question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>If a particle with mass $m$ collides with a wall at right angles, and the collision is perfectly elastic. The particle hits the wall at $v\ ms^{-1}$. There is no friction or gravity.
So the particle will rebound at $-v\ ms^{-1}$?</p>
<p><img src="http://i.stack.imgur.com/Xp73i.png" alt="image description"></p>
<p>... | g7406 | [
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<p>My science teacher used to say a lot of weird stuff, but I'm just making sure on this one.</p> | g7407 | [
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<p>I know that half silvered mirrors are used in the production of laser emission. Can half silvered mirrors be used outside the instrument so the rays get reflected back on one side of the mirror and pass through the other side? </p>
<p>What will be the result if a half silvered mirror is kept rotating and laser is m... | g7408 | [
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<p>Next semester, I am going to lecture about (the mathematics of) general relativity and I am still thinking hard how to organize and even more importantly how to motivate all the stuff.</p>
<p>I am wondering what minimal assumptions I have to make about the objects and their relations to be able to interpret the for... | g7409 | [
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<p>Yesterday my wife asked me that question, and I couldn't answer.</p>
<p>Consider a car, in a sunny day, and that is consumes x gallons per mile. Considering that everything is equal, except that it's traveling in a rainy day, but at the same temperature as the sunny day so that air density is the same.</p>
<p>Will... | g7410 | [
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<p>Since by definition we cannot observe black holes directly, how do astronomers determine the mass of a black hole?</p>
<p>What observational techniques are there that would allow us to determine a black hole's mass?</p> | g7411 | [
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<p>How much of the Earth would a spoonful of the Sun scorch if held at ground level?</p>
<p>I basically would like to conceptualize the heat of the Sun on a smaller scale, please.</p> | g7412 | [
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<p>The viscosity of water creates drag on swimmer's body so its effect is to slow down the swimmer. However the viscosity seems to be essential for pushing the water backwards by the swimmer's arms and legs. Would a human be able to swim in water with much lower viscosity? What standard stroke (front crawl, breaststrok... | g7413 | [
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<p>Water pressure is simply $pgh/2$ for a vertical wall parallel to the depth of the water at exactly the half the water's depth. Suppose the wall is tapered (angled) slightly at around 2 degrees from the y-axis (parallel to the wall). How would you measure the pressure at this point? Would it be the contributing press... | g7414 | [
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<p>During a random reading through this site, I found this one: <a href="http://physics.stackexchange.com/questions/7131/origin-of-elements-heavier-than-iron-fe">Origin of elements heavier than Iron (Fe)</a>...</p>
<p>The answer was "The formation of many elements in earth was due to <a href="http://en.wikipedia.org/w... | g7415 | [
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<p>consider me sitting on the top of a train which is travelling close to the speed of light, will I be able to see my image on a mirror which I'm holding in my hand??</p> | g248 | [
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<p>I'm reading some chemistry-related papers that employ concepts of droplet evaporation. Since I am no chemist, I am wondering:</p>
<p>How can I estimate the actual size of a molecule, say <a href="http://en.wikipedia.org/wiki/Succinic_acid" rel="nofollow">succinic acid</a>?</p>
<p>An order of magnitude would suffi... | g7416 | [
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<p>I am rather a theoretician and looking for a formalism to represent biological clocks by Hermitian operators.</p>
<p>The simplest thought model I am looking for is a formal representation of a clock (for instance 12 hours clock) by applying a Hermitian operator (e.g. Hamiltonian)?</p>
<p><em>Note: a clock is a dis... | g7417 | [
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<p>What is going on here <a href="http://youtu.be/LQFmKPA-iAg" rel="nofollow">http://youtu.be/LQFmKPA-iAg</a></p>
<p>Is ethanol leaving the liquid? If so, why?</p>
<p>Does the pressure add energy to the ethanol molecules causing them to gasify and move rapidly near border of gas/liquid and rapid depressurization allo... | g7418 | [
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<p>Consider a big commercial airliner, like a 727, 747, or a 787. </p>
<p>At cruising altitude, under standard conditions, how much of the lift of the aircraft comes from the wings, and how much from the rest of the airframe -- the tube that holds all the people? </p>
<p>My general impression from watching airplanes... | g7419 | [
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<p>One way how to look at refraction by a dielectric medium like water or glass is that (phase) velocity of light decreases because it is the wavelength rather than the frequency of the light which changes.</p>
<p>I have read somewhere (but can't recall where) that the frequency must remain the same because otherwise ... | g7420 | [
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<p>So I have faced a problem dealing with transient conduction and I need a little help with the problem solving concepts. I need to determine how long it would take to reach the final temperature but I need to know the convection coefficient for that.</p>
<p>I have done steady state and calculation of Reynolds'/Nusse... | g7421 | [
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<p>Why is the number of molecules in a standard volume of gas at a standard temperature and pressure a constant, regardless of the molecule's composition or weight?
Let's say I have a closed box full of a heavy gas, one meter on a side. It has a certain number of molecules inside. I want to be able to add a lighter g... | g7422 | [
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<p>In popular science books and articles, I keep running into the claim that the total energy of the Universe is zero, "because the positive energy of matter is cancelled out by the negative energy of the gravitational field".</p>
<p>But I can't find anything concrete to substantiate this claim. As a first check, I di... | g27 | [
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<p>Take an initial state and its environment, $E$, as follows,
$$
|\psi\rangle_i = |0\rangle |E\rangle + \sqrt{2}|1\rangle |E\rangle.
$$
Suppose that I've written it already in the basis in which the state de-coheres, such that after de-coherence, the wave-function is
$$
|\psi\rangle_f = |0\rangle |E_0\rangle + \sqrt{... | g7423 | [
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<p>If we observe light that originates X light years away, but it passes between black holes X/2 light years away, will it be normal or red shifted or blue shifted? What if the black holes were X/4 or 3X/4 light years away?</p>
<p>I have always wondered if the apparent red shift of distant galaxies must be due to r... | g7424 | [
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<p>There are 2 balls in a vacuum, next to each other but not touch. They are on the edge of a surface they will both leave the table at exactly the same time. One gets pushed harder than the other. The earth is completely flat. Apparently both balls will hit the floor at exactly the same time and even further be at the... | g7425 | [
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<p>I connected a bulb to a battery positive terminals with positive and negative terminals with negative .
It glows as it should but when i connect the positive terminal of the same bulb to the positive terminal of one battery and negative terminal of the same bulb to the negative terminal of another battery. The bul... | g7426 | [
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<p>I'm confused about the relation between the velocity expansion of a scattering cross section and the angular momentum (partial wave) expansion. For example, for dark matter annihilation, we write </p>
<p>$\sigma v = \sigma_s + \sigma_p v^2 + \cdots$, </p>
<p>where $v$ is the velocity and $\sigma_s$ corresponds to ... | g7427 | [
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<p>The system is as follows -</p>
<p><img src="http://i.imgur.com/9hwHHIh.png" alt=""></p>
<p>Friction exists only between the 2 blocks.</p>
<p>I am trying to find out the accelerations of $m_1$ and $m_2$.</p>
<p>Let $a_2$ be acceleration of $m_2$, and $a_x$ and $a_y$ be the accelerations of $m_1$ in the respective... | g7428 | [
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<p>Given an alcohol solution and a mass of ice in whatever shape you like, is shaping it into a sphere the worst possible way to cool your drink without diluting it?</p>
<p>If the ice starts off at a sub-zero temperature, it is able to cool the drink without diluting it by first warming to 0 °C. After the periphery o... | g7429 | [
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<p>Thinking about the concept of symmetry breaking led me to the following question:
Let's say that I have a theory described by a Lorentz invariant Lagrangian, and the true vacuum of the theory is not invariant under Lorentz transformation, will there be massless Goldstone bosons (or fermions) similar to the breaking ... | g7430 | [
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<p>I am reading a paper on quantum gravity (written circa 1988 but I don't think it's relevant to give a more precise reference) where I read the following statement: "universe loops will in general induce nonlocality, just as field theory loops induce nonlocality in relativistic-particle path integrals, and string loo... | g7431 | [
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<p>I know that light does not interact with other light, but can interfere it, at least its amplitude. With that said, lights frequency can be changed via bouncing off matter, where matter might absorb some of that photons energy changing the frequency.. Does this imply that a high energy beam of light that intersects ... | g7432 | [
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<p>Is there an easy way to understand and/or visualize the reciprocal lattice of a two or three dimensional solid-state lattice? What is the significance of the reciprocal lattice, and why do solid state physicists express things in terms of the reciprocal lattice rather than the real-space lattice?</p> | g7433 | [
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<p>For two different chemical substances there are two open valves with <a href="http://en.wikipedia.org/wiki/Flow_rate" rel="nofollow">flow rates</a> $$Q_1=a\frac{m^3}{h}\ \text{ and }\ \ Q_2=b\frac{m^3}{h},$$ leading into seperate cables. </p>
<p>Next, the cables join, the substances mix perfectly and they flow alon... | g7434 | [
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<p>I recently found <a href="http://www.mnn.com/food/beverages/stories/why-is-it-so-hard-to-walk-and-not-spill-your-coffee-physicists-have-the-answe" rel="nofollow">this article</a>, which describes how...</p>
<blockquote>
<p>It just so happens that the human stride has almost exactly the right frequency to drive th... | g7435 | [
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<p>Let us assume that there are two astronauts A and B who are floating in space. A sees B passing by and vice versa. A sends signals to B every minute. According to A since B is moving his clock will be slower. So B will receive the signals prior to the appointed minute. The same argument can be applied for B who will... | g7436 | [
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<p>I came across this proportionality statement in my quantum mechanics notebook:
$\psi(x,t)$ is proportional to </p>
<p>$$
\begin{align}
\cos(kx - wt) &= \exp(i(kx-wt)) + \exp(-i(kx-wt)) \\
&= \exp (i(kx-wt))
\end{align}
$$
I looked through most commonly used textbooks for quantum mechanics and I couldn't fi... | g7437 | [
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<p>if a lightbeam is fired from space to earth is it blueshifted? I heard this happens with special relativity but not sure if it happens with genreal relativity</p> | g7438 | [
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<p>QFT says that an unlimited number of bosons can occupy the same "state" (what I mean by that is that the whole system's wavefunction is composed of a product of many identical wavefunctions).</p>
<p>However, gravity increases monotonically with energy density. It seems that at some point, one additional boson woul... | g7439 | [
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<p>This question is closely related to <a href="http://physics.stackexchange.com/q/28834/7670"><em>Event horizons without singularities</em></a> from about a year ago (May 2012), which <a href="http://physics.stackexchange.com/users/1325/john-rennie">John Rennie</a> answered nicely and persuasively.</p>
<p>My variant ... | g7440 | [
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0.032... |
<p>I understand that in general if we're adding more planes of atoms (increasing thickness of sample) then the intensity would increase because we have more constructive interference. But isn't there a breaking point for this? Shouldn't there be a finite thickness past which the intensity decreases? </p> | g7441 | [
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<p>In the usual covariant approach to the development of surface charges of an asymptotic symmetry group, one works with the linearized theory as this ensures that the charges are integrable.</p>
<p>I also read </p>
<blockquote>
<p>In the full interacting theory with prescribed asymptotics, the expressions are one-... | g7442 | [
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<p>This question is motivated by <a href="http://physics.stackexchange.com/questions/71947/does-a-charged-particle-revolving-around-another-charged-particle-radiate-energy">similar one.</a>
If an accelerated point charge $q$ radiates with power $W$ then I assume the same particle with charge $-q$ will radiate with the... | g7443 | [
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<p>Well I imagine that there is a very fast rocket moving alongside the Earth and I know that people in the Earth regard the events on the rocket as happening more slowly as it is moving and time expands, and the same for people in the rocket as they could consider themselves at rest and the Earth moving so they would ... | g249 | [
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<p>I'm trying to get Ward-Takahashi identities using the approach used in <a href="http://books.google.com.br/books?id=nnuW_kVJ500C&pg=PA264&lpg=PA264&dq=%22leads%20to%20a%20differential%20equation%20for%20Z%22&source=bl&ots=vpxudGVM4Y&sig=b9ByfCjLwU9oT9wMXIInGj7z8vk&hl=pt-BR#v=onepage&q... | g7444 | [
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<p>I guess that these questions were being asked by many people on the Northern Hemisphere during this summer (and other summers) and someone may give a nice, coherent answer. The general question is how many times more slowly one is getting suntan or damages his skin in the evening, relatively to the noon?</p>
<p>The... | g7445 | [
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<p>A very rough approximation from first principles, from the elementary charge and hbar, would suffice. But is there such an approximation at all? </p>
<p>(Alternatively, if water is too difficult: is there any other material or gas for which such a calculation is possible?)</p> | g7446 | [
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<p>I have asked the question <a href="http://math.stackexchange.com/q/188313/28724">in math.stackexchange</a>, but perhaps it should be more relevant here. Hence I am re-posting it with necessary reediting.</p>
<p>Let $\mathcal{H}=\mathbb{C}^n$ be a Hilbert space. A state $\rho\in\mathcal{B(H)}$ is a positive semi-d... | g7447 | [
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<p>On page 92, my still favorite supersymmetry <a href="http://rads.stackoverflow.com/amzn/click/0071636412">book</a> says, by making the global infinitisimal parameter of a SUSY tranformation spacetitime dependent (gauging) it forces one to introduce a new gauge field which turns out to have the properties of a gravit... | g7448 | [
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<p>I would like to understand better a phenomenon of a quantum heat bath. </p>
<p>Below I present one example, which seems quite clear to me. It would be great to see some less-discrete models, and more specific open quantum systems (with a given concrete Hilbert space). </p>
<p>(Discrete Picture)</p>
<p>Let $S$ be ... | g7449 | [
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<p>We've got two long straight wires carrying current of 5A and placed along x and y axis respectively current flows in direction of positive axes we have to find magnetic field at a) (1 m,1 m)
b) (-1 m,1 m)
c) (-1 m,-1 m)
d) (1 m,-1 m)
now using ampere's law $$ \oint_{}^{}B.dl=\mu_oi $$ i found magnetic field for in... | g7450 | [
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... |
<ol>
<li><p>If you were to draw a person on a Minkowski diagram, that was unmoving (though time was still passing) what would that look like?
(As a light cone and ignore the observer.)
<img src="http://i.stack.imgur.com/3y46m.jpg" alt="Minkowski diagram"></p></li>
<li><p>Also what would it look like if you drew a pers... | g7451 | [
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0.016534876078367233,
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-0.... |
<p>I'm trying to understand Noether's theorem, and it's application to gauge symmetry. Below what I've done so far. </p>
<p>First, the global gauge symmetry. I'm starting with the Lagragian
$$L_{1}=\partial^{\mu}\Psi\partial_{\mu}\Psi^{\ast}-m^{2}\left|\Psi\right|^{2}$$
with classical complex fields. This Lagragian ... | g7452 | [
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0.017890384420752525,
0.0037931555416435003,
0.01... |
<p>Assuming it's possible to vibrate a human at near light speed without harming him, would a few minutes of this from his point of view be much longer from a stationary observer's point of view?</p>
<p>In other words do vibrations work the same as normal movement with regards to time dilation?</p>
<p>So a person cou... | g7453 | [
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<p>Question:-</p>
<blockquote>
<p>When a beam of $1.06eV$ photon of
intensity = $2.0 W/m^2$, falls on a platinum surface of area $1.0*10^{-4}m^2$, and work function $5.6eV$, $0.53$% of incident photons ejected photo electrons. Find the number of photoelectrons emitted per second and their minim and maximum energi... | g7454 | [
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0.03438... |
<p>What is <a href="http://en.wikipedia.org/wiki/Viscosity#Bulk_viscosity" rel="nofollow">bulk viscosity</a> and how does it affect the flow?</p>
<p>Explain the idea of introducing such a term in the Navier-Stokes equation. </p>
<p>What are the consequences if not taken into account?</p> | g7455 | [
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<p>Can anyone clarify what does mean the angular frequency of a system in case of the vibrating membrane. </p>
<p>Angular frequency is measured in radians per second, what does this have with the vertical displacement in case of the wave equation.</p> | g7456 | [
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<p>For example, if you have two hydrogen atoms and an oxygen atom, they are all electrically neutral and don't attract each other. But then if they manage to get "close enough" somehow they snap together releasing energy, and to get them apart again requires energy be input into the system. </p>
<p>This says that the ... | g7457 | [
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<p>I use a bike to commute, so I spend a lot of time thinking about how to get the most bang out of my momentum.</p>
<p>Aside from the extra distance traveled in a wide turn, does making a sharp turn save you any energy? My guess is no, because these things tend to even out, but it definitely <em>feels</em> like I'm g... | g7458 | [
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<p>Do quantum computer's tell us anything about the foundations of quantum theory? In particular Shor argued in the famous thread by 't Hooft </p>
<p><a href="http://physics.stackexchange.com/questions/34217/why-do-people-categorically-dismiss-some-simple-quantum-models">Why do people categorically dismiss some simple... | g7459 | [
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0.... |
<p>According to numerous sources online, the percentage of oxygen is approximately the same at sea level and 10,000 meters. Since oxygen is heavier than nitrogen, shouldn't the percentage of oxygen decrease with altitude?</p> | g7460 | [
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<p>If I had a 3V battery, and when no load connected it reads 3.2V, and with a load 2.8V (just a hypothetical example), what is the name for these two terms, with a load or no load?</p>
<p>I know the voltage drop occurs due to its internal resistance when a load is connected, however I still am not sure of the terms. ... | g7461 | [
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<p>I remember reading about an experiment where fine rods of tungsten were super-heated with millions of amps of electricity, melting them into ionised gas and were then compressed (by magnetic fields?) into plasma.</p>
<p>The plasma heated up to temperatures never before reached. I can't remember exactly, but I beli... | g7462 | [
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<p>What is the difference between air resistance/friction force and up thrust force?
I always think that air friction is the same as up thrust but it does not seem that way.</p> | g7463 | [
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<p>I did see some posts on stackexchange on this matter, but I find them to be beyond my scope or not directly related to what I am looking for.</p>
<p>I am reading Feynman Lectures III, chapter 4. It talks about scattering of two particles $a$ and $b$ and it defines $f(\theta)$ to be the probability amplitude of part... | g7464 | [
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-0.0272... |
<p>How can the transformer transfer exact power from primary winding to secondary winding if there are core losses, eddy current losses and hysteresis losses?</p> | g7465 | [
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... |
<p>So I've had a problem for a long time now understanding energy-mass equivalence, in particular I've had a lot of trouble understanding how something like interatomic potentials can be seen as mass. I've heard other people on the site say it depends on how you probe the system, which doesn't make too much sense to m... | g7466 | [
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<p>The Rarita-Schwinger action in curved $n$-dimensional spacetime is</p>
<p>$$
\int \sqrt{g} \overline{\psi}_a \gamma^{abc} D_b \psi_c
$$</p>
<p>Here $g = \det(g_{\mu \nu})$, and the indices $a, b \dots$ are 'internal' indices that transform under e.g. $\mathrm{SO} (3,1) $ in $3+1$ dimensions. $\gamma^{abc} = \gamma... | g7467 | [
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<p>A moving star's relativistic mass is larger than its rest mass. Is its gravitational pull larger? </p>
<p>What about its inertial mass? Does it have larger inertial mass, keeping in mind that inertial mass should equal gravitational mass according to the equivalence principle.</p>
<p>I suppose this quote from wiki... | g153 | [
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... |
<p><strong>Note:</strong> Both diagrams are 2d(they might look 3d because I drew them manually.)
I have a prismatic frame that looks like this:<img src="http://i.stack.imgur.com/obZR5.png" alt="Frame"><br>
I made a section on the half of the first pillar(the red line represents the section), to study the internal force... | g7468 | [
0.027117840945720673,
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-... |
<p>I read that as the air density is lower at high altitudes, the scattering is less, hence the darker blue but then other colors are scattering lesser than blue, why don't we see a darker shade of the other colors?</p> | g7469 | [
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<p>Is there any open database of elemental sensitivity factors for Auger electrons?</p>
<p>I'm trying to figure out graphite oxidation degree from AES spectra, so relative sensitivity of O to C is required. Spectra were registered with the primary electron energy of 1500 eV. I found some reference data in Perkin Elmer... | g7470 | [
0.04444311559200287,
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0.01862... |
<p><a href="http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Special_relativity_rel_sim/index.html" rel="nofollow">http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Special_relativity_rel_sim/index.html</a></p>
<p>Talking about the situation of clocks shown on this page. Clocks A&B. Now suppose cloc... | g7471 | [
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<p>I am looking at a manifold of dimension $n$ (And I am considering a local co-ordinates system $x_1,x_2,\ldots x_n$) and the metric defined by the components $g_{ij} = \frac{\delta_{ij}}{x_1^2}$. I'm wanting to find the components of the corresponding Riemann tensor. This should be a pretty straight forward task but ... | g7472 | [
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<p>Refraction gives rise to a momentum change orthogonal to the propagation direction. This must result in an equal and opposite change to the medium at the boundary. Entry and exit cancel, and the medium experiences no net force. The problem is that the forces on the medium do not in general line up, so we have a pair... | g7473 | [
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<p>For a significant part of my life I have been taught that, if a photon of the "correct" energy meets an excited atom, the atom will then (with a certain probability) undergo transition to a lower energy state, emitting a photon, which
1)has the same energy as the incident photon,
2)propagates in the same direction,
... | g7474 | [
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<p>I'm a physics tutor tutoring High School students. A question confused me a lot.</p>
<p>Question is:</p>
<blockquote>
<p>Suppose a mass less rod length $l$ has a particle of mass $m$ attached at its end and the rod is hinged at the other end in vertical plane. Another point object of mass $m$ is moving with velo... | g7475 | [
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<p>I am a <a href="http://en.wikipedia.org/wiki/Geographic_information_system" rel="nofollow">GIS</a> programmer implementing a visualization.</p>
<p>I am modeling the idealized trajectory of a particle ejected from a volcanic vent using:</p>
<p>$$\text{distance} = \frac{(v^2 \times sin(2\theta))}{g}.$$</p>
<p>Wher... | g7476 | [
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<p>If an equal torque of equal radius and size is produced on two bodies of the same weight and same center of gravity, but with different weight distribution (say one has a 1kg mass 1 meter above the center of mass, while the other has it 10 cm above). Will this affect the angular velocity of it?</p> | g7477 | [
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<p>I am currently a high school student interested in a research career in physics. I have self taught myself single variable calculus and elementary physics upto the level of IPHO . And I am comfortable with euclidean geometry upto the point of some basic theorems like Pythagoras or Thales and the geometry in Cartesia... | g108 | [
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<p>I understand that quantum teleportation fidelity is the overlap of the initial quantum state with the teleported quantum state. If the teleportation is perfect, then the fidelity would equal 1 or 100% successful of retrieving the quantum state at the desired location.</p>
<p>In all real experiments I've glanced at ... | g7478 | [
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0.04967501014471054,
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<p>Looking at the Moody chart I think to myself, the <em>friction factor</em> doesn't decrease much at all with Reynolds number after a certain point. I wonder if laminar flow is more efficient in a sense, and what sense would that be?</p>
<p><img src="http://i.stack.imgur.com/1bIeg.jpg" alt="Moody diagram"></p>
<p>... | g7479 | [
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<p>I was told by a former physicist that he thinks that the now dormant S-Matrix Theory has the potential to lead to a breakthrough in formulating a Grand Unified Theory. He stated several reasons for this; all of which I do not remember except for one: The non-linearity of the differential equations that constitute it... | g7480 | [
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... |
<p>Given that the boiling point of a liquid is the temperature at which the vapor pressure is equal to the ambient (surrounding) pressure, what significance does a liquid's vapor pressure have in the formation of bubbles that happens at and above the boiling point? </p>
<p>The definition of boiling point seems to imp... | g7481 | [
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0... |
<p>It is my understanding that in quantum mechanics (for 1/2 spin particles) the </p>
<p>probability function that describes the direction of a particle's spin state is </p>
<p>proportional to the overlap of the theoretical hemispheres formed by the motion of </p>
<p>the particle (in either spin state). However, wit... | g7482 | [
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<p>I ask <a href="http://math.stackexchange.com/q/884412/">this question</a> on math stackexchange but got no answer. Not sure how to move the post so I'm reposting it here.</p>
<p>I was arguing with my friend that <a href="http://en.wikipedia.org/wiki/Brownian_motion" rel="nofollow">Brownian motion</a>, in the sense ... | g7483 | [
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0... |
<p>This is a continuation of <a href="http://physics.stackexchange.com/q/22183/2451">this question</a>.</p>
<p><a href="http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-1/" rel="nofollow">http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-19... | g7484 | [
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0.0867912769317627,
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0.01727120578289032,
-0.005... |
<p>I would like to know if there is an equation to predict the pressure drop in a <a href="http://en.wikipedia.org/wiki/Venturi_tube#Venturi_tubes" rel="nofollow">venturi</a> device using a compressible fluid as the working medium. In particular, I'd like to use this equation to predict the amount of vacuum created for... | g7485 | [
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... |
<p>I am currently struggling with the formula for an exact current in QFT, a fermion with an upcoming momentum $p$ and an outgoing momentum $p'$. My problem is to show whether or not a term of the form $\bar{u}(p')F(q^2)i\sigma^{\mu\nu}(p+p')^{\nu}$ where $\sigma^{\mu\nu}=\frac{i}{2}[\gamma^{\mu},\gamma^{\n... | g7486 | [
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... |
<p>For a centrifugal compressor, as found in most turbochargers on internal combustion engines, is there a noticeable change in flow rate versus a naturally aspirated flow rate? In other words, does the pump effectively increase the pressure of the gas only, or does it also increase the flow rate? Really what I'd like ... | g7487 | [
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<p><strong>Note:</strong> This question may be difficult or impossible to answer within the rules of these forums due to its philosophical nature. I will delete the question if I am violating the rules.</p>
<p>Onto the question! Recently I have been curious whether classical electromagnetism is fully solved (up to the... | g7488 | [
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<p>What are the differences between comet versus asteroid versus meteoroid versus meteor versus meteorite in practical terms?</p> | g7489 | [
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<p>As far as I know, particles vibrate with a frequency and wavelength determined by their energy level.</p>
<p>Is this vibration in 3D space?</p> | g7490 | [
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<p>Right now, our resolution + light gathering power are still far too low to take direct images of exoplanets, so we're limited to subtracting the planet spectra from the parent star spectra when the planet undergoes a transit (and this isn't going to be possible for decades, according to Jim Kasting's latest book). S... | g7491 | [
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<p>On the new <a href="http://astronomy.stackexchange.com/">Astronomy.SE</a> site, I was having a short discussion on one of my answers. The basic discrepancy was; can MACHOs like black holes/brown dwarfs/neutron stars be termed "dark matter"?</p>
<p>My reasoning is that these objects do not radiate EM radiation on th... | g7492 | [
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<p>The FRW is a nice isotropic and symmetric metric but I think its assumptions are too many. I was wondering about alternative models. Specifically are there any prominent alternatives that have more fleshed out local detail? For example, are there any models that can ascribe a more local interpretation to data which ... | g7493 | [
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0.0... |
<p><a href="http://space.stackexchange.com/questions/604/is-it-possible-to-get-pregnant-through-natural-means-in-space">http://space.stackexchange.com/questions/604/is-it-possible-to-get-pregnant-through-natural-means-in-space</a> indicates cosmonauts are at risk of irradiation whilst in space. </p>
<p>What little I k... | g7494 | [
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<p>Related: <a href="http://physics.stackexchange.com/questions/72368/why-are-most-metals-gray-silver">Why are most metals gray/silver?</a></p>
<p>After reading Johannes’ impressive answer to Ali Abbasinasab question of why do most metals appear silver in color with the exception of gold (and copper), my lack of exper... | g7495 | [
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<p>Why is there an absolute entropy? Given any non-discrete probability distribution, we don't really have an absolute entropy because the entropy depends on the parametrization of the distribution (e.g. Beta vs. Beta-prime) which was arbitrarily chosen. Another way to put it is that instead of entropies we only have... | g7496 | [
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<p>I am working on a game involving flying and steering a paper airplane for WP7. I want the plane to fly just like how normal paper airplanes fly (see this game for an example <a href="http://armorgames.com/play/7598/flight" rel="nofollow">http://armorgames.com/play/7598/flight</a>) but I can't seem to find an equatio... | g7497 | [
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<p>Euler's laws of motion for a distributed mass are:</p>
<p>$$F = \frac{d}{dt} MV_{cm},\ N = \frac{d}{dt} L$$</p>
<p>$F$ are the sum of the external forces, $M$ the total mass, $V_{cm}$ the velocity of the centre of mass. $N$ are the sum of the moments of the external forces about some given point, L the total angu... | g7498 | [
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<p>Clouds are made up of tiny water or ice droplets, depending on temperature. This implies that cloud density is greater than that of dry air. Why don't clouds sink through their surrounding atmosphere rather than float by in a variety of formations? </p> | g260 | [
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<p>Matt in <a href="http://photo.stackexchange.com/questions/9597/what-does-a-hexagonal-sun-tell-us-about-the-camera-lens-sensor/9601#9601">his answer</a> on <a href="http://photo.stackexchange.com/q/9597/64">What does a hexagonal sun tell us about the camera lens/sensor?</a> mentions</p>
<blockquote>
<p>Incidentall... | g7499 | [
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-... |
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