What is mass?

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• What is mass?
• How much better equipped would we be today at rehabilitating the Red Zone at the eastern French border than in the 1920s?
• If you took a coil into space and spun a magnet inside it, will it ever stop spinning? Assuming you're a vacuum and zero gravity. Also, how much electricity would that produce?
• We know of an absolute zero, in which the speed of the molecules at this temperature reaches zero. Is it possible that there is an absolute max temperature, in which the speed of molecules is equal to the speed of light?
• I was watching Apollo 13 and they had a couple burns to help their momentum back to Earth and it got me curious. How does it work when spacecraft thrusts in a vacuum, I mean if there's nothing to thrust against how does it affect the momentum?
• Will the jets of Enceladus ever run dry?
• What determines what surfaces a given pen can write on?
• Why is alpha radiation more desctructive than gamma radiation although gamma radiation has more energy?
• Can computing help solve a thought experiment? Random Generation of the Mona Lisa
• At What Concentration Does Tetrachloroethylene Break Down Calcium in Plumbing?
• The Earth spins at roughly 1000 mph. A ball thrown in the air doesn't fall behind the Earth like a ball thrown from a moving vehicle. Is this because of the momentum at 1000 mph or does the Earth's gravity play a part?
• Should things disappear due to smell?
• When a charged particle accelerates under an applied electric field, what's 'pushing' it?
• Why is 0! = 1?
• If you had a large container that was filled with gas, and 2 perfectly stationary balls positioned near each other in it, if gravity didn't exist, would the pressure of the gas move these balls towards each other?
• What is the point of minus sign in Minkowski space?
• I have a magnet and I attach paperclips to it. Does the magnetic force stay constant? Is the force attracting the first paper clip the some strength as the force attracting the 100th?

What is mass? Posted: 10 Jun 2016 03:20 AM PDT And how is it different from energy? submitted by /u/hmpher [link] [comments]

How much better equipped would we be today at rehabilitating the Red Zone at the eastern French border than in the 1920s? Posted: 10 Jun 2016 05:32 AM PDT The Red zone in France is an area which was deemed unsuitable for human activities on account of the large amount of unexploded ordnance, heavily polluted soils and chemical weapons hidden throughout the land. The decision to set this land apart was taken right after WWI, and the criteria used to define this territory were based on late 1920s assessment of technology and capabilities. Reconsidering the Red Zone from the perspective of the technology and capabilities of 2016, how much better equipped would we be today at rehabilitating and decontaminating that land today compared to back in the 1920s? What would reclaiming this land and making safe for human activities entail? Would it be feasible, how long would it take, would it be worth the effort? submitted by /u/Gargatua13013 [link] [comments]

If you took a coil into space and spun a magnet inside it, will it ever stop spinning? Assuming you're a vacuum and zero gravity. Also, how much electricity would that produce? Posted: 09 Jun 2016 07:50 PM PDT Wouldn't this be an easy way to generate power for the space station? submitted by /u/panchugo [link] [comments]

We know of an absolute zero, in which the speed of the molecules at this temperature reaches zero. Is it possible that there is an absolute max temperature, in which the speed of molecules is equal to the speed of light? Posted: 09 Jun 2016 02:40 PM PDT submitted by /u/walleye275 [link] [comments]

I was watching Apollo 13 and they had a couple burns to help their momentum back to Earth and it got me curious. How does it work when spacecraft thrusts in a vacuum, I mean if there's nothing to thrust against how does it affect the momentum? Posted: 09 Jun 2016 11:13 PM PDT submitted by /u/Spuddups84 [link] [comments]

Will the jets of Enceladus ever run dry? Posted: 09 Jun 2016 10:50 PM PDT I was watching Space's Deepest Secrets and they talked about the moon Enceladus and the jets it has blasting water into space. My question is, why hasn't Enceladus run out of water? I don't normally post here so I apologize if this is a stupid question. http://www.nasa.gov/multimedia/imagegallery/image_feature_1856.html submitted by /u/ElectricBlueVelvet [link] [comments]

What determines what surfaces a given pen can write on? Posted: 09 Jun 2016 02:33 PM PDT submitted by /u/redditpirateroberts [link] [comments]

Why is alpha radiation more desctructive than gamma radiation although gamma radiation has more energy? Posted: 09 Jun 2016 11:26 AM PDT submitted by /u/glatteis [link] [comments]

Can computing help solve a thought experiment? Random Generation of the Mona Lisa Posted: 09 Jun 2016 06:13 PM PDT When I was 10ish (33 now) I was flicking through the channels and landed on a debate i'm not sure what the debate was about but the speaker at the time said something along the lines of "The odds of the universe being created without a God is less likely than a dump truck driving into a wall where the rubbish that hit the wall will recreates the Mona Lisa" This has stuck with me ever since, not that I believed what he said but me just wanting to know how possible, if possible at all will it be that a dump truck driving into a wall can re create the Mona Lisa. In a universe that's timeless and has trucks driving into walls every second surely there's at the least the possibility of a recreation. No doubt there aren't enough trucks on this earth and maybe not even enough time in the earths existence to have success with this experiment but what I am wondering is can computing help? A system I can think of could be something like this. •The software has a canvas, lets say 800 x 800 pixels •A script is then executed which assigns each pixel its own color •Once executed there the image will be saved in a location •The process repeats itself •A reverse lookup can then be used in attempts to find the Mona Lisa With the current computing power (how many saves a second is possible?) (how big of a HDD is needed for such an operation?) how likely is a result from such an experiment? submitted by /u/Furryfeet123 [link] [comments]

At What Concentration Does Tetrachloroethylene Break Down Calcium in Plumbing? Posted: 10 Jun 2016 12:45 AM PDT I'm referring to the Newmark Groundwater Contamination Site; Health Officers had found levels of lead in excess of 15ppb at two locations, but investigations were impaired when they were all but wiped out in the San Bernardino shooting. Does this substance make water inherently more corrosive to lead and solder? submitted by /u/Teachtaire [link] [comments]

The Earth spins at roughly 1000 mph. A ball thrown in the air doesn't fall behind the Earth like a ball thrown from a moving vehicle. Is this because of the momentum at 1000 mph or does the Earth's gravity play a part? Posted: 09 Jun 2016 02:49 PM PDT Also hypothetically, how would you stop an object so that the ground speed is 1000 mph faster? submitted by /u/Frigg-Off [link] [comments]

Should things disappear due to smell? Posted: 09 Jun 2016 02:38 PM PDT So smell is basically just small particles in the air right? Like when you smell bacon it's due to teeny particles of bacon in the air being picked up in your nose. So technically shouldn't things eventually just disappear due to smell? Or at least get smaller? If so how long would it take for a specific object to become noticeably smaller or be gone? submitted by /u/ponguinn [link] [comments]

When a charged particle accelerates under an applied electric field, what's 'pushing' it? Posted: 09 Jun 2016 04:50 PM PDT I'm confused as to how a field mediated by photons would impart a force on a charged object. For instance, why should a larger charge result in a larger resultant force? What's actually going on when the particle starts to accelerate under the influence of the field? submitted by /u/myallergies [link] [comments]

Why is 0! = 1? Posted: 09 Jun 2016 03:51 PM PDT submitted by /u/ozzric [link] [comments]

If you had a large container that was filled with gas, and 2 perfectly stationary balls positioned near each other in it, if gravity didn't exist, would the pressure of the gas move these balls towards each other? Posted: 09 Jun 2016 09:21 PM PDT As in, there is less gas between the balls than there is everywhere else, so would the balls move towards each other? submitted by /u/somerandomrubbish [link] [comments]

What is the point of minus sign in Minkowski space? Posted: 09 Jun 2016 03:09 PM PDT I am failing to understand the full usefulness of Minkowski's choice to give time a sign opposite of space (-+++ or +---) in his famous s2 = x2 + y2 = z2 – (ct)2 . The answers (other than: "that's just how it is") fall into two categories: 1) It's completely random, but convenient because it makes is easy to tell events which can no cause each other ("space-like separation") from ones that can ("time-like separation") by the sign of the answer. (Which is nice, but seems hardly a big deal) 2) Because it's consistent with reality by making the spacetime interval (S2) be invariable in all inertial frames. First of all, the two answers seems to be mutually exclusive. Second, answer #2 is not much of an answer unless you explain HOW it's consistent with reality whereas having same sign would not be. It seems to me that one can use a coordinate system with all same-signs for time and space that also has the spacetime interval be invariant. If we were to draw an X & T two dimensional chart where both axes have positive values, then a shifting of frames would rotate simply rotate both axes by same degree keeping them 90deg to each other instead of moving them toward each other. Frameshift image Looking at using good-old Pythagoras theorem, one would write X2 + (CT)2 = S2 But X'2 + (CT')2 also equals S2. I.e. - X'2 + (CT')2 = X2 + (CT)2 = S2 Meaning S2 is still showing to be invariable and without the use of any minus signs. So why add all the awkwardness of negative CT? submitted by /u/alikp [link] [comments]

I have a magnet and I attach paperclips to it. Does the magnetic force stay constant? Is the force attracting the first paper clip the some strength as the force attracting the 100th? Posted: 09 Jun 2016 09:07 PM PDT Assuming each paper clip is contacting the magnet with equal surface area submitted by /u/swill128 [link] [comments]

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Is there a limit to how many photons you can pack into a beam of defined width? Or to ask the other way - can an infinite number of photons occupy the same space?

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• Is there a limit to how many photons you can pack into a beam of defined width? Or to ask the other way - can an infinite number of photons occupy the same space?
• How does sorting by "Relevance" work? How does a computer determine what's relevant and what isn't?
• What is energy?
• Has there been any attempt to create one of the elements thought to be in the island of stability?
• What would happen if you took dry ice to the deepest part of the ocean?
• Anyone know where I can find a reference to cube/box (3D) in uniform electric field with numerical results?
• What is a "finite" Reynold number flow? As opposed to infinite?
• Why does heat capacity generally goes up with temperature?
• How do scientists still find new elements?
• What is the difference between straight hair and curly hair?
• How is it even possible to detect a star that's 13 billion light years away if inverse-square law is true, if my math is correct all the photons would dissipate (disperse) (not be detectable in a point in space) well before they reach even 1 billion ly in a 3 dimensional field?
• How long does airway endothelial metaplasia take to develop?
• Does sound travel differently depending on how much light is present?
• Rockets need to expell mass to go forward, but if you expell the mass at greater speed then less mass need to be expelled, couldn't Rockets just expell the mass at very high velocity to reduce the amount off mass needed to be carried?
• Ask Anything Wednesday - Engineering, Mathematics, Computer Science
• How do neurons fire phasically without ligand gated channels being opened? (as oppose to firing when glutamate binds their receptors)
• Why do some planets have rings whereas others don't? Could Earth have a ring(s)?
• I was just linked to NASA's Clean Air Study. Are there any known plants that would clean other toxins or even debris from the air?
• How good were the optics in Galileo's telescope compared to today's cheap telescopes?
• Is there a way to explain classical physics using quantum physics?
• If I weigh X and add Y weight to my body during exercise, do I burn the same calories as a person who weights X+Y?
• Why isn't the F-wave seen in Nerve Conduction Studies prevented by the refractory period?

Is there a limit to how many photons you can pack into a beam of defined width? Or to ask the other way - can an infinite number of photons occupy the same space? Posted: 09 Jun 2016 05:06 AM PDT submitted by /u/iphark [link] [comments]

How does sorting by "Relevance" work? How does a computer determine what's relevant and what isn't? Posted: 09 Jun 2016 06:05 AM PDT A lot of search tools let you change the thing you sort by. You can look at the most recent, the newest, or the most popular, and I can understand the criteria they're sorting by. But sometimes you have a sort by "relevance" option (like this), and I don't understand what that's doing. And just to be specific, I'm not talking about algorithms like pagerank that can use outside information like cross linking to determine the weights of specific entries, but specifically something like reddit's search, that only has the entries themselves to determine relevance from. Unless, of course, that's how all of these relevance sorts work on the back end. submitted by /u/therationalpi [link] [comments]

What is energy? Posted: 08 Jun 2016 04:47 PM PDT All of matter is just energy, we look at it closer and closer, and we get to something like quantum foam or the vacuum energy. Isn't this just a measurement of energy? It doesn't really tell us what energy is. So what exactly is energy? submitted by /u/Raikounrlla [link] [comments]

Has there been any attempt to create one of the elements thought to be in the island of stability? Posted: 08 Jun 2016 02:40 PM PDT Is it even possible to create such large nuclei? How does one go about to create one? submitted by /u/Angriestmanever [link] [comments]

What would happen if you took dry ice to the deepest part of the ocean? Posted: 08 Jun 2016 05:47 PM PDT Would it bubble just like it would in 5 feet of water or could the immense pressures keep it solid or force it to be a liquid instead of sublimating? submitted by /u/SatanV2 [link] [comments]

Anyone know where I can find a reference to cube/box (3D) in uniform electric field with numerical results? Posted: 09 Jun 2016 01:50 AM PDT Hi! I hope this is the right subreddit. I'm doing simulations where we look at a conducting (aluminium) cube and its effects on the external uniform electric field (essentially parallel plates with a conducting object inbetween) and I'm having a really hard time finding any numerical results to compare with. A sphere was not a issue and simulations are agreeing with the analytical solution, but I also want to have some sort of reference to a cube/box in a field. If anyone could point me in the right direction to an article or similar that would be very helpful. submitted by /u/Cornelisen [link] [comments]

What is a "finite" Reynold number flow? As opposed to infinite? Posted: 09 Jun 2016 06:18 AM PDT This is in a paper I am reading. I understand that Reynold number is directly correlated with turbulence, so would an infinite Reynold number just mean something is infinitely turbulent? This seems pointless to say, since turbulence can't be infinite, correct? Thanks. I am flairing as Physics, but the paper I am reading is about biology, and this also has mathematics applications I suspect. submitted by /u/asdf629 [link] [comments]

Why does heat capacity generally goes up with temperature? Posted: 08 Jun 2016 05:48 PM PDT Hello Reddit, first time here! I understand that heat capacities need to go to infinity as one approaches the boiling/melting of a given substance, but why does it always have to increase? In other words, is there a physical explanation for why dCp/dT>0 for all T different from boiling/melting points? submitted by /u/gustavohrg [link] [comments]

How do scientists still find new elements? Posted: 09 Jun 2016 04:25 AM PDT submitted by /u/Guguskis [link] [comments]

What is the difference between straight hair and curly hair? Posted: 08 Jun 2016 03:06 PM PDT I was wondering about the physical difference, if any, between curly hair and straight hair. submitted by /u/Daersk [link] [comments]

How is it even possible to detect a star that's 13 billion light years away if inverse-square law is true, if my math is correct all the photons would dissipate (disperse) (not be detectable in a point in space) well before they reach even 1 billion ly in a 3 dimensional field? Posted: 08 Jun 2016 12:54 PM PDT https://en.wikipedia.org/wiki/Inverse-square_law submitted by /u/itseinsteiniswear [link] [comments]

How long does airway endothelial metaplasia take to develop? Posted: 08 Jun 2016 04:27 PM PDT I just read in my paramedic text book about simple squamous cells replacing columnar and cuboidal cells in the airway in chronic smokers. How long does this process take to occur and then return to normal? submitted by /u/WalksOnSaline [link] [comments]

Does sound travel differently depending on how much light is present? Posted: 08 Jun 2016 03:15 PM PDT submitted by /u/JoshuaChristmas [link] [comments]

Rockets need to expell mass to go forward, but if you expell the mass at greater speed then less mass need to be expelled, couldn't Rockets just expell the mass at very high velocity to reduce the amount off mass needed to be carried? Posted: 08 Jun 2016 02:51 PM PDT The biggest problem with rockets is that they need to carry a large amount of fuel, but what I'm wondering is that a possible future solution to this is to use ion drives that use magnets to expell some amount off mass but to just use a nuclear reactor to increase the amount of energy in the magnets and expell the mass at higher speed to carry less off it. Also could it then be possible to expell only a few particles at extremely high velocity to only have to carry an extremely low amount or am I missing something? Now I know that you can't expell the mass at or beyond the speed of light but even then you can still add and ever increasing amount of energy and therefore momentum giving you greater thrust. Is this possible or is there some physical reason of why it can't happen, I'm speaking from a purely hypothetical standpoint and using technology in the distant future, maybe using super conducting magnets or something. I would love to know some thoughts on this. Thank you P. S. I'm new to reddit so I'd just like to say hi and sorry if I'm doing something wrong, I'm not too clear yet on the rules :) submitted by /u/simonhugh94 [link] [comments]

Ask Anything Wednesday - Engineering, Mathematics, Computer Science Posted: 08 Jun 2016 08:05 AM PDT Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Engineering, Mathematics, Computer Science Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical /r/AskScience post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Asking Questions: Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit /r/AskScienceDiscussion , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Answering Questions: Please only answer a posted question if you are an expert in the field. The full guidelines for posting responses in AskScience can be found here. In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for /r/AskScience. If you would like to become a member of the AskScience panel, please refer to the information provided here. Past AskAnythingWednesday posts can be found here. Ask away! submitted by /u/AutoModerator [link] [comments]

How do neurons fire phasically without ligand gated channels being opened? (as oppose to firing when glutamate binds their receptors) Posted: 08 Jun 2016 03:31 PM PDT How is the depolarization timed? submitted by /u/medicinedelete [link] [comments]

Why do some planets have rings whereas others don't? Could Earth have a ring(s)? Posted: 08 Jun 2016 10:29 AM PDT submitted by /u/joshslattery [link] [comments]

I was just linked to NASA's Clean Air Study. Are there any known plants that would clean other toxins or even debris from the air? Posted: 08 Jun 2016 02:54 PM PDT NASA's study looked at benzene, formaldehyde, trichloroethylene, xylene, toluene, and ammonia. Let me know if I should change the flair to chemistry. submitted by /u/DaughterEarth [link] [comments]

How good were the optics in Galileo's telescope compared to today's cheap telescopes? Posted: 08 Jun 2016 05:32 AM PDT Amateur astronomers try to warn well-meaning parents away from the $50 Wal Mart telescopes, with good reason. However, the telescope that Galileo used would have had limited optics compared to what's available to a well-funded amateur today, and he saw quite a lot with it. How would Galileo's telescope compare to the cheap end of today's models? submitted by /u/frezik [link] [comments]

Is there a way to explain classical physics using quantum physics? Posted: 08 Jun 2016 08:48 AM PDT For instance, how are you able to explain how a box moves with applied force? Is quantum physics limited only to the very small? submitted by /u/ChurchOfChung [link] [comments]

If I weigh X and add Y weight to my body during exercise, do I burn the same calories as a person who weights X+Y? Posted: 08 Jun 2016 12:31 PM PDT For example, suppose I weigh 200 pounds and add a 20 pound weighted vest to my body. Do I burn the calories of a 220-pound person, or am I burning the calories of a 200-pound person who is carrying around 20 pounds of weight? Or, is there even any difference? submitted by /u/Me_for_President [link] [comments]

Why isn't the F-wave seen in Nerve Conduction Studies prevented by the refractory period? Posted: 08 Jun 2016 10:15 AM PDT From my understanding of action potentials this shouldn't be possible. submitted by /u/ferretersmith [link] [comments]

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What is the limit to space propulsion systems? why cant a spacecraft continuously accelerate to reach enormous speeds?

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• What is the limit to space propulsion systems? why cant a spacecraft continuously accelerate to reach enormous speeds?
• Would a field that reduces your inertia violate any important laws of physics?
• There's a massive ball of water floating in space. How big does it need to be before its core becomes solid under its own pressure?
• What exactly is radiation?
• How can the auto-focus feature on my cellphone's camera tell when a shot is in focus or not in focus?
• What exactly are polynomials used for?
• (Physics and Chemistry) In density functional theory, the KS formulation derivation usually involves a Lagrange multiplier portion, what is the purpose of this step?
• How are the rotational speeds of planets determined?
• Virtual particles annihilation, where are the photons?
• Can you identify the source of a radio transmission using trigonometry and the location of two known radio receivers? From novel 'All the Light you Cannot See'.
• If you hold a spring compressed for long enough, will it eventually hold that shape (ex. not uncompress when the force is removed)? If so, what has happened at a molecular level?
• What is the reason for so few chemicals are liquid at room temperature?
• Does a sub-atomic particle travelling in its own field produce a _wake_ in that field? Or is that too simplistic?
• I made a very acidic PBS solution, how?
• Where does our atmospheric oxygen come from?
• What would happen if 2 persons have the same public key for encryption? How is it prevented?
• How can non-ionizing radiation affect matter like the receptors in my eye or chlorophyll?
• If Earth's gravity suddenly desappeared, would my body feel the gravitational pull from the Sun?

What is the limit to space propulsion systems? why cant a spacecraft continuously accelerate to reach enormous speeds? Posted: 07 Jun 2016 12:40 PM PDT the way i understand it, you cant really slow down in space. So i'm wondering why its unfeasible to design a craft that can continuously accelerate (possibly using solar power) throughout its entire journey. If this is possible, shouldn't it be fairly easy to send a spacecraft to other solar systems? submitted by /u/Challenn [link] [comments]

Would a field that reduces your inertia violate any important laws of physics? Posted: 07 Jun 2016 10:35 AM PDT I was thinking about some sort of energy field that reduces the inertia of a body or area. I was wondering if this would violate any laws of physics. Specifically it wouldn't change gravity, so you couldn't violate the conservation of energy by building an overbalanced wheel. The part I have questions about is conserving kinetic energy. It would also have to speed you up and slow you down as you turned it on and off to conserve kinetic energy. But does this fly in the face of relativity? Since as far as I know, you have different amounts of kinetic energy depending on the location of the observer, right? You wouldn't be able to exceed lightspeed as that would either require a field that reduced your inertia to 0, or still require infinite energy. So I suppose my question is would a field that reduced your inertia conserve kinetic energy if you sped up and slowed down as it increased and decreased in strength, or would that still break conservation of energy? submitted by /u/zimirken [link] [comments]

There's a massive ball of water floating in space. How big does it need to be before its core becomes solid under its own pressure? Posted: 08 Jun 2016 03:31 AM PDT So under the assumption that - given enough pressure - liquid water can be compressed into a solid, lets imagine we have a massive ball of water floating in space. How big would that ball of water have to be before its core turned to ice due to the pressure of the rest of the water from every direction around it? I'm guessing the temperature of the water will have a big effect on the answer. So we'll say the entire body of water is somehow kept at a steady temperature of 25'C (by all means use a different temperature - i'm just plucking an arbitrary example as a starting point). submitted by /u/TheGrog1603 [link] [comments]

What exactly is radiation? Posted: 08 Jun 2016 12:29 AM PDT What is radiation? What is it made of? What determines how much energy it has? Amplitude of waves? Frequency? Why can we only see light on the EMS? Why only infrared carries heat? Are photons of different colours? What are alpha, beta, gamma particles? Do gamma particles make up gamma rays? i have soo many questions. I want to become a physicist and have no clue to radiation. So wanted to start somewhere. submitted by /u/shithappenedbrah [link] [comments]

How can the auto-focus feature on my cellphone's camera tell when a shot is in focus or not in focus? Posted: 07 Jun 2016 05:09 PM PDT It will sometimes take a moment and cycle through various focus levels, but it will very often settle on a good focus level. I can touch the screen to tell it where I want it to focus, and it will in most cases manage to do this. I don't understand how the computer can tell what is in focus and what is not in focus. submitted by /u/MaggyMax [link] [comments]

What exactly are polynomials used for? Posted: 07 Jun 2016 05:59 AM PDT So I have been learning about polynomials in school for the past couple of weeks (graphing them) and our teacher told us that we won't need to actually use them later in life. So what exactly are they used for? submitted by /u/Maaley [link] [comments]

(Physics and Chemistry) In density functional theory, the KS formulation derivation usually involves a Lagrange multiplier portion, what is the purpose of this step? Posted: 07 Jun 2016 04:50 PM PDT So I can follow the Hohenberg Kohn Theorems E = E[n(r)] and E0[n(r)] = min <H> over n(r) In a lot of derivations of the Kohn Sham equations, I see some steps involving the Lagrange multiplier method, but since we do not know how to write <T> explicitly as a functional of the density, it doesnt work out. This is done for both an electron non-interacting and interacting systems to show that they have the same form. The related SE equations are the KS equations. What is the purpose of the Lagrange multiplier portion of the derivation? Is the KS formulation just an perturbation-esque expansion with the non-interacting system as the starting point? Is whole exchange correlation functional just a consequence of sweeping everything we dont understand into one pile (the portion of the Kinetic energy missed by the non-interacting system, the election-electron self-interacting portion, the quantum election-electron interacting bits (having to do with electron being a fermion), etc)? How does the KS equations guaranteed an energy minimized electron density? (I think this is probably somewhat off topic, because this is probably related to variation calculus) submitted by /u/Trollsofalabama [link] [comments]

How are the rotational speeds of planets determined? Posted: 07 Jun 2016 03:13 PM PDT I've heard about how it can take some planets longer to rotate once than complete their orbit, but how was this figured out? submitted by /u/XcmByte [link] [comments]

Virtual particles annihilation, where are the photons? Posted: 07 Jun 2016 04:39 PM PDT I keep reading about pairs of particles and their anti particle being created then annihilating each other soon, so that the conservation of mass and energy is preserved. But, won't such annihilation also give off photons? For example, an electron and positron will give a photon. So, why isn't empty space very bright? submitted by /u/covor [link] [comments]

Can you identify the source of a radio transmission using trigonometry and the location of two known radio receivers? From novel 'All the Light you Cannot See'. Posted: 07 Jun 2016 07:44 PM PDT In Anthony Doerr's 'All the Light you Cannot See' the main character calculates the location of radio broadcasts using trigonometry. The character using two radio receivers is able to track the location of transmissions of illegal radio activity of members of the French resistance in german occupied france during WW2. The characters then proceed calculate with trigonometry the location of the radio transmission zero in on the source and eliminate the radio operators. Is this pure fiction or is something like this possible. submitted by /u/ImNotFunny2 [link] [comments]

If you hold a spring compressed for long enough, will it eventually hold that shape (ex. not uncompress when the force is removed)? If so, what has happened at a molecular level? Posted: 07 Jun 2016 02:54 PM PDT Hopefully I worded the title okay... submitted by /u/Juno_Malone [link] [comments]

What is the reason for so few chemicals are liquid at room temperature? Posted: 07 Jun 2016 02:08 PM PDT Most liquids we see are water based. What is the reason there are so few non water based liquids? because there are lots of solids and lots of gasses but few liquids? Is it because the range that chemicals are liquid is smaller than the range for them to be gas/solid and so whatever the temperature we would only find a few liquids? if so why is the range for liquid so small? Is it because most things are liquid at a certain temperature range and we just happen the be at a temperature that is anomalous? if so why are most things liquid at whatever temperature is the normal liquid temp? edit: eugh this title. submitted by /u/ugotpauld [link] [comments]

Does a sub-atomic particle travelling in its own field produce a _wake_ in that field? Or is that too simplistic? Posted: 07 Jun 2016 02:35 PM PDT submitted by /u/cthuluatemypenis [link] [comments]

I made a very acidic PBS solution, how? Posted: 07 Jun 2016 06:27 AM PDT I do small dumb work for a lab and I had to make 1L of 20x PBS solution. The "recipe" I used was 4g of KCl, 4g of KH2PO4, 160g of NaCl and 43.2g of Na2HPO4, in mq water. The PH turned out to be 3.5! A collegue gave me "another recipe", which turned out to be the exact same thing, same masses and compounds, but with Na2HPO4 - 7H2O instead of just Na2HPO4. I made that solution and the PH was 6.80, so totally normal according to my collegues. Now, I thought hey, the issue must have been that I put way too much Na2HPO4 since it wasnt the hydrated mass, but apprently Na2HPO4 is "slightly basic", so the Ph should've been too basic, not too acidic... Right? Am I fundamentally not understanding acids and bases, or did the issue have to come from something else, like using the wrong compound? Thanks a lot submitted by /u/QueenLadyGaga [link] [comments]

Where does our atmospheric oxygen come from? Posted: 07 Jun 2016 01:21 PM PDT Chemistry major here. I'm currently doing a literature study on manganese for a boring-ish group project I've been assigned, and my focus is on the biochemical properties of manganese. Now, there's also a small presentation to be given about the project. During a practice talk with our supervising professor, I mentioned that virtually all atmospheric oxygen is produced by the (manganese-containing) Photosystem II enzyme complex, which is present in plants, bacteria and archaea. The professor totally shot me down on this statement and said that I shouldn't include such populistic remarks in my bit. However, he refused to tell me why my remark was incorrect. So, in short: if the Photosystem II enzyme complex isn't responsible for most of our atmospheric oxygen, what other things are out there? submitted by /u/TheLarch1 [link] [comments]

What would happen if 2 persons have the same public key for encryption? How is it prevented? Posted: 07 Jun 2016 03:09 PM PDT What would happen if 2 persons have the same public key for encryption, assuming same algorithm? How is that case prevented? Is it feasible to collect and build tables of known keys? I know these questions are rather general, but right now I am not sure where and how to be more specific. submitted by /u/danielcw189 [link] [comments]

How can non-ionizing radiation affect matter like the receptors in my eye or chlorophyll? Posted: 07 Jun 2016 07:00 AM PDT Whenever I have the discussion about if EM radiation from phones can be damaging I use the argument that the energy of the photons is to low to affect our cells, it can only be converted to heat. I know that blue light has enough energy to free electrons form a metal surface, but not green or red. How can we perceive these colors when the energy is so low? And is there a possibility that EM radiation can bring changes to our cells? submitted by /u/Faultybrains [link] [comments]

If Earth's gravity suddenly desappeared, would my body feel the gravitational pull from the Sun? Posted: 07 Jun 2016 02:57 PM PDT submitted by /u/kugelblit [link] [comments]

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