question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I've just learned of the Weyl Large Number Coincidence on the Wikipedia. It looks interesting. Here is my interpretation of it.</p>
<p>What is the smallest "quantum" of energy in the Universe?
$$E_{min} = \hbar H$$
where $H$ is the Hubble parameter. This make sense as the Hubble parameter is roughly the inverse of ... | g7687 | [
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<p>I was watching this video on YouTube: <a href="http://www.youtube.com/watch?v=DxYwdgHpbKM" rel="nofollow">2 Spiral Galaxies w/Supermassive Black Holes Collide</a></p>
<p>Around half way, and again almost at the end, the black holes seem to suddenly give off some sort of force which blasts away a lot of the matter a... | g7688 | [
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<p>I am trying to find out which 'element to take' (and why),
When trying to find the resistance of some material with non-uniform resistivity
$\rho$.</p>
<p><em>I'll give an example</em>:</p>
<p>Say we have a co-axial cable with length $L$, inner radius $a$ and outer radius $b$
with resistivity $\rho(r)$</p>
<ul>
<... | g7689 | [
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<p>What is the difference between a divisor and a homology cycle? What is the difference between a D-brane wrapped around a divisor and a D-brane wrapped around a cycle? </p>
<p>Thanks.</p> | g7690 | [
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<p>If I know the:</p>
<ul>
<li>Frequency</li>
<li>Effective Radiated Power</li>
<li>Height Above Average Terrain</li>
<li>Radiation Center Above Mean Sea Level</li>
<li>Radiation Center Above Ground Level</li>
</ul>
<p>of a radio signal / tower, is there a way to determine the rough range of the radio signal?</p> | g607 | [
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<p>In (pure) de Sitter spacetime, the cosmological horizon is said to be ‘observer dependent’. I imagine that as the observer always being in the center of that horizon. Another (spacelike separated) observer also has spherical horizon, but a different one. </p>
<p>Consider a test mass in the shared region of both ob... | g7691 | [
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<p>First of all, I am sorry if this is a stupid question but:</p>
<p>I've heard that atoms interact with each other at the speed of sound (when you for instance push a chair, the atoms collide with each other in a chain reaction at the speed of sound, making the chair move).</p>
<p>How can then airplanes fly faster t... | g7692 | [
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<p>I have a question about the following problem:</p>
<blockquote>
<p><img src="http://i.stack.imgur.com/nOtw4.png" alt="enter image description here"></p>
</blockquote>
<p>I got the solution $v=\frac{M+m}{m} \sqrt{2gh}$.</p>
<p>But my real question is in the following picture:</p>
<blockquote>
<p><img src="htt... | g7693 | [
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<p>Given the recent news <a href="http://www.guardian.co.uk/science/2012/oct/16/earth-like-planet-alpha-centauri">about the discovery of an "Earthlike" planet orbiting Alpha Centauri</a> (our nearest stellar neighbour) it got me wondering just how fast would spaceship have to travel to be able to reach Alpha Centauri w... | g7694 | [
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<p>I was doing the following thought experiment: imagine a particle that moves at a certain velocity. Imagine also that the particle generates a field that propagates at velocity $v_f$. Well, if the particle's velocity is higher than $v_f$ then it will interact with its own field if for some reason the particle deceler... | g7695 | [
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<p>You know how there are no antiparticles for the Schrödinger equation, I've been pushing around the equation and have found a solution that seems to indicate there are - I've probably missed something obvious, so please read on and tell me the error of my ways...</p>
<p>Schrödinger's equation from Princeton Guide to... | g7696 | [
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<p>A hollow metal sphere is electrically neutral (no excess
charge). A small amount of negative charge is suddenly
placed at one point P on this metal sphere. If we check on
this excess negative charge a few seconds later we will find
one of the following possibilities:</p>
<p>(a) All of the excess charge remains righ... | g7697 | [
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<p>This article about "crystals of time" just appeared on the PRL website.</p>
<p><a href="http://physics.aps.org/articles/v5/116" rel="nofollow">Viewpoint: Crystals of Time (http://physics.aps.org/articles/v5/116)</a></p>
<p>The authors (including famous Frank Wilczek) claim that some systems in their ground state a... | g7698 | [
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<p>Are there isotopes that only go through beta decay and nothing else to become stable ?</p> | g7699 | [
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<p>I understand how spin is defined in analogy with orbital angular momentum. But why must electron spin have magnetic quantum numbers $m_s=\pm \frac{1}{2}$ ? Sure, it has to have <em>two</em> values in accordance with the Stern-Gerlach experiment, but why precisely those values?</p> | g7700 | [
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<p>I was reading the following paper: <a href="http://arxiv.org/pdf/1310.4056v2.pdf" rel="nofollow">http://arxiv.org/pdf/1310.4056v2.pdf</a></p>
<p>There were a few things I couldn't follow:</p>
<p>1)Equation (0.1)</p>
<blockquote>
<p>$T_C/r=\lambda v^2/r$</p>
</blockquote>
<p>I understand this takes the form of ... | g7701 | [
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<p>Electromagnetic waves are generally depicted like this:</p>
<p><img src="http://i.stack.imgur.com/Gn4wv.png" alt="enter image description here"></p>
<p>Where the electric fields and magnetic fields exist in the planes perpendicular to the direction of propagation. I also realize that as the electric field changes ... | g7702 | [
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<p>Some authors claim the Poisson equation is $$\nabla^2 \psi = -\dfrac{\rho}{\epsilon\epsilon_0}$$ (e.g. <a href="http://en.wikipedia.org/wiki/Poisson%E2%80%93Boltzmann_equation" rel="nofollow">Wikipedia</a>) whereas other ones (e.g. <a href="http://hwiki.liebel-lab.org/wiki/images/9/90/AndelmannReview.pdf" rel="nofol... | g254 | [
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<p>When a piece of iron is magnetized, and the domains are aligned,
Is there energy stored? If so, how much energy is stored?
If there is an attraction between that same iron and the source of the exterior magnetic field,where work is done, and there is energy that is transferred. Is the energy equal to that of which i... | g7703 | [
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<p>In season 1, episode 7 of <a href="http://en.wikipedia.org/wiki/King_of_the_Nerds" rel="nofollow">King of the nerds</a> the contestants are asked to calculate how many sheets of glass will be broken by a falling object. They are shown 1 example case and then asked to calculate the result for the fallowing 3 test, fo... | g7704 | [
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<p>Total number of subatomic particles in the universe. Are they finite ? assuming any of GR or QM or even ST.</p> | g7705 | [
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<blockquote>
<p>1.The magnitude of the total force acting on a ball rolling without
slipping down a ramp is greater than
the magnitude of the total force
acting on the same ball if it slides
down the ramp without friction. True
or false?</p>
</blockquote>
<p>I chose true for this one, as I figured that if ... | g7706 | [
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<p>I've ran into conflicting information on how to calculate the Gibbs free energy of fuels during combustion per unit mass, volume and mole.</p>
<p>A sample solution for hydrogen would be really appreciated!</p> | g7707 | [
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<p>What would I need to do to create water droplets of a consistent size and shape over a distance of 3 to 10 feet? Are there any special requirements for the nozzle?</p>
<p>Can I use pure water or should I have some kind of additive?</p>
<p>Any special requirements on the valve, etc, that is produced?</p> | g7708 | [
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<p>Clearly there will be differences like air resistance; I'm not interested in that. It seems like you're working against gravity when you're actually running in a way that you're not if you're on a treadmill, but on the other hand it seems like one should be able to take a piece of the treadmill's belt as an inertial... | g69 | [
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<p>After reading this fascinating story about a <a href="http://www.kurzweilai.net/planet-found-in-star-system-nearest-earth?utm_source=KurzweilAI%20Daily%20Newsletter&utm_campaign=94881c12ca-UA-946742-1&utm_medium=email" rel="nofollow">new exoplanet</a>, I was wondering about how mass, speed and distance deter... | g375 | [
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<p>I am doing multi-dimensional plots of $\beta_j$ for SU(2) for infinite volume to understand the flow behavior and I was wondering, before I go too much further, if anyone knew off the top of their head whether the value of SU(2)'s critical point on the phase diagram has any volume dependence? I have tried to find o... | g7709 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Euler%E2%80%93Lagrange_equation" rel="nofollow">Euler-Lagrange</a> equations can be derived from the <a href="http://en.wikipedia.org/wiki/Principle_of_least_action" rel="nofollow">Principle of Least Action</a> using integration by parts and the fact that the variation is ze... | g7710 | [
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<p>I'm starting to study Thermodynamics and I'm pretty confused about what a thermodynamic system really is. When studying mechanics we focus our attention on systems of particles. So when we talk about systems of particles we know what is it all about, a collection of some particles in space subject (or not) to a coll... | g7711 | [
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<p>I have noticed that when particles of metal are captured by a magnetic field. They separate into clearly visible patterns of lines. Why don't the particles form a more even distributed pattern?</p>
<p>Do these gaps/lines exist in the magnetic field itself?</p>
<p>Can someone explain why this happens?</p>
<p>As il... | g7712 | [
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<p>I would like to know the stages of how the universe would end and what would happen and what the possible scenarios are.</p>
<p>I understand that eventually all the stars would burn out and that would introduce a big freeze that would make it harder to sustain life. Forgive me if this is incorrect as I do not have ... | g7713 | [
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0.... |
<p>I just wish to confirm whether my understanding is correct.</p>
<p>I know that photon absorption/emission brings about quantised changes in electron energy levels. Photons (infrared) also interact with chemical bonds to bring about quantised changes in rotational and vibrational kinetic energy in greenhouse gases f... | g7714 | [
0.020837578922510147,
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<p>When peeling a sticker off its base, the immediate reaction is that it curls; why is this? I am having trouble finding an answer to this. Could it be that the glued side expands upon contact with the air? And, on a somewhat related note, is this a similar reason for why a ribbon curls when glided over with a blade?<... | g7715 | [
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<p>I'm trying to solve for a challenging problem : a moving inclined plane with a block
<img src="http://i.stack.imgur.com/OUAsX.jpg" alt="picture and free body diagrams">
I want to solve for the acceleration components for the block and the plane and the normal force acting on the block.</p>
<p>Let $O=(0,0)$ be an ex... | g7716 | [
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0.012765915133059025,
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<p>I am a physics undergrad, and interested to learn Topology so far as it has use in Physics. Currently I am trying to study Topological solitons but bogged down by some topological concepts. I am not that interested for studying it for its own sake. Please could you mention the topics of Topology that are required in... | g851 | [
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<p>Even in a non-relativistic theory Spinors can arise as irreducible representations of the rotation subgroup of the symmetries of the theory. Why do people then put so much emphasize on the role of Relativity and the Dirac's equation in the topic? Is it just for historical reasons?</p> | g7717 | [
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<p>Some (generous) assumptions:</p>
<ul>
<li>We have a spaceship that can reach a reasonable fraction of light speed.</li>
<li>The ship is able to withstand the high energies of matter impacting at that speed.</li>
</ul>
<p>Given the amount of matter in inter-stellar space, at high speed, would it encounter enough of... | g7718 | [
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<blockquote>
<p>A cart filled with a mass $m_0$ of sand leaks it at a constant rate of
$\mu \ \mathrm{kg/s}$ through a hole at the bottom of the cart.
Suppose that the cart is moving on rails. Find the normal reaction
force from the rails as a function of time. Ignore the mass of the empty cart.</p>
</blockqu... | g7719 | [
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<p>So, I know $\oint E\centerdot dA = 4\pi Q_{enc}$</p>
<p>I'm trying to solve for a TEM mode with two concentric (infinite) cylindrical wave guides of radius a and b, $a<b$. I know that for TEM modes, I can solve by assuming that the outside and inside are at two different potentials, $\pm V$. </p>
<p>I'm told th... | g7720 | [
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<p>My idea of physics is that it is a collection of mathematical laws relating observables. And that one can perform alot of mathematical derivations on these laws to produce new laws between observables. My question is how does one translate a mathematical equation into 'there exist other universes like ours'?</p>
<p... | g255 | [
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<p>From the perspective of a person, a rainbow is formed when the Sun is behind the person, and there is a critical angle made by the rainbow.</p>
<p>However, on several occasions, usually at noon when the Sun is higher, I saw a ring around the Sun made of the colors of the rainbow. Is that a rainbow? Is within the ... | g7721 | [
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<p>In mechanics problems, especially one-dimensional ones, we talk about how a particle goes in a direction to minimize potential energy. This is easy to see when we use cartesian coordinates: For example, $-\frac{dU}{dx}=F$ (or in the multidimensional case, the gradient), so the force will go in the direction of minim... | g7722 | [
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<p>I have 2 objects which are intially connected together, $O_1$ and $O_2$. When they are connected together, they have a rotation rate about their center of mass of $w_1$. $O_2$ is cleanly released from the connected system, and $O_1$ is now rotating at a rate of $w_2$. </p>
<p>Given that any mass properties of the s... | g7723 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Plummer_model" rel="nofollow">Plummer's sphere</a> is an model for the mass density in a globular cluster of stars. For an $N$-body simulation I have initialized the position of $N$ masses with a Monte-Carlo technique but cannot find a way of initializing the velocity initia... | g7724 | [
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<p>A very simple question; why does it cost me more energy to <strong>very slowly</strong> lift a mass $m$ over my head compared to very fast? The definition of work does not state anything about velocity, only the distance travelled, but I definitely feel more exhausted in the first case.</p> | g7725 | [
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<p>I've been in an argument with a friend.</p>
<p>He claims that when a rocket engine is fired in air, it get significantly more thrust due to the rocket pushing gas into the atmosphere, and the atmosphere expands (due to there suddenly being more "air" in the same area of space), and that expansion helps to propel th... | g7726 | [
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<p>Can we scan the universe in magnetic spectrum and then separate the paramagnetic , diamagnetic and ferromagnetic objects and get a new picture of the cosmos.</p> | g7727 | [
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<p>What does it mean to have a QFT that can not be encoded by an action. What is by far the most powerful approach of study in such a case. What is the best studied physical theory that falls into this category. What is QFT? I think it is a set of rules that facilitate descriptions of things we can observe, but what... | g7728 | [
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<p>Occasionally people get killed in their bathtubs by having an electrical device such as a hair-dryer take the bath with them - in movies.</p>
<p>It seems to be a common belief that this is realistic, even though it makes no sense to me.</p>
<p>There are two scenarios:</p>
<ol>
<li>The device short-circuits intern... | g7729 | [
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<p>In one of my homework questions, I was given the following setup. I was asked to determine if the induced current flows from X to Y, or from Y to X.</p>
<p><img src="http://i.stack.imgur.com/Ie7uM.jpg" alt="enter image description here"></p>
<p>From Lenz's Law I know that the current in the tube flows in the direc... | g7730 | [
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0.05501936003565788,
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0.02... |
<p>I am trying to solve an assignment on solving the Bogoliubov de Gennes equations self-consistently in Matlab. BdG equations in 1-Dimension are as follows:- </p>
<p>$$\left(\begin{array}{cc}
-\frac{\hbar^{2}}{2m}\frac{\delta^{2}}{\delta z^{2}}-\mu+V\left(z\right) & \triangle(z)\\
\triangle(z) & \frac{\hbar^{... | g7731 | [
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0.011098727583885193,
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0.064... |
<p>For a school project, I'm trying to make an automated flight planner, considering mainly the differences in flight paths according to wind.</p>
<p>Now I've heard that flying with/against the wind affects airspeed. But I really don't know any specific(even empirical) laws on determining by how much it does so. </p>
... | g7732 | [
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0.02428976446390152,
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0.039450377225875854,... |
<p>To calulate motional $\epsilon$, we use the following formula: $\epsilon$ = $-vBL$</p>
<p>To calculate the velocity so the motional $\epsilon$ can be calculated, what is the proper formula from what is below?
Assuming acceleration is constant.</p>
<p>$$
v = \frac{\Delta x}{\Delta t}
$$
or,</p>
<p>$$
a = \frac{... | g7733 | [
0.06970901042222977,
0.05579325556755066,
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0.03857358545064926,
0.047435492277145386,
0.042... |
<p>This here is a question that I just don't know what to do with. I don't know what I'm doing wrong.</p>
<p>"<em>A plate capacitor consists of two plates with area 2.5 cm$^2$ at a distance of 1.6 mm from each other.</em> </p>
<p><em>a) Calculate the capacitors capacitance</em></p>
<p><em>b) How large is the charge ... | g7734 | [
0.07064980268478394,
0.009795118123292923,
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0.030675463378429413,
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0.008151063695549965,
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0.09699198603630066,
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0.0206... |
<p><img src="http://i.imgur.com/EpuQK5G.png" alt="Bolts"></p>
<p>I have this question asking me about the thermal expansions of two bolts, a steel one, and a brass one. I have the equation:</p>
<p>$\ (\delta L/L)/T = \alpha $</p>
<p>I don't understand how I can use this equation to manipulate the temperature for the... | g7735 | [
0.05953744798898697,
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0.016312669962644577,
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0.027234219014644623,
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0.0328638069331646,
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<p>When people are skateboarding, sometimes they kind of push out their back foot when they turn while carving, causing the board to skid a bit. I was wondering the physics behind this, any details on the subject. One thing in particular I was wondering was why it's harder to do this on smaller boards.
Here's a video o... | g7736 | [
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0.015262038446962833,
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0.027... |
<p>I'm a third year maths undergrad doing a project on minimal surfaces. However I'm really struggling to understand what the PMT is trying to explain?</p>
<p>Could anyone help explain this (as simply as possible) </p> | g256 | [
0.028169574216008186,
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<p>From the actions in $d$ dimensions given by </p>
<p>$$S = \int d^dx \,\, \partial_{\mu}\phi \partial^{\mu} \phi + g \phi^k$$.</p>
<p>What is the condition that needs to be $k$ so that the theory is invariant under conformal transformations?</p>
<p>Initially, I have been trying to tackle the special case of pure s... | g7737 | [
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0.01792459562420845,
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0.035518527030944824,
0.0054695988073945045,
0... |
<p>given the differential equation</p>
<p>$$ -\hbar^{2}D^{2}y(x)+ae^{bx}y(x)=E_{n}y(x) $$</p>
<p>here $ D=d/dx $ derivative</p>
<p>are there examples in physics where this potential appears ??, i know how to solve it but i do not know pratical examples where the exponential potential appears </p>
<p>the solution is... | g7738 | [
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0.02899629808962345,
0.05869404226541519,
0.028822... |
<p>This is our first time (as an engineer) seeing this type of graph that we can't interpret.
This is a rough comparision of thermal conductivity from the Wiki page.
<a href="http://en.wikipedia.org/wiki/Thermal_conductivity" rel="nofollow">http://en.wikipedia.org/wiki/Thermal_conductivity</a></p>
<p><strong>What we ... | g7739 | [
0.049872249364852905,
0.07988640666007996,
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0.016698865219950676,
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0.033839862793684006,
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0.06636708229780197,
0.003236872609704733,
-0.01... |
<p>Weinberg writes in his Cosmology text "Likewise,isotropy requires the mean value of any three-tensor $t_{ij}$ at $x=0$ to be proportional to $\delta_{ij}$ and hence to $g_{ij}$, which equals $a^2\delta_{ij}$ at $x = 0$"
May someone please illuminate the point.</p> | g7740 | [
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-0.... |
<p>so this is the question that's been bothering me:</p>
<p>Say you have a simple rigid body in space that is at rest or travelling with only translational motion at a constant speed. Say that the body is something like a rod and it's not rotating. So, at some point, an external force is acted on the rod, just for an ... | g7741 | [
0.0499085858464241,
0.038759563118219376,
0.005241646897047758,
0.02443978749215603,
0.05370370298624039,
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0.04487329348921776,
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-0.04040117189288139,
-0.020356813445687294,
0.009313485585153103,
0.024637550115585327,
-0.07740... |
<p>Among others, <a href="http://www.dailygalaxy.com/my_weblog/2010/10/do-black-holes-eject-antimatter-.html">this page</a> says there is a giant cloud of antimatter at centre of the Milky Way, which was discovered in the 1970s.</p>
<p>My brother doesn't believe there is any such cloud. I'm prepared to believe it does... | g7742 | [
0.061449866741895676,
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0.0032573712524026632,
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0.0724329873919487,
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-0.06202389672398567,
0.047528836876153946,
0.00917121209204197,
0.07290872186422348,
0.0231... |
<p>I am having some trouble with Green functions in electrostatics</p>
<p>What is the meaning of this trick:</p>
<p>Given $$\vec{\nabla}^2 V(\vec{r}) = \frac{-1}{\varepsilon_0}\rho(\vec{r}) = \frac{-1}{\varepsilon_0} \int \delta ^3(\vec{r}-\vec{r}')\rho(\vec{r}') d^3 \vec{r}' = \frac{1}{4 \pi \varepsilon_0} \int \vec... | g7743 | [
0.06012565642595291,
0.018934505060315132,
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0.023569609969854355,
0.07926925271749496,
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0.006808077450841665,
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0.009219673462212086,
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0.020... |
<p>Let $C^p(M)$ denote the group of closed $p$-forms on the manifold $M$, and $Z^p(M)$ the group of all exact $p$-forms on the manifold $M$. The <a href="http://en.wikipedia.org/wiki/De_Rham_cohomology" rel="nofollow">de Rham cohomology</a> is given by the quotient,</p>
<p>$$H^p(M)=C^p(M) \, / \, Z^p(M)$$</p>
<p>I am... | g7744 | [
0.008970721624791622,
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0.06390292197465897,
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0.020768947899341583,
0.006093465257436037,
-0.029881516471505165,
0.042061012238264084,
0.... |
<p>is a Standard Model particle with (u, d, b) quark content. What are the
electric charge, baryon number and lepton number of this particle? Is this the
only particle expected to exist with this quark content? Justify your answer</p>
<p>I know that the overall charge is 0, baryon number is 1. But what is the lepton n... | g7745 | [
0.05079832300543785,
0.027787597849965096,
0.00296094105578959,
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0.07374431192874908,
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0.008021061308681965,
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... |
<p>In the majority of the literature and lectures I see when a system of particles is involved, I usually see the following expression (or similar) for the total force on particle $i$:</p>
<p>$$\vec{F}_i = \vec{F}_{i_{ext}} + \sum_{i\neq j}\vec{F}_{ji}$$</p>
<p>Why is it necessary to include the condition $i\neq j$ i... | g7746 | [
0.02964991144835949,
0.05998295545578003,
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0.01020082551985979,
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0.0185362... |
<p>In the Clay institute problem description of the <a href="http://en.wikipedia.org/wiki/Yang%E2%80%93Mills_existence_and_mass_gap" rel="nofollow">Yang-Mills existence and mass gap problem</a> it states that the quantum Yang Mills needs to be formulated in $\mathbb{R}^4$ space. I was wondering whether this meant it ne... | g7747 | [
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... |
<p>I have a real-world problem that I'm quite certain can be solved with a formula. Unfortunately I myself am not particularly skilled in the realm of physics or math. Any and all help is very much appreciated!</p>
<p>I have a cassette tape. It's on a transport that does not use a capstan to drive the tape. As the tap... | g7748 | [
0.06035827100276947,
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0.016427384689450264,
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0.003419481450691819,
... |
<p>Are the energy of the electric field and the energy of the magnetic field concentrated on their sources OR are they scattered in the environment where the fields arent zero? Can you base your answer on a formula so I can understand it better?</p> | g7749 | [
0.04943985119462013,
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-0... |
<p>I would like to know of a list of pedagogical/classic/nice papers that study stringy effects in the bulk. May be a sequence which a student follows to understand the stringy nature that is at play. </p> | g7750 | [
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<p>Whenever there are high winds, such as in storms, thin metal roofs on sheds as well as concave roofs on huts are sometimes blown away.</p>
<p>One explanation provided to me said that the higher velocity of the air outside causes the air pressure above the roof to decrease and when it has decreased to a certain exte... | g7751 | [
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0.004672705195844173,
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0.00013330104411579669,
... |
<p>So I don't want to give the full details of the problem I'm working on, since I want to solve it myself. But I'm not sure which physical principles I'm supposed to use, since this is a Calc 2 question, and I'm not that familiar with Physics.</p>
<p>Basically, I need to pump water out of a tank, which is shaped lik... | g7752 | [
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0.014515433460474014,
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0.022085441276431084,
0.04411867633461952,
... |
<p>i couldnt just figure out when i got to know that declination can be zero also. How can true and magnetic north ever align themselves in a straight line in any place?
Also if a compass aligns in the direction of horizontal component of MF at that place does this mean that at any place horizontal component is directe... | g7753 | [
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<p>In lots of papers I read about <a href="http://en.wikipedia.org/wiki/Gauge_anomaly" rel="nofollow">gauge anomalies</a>. For example, avoiding gauge anamolies in the MSSM is the reason for introducing an extra Higgs doublet. Gauge anamolies in the Standard Model are cancelled due to accidental symmetries etc. Can som... | g7754 | [
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0.012551205232739449,
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0.05... |
<p>Does the exist any mathematical formalism (model) describing the behavior of light and incorporating its particle character (divisibility, quantization) and wave character? (i.e. quantized wave model)</p> | g7755 | [
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0.038... |
<p>What would be defining about a strongly coupled electromagnetic force? Would it mean that separating two oppositely charged particles makes another particle-antiparticle pair, rather than continuing to separate the particles? Would it make the electromagnetic force "hadronic", in a sense? </p> | g7756 | [
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0.0... |
<p>This is the sine-Gordon action:
$$
\frac{1}{4\pi} \int_{ \mathcal{M}^2} dt \; dx \; k\, \partial_t \Phi \partial_x \Phi - v \,\partial_x \Phi \partial_x \Phi
+ g \cos(\beta_{}^{} \cdot\Phi_{})
$$
Here $\mathcal{M}^2$ is a 1+1 dimensional spacetime manifold, where 1D space is a $S^1$ circle of length $L$.</p>
<... | g7757 | [
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0... |
<p>If stars start with a finite density and light can escape from them, how can they be compacted to form a mass with infinite density which light cannot escape? The black hole will have the same mass as the original star (correct?) and therefore will act on the photons with the same force of gravity, right?</p> | g7758 | [
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0.018688062205910683... |
<p>My book says the following:</p>
<blockquote>
<p>If the body is acted upon by a system of forces, the resultant moment of the forces about point O can be determined by vector addition of the moment of each force. The resultant can be written symbolically</p>
<p>$$(M_R)_O = \Sigma (r \times F)$$ </p>
</blockqu... | g7759 | [
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0.0... |
<p>Was siting in class thinking about this problem, did some rough sketches of a solution but never really managed to solve it.</p>
<p><img src="http://i.imgur.com/D8XAh.png" alt="Ice cream cone and a loop-de-loop"></p>
<blockquote>
<p>Assume a boy starts at the top of a circle with radius R as described in the pic... | g7760 | [
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0.018444087356328964,
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0.02730737254023552,
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0.0128434... |
<p>Fish like electric eels and torpedoes have specially designed nerve cells that allow them to discharge hundreds of volts of electricity.</p>
<p>Now, while pure water is usually nonconductive, the dissolved salts and other stuff in both sea and fresh water allow them to be conductive. If an electric fish is able to ... | g7761 | [
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0.004117727745324373,
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0.03358206897974014,
0.00265... |
<p>Suppose one knows almost nothing about the nature of radioactivity (like the discoverers of this phenomenon). </p>
<p>What are the detailed/rigorous logical steps/arguments to show experimentally that radioactive radiation ionizes air?</p> | g7762 | [
0.03682103380560875,
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0.0... |
<p>Not sure if this is a 'real' question, but what is the relation between physics and computer science? A lot of physicists are also computer scientists and vice versa. My professor has a PhD in Physics but is a Computer Science professor. Whats the relation? Why is this so common?</p> | g7763 | [
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0.04806268587708473,
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-0.00... |
<p>This new <a href="http://www.newscientist.com/article/mg20928054.000-bestever-quantum-measurement-breaks-heisenberg-limit.html" rel="nofollow">Best-ever quantum measurement breaks Heisenberg limit</a> </p>
<blockquote>
<p>PHYSICISTS have made the most accurate
quantum measurement yet, breaking a
theoretical ... | g7764 | [
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0.012700313702225685,
0.020340392366051674,
0.0008283224306069314,
-0.06399378925561905,
0... |
<p>The sun is 5778K and Earth is ~290K. Using the sun as the hot reservoir and earth as a cold reservoir we get 95% Carnot efficiency. However, the solar power efficiency limit is only 86%, see: <a href="http://www.energy.udel.edu/pdf/Honsberg_UDEI_Symposium.pdf" rel="nofollow">http://www.energy.udel.edu/pdf/Honsberg_U... | g7765 | [
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0.04278048500418663,
0.07362384349107742,
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0.005... |
<p>How does one calculate the polarization state of random light after having been totally reflected by a single dielectric interface? Please consider pure specular reflexions from a plane interface between two dielectric mediums of indexes $n_1,\,n_2$ when the angle of incidence $\theta_1$ is greater than the critical... | g7766 | [
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0.032910533249378204,
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0.05197921022772789,
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0.018895355984568596,
0.00851837545633316,
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0.0230207908898592,
0.03181171417236328,
-0.01... |
<p>Consider there are 2 identical springs.</p>
<ul>
<li><p>One end of the first spring is attached to the wall and the other end is pulled by a force $\vec{F}$. It is depicted as shown in the first figure below.</p></li>
<li><p>Both ends of the second spring is pulled by a force $\vec{F}$. It is depicted as shown in t... | g7767 | [
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0.021262511610984802,
0.01763770543038845,
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-0.022606587037444115,
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-0.0012001158902421594,
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<p>The rumor was you could make a magnet by leaving a piece of iron on a train track. The train going over it would magnetize it. </p>
<p>Is it true?</p> | g7768 | [
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-0.0... |
<p>I would like to get an explanation on how to understand such a lens spot diagram: <img src="http://i.stack.imgur.com/ff8UF.png" alt="Spot diagram in Zemax"></p>
<p>Thanks</p> | g7769 | [
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0.028547147288918495,
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-0... |
<p>In today lecture of microwave and radar my teacher explained about the Gunn diode.<br>
He said it is made up of only one type of matrial e.g. $GaAS$ as shown in (a) part of the image.<br>
<img src="http://britneyspears.ac/physics/highfields/images/Image93.gif" alt="image 1"><br>
He said that there is no depletion la... | g7770 | [
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0.01345242839306593,
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0.06725393235683441,
0.029... |
<p>If an observer approaches a clock at a significant fraction of the speed of light, would they see the clock's hands moving at a faster or slower than usual rate?</p>
<p>I figure there are two competing effects at play - time dilation and diminishing distance.</p> | g979 | [
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0.02... |
<p>My question arise and is connected to the "strange" fact
that many things seem to come in pair or in number of two
similar "objects".</p>
<p>Why are there chiral "pairs" and not groups of 3,4, or more? What happens in higher dimensions.</p> | g7771 | [
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0.041328396648168564,
0.008001832291483879,
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0.008902188390493393,
-0.0010654741199687123,
0... |
<p>Strain can be directly observed using e.g. a ruler. Can (internal) stress be directly observed?</p> | g7772 | [
0.01658651791512966,
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0.004137251526117325,
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0.03349060192704201,
-0.066... |
<p>We all know that light is an electro magnetic wave. but is electricity a EM wave? If it is then why light does not requires a medium to travel and why on the other side electricity needs a conductor ( I mean a medium) to travel. WHY? Or HOW?</p> | g7773 | [
-0.05266207084059715,
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0.... |
<p>My query is: how does an atom stable itself. When we break something, what actually happens in the chemical bonding of its atoms, does it rupture or remain intact?</p> | g7774 | [
0.0037717577069997787,
-0.005981616210192442,
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-0... |
<p>When Dirac found his equation for the electron $(-i\gamma^\mu\partial_\mu+m)\psi=0$ he famously discovered that it had negative energy solutions. In order to solve the problem of the stability of the ground state of the electron he invoked Pauli's exclusion principle and postulated that negative energy states well a... | g7775 | [
0.0871119424700737,
-0.03501186519861221,
-0.0008919691317714751,
-0.06398429721593857,
0.03440364822745323,
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-0.03184940293431282,
0.04248063266277313,
-0.034579794853925705,
0.030212098732590675,
0.0189... |
<p>My friend went to an interview for a reputed scholarship program and was asked this question.
A wave has an equation $a\sin(\omega t-kx)$.
Sometimes k surely can become -ve.
We know that $k=\frac{2\pi}{\lambda}$.
So $\lambda$ is -ve?
How can this be?</p>
<p>What he said was that we can write $k=\frac{\omega}{v}$.... | g7776 | [
-0.009391363710165024,
-0.041957441717386246,
0.0075331139378249645,
-0.04570922255516052,
0.09230830520391464,
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0.005435093771666288,
0.018094660714268684,
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-0.030816955491900444,
0.005587450694292784,
0.0730515718460083,
-0.005083662923425436,
0... |
<p>I've a system of two particles of the same mass who rotate in a circle about the centre of mass of the two particles. Is the force experienced by the particles $F=MV^{2}/r$ or should I use $Torque=$Moment of Inertia*angular acceleration?</p> | g7777 | [
0.030599519610404968,
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... |
<p>We were taught in school that the law of inertia indicates that an object tend to stay the way it is, so if you throw something in space it will tend to go on forever and ever. The reason an object falls down when you throw it on Earth is because of gravity and air resistance. If that's the case, why don't rockets a... | g7778 | [
0.02217416651546955,
0.03433557227253914,
0.0002927912282757461,
0.027011971920728683,
0.041487257927656174,
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0.029129160568118095,
-0.04816839098930359,
-0.0034010575618594885,
0.03... |
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