question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I am not a mechanics or physics student but a computer science student. I came across a question related to find <a href="http://en.wikipedia.org/wiki/Neutral_axis" rel="nofollow">neutral axis</a> of figure but I do not have slightest idea of what it is and how to find it. </p>
<p>Can someone please tell what would... | g11204 | [
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<p>I am wondering whether there is a version of adiabatic theorem in the regime of quantum optics. My understanding of quantum optics involves with the interaction between photon and atom. This interaction has always been almost instant. But the perturbation for adiabatic theorem needs to be as slow as possible. This i... | g11205 | [
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<p>I have performed experiments in my college laboratory on Newton's rings to find radius of curvature of a convex lens used.i always get a dark center.Is it possible to get a bright center?If yes,then how?</p> | g11206 | [
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<p>For instance, consider number 4 and 5 in the following sample:</p>
<p><img src="http://i.stack.imgur.com/PP8Eo.png" alt="enter image description here"></p>
<p>Using the right hand rule, B points downwards, conventional current points to the right (because of the 5V battery), and therefore, the force on electrons p... | g11207 | [
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<p>Suppose that we have two cars on a track, each with a different mass. Now suppose that the cars are connected with a spring. We smack one car. I would like to write down the equations of motion for this scenario and solve them but I am just a lowly mathematician who has never really studied physics. My attempt yield... | g11208 | [
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<p>I was reading an article online pertaining to quantum mechanics and I stumbled across these few sentences. </p>
<blockquote>
<p>A look at the corresponding energy regimes shows (Beck and Eccles 1992) that quantum processes are distinguishable from thermal processes for energies higher than $10^{-2}$ eV (at room t... | g11209 | [
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<p>This answer gives a great explanation of how surface charge builds up to force the current to move perpendicular to the wire: <a href="http://physics.stackexchange.com/a/102936/41086">http://physics.stackexchange.com/a/102936/41086</a></p>
<p>However, it fails to address the <em>magnetic field</em>. Moving charges ... | g11210 | [
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<ol>
<li><p>I'm wondering of the Dirac Lagrangian density
$$\mathcal{L} =\overline{\psi}(-i\gamma^\mu \partial_\mu +m)\psi $$
is an hermitian operator, since upon complex conjugating one gets
$$\mathcal{L}^\dagger =\psi^\dagger(i\gamma^0\gamma^\mu \gamma^0 \partial_\mu +m)\gamma^0\psi$$
$$ =\overline{\psi}(i\gamma^\mu ... | g11211 | [
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<p>According to quantum mechanics, for multi-electron atoms, a single electron around the nuclei can be in the state of linear combination of different eigen energy states. In that case, even the energy of the electron is not one of the eigen energies.</p>
<p>In chemistry, we often say that an electron is in an orbita... | g11212 | [
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<p>I understand that Energy is a conserved quantity in a system.
A number, that's always the same to the system. However, don't we determine such a number?
I mean, we can create systems(Or study them usually) and see the amount of Energy tit can have. Correct?
Because to me, Energy is a confusing concept... Why was it ... | g11213 | [
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<p>In the following equation</p>
<p>$$V = -\mathbf{P}\cdot \mathbf{E}$$</p>
<p>why I have to take Potential Energy as negative. Is there any simple reason behind this ?</p>
<p>I am preparing for my high school examination.</p> | g11214 | [
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<p>Do they all fit Schwarzschild black holes? How people compare them with more complicate BH solutions as spinning BH solutions (even if they are not known analytically), say. </p>
<p>I'd like more than qualitative comments, if possible.</p> | g11215 | [
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<p>Basically what the question says -- there is reason to expect that, if allowed to continue long enough for the radiation to reach future null infinity, the fact that the radiation will fall off at $\frac{1}{r}$ will break the set of conditions required for the enveloping metric to stay asymptotically flat, which wil... | g11216 | [
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<p>In <a href="http://en.wikipedia.org/wiki/Isothermal_process" rel="nofollow">isothermal process</a> $\Delta U =0$. But I am having trouble understanding it.</p>
<p>Say we have an ideal gas, and say my temperature is constant but I move the pressure, volume from $(P, V) \to (P-dP, V+dV) $. So the volume has expanded ... | g11217 | [
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<p>This is <strong>not</strong> a question about traditional nuclear power plants vs the thorium based. But about the Fukushima plant itself and the very negative environmental effects from its meltdown of reactors 1 and 3 vs a Thorium based design under similar natural stressors. </p>
<p><a href="http://rt.com/news/j... | g11218 | [
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<p>I am doing some self-study in between undergrad and grad school and I came across the beastly <a href="http://en.wikipedia.org/wiki/Wigner%E2%80%93Eckart_theorem" rel="nofollow">Wigner-Eckart theorem</a> in Sakurai's <em>Modern Quantum Mechanics.</em> I was wondering if someone could tell me why it is useful and pe... | g11219 | [
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<p>What causes gravity? Why is there attraction between masses? Is it due to time or space distortion?</p> | g11220 | [
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<blockquote>
<p>Consider one parameter transformation: $y = y ( \tilde{y}, \alpha)$ such that lagrangian satisfies: $\tilde{L}(\tilde{y}, \alpha) = L(y ( \tilde{y}, \alpha))$. We say that equation is invariant under this transformation if: $$\tilde{L}(\tilde{y}, \alpha) = L(\tilde{y}) + \frac{dF(\tilde{y},\alpha)}{d... | g11221 | [
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<p>One thing I've heard stated many times is that "most" or "many" physicists believe that, despite the fact that they have not been observed, there are such things as magnetic monopoles.</p>
<p>However, I've never really heard a good argument for why this should be the case. The explanations I've heard tend to limit ... | g11222 | [
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<p>I'm working on an AI for a pinball-related video game. The ultimate goal for the system is that the AI will be able to fire a flipper at the appropriate time to aim a pinball at a particular point on the table. We are using an engine that will handle the underlying physics interactions when the ball is hit (Unreal... | g11223 | [
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<p>I've read several posts here where people talk about the history of the developement of the theory of strong interactions. And they mention Regge theory, pomerons, S-matrix and so on. </p>
<p>I'm confused because I see the S-matrix in my QFT books, <a href="http://en.wikipedia.org/wiki/S-matrix_theory" rel="nofollo... | g11224 | [
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<p>This will probably be considered very simple, but I am just a beginner:</p>
<p>I'm developing a software application where temperatures need to be added and subtracted. Some temperatures are in Celsius, some in Kelvin. I know how to convert to/from Kelvin (273.15), but how should one go about adding and subtracting... | g11225 | [
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<p>Electrons make transition between different energy levels - say, $n =3$ to $n=2$ or $n =1$, as per the applicable selection rules. </p>
<p>My question is: <em>can an electron make transitions between sub energy states of the same energy level?</em></p>
<p>For example: if an electron is in the $n=3$ energy level, ... | g11226 | [
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<p>It seems to me that Dark Matter is just an indication that our models of gravity do not scale to the level of galaxies, and thus like Newtonian physics, it is a powerful but incomplete model of the universe. Why do most physicists believe that it is more likely that there is some mysterious previously undetected sub... | g360 | [
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<p><a href="http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion" rel="nofollow"><strong>Third law:</strong></a></p>
<blockquote>
<p>When one body exerts a force on a second body, the second body
simultaneously exerts a force equal in magnitude and opposite in
direction to that of the first body.</p>
</blockqu... | g11227 | [
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<p>I picked this up on the net:</p>
<p><em>Einstein came to realize the principle of equivalence, and it states that an accelerated system is completely physically equivalent to a system inside a gravitational field.</em></p>
<p>When I am being accelerated I will pick up speed over time. This will have a noticeable e... | g11228 | [
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<p>I have been listening to my friends brag about electric cars and I can't seem to convince them that electricity is not some magic force that comes out of the wall outlet. It must be produced somewhere, in most cases by a coal fired plant, where the chemical energy of hydrocarbons are are transformed to electrical e... | g11229 | [
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<p>I am not very familiar with the quirkiness of relativity, and I was wondering how to explain this situation.</p>
<p>If a beam of light is shining at some object at some distance from the origin of the beam, does relativity imply that photons in the beam lack time flow and, thereby, never actually experience contact... | g361 | [
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<p>The following is my reasoning: Suppose $\vec{F}$ is a conservative force field. Then the total mechanical energy, $E$, of the isolated mechanical system is a conserved quantity which implies that $E=T+U=k_{0}$, where $k_{0}$ is a constant, $T$ is the kinetic energy and $U$ is the potential energy. Now, $\nabla{E} =\... | g11230 | [
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<p><img src="http://i.stack.imgur.com/SGAoC.jpg" alt="enter image description here"></p>
<p>Consider an object at infinity. The rays coming from it are parallel to each other. Let one of the parallel rays pass through the focus $F_1$ of a thin lens, and let a second ray pass through the optical center $O$. The ray whi... | g11231 | [
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<p>In Peskin's introduction to QFT, he wrote: </p>
<blockquote>
<p>only fully connected diagrams, in which all external lines are connected to each other, contribute to the T matrix. </p>
</blockquote>
<p>I don't understand this statement.</p>
<p>Suppose we have many particles in initial and final state, and two i... | g11232 | [
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<p>I am developing a mathematical model of a mechanical device consisting basically of coupled harmonic oscillators. It turns out that the system mass matrix is asymmetric. I seem to read somewhere that a mass matrix has to be symmetric, but I am not sure. So I would like to know whether it is possible for a mass matri... | g11233 | [
-0.0016368889482691884,
0.012436253018677235,
0.008818103931844234,
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0.09303383529186249,
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0.01885841228067875,
0.006270941346883774,
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<p>I have a problem deriving displacement from an accelerometer; I want a time series of displacement so I used numerical integration twice;</p>
<p>I based my code on the trapezium rule and so did something like this to get velocity and again to get displacement;</p>
<p>while (i
<p>However, I just tested my method a... | g11234 | [
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0.04607348144054413,
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0.02077982760965824,
0.041... |
<p>This question relates and stems from my original question. Please read this one and the comments before answering this question.
<a href="http://physics.stackexchange.com/questions/55380/quantum-teleportation-fidelity">Quantum Teleportation Fidelity</a></p>
<p>I know that for discrete variables quantum teleportatio... | g11235 | [
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0.001259739394299686,
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0.010188737884163857,
... |
<p>The cosmological constant problem arises because the <a href="http://en.wikipedia.org/wiki/Naturalness_%28physics%29" rel="nofollow">natural</a> scale of the cosmological constant is $10^{120}$ times larger than what we observe. This implies that the dimensionless constant is much smaller than one and that is consid... | g11236 | [
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0.0551716573536396,
0.0018036410911008716,
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<p>I have that the surface gravity (at the outer event horizon) for a Kerr-Newman black hole is
$$
K_+ = \frac{r_+-r_-}{2(r_+^2+(J/M)^2)} = \frac{\sqrt{M^2-Q^2-J^2/M^2}}{2M^2-Q^2+2M\sqrt{M^2-Q^2-J^2/M^2}}
$$
where $r_\pm$ are the outer and inner event horizons, $M$ is the mass, $Q$ is the charge, and $J$ is the angular... | g11237 | [
0.0005996340769343078,
-0.027598384767770767,
0.0019020019099116325,
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0.022224364802241325,
0.009394539520144463,
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0.015803774818778038,
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<p>One often come across in QFT sentences like the following, for instance: </p>
<blockquote>
<p>...under a Lorentz transformation $\Lambda$ implemented by the unitary
operator $U(\Lambda)$, a Dirac field transforms as </p>
<p>$$ U(\Lambda)^{-1}\Psi(x)U(\Lambda) = D(\Lambda)
\Psi(\Lambda^{-1}x),$$ where the ... | g11238 | [
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0.04967259615659714,
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0.05446000024676323,
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-0.037179164588451385,
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0.06324470043182373,
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-0.... |
<p>Why in 1d and 2d systems, all states will be localized for infinitesimal disorder, but in 3d only states with energy lower below mobility edge will be localized? </p> | g11239 | [
0.02607673965394497,
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<p>The probability that an energy state in the conduction band is occupied by an electron is 0.001. Would this semiconductor then be n-type, p-type, or intrinsic?</p>
<p>Notation that I use: $E_F$ represents the fermi energy level, $E_C$ represents the energy level of the conduction band, and $E_V$ represents the ener... | g11240 | [
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<p>Is it possible to convert Tesla to Newtons of force?<br>
Or magnetization force H:(A/m) to newtons? </p> | g11241 | [
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0.03216579556465149,
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<p>Suppose you have a field theory with a real scalar field $\phi$ and a potential term of the form $\lambda \phi^4 - \mu \phi^2$ that breaks the symmetry $\phi \to - \phi$ in the ground state. Is this symmetry restored in a scattering with high momentum transfer in any physically meaningful way? My problem is that the... | g11242 | [
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0.02149752713739872,
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<p>The different mass states of <a href="http://en.wikipedia.org/wiki/Neutrino" rel="nofollow">neutrinos</a> are <a href="http://pdg.lbl.gov/2012/reviews/rpp2012-rev-neutrino-mixing.pdf" rel="nofollow">generally</a> named $\nu_1, \nu_2, \nu_3$.</p>
<p>By comparison, the names of quark mass states (<code>up</code>, <co... | g11243 | [
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0.03011331893503666,
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-0.0... |
<p>I know that</p>
<p>$$\tag{1}\hat{p}~=~-i\hbar \frac{\partial}{\partial x}~.$$</p>
<p>How can I get</p>
<p>$$\tag{2}\hat{x}~=~i\hbar \frac{\partial}{\partial p}~?$$</p>
<p>I think this simple and I'm just over thinking it, but knowing the momentum operator (1), how can I get the position operator (2)?</p> | g11244 | [
0.025753259658813477,
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0.001164308749139309,
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0.004459897521883249,
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<p>My question is pretty standard and easy,I wonder all my life how Einstein get energy equation <a href="http://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence" rel="nofollow">$E=mc^2$</a>.</p>
<p>Also I some videos about that equation on YouTube and some of the peoples said there that the equation $E=mc^2$ isn... | g68 | [
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0.05073411017656326,
0.0... |
<p>Perhaps is it the magnet's own magnetic field that causes it to lose its superconductive state? It seems as though these systems could become incredible energy dense.</p> | g11245 | [
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<blockquote>
<p><em>A man walks in the same direction as a slowly moving train ($v_{man} > v_{train}$). He counts the train to be 18 steps long. Then he turns around and counts the train to be 11 steps long.</em></p>
<p><em>(Suppose both man and train are moving at a constant speed; every step is the same len... | g11246 | [
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<p>Guys I have a doubt Is it possible to maintain the temperature of any Substance Below the Absolute Scale?</p> | g278 | [
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<p>I just started reading <em>PCT, Spin and Statistics, and All That.</em> Can someone explain why we use operator valued distributions to describe fields? I read somewhere that it would take infinite energy to measure an observable at a single point. Why don't we instead use functions from some collection of subsets (... | g11247 | [
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0.04940418899059296,
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<p>If there were a light cone centered at some point $P$, and you were to look at that light cone from different reference frames, would it change its shape? I know that points inside and outside the light cone would remain inside/outside of the light cone in every frame, but does the light cone itself shift?</p>
<p>I... | g11248 | [
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0.020730238407850266,
0.07023625820875168,
... |
<p>I was driving down the road at roughly the speed of traffic. I saw a police officer parked on the side of the road, and also noticed that a Semi was traveling in the lane right next to him. This got me thinking, is it possible to avoid being seen from the officer by using the Semi Truck and how fast would I have t... | g11249 | [
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0.0013275818200781941,
... |
<p>Can someone give me an example of a physical process - some (realistic) scattering process - in which one can observe that the particle number has decreased?</p>
<p>I was wondering, because it is relatively easy to create antiparticle-particle pairs, but is there a process that in some sense makes up for that, or d... | g11250 | [
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0.024473629891872406,
0.04088457301259041,
0.0537... |
<p>I have a quick question from thermodynamics. </p>
<p>I remember that we take kT/2 as the kinetic energy per degree of freedom in kinetic theory of gases. But when we do langevin forces (for example in cavity dynamics), do we take the average thermal energy as kT/2 or kT ?</p> | g11251 | [
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0.014121667481958866,
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0.023236218839883804,
... |
<p>Could anyone tell me what is band filling effect? I have search Physics.stackexchange and Google, but didn't find any useful information. I'll appreciate it if anyone can tell me the physical image of band filling effect.</p> | g11252 | [
0.029155435040593147,
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<p>I've often read that, for a mechanical system which can be described by $n$ generalized coordinates $q_1,...,q_n$, a point $\mathbf{Q}=(Q_1,...,Q_n)$ is a point of equilibrium if and only if the potential energy $U$ is stationary at that point, i.e. iff $\frac{\partial U}{\partial q_i}(\mathbf{Q})=0$ for all $i$. I'... | g11253 | [
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0.039397601038217545,
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0.010407572612166405,
0.0158400759100914,
0.00... |
<p>The chapter 2 section 4 of volume 1 is on nuclei and particles.</p>
<p>Here are a few things that trouble me. Dr. Feynman says that</p>
<blockquote>
<p>Another most interesting change in the ideas and philosophy of science
brought about by quantum mechanics is this: it is not possible to predict exactly
what... | g11254 | [
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0.010977832600474358,
0.014360189437866211,
-0.0037521906197071075,
... |
<p>In every textbook on <a href="https://en.wikipedia.org/wiki/Chaos_theory">chaos</a>, there are a lot of numerical simulations. A typical example is the <a href="https://en.wikipedia.org/wiki/Henri_Poincar%C3%A9#Astronomy_and_celestial_mechanics">Poincare section</a>.</p>
<p>But why is numerical simulation still mea... | g11255 | [
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0.... |
<p>Imagine a simple circuit consisting of an alternating current source connected to an inductor. Assume they are connected in the following fashion: AC source - terminal A - Inductor - terminal B - AC source. When the current flows from terminal A towards terminal B and is increasing, the inductor should generate elec... | g11256 | [
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0.... |
<p>I am relatively used to the <a href="http://en.wikipedia.org/wiki/Riemann_curvature_tensor" rel="nofollow">coordinate free</a> expression of the Riemann tensor:
$$
R(X, Y)Z=\nabla_X\nabla_Y Z - \nabla_Y\nabla_X Z - \nabla_{[X, Y]} Z, $$
where $\nabla$ is the Levi-Civita connection on a (pseudo)-Riemannian manifold ... | g11257 | [
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0.029668118804693222,
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0.03445318713784218,
0.03476843982934952,
-0.... |
<p><em>[EDIT] In the spirit of asking a "good question", this question is considerably more refined that the one I decided to blurt out earlier thanks to a little additional research and nudges from comments.</em></p>
<p>I'm not a physicist, but love to let ideas roll around in my head - so please excuse any crossed b... | g11258 | [
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<p>What is a <a href="http://en.wikipedia.org/wiki/Physical_law" rel="nofollow">physical law</a>, a <a href="http://en.wikipedia.org/wiki/Theory" rel="nofollow">theory</a>, and what is the relationship among them?</p>
<p>I know this is a very basic question, so any reference to epistemology will be greatly appreciated... | g803 | [
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<p>I am interested to understand how positive entropy Bose Einstein condensation for cold atoms (say) behave. The way I think about it is as follows: We have an ideal pure state where every atom is in the same ground state which depends on a geometry of a certain trap and the atoms do not interact. Now, naively, I thou... | g11259 | [
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<p>If the water were uniform temperature, it would have uniform density, so a bubble should either be all the way at the top (if it's lighter than water) or all the way at the bottom (if heavier). But in reality you don't see this neat separation. Sometimes you see bubbles hovering in the middle.</p>
<p>Is this becaus... | g11260 | [
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0.020... |
<p>I'm trying to understand this reading article linked below and I still don't know how to explain this simply, without need to derive everything mathematically. Can someone just write here how do SP's and SPP's differ?</p>
<p><a href="http://dipc.ehu.es/etxenike/admin/documentos/archivos/publicaciones/307RPP2007.pdf... | g11261 | [
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<p>I know black conducts heat while white reflects it.</p>
<p>But they are colors after all.</p>
<p>If a metal is painted black, it conducts more heat or at a rapid speed than it would do before it was coated.</p>
<p>But, as far as I know, colors don't have any special "substance" in them, which might trigger the su... | g11262 | [
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<p>Let's say I am taking a picture, and I know <em>a priori</em> that the image is of a single ideal point source of light at infinity.</p>
<p>With a perfect imaging system <strong>in focus</strong>, the image shows an Airy disk. I already <em>knew</em> to expect an Airy disk, so I can do some mathematical fitting to ... | g11263 | [
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<p>If a car was going at near mach-1 speed heading towards a wall and honked its horn. What frequency would the driver measure the reflected sound wave? I trying to think about this reasonably, but the answer I get is somewhat not what I initially expected.</p>
<p>Here is my current thinking, correct anything you migh... | g11264 | [
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<p>Consider measuring the length of an object in another frame of reference.<br>
Of course this should happen at the same instance in the frame of reference the measurement takes place in.<br>
but using Lorentz transformation the time in the other frame of reference would be different and there would be a period<br>
\b... | g11265 | [
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<p>Nine out of 15 subatomic particle masses begin with the digit one. <a href="http://en.wikipedia.org/wiki/Benford%27s_law" rel="nofollow">Benford's Law</a> would imply 30% with one as the leading digit. Is there any significance to this frequency distribution, such as perhaps it implies 15 undiscovered subatomic part... | g11266 | [
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<p>Lets say there's two astronauts, Alice and Bob, going on a space trip to a super-massive black hole. So large that they wouldn't notice any significant spaghettification forces at the event horizon. Alice is sitting on the left, and Bob on the right.</p>
<p>They go so close to the event horizon, that Bob enters the... | g11267 | [
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<p>So I was reading a document that stated that when traveling through a material (I'll use a liquid here, maybe water), a photon actually always traveled at 300,000 km/s, it was just that it occasionally 'hit', was absorbed and then re-emitted by water molecules along its path.</p>
<p>It was this absorption and re-e... | g11268 | [
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<p>I want to know how to deduce the equation $\vec{\tau}=\vec{\omega} \times \vec{L}$, where </p>
<p>$\vec{\tau}$ is the moment of force (also known as torque), </p>
<p>$\vec{L}$ is the angular momentum, </p>
<p>$\vec{\omega}$ is the angular velocity. </p> | g11269 | [
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<p>Why are available frequency of light continuous ? I keep hearing that atoms absorb (and emit ) photons of particular frequency which correspond to their energy levels of their electron. Where do all other colours come from ?</p> | g11270 | [
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<p>Usually a quantity of a matrix is defined as the eigenvalues of the matrix. If so, how can anyone express continuous values, as in Schrodinger picture, into a matrix?</p> | g11271 | [
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<p>What exactly is a field theory? </p>
<p>How do we classify theories as field theories and non field theories? </p>
<p><strong>EDIT:</strong></p>
<ol>
<li>After reading the answers I am under the impression that almost every theory is a field theory. Is this correct?</li>
<li>What is difference between QM and QFT?... | g11272 | [
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... |
<p>Title says it all. If hydrogen and helium are lighter than air, why won't liquid hydrogen and liquid helium defy gravity?</p> | g11273 | [
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<p>I know that rank 2 tensors can be decomposed as such. But I would like to know if this is possible for any rank tensors?</p> | g11274 | [
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<p>In printed paper 3-vectors can be denoted bold italic while 4-vectors can be denote just bold. </p>
<p>While handwriting 3-vectors are denoted by arrows above letters.</p>
<p>Is there a similar way to denote 4-vectors? </p>
<p>I mean except indexed Einstein notation.</p>
<p><strong>UPDATE</strong></p>
<p>I am j... | g11275 | [
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<p>What maintains quark spin alignments in baryons?</p>
<p>The $uud$ proton and $udd$ neutron are both spin 1/2, implying that two of their spin 1/2 quarks are always parallel and the other is always opposed.</p>
<p>In contrast, the $\Delta^+$ particle (which like the proton is $uud$) and the $\Delta^0$ particle (whi... | g11276 | [
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<p><strong>Setup:</strong> A radioactive source is placed at alternating distances from a Geiger Counter. Counts per second for 10 different distances (each spaced 1 cm apart) were taken for preset times ranging from 200 to 2000 seconds (depending on how far the source is from the counter). </p>
<p><strong>Objective a... | g11277 | [
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<p>It has come to the point in my computing program now where I have 5 swinging pendulums that are all modified at once by slider values. These values are drawn onto the from and passed through the class pendulum. To change the values the update button is run, and their is a default option to use a setup that works. Th... | g776 | [
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<p>There is an uniqueness theorem in electromagnetism. It says that the solution of Maxwell's Equations is determined uniquely by boundary conditions.</p>
<p>We can treat superconductivity as a completely diamagnetic material with magnetic susceptibility $\chi=-1$.</p>
<p>I think the uniqueness theorem is still corre... | g11278 | [
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<p>There is <a href="http://physics.stackexchange.com/questions/80852/local-guage-symmety-implies-causality/">a question</a> and corresponding downvoting of my answer, so I decided to ask this question.</p>
<p>There is my answer on it:</p>
<p>"...The most theories of free fields are invariant under global gauge trans... | g11279 | [
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<p>I know, that voltage is analogous to pressure for charge, but analogies lie. I don't see charge pressing anything and I don't understand definition of $U=A/q$ (voltage = work/charge), cause I can't see what is that work.</p>
<p><img src="http://i.stack.imgur.com/EAxef.png" alt="enter image description here"></p>
<... | g11280 | [
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<p>I'm dealing with a problem here.
I'm not sure about the answer of this question: "What is the difference between periodic oscillation and periodic movement?".
-For my opinion the difference is that the periodic oscillation changes the side but the periodic movement doesn't(if it changes the side than it is an oscill... | g11281 | [
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<p>Could it be possible that the mass of the proton can be calculated by a series of integer sequences? Or is this just a curiosity?</p>
<p>$$\sum_{m=1}^{\infty } \frac{1}{10^{26}(m^2+1)_{2m}}=$$</p>
<pre><code>NSum[1/Pochhammer[m^2+1,2m], {m,1,\[Infinity]}, WorkingPrecision -> 50] /10^26
</code></pre>
<p>First... | g11282 | [
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<p>We have BdG equation,
$$\left(\begin{array}{cc}
\mathbf{p}\cdot\boldsymbol{\sigma} - V & \Delta_{0}e^{i\phi} \\
\Delta_{0}e^{-i\phi} & V - \mathbf{p}\cdot\boldsymbol{\sigma}
\end{array}
\right)
\left( \begin{array}{c}u\\v\end{array}\right)
= \mathcal{E}\left( \begin{array}{c}u\\v\end{array}\right)$$
with de... | g11283 | [
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<p>Probably a stupid question here - I think it's a case of me not having sufficient mathematical background to follow this through. In Leonard Susskind's <em>Theoretical Minimum</em> book, he represents the ket-vector A as such:
$$
|A\rangle = \displaystyle\sum_{i} a_{i}|i\rangle
$$</p>
<p>Which I follow, as I do whe... | g11284 | [
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<p>I was recently looking at a Wurlitzer juke box, and noticed something strange. It's decorated with liquid-filled tubes. Gas bubbles are injected at the bottoms of the tubes, and the bubbles naturally rise.</p>
<p>What was strange was that, as the bubbles rise, they shrink! Not just a little bit, but very noticeably... | g11285 | [
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<p>I'd like to fit a function to the Sun's electrons flux data (blue dots), please note that x,y axis are in the log scale. The green dots are the "best" fit from the gnuplot program. I have taken the a/x as a test function, but in the log scale that is a linear function. Could anyone give me advice which test function... | g11286 | [
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<p>Consider a mass $m$ which is constrained to move on the frictionless surface of a vertical cone $\rho = cz$ (in cyclindrical polar coordinates $\rho, \theta, z$ with $z>0$) in a uniform gravitational field $g$ vertically down. Set up Hamilton's equations using $z$ and $\theta$ as generalized coordinates. </p>
<p... | g11287 | [
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<p>On a principal bundle, at each point you have a tangent vector space. At a given point, the vectors tangent to the fiber form the vertical vector space. Then the vector space at that point is a direct sum of the vertical vector space and what's called the horizontal vector space. </p>
<p>This is all standard stuff ... | g11288 | [
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<p>For example, diesel has about 40 MJ/kg, what does it mean? Is that if we burn it we will get 40 MJ of energy per kg, but we can not get all of it to mechanical work?</p>
<p>If that is the case, then why can't we get all of the energy to mechanic like in burning?</p> | g11289 | [
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<p>This question is pretty vague and open. I'm just curious if anyone has considered this.</p>
<p>Morse theory has a nice physical formulation: a Morse function can be thought of as a potential, so the gradient flow is the force experienced by a particle. The equilibria are the critical points of the potential. If we ... | g11290 | [
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<p>What I understand about the twin paradox is that if a person stays at rest with something lets say the earth and a traveller moves with a great velocity with respect to the firsy person, then the time of traveller becomes very much smaller than the time of person who stays back, which led to the conclusion that one ... | g11291 | [
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<p>A truly reversible thermodynamic process needs to be infinitesimally displaced from equilibrium at all times and therefore takes infinite time to complete. However, if I execute the process slowly, I should be able to get close to reversibility. My question is, "What determines when something is slow?"</p>
<p>For... | g11292 | [
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<p>The Schrodinger equation governs the possible time evolution of a wave function, expressed as a partial differential equation. Isn't this equivalent to the simpler equation</p>
<p>$$\omega = \hbar k^2/2m$$</p>
<p>i.e. any wave function that satisfies this dispersion relation will also satisfy Schrodinger's equati... | g11293 | [
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<p>For instance do the planets around the sun experience drag from the near vacuum of space? Or do the (hydrogen) atoms in interplanetary have a mean velocity near orbital speeds? And if so would (small) celestial objects orbiting the sun in the opposite direction (not sure if these would all me comets, or also might b... | g11294 | [
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<p>According to <a href="http://en.wikipedia.org/wiki/Carnot_cycle" rel="nofollow">widipedia</a>:</p>
<blockquote>
<p>During step 1 (isothermal heat addition or absorption) the gas is
allowed to expand and it does work on the surroundings. The
temperature of the gas does not change during the process, and thus
... | g11295 | [
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... |
<p>In Monte Carlo simulations of <em>solid state</em> phase transitions, why often Isobaric Isothermal ensemble (NPT) is used ? Why not NVT ?
Here, N is number of atoms, P is pressure, T is temperature and V is volume.</p> | g11296 | [
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<p>Apologies in advance if some of the questions below seem overly simple.</p>
<p>In an introductory GR book, I find the following expression for the autoparallel of the affine connection (the upper bound of the summation operators should be 3, for brevity's sake I reduce it to 1; also I leave the summation operators ... | g11297 | [
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0... |
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