question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I am trying to simulate liquid film evaporation with free boundary conditions (in cartesian coordinates) and my boundary conditions are thus:
$$
\frac{\partial h}{\partial x} = 0, \qquad (1)
$$
$$
\frac{\partial^2 h}{\partial x^2} = 0, \qquad (2)
$$
$$
\frac{\partial^3 h}{\partial x^3}=0. \qquad (3)
$$
However... | g6939 | [
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<p>Sometimes I volunteer to help freshmen and sophomore students with introductory physics and calculus courses. The problem is most of them are not stimulated and take these courses because they are obligatory.</p>
<p>On the other hand some TV series, such as CSI Miami, contains scenes which show how some of the tech... | g6940 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/7470/chemical-potential">Chemical potential</a> </p>
</blockquote>
<p>The chemical potential of electron and positron is equal but with opposite sign. How one can visualize the negative chemical potenti... | g239 | [
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<p>I am familiar with the true (or general) notion of orthogonality, given in the Linear Algebra and <a href="http://math.stackexchange.com/a/11516/39930">Pythagoras theorem derived from the $\vec x \cdot \vec y = 0$</a>. I have also recently got to know that true or general definition of orthogonality is that orthogon... | g6941 | [
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<p>Based on my understanding of physics after seeing <em>The Distinction of Past and Future</em> on <a href="http://research.microsoft.com/apps/tools/tuva/#data=3%7C4dbfe549-e795-47a0-bda2-9597fe5bb344%7C%7C" rel="nofollow">Project Tuva</a>, there is no distinction between past and future on a fundamental level- all pa... | g6942 | [
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<p>What would be the rate of temperature loss for an average sized human in space without a suit? A human generates about 100 watt at rest. But how can we use that to calculate how fast the temperature will go down? Also how much heat would be absorbed by the sun? Assume the person is somewhere between the earth and th... | g6943 | [
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<p>Warning: I am not a physicist so please excuse my naivety!</p>
<p>As you all know, physicists think that there exist four fundamental forces.</p>
<p>Would a universe with zero fundamental forces be possible, at least in principle? Would elementary particles be able to exist in such a universe? On a larger scale, w... | g6944 | [
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<p>Consider a spherical symmetric thin cell of photons converging to a point. At some moment, there is a formation of an horizon and a black hole. But each black hole is evaporating,and so, after some time, all the black hole has evaporated.</p>
<p>So, we could consider an "initial state", well before the creation of ... | g6945 | [
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<p>How to focus beam from the fresnel lens on a flat surface.</p>
<p><img src="http://i.stack.imgur.com/tINjl.png" alt="enter image description here"></p>
<p>In my case, instead of producing the light beam, I am receiving the light beam.
So, the beam comes from the right and then focuses at a focal point.</p>
<p>My ... | g6946 | [
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<p>I'm trying to find the relation between current density $\boldsymbol{j}$, voltage $v$, and magnetic field $\boldsymbol{B}$ for the time-harmonic approximation in a cylindrically-symmetric coil (a torus if you will) onto which a current is applied. The coordinates are $r$, $z$, $\theta$.</p>
<p>What I got so far is:... | g6947 | [
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<p>There was a Question bothering me.</p>
<p><img src="http://i.stack.imgur.com/qXmBT.png" alt="enter image description here"></p>
<p>I tried solving it But couldn't So I finally went up to my teacher asked him for help . He told me that there was a formula for Electrostatic pressure $\rightarrow$</p>
<p>$$\mbox{Pre... | g6948 | [
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<p>Obviously in a simple, classroom style experiment the energy required to increase water temperature is a constant and thus wouldn't change, but what if we made the experiment just slightly more real world?</p>
<p>Imagine the following set up: a typical metal pot filled with a gallon of water with a heat source belo... | g6949 | [
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<p>I understand that gravity in GR is a manifestation spacetime curvature dictated by the field equations by the principle that objects follow the geodesic path in spacetime. </p>
<p>And, I get how gravitational radiation travels like waves because there are wave equations in the field equations.</p>
<p>But, I have t... | g6950 | [
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<p>Apparently <a href="http://en.wikipedia.org/wiki/Huygens%E2%80%93Fresnel_principle">Huygens' principle</a> is only valid in an odd number of spatial dimensions:</p>
<ul>
<li><p><a href="http://mathoverflow.net/a/5396/21349">http://mathoverflow.net/a/5396/21349</a></p></li>
<li><p><a href="http://physics.stackexchan... | g6951 | [
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<p>I have a bit of an understanding issue why the representations of $SO(3)$ are so important for Quantum Mechanics. When looking at its Irreps one gets the Spin and Angular Momentum operators and thus their physical significance is fairly obvious.</p>
<p>What I don't get is WHY these Irreps give what they give. When ... | g6952 | [
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<p>It is generally assumed, from a person's perspective, that pushing a cart is more easier than pulling one. But why?<br>
Is there any difference in terms of force required to achieve the same amount of displacement?</p>
<p>Or is it merely human perception?</p>
<p>Why is it that almost all automobiles transfer torqu... | g746 | [
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<p>If I'm moving through MY reference frame at the speed of light, isn't time still passing by normally for me? </p>
<p>Help me think about this fourth dimension- space-time. I want to intuitively understand it. I understand some thought-experiments (Einstein's train experiment, for example, and why events occur sl... | g6953 | [
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<blockquote>
<p>A cockroach is crawling along the walls inside a cubical room that has an edge length of 3 m. If the cockroach starts from the back lower left hand corner of the cube and finishes at the front upper right hand corner, what is the magnitude of the <a href="http://en.wikipedia.org/wiki/Displacement_%28v... | g6954 | [
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<p>So the <a href="http://en.wikipedia.org/wiki/Electric_field" rel="nofollow">electric field</a> between two parallel plates is given by $E = V/d.$ How do you derive this? </p> | g6955 | [
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<p>In Peskin & Schroeder chapter 19 page 656, where the axial current anomaly of massless 2D QED is discussed, the authors go from: $$ \bar\psi(x+\varepsilon/2)\Gamma(x)\psi(x-\varepsilon/2)\tag{19.25} $$
(where $\Gamma(x)$ is some operator)
to: $$ \bar\psi(x+\varepsilon/2)\Gamma(x)\psi(x-\varepsilon/2) \tag{19.27}... | g6956 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/5587/a-pendulum-clock-problem">A pendulum clock problem</a> </p>
</blockquote>
<p>There are two pendulums.</p>
<p>First pendulum consists of a rod of length L and flat heavy disk of radius R (R < L),... | g240 | [
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<p>I'm questioning if there's a way to make use of the priciple of steam engines again. </p>
<p>The idea of a steam engine is a little primitive and outdated maybe, but the principle isn't that at all<br>
if you ask me.
In the 19th century, they used water for steam engines and I assume this fluid was chosen because... | g6957 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/7041/speed-of-gravity-and-speed-of-light">“Speed” of Gravity and Speed of Light</a> </p>
</blockquote>
<p>I'm wondering if gravitational waves have the same speed of light? They must if gravi... | g158 | [
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<p>I know how we define a vacuum in flat space QFT and also in a curved space QFT. But, can somebody tell me how do the choice of vacuum state in (say) the CFT side of AdS/CFT changes the choice of vacuum state in gravity side? Let me ask the other way. I mean if we pick a vacuum (say in bulk side, because it may not b... | g241 | [
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<p>Measurements of consecutive sites in a many body qudit system (e.q. a spin chain) can be interpreted as generating a probabilistic sequence of numbers $X_1 X_2 X_3 \ldots$, where $X_i\in \{0,1,\ldots,d-1 \}$.</p>
<p>Are there any studies on that approach, in particular - exploring predictability of such systems or ... | g6958 | [
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<p>According to <a href="http://www.nature.com/news/proof-found-for-unifying-quantum-principle-1.9352" rel="nofollow">this</a> recent article in <em>Nature</em> magazine, John Cardy's <em>a</em>-theorem may have found a proof.</p>
<p>Question:</p>
<ol>
<li><p>What would the possible implications be in relation to fur... | g6959 | [
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<p>I could understand the derivation of the "bulk-to-boundary" propagators ($K$) for scalar fields in $AdS$ but the iterative definition of the "bulk-to-bulk" propagators is not clear to me. </p>
<p>On is using the notation that $K^{\Delta_i}(z,x;x')$ is the bulk-to-boundary propagator i.e it solves $(\Box -m^2)K^... | g6960 | [
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<p>I'm reading through a <a href="http://www.vis.uni-stuttgart.de/~dachsbcn/download/rsm.pdf" rel="nofollow">computer graphics paper</a> and author says that the radiant intensity emitted by an infinitely small surface point $p$ with normal $ n $ into direction $ \omega $ is</p>
<p>$$
I_p(\omega) = \phi_p max(0,<n|... | g6961 | [
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<p>I'm a retired police officer trying to learn classical mechanics on my own. I have gone through many links on the Internet including the classical mechanics quick reference textbooks from Physics Stack Exchange. But, I always have the same problem just as anyone trying to learn classical mechanics <em>on his/her own... | g98 | [
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<p>As an exercise for myself, I have been working on rewriting the massive vector boson propagator (unitary gauge). I have run into a problem interpreting some of the terms that stick around when the propagator is rewritten this way. Here's what I have: I've taken the unitary gauge vector propagator</p>
<p>$$
D_{\mu\n... | g6962 | [
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0.036446746438741684,
0.0226807... |
<p>Is there formula that gives reflectance of very thin film of given metal (tens of nanometers) to the visible light of given wavelength(808nm) ? Which properties of metals are needed for the formula ?</p>
<p>I would like to draw a plot of reflectance that is a function of titanium film thickness. Thanks</p> | g6963 | [
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0.048498041927814484,
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<p>I'm looking at torque-free precession, occurring when the angular velocity isn't aligned with a principal axis of an object. I've looked at some Euler arguments, some decompositions of $\vec{\omega}$ into $\vec{\Omega} + \vec{\omega_0}$, where $\vec{\omega_0}$ is the rotation around the principal axis, etc.</p>
<p>... | g6964 | [
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0.022677229717373848,
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0.017703508958220482,
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<p>I have read that polarized light is treated by Jones vectors and that to treat partially polarized light you have to use Stokes vectors and mueller matrices.</p>
<p>Nonetheless, the optics notes that my professor have given us have no mention of mueller calculus, and we have assigned exercises involving partially p... | g6965 | [
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<p>I have always wondered about how <a href="http://en.wikipedia.org/wiki/Cosmological_constant" rel="nofollow">cosmological constant</a> is characterized. So since it is still a hypothesis you often read the “cosmological constant measured to be ….”. Shouldn't the statement read “cosmological constant calculated to be... | g6966 | [
0.0006448930944316089,
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0.036859218031167984,
0.0... |
<p>In the literature, spin liquids are only possible in Mott insulators, however, I'm not entirely sure why the nuclear spin can't create a spin liquid in a band insulator.</p>
<p>Is this possible? If so, is there any specific reasons that it is not mentioned in the literature? If it is not possible, why not?</p> | g6967 | [
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<p>To explain the expansion of space I have often heard people saying that space is continuously created. This picture is usually applied to cosmological scales but I`m nevertheless curious if some microscopic description of this process could be found (or probably is already available?).</p>
<p>The first thing which ... | g6968 | [
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0.0586... |
<p>I do not know how to calculate the direction, or unit vector of the force that appear between two magnetic field sources.
For example, let's assume I mean a current-carrying-wire by 'source of magnetic field'.</p>
<p><img src="http://t0.gstatic.com/images?q=tbn%3aANd9GcRdMJaUEnmPBVpQUAuhTDC-n_MDYjbgxzYqaBFPqBj0wUYM... | g6969 | [
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<p>In the Physics classes, the professor did an experiment using de Van de Graaff generator, by which he held a neon tube radially outward to the V d Graaff dome, and the neon lit up. I understood that this was because there was a potential difference between the 2 ends when placed radially which caused the electrons t... | g6970 | [
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<p>Stated: The atomic spectra of hydrogen and deuterium are similar however shifted in energies. </p>
<p>So im trying to explain why it is that the emission lines are shifted and how they are shifted.</p>
<p>Since the nucleus of deuterium contains both a proton and a neutron its notably heavier than the nuclueus of h... | g6971 | [
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<p>I believe that we can take a single photon state as a tensor product of a frequency Hilbert space (infinite dimension) and a polarization Hilbert space (dim 2). Does this mean we can measure the polarization and the frequency at space-like separated regions a the same time?</p>
<p>My second question is about frequ... | g6972 | [
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<p>Assume we have two charged particles colliding.
He have particle 1 with mass $m_1$, charge $Z_1 \cdot e$ which travels in $x$-Direction passing by a STATIONARY particle 2 (mass $m_2$, charge $Z_2 \cdot e$) at distance $b$ (impact parameter).</p>
<p>I want to calculate the change in momentum in $y$-Direction (as th... | g6973 | [
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<p>Is it possible to see the oscillations with plasma frequency in a gas of particles of the same charge (not mixture of positive and negative charges)? </p> | g6974 | [
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<p>I am calculating the phase diagrams for Li-Mg binary alloy with reference to the following text:
<a href="http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=5600701" rel="nofollow">http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=5600701</a></p>
<p>In the equation used in the above paper, i am con... | g6975 | [
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<p>What is difference between the miltary radar in 1940's from commercial antenna that is for the use of TV?</p>
<p>I have read article from some of the WW2 history website that call the German radar the antenna, so does the WW2 radar have features that is more powerful than today's antenna</p> | g6976 | [
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<p>I am wondering if my line of thought is correct - and thus the resulting answer to the problem above would be correct.</p>
<p>As we know the gravitational force (of two point masses) is given by $$F = G\frac{m_1m_2}{r^2}.$$</p>
<p>So the gravitational force/vector field reduces with the distance squared. Now this ... | g91 | [
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<p>I tryed to understand the Bohm interpretation and this is what picture appeared to me.
Please tell me if I understood something incorrectly.</p>
<ul>
<li><p>All particles have definite positions and follow deterministic rules of dynamics</p></li>
<li><p>Any future configuration of an isolated subsystem is only depe... | g6977 | [
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<p>The current definition of a second is stated <a href="http://en.m.wikipedia.org/wiki/Second" rel="nofollow">here</a> and I found a presentation on the <a href="http://www.bipm.org/" rel="nofollow">BIPM</a> site which discusses plans to change to a "better" definition of a second. You can find the presentation <a hre... | g6978 | [
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<p>How do I extend the general Lorentz transformation matrix (not just a boost along an axis, but in directions where the dx1/dt, dx2/dt, dx3/dt, components are all not zero. For eg. as on the Wikipedia page) to dimensions greater than 4?</p>
<p>Thanks</p> | g6979 | [
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<p>I was wondering if for a point-like charged object, does the gradient of the electric potential point in the direction of maximum increase or maximum decrease of the function $V$? </p> | g6980 | [
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<p>We know gravitational is continuously acting on us. But let us assume that we are hanging in the space alone away from anything to affect our position. And suddenly a giant planet appear's a few million km from us then we will feel it's gravitational force on our body. But I wanted to know will it work instantly or ... | g4 | [
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<p>I am manipulating an $nxn$ metric where $n$ is often $> 4$, depending on the model. The $00$ component is always tau*constant, as in the Minkowski metric, but the signs on all components might be + or - , depending on the model. (I am not trying to describe physics with this metric). Can I call this metric a M... | g6981 | [
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<p>If $i$ and $j$ are two variables then Kronecker delta is written as</p>
<p>$$\delta_{i,j}~:=~\begin{cases}1 \hspace{3mm} \mbox{if} \hspace{3mm} i=j,\\
0 \hspace{3mm}\mbox{if} \hspace{3mm}i \neq j. \end{cases}$$</p>
<p>same definition is used for orthogonality. </p>
<p>My question is when will we use K... | g6982 | [
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<p>Another way of stating it: When you have leaves in a (cylindrical) tea cup, if you rotate the cup (eg clockwise), the leaves largely stay in place relative to the table, but spin clockwise a little. What factors go into determining how much force (spin? torque?) transfers to the tea leaves (or to a neutrally buoyant... | g6983 | [
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<p>I need to get the x/y values of a fired projectile given the angle of the initial power, and air resistance.</p>
<p>The formulas I have are</p>
<p>$$V_x=V_o \cos\theta$$</p>
<p>$$X=V_o \cos \theta t$$</p>
<p>$$V_y=V_o \sin \theta -gt$$</p>
<p>$$Y=V_o \sin \theta t-(1/2)gt^2$$</p>
<p>To calculate the initial ve... | g6984 | [
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0.04430723935365677,
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0.05663328990340233,
0.0328320674598217,
0.035... |
<p>I am trying to confirm the proof of Langreth's theorem / rules as seen in <a href="http://www.iue.tuwien.ac.at/phd/pourfath/node52.html" rel="nofollow">http://www.iue.tuwien.ac.at/phd/pourfath/node52.html</a> .</p>
<p>My problem is equation 3.55. I would do it like this:</p>
<p>$\int_{C_{1}} \mathrm{d}\tau A(t,\ta... | g6985 | [
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<p>Let's imagine a plastic container completely closed. We put alcohol inside it filling it at half. Now we make a hole to introduce 2 little Conductor one near the other so that they don't let the air pass. We make eletricity pass trough one of the conductor so that a Spark being created. </p>
<p>The question is: doe... | g6986 | [
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-0.0... |
<p>I am just looking on the TopQuark production via proton antiproton collision and strong interaction. There seem to be three basic possibilities. </p>
<ol>
<li><p>$q + \bar q \rightarrow Gluon \rightarrow t +\bar t $</p>
<p>This method is clear</p></li>
<li><p>$Gluon + Gluon \rightarrow Gluon \rightarrow t + \bar t... | g6987 | [
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<p>I have a paper which lies on a flat surface. The paper is fixed on one side and the opposite side can slide in the direction of the opposing side. As side end slides toward the other, a "bump" forms. I want to know what the solution is to the shape of this bump. There must be some standard solution for this case.</p... | g6988 | [
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<p>I already understand that light cannot escape a black hole after passing the event horizon, so please do not explain that to me. What I would like to know is this:
a well known fact about light (a photon specifically) is that it travels at the speed of light, and at no other speed, which means that it has no rest ma... | g6989 | [
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<p>Related to this question
<a href="http://physics.stackexchange.com/questions/35/where-do-magnets-get-the-energy-to-repel">Where do magnets get the energy to repel?</a></p>
<p>If I have a magnet repelling another, eg one in my hand, the other being pushed along the desk, how do the each of the magnet's fields actual... | g6990 | [
0.07995644956827164,
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0.0018373439088463783,
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<p>According to Bohr, electron revolves around the nucleus because of force of attraction between electron and proton. This force of attraction gives energy to the electron. So my question is this that- In which form does this electron get the energy?</p> | g6991 | [
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-... |
<p>I have a spin system:
<img src="http://i.stack.imgur.com/iRS4g.png" alt="enter image description here"></p>
<p>As shown in the picture, there are two spins S1 and S2, and a pair of interactions between them. One is a ferromagnetic interaction and the other is anti ferromagnetic interaction. I am trying to calculate... | g6992 | [
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<p>I'm working on a science fiction story that involves two spaceships engaged in combat while in orbit around a planetoid. My original idea called for spaceship A to trick spaceship B into firing a passive projectile such that it would orbit the planetoid and strike spaceship B. This was meant to happen within a matte... | g6993 | [
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<p>EDIT:Recently , I have been observing the moon and i realised the moon seems to be moving very quickly from one place to another, and back to its initial position in a short cycle(few minutes),the movement seems like it's moving back and forth about some axis at very small radius., I don't think this is due to orbit... | g6994 | [
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<p>Based on how light behaves when it passes through mediums, i.e. the wavelength of light changes when it passes through mediums of different refractive indexes, wouldn't it be possible to convert infrared light into visible light by passing it through a medium (e.g. $CO_2$)? Also, is it possible to make holograms fro... | g6995 | [
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<p>This is an example problem with solution in a book I am reading on electrostatics. </p>
<p>"We have two square parallel plate capacitors with length $a$ and separation $d$ with $d<<a$. If we triple all dimensions of the capacitor, by what factor does the capacitance change?"</p>
<p>$C=\frac{\epsilon_0A}{d}... | g6996 | [
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<p>With what we know about physics, is it possible that when the universe 'began', around when quarks and leptons were produced, another particle, which doesn't couple to either quarks, leptons or photons was also produced ? The only other way that we can observe its existence is via the effects of its gravitational fi... | g6997 | [
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<p>I am having trouble understanding how to obtain a spacelike slicing of the Schwarchild black hole. I understand there is not a globally well defined timelike killing vector, so we can define t=cte slices outside the horizon and r=cte slices inside the horizon. </p>
<p>In the literature people define connector slice... | g6998 | [
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<p>Let's say we have a normal circuit with a light bulb, with wires and a battery. </p>
<p>When one places a capacitor in this circuit, how is the light bulb able to light up, even when the capacitor prevents the flow of charge? Also, why does it dim and then go out eventually?</p>
<p>Then when the battery is remove... | g6999 | [
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<p>As we know, if an ideal gas expands in vacuum, as its energy is unchanged, the temperature remains the same. An ideal gas's energy does not depend on volume. In general, the energy is $kT$ times the total degrees of freedom, like in an ideal gas, the total degrees of freedom is $N$ particles plus three dimensions, $... | g7000 | [
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<p>I'm going over some (molecular dynamics) related literature - specifically the derivation of the <a href="http://lib.jncasr.ac.in:6060/jspui/bitstream/123456789/570/1/464174.pdf" rel="nofollow">Weighted Histogram Analysis Method (WHAM)</a>. </p>
<p>As a quick backdrop WHAM is a method for stitching together concept... | g7001 | [
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<p>I'm struggling with a seemingly simple problem in 2D motion. Basically, the question is, given accelerations in $x$ and $y$ ($a_x$ and $a_y$) as well as the angular velocity ($\omega$), how can we find the trajectory of the motion? Also, how can we report the motion like a computer mouse, i.e. in the reference frame... | g7002 | [
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0.04630... |
<p>Once, I read that Einstein founded the special relativity theory by imagining how an observer moves at the speed of light.</p>
<p>How does this thought experiment work? How to reach from this imagination to the relativity of time?</p> | g7003 | [
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<p>Whenever I light up a tube-light it makes 'ting' 'ting' sound every-time it blinks. </p>
<p>I am talking about this tube-light<br>
<img src="http://i.stack.imgur.com/j5j97.jpg" alt="enter image description here"> </p>
<p>Why is it so? </p>
<p>I think its because of sparking(inside glass tube)</p>
<p>similar s... | g7004 | [
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<p>I'm a master student working on networks analysis in general. A network is something that has nodes and there are links between the nodes. Nodes and links could have attributes. An evolving network is one that changes overtime (new nodes and links are added..etc). An example of that is Facebook. Nodes are users and ... | g7005 | [
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0.013885254971683025,
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<p>If I hang a rope from two points that are at the same height above the ground, what is the mathematical function that describes the shape of the rope between the two points? Assuming the mass of the rope is evenly distributed between the two points.</p>
<p>Upon visual inspection, it appears to be parabolic, but loo... | g7006 | [
0.07325000315904617,
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0.004066021181643009,
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0.039100173860788345,
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0.002705942839384079,
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/14212/the-collision-of-phobos">the collision of Phobos</a> </p>
</blockquote>
<p>Mars has two moons: <a href="http://en.wikipedia.org/wiki/Phobos_%28moon%29" rel="nofollow">Phobos</a> and <a href="http:/... | g242 | [
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0.04406125470995903,
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0.01720363087952137,
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0.039168041199445724,
0.01639431156218052,
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<p>Can our moon qualify as a planet? With regard or without regard to the exact definition of the planet, can the moon be considered as planet as Mercury, Venus and Earth etc. not as the satellite of the planet Earth.</p> | g7007 | [
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<p>I'm looking for a webpage or a book or reference that might give me a better (and hopefully more scientific) understanding of how the Bahtinov mask works (which I understand to be the same as diffraction around the mirror arms, but I don't fully grasp how that occurs). Can anyone think of any good links here?</p> | g7008 | [
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<p>If it was possible for charge to assume arbitrary densities, like we often see electrostatic exercises, and one could spread charge density uniformly over a ring, then how one would, theoretically, distinguish between the situations when there is a current on the ring and when there is not? In both situations, the d... | g7009 | [
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<p>Submitting a semi-conductor to stress leads to a deformation in the energy-bands, roughly described by:$$H_{ij} = {\cal{D}}_{ij}^{\alpha\beta}\;\epsilon_{\alpha\beta}$$
$\epsilon$ being the strain (linked to the stress by Hooke's law), $H$ the perturbation Hamiltonian to the Hamiltonian describing a stress-free semi... | g7010 | [
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... |
<p>This is a question I asked in Maths SE, and it was suggested I ask it here. This is a direct copy of <a href="http://math.stackexchange.com/questions/466883/are-electrodynamic-problems-in-the-complex-plane-relevant-to-real-life">that question</a>.</p>
<p>I have been reading Tristan Needham's excellent Visual Comple... | g7011 | [
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0.016915079206228256,
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<p>My friend thinks it's because she has less air resistance but I'm not sure.</p> | g7012 | [
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... |
<p>I am in the process of conceptualizing an iOS or computer game (a modification of Tetris) that would be suitable for motivated high school students and university undergraduates. It is meant to be an educational game that will convey concepts. Any ideas of what quantum phenomena I could represent in the game that wo... | g7013 | [
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<p>The spin of fundamental particles determines if they are bosons or fermions. The atoms also have bosonic or fermionic behavior, for example $\require{mhchem}\ce{^4He}$ has bosonic and $\ce{^3He}$ has fermionic statistics. Which quantity of atom determines its statistics? </p> | g243 | [
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0.005965157877653837,
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0.010... |
<p>I'm trying to simulate an RLC circuit using transfer function. Circuit is there: <a href="http://i.stack.imgur.com/MC8ME.png" rel="nofollow">http://i.stack.imgur.com/MC8ME.png</a> (I'm a new user therefore I cannot post images)</p>
<p><img src="http://i.stack.imgur.com/W8N1q.png" alt="alt text"></p>
<p><em>But I c... | g7014 | [
0.010392716154456139,
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0.05018996074795723,
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0.07669558376073837,
0.03593210503458977,
0.007251... |
<p>All I found in Google was very broad. From a physics models perspective, why can photons emitted from a laser cut? Does this cut mean that the photons are acting like matter?</p> | g7015 | [
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<p>Usually, it is said that systematic errors can not be handled in a well-defined way, unlike statistical errors. </p>
<p>My question(s): </p>
<p>A) How can systematical errors be calculated for any experimental device or experiment? Maybe does it involve a "calibration" of experimental devices?</p>
<p>B) I have he... | g7016 | [
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0.025299... |
<p><a href="http://en.wikipedia.org/wiki/Energy" rel="nofollow">Energy</a> versus <a href="http://en.wikipedia.org/wiki/Free_energy" rel="nofollow">free energy</a> diagram. I haven't been able to find an adequate definition of these two terms in relation to each other. Could someone point me in the right direction, ple... | g7017 | [
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0.0094261... |
<blockquote>
<p>Sparked off by <a href="http://physics.stackexchange.com/questions/21813/is-sea-water-more-conductive-than-pure-water-because-electrical-current-is-tran/">Is sea water more conductive than pure water because "electrical current is transported by the ions in solution"?</a></p>
</blockquote>
... | g7018 | [
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0.030410535633563995,
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0.0364... |
<p>Let's start from a very simple argument: If $A$ and $B$ are some operators, then I can write their product as<br>
$$AB = (A-\langle A\rangle)(B - \langle B \rangle) + \langle A \rangle B + A \langle B \rangle + \langle A \rangle \langle B \rangle$$
In a mean-field approximation, I would then go on to neglect the fir... | g7019 | [
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<p>This maybe a very naive question. </p>
<p>I have just started studying CFT, and I am confused by why we have two separate parts of everything in CFT (operator algebras and hilbert space), the holomorphic and anti-holomorphic, which are decoupled from each other. We initially introduced $z$ and $\bar{z}$ as two inde... | g7020 | [
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<p>When you have your X-Ray tube, and want to make X-Ray for your X-Ray scanner or whatever. Then you get electrons from the cathode, which hit the anode, and from that produce a spectrum of X-Rays due to Bremsstrahlung, and characteristic lines from electrons jumping from shell to shell.
This gives the continuous spec... | g7021 | [
0.031042635440826416,
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0.006636749021708965,
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-0.01... |
<p>I have a question regarding an equation in Polchinski's "String Theory, Volume 1, An introduction to the bosonic string". The equation is (4.3.27) on p.135.</p>
<p>This section is about the brst-cohomology of the open bosonic string. My question in particular is about the N=1 level and the derivation of the cohomol... | g7022 | [
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<p>I recently watch a lecture by Neil Tyson where he said the closest thing we have to a vacuum is interstellar space. I believe he said there will be one atom per 1 cubic meter or something close to that. I know that pressure equalizes, meaning that a higher pressure systems will move towards low pressure systems to r... | g7023 | [
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0.... |
<p>Why does a spring lose a part of its energy when compressed for a long period of time? Is it because the material gets bent?</p> | g7024 | [
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<p>why accelerated electrons "scatter" light?
From Yale's chemistry open class, the professor said when a light passes by an electron, it "pulls" the electron up and down, and emit radiation in all direction. How does this happen? And another question is about the X-ray diffraction. From the picture the textbook show... | g7025 | [
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<p>I need to show that helicity is Lorentz invariant (under the proper Lorentz transformation) for the massless particles. I heard about most frequently used argument which contains an idea of impossibility to "outrun" the massless particle, so the sign of helicity is Lorentz invariant. But how about the absolute value... | g7026 | [
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<p>We embed the rotation group, $SO(3)$ into the Lorentz group, $O(1,3)$ : $SO(3) \hookrightarrow O(1,3)$ and then determine the six generators of Lorentz group: $J_x, J_y, J_z, K_x, K_y, K_z$ from the rotation and boost matrices.</p>
<p>From the number of the generators we realize that $O(1,3)$ is a six parameter mat... | g7027 | [
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<p>Who coined the word <a href="http://en.wikipedia.org/wiki/Permittivity" rel="nofollow">"permittivity"</a>? It appears that first usage was in 1887. Please cite your source. </p> | g7028 | [
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0... |
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