question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I came across a physics question recently about accelerating electrons with potential differences and it got me wondering.</p>
<p>Here is the question that brought the concept to mind.</p>
<p><img src="http://i.stack.imgur.com/w0coO.jpg" alt="Physics Question"></p>
<p><strong>First off, imagine if the potential d... | g8703 | [
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<p>Whenever we fill a bottle with cold water and place back the cap tightly closing it, why is it that after a few seconds we notice cold water droplets outside the bottle as if the water is coming out of the non porous plastic bottle? Also the same thing happens when the bottle contains hot water, so we can associate ... | g8704 | [
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<p>Two masses $m_1$ and $m_2$ are connected by a spring of spring constant $k$ and slide freely without friction along horizontal track. What is period of oscillation? No force influence.</p> | g216 | [
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<p>In <a href="http://arxiv.org/abs/0807.3040v1" rel="nofollow">this</a> article it is explained how on can (in suitable coordinate basis) get a so called warped AdS${}_3$ black hole, by introducing a warping factor. The original metric in 'Euler coordinates' for AdS${}_3$ is</p>
<p>$$ds^2=\frac{\ell^2}{4}(-d\tau^2+d\... | g8705 | [
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<p>For an interval of this spacetime,</p>
<p>$$
ds^{2} = c^{2}dt^{2} - c^{2}t^{2}(d \psi^{2} + sh^{2}(\psi )(d \theta^{2} + sin^{2}(\theta )d \varphi^{2})),
$$</p>
<p>scalar curvature is equal to zero. Also, Ricci tensor is equal to zero. How can it be for curved space-time (the metric tensor isn't represented as dia... | g8706 | [
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<p>I'm trying to see that the invariance of the Klein–Gordon field implies that the Fourier coefficients $a(\mathbf{k})$ transform like scalars:
$a'(\Lambda\mathbf{k})=a(\mathbf{k}).$</p>
<p>Starting from the mode expansion of the field</p>
<p>$$\phi'(x)=\phi(\Lambda^{-1}x)=
\int \frac{d^{3}k}{(2\pi)^{3}2E_{k}}
\l... | g8707 | [
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<p>Been looking at heat equation and it's derivation, according to Wikipedia it uses 2 mathematical assumptions. My problem is that although it all seems OK, what is the physics of heat transfer in solids? so far haven't seen answer to the following questions regarding heat equation:</p>
<ol>
<li><p>Given 2 adjacent ... | g8708 | [
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<p>Linked Article: <a href="http://www.straitstimes.com/BreakingNews/TechandScience/Story/STIStory_759539.html">Fusion: X-ray laser zaps solid to 2 million degrees</a></p>
<blockquote>
<p>The quest to create nuclear fusion may have come a step closer when scientists heated solid matter to two million degrees with th... | g8709 | [
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<p>I read the definition of <a href="http://en.wikipedia.org/wiki/Work_%28physics%29">work</a> as
$$W ~=~ \vec{F} \cdot \vec{d}$$
$$\text{ Work = (Force) $\cdot$ (Distance)}.$$<br>
If a book is there on the table, no work is done as no distance is covered. If I hold up a book in my hand and my arm is stretched, if ... | g315 | [
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<p>I need a (very) approximate model of a propeller on an aircraft. </p>
<p>My principal question is this: what would the relationship be between:</p>
<ul>
<li>Propeller rate of rotation</li>
<li>Aircraft speed</li>
<li>Force generated by propeller</li>
</ul>
<p>As an aside, what would the relationship be between th... | g8710 | [
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<p>I just recently got into particle physics and the quantum world and I love it. </p>
<p>So my first big question is.
I watch all these videos and people explain the quarks (up, down, top, bottom, strange, charm). And they all say there are 6 quarks. But every so often someone speaks of an anti-quark. What is this a... | g8711 | [
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<p>This question is in reference to the paper <a href="http://arxiv.org/pdf/hep-th/9702076.pdf" rel="nofollow">here</a> (Equation 3).The extremal 3-brane metic in $D=10$ can be written as:
\begin{equation*}
ds^2 = A^{-1/2}(-dt^2 +dx_1^2 +dx^2+ dx^3) + A^{1/2}(dr^2 +r^2 d\Omega_5^2)
\end{equation*}
where
\begin{equatio... | g8712 | [
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<p>I've seen a few questions about sound waves and sound travel here on Physics SE, so I'm hoping this question is a good fit for this site.</p>
<p>During my internet research on soundproofing, I've come across many acoustics gurus who say that, when soundproofing a wall, you have to account for every single little op... | g8713 | [
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<p>First assertion</p>
<p>If a system is already in a high temperature, adding energy, will increment the entropy in a low amount (compared with a system in a lower temperature).</p>
<p>Question (if assertion is right)</p>
<p>What if the heat is enough that let molecules breaks (activation energy), this would lead t... | g8714 | [
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<p>If I set up a snowmaker in the tropics and sprayed water with it how much water would I evaporate? How would I calculate?</p> | g8715 | [
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<p>I am attempting to implement the particle mesh ewald method (<a href="http://dx.doi.org/10.1063/1.470117" rel="nofollow">http://dx.doi.org/10.1063/1.470117</a>) in two dimensions. I am wondering what needs to be changed in the method from three dimensions to two dimensions? One thing I have recently discovered is th... | g8716 | [
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<p>An answer I gave <a href="http://physics.stackexchange.com/a/40852/2451">elsewhere</a>.</p>
<blockquote>
<p>Some cases to ponder over.</p>
<p>A closed string splits into two closed strings, which then merge again into a single closed string. The overall string worldsheet has the topology of a torus. There is... | g8717 | [
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<p>Let's say I have an operator $\hat{A}$ and a state $|\psi\rangle$. What exactly <em>is</em> the state $\hat{A}|\psi\rangle$? Is it just another different state that I am describing using my $\hat{A}$ and $|\psi\rangle$? For example, if </p>
<p>$$\hat{A} \doteqdot \text{put chocolate syrup}$$</p>
<p>Then is $\hat{A... | g8718 | [
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<p>In the <a href="http://en.wikipedia.org/wiki/Star_Wars" rel="nofollow">Star Wars</a> universe, there are mentioned (or rather shown) two planets that had some kind of great explosion in their history. First is <a href="http://starwars.wikia.com/wiki/Peragus_II" rel="nofollow">Peragus</a>, with its exposed core, that... | g8719 | [
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<p>In a few videos I've seen where he discusses the new approach to calculating the super Yang Mills scattering amplitudes, Nima Arkani-Hamed sometimes alludes to the use of Motivic methods as being relevant. (For example in the last few seconds of <a href="http://media.scgp.stonybrook.edu/video/20120411_2_Arkani-Hame... | g8720 | [
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<p>Is there a precise mathematical derivation for the correspondence principle for which I can replace $E \rightarrow i \hbar \frac{\partial}{\partial t}$ and $p \rightarrow -i \hbar \nabla$?</p> | g8721 | [
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<p>I'm wondering if my train of thought is correct. Say you have Point $A$ which is $A$ distance away from the center of an isolated spherical conductor, and Point $B$ which is $B$ distance away from the center. If I'm to find the electric potential difference, $V_A-V_B$, I know I can use the relationship $V_A-V_B= -\i... | g8722 | [
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<p>Sorry if this question is naive. It is just a curiosity that I have.</p>
<p>Are there theoretical or experimental reasons why gravity should not be an emergent property of nature?</p>
<p>Assume a <em>standard model</em> view of the world in the very small. Is it possible that gravity only applies to systems with a... | g8723 | [
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<p>For example, why is the semileptonic $B$ decay $B \to X\ell\nu$ inclusive?</p>
<p>I can't find any definition of these frequently used terms, strange.</p> | g881 | [
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<p>IN QM, the space translation operator, or generator of Translations is set to be Ie-ie/h_bar*P up to order e. </p>
<p>Now my question is what is the physical justification of only going up to order e and do the higher order terms have any meaning?</p>
<p>Is it correct to say(if we are only including up to order e)... | g8724 | [
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<p>What interactions can be expected to take place between a free proton and a <a href="http://phys.org/news/2012-04-physicists-quantum-tunneling.html" rel="nofollow">dipolariton</a>, (a) at high energies and (b) at lower energies?</p>
<p>A dipolariton is a bosonic quasi-particle mentioned in a <a href="http://www.sci... | g8725 | [
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<p>Given our current technology (or technology that is near implementation), how close would a clone of our Solar System (and so also Earth) have to be to us in order to detect that the cloned Earth was in habitable, and also how close would we have to be to detect that there is life on the planet (excluding radio sign... | g8726 | [
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<p>I have measured $k_1$ and $k_2$ in two measurements and then I calculated $\Delta k_1$ and $\Delta k_2$. Now I want to calculate $k$ and $\Delta k$.</p>
<p>$k$ is just the mean of $k_1$ and $k_2$. I thought that I would need to square-sum the errors together, like so:</p>
<p>$$ \Delta k = \sqrt{(\Delta k_1)^2 + (\... | g8727 | [
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<p>Often, for thermodynamic processes only a p-V diagram is shown.
Even without hard figures, the shape of the curve can be helpful to evaluate the process.
However, it is hard to figure out for real processes. Are there good rules of the thumb to arrive at a T-S diagram from a p-V diagram?</p> | g8728 | [
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<p>I've been trying to solve a problem for some time. I have been given conflicting information by both literature, colleagues and people on this very forum.</p>
<p>It's a very simple question: <strong>What is the definition of <a href="https://en.wikipedia.org/wiki/Power_%28physics%29#Mechanical_power" rel="nofollow"... | g8729 | [
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... |
<p>Can you think of examples where a macroscopic law coexists with a fully known microscopic law, but the former hasn't been derived from the latter (yet)? Or maybe a rule of thumb, which works but hasn't been understood yet. Or some emergence which is hard to see from the individual interacting parts. The microscopic ... | g8730 | [
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<p>What conditions would make it possible to see a naturally occurring fully 360° circular <a href="http://en.wikipedia.org/wiki/Rainbow" rel="nofollow">rainbow</a>? Would it even be possible?</p> | g8731 | [
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<p>I'm curious to know if it's useful to study Feynman article "Quantum Mechanical Computer" nowadays.
I'm a computer scientist, and i don't know any of the literature in quantum computers. Since long time has passed from 1985 it's a waste of time studying that article? If yes, why?</p>
<p>The article can be found at... | g8732 | [
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<p>I'm trying to understand solution of the following problem from Landau, Lifshitz, Classical Theory Of Fields:
<img src="http://i.stack.imgur.com/1cLN9.png" alt="enter image description here"></p>
<p>(ending skipped).</p>
<p>What I see when I "write out the expression for $w^iw_i$", using definition $w^i=\frac{du^i... | g8733 | [
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<p>Empty the universe of all matter. Place the Earth in that universe sitting in an inertial frame. Take a pair of twins. One twin gets into a space ship and takes off from Earth (t=a). He accelerates rapidly and obtains .9c within a day of Earth's time and then turns off his engines (t=b). He then glides for 4 Ea... | g8734 | [
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<p>In 2009 <a href="http://xxx.lanl.gov/abs/0906.3219" rel="nofollow">Alday, Gaiotto and Tachikawa conjectured</a> an expression for the Liouville theory conformal blocks and correlation functions on a Riemann surface of genus g and n punctures as the Nekrasov partition function of a certain class of $N=2$ super-confor... | g8735 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/23753/information-conservation-during-quantum-measurement">Information conservation during quantum measurement</a> </p>
</blockquote>
<p>I asked a version of the following quesiton previously <a href="ht... | g288 | [
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<p>I've been reading some of the literature on "open quantum systems" and it looks like the following physical interpretations are made:</p>
<ul>
<li><strong>Reversible</strong> dynamics of a <strong>closed</strong> quantum system are represented by a <strong>group of automorphisms</strong> (of a $C^∗$-algebra, von Ne... | g8736 | [
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<p>After going through several forums, I became more confused whether it is DC or AC that is more dangerous. In my text book, it is written that the peak value of AC is greater than that of DC, which is why it tends to be dangerous. Some people in other forums were saying that DC will hold you, since it doesn't have <e... | g8737 | [
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<p>It's well-known that hydrogen atom described by time-independent Schrödinger equation (neglecting any relativistic effects) is completely solvable analytically.</p>
<p>But are any initial value problems for time-dependent Schrödinger equation for hydrogen solvable analytically - maybe with infinite nuclear mass app... | g8738 | [
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<p>For any person even remotely familiar with music it is obvious that rap and singing are easily distinguishable (save for some interesting mix styles). This means that there must be a clear difference, but as with many things (e.g. image recognition) it might be that humans are better at picking up the subtleties. Wh... | g8739 | [
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<p>Take the 3rd and the 4th equation from <a href="http://en.wikipedia.org/wiki/Maxwell%27s_equations#Conventional_formulation_in_SI_units" rel="nofollow">this</a> table.
The first tells us that an electric field can be generated by a magnetic field.
The second, says that a magnetic field can be generated from an elect... | g8740 | [
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<p>The following equations are equations of electrostatics:
$$\nabla \times \vec E=0$$
$$\nabla\cdot\vec E=\dfrac{\rho}{\epsilon_0}.$$</p>
<p>These are 4 independent equations, while $\vec E$ has only 3 independent components. Yet these equations do not completely specify the field, as after adding the gradient of a s... | g289 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Homestake_Experiment" rel="nofollow">Homestake experiment</a> was designed to detect solar neutrinos. In order to shield it from the background, it was set up in a deep underground mine. It was found that the only one third of expected neutrinos were detected, leading to the... | g8741 | [
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<p>I've been reading through a manual about MRI operating procedures for a large healthcare provider. The manual (written by Siemens) states that the MRI machines use 9kW in stand-by mode and 20.1kW while operating - yet the cooling system is required to move 204K+ BTU/h.</p>
<p>I'm confused as to where all the extra ... | g8742 | [
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<p>I was reading an answer about torque acting on a rectangular current carrying loop kept in a uniform magnitude field B.
Force acting on each sides is $F_1$, $F_2$, $F_3$, $F_4$.
It's written here : Force $F_2$, $F_4$ acting on these sides has same magnitude $F' = Blb \sin(90-\theta) = Blb \cos\theta$.
And $F1$ an... | g8743 | [
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<p>Sorry guys i went wrong in my previous question , actually my question is what is the minimum possible absolute temperature in the universe of what ever substance...?</p> | g290 | [
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<p>Given a propagator of some system, is there a way of finding the expectation value of some operator without knowing the eigenstates involved?</p>
<p>For example, if I have the propagator of a particle in a harmonic potential, and I would like to calculate $\langle\psi|p^2|\psi\rangle$ where $|\psi\rangle$ is the gr... | g8744 | [
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<p>My understanding of the Minkowski Metric is that we have the freedom to choose whether to place the negative sign on the time-component or on the spatial-components. That is, either basis should yield the same physics when dealing with Lorentz invariant Terms. Thus, if we have a Lorentz invariant Lagrangian, we sh... | g8745 | [
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<p>When someone moves, time slows down for him. Let, a man standing still and another moving very very very fast, this happens for an hour (as measured by the standing man). Time has moved slower for the moving man than for the still man. The fast has got less aged than the still. I've heard that length shortens for a ... | g8746 | [
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<p>Effective field theory of 3d topological insulators (TI) predict some novel electromagnetic effects. Unfortunately it require a gapped surface which is hard to achieve experimentally. Then I have two questions.</p>
<p>1.</p>
<blockquote>
<p>Is $\nabla P_3=0$ for a bare TI (without magnetic coating), and hence it... | g8747 | [
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<p>After completion of graduate courses when a student is supposed to start real research in Physics, (to be more specific, suppose in high energy physics), how does one select the problem to work on? The area is vast, mature and lots of problems remain to be solved. This vastness of the field and various levels of dif... | g8748 | [
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<p>I've read critique on ITER project (in Russian), and one of points was that cross section of ion-ion fusion is much lower than ion-atom and atom-atom, and that's the reason why it likely to not work.</p>
<p>Can anyone suggest where I can find how much lower cross sections are?
I am mainly interested in D-D, D-T and... | g8749 | [
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<p>Why Gravity attracts all objects with the same speed? Is this question was solved? What is the exact answer?</p> | g8750 | [
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<p>In general, the product of two Hermitian operators $\phi$ will not be Hermitian, unless the two operators commute. </p>
<p>Question: is $X = T \phi(t_1) \phi(t_2)$ Hermitian? It doesn't seem to be if </p>
<p>$T \phi_1 \phi_2 = \phi_1\phi_2\theta(t_1-t_2) + \phi_2\phi_1\theta(t_2-t_1).$ (Weinberg) </p>
<p>If not,... | g8751 | [
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<ol>
<li><p>The free fall acceleration of an object under earth's gravity is directed toward?</p></li>
<li><p>When the same amount of force is applied to two different masses, the smaller mass will be accelerated <strong><em>_</em>___</strong> than the larger?</p></li>
</ol> | g8752 | [
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-0.0... |
<p>Imagine that I have some observable value predicted with a theory for some process to be:
$1+a x + b x^2$ and observed value is 1.3 with an error 0.2; a and b are some numerical constants. I also have another observable influenced by the same x to be $1 + cx+ dx^2$ and the measured value 1.2 with an error 0.6, c and... | g8753 | [
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... |
<p>This questions started with a question I had about gravity. If two objects of different weights fall to the earth at the same rate of acceleration, then it seems to me that gravity is in some ways 'calculating' the weight of each item and applying the appropriate force to each item so as to have it fall at the same... | g8754 | [
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<p>When I <a href="https://www.google.com/search?tbm=isch&q=diurnal+uv+index" rel="nofollow">dig up a graphs of UV index versus time-of-day</a>, most graphs are characteristically shaped like one of the plots shown here:</p>
<p><img src="http://i.stack.imgur.com/IaKjX.png" alt="enter image description here"></p>
... | g8755 | [
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-0.... |
<p>In textbooks the characteristic length scale of an exciton, or an electron bound to dopant atom, in silicon is calculated by analogy to the vacuum case.</p>
<p>Bohr radius in vacuum:</p>
<p>$$a_0 = \frac{4 \pi \varepsilon_0 \hbar^2}{m_0 e^2} = 0.53\ {\rm Å}$$</p>
<p>where $\varepsilon_0$ is the vacuum permi... | g8756 | [
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<p>Is time affected by the gravitational force?</p>
<p>If so, what might be the effect on time at the centre or near centre of earth ?</p> | g291 | [
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<p>What variables affect the damping of a spring executing simple harmonic motion?</p>
<p>What are the independent variables, and what variables would need to be controlled in an experiment?</p>
<p>I'm attempting to complete an investigation where I measure the decrease in amplitude of a damped spring, and to prove t... | g8757 | [
0.0823969915509224,
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0.01374304573982954,
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0.043... |
<p>In his popular book on relativity, in chapter IX, "The relativity of simultaneity", Einstein describes an experiment in which a flash happens simultaneously on A and B, as defined by the fact that an observer at the middle point M can see the light coming from A and B at the same moment:</p>
<blockquote>
<pre><code... | g8758 | [
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0.06045655533671379,
0.0116... |
<p>Why do electrons (and other very small particles) sometimes behave as particles (i.e. when we are not looking at them) where as other times they behave as waves?</p> | g8759 | [
0.053101085126399994,
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0.0391... |
<p>I have the formula for Compton wavelength:
$$\lambda_{c}= \frac{h}{m_{0}c}$$
In this equation, is $m_0$ the mass of the electron that the photon hit?</p>
<p>I got online that this might be the photon rest mass, but it is basically 0, and it is impossible to do the calculation to get $\lambda_c$ if it is equal to 0.... | g8760 | [
0.018013404682278633,
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0.00... |
<p>Could there be a method to obtain and send worldwide electricity through WiFi? I mean if we have internet everywhere and only need a WiFi device, can we apply the same to electricity technology? or electrons conducted by WiFi waves? </p> | g8761 | [
0.010207593441009521,
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<p>A black hole exists. Eventually, it will completely evaporate away.</p>
<p>Alice falls into the hole. Imagine you are Alice. According to logical positivism, the interior of the black hole exists. But you will die at the singularity. You can't measure anything after you're dead, so any event outside after the black... | g8762 | [
0.018310662358999252,
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<p>The great physicist Raphael Bousso predicted time will end in <a href="http://arxiv.org/abs/1009.4698" rel="nofollow">this article</a>. We can't measure anything after our death in principle. So, does time end when we die?</p> | g8763 | [
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<p>Recall the <a href="http://www.schoolphysics.co.uk/age11-14/glance/Mechanics/Law_of_moments/index.html" rel="nofollow">Law of Moments</a> for a one dimensional rod:</p>
<blockquote>
<p>"<em>When an object is in equilibrium the sum of the clockwise moments is equal to the sum of the anticlockwise moments.</em>"</p... | g8764 | [
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<p>I found a pair of polarizing "3D glasses" lying around, and tried to look at myself in the mirror while wearing them.</p>
<p>To my utter confusion, when closing the left eye and only looking through the right eye, I could not see the right eye in the mirror. The light could not pass through the same polarized lens... | g8765 | [
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<p>I'm trying to understand boundary layer theory in fluids. All I've found are dimensional arguments, order of magnitude arguments, etc... What I'm looking for is more mathematically sound arguments. Not rigorous as in keeping track of all epsilons and deltas, but more rigorous than an heuristic argument. Hope you un... | g8766 | [
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<ol>
<li><p>For grand partition ensemble, is it true that the introduction of chemical potential allows us to have the sum of number of the particles in each state to be the total number of particles ("On average")? and this fluctuation in the constraint of $N$ will shrink as the number of particles you got is large.</... | g8767 | [
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<p>When you put a <a href="http://en.wikipedia.org/wiki/Duvet" rel="nofollow">duvet</a> cover in a washing machine without buttoning it up any other items of bedding (e.g. pillow cases) inevitably end up inside it. Instinctively, I would think that the opposite would happen (although I have no rigourous basis for belie... | g8768 | [
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<p>I've heard that decompression speed or rate in which the gas will leave the greater pressured container is equal to the speed of sound.</p>
<p>For example, if the spacecraft gets damaged the air cannot exit out to vacuum faster than about 340 m/s</p>
<p>I don't understand how the flow rate of the fluid is determin... | g8769 | [
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<p>This is a short and simple question...</p>
<p>I have been reading my book on particle physics and quantum physics when I had thought of a question that it failed to answer: "Does a particle enter/interact with the Higgs Field when created, or at some other time? And if the answer is neither of these two, does it co... | g8770 | [
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<p>Quantum wavefunctions of infinite variables can be written that describe certain Fractional Quantum Halls states, such as the Laughlin family of wavefucntions $ \Pi_{i<j} (z_i-z_j)^k $ that describe the the $ \frac{1}{k} $ states. However, can wavefunctions also be written that describe the called "crystal" state... | g8771 | [
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<p>I think this is a simple question. If I have that $E(L)=\tau L$ and we are told that $\tau=BTL$ would this mean that $E=BTL^2$ implies $dE=(2BTL)dL$ or should I sub $\tau$ straight into the second law giving $dE=\tau dL=(BTL)dL$?</p>
<p>$\tau=tension \ L=length \ T=temperature \ B= constant$</p> | g8772 | [
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<p>I am mathematician and have paper which models situation when homogeneous magnetic field is applied to moving electrically conducting fluid. There is such Lorentz force formula on which all the work is made:</p>
<p>$$F= \sigma (E + V \times B) \times B $$</p>
<p>But I think that the last $\times B$ is not needed. ... | g8773 | [
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<p>The FLRW metric which I am using is $$ds^2 = dt^2 - \frac{a(t)^2}{c^2} \left( dx^2 + dy^2 + dz^2 \right)$$
where $a(t)$ is the so-called 'scale factor'. I did not want to calculate the Christoffel symbols directly by using the metric and its derivatives. Instead, I took the Lagrangian,
$$\mathcal{L} = g_{\mu \nu} \... | g8774 | [
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<p>Has anyone tried to develop relativistic quantum theory along the lines of the Heisenberg picture and what's so difficult about promoting time to an operator??</p> | g8775 | [
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<p>I'm studying rigid body mechanics and I've seen several proofs of properties related to total angular momentum, kinetic energy, etc. that all regard discrete set of points. For example, to show that in an inertial frame $\frac{\text d \mathbf {L}}{\text d t}=\mathbf{\Gamma}^{\text {ext}}$, one writes down the sum $... | g8776 | [
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<p>I know that the distance travelled in non constant acceleration is $d=\int_a^b f(x)\mathrm{d}x$, but is it possible to calculate the distance without knowing the value of $f(x)$?</p> | g8777 | [
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<p>I'd like to estimate the colour-temperature of sunlight (as applied in photography) based on the position of the sun in the sky for a mobile phone app I'm working on (app link from a more appropriate question -<a href="http://photo.stackexchange.com/a/39659/20190">Are there any mobile applications that calculate sun... | g8778 | [
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<p>I'm looking for data on Debye temperature of steel (ideally with a known carbon concentration, structure, and set of phases), but find only data on elements. Do You happen to meet the data in papers, or textbooks?</p> | g8779 | [
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<p>I would like to compute the Christoffel symbols of the second kind using the geodesic equation. To practice, I have tried the Schwarzschild Ansatz
$$ g_{00} = \mathrm e^\nu,\quad g_{11} = - \mathrm e^\lambda,\quad g_{22} = -r^2,\quad g_{33} = -r^2 \sin(\theta)^2, $$
where $\nu$ and $\lambda$ are functions of $r$.</p... | g8780 | [
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<p>Suppose there are two observers moving at a speed c/2 w.r.t. each other. Now they won't agree on simultaneity of space separated events.</p>
<p>Now they decide to host a race between two racers, with common starting point but different ending points.
They bet on their racers, that whosoever wins will pay the other ... | g8781 | [
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<p>The parameters of $\rm\Lambda CDM$ model have been determined to an amazing high precision from the measurements made by the Planck mission. In particular, the Hubble "constant" (the value of Hubble parameter at the present day) has been determined to be $H_0 = (67.3 \pm 1.2 )\, \text{km} \, \text{s}^{-1} \text{Mpc}... | g8782 | [
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<p>I've recently has special-relativity explained to be in a rather elegant way. All objects travel at the speed of light in space time. Thus, when you travel faster through the three dimensions of space, the speed at which you travel through time decreases. Photons do not experience time because all their velocity is ... | g8783 | [
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<p>In a many-body system, we can know the spectrum function at a particular temperature from Green function. It means density of states. A peak of spectrum represents one mode. My question is that in the same model why the peak of the spectrum gets broader with lower dimension? </p> | g8784 | [
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<p>When doing research in theoretical physics, a frequent task one encounters is trying to express some physical quantity as a function of other quantities. A lot of times this can't be done analytically, but even when it can - it sometimes results in very long and complicated symbolic expressions. </p>
<p>Although t... | g8785 | [
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<p>This is a quote from the book <em>A first course in general relativity</em> by Schutz:</p>
<blockquote>
<p>What we shall now do is adopt a new unit for time, the meter. One meter of time is the time it takes light to travel one meter. The speed of light in these units is
$$\begin{align*}\end{align*}$$</p>
... | g8786 | [
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<p>To be clear, this is not a homework question, but it is something I am studying for an exam. The question is about a hilsch tube which separates a stream of high pressure air to a high temperature and cold temperature stream. After this, a carnot engine is placed between the streams to convert some of the heat fr... | g8787 | [
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<p>charges are transferred by electrons which we all know but why it cant but it cant be transferred by protons.Well i searched on google where i found similar questions already being asked on many sites.But i ddnt found any answers of them convincing.they were saying that electrons are mobile and similarly protons are... | g8788 | [
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0.02526918239891529,
0.012328465469181538,
-0.006735833361744881,
-0.052207257598638535,
0.01671595685184002,
0.016175175085663795,
0.00201032... |
<p>The <a href="http://www.smh.com.au/technology/sci-tech/newly-discovered-planets-include-superearth-20110913-1k7tl.html">recent discovery</a> of <a href="http://en.wikipedia.org/wiki/HD_85512_b">HD85512b</a> only 36 light years from Earth has promising attributes to harbor life. Assuming we want to travel there, we c... | g8789 | [
-0.007629514671862125,
0.07925518602132797,
-0.0006750825559720397,
0.055820729583501816,
-0.012744695879518986,
0.027473650872707367,
0.035496629774570465,
0.01674083061516285,
-0.04190872609615326,
-0.010837645269930363,
0.041839394718408585,
0.018690405413508415,
0.030437590554356575,
-... |
<p>In classical mechanics about rotation of rigid object, the general problem is to study the rotation on a given axis so we need to figure out the moment of inertia around some axes. In 3-dimensional case, we have a matrix (i.e. moment of inertia tensor)</p>
<p>$$
I =
\left(
\begin{matrix}
I_{xx} & I_{xy} &... | g8790 | [
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0.0008542666910216212,
0.010690013878047466,
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0.0355226993560791,
0.014652703888714314,
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0.018887870013713837,
0.00034713713102974,
0.007307562977075577,
-0.02907034382224083,
-0.082... |
<p>I'm reading some papers for calculating the vapor pressure of alkali metals as a function of temperature, and I've come across some familiar-looking virial expansions, but when I tried to work out the unit analysis, it was very much unclear how to make everything work out.</p>
<p>Here's the first equation (where th... | g8791 | [
0.03878205269575119,
-0.03691411018371582,
0.01467674970626831,
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0.0577588826417923,
0.012928956188261509,
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0.01635102555155754,
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0.041948966681957245,
0.042553771287202835,
0.049465350806713104,
0.03234858438372612,
-0.02444... |
<p>I've recently learned that the general consensus is that several (if not, most) galaxies have super massive black holes in their center, in particular the Milky Way. This, at least to me, makes perfect sense seeing as we are in a spiral galaxy which means we need something to "spiral" around (a large body or a bunch... | g405 | [
0.009608480148017406,
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0.019708674401044846,
0.010458276607096195,
0.026671461760997772,
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-0.0031168977729976177,
0.018445763736963272,
0.017374204471707344,
0.0032097564544528723,
-... |
<p>I have a doubt regarding the significance of a force on a wire. Well, first of all, I know that if I have a particle and if there are several forces acting over it, then we can compute one total force $F$ that gives the same effect as the combination of the several forces, and this force is just the vector sum.</p>
... | g8792 | [
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-0.04446445778012276,
0.0... |
<p>How to find the frequency of small oscillation of a particle under gravity that moves along curve $y = a x^4$ where $y$ is vertical height and $(a>0)$ is constant?</p>
<p>I tried comparing $V(x) = \frac 1 2 V''(0) x^2 + \mathscr O(x^3) = \frac 1 2 kx^2$ (assuming $V(0)$ is ground state and $V'(0)$(slope) remain... | g8793 | [
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0.005200859624892473,
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0.0004662532010115683,
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0.0662304013967514,
0.01590023748576641,
-0.0053932... |
<p>How do I calculate sky irradiance from radiance (L) from a hemisphere above a surface which is tilted relative to the normal (x=0,y=0,z=1). I have L as a function of zenith (0 to 180deg) and azimuth (0 to 360 deg)? Any known MAtlab functions doing this kind of thing?</p> | g8794 | [
-0.008952037431299686,
-0.02893979288637638,
0.000003945576736441581,
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0.03848351165652275,
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0.02253817394375801,
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0.09423156082630157,
0.045318715274333954,
-... |
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