom - but can they be anywhere? Does the probability work like a function where the limit approaches infinity - asked in a simple way; the further away from the nucleus the less likely it will be you find an electron with a certain quantum number but there will always be a tiny possibility?",
"For large distances from the nucleus the probability of finding an electron there decays exponentially as you're describing. However, for many quantum numbers the radial portion of the wave function has a node (psi=0) at one or more values of r. These correspond to positions where you will never find an electron. (",
"http://panda.unm.edu/Courses/Finley/P262/Hydrogen/WaveFcns.html",
" has some plots showing some wavefunctions with nodes and some without)",
"I've learnt that when an electron changes to a lower states a photon(light) \"appears\", how does this fit in with modern theory as there are no \"shells\" but electrons can be \"anywhere\"? When is light created? When the quantum number changes? Due to the energy level changing?",
"A photon will be created (or absorbed) for any transition between states of different energy.",
"In any molecule is it still true that electrons \"belong\" to a nucleus? Do we know if seamlessly electrons can \"move\" to circle another nucleus? I'm having great difficulty explain my thoughts here so please bare with me... Imagine water H2O, oxygen has 2 electrons in its outer shell (of a certain quantum number I guess?) so it binds to two hydrogen atoms and \"borrows\" two atoms so that it's \"complete\". Then the hydrogen atoms binds to other hydrogen atoms so it has 2 electrons making them \"complete\" too - hence we have amazing water. My question is: can for instance two electrons in one instance belong to a certain nucleus but in the next instance they could swap places?",
"Inner shell electrons remain bound to their respective nuclei, but it isn't a good description of valence shell electrons in a molecule to consider them as belonging to an individual nucleus. They occupy molecular orbitals involving the whole molecule (check out ",
"http://en.wikipedia.org/wiki/Molecular_orbital_theory",
").",
"A basic example to explain my next and final question: Euro coins are an \"alloy\" of copper-brass and copper-nickel but for my example lets say they are gold and silver instead. When for instance two different metals are \"fused\" together like this can (and do they) electrons move between the \"outer shell\" of two atoms of two different metals? (If they don't how do they stick together, is there a very small space between them where the two metals have mixed into a sort of \"gold-silver\" molecule?)",
"Solid state makes things a bit more complicated. In contrast to single atoms and molecules where the allowed energy states are discrete, in solids there are continuous bands of energy containing many possible states. Speaking about individual atoms in the solid having \"outer shells\" isn't really meaningful. The possible electronic states are tied to the structure of the solid as a whole and are not necessarily localized to individual atoms. Check out ",
"http://en.wikipedia.org/wiki/Electronic_band_structure",
" for more details if you're interested."
] |
[
"Is it still correct that electrons travel in orbit around a nucleus? Do they all travel in the same direction?",
"No, the entire concept of classical trajectories is invalid in quantum mechanics, because a particle can't have an exact momentum and position at the same time. So both the concept of 'orbit' and 'direction' pretty much go out the window. Knowing where an electron is at one point in time doesn't enable you to predict where it'll be next.",
"Is it correct to say that electrons are negatively charged and the nucleus is positively charged?",
"Yes.",
"I understand that an electron with a certain quantum number is much more likely to appear in certain regions around the atom - but can they be anywhere? ",
"An orbital is, by definition, a time-independent state of an electron. ",
"This ties in with my previous question, is there a strict theoretical limit to how \"far away\" from the nucleus you could find electrons without it being a \"free electron\"? ",
"This isn't really quantum-mechanical; An electron is considered 'free' if its energy exceeds the ionization potential, rather than how far it is from the nucleus. In much the same way a celestial body is a satellite depending on whether its orbiting or not, not how far away it is.",
"I've learnt that when an electron changes to a lower states a photon(light) \"appears\", how does this fit in with modern theory as there are no \"shells\" but electrons can be \"anywhere\"? ",
"There are shells; these are defined by the different possible combinations of quantum numbers. It's just that a shell doesn't imply the electron is at a certain fixed radius. ",
"When is light created? When the quantum number changes? Due to the energy level changing?",
"The electron has to change state (meaning a change of quantum numbers), and has to change its energy, but it also has to change its angular momentum or spin, to match the angular momentum of the photon that's created. (these are known as ",
"selection rules",
")",
"In any molecule is it still true that electrons \"belong\" to a nucleus? ",
"No, electrons are indistinguishable, so we don't actually deal with specific electrons but the possible electronic ",
" (orbitals, or sub-shells). Depending on the orbital, it can be strongly located to a single atom, or it can be shared between two atoms (forming a bond), or it can even be 'delocalized' across the entire molecule.",
"Do we know if seamlessly electrons can \"move\" to circle another nucleus? ",
"Certainly. That's what chemists visualize with 'resonance structures'. E.g. a benzene molecule can be visualized as having 3 double bonds and 3 single bonds, whose locations are alternating. The underlying reality being that the double-bonding electrons are spread out equally among the six carbon atoms.",
"can (and do they) electrons move between the \"outer shell\" of two atoms of two different metals?",
"Yes, that's why metals are conductors. The electrons are delocalized across the entire solid."
] |
[
"There does exist a \"shell\" or ",
" for each electron energy in an atom. If you free a core electron, one that is near to the nucleus, and a higher energy electron will drop down to fill that new vacancy. In order to compensate for the energy change, a photon of energy equivalent to the electron energy drop will be produced. The energy of the photon is actually a characteristic of the material, as every element has different binding energies for electrons. Therefore, by measuring the energy of the photon, one can determine chemical composition. ",
"Electrons do maintain a negative charge, while the protons in the nucleus maintain positive charge. ",
"As far as the direction, that's a tricky one. However, two electrons in the same orbital will have opposing spins, as you cannot have two electrons with the same quantum number in an atom (which includes energy level and spin).",
"For the last question, yes, electrons can migrate around to other nuclei in the system, this happens in covalent and metallic materials. In ionic materials, one element will give an electron to another, and due to this the individual atoms become charged. They see that the atom they gave an electron two is oppositely charged so the two atoms get cozy together (opposites attract).",
"Metals are considered a \"sea of electrons\" that is, electrons are delocalized and flow around like water. "
] |
[
"Why hasn't the double slit experiment been tried with \"non quantum\" objects?"
] |
[
false
] |
The double slit experiment has been tried with several particles. All of them are very small. Buckeyballs have 60 carbon atoms; "Thomas Juffmann" in Vienna used molecules with 58 and 114 atoms. But has anyone tried with items that are large? (Human proteins, for example.) How are the sizes and distances calculated for double slit experiments? How big would the slits need to be; how far away would the screen need to be for a macro object? For example, the "nano scale" zinc oxide used in modern sun screen.
|
[
"Here's the simple answer:",
"The double slit experiment for particles is interesting because it demonstrates the wave-like nature of mass. However, that wave like nature is only observable for ",
" small things. If you look at the wave function of an electron, the position distribution is large enough that you get an interference pattern in the DS experiment. However, if you calculate the same wave function for a macroscopic object, the position distribution is ",
" small. If you were to put that object through the DS experiment, you would see no interference, only a classical result."
] |
[
"I believe you. But is that supported by any experiment?",
"The larges objects successfully to see an interference pattern I know of were ",
"fullerenes",
" and specifically C-60 balls from what I remember.",
"Thing is, the math for the interference pattern makes it so that, the heavier the object, the shorter it's ",
"DeBroglie wavelength",
". The shorter this wavelength, the smaller the interference pattern. The smaller the interference pattern, the longer the distance has to be from the slits to the projection screen to see it. Someone told me that for an interference pattern to see in human beings, you would probably need a distance between slit and projection screen of about the diameter of our galaxy. It SHOULD be there, but well ... it's impractical to measure."
] |
[
"The double slit experiment only produces an interference pattern if the diffraction from each of the two slits overlaps. The intensity of light in the diffraction pattern from a single slit is ",
"I(theta) = I sin",
" (delta/2) / (delta/2)",
" ",
"where ",
"delta = 2 pi a sin(theta) / (lambda). ",
"Here, a is equal to the width of the aperture, lambda is the wavelength of the light being diffracted, and theta is the angle away from the slit you are along the screen.",
"The intensity of a diffraction pattern is maximum at theta = 0. This is directly in front of the slit on the screen. We find minima when the intensity is equal to 0, aka when sin(delta/2) = 0. We know that when theta = 0, +/- pi, +/- 2pi, ..., also written as theta = n pi, where n = 0, +/-1, +/-2, ..., then sin(theta) = 0. This, delta/2 = n pi, or",
"2 pi a sin(theta) / (lambda) = n pi",
"sin(theta) = n (lambda) /2a",
"For most scenarios, where the distance between the screen and the slit is >> the height we're moving up along the screen, sin(theta) is approximately equal to y/d, where d is the distance between the screen and the slit and y is the distance along the screen we've moved from the initial maximum. Thus, minima occur at y = n (lambda) d/2a.",
"For two slits to cause double-slit interference, the envelope of of light before their first minima must overlap. So, the distance to the first minimum must be greater than half of the distance between the slits, assuming both slits are the same size. aka, n (lambda) d/2a > a/2.",
"Now, it is necessary to introduce the idea of the De Broglie (pr. de broy) wavelength. Any object has a De Broglie wavelength. lambda = h/p, where h is planck's constant and p is its momentum. For substantially small objects, p = mv is rather small because their mass is low, especially when they are accelerated to high velocities. Given that h is on the order of 10",
" a small p is necessary to give any sort of reasonable wavelength. Remember, the wavelength is in the denominator of the equation describing the distance to the first minimum. If it's too small, then the interference pattern from any one slit will be negligible. As objects get larger - say, for example, to the size of a human protein - their momentum increases, decreasing their de broglie wavelength and causing the diffraction pattern from one slit to decrease. To get two-slit interference from a particle of such a size, it would be necessary to accelerate it to massive speeds in order to give it a substantial de broglie wavelength, or place the slits impossibly close together, or make them insanely small. All three of these would increase the size of the diffraction pattern, but setting up an experimental apparatus for this to occur is either too difficult, too expensive, or impossible.",
"Source: Modern Physics class."
] |
[
"What happens to The vibration of a subwoofer when The Volume is increased/decreased?"
] |
[
false
] | null |
[
"The amplifier controls the power (wattage) of the electrical signal going to the subwoofer. ",
"In the subwoofer itself, an electromagnet (the \"voice coil\") is attached to the speaker cone. The voice coil becomes magnetized depending on the strength of the electric signal- a more powerful signal at any given time makes it more magnetic, a less powerful signal makes it less magnetic. The voice coil's variable magnetic field and its interaction with another magnet in your subwoofer causes the speaker cone to move in and out, generating sound. ",
"In other words,\n1. The amplifier increases or decreases the power of the electric signal.\n2. The voice coil increases or decreases its magnetic strength according to the power of the electric signal from the amplifier.\n3. The speaker cone moves in/out more (generating a louder sound) or less (generating less sound) depending on the voice coil's magnetic strength. "
] |
[
"Yes. The frequency determines the pitch, the distance it goes in and out (amplitude) determines the volume. "
] |
[
"So the distance it goes in and out increases when the volume gets louder? But at the same frequency"
] |
[
"Is it possible to describe knots using mathematical functions?"
] |
[
false
] | null |
[
"There's a whole branch of mathematics called knot theory, part of which involves finding unique ways to describe different knots. Knots are generally described by the number of times they cross over themselves (e.g. the simplest knot crosses over itself three times, ",
"here",
" is a table of all knots with seven crossings or less), and you can describe a knot with a parametric function in three dimensions. An example is given ",
"here",
". There are also functions based on knots that give a unique value depending on the type of knot, one example is the Alexander polynomial."
] |
[
"That's a very vague question, can you explain better what you mean?"
] |
[
"No formula is known, but there are ",
"exponential lower and upper bounds"
] |
[
"Is there a speed of gravity similar to the speed of light?"
] |
[
false
] |
For example: If you were measuring the gravitational effect that a single object(A) exerted on a second object(B), and if you were to shift A so as to alter the effect exerted on B; is there a delay between the action and the observation dependent on the distance between A and B? Secondary question: Would the substrate (or lack thereof) through which the force is exerted affect the speed of this transmission?
|
[
"Yes, it's believed to be the same as the speed of light, but our observations are limited so we can only put this within about 20%."
] |
[
"http://www.nrao.edu/pr/2003/gravity/",
"tldr: Measuring the change in electromagnetic waves from a quasar as they passed through Jupiter's gravitational field."
] |
[
"Wouldn't that allow you to send information faster than the speed of light using gravity and thus allow you to violate causality?"
] |
[
"What might the surface of the moon look like (were you standing upon it) during a \"blood moon\" like last night? Would the ground have a red glow, or would it be too subtle to notice up close?"
] |
[
false
] | null |
[
"A blood moon is a result of the Earth's atmosphere filtering out the non red light which hits the moon, then bounces back, gets filtered again, and hits your eyeballs. It would be the same color you see, minus about 50-80% redness. The math would depend on the precise moment that you're talking about, because... atmosphere... spheres... magnetic... ugh. Too long, not doing it."
] |
[
"The red tinge you see on the Moon happens for the exact same reason you see the sky turn red during a sunset.",
"Light from the Sun will pass through the Earth's atmosphere on its way to the Moon, and certain wavelengths will be scattered. The red is all that remains. ",
"You would certainly be able to see this effect on the Moon. It's essentially just a sunset, but if anything, the light has to pass through more of the Earth's atmosphere, hence why it's more red than on Earth."
] |
[
"Right. The moon has virtually no atmosphere. ",
"The refraction of light we're discussing is occurring as the light passes through Earth's atmosphere ",
" hitting the moon."
] |
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