question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>It has been recently pointed out to me that the solution of the heat equation in a semi-infinite material with an oscillating boundary condition at the surface is <strong>not an evanescent wave</strong>. The argument was that in the solution to the equation (which is a temperature field that oscillates in an exponen... | g13600 | [
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<p>How long does it take for a photon to be reflected? Starting with the photon being absorbed by some atom to the point it's reemitted?</p>
<p>And what's the same point with pressure waves, like sound?</p> | g13601 | [
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<p>Suppose two pointed masses are given in space. Suppose further that one of the masses has a given velocity at (local) time 0. Is there a way to compute its position in a future time?</p>
<p>Neglecting general relativity, I will simply compute an integral, but with general relativity, we see that the metric of the s... | g998 | [
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<p>This question is motivated by <a href="http://physics.stackexchange.com/questions/52211/is-the-quantization-of-gravity-necessary-for-a-quantum-theory-of-gravity">this question</a> and <a href="http://physics.stackexchange.com/questions/55333/is-the-quantization-of-gravity-necessary-for-a-quantum-theory-of-gravity-pa... | g13602 | [
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<p>I want to create a set of silicon based materials that have been doped with different materials and/or different amounts of dopants. The purpose of this is to see how the spring constant of silicon changes with the different electrical properties, specifically, with the change in resistivity (because we are all set... | g13603 | [
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<p>Could the gravitational force be what holds the charge of the electron together? It seems to be the only obvious possibility; what other ideas have been proposed besides side-stepping the issue and assuming a "point charge"? How would this affect the electron "self-energy" problem? The question is related to the ide... | g13604 | [
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<p>The magnetic part of the Lorentz force acts perpendicular to the charge's velocity, and consequently does zero work on it. Can we extrapolate this statement to say that such a nature of the force essentially makes its corresponding work independent of the choice of path, and hence that the magnetic force is conserva... | g212 | [
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<p>Could someone kindly elaborate more on the <a href="http://en.wikipedia.org/wiki/Ginzburg%E2%80%93Landau_theory#Simple_interpretation" rel="nofollow">Simple Interpretation section from this Wikipedia Article</a>? I refer to the part on the natures of $\alpha , \beta$. Why can one assume that $\alpha(T)=\alpha_0(T-T_... | g13605 | [
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<p>What shape is formed by the set of all raindrops which create a rainbow to specific observer?</p>
<p>Maybe it's easier to narrow this down and consider it this in parts: what's the set of positions from which a raindrop can refract and reflect a beam of red light in the primary rainbow? What shape does that set for... | g13606 | [
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<p>How do I calculate the pull force of a cylindrical electromagnet to Iron as a function of distance? </p>
<p>Is there any difference betweeen magnets and electromagnets? </p> | g13607 | [
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<p>So I have a solid state and thermodynamic exam next week and I've been going through some of the previous exams from years gone by to prepare. I came across this question "Distinguish electron-like and hole-like orbits in reciprocal space, with reference to the Brillouin Zones of squarium by sketching an example of ... | g13608 | [
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<p>I have to build a simple electromotor in the following way: I attach a permanent magnet to a battery, connect some metal supports to the terminals of the battery, and place a coil of wire on the supports, suspended above the magnet. My question is, will it still work just as well (or at all) if the wire is insulated... | g13609 | [
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<p>is this possible? To absorb kinetic energy and disable inertia force?</p>
<p><a href="http://www.youtube.com/watch?v=KnKPbAbJI0w" rel="nofollow">http://www.youtube.com/watch?v=KnKPbAbJI0w</a></p>
<p><a href="http://www.youtube.com/watch?v=4_5oseSVUc4" rel="nofollow">http://www.youtube.com/watch?v=4_5oseSVUc4</a></... | g13610 | [
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<p>Putting aside quantum mechanics (or at least putting aside the question of fermions), is our knowledge of extremal General-Relativity solutions good enough that we would be able to rule out a classical theory of spinning charged relativistic particles based on extremal black holes? I ask this in the context of my cu... | g13611 | [
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<p>I'm little confused here. <a href="http://en.wikipedia.org/wiki/Work_%28physics%29" rel="nofollow">Work</a> done on the body when we lift it and put it on the table is zero, because according to work energy theorem, change in kinetic energy of the body is zero. So, the net work done is zero. </p>
<p>Fine, but now t... | g13612 | [
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<p>From <a href="http://www.alexwg.org/publications/PhysRevLett_110-168702.pdf" rel="nofollow">Causal Entropic Forces, A. D. Wissner-Grossand C. E. Freer, Physical Review Letters</a></p>
<p>Regarding a particle exhibiting brownian motion within a box...</p>
<blockquote>
<p>...In contrast, if the particle had merely... | g13613 | [
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<p>Ok so I saw this video by Brian Cox where he explains how no 2 particles can have same energy level.</p>
<p>Later I watched video "Was Brian Cox wrong?". Where they explained that he (probably on purpose) oversimplified it. And in fact it means that in fact no 2 particles can be in same quantum state. And that quan... | g13614 | [
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<p>I was told by a condensed matter physicist that glass is a liquid with a very high viscosity (it would be more precise to say that it is a <a href="https://en.wikipedia.org/wiki/Supercooling">supercooled liquid</a>). The example given was that in cathedral windows the glass flows very, very slowly, so they are thick... | g13615 | [
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<p>I am not good in physics.You can say I am beginner in this field.</p>
<p>I have some basic questions.</p>
<p>I ju st want to know that</p>
<p>[1] If there is repulsive force between same charges proton-proton then why they are bound<br>
together in nucleus?</p>
<pre><code>when I just tried to find out on Goo... | g425 | [
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<p>I have recently been doing research on the AGT Correspondence between the Nekrasov Instanton Partition Function and Louiville Conformal Blocks (<a href="http://arxiv.org/abs/0906.3219">http://arxiv.org/abs/0906.3219</a>). When looking at the Nekrasov Partition Function one defines a deformed metric in terms of the "... | g13616 | [
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<p>How to calculate the current between two superconducting rings with radius r separated by a distance d?</p>
<p>Please note that being unfamiliar to the concept of superconducting rings, I can't approach this problem. It would also be useful if anyone tells me which special property of superconductors can be used he... | g13617 | [
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<p>Question: what is the energy balance in this situation?</p>
<p>(Fig A)<br>
Two gamma rays collided and produced an electron/positron pair $(e-/e+)$. </p>
<p>(Fig B)<br>
1. because all particles are accelerating electromagnetic energy
(photons) were radiated and spread away.<br>
2. they evolved and nearby n... | g13618 | [
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<p>I got to read things like </p>
<blockquote>
<p><em>In case of a first order phase transition, the volume and temperature change in a discontinuous manner. However for phase transitions of higher order the change in volume and temperature can be continuous.</em> </p>
</blockquote>
<p>I could not exactly understa... | g13619 | [
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<p>It seems to me that I can express the work required to put an object under water in the same way that I express lifting an object up against gravity. I. e., in both cases I increase the potential energy of the object by moving it vertically against the direction of the force. Conversely, when the object is allowed t... | g13620 | [
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<p>What is the difference between indistinguishable particles and <a href="http://en.wikipedia.org/wiki/Identical_particles" rel="nofollow">identical particles</a>?</p> | g13621 | [
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<p>I've heard the Schrödinger's cat "paradox" (although there's nothing particularly paradoxical about it, just counterintuitive), but I've never been clear on whether or not it's meant to be taken with a grain of salt.</p>
<p>I've always assumed it was just a metaphor for the behavior of particles at the quantum scal... | g13622 | [
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<p>What's the weight of the earth?</p>
<p>That is, what's the weight of the earth in the gravitational field of the sun? I imagine it's either</p>
<ul>
<li>$0$, because there's no net fall toward the sun, so the downward component of acceleration is $0$ and $F=ma=0$, or</li>
<li>$Gm_1m_2/r^2\approx7\cdot10^{-11}\cdot... | g13623 | [
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<p>In Wikipedia's article on <a href="http://en.wikipedia.org/wiki/Fermi_gas" rel="nofollow">Fermi Gases</a>, they have the following equation for the chemical potential:</p>
<blockquote>
<p>$$\mu = E_0 + E_F \left[ 1- \frac{\pi ^2}{12} \left(\frac{kT}{E_F}\right) ^2 - \frac{\pi^4}{80} \left(\frac{kT}{E_F}\right)^4 ... | g13624 | [
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<p>Is randomness based on lack of knowledge or behavior of universe is true random?</p>
<p>Or in other words,</p>
<p>are the allegation by EPR about hidden variable in the QM theory justifiable? What evidence can disprove/prove EPR?</p> | g13625 | [
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<p>I'm trying to rework this old homework problem, and I am having problems arriving at the same solution on the answer sheet:</p>
<blockquote>
<p><em>Let $$V(x)=\begin{cases}\infty &\text{ if } x < 0\\ \alpha\delta(x-a) &\text{ if } x \geq 0 \end{cases}$$ where $a$ and $\alpha$ are of the appropriate uni... | g13626 | [
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<p>Let's suppose there is a straight rigid bar with height $h$ and center of mass at the middle of height $h/2$. Now if the bar is vertically upright from ground, how long will it take to fall on the ground and what is the equation of motion of the center of mass (Lagrangian)?</p> | g13627 | [
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-0.029389526695013046,
0.00032... |
<p>In the tutorial I'm following, the guy uses 6 snapple bottles to make capaciter (by covering them with foil and filling them with salt water) for a 9kV 30mA input. I have a stronger transformer (15kV 60mA), and no snapple bottles. I do have an assortment of other cans and jars (jam and suchlike) which togeather have... | g13628 | [
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0.0340166874229908,
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<p>I need to calculate the approximate total amount of energy radiated, via Cerenkov, by a muon as it traverses $10\:\rm{cm}$ of quartz glass. Unfortunately I've spent so much time fiddling with electronics in the lab recently that I've completely forgotten how to do maths.</p>
<p>The formula to use is the <a href="ht... | g13629 | [
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0.022280922159552574,
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<p>I am reading Kolenkow and Kleppner's <em>Classical Mechanics</em> and they have tried to calculate the gravitational force between a uniform thin spherical shell of mass $M$ and a particle of mass $m$ located at a distance $r$ from the center.</p>
<p>The shell has been divided into narrow rings.$R$ has been assumed... | g13630 | [
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<p>Given that the Sun is a bit less than 10 light minutes away from Earth, is it correct to assume in principle (I understand actual processes in the <a href="http://en.wikipedia.org/wiki/Photon#Photons_in_matter" rel="nofollow">core</a> of the Sun make the situation at a photon's emission far more complicated) that th... | g13631 | [
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<p>I read that force due to electric field on some particle in one reference frame can exhibit itself as force due to magnetic field in some other reference frame and that electric and magnetic fields are two aspects of same underlying electromagnetic field. </p>
<p>My question is what is the mechanism which can expla... | g13632 | [
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<p>Can you tell me how graph theory comes into physics, and the concept of small world graphs?</p>
<p>(inspired to ask from comment from sean tilson in): </p>
<p><a href="http://physics.stackexchange.com/questions/1862/which-areas-in-physics-overlap-with-those-of-social-network-theory-for-the-analys">which areas in p... | g13633 | [
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<p>Here is a link to a <a href="http://www.youtube.com/watch?feature=player_embedded&v=0JOgTKigxGs" rel="nofollow">video of a self-balencing unicycle</a>. I'm curious as to how this works. In particular:</p>
<ul>
<li><p>What provides the torque to keep the rider from falling over? I know it's somehow provided by t... | g13634 | [
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<p>I realize that path integral techniques can be applied to quantitative finance such as option value calculation. But I don't quite understand how this is done. </p>
<p>Is it possible to explain this to me in qualitative and quantitative terms?</p> | g13635 | [
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<p>So in photonic crystals when looking at diffraction the refraction of light has to be taken into account. I am told this would lead to the "photonic bragg's law" which is
$$n \lambda = 2d\sqrt{n-sin^2\theta_i} $$</p>
<p><img src="http://i.stack.imgur.com/1W33r.png" alt="The situation in question"></p>
<p>Where $\t... | g13636 | [
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<p>Is it possible on Earth?</p>
<p>Roughly what size would an impactor have to be to cause a tsunami of this height? And it's speed, energy equivalent in tons, megatons, etc.?</p> | g13637 | [
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<p>Most of the forces in physics obey inverse square law, but why molecular forces don't obey it.. Since molecular forces is also a form of electromagnetic force..</p> | g13638 | [
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<p>What is the real cause behind the cohesive and adhesive forces?</p> | g13639 | [
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<p>I'm having trouble understanding some of the stuff regarding movement in my introductory physics class (I never thought I'd say that...)</p>
<p><a href="http://en.wikipedia.org/wiki/Acceleration" rel="nofollow">Acceleration</a> is defined as $ a = \frac{s}{t^2}.$
Distance can be calculated as the area under velocit... | g13640 | [
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<p>I am tasked with reading and reproducing all the steps in J.J. Hopfield's 1958 paper <a href="http://prola.aps.org/abstract/PR/v112/i5/p1555_1" rel="nofollow">"Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals"</a>. Embarrassingly I am stuck on equation (3). Hopfield takes the Lag... | g13641 | [
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0.01... |
<p>Since we will (maybe) never observe free quarks which has fraction charge, is it logically correct to say that the fraction (1/2,2/3 etc) electric charge is also confined. I.e. the charges that we do se (+1,-1 etc) are "white" in the sense of color?</p> | g13642 | [
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<p>I can picture a bound state in a <a href="http://en.wikipedia.org/wiki/Quantum_harmonic_oscillator" rel="nofollow">harmonic oscillator</a>, or in an <a href="http://en.wikipedia.org/wiki/Particle_in_a_box" rel="nofollow">infinite square well</a>, but where is a particle bound in a <a href="http://en.wikipedia.org/wi... | g13643 | [
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<p><strong>I've got this far:</strong></p>
<p>Suppose a spin-1 particle with $j$,$l$,$s$ decays into a system of two identical spin-0 particles with $J$,$L$,$S$.</p>
<p>The RHS must have total spin $S=0$, so $J=L$ which must be even since the particles are Bosons and their states must be symmetric in their exchange.<... | g13644 | [
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<p>I heard a claim that due to holographic principle, the surface area of the cosmic horizon corresponds to the universe's total entropy.</p>
<p>As such the initial state had zero surface area and later expanded. </p>
<p>Given this, I wonder whether any increase in entropy (such as producing heat by means of electric... | g13645 | [
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<p>Let $${\bf H}=\hat{x}^3\hat{p}+\hat{p}\hat{x}^3$$ where $\hat{p}=-id/dx$.
Clearly ${\bf H}^{\dagger}={\bf H}$, because ${\bf H}={\bf T} + {\bf T}^{\dagger}$, where ${\bf T}=\hat{x}^3\hat{p}$. In this sense ${\bf H}$ is "formally" self-adjoint. </p>
<p>It turns out that </p>
<p>$$ \psi_{\lambda}(x)=\frac{1}{|x|^{3/... | g13646 | [
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<p>I was having problems with ionization energy - but all it is is the energy required to remove first electron that pops off right? In the case of Bohr's atom, there's only one electron, so it's that electron in it's ground state. In the case of a multielectron atom, it's the energy required to remove the outer electr... | g13647 | [
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0.010... |
<p>According to wikipedia: <a href="http://en.wikipedia.org/wiki/Siphon#Velocity" rel="nofollow">Siphon</a>, the velocity of liquid in a siphon is equal to $\sqrt{2gh}$, where h is the difference in level between the water surface and the opening of the siphon.</p>
<p>But it also mentions that there exists a maximum v... | g13648 | [
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<p>I am trying to simulate a collision between two molecules. I know the energy for every position/orientation, from which I can calculate the forces. The treatment is classical and the molecules are assumed to be rigid.</p>
<p>I converted this situation to the center of mass frame so I only need the relative position... | g13649 | [
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<p>Could anybody tell me what does <a href="http://en.wikipedia.org/wiki/Scale_invariance" rel="nofollow">scale invariance</a> means?</p>
<p>Is there any book or article that describes [ and gives examples ] about it.</p> | g13650 | [
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<p>If you ask any person about time, she/he will give you some answer.
I suspect that it is extremely difficult, (if not impossible) to define time.
Is there a definition of what it is in physics? Is it an "axiom" that has to be taken as it is, without explanations? I also noticed that the tag "time" has no pop-ups wi... | g13651 | [
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<p>The entire question is in the title .</p>
<p>It's the case for the solar system but is it always the case ? Can a planet do a revolution faster than another that is closer to the center ?</p>
<p>As far as I searched , it's not but I prefer ask here to be sure.</p>
<p>Of course I'm talking about similar orbits (al... | g13652 | [
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<p>In this <a href="http://arxiv.org/abs/0802.3525" rel="nofollow">article</a>* I want to get the Equation(9) with comparing the equation (2). Please elaborate the left side of equation (9).</p>
<p>*<em>Small amplitude quasi-breathers and oscillons</em> by G. Fodor, et al.
arXiv:0802.3525.</p> | g13653 | [
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<p>A simple question I hope... </p>
<p><strong>Initially</strong>, have two separate containers of 2 different ideal gases, 1.) N1, P, T, V1 and 2.) N2, P, T, V2.</p>
<p><strong>After mixing</strong>, the pressure and temperature are still P and T, but the volume is additive. Assuming isolated system.</p>
<p>So I ca... | g13654 | [
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<p>Seems not a trivial problem:</p>
<p>There is a semi-cylindrical cavity, with radius $R$ as shown in the Figure. A small ball (point mass for simplicity) with an initial horizontal velocity $v$ flies into the cavity. Friction is absent, blows against the cavity's wall are absolutely elastic. What should be the val... | g13655 | [
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<p>I have a very large movable trash container, and I have mounted four scales, one on each corner. How do I get the <strong>total weight</strong> of the entire container? Is it simply a sum of the four weights, or is it more complex than that?</p>
<p>The contents of the container are not evenly distributed, one corne... | g13656 | [
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<p>I'm a sci-fi writer, and I have a question regarding a hypothetical planet that orbits an A-class or B-class Star.</p>
<p><strong>Assuming Rayleigh Scattering occurs roughly the same way on this planet as it does on Earth, what colors would we see at Sunrise and Sunset?</strong></p>
<p>I understand that what colou... | g13657 | [
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<p>I wonder if there ever could be a star (really small) which may orbit around a planet (really big)?</p> | g102 | [
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-0.05158177390694618,
0.010645424015820026,
0.062453851103782654,
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-0... |
<p>Situation: A fly is in the cockpit of a fighter jet, and flying directly in front of the pilot. The pilot becomes annoyed and decides to get rid of the fly by executing a sudden, high speed turn. The cockpit is so dark the fly cannot see any of the cockpit. will the fly continue to be in front of the pilot, or wi... | g13658 | [
0.02037639543414116,
0.009433344006538391,
0.003611941123381257,
0.01809876598417759,
0.03275120630860329,
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0.014228424057364464,
0.008226381614804268,
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-0.04789672791957855,
0.011905277147889137,
0.011766145937144756,
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0.04158... |
<p>In the <a href="http://nlab.mathforge.org/nlab/show/Haag-Kastler+axioms">Haag-Kastler approach to axiomatic quantum field theory</a>, it is assumed that observables are 'associated' to spacetime regions. What this actually means is that there is a map $\mathcal{A}: R \mapsto \mathcal{A}(R)$, which associates to a ... | g13659 | [
-0.021037288010120392,
0.019461918622255325,
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0.007880430668592453,
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0.03057914413511753,
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0.003808833658695221,
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0.... |
<p>If a pump is discharging a fluid into a pipe, is it possible to add a long enough pipe such that the flow of the liquid will be stopped and none will come out of the open end of the pipe? </p> | g13660 | [
0.03446462005376816,
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<p>Carbon-14 has a half-life of 5,730 years. That means that after 5,730 years, half of that sample decays. After another 5,730 years, a quarter of the original sample decays (and the cycle goes on and on, and one could use virtually any radioactive isotope). Why is this so? Logically, shouldn't it take 2,865 years... | g426 | [
0.03738822788000107,
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0.020970404148101807,
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-0... |
<p>Let us assume that we have have an infinite Newtonian space-time and the universe is uniformly filled with matter of constant density (no fluctuations whatsoever), all of it at rest. By symmetry, the stuff in this universe should not collapse or change position in any way if gravity is the only force acting on it.
N... | g427 | [
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... |
<p>how to measure the wavelengths of ultraviolet radiation isn't it invisible?
it's possible to measure visible radiation but how to measure invisible radiation?</p> | g13661 | [
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0.04937507584691048,
0.00835325289517641,
0.042944... |
<p>I am wondering about the drag coefficient for a flow past a cylinder. I am reading <a href="http://www.grc.nasa.gov/WWW/k-12/airplane/dragsphere.html" rel="nofollow">this article</a>.</p>
<p>I understand why the drag is high to begin with (point 2), when the boundary layer separates and the recirculations appear, t... | g13662 | [
0.007155298255383968,
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<p>Sometimes, mostly in winter, when somebody touches the tap it passes current (especially when the hands are soaked in water or soap water). I read 3-4 years back in physics book that the tap circuit is connected to some copper plate which is dug inside the ground (called earthing). And then somebody suggested that i... | g13663 | [
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0.08... |
<p>Every supersymmetry text starts off mentioning the Coleman-Mandula theorem. Often it is introduced using rather colloquial terminology. I was wondering if anyone knew a precise mathematical formulation of the theorem.</p> | g13664 | [
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<p>Think about an electron been accelerated from rest in a static electricfield. If we treat the problem classically, in which the electron is just a point charge. The velocity of the electron would increase linearly with respect to time. </p>
<p>Now if we treat this problem quantum mechanically, in which the electro... | g13665 | [
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0.05924227461218834,
0.028553299605846405,
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<p>Newtons law of gravity for two particles of mass $m_1$ and $m_2$ is:</p>
<blockquote>
<p>$G\frac{m_1.m_2}{r^2}$. </p>
</blockquote>
<p>Supposing that the particles are point particles then gravitional attraction will bring them closer together, and in fact infinitesimally closer together. Now in Newtons time th... | g465 | [
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<p>The method of separation of variables produces an undetermined separation constant and a family of solutions indexed by the values of this constant.</p>
<p>For instance, in the case of an infinitely long rod along the positive x axis (with suitable boundary conditions, like a fixed temperature at the beginning, and... | g13666 | [
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<p>In $E=mc^2$ what type of energy is $E$?
For instance, you can find the kinetic energy of an electron by using $\frac{1}{2}mv^2$ but you can also find the energy from $E=mc^2$. How are those two different besides the values?</p> | g13667 | [
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<p>This is a part of my wider attempts at accounting matter in the observable universe.</p>
<p>The total light ever emitted by stars and other space objects is capped around 1% of baryonic mass (in energy equivalent).</p>
<p><a href="http://physics.stackexchange.com/questions/27799/how-much-light-is-there-in-space-an... | g13668 | [
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0.006507943384349346,
... |
<p>The book <em>QM Demystified</em> states this about black body radiation spectrum:</p>
<blockquote>
<p>An attempt to explain these results using classical theory was codified in the Rayleigh-Jeans formula, which is an expression that attempts to give us the energy density u(ν,T) of radiation in the cavity, where ν... | g13669 | [
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0.05894112214446068,
0.022125113755464554,
... |
<p>When we talk about shear stresses in a fluid, we find that the shear stress is given by $$\tau_{xy} = \mu(\partial_y u + \partial_x v) = \tau_{yx}$$ This relation we get when only looking at one side of our fluid-"cube". Now, in order to take into account the opposite side we assume that the fluid element is so smal... | g13670 | [
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<p>wasn't 100% sure which StackExchange to ask this on, as it could be related to Gamedev (as it's for a game), maths (as it's a approximation model rather than a physical description) or StackOverflow (as I'm implementing it in a programming language, lua to be specific), so sorry if this is the incorrect place. </p>
... | g13671 | [
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0.034410588443279266,
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0.07063183188438416,
... |
<p>Say I have some dye molecule in some low level triplet state, e.g. $T_1$, and it's decaying slowly to the ground state via phosphorescence. However, there are also events where the dye in the $T_1$ state can undergo intersystem crossing to transition to the first singlet excited state, $S_1$, which then decays rapi... | g13672 | [
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0.06904077529907227,
-0.0280888... |
<ol>
<li><p>The mass of a particle used to be considered a fundamental and intrinsic property of the particle; on the same level as other properties such as charge, spin, chirality/helicity. Due to the Higgs mechanism this has changed. The mass is now considered a property that is acquired as the result of interaction ... | g13673 | [
0.07602138072252274,
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0.06805136054754257,
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0.0001586009020684287,
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0.020... |
<p>In discussing <a href="http://physics.stackexchange.com/questions/74013/rocket-propelled-by-a-giant-monochromatic-laser">this question</a> about propelling a spacecraft with photons and their relativistic momentum, the author asked that I restate my comment as another question.</p>
<p>If photons can really be used ... | g13674 | [
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0.056177593767642975,
0.043754059821367264,
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<p>To calculate air flow capacity of a fan in cubic feet per minute (cfm): multiply the average air speed you measured in feet/minute (fpm) by the area of the fan face in square feet. (Area of circle =þ d2/4; where d = diameter in feet). Example: you calculated an 524.93 ft/min average air speed across the face of a 12... | g13675 | [
0.034483373165130615,
0.03038875386118889,
0.02679743617773056,
0.015204411000013351,
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0.031004128977656364,
-0.... |
<p>I (desperately) need help with the following:</p>
<p>What is the null geodesic for the space time $$ds^2=-x^2 dt^2 +dx^2?$$</p>
<p>I don't know how to transform a metric into a geodesic...! There is no need to start from the Lagrangian. I know that $$0=g_{ij}V^iV^j$$ where $V^i={dx^i\over d\lambda}$
where $\lambd... | g13676 | [
0.03325244411826134,
0.03221025690436363,
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0.02286474034190178,
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0.10078132897615433,
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<p>In Bose-Einstein statistics, the grand canonical partition function is
$$\mathcal{Z}=1+e^{-\beta(\epsilon-\mu)}+e^{-2\beta(\epsilon-\mu)}+e^{-3\beta(\epsilon-\mu)}+\cdots$$</p>
<p>In Maxwell-Boltzmann statistics, the grand canonical partition function is
$$\mathcal{Z}=1+e^{-\beta(\epsilon-\mu)}+\frac{e^{-2\beta(\ep... | g13677 | [
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0.04647402837872505,
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0.019968... |
<ol>
<li><p>I understand the construction of the Clifford algebra $C(r,s)$ and in turn the corresponding $Pin$ and $Spin$ groups. I would like first to clarify that $Spin(r,s)^e$ is the universal covering group (a 2 to 1 covering) of $SO(r,s)^e$ ?</p></li>
<li><p>It is true that for $r+s:=n$ even, there is an isomorphi... | g13678 | [
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0.01138726994395256,
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0.010388696566224098,
-0.... |
<h1>Problem 8.79 - Combining Conservation Laws</h1>
<p>A 5.00-kg chunk of ice is sliding at 12.0 m/s on the floor of an ice-covered valley when it collides with and sticks to another 5.00-kg chunk of ice that is initially at rest. Since the valley is icy, there is no friction. After the collision, how high above the v... | g13679 | [
0.05417022854089737,
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0.018630191683769226,
0.052524078637361526,
0.030797079205513,
0.030857518315315247,
0.03401731699705124,
0.01790803112089634,
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0.019121060147881508,
-0.009443303570151329,
0.011821689084172249,
-0.037166528403759,
-0.0185792... |
<blockquote>
<p><em>A bead with mass $m$ is free to glide on a ring that rotates about an axis with constant angular velocity. Form the Lagrange-Euler equations for the movement of the bead.</em></p>
</blockquote>
<p>Solution: Let us introduce the generalized coordinates $\theta$ to determine the beads position.
$$\... | g13680 | [
0.06990639865398407,
0.021709460765123367,
0.0018442736472934484,
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0.03675825148820877,
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0.11422399431467056,
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0.044788748025894165,
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0.07131268829107285,
0.03717122972011566,
-0.0028... |
<p>In everyday life, most of us assumes every event and object has a cause in some sense. I am wondering if the same is true for quantum physics. </p>
<p>Does the random nature of quantum phenomena mean they have no cause or does the theory say that causes of quantum randomness are unknown?</p>
<p>The word "random" i... | g13681 | [
0.015110772103071213,
0.027299050241708755,
0.02032831497490406,
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0.04045695811510086,
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0.0281724501401186,
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0.02656189724802971,
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0.036... |
<p>Is it the same as the space of all possible descriptions of a single electron?
If not, how do they differ?</p>
<p>Please give the mathematical name or specification of this space or these spaces.</p> | g13682 | [
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0.01993688754737377,
-0.003426711307838559,... |
<p>If I have an uncharged floating capacitor and I instantaneously connect one plate to some potential, then that plate will acquire some charge. In practice, the other floating plate will instantaneously rise to the same potential as the first one. But wouldn't this require the second plate having the same charge as t... | g13683 | [
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0.05270707234740257,
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0.... |
<p>When a <a href="http://en.wikipedia.org/wiki/Black_hole" rel="nofollow">black hole</a> destroys things until they are smaller than molecules, where does it go and what happens when it clogs up?</p> | g428 | [
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0.05255470052361488,
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<p>Consider a cylindrical rope of rubbery elastomer with a radius (in inches) equal to the square root of the inverse of $\pi \rightarrow \sqrt \frac{1}{\pi} $ so that the cross sectional area is $1 \, \mathrm{inch^2}$ in its relaxed state of no tension.</p>
<p>Now, toss the rope over a tree limb and hang a horse-th... | g13684 | [
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0.004660523030906916,
-0... |
<p>Both 1D Polyacetelene and 2D fractional quantum Hall state can support fractional excitations. </p>
<p>But as I can see, there are some differences: the ground state of Polyacetelene breaks translational invariance but FQHE does not. In general a symmetry breaking state in 2D are considered as conventional state an... | g13685 | [
0.0455995574593544,
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0.004000964108854532,
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0.04... |
<p>Could the acceleration in the rate of expansion of the universe be due to the weakening of gravitational forces, as the distance between objects continues to increase?</p> | g13686 | [
0.060671187937259674,
0.07632570713758469,
0.004361347761005163,
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<p>I used the package 'EUREQA', version <em><a href="http://formulize.nutonian.com/formulize-eureqa-comparision" rel="nofollow">Formulize</a></em>, to analyse the monthly smoothed sunspot timeseries from 1750 till 2010.</p>
<p>It gives me a simple formula, with 8 coefficients, that match data with a correlation coeffi... | g13687 | [
0.008002732880413532,
-0.016392212361097336,
-0.007879051379859447,
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-0.01446040440350771,
0.018137237057089806,
0.06624896079301834,
0.08489616215229034,
0... |
<p>A block of mass $m$ rests on a frictionless wedge of angle $\theta$ as in the figure. The wedge is given an acceleration $a$. What is the minimum value of $a$ so that the mass $m$ falls freely?</p>
<p><img src="http://i.stack.imgur.com/2pnw3.png" alt="enter image description here"></p>
<p>I have solved a similar p... | g13688 | [
0.08523596823215485,
0.06555737555027008,
0.0068152048625051975,
0.04001975804567337,
0.04885011166334152,
0.012674486264586449,
0.046934328973293304,
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0.005064304452389479,
0.016936859115958214,
0.007547907996922731,
0.05... |
<p>Flow-straighteners are used before flow-meters because they remove disturbances from the flow and achieve nearly-fully developped velocity profiles. But is there any other uses of flow straighteners than flow-metering ? Car companies like Mitsubishi, for instance, developped their own models of flow straighteners, w... | g13689 | [
0.06239020451903343,
0.009085973724722862,
0.010120756924152374,
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0.049948275089263916,
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0.010736401192843914,
0.024... |
<p>How can I measure the mass of the earth at home? </p>
<p>How was the mass of the earth first measured?</p> | g13690 | [
0.08440909534692764,
0.05350190028548241,
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0... |
<p>I'm interested in looking at standing wave solutions for the wave equation on a 2D annulus, with the twist that the annulus is "streched" in to a helix in 3D, but so that the rings themselves are 2-dimensional. For the wave equation in polar coordinates, it seems straightforward enough to extend the azimuthal bounda... | g13691 | [
0.04364699497818947,
0.009801262989640236,
0.00854505505412817,
0.007204501889646053,
0.017143506556749344,
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0.032816044986248016,
-0.01744360662996769,
0.003137241816148162,
-0.004649959970265627,
-0.0... |
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