question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>How much force (Newtons) is required to compress normal air in a chamber to 2 atm?
For example, if I had a sealed piston pump, how much force would need to be exerted in order for the air to be compressed to 2 atm?</p>
<p>Also, a side note, if I were to compress air from 1 atm to 2 atm, would this have the total vo... | g11113 | [
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<p>I have been going back over this problem with a friend for the better part of a day:</p>
<p>A potential is glued to a cube-shaped insulator so that outside of the insulator the field is the same as a point particle. How can we calculate the surface charge distribution and the volume charge distribution?</p> | g11114 | [
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<p>Suppose there are two light beams. One is red while the other is violet. The energy of both is the same.</p>
<p>Which one of these beams has a larger number of photons, or is the number of photons relevant?</p> | g11115 | [
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<p>I'm reading a paper on 2D hydrodynamics, specifically on the drag of a rod in a 2D fluid. It is a low-Reynolds number regime, therefore linear hydrodynamics and the velocity of the rod can be expressed via:</p>
<p>$$v_i^{rod} = \mu_{ij}F_j$$</p>
<p>then it says: By in-plane rotational symmetry combined with the $\... | g11116 | [
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<p>A rear-wheel driven large sedan, weighing $4 ,120$ lbs, with a $10¼$-foot wheel base, traveled up an inclined ramp of $11$ degrees. The vehicle left the ramp at $22$ mph, traveled through the air for $26$ feet, tumbled forward (flipped) about $60$ degrees, and landed on its windshield upside down in a ditch $7$ fe... | g11117 | [
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<p>paraxial plane wave = $\exp{(-jkz)}$ for waves propagating to the right</p>
<p>I can't figure out why it's not $\exp{(+jkz)}$. Any help would be greatly appreciated, thank you.</p> | g11118 | [
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<p>When we have Hubble constant and it's inverse Hubble Time (1/H) what units are they measured in? I know Hubble constant is in "km/s per Mpc" but is there any other units which are popular used with it, and if so is there any conversion between the two?
And would Hubble Time unit still be in billion years, seeing it ... | g11119 | [
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<p>I am confused about the set of quantum states.</p>
<p>I have seen it written that in classical physics, the set of all states is a simplex. (I think this refers to the probability simplex.)</p>
<p>In quantum physics, the set of all states is not a simplex. Does this have anything to do with the superposition princ... | g11120 | [
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<p>In my general relativity textbook (Carroll), he says that "the geodesic equation (together with metric compatibility) implies that the quantity</p>
<p>$\epsilon =-g_{\mu\nu}\frac{dx^\mu}{d\lambda}\frac{dx^\nu}{d\lambda}$</p>
<p>is constant along the path. For any trajectory we can choose the parameter $\lambda$ su... | g11121 | [
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<p>The second answer to this <a href="http://physics.stackexchange.com/questions/54323/collision-of-two-photons">question</a> describes how this process might occur, and I'm curious for more details about it:</p>
<ol>
<li>What is the probability distribution of the interaction producing electron-positron pairs (and wh... | g11122 | [
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<p>Lawrence Krauss and James Dent <a href="http://prl.aps.org/abstract/PRL/v111/i6/e061802" rel="nofollow">recently proposed a mechanism</a> for producing the observed scale of dark energy. This proposal was inspired by the <a href="http://en.wikipedia.org/wiki/Seesaw_mechanism" rel="nofollow">see-saw mechanism</a> tha... | g11123 | [
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<p>I am having trouble understanding how Eq (2.6) in <a href="http://arxiv.org/abs/0706.3384" rel="nofollow">this</a> paper <a href="http://arxiv.org/pdf/0706.3384v2.pdf" rel="nofollow">(PDF)</a>
$$Z[\mathcal{L},\mathcal{M}_{n}]\propto\langle\Phi(u,0)\tilde{\Phi}(v,0)\rangle_{\mathcal{L}^{(n)},\mathbb{R}^{2}}$$</p>
<p... | g11124 | [
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<p>I understand that <a href="http://en.wikipedia.org/wiki/Quantum_field_theory" rel="nofollow">QFT</a> is the theoretical framework for combining <a href="http://en.wikipedia.org/wiki/Quantum_mechanics" rel="nofollow">QM</a> and <a href="http://en.wikipedia.org/wiki/Special_relativity" rel="nofollow">Special Relativit... | g11125 | [
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<p>The formula of time dilation at constant speed v is known.
The formula $T_0'= T /\gamma$ where gamma is the Lorentz factor. </p>
<p>I would be interested, as Einstein's original formula was. </p>
<p>I've checked in "Zur Elektrodynamik bewegter Körper".
Something was on page 904 (original page number of Einstein)... | g11126 | [
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<p>In relativity, an event A can occur before another event B in one frame while A may occur after
event B in another. In quantum mechanics, we may measure the spin of two entangled electrons: If you measure spin of an electron to be +1/2 then the other would have opposite spin, so when you measure the spin of one ele... | g11127 | [
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<p>I've been having a go at programming an orbital simulator from scratch (without using any existing libraries) using the formula below to find the acceleration first for particle A and then for particle B towards each other.</p>
<p>$$F = \frac{m_Am_BG}{r^2}$$</p>
<p>$$a_{AB} = \frac{m_BG}{r^2}$$
$$a_{BA} = \frac{m_... | g11128 | [
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<p>I wonder how I can solve the <a href="http://mathworld.wolfram.com/BrachistochroneProblem.html" rel="nofollow">Brachistochrone problem</a> for 3 points?
The matter starts from point A that is the highest point and it must pass from B and must finish with point C. (No any friction in the system)
I wonder what the sho... | g11129 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation" rel="nofollow">cosmic microwave background</a> (CMB) has a modern temperature of about 2.7 K. At the time of the origin of the CMB, about 13.6 billion years ago, it had a temperature of about 3000 K.</p>
<p>There is a well-kn... | g11130 | [
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<p>For elastic collisions of n particles, we know that momentum in the three orthogonal directions are independently conserved:$$ \frac{d}{dt}\sum\limits_i^n m_iv_{ij} =0,\quad j=1,2,3$$</p>
<p>From this, it follows there's also a corresponding scalar quantity conserved:$$\frac{d}{dt}\sum\limits_i^n m_i(v^2_{i1} + v^2... | g501 | [
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<p>Since GR assumes that gravity waves travel at speed c, we expect we would be able to some day detect an aberration effect similar the that of light. Of course, gravity waves are so tiny in magnitude, we haven't yet unambiguously detected them, so aberration measurements aren't yet possible.
However, planetary orbits... | g11131 | [
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<p>The Dieke diagrams like this:</p>
<p><img src="http://i.stack.imgur.com/2CVSU.jpg" alt="Dieke diagram"></p>
<p>could be easily found in internet.</p>
<p>But it is impossible to determine from where they get values initially, everyone is making cross-links. I'm especially interested in $\rm Tb^{3+}$ ion. </p>
<p... | g11132 | [
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<p>National Geographics TV has a series called "None of the above". In one episode the presenter shows that by stacking 4 bricks (here shown as 'xxxxxxxx') you can have one of the bricks completely hang free of the edge:</p>
<pre><code> xxxxxxxx
xxxxxxxx
xxxxxxxx
xxxxxxxx
[edgeedge]
[edgeed... | g11133 | [
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<p>When we calculate the spin-orbit interaction in a Hydrogen atom we just work in the electron's frame of reference: the proton is moving and produces a magnetic field which the electron's spin interacts with.</p>
<p>We can show <a href="http://en.wikipedia.org/wiki/Spin%E2%80%93orbit_interaction" rel="nofollow">here... | g11134 | [
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<p>Physicists define the trace of an operator $\rho$ as the follows,</p>
<blockquote>
<p>$Tr(\rho)=\sum\limits_{|s\rangle \in B} \langle s| \rho |s\rangle$ </p>
</blockquote>
<p>where B is some orthonormal basis, and this quantity is basis independent. </p>
<p>If we swapped B with a non-orthogonal basis,C , which,... | g11135 | [
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<p>I'm asked to establish the following relations:</p>
<p>$\left( \frac{\partial C_V}{\partial V} \right)_{T,N} = \frac{T}{N} \left( \frac{\partial^2 P}{\partial T^2} \right)_{V,N} $</p>
<p>$\left( \frac{\partial (\beta F)}{\partial \beta} \right)_{V,N} = U $ where $\beta = \frac{1}{k_B T}$</p>
<p>I'm a bit puzzled... | g11136 | [
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<p>I'm trying to model isotropic linear elastic deformation in two dimensions. In one dimension, I know that a linear elastic material can be thought of as a spring which obeys Hooke's law $F=-k\Delta x$. In two dimensions, I want to describe a material that obeys Hooke's law in both directions (for simplicity, let's... | g11137 | [
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<p>So I'm reading <a href="http://rads.stackoverflow.com/amzn/click/1563475189" rel="nofollow">this book</a>, where after the preface and before the models there is a section called <em>General Notions and Essential Quantities</em>, which introduce some things I don't understand. They regard different temperatures of o... | g11138 | [
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<p>Is the detection of <a href="http://en.wikipedia.org/wiki/Gravitational_wave" rel="nofollow">gravitational waves</a> a reality with nowadays technology?
Are there recent news?</p> | g357 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/7819/why-does-venus-rotate-the-opposite-direction-as-other-planets">Why does Venus rotate the opposite direction as other planets?</a><br>
<a href="http://physics.stackexchange.com/questions/12140/why-does... | g231 | [
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<p>I have two pipes divided from main pipe. If I add one more pipe, what would be the amount of velocity in each pipes. I know the velocity of main pipe, then diameter and radius of each pipe.</p>
<p>Edit:</p>
<p>1) Viscosity - The liquid is Ethanol, viscosity would be 1.07 * 10^-3 Pa.s<br/>
2) Flow profile - can be ... | g11139 | [
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0.0... |
<p>Most of you will be familiar with the phenomenon: you have bought a new towel and you first have to wash it or use it a couple of times before it starts to work properly, i.e. dry your body after taking a shower instead of smearing out the water .</p>
<p>My simple question is: why is this the case? Why do new towel... | g11140 | [
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0.011617... |
<p>In Wikipedia article <a href="http://en.wikipedia.org/wiki/EPR_paradox#Description_of_the_paradox" rel="nofollow">EPR paradox</a>,</p>
<blockquote>
<p>The original paper purports to describe what must happen to "two systems I and II, which we permit to interact ...", and, after some time, "we suppose that there i... | g11141 | [
0.005041142925620079,
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0.0... |
<p>Can anyone explain the path of light to me, using a wave model, that show the angled path in different reference frames?</p> | g11142 | [
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<p>Does the <a href="http://en.wikipedia.org/wiki/Special_relativity" rel="nofollow">Special Theory of Relativity</a> "form" the foundation of Modern Physics?</p>
<p>My question is in reference to Geoff Brumfiel's Scientific American article "<a href="http://www.scientificamerican.com/article.cfm?id=particles-found-to... | g11143 | [
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0.00994... |
<p>Below is a picture of a typical transmission line(about 200 kV). Is there a simple physics experiment which can be performed safely near the line, to determine the power flow direction. Or in other words: where is the generator and where a consumer. </p>
<p><img src="http://i.stack.imgur.com/JByCq.jpg" alt="enter i... | g11144 | [
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<p>Since the Earth is moving around the Sun, which is moving around Milky Way, etc... What reference frame is used for the complete motion of the begin/end points (which are non-inertial right?)?</p> | g11145 | [
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<p>Using the electron bombardment method, if I wanted to ionize, for example, Xenon gas electrons with an electron gun, under what conditions is it possible to do so? (Heat, pressure?)</p> | g11146 | [
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<p>As a programming (technology), physics and math project in school, I'm considering programming my own 3D physics engine as a learning exercise. The physics engine should then be able to be used in a simple game.</p>
<p>Is this a viable project to do over a year? I want a prototype up pretty quick (even if it can be... | g11147 | [
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<p>What's the relationship between <a href="http://en.wikipedia.org/wiki/Uncertainty_principle" rel="nofollow">uncertainty principle</a> and <a href="http://en.wikipedia.org/wiki/Symplectic_group" rel="nofollow">symplectic groups</a>? Does the symplectic groups mathematically capture anything fundamental about uncerta... | g11148 | [
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<p>This question has been asked many times all over the Internet and answers can be found on places such as yahoo and ask.com, but I'm not satisfied with those answers and I don't trust the validity of those places. This seems like a more appropriate place to ask. So, here's my train of thought and I would like to as... | g11149 | [
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<p>When discussing the quantum mechanical harmonic oscillator we are talking about energy eigenstates. How would one actually measure in which state an harmonic oscillator is in? Could you weigh it and use Einstein's relation $E=mc^2$ to derive the energy?</p> | g11150 | [
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<p>This may seem like a simple question, but I cant seem to make any headway. </p>
<p>Consider the following; I have two beams of light, a reference beam $(A=\cos(wt))$ and phase shifted beam $(B=\cos(wt+\phi))$.</p>
<p>What is the normal way (say in a lab) that $\phi$ is detected & measured with respect to the r... | g11151 | [
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<p>In quantum mechanics, when hamiltonian $H$ is constrained ($H = \sqrt{m^2 - \hbar^2 \nabla^2} $) so that it would produce simple "relativistic" model of quantum mechanics, we can show that it results in non-locality (Reference: <a href="http://physics.stackexchange.com/questions/39415/nabla-and-non-locality-in-simpl... | g11152 | [
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<p><strong>Easy</strong></p>
<p>Consider the following figure</p>
<p><img src="http://i.stack.imgur.com/brY4S.jpg" alt="enter image description here"></p>
<p>Each red point is a particle of a known mass that carries charge Q/2 and connected to a the box by a thread of known length. This problem can be solved easily ... | g11153 | [
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<p>Inside a single proton for example, what is the force(s) that keeps the quarks together? Why don't they leave the proton? If they do, how does that even happen?</p>
<p>And maybe an additional sub question: Is it always three quarks inside the protons/neutrons? Why?</p> | g11154 | [
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<p>is well known that composition of point reflections generate <a href="http://en.wikipedia.org/wiki/Point_symmetry#Point_reflection_group" rel="nofollow">pure displacements</a>. This implies that the commutator of two point reflections will be a pure displacement. Are there similar elemental transformation operations... | g11155 | [
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<p><a href="http://www.quantumdiaries.org/2011/03/25/an-idiosyncratic-introduction-to-the-higgs/" rel="nofollow">Quantum Diaries</a> has an interesting introduction to the higgs. It makes it seem like the way that the higgs field gives mass to particles is via all of the interactions with virtual higgs particles.</p>
... | g11156 | [
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<p>Why are "Laue Spots" spots instead of rings? Or is there an effective way to estimate the number of Laue spots? I can't find any formulas or theory concerning this issue. Thanks for your attention! </p> | g11157 | [
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<p>I'm trying to understand the mechanics which determine if a car making a turn will skid.</p>
<p>Are the following correct or incorrect:</p>
<ol>
<li><p>A vehicle making a turn will skid unless the centripetal force is adequate to produce the centripetal acceleration. In a simple turn, where $r$ is constant, the f... | g11158 | [
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<p>Why must an <a href="http://www.labsphere.com/products/spheres-and-components/general-purpose-spheres/default.aspx">integrating sphere</a> be a sphere? Why can't it be an integrating cube? What is the difference? Could I use a cube to measure total illuminance like an integrating sphere does?</p>
<p><img src="http:... | g11159 | [
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<p>Everyone has seen cartoons of bombs being dropped, accompanied by a whistling sound as they drop. This sound gets lower in frequency as the bomb nears the ground.</p>
<p>I've been lucky enough to not be near falling bombs, but I assume this sound is based on reality.</p>
<p>Why does the frequency drop? Or does it ... | g11160 | [
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<p>It seems common for an ordered phase to have some amount of disorder present. For example, the average moment of a ferromagnet is less than maximum except at T=0 due to the presence of fluctuations. Also, a liquid is typically only in equilibrium if a portion of it is vapor at the right vapor pressure. Is there an a... | g11161 | [
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<p>I am currently working on my bachelor's thesis on the anapole / toroidal moment and it seems that I am stuck with a tensor decomposition problem.</p>
<p>I have actually never had a course about tensors, so I am a complete newbie.</p>
<p>I need to expand a localized current density, which is done by expressing the ... | g11162 | [
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<p>This question is more a philosophical question than a physics one.
When we appreciate particle physics we study that in order to explain some experimental results we have to introduce a new particle (for instance thinking about neutrinos). This is obviously true but I just want to ask you: is there a wave interpreta... | g11163 | [
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<p>I was watching Nima's very popular <a href="http://susy2013.ictp.it/video/05_Friday/2013_08_30_Arkani-Hamed_4-3.html" rel="nofollow">talk (download if you're using chrome)</a> (also mirrored at youtube <a href="http://www.youtube.com/embed/q4Dj8fq30sk" rel="nofollow">here</a>) about the "Amplituhedron", which has su... | g11164 | [
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<p>I'm confused: Big Bang nucleosynthesis is adamant about the 1 neutron to 7 proton ratio which yields 75% hydrogen to 25% helium (with a nominal amount of partially-reacted deuterium and heavier lithium). But everything I read about the interstellar medium gives a helium figure closer to 10%, so what happened to the ... | g11165 | [
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<p>I would like to understand basic concepts of the general relativity in 2+1 spacetime. As far as I know, GR predicts that such a spacetime is flat everywhere except for the point masses which create angular deficit proportional to their mass. Flatland with one point mass is like surface of cone. I imagine that when o... | g11166 | [
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<p>In David Chandler's 'intro to statistical mechanics' he states that for an ideal gas at high-temperature</p>
<p>$$
\langle n_j\rangle=\langle N\rangle\frac{e^{-\beta \epsilon_j}}{\sum e^{-\beta \epsilon_j}}
$$</p>
<p>Which I can believe from intuition, but he losses me on the derivation. </p>
<p>Starting with the... | g11167 | [
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<p>I want the basic reason. I want the description of answer graphically also.</p> | g358 | [
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<p><img src="http://i.stack.imgur.com/lm41R.jpg" alt="Wheatstone bridge Capacitor,Dead Capacitor"></p>
<p>I want to know that if in a Wheatstone Bridge ,that is made of capacitors only
we have this condition $c_1c_3=c_2c_4$. </p>
<p>The $c_5$ capacitor would be dead and it's voltage would be zero? Actually I am looki... | g11168 | [
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<p>I was reading on up <a href="http://en.wikipedia.org/wiki/Lagrangian_point" rel="nofollow">Lagrangian points</a> and the restricted three-body problem.</p>
<p>From what I was able to tell, the Lagrangian points are 5 points in a two-body system such that a third body would be relatively at rest. The first three are... | g11169 | [
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-0.0131... |
<p>In recent publications there is a frequent mentioning of the so-called "Higgs transition" in connection with magnetic monoples. Can anybody please describe the phenomenon in simple terms?</p>
<p>For example, it seems that <a href="http://www.sciencedaily.com/releases/2012/08/120807113243.htm" rel="nofollow">here</a... | g11170 | [
0.0102565111592412,
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0.013999776914715767,
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<p>I actually want to know whether space-time supersymmetry is important for string theory consistency? I see that NS and GS supersymmetric strings have worldsheet supersymmetry, but the first one does not have a manifest space-time SUSY while the second one has it manifest. I want to know if this space-time SUSY is re... | g11171 | [
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0.032804038375616074,
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0.02132168971002102,
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0.... |
<p>I started learning a bit ahead from an old physics book, and they were discussing the photoelectric effect and after that Planck's hypotheses and energy quantas.</p>
<p>The book said that the mass of a microscopic oscillator (what is that?) is not continuous, but discrete and the difference between states is an ene... | g11172 | [
0.04654276743531227,
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0.036222442984580994,
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0.016386277973651886,
0.015241652727127075,
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-0.01786738634109497,
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0.03246753662824631,
... |
<p>I'm porting <a href="http://en.wikipedia.org/wiki/Maxwell%27s_equations_in_curved_spacetime" rel="nofollow">Maxwell's equations to curved spacetime</a> and am having trouble reconciling the tensor and forms treatments. I think the problem boils down to a misunderstanding on my part concerning the exterior covariant ... | g11173 | [
-0.0032880855724215508,
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0.058010004460811615... |
<p>When we can say that two particle are momentum entangled ? I just read an article where it's said that two momentum entangled particles share the same momentum value in opposite directions no matter how far they are when it's provided a measurament
...It's a correct description?</p> | g11174 | [
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<p>I understand that the maximum free charge carrier density for aluminum has been measured using the Hall effect (in the case of electric current). However, I'm not clear how to determine the maximum surface charge density to which aluminum (or any conductor) can be charged, assuming the neighboring medium does not br... | g11175 | [
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0.026594458147883415,
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<p>Why is gravitational potential energy negative? How is it different from other forms of energy? I recently saw a video by Dr. Michio Kaku, he said that the total energy content of the universe is zero, since gravitational potential energy is negative, thus balancing all the positive energy. Can anyone help me out he... | g27 | [
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<p>Generally, to let my bolognese thicken, I leave the lid off in order to "let water vapor escape." I am however distracted from enjoying the taste because I'm having doubts that my physical reasoning is sound.</p>
<p>Given a constant power output from my stove, it seems a given that having the lid on to make the con... | g11176 | [
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<p>I am looking for a resource that clearly exposes the concepts of a particle source and a particle detector in the context of Quantum Field theory. I want to understand <a href="http://en.wikipedia.org/wiki/Irreversible_process" rel="nofollow">Irreversibility</a> in this context. </p> | g11177 | [
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<p>Discussion about Landau's "Theoretical Minimum" has already been posted <a href="http://physics.stackexchange.com/questions/13861/lev-landaus-theoretical-minimum">here</a>. Unfortunately I couldn't find much about some examples of questions he gave to students. There are three questions in the post I linked and also... | g11178 | [
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0.03096623905003071,
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0.0... |
<p>I am unable to find the solution to the following equation:<br></p>
<p>Tr$_{2}[U(|\psi\rangle \langle\psi|\otimes \rho)U^{\dagger}]=\rho$</p>
<p>Here $\psi$ is state vector representing a qubit and $\rho$ state of second qubit(the partial trace is over its subspace).<br></p>
<p>Also $U$ is a unitary operator give... | g11179 | [
0.015370066277682781,
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<ol>
<li><p>I'd like to learn how much energy I need to lift a 200 kilograms weight on normal earth conditions? </p></li>
<li><p>For example how much electric power do we need?</p></li>
</ol>
<p>I'm not a physicist and not a student and this is not my hw:) I just wondering. </p> | g11180 | [
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0.004907782655209303,
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... |
<p>Hamiltonian is defined by $H_I = \hbar \omega (\hat{a}^+ \hat{a} + 1/2)$</p>
<p>What is the expectation value of the energy on the number state </p>
<p>$$\vert \psi \rangle = \frac{1}{\sqrt{2}} ( \vert 1 \rangle + \vert 2 \rangle )$$</p>
<p>So I think that its</p>
<p>$$\langle E \rangle = \langle \psi \vert H_I ... | g11181 | [
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<p>Why is that when I'm standing in a moving double deck bus, my body doesn't move a lot; whereas, in a moving single deck bus, my body moves quite a bit? It seems like I swing a lot in single deck buses, much more than in double-decked buses. Why is this?</p> | g11182 | [
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0.0476... |
<p>I am interested in computing the integral of this function:
\begin{align}
\int_0^\infty\frac{2du(u^2+1)}{(1-e^{2\pi u})},
\end{align}
which of course at first sight, does not converge. But in QFT it's usually possible to regulate such a function. Thus, the question is, does anyone know how to regulate this function... | g11183 | [
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0.03823787719011307,
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0.05337994918227196,
0.021498875692486763,
0.01... |
<p>Let's consider a 0-dimensional $N \times N$ Hermitean one matrix model.
It is defined by a potential V(M). Its partition function
is
$Z = \int_{H_{N}} dM e^{-\frac{1}{g}V(M)}$
where $H_{N}$ is the space of $N \times N$ Hermitean matrices
and g is the coupling constant. I usually think at such a matrix model as
a ... | g11184 | [
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0.07779046893119812,
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<p>From basic principals, how does one prove that energy is conserved? Or a little more specifically - Why does this hold:</p>
<p>$$\Delta \mbox{ PotentialEnergy} + \Delta \mbox{ KineticEnergy} = 0 $$</p>
<p>Or, for extra credit, why does this hold:</p>
<p>$$\Delta \mbox{ PotentialEnergy } + \Delta \mbox{ KineticEne... | g307 | [
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0.0... |
<p>It seems that the limitation to subluminal travel can be practically circumvented (so to speak...not breaking any physical laws here) if we consider the viewpoint of the traveler, not some outside observer:</p>
<ul>
<li>As your ship approaches $c$ (as measured from some inertial observer) the proper time of the tri... | g11185 | [
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<p>I need a part or material for a planned experiment (the experiment is similar to those described in my articles <a href="http://arxiv.org/abs/1208.0066" rel="nofollow">http://arxiv.org/abs/1208.0066</a> and <a href="http://arxiv.org/abs/1109.1626" rel="nofollow">http://arxiv.org/abs/1109.1626</a> ). The problem is t... | g11186 | [
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... |
<p>Ring cavity lasers usually has a intracavity element like a optical diode to forbid standing wave pattern and, consequently, spacial hole burning and related instabilities. So, my question is: why to beams exist (before install the optical diode-like element) inside the cavity, since (as far as I know) stimulated em... | g11187 | [
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0.06502553075551987,
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0.00817... |
<p>If I understand correctly, Einstein's theory of General Relativity predicted the expansion of space itself, and Hubble confirmed this prediction by observing the red shift of receding galaxies.</p>
<p>I have always wondered how physicists know that this red shift indicates that space itself is expanding, as opposed... | g359 | [
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0.06781777739524841,
0.032679... |
<p>Is it same as the direction?Then , why another term "sense"is used ,instead of direction?
Can anyone illustrate it?</p> | g11188 | [
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0.0229862779378891,
... |
<p>I have been reading lately about <a href="http://en.wikipedia.org/wiki/Lie_group">Lie groups</a>, and although all books keep listing the groups, and talk about Lie algebras and all that, one thing I still don't know how is it made, and I guess it's the most important question as much as my understanding goes, but m... | g11189 | [
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<p>so I had my first approximation to the gravity equation</p>
<p>\begin{equation}
F=GmM/r^2
\end{equation}
and some questions arose that my teacher couldnt respond:<br>
if r approximates to 0 with mM being constant, then the force should tend to infinity, right? so that being true, then if we would travel to the cent... | g11190 | [
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<p>I'm a PhD student in maths, and attended my last physics class some 15 years ago, so you can imagine my competences in the field.
My supervisor (also not a mechanist) cant tell me how to proceed either, and after having spent already way too much time on wikipedia to try to understand the elementary concepts, I am t... | g11191 | [
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... |
<p>I have often heared, that Leyden jars are used because they have a high breakdown voltage. For that reason the are used for example in Whimshurst machines. </p>
<p>But what is the physical reason that they have a high breakdown voltage? And what means "high" in this context? Compared to what? How does it compare fo... | g11192 | [
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0.... |
<p>If I have a wavefunction $\psi = \sum_{n=0}^{\infty} a_n e^{i \phi_n} | n \rangle$ and $(|n \rangle)$ is a set of orthonormal functions. Is it correct that the probability to be in a state $|k\rangle $ is given by $|a_k|^2$?-So is it really true, that the probability to be in this state is independent of the phase ... | g11193 | [
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... |
<p>I'm new to this forum. This is half a question, half a challenge. And it's more engineering then physics but I thought I might get good insights from a physics forum.</p>
<p>I would like to cure a UV activated resin using a collimated 390 to 420nm light source. The area I need to cure is 3" (7.5cm) by 3". ( althoug... | g11194 | [
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-0.01934455707669258,
0.06206725910305977,
0.0471220389008522,
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0.00... |
<p>Say you have two objects colliding, and there is some elasticity between them. Some of the kinetic energy of the objects will change into elastic potential energy when they collide, but when they bounce off each other again, the energy does not return to being kinetic. What happens with it? Does it stay stored as el... | g11195 | [
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0.0012975343270227313,
... |
<p><img src="http://i.stack.imgur.com/oc8js.png" alt="enter image description here"></p>
<p>Normally, when a distributed force is acting on a bar, if it's 'rectengular' we multiply the length with q, but I have no idea what I'm supposed to do at this situation.</p>
<p>I first need to calculate to forces acting on C s... | g11196 | [
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<ol>
<li><p>Is there any other solar system far away from ours in the universe?</p></li>
<li><p>Why don't we expect another solar system based on another star similar to sun in the universe? </p></li>
<li><p>If so, Why probably there wouldn't be some life based on those atmospheric conditions?</p></li>
</ol> | g11197 | [
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<p>Question is inspired by a recent burst of <a href="http://en.wikipedia.org/wiki/Perpetual_motion" rel="nofollow">perpetuum mobile</a>-type questions. It would be nice if one could simply discard them all by an argument that shows it's impossible to create a perfect vacuum. Intuitively, I have some hope that there wi... | g11198 | [
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<p>A $(d,\lambda)$-quantum expander is a distribution $\nu$ over the unitary group $\mathcal{U}(d)$ with the property that: a) $|\mathrm{supp} \ \nu| =d$, b) $\Vert \mathbb{E}_{U \sim \nu} U \otimes U^{\dagger} - \mathbb{E}_{U \sim \mu_H} U \otimes U^{\dagger}\Vert_{\infty} \leq \lambda$, where $\mu_H$ is the Haar meas... | g11199 | [
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<p>By the "No Hair Theorem", three quantities "define" a black hole; Mass, Angular Momentum, and Charge. The first is easy enough to determine, look at the radius of the event horizon and you can use the Schwarzschild formula to compute the mass. Angular Momentum can be found using the cool little ergosphere Penrose "d... | g709 | [
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<p>I am confused about a method used in the following problem. There is an arrangement as shown below. The surface is smooth, and the pulleys are light. We have to find the acceleration $a_0$ of $m_1$.</p>
<p><img src="http://i.stack.imgur.com/X1esM.png" alt="Problem"></p>
<p>The method I used to solve it was to cons... | g11200 | [
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<p>In his first lesson (transcripted in "Tips on Physics"), Feynman talks about math for physicists in a very cool and practical way. And at the end of the section he talks something like "so the first thing to do is to learn to learn derivative, integral and algebra" (I don't know how much precise I'm being because I'... | g98 | [
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<p>So a coil is rotating in a magnetic field, and at $\theta=0$ the coil is perpendicular to the field lines. At $\theta=90$ the coil is parallel to the field lines.</p>
<p>The the angle, theta, is the angle between the normal to the coil and the direction of the magnetic field lines.</p>
<p>This implies that the mag... | g11201 | [
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<p>I know how to detect when resistors are arranged in parallel or series arrangement and<br>
I can also find their equivalent resistance in simple circuits or when resistances are connected in form of<br>
triangle but what happens when the arrangement is complex like this :<br>
<img src="http://i.stack.imgur.com/MM06V... | g11202 | [
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<p>I have been viewing this video :<BR><a href="http://www.youtube.com/watch?v=Ehlw-9PJkIE" rel="nofollow">Masaru Emoto's Rice Experiment</a> <BR>
Anybody has any physical explanation of this phenomena? </p> | g11203 | [
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