question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>I have performed a calculation the tensor of elastic constants (or stiffness tensor) for a given crystalline material. From there, I calculated various elastic properties, such as Young’s modulus, shear modulus, etc. I have, however, received advice to analyze it by</p>
<blockquote>
<p>further decomposing the ela... | g14448 | [
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<p>The s orbital have higher probability to be closer to the core and feels larger attraction than the p orbital and on average is further away and in addition p has repulsive potentilal l(l+1)h^2/2mr^2. But is there name for this effect and is it this the only way to explain ? </p>
<p>What is the usual energy differe... | g14449 | [
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<h1>Background</h1>
<p>This issue has been bothering me for a few days now. It's actually part of my homework, but I've already finished them and in a sense they're not part of the question here. What I would like to know is more of a theoretical question about this formulation.</p>
<p>Now my professor's book and man... | g14450 | [
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<p>Suppose that a matrix</p>
<p>$$A ~=~ x_1 B + x_2 C$$</p>
<p>is a linear combination of two self-adjoint matrices $B$ and $C$.</p>
<p>I'm interested in when $A$ represents a physical quantity. </p>
<p>When the linear combination is a complex combination, then $B$ and $C$ have to be commutable for $A$ to represent... | g14451 | [
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<p>The galaxy moves of the celestial sphere. It is given that proper speed is transverse to the observer and it must to find this speed in the moment of light emission. The motion is in the FLRW universe. Does it relate to the comoving distance?</p> | g14452 | [
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<p>I know that this is a simple question! But I would like to know the details.
How we can show that the term</p>
<p>$$A_\mu(x)\dot{x}^\mu$$</p>
<p>is global and local Poincare invariant? Where $A_\mu(x)$ is supposed to be a four-covector and
This term is a part of reparametrization-invariant square-root Lagrangian
$... | g14453 | [
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<p>Recently, I've been watching "The Big Bang Theory" again and as some of you might know, it's a series with a lot of scientific jokes in it - mostly about Physics or Mathematics. I understand most of the things mentioned in the series and whenever I don't understand a joke, I just look up the knowledge I'm missing on... | g14454 | [
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<p>I'm studying from Goldstein's <em>Classical Mechanics</em>. In section 2.4, he discusses nonholonomic systems. We assume that the constraints can be put in the form $f_\alpha(q, \dot{q}, t) =0$, $\alpha = 1 \dots m$. Then it also holds that $\sum \lambda_\alpha f_\alpha = 0$. Using Hamilton's principle (i.e. that th... | g14455 | [
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<p>Lie algebra of nonabelian group is $[T^a,T^b]=if^{abc}T^c$.
For $SO(3)$ case, is the representation $T^a_{ij}=-i\epsilon^{aij}$ fundamental or adjoint?
The fundamental representation is defined as identifying $T^a$ the original generator. The adjoint representation is defined as identifying $T^a$ as structure const... | g14456 | [
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<p>I'm only in high school (junior) so goes easy on me. But, how do physicist refute these paradoxes? Considering there are a number of theories regarding the origin of the universe and some postulate that the universe is infinite, I assume they've come across this. Just looking for a direct answer to what should be a ... | g14457 | [
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<p>Say I have a metric representation $g_{\mu\nu}$ in a coordinate system $x$ and I want to find the representation of the metric in a new set of coordinates $y = y(x)$. I know how to do this if you are given $x(y)$, as in <a href="http://physics.stackexchange.com/questions/16681/metric-tensor-of-coordinate-transforma... | g14458 | [
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<p>Can you explain to me what causes the <a href="http://en.wikipedia.org/wiki/Buoyancy" rel="nofollow">buoyant force</a>? Is this a result of a density gradient, or is it like a normal force with solid objects?</p> | g14459 | [
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<p>I wanted to know that if FIRE is Matter or Energy. I know that both are inter-convertible. but that doesn't mean there is interconversion taking place just like nuclear fusion or fission. If it is matter, then its has to occupy space and have mass. I really doubt that fire has mass. If it is energy, then i don't get... | g546 | [
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<p>In the Physics Today article by Avron et.al. "<em>A Topological Look at the Quantum Hall Effect</em>" Physics Today (2003) it is suggested that to observe ordinary Hall effect, planar geometry is preferred to bar geometry as below. I am trying to understanding the reason behind this. Can someone help me? Any referen... | g14460 | [
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<p>Galileo is reputed to have demonstrated that unequal masses fall at an equal rate by dropping them off the tower of Pisa and observing that they hit the ground simultaneously. Has anyone tried to push this experiment to the limit at small scale or is the result observable from some other experiment? </p> | g14461 | [
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<p>Earlier I studied about the three states of matter-gaseous,liquid ans solid. Then, I came to know about Plasma and Bose-Einstein Condensate. Now, scientists are trying to explain superconductivity as a state of matter. But, I would like to know on what factors does scientists rely to decide whether a particular stat... | g14462 | [
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<p>I think I understand how pressure works with gases. More molecules bouncing around -> more random impacts -> stronger force. </p>
<p>But I realized to my embarrassment that I don't understand how solid things press on each other, on a molecular level. Say I put a block of iron on my head. If I put another one on to... | g14463 | [
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<p>For a function applying the fourier transform twice is equivalent to the parity transformation, applying it three times is the same as applying the inverse of the fourier transform, and applying four times, is the identity transformation. Wikipedia has a good description of this.</p>
<p>What do we get when we apply... | g14464 | [
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<h2>Introduction</h2>
<p>I'm trying to make some strawberry liqueur. The recipe I got says I should put alcohol, strawberries and sugar in a bowl and leave it soaking for 4-5 weeks. I read that making liqueur is not a chemical reaction, but only a solvent (mostly alcohol) acting on some fruit, herb or nut. So, intuiti... | g14465 | [
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<p>We have
$$X^\textrm{t}gX = 0 \iff X^\textrm{t}L^\textrm{t}gLX = 0,$$
where $X$ is a column vector of length four, $L$ is a non-singular $4 \times 4$ matrix, 't' denotes matrix transpose, and
$$g = \left(\begin{matrix}
1 & 0 & 0 & 0 \\
0 & -1 & 0 & 0 \\
0 & 0 & -1 & 0 \\
0 &... | g14466 | [
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<p>I'm not a physicist or cosmologist, so I hope I am asking the right question with the right words here. </p>
<p>My question regards the word "energy" as it pertains to quantum vacuum states, and to concepts such as Lawrence Krause's "something from nothing" theory. </p>
<p>When I hear the word "nothing" I envision... | g14467 | [
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<p><a href="http://en.wikipedia.org/wiki/Jenga" rel="nofollow">Jeng</a>a is a game place with wooden blocks stacked on top of one another in an alternating pattern. Players take turns removing blocks from any layer and placing them on top. </p>
<p><img src="http://i.stack.imgur.com/NxBEl.jpg" width="200"></p>
<p>As ... | g14468 | [
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<p>A mobile phone move aside when it vibrates. How is that happening ? and most importantly is it possible to make any changes to the vibration motor to stop moving when vibrating or any other methods to stop that ?
I have already read following links
<a href="http://physics.stackexchange.com/questions/61436/would-a-ph... | g14469 | [
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<p>The nuclear fusion taking place inside the stars opposes its gravitational self collapsing force. But, how does physicists calculate it? I just know the classical gravitational theory and not a bit of general relativity. So, I would like to take the situation in a classical way.
For example, in terms of Lyttleton-Bo... | g14470 | [
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<p>According to Einstein's Mass-energy equivalence,</p>
<p>$ E = mc^2$ OR
$ m = \frac E{c^2}$..... (1)</p>
<p>and According to Newton's Second Law of motion,</p>
<p>$ F = ma$ OR $m = \frac Fa$ ..... (2)</p>
<p>If we compare eq. (1) and eq. (2), we obtain; </p>
<p>$\frac E{c^2} = \frac Fa$..... (3)</p>
<p>If we mu... | g14471 | [
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<p>People wait for decades to catch the chance of a solar eclipse to observe the sun. </p>
<p>Why cannot they do it every noon? </p> | g14472 | [
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<p>The hydroelectricity plants extract the potential energy of highly deployed massive object (water) as it falls down. Without turbine, all that energy would be converted into speed (kinetic energy) at the bottom of the waterfall and further into heat. The turbine produces energy by slowing water down. </p>
<p>The ef... | g14473 | [
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<p>My intention is to establish a Soliton equation. I have cropped a page from Mark Srednicki page no 576.
I have understand the equation (92.1) but don't understand that how they guessed the potential in equation (92.2).<img src="http://i.stack.imgur.com/YIlt3.jpg" alt="enter image description here"> </p>
<p>EDI... | g14474 | [
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<p>Recently, I read an article on time reversed laser. I don't know why they call it a time reversed. I have a doubt that why they use two laser in the device. And what is an anti-laser?
The device absorbs the particular frequency of light which means some energy is lost. What happens to the lost energy?</p> | g14475 | [
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<p>I have heard that when the speed of the object increase, the mass of the object also increase. (<a href="http://physics.stackexchange.com/q/45320/">Why does an object with higher speed gain more (relativistic) mass?</a>)</p>
<p>So inertia which is related to mass, increase with speed?</p>
<p>So, if I accelerate on... | g14476 | [
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<p>Right now I'm working on a hot air balloon in Physics formulas. At the moment it's flying up like it should, but once it is at a certain height we want it to go back down.</p>
<p>After some research about hot air balloons we found out that they drop down by opening a valve at the top. So what we want to do is once ... | g14477 | [
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0.016514470800757408,
0.000544615148101002,
0.039220403879880905,
0.005770158488303423,
-0.07945238053798676,
-0.016235707327723503,
-0.03235409036278725,
0.09234973043203354,
0.035712726414203644,
0.01... |
<p>In $φ^4$ theory we often write the Lagrangian as $$\mathcal{L}=\frac{1}{2}\partial^\mu \phi \partial_\mu \phi -\frac{m^2}{2}\phi^2 -\frac{\lambda}{4!}\phi^4 \tag {1}$$</p>
<p>If I want to write from the Relativistic Lagrangian then it takes $$\mathcal{L}=\frac{1}{2}\partial^\mu \phi \partial_\mu \phi -V \tag{2}$$... | g14478 | [
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0.018914083018898964,
0.054... |
<p>For a region devoid of charge, maxwell's equation yields $\nabla \cdot \mathbf{E} = 0$ which still allows a constant field. So why is in electrostatics for the vacuum always $\mathbf{E} = 0$ assumed?</p> | g14479 | [
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<p>I've been learning about the theta parameter of QCD and I'm confused about the fact that it's supposed to be very small but at the same time some sources say that the Yang-Mills theory should be invariant to 2$\pi$ shifts in $\theta$</p>
<p>Sources that says that $\theta$ is small:</p>
<p>(1)<a href="http://www.go... | g14480 | [
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<p>If I have two operators A and B living in the Composite Hilbert Space $H_I \bigotimes H_{II} $ and I want to take the partial trace of $C=AB$ over the subspace $H_I$, i.e., $Tr_I[AB]$, is there any identity that can help me do this in terms of $Tr_I[A]$ and $Tr_I[B]$. Actually what I am interested in is the partial ... | g14481 | [
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0.0159411933273077,
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<p>For a pure dipole situated at the origin, I don't understand why the dipole moment vector is
$$
\vec{p} = p\cos \theta \hat{r} - p\sin \theta \hat{\phi}
$$
Since the vector does not have any $r$ in it, the value of the vector is same any distance away from the origin if the angle is constant, which doesn't make sen... | g14482 | [
0.0005225026980042458,
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-... |
<p>Why is the earth's iron core stationary, while the liquid matal circles around it creating the magnetic shield. Don't understand how can the entire planet rotate where as the planet's center is stationary. Anyone could explain this?</p> | g14483 | [
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<p>It is known that there are real numbers that can't be calculated (non-computable numbers). Quite probably that some physical phenomena (it is possible still undetected) depend on this numbers. Whether means it, what we can't construct the theory of this phenomenon and-or (if probably to construct) to do predictions ... | g14484 | [
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<p>Regarding a question on <a href="http://bricks.stackexchange.com/a/466/132">another Stack Exchange site</a> which identifies a weighted Lego brick to be some kind of metal, I wanted to know how to identify a metal, perhaps limited to household objects like scales or a bowl of water to measure volume. </p> | g14485 | [
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<p>I know this may actually be a chemistry question, but I don't know where else to ask.</p>
<p>When I have a soda plastic bottle, I turn it upside down so the soda fills the empty space, and bubbles start growing on the walls of the plastic.</p>
<p>So, why does this happen?
I can think of something like a film formi... | g14486 | [
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<p>For a physics major, what are the best books/references on Greens functions for self-studying?</p>
<p>My mathematical background is on the level of Mathematical Methods in the physical sciences by Mary Boas.</p> | g14487 | [
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<p>Each spring enormous amounts of water rise up in trees and other vegetation. What causes this stream upwards? </p>
<p>Edit: I was under the impression that capillary action is a key factor: the original question therefore was: what are the fundamental forces involved in capillary action?</p>
<p>Can perhaps anybody... | g14488 | [
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<p>I'm following Zettili's QM book and on p. 39 the following manipulation is done,</p>
<p>Given a localized wave function (called a wave packet), it can be expressed as $$\psi(x,t) = \frac{1}{\sqrt{ 2 \pi}} \int_{-\infty}^{\infty} \phi(k) e^{i(kx-\omega t)} dk$$ Now use the de broglie relations: $p = \hbar k$ and $E... | g14489 | [
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0.004657462239265442,
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0... |
<p>I would like to derive the following two well-known formulas that work for crystal lattice [1]:
$$
F[f(\mathbf{x})] \equiv \tilde f(\mathbf{G})
= {1\over\Omega_\mathrm{cell}} \int_{\Omega_\mathrm{cell}} f(\mathbf{x})
e^{-i\mathbf{G} \cdot \mathbf{x}}\,d^3 x
$$
$$
F^{-1}[\tilde f(\mathbf{G})] ... | g14490 | [
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<p>In the <a href="http://en.wikipedia.org/wiki/Drude_model" rel="nofollow">Drude model</a> they derive a formule for the conductivity of a conductor.
I wonder though how the main free time $\tau$ is defined in this formula.
Wikipedia says that it is "the average time between subsequent collisions".
But I have two po... | g14491 | [
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0.019010677933692932,
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0.0592186264693737,
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0.045101966708898544,
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0.017620917409658432,
0.04079968109726906,
... |
<p>So, in my previous question <a href="http://physics.stackexchange.com/questions/88001/where-does-this-formula-for-prediction-of-a-multiple-wave-come-from">Where does this formula for prediction of a multiple wave come from?</a>, I get that using this picture: </p>
<p><img src="http://i.stack.imgur.com/NPiCC.png" al... | g14492 | [
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0.0029040018562227488,
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0.04308247193694115,
0.011... |
<p>I was always taught that any accelerating charge produces radiation, but I don't think this condition is sufficient condition. For instance, any free charge on Earth is accelerated due to Earth orbiting the Sun but it doesn't produce radiation. </p> | g14493 | [
0.05785328149795532,
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0.0120... |
<p>I came accross a question about verifying the transverse of electric field in Peskin and Schroeder's QFT p179.</p>
<p>Given</p>
<blockquote>
<p>$$ \mathcal{A}^{\mu}(\mathbf{k}) = \frac{ -e}{| \mathbf{k} | } \left( \frac{p'^{\mu}}{k \cdot p'} - \frac{p^{\mu}}{k \cdot p} \right) \tag{6.7} $$</p>
</blockquote>
<... | g14494 | [
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0.010894249193370342,
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0.027677156031131744,
0.0034114629961550236,
0.00... |
<p>If an astronaut leaves planet $A$ for planet $B$ at speed $v$, will the time (measured by the astronaut's clock) that it takes for the astronaut to reach planet $B$ be less than the distance between the planets divided by the speed because of length contraction?</p> | g14495 | [
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<p>I was reading about WiTricity (<a href="http://en.wikipedia.org/wiki/WiTricity" rel="nofollow">http://en.wikipedia.org/wiki/WiTricity</a>) a technology developed by MIT to wirelessly transmit electricity through resonance, and I have this question:</p>
<p>Given the phenomenon of resonant inductive coupling which wi... | g14496 | [
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-0.0008691713446751237,
0.004769127815961838,
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0.01621430553495884,
0.02174164541065693,
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... |
<p>Do you think it is possible to earn a PHD degree in Theoretical Physics on your own? I have a M. Sc. in Applied Computer Science but I really want to go in the direction of Physics. Is there a way one could perform a significant work in this field without a team of other PHD-students and/or lab experiments? Is it ev... | g14497 | [
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0.006385683082044125,
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0.01489215437322855,
0.009375154040753841,
0.02265201322734356,
0.01240199338644743,
0.008... |
<p>Question: In order to protect himself from the rain, a person is standing holding an umbrella at right angle to the horizontal surface. The rain is falling at 10m/s when the velocity of the wind is zero. Suddenly, wind begins to blow at a speed of 20m/s, towards 30 degrees south of west. Now by what angle does the p... | g14498 | [
0.05906971916556358,
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0.007415079511702061,
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0.07079971581697464,
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0.10460110008716583,
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0.004615101031959057,
0.02724311500787735,
-0.020794929936528206,
-0.04... |
<p>When taking a picture with old fashioned film what sets the resolution of the picture? Is it the wavelength, or the chemical makeup of the film?</p> | g14499 | [
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0.02386835403740406,
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0.013602238148450851,
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0.025916507467627525,
0.010577964596450329,
... |
<p>Can anyone give examples of mechanics problems which can be solved by <a href="http://en.wikipedia.org/wiki/Lagrangian_mechanics" rel="nofollow">Lagrange equations</a> of the <a href="http://www.encyclopediaofmath.org/index.php?title=Lagrange_equations_%28in_mechanics%29&oldid=17218" rel="nofollow">first kind</a... | g14500 | [
0.08526469022035599,
0.006495836656540632,
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0.05848349630832672,
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0.05537876486778259,
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0.03155342862010002,
0.0032170661725103855,
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0.03500397503376007,
0.0... |
<p>I understand what are virtual photons and the difference between the real and virtual photons.</p>
<p>However, I am not able to clearly distinguish the difference between the '<a href="http://en.wikipedia.org/wiki/Phonon" rel="nofollow">phonons</a> and virtual photons'. Both are involved in non radiative energy tra... | g14501 | [
0.014846784062683582,
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0.008203980512917042,
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0.03580032289028168,
0.01598472148180008,
-0.012412327341735363,
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0.04076722264289856,
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-0.001... |
<blockquote>
<p>A disk with a rotational inertia of 5.0 kg·m2 and a radius of 0.25 m
rotates on a fixed axis perpendicular to the disk and through its
center. A force of 2.0 N is applied tangentially to the rim. As the
disk turns through half a revolution, the work done by the force is:</p>
</blockquote>
<p>... | g14502 | [
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0.004378039389848709,
0.014076575636863708,
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0.005195378325879574,
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0.08954756706953049,
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0.03795969486236572,
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-0.014874720945954323,
-0.027652936056256294,
-... |
<p>Do surfaces that reflect visible light efficiently also reflect UV light? If not, are there surfaces that do? </p>
<p>(I have a large array of UV LEDs that I need to make larger and more diffuse, so I'm considering reflecting it off nearby surfaces and into some diffuse material.)</p> | g14503 | [
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0.011909506283700466,
0.031524818390607834,
0.... |
<p>Apologies if this question is a bit too chemistry-flavoured.</p>
<p>In electron paramagnetic resonance spectroscopy, there's a practically ubiquitous convention of plotting the first derivative of the absorption with respect to field, rather than the simple absorption. Why is this?</p> | g14504 | [
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0.022533932700753212,
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0.03829314187169075,
0.01526... |
<p>So it has been asserted that a Stirling engine with proper regeneration can be made reversible. It will consist of two isothermal quasi-static processes connected by two constant-volume processes. The working gas is supposed to be heated/cooled through infinitesimal temperature differences (thus preventing the creat... | g14505 | [
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0.03641035407781601,
0.009473169222474098,
-0... |
<p>As described in the wikipedia article on <a href="http://en.wikipedia.org/wiki/Wave_function_collapse#History_and_context" rel="nofollow">wave function collapse</a>, the mathematical formulation of quantum mechanics postulates that wave functions change according to two processes:</p>
<ol>
<li>When not being observ... | g14506 | [
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0.02477373741567135,
0.07213515043258667,
0.... |
<p>A cannon is placed at the bottom of a cliff 85 m high. If the cannon is fired straight upward, the cannonball just the reaches the top of the cliff. </p>
<p>a) Calculate the initial speed of the cannonball.
b) Suppose a second cannon is placed at the top of the cliff and fired
horizontally with the same initial spe... | g14507 | [
0.08117172122001648,
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0.0528142936527729,
0.01650480180978775,
0.008003... |
<p>I would like some help in solving this problem. </p>
<p><img src="http://i.stack.imgur.com/fjVLX.png" alt="Height is 15 cm , base is 88 cm"></p>
<p>Height is 15 cm , base is 88 cm</p>
<p>My attempt:
$$(119.3 + m)(\sin(\theta)) = (88*9.8)$$
$$ 15^2 + 88^2 = 89.269^2 $$</p>
<p>$$ \sin^{-1} = 15/89.269 $$</p>
<p>$... | g14508 | [
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-0.008602324873209,
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-0.0350588895380497,
-0.0280271... |
<p>Can retrocausality resolve the paradoxes of quantum mechanics? The Copenhagen interpretation presumes something has no property until it is measured, but retrocausal interpretations explain that away by claiming that thing has a definite property before measurement, but the choice of which property is affected by th... | g14509 | [
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0.006907339673489332,
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0.01... |
<p>Engineering textbooks constantly use the concept of 'phase space' (see e.g. <a href="http://www.cs.cmu.edu/~baraff/sigcourse/notesc.pdf" rel="nofollow">http://www.cs.cmu.edu/~baraff/sigcourse/notesc.pdf</a>). That is, they think of the state of a mechanical system as a high-dimensional geometric space. For example, ... | g14510 | [
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-... |
<p>This is prompted by the strong claims made in <a href="http://www.sciencemag.org/content/332/6034/1170.full.html">Science 332, 1170 (2011)</a> to have observed trajectories of photons, "something all of our textbooks and professors had always told us was impossible". I'm suspicious of this claim because they work en... | g14511 | [
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<p>Hi I read the following puzzle from an old text book long time ago. However it doesn't provide the answer. So what is the solution?</p>
<p>Let's suppose a car is going to park to a garage and the garage is exactly the same size of the the static size of the car. Now the car is running in a speed that in its point o... | g14512 | [
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... |
<p>There's ample direct evidence for the existence of galactic and stellar mass black holes. However, there is no such direct evidence of primordial black holes, those formed after the Big Bang. A recent paper [http://arxiv.org/abs/1106.0011] describes oscillations the Sun might undergo if it encountered a primordial b... | g14513 | [
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0.0434313... |
<p><a href="http://physics.stackexchange.com/questions/290/what-really-allows-airplanes-to-fly">A previous question by David Zaslavsky</a> was a request for a broad, "how things work" type of explanation of the lift of an airfoil. The answers given there are enlightening, but don't address a more specific question I ha... | g14514 | [
0.023872053250670433,
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<blockquote>
<p>A man walking in rain at a speed of 3kmph find rain to be falling
vertically. When he increases his speed to 6 kmph, he finds rain
meeting him at an angle of 45 deg to the vertical. What is the speed
of the rain??</p>
</blockquote>
<p>My approach:</p>
<p>$ \overline{V_{\operatorname{rain}}} -... | g14515 | [
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0.028013629838824272,
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0.029183460399508476,
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... |
<p>I have a question, has the <strong>Universe</strong> been found to come in Discrete Quantum, like Quantum Physics or is it Continuous in Nature?</p>
<p>I was wondering if time was like a <strong>Continuum</strong>, like the fluid in a soft drink for example, and if it "comes into existence" in <strong>Discrete Quan... | g446 | [
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... |
<p><img src="http://i.stack.imgur.com/1bLlk.png" alt="elevator pulley system"></p>
<p>This is the scenario where my mass is $60 kg$, the mass of the elevator is $30kg$, and due to a malfunction, I have to hold myself and the elevator at rest. The question is, if there is a weighing scale under me, (of negligible mass)... | g14516 | [
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-... |
<p>How can any matter contract to its <a href="https://en.wikipedia.org/wiki/Schwarzschild_radius" rel="nofollow">Schwarzschild radius</a> if gravitational time dilation clearly states that all clocks stop at that point. So any contraction any movement would stop. If that is so why all this talk about objects which can... | g447 | [
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0.02... |
<p>Say you have a magnetic field $\vec{B}=(0,0,B_0)$. Then the Schrodinger Equation Hamiltonian for a spin-2 particle of charge $e$ moving in this field is:</p>
<p>$$H = \frac{1}{2m}[\vec{p}-e\vec{A}]^2-\vec{\mu}\cdot\vec{B},$$</p>
<p>where $\vec{A}=(-\tfrac{1}{2}y,\tfrac{1}{2}x,0)$ is the magnetic vector potential.<... | g14517 | [
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0.03232048451900482,
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0.002617964055389166,
0... |
<p>Let the Einstein-Hilbert action be rewritten as a functional of the tetrad $e$ (units shall be set to $1$) such that
$S_{EH}(e)=\int \frac{1}{2}\epsilon_{IJKL}~e^I\wedge e^J\wedge F^{KL}(\omega(e))$, where $\epsilon$ is the Levi-Civta-symbol as usual, $F$ is the curvature of the spin connection $\omega$ and $I,J,K,L... | g14518 | [
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0.05113649368286133,
-0... |
<p>There are countless of hilarious youtube videos like <a href="http://www.youtube.com/watch?v=pegHuqSHCRg" rel="nofollow">this</a> one here, in which you can see that the carousel causes people to be pulled outwards. </p>
<ul>
<li><p>What force is actually working on them, and why does it pull them outwards (instead... | g14519 | [
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0.0382755883038044,
-0... |
<p>When i studyed QM I'm only working with non time-dependent Hamiltonians. In this case unitary evolution operator has the form $$\hat{U}=e^{-\frac{i}{\hbar}Ht}$$ that follows from this equation
$$
i\hbar\frac{d}{dt}\hat{U}=H\hat{U}.
$$
And in this case Hamiltonian in Heisenberg picture ($H_{H}$) is just the same tha... | g14520 | [
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0.023699477314949036,
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0.010390393435955048,
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0.... |
<p>After watching the recent "space jump" a question arose. Why can a balloon not float into space? Can one be made/designed to do this?</p>
<p>Next, everything in orbit is falling back to earth. It only maintains its altitude with speed, about 26,000mph give or take. This number means what, 20,000+ mph relative to ... | g14521 | [
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0.047146547585725784,
0.020662600174546242,
-0.013... |
<p>This question came up as an exercise in a first year undergraduate course I was a TA for. It turned out to be a lot more difficult (impossible?) than anticipated...</p>
<blockquote>
<p>Two platforms of mass $M_1$ and $M_2$ ($M_1\neq M_2$) are connected by
a spring of constant $k$, and are initially at rest with... | g14522 | [
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0.014885392040014267,
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-0.04684605076909065,
0.0287358835... |
<p>Wikipedia <a href="http://en.wikipedia.org/wiki/Spontaneous_symmetry_breaking#Chiral_symmetry" rel="nofollow">states</a> that the spontaneous breaking of chiral symmetry <em>"is responsible for the bulk of the mass (over 99%) of the nucleons"</em>.</p>
<p>How do the nucleons gain mass from the spontaneous breaking ... | g14523 | [
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0.0031777899712324142,
0.0406... |
<p>The DMV manual says that </p>
<blockquote>
<p><em>The faster you go, the less time you
have to avoid a hazard or collision.
The force of a 60 mph crash is not
just twice as great as a 30 mph crash;
it’s four times as great!</em></p>
</blockquote>
<p>My physics is quite rusty, so I could not figure it out... | g436 | [
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0.01146798487752676,
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0.0334809273481369,
-0.031605903059... |
<p>I am trying to understand the Feynman path integral by reading the book from Leon Takhtajan.</p>
<p>In one of the examples, there is a full explanation of the calculation of the propagator </p>
<p>$$K(\mathbf{q'},t';\mathbf{q},t) = \frac{1}{(2\pi\hbar)^n} \int_{\mathbb{R}^n} e^{\frac{i}{\hbar}(\mathbf{p}(\mathbf{q... | g14524 | [
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0.05992862582206726,
0.0064315591007471085,
0.004329870454967022,
-0.02019346132874489,
0.05108... |
<p>I'm very new to quantum mechanics. I'm thinking of writing a quantum computer simulator, would the following work?</p>
<ul>
<li>Each qubit is stored as a single bit,</li>
<li>For each operation, the qubits involved are transformed into a complex vector of amplitudes of size 2^N. This will result in a vector contain... | g14525 | [
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0.03452983498573303,
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0.0041574835777282715,
... |
<p>I have a rather poor understanding of what a tensor is, but enough to apply it to the biggest part of the classical mechanics I'm studying.<br>
However, I've run into a small problem while studying "Free vibrations of a linear triatomic molecule". (We're assuming all 3 atoms are in 1 straight line and the forces the... | g14526 | [
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0.0023215175606310368,
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0.020760025829076767,
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0.0459463894367218,
-0.020979614928364754,
-0.026616236194968224,
0.061122406274080276,
-0.0... |
<p>Here's the problem I am trying to find a solution to:</p>
<blockquote>
<p>Consider a heavy point particle of mass $m_2$ fixed at a point (preferably the origin) and another light point particle of mass $m_1$ at an initial separation of $r_i$ from the fixed particle. There are no other bodies that can interfere wi... | g14527 | [
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0.0007135880878195167,
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0.013667166233062744,
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0.03978712484240532,
0.01321030966937542,
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0.053595706820487976,
-0.013234487734735012,
0.07701709121465683,
-0.050910331308841705,
-... |
<p>Is it practical to attempt to build a 3D hologram generator that is full color and big enough to recreate a watermelon full size? If so, is real-time control feasible?</p> | g14528 | [
0.005305808503180742,
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0.007989364676177502,
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0.013080473057925701,
-0.0... |
<p>UT1, UTC, TAI, TDB, or what?</p>
<p>I need to determine the time difference between a given observation and the epoch from which certain constants apply. I typically work with the J2000.0 epoch. This is to determine how much time has passed and how far motions have propagated.</p>
<p>I recently learned that when ... | g14529 | [
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0.002743049059063196,
0.01813543029129505,
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0.015233265236020088,
0.009019236080348492,
-0.03547213226556778,
0.048262350261211395,
... |
<p>The following does not include all scientific details and parameters, only a common summary of "thoughts". What is scientifically wrong with this summary? </p>
<p>When you take your beer and tap the top of a friends beer bottle, the beer shoots out the top as the CO2 is taken out of solution and rebounds off the ... | g14530 | [
0.04987917095422745,
0.023753779008984566,
0.005533796735107899,
0.06539899110794067,
0.03572564199566841,
0.08749940991401672,
0.044756416231393814,
0.009568644687533379,
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0.04291832074522972,
-0.026150217279791832,
0.007906671613454819,
0.049... |
<ol>
<li>See the scan attached below. Brown, in his QFT book, argues a certain way to do an integral. I understand that 1.8.13 or equivalently 1.8.14 can be performed once analytic continuation is done. I also understand that under this transformation the LHS of 1.8.12 would not change when viewed as an integral over $... | g14531 | [
0.04427690804004669,
-0.008083250373601913,
-0.00646198308095336,
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0.0177248977124691,
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0.041504982858896255,
0.03526010736823082,
-0.0077422079630196095,
-0.014539637602865696,
-0.048616793006658554,
-0.0005617258721031249,
-0.017594698816537857,
... |
<p>The Pauli spin matrices
$$
\sigma_1 ~=~ (\begin{smallmatrix} 0 & 1 \\ 1 & 0 \end{smallmatrix}),
\qquad\qquad
\sigma_2 ~=~ (\begin{smallmatrix} 0 & -i \\ i & 0 \end{smallmatrix}),
\qquad\qquad
\sigma_3 ~=~ (\begin{smallmatrix} 1 & 0 \\ 0 & -1 \end{smallmatrix}),$$ </p>
<p>are ma... | g14532 | [
0.0015811914345249534,
0.010234791785478592,
-0.025469180196523666,
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0.039094191044569016,
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0.07416051626205444,
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0.04064951464533806,
-0.03744500130414963,
0.029466208070516586,
0.0584370493888855,
0.00... |
<p>I understand that if the wire is not aligned with the magnetic field, it won't rotate, but I'm still confused on how so.
Also, which direction is the current flowing? </p> | g14533 | [
-0.01500350795686245,
0.009249803610146046,
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0.024798989295959473,
0.0738440677523613,
0.0292776171118021,
0.07485458254814148,
0.015051196329295635,
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-0.047756802290678024,
-0.04346352443099022,
0.04830746352672577,
-0.032080963253974915,
-0.012... |
<p>I've been trying to solve this using the method the prof. taught us, and I happen to know the answer but I can't reach it no matter how many times I've tried. The circuit in question is below:</p>
<p><img src="http://i.stack.imgur.com/X6wgG.jpg" alt="image"></p>
<p>I am asked to use Maxwell's circulating current t... | g14534 | [
0.03263173624873161,
0.006320952903479338,
0.0012252859305590391,
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0.046550244092941284,
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0.10595116019248962,
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0.061628468334674835,
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0.06655599921941757,
-0.0627712830901146,
0.04256... |
<p>In many aerial war face movies they show that aircraft is locked by missile ,particularly in movie <strong><em>behind enemy line</em></strong> " F/A-18 Hornet" is locked by 2 <strong><em>SAM missile</em></strong>,pliot try to break the lock but aircraft get shot down. <br>
i find wikipedia have some <a href="http://... | g14535 | [
-0.04515143856406212,
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<p><img src="http://i.stack.imgur.com/fzIUA.png" alt="enter image description here"></p>
<p>This is the question, and the answer is given as 2).</p>
<p>Now my basic doubt is, are they asking us the direction of the total contact force on the object by the floor? Or, are they asking the direction of the static frictio... | g14536 | [
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<p>The phenomenon of observing one entangled particle and noticing the other take on corresponding values... Does this take a finite speed at all or is it instantaneous?</p> | g14537 | [
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<p>For a given Hamiltonian, is the space of histories of a classical system the same as the symplectic manifold? </p>
<p>Do I have to take care of gauge equivalences and if so, is this only an issue for fields (not for trajectories)?</p> | g14538 | [
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<p>When thinking about how the <a href="http://physics.nist.gov/cgi-bin/cuu/Value?asil" rel="nofollow">lattice constant of silicon</a> can be given up to eight decimal places without a remark for the temperature I realized that, it seems</p>
<p><em>most insulators and semiconductors seem to expand less than metals whe... | g14539 | [
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<p>There is <a href="http://astarte.csustan.edu/~tom/SFI-CSSS/info-theory/info-lec.pdf" rel="nofollow">a book from Tom Carter</a> on entropy. In the Economics I application (page 111), he ingeniously computes that the distribution of fixed amount of M money over N individual tends to </p>
<p>$$p_i = {1 \over T}\, e^{-... | g14540 | [
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<blockquote>
<p><em>A car is on a banked curve, following a path which is part of a circle with radius $R$. The curve is banked at angle $\theta$ with the horizontal, and is a frictionless surface. What is the speed the car must go to accomplish this?</em></p>
</blockquote>
<p>What I don't understand about this pr... | g14541 | [
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<p>If you look at the Feynmann Diagram of an electron capture:
<img src="http://i.stack.imgur.com/3mS4E.jpg" alt="enter image description here"></p>
<p>Whe W+ boson turns the electron into a neutrino. How is this possible? I thought the the boson carries the positive charge and converts the electrons into a positron. ... | g14542 | [
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<p>In the perturbation theory for non-degenerate levels, the energy $E_n(\lambda)$ of an eigenstate $|\psi_n(\lambda)\rangle$ of the hamiltonian $\mathcal{H}=\mathcal{H}_0+\lambda \mathcal{H}_1$ (where $\mathcal{H}_0$ is the unperturbed hamiltonian with eigenstates $E_n^0$ and $\lambda\mathcal{H}_1$ is the perturbation... | g14543 | [
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0.... |
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