question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Suppose that you want to launch an object that travels the longest distance, given the starting speed (or the force applied). You have to determine the angle that al you to reach the longest distance, before it touches the ground.</p>
<p>For simplicity, the launch happens at the ground level, so no change in altitu... | g11022 | [
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<p>So I've had this question bugging me ever since I saw sound at physics class:</p>
<p>How is it possible to match the resonance frequency of a column of air in an organ pipe and form a standing sound wave by simply blowing air into the column? </p>
<p>The main reason I see this problematic is because I can't figure... | g11023 | [
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<p>How can i check and calculate if a certain vacuum pump can hold an object that weights X kg? By "hold" I mean not let that object fall to the floor due to gravity</p> | g11024 | [
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<p>Is there a good reference for the distinction between projection operators in QFT, with an eigenvalue spectrum of $\{1,0\}$, representing yes/no measurements, the prototype of which is the Vacuum Projection Operator $\left|0\right>\left<0\right|$, which allows the elementary construction of a panoply of projec... | g11025 | [
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<p>I am a beginner in QFT, and my question is probably very basic. </p>
<p>As far as I understand, usually in QFT, in particular in QED, one postulates existence of IN and OUT states. Unitarity of the S-matrix is also essentially postulated. On the other hand, in more classical and better understood non-relativistic s... | g11026 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/45105/does-fire-conduct-electricity-why">Does Fire Conduct Electricity? Why?</a><br>
<a href="http://physics.stackexchange.com/q/23469/520">Is fire plasma?</a></p>
</blockquote>
<p>Does a flame produce ... | g354 | [
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<p>To make it simple, take the spin foam formalism of ($SU(2)$) 3D gravity. My question is about the choice of the data that will replace the (smoothly defined) fields $e$ (the triad) and $\omega$ (the connection) on the disretized version of space-time $\mathcal{M}$: the 2-complex $\Delta$: why choose to replace $e$ b... | g11027 | [
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<p>I understand the idea of swapping from unit systems, say from ms$^{-1}$ to kms$^{-1}$, but why can we just delete the units altogether?</p>
<p>My question is: what exactly are we doing when we say that $c=1$?</p> | g11028 | [
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<p><img src="http://i.stack.imgur.com/zs2Uz.png" alt="enter image description here"></p>
<p>Suppose we have a setup like this. Here $a_1,a_2,b_1,b_2$ are acceleration magnitudes($b_1,b_2$ being relative) and $P,Q,R,S$ are not pulley/blocks but are points on the rope. If I use a geometrical constraint then ($k$ is cons... | g11029 | [
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<p><a href="http://en.wikipedia.org/wiki/Orders_of_magnitude_%28magnetic_field%29" rel="nofollow">This Wikipedia article</a> provides a wonderful way to fathom the scale of the tesla. I cannot seem to find a similar set of examples about magnetic flux. I know that the milli-, micro- and nanoweber are the most widely us... | g11030 | [
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<p>Why a day is divided by 12/24 hours? Why the number 12? Why not using 10 or 6 or 14, 16? Who invented this? Any physical reasons behind this?</p> | g11031 | [
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<p>As a foreigner, United States has a very complex time system for me. <code>Central Time Zone</code>, <code>North American Eastern Time Zone</code>, <code>Mountain Time Zone</code>, <code>Alaska Time Zone</code>, <code>Pacific Time Zone</code>, <code>Samoa Time Zone</code>, <code>Atlantic Time Zone</code>, <code>Hawa... | g11032 | [
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<p>I have derived geometric optics for gravitational waves and I am trying to interpret one of the results. I have </p>
<p>\begin{equation}
k_{\rho}k^{\rho}=0
\end{equation}</p>
<p>for the wavevector. For the case of electromagnetic waves, Misner, Thorne and Wheeler say that this means the wavevector is "null". What ... | g11033 | [
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<p>Suppose a particle is moving on a surface of a sphere,then it contains a holonomic constraint and so the three Cartesian co-ordinates are available with a constraint equation(equation of surface in Cartesian co-ordinate system). Then there must exist two generalized co-ordinates in form of which Lagrange equation ca... | g11034 | [
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<p>Is my derivation of the action of the parity operator $\mathbb{P}$ on the $|p\rangle$ representation correct?</p>
<p>$$\left( \mathbb{P}\tilde\psi \right)(p)= - \tilde\psi (p).$$</p>
<p>Obtained from</p>
<p>$$\left( \mathbb{P}\tilde\psi \right)(p) = \frac{1}{\sqrt{2\pi\hbar}}\int_{-\infty}^{\infty} dx \, e^{-\fra... | g11035 | [
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<p>This piece of argument has been repeated again and again by experts, that is</p>
<blockquote>
<p>Since the fermions are gapped, then I can integrate it out.</p>
</blockquote>
<p>but I have no idea of what will happen if the fermions are not gapped. </p>
<p>Can I still integrate it out safely?</p>
<p>For an ord... | g11036 | [
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<p>Does anyone have images of the electric field created by a <strong>real</strong> plate of charge? I'm not looking for an image of a theoretical infinite sheet of charge, I'm looking for an image of a real large one.</p>
<p>By a real plate, I mean a finite one.</p>
<p>Thanks a lot.</p> | g11037 | [
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<p>What speed should have an alone planet to have a habitable zone due to relic radiation, without any star involvement?</p>
<p>How much time the planet will be able to remain in the habitable zone before the speed drops, given the planet has no engines?</p>
<p>Are such speeds achievable using gravity assist of the g... | g11038 | [
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<p>A few sequential questions:</p>
<ul>
<li>Is it possible for a nuclear explosion to be small enough to produce a 250-ml (one cup) mushroom cloud?</li>
<li>If so, how much uranium would that take?</li>
<li>How close to the explosion could one be (in normal clothing) not to suffer from burns or excessive radiation exp... | g11039 | [
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<p>If water is cycled through a thin pipe by a pump, and a certain spot on that pump is made of thin copper that is being heated by a 1000 C source, will the water, as a whole, attain a heat of 1000 C (or close to it) and keep cycling, making the entire pipe incredibly hot? Oh, and this would be a closed loop cycle.</p... | g11040 | [
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<p>Wikipedia <a href="https://en.wikipedia.org/wiki/Nordstr%C3%B6m%27s_theory_of_gravitation#Development_of_the_theories" rel="nofollow">says</a> that Nordstrom theory with equations of motion of the test particle
$$\tag{1}
\frac{d (\varphi u_{\alpha})}{d \tau} = \partial_{\alpha} \varphi
$$
and field equation
$$\tag... | g11041 | [
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<p>Suppose two rings are kept facing each other and that one ring have some current which increases constantly. Will the other ring be attracted or repelled? Does this also depend on <em>how they are kept</em>?</p> | g11042 | [
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<p>I've recently restored my interest on theoretical physics (I have a master degree in Electrical Engineering) and began my study with first volume of the Physics Course by Landau and Lifshitz. This is a very good and interesting book, and it just blows my mind (both in a positive and negative ways) - you spend really... | g98 | [
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<p>The NY Times article on Firewalls today has the following paragraph:</p>
<blockquote>
<p><em>Quantum field theory is how the world works [quoting a physicist]. It had a major triumph just a year ago, when the Higgs boson, a subatomic particle responsible for the mass of other subatomic particles, was discovered a... | g11043 | [
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<p>From Surely you must be joking, Mr Feynman.</p>
<blockquote>
<p>You blast off in a rocket which has a
clock on board, and there's a clock on
the ground. The idea is that you have
to be back when the clock on the
ground says one hour has passed. Now
you want it so that when you come
back, your clock is... | g11044 | [
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<p>In Newton's ring experiment, it is said that the Newton's ring experiment is used to explain this phenomena as depicted in the image.
<img src="http://i.stack.imgur.com/F1Njj.jpg" alt="enter image description here"></p>
<p>Now, the interference pattern here is forming on the surface of the lens itself.
<img src="ht... | g11045 | [
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<p>What is the difference between <a href="http://en.wikipedia.org/wiki/Fraunhofer_diffraction" rel="nofollow">Fraunhofer diffraction</a> and <a href="http://en.wikipedia.org/wiki/Fresnel_diffraction" rel="nofollow">Fresnel diffraction</a>? I mean diffraction is just bending of light waves or waves in general around a ... | g11046 | [
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<p>I believe I understand how tuning a radio with an analog tuner works: turning the dial physically changes the length of the antenna, which determines which broadcast wavelength will resonate in the antenna and get picked up. In contrast, what is the mechanism that makes a digital tuner work? My guess is it'll be som... | g11047 | [
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<p>Imagine there is a string, not a massless one but a heavy one, which is attached to the ceiling where the angle between the ceiling and the tangent at the end of the string is $\theta$. (First visualize it, or draw it somewhere). Let at any point the tension in the string be T. Now obviously there are components of ... | g11048 | [
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<p>Instead of using tokomak/torus shaped tubing to confine plasma and slow it down to "useable" speeds. Is it practical to slow down plasma (with a magnetic field) over a long path using a spiral shaped confinement to increase direct plasma converter efficiency ?</p> | g11049 | [
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<p>Let's imagine this in an situation where a person jumps down from a smaller building, a garage for example. The exact numbers aren't really important here, since I'm not aiming for an exact answer, but we can call it 2 metres in height.</p>
<p>To have both situations as similar to each other as possible, let's defi... | g11050 | [
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-0.015343667939305305,
-0.00... |
<p>Is it possible to ionized a liquid and use magnetic field lines to guide the free electrons like a gas in a tokamak ?</p> | g11051 | [
-0.029266048222780228,
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0... |
<p>A friend of mine fell while he was snowboarding which led to a discussion. He mentioned that, in general, if your center of mass is traveling at a certain velocity, and you fall forward, your head would contact the ground at twice the velocity that your center of mass was traveling. Is this true? And if so can you e... | g11052 | [
0.07137839496135712,
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<p>What is the the cosmological footprint of humanity? By this I mean, how might a cosmological observer detect humanity or its products on earth?</p>
<ul>
<li>How far away can humanity or it's products (not mere landscape changes that might have happened naturally) be detected by humanly visible Light? (The story of ... | g11053 | [
-0.010898892767727375,
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<p>It is often said that faster than light travel would violate causality.</p>
<p>However, because the universe is expanding, there are actually distant stars that move away from us at a speed greater than the speed of light.</p>
<p>Why is this allowed, even though it could violate causality?</p> | g11054 | [
0.06172754615545273,
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<p>A common justification for prohibiting many unusual phenomena such as faster than light travel is that if they were possible, causality would be violated.</p>
<p>Let's define causality as:</p>
<blockquote>
<p>You cannot change the past.</p>
</blockquote>
<p>Meaning that at any given moment $t_1$, it is impossib... | g11055 | [
0.03922712802886963,
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<p>Why is the alpha, beta or gamma decay of an unstable nucleus unaffected by the chemical situation of an atom, such as the nature of the molecule or solid in which it is bound? The chemical situation of the atom can, however, have an effect on the half life in <a href="http://en.wikipedia.org/wiki/Electron_capture" r... | g11056 | [
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<p>We can use Gauss's law to find out the electric field $\vec{E}(\vec{r})$ due to an infinite cylinder of charge.</p>
<p><img src="http://i.stack.imgur.com/SNR2j.jpg" alt="enter image description here"></p>
<p>But if the cylinder is of finite length then it is said that $|\vec{E}(\vec{r})|$ is valid at $\vec{r}$ whe... | g11057 | [
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<p>Suppose a charge $q = +Z e$ is moving along positive $+x$ direction with electron below $x-$axis and the charge is moving fast enough to consider electron at rest, then what is the maximum value of energy that is transferred to electron? </p>
<p>According to my note, </p>
<blockquote>
<p>"it can be showed that ... | g11058 | [
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<p>I have a single 1 meter array of 5 fiber bragg gratings that has FC/APC connectors on both ends. I will be embedding the array in a material and want to be able to do a quick check that the array is ok and can transmit light before I ship it off somewhere. </p>
<p>I have a fiber meter to recieve the light, but I ne... | g11059 | [
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... |
<p>I've always heard fusion depends on incredible temperatures and pressures, but I'm curious what the temperature dependence of fission is.</p>
<p>For instance, if I had uranium and heated it to a sufficiently hot temperature wouldn't it decay at a faster rate at some point? I'm not talking about 300 K, but instead s... | g11060 | [
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<p><a href="http://electronics.stackexchange.com/questions/111582/capacitance-between-earth-and-moon">This question (What is the capacitance between the Earth and Moon?)</a> on EESE makes me wonder: How can a vacuum have a breakdown voltage? </p>
<p>If electrons can find the shortest path through a vacuum, how is th... | g11061 | [
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<p>so I'm working on length contraction in relativity theory. I feel pretty confident time dilation and have not really gone over Lorentz Transformations that much.</p>
<p>The question itself lies at the bottom if you want to skip to there. The following just shows my process and conclusion</p>
<p>So, I'm working on ... | g11062 | [
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0.011103... |
<p>MRI expert Pierre-Marie Robitaille on the design flaws of COBE, WMAP, & Planck and the violation Kirchhoff's Law:</p>
<p>Here are his talks:</p>
<p><strong><a href="https://www.youtube.com/watch?v=i8ijbu3bSqI" rel="nofollow">Pierre-Marie Robitaille: The Cosmic Microwave Background</a></strong></p>
<p><strong>... | g355 | [
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<p>I have a rather broad question and a specific problem. Let's take a orthonormal single-particle basis $\{ \vert i \rangle \}$, a simple single-particle Hamiltonian
$$\tilde{H} = \sum_{i, j} h_{i j} \vert i \rangle \langle j \vert$$
and its second-quantized form
$$ H = \sum_{i, j} h_{ij} a^\dagger_i a_j ~.$$
Now I a... | g11063 | [
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0.011... |
<p>I am unable to figure out how we get two peaks in the <a href="http://en.wikipedia.org/wiki/Electron_paramagnetic_resonance" rel="nofollow">Electron Spin Resonance</a> (ESR) experiment, in which we use Helmholtz coils as B source with modulation, and a basic unit as a source of radio waves.</p> | g11064 | [
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<p>When the current in 2 parallel wires flows in same direction they attract each other.Shouldn't the electrons travelling in opposite direction should also repel ?</p> | g11065 | [
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<p>I've heard that light can form a curve if they travel near high-mass stars or even a black hole with strong gravity. Which is according to this <a href="http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation" rel="nofollow">Newtonian formula</a></p>
<p>$$\large F_{g}=\dfrac{Gm_1m_2}{r^2}.$$</p>
<p>Bu... | g143 | [
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0.0046983566135168076,
0.0241584349423646... |
<p>Voyager I, as an example, taking account gravity<br>
and setting aside effects of speed as cause of time dilation.</p>
<p>If it is very far away from earth and sun,
so then there must be a difference in the spacetime curvature there
in the ship compared with here in earth,
It means a detectable difference between... | g11066 | [
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0.04496769... |
<p>I am trying to get the distance a projectile travels, so I can display it in my program.</p>
<p>I'm sort of new to physics, but I've tried looking this up.</p>
<p>I'm not getting the right results however, and me being new to physics, I'm not sure if I'm just using the wrong formula or what.</p>
<p>This is the fo... | g11067 | [
0.05514221638441086,
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0.06889494508504868,
0.08994805812835693,
-0.032... |
<p>Given a Quantum field theory, for a scalar field $\phi$ with generic Action $S[\phi]$, we have the generating functional $$Z[J] = e^{iW[J]} =
\frac{\int \mathcal{D}\phi e^{i(S[\phi]+\int d^4x J(x)\phi(x))}}
{\int \mathcal{D}\phi e^{iS[\phi]}}.$$ </p>
<p>The one-point function in the presence of a source $J$ is.</... | g11068 | [
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0.01847437024116516,
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0.055758967995643616,
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0.01... |
<p>I am trying to calculate the Hawking temperature of a Schwarzschild black hole in a spacetime which is asymptotically dS. Ignoring the 2-sphere, the metric is given by
$ds^2=\left(1-\frac{2M}{r}-\frac{r^2}{L^2}\right)d\tau^2+\left(1-\frac{2M}{r}-\frac{r^2}{L^2}\right)^{-1}dr^2$ </p>
<p>where $\tau=it$ the Euclidean... | g11069 | [
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0.02215787023305893,
0.04409416392445564,
0.050763726234436035,
0.01840810850262642,
0.0692... |
<p>When throwing a ball straight up, most experts say that it momentarily comes to a stop at its apex before its return fall. If it stops, wouldn't we know its velocity and position and wouldn't this violate the uncertainty principle?</p> | g11070 | [
0.06455006450414658,
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-... |
<p>For a presentation in physics I am going to talk about black body radiation since our book just mentions <a href="http://en.wikipedia.org/wiki/Planck%27s_law" rel="nofollow">Planck's law</a>, Wien's displacement law and Stefan-Boltzmann's law. I want to derive Wien's law and Stefan-Boltzmann's law from Planck's law.... | g144 | [
-0.021384846419095993,
-0.012501503340899944,
0.00291204615496099,
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0.035695306956768036,
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0.03452792391180992,
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0.0033... |
<p>Let's say you had 2 nano-engineered surfaces of diamond which were as 'flat' as possible (of course considering the radii of each carbon atom in the lattice)... would there be any friction between these 2 flat diamond surfaces when rubbed together? </p>
<p>My thinking is that there would be very little to no fricti... | g11071 | [
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0.009888618253171444,
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0.012078282423317432,
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<p>Pretty simple question (I think), probably stemming from my lack of formal background in physics.</p>
<p>I've been reading questions like <a href="http://physics.stackexchange.com/questions/11542/why-is-gravitation-force-always-attractive">this one</a> related to attraction with respect to spin (a term I'm not fami... | g11072 | [
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0.02163608931005001,
0.05109858140349388,
0.03969387337565422,
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<p>To calculate the angular momentum of a body we need to specify a point (or an axis?) from which to define the displacement vector $\vec{r}$, so that $\vec{L} = \vec{r} \times \vec{p}$.</p>
<p>For a rigid body, the formula becomes $\vec{L}=I\vec{\omega}$, assuming the moment of inertia is not a tensor. So in this ca... | g11073 | [
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0.04069162905216217,
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0.008229491300880909,
-... |
<p>I need to produce custom star charts for my website. I want to be able to do the following:</p>
<ol>
<li>Specify a region, maybe a constellation or just an arbitrary region</li>
<li>Specify what appears on the chart (e.g. the Messier objects or the objects in some other AL observing list)</li>
<li>Specify which ma... | g11074 | [
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-0.07465273141860962,
0.04482804983854294,
0.0029835645109415054,
0.13525789976119995,
... |
<p>I have a set of data on all the stars (well, to a magnitude of 9 or so) with the values of the following properties:</p>
<ul>
<li>magnitude, </li>
<li>right ascension and,</li>
<li>declination.</li>
</ul>
<p>Now I'd like to create a planar (rectangle in shape) map of the entire sky (both hemispheres), without stre... | g11075 | [
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0.01149534061551094,
0.07459127902984619,
0.... |
<p>How to derive <a href="http://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law" rel="nofollow">Stefan</a> constant from <a href="http://en.wikipedia.org/wiki/Planck%27s_law" rel="nofollow">Planck</a>'s <a href="http://en.wikipedia.org/wiki/Black-body_radiation" rel="nofollow">Blackbody radiation</a>?
Consider the ... | g11076 | [
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0.015163484029471874,
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0.02013421431183815,
0.011583483777940273,
-0... |
<p>I've always wondered, that since the Earth is moving at a very fast velocity around the Sun, why is it that when astronauts leave the Earth, the Earth doesn't immediately move away from them at extremely large speeds? </p> | g11077 | [
0.05847496539354324,
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0.00695... |
<p>Could someone provide me with a mathematical proof of why, a system with an absolute <a href="http://en.wikipedia.org/wiki/Negative_temperature">negative Kelvin temperature</a> (such that of a spin system) is <a href="http://en.wikipedia.org/wiki/Negative_temperature#Heat_and_molecular_energy_distribution">hotter</a... | g278 | [
0.05664103478193283,
0.004263055976480246,
-0.009117343463003635,
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0.006901542656123638,
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0.019292108714580536,
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0.02276766486465931,
0.006948561407625675,
0.011472251266241074,
0.036287736147642136,
-0.0... |
<p>I am considering purchasing an EMF reader, to collect data about what is being thrown off of power lines and various other sources in the house to reach some conclusions.</p>
<p>An issue is, the meter can only read in Teslas or gauss. This is fine, however a Tesla is equal to $\frac{Wb}{m^2}$ and one Weber being on... | g11078 | [
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... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/16781/how-long-does-it-take-for-expanding-space-to-double-in-size">How long does it take for expanding space to double in size</a> </p>
</blockquote>
<p>According to the standard concordence model, I hea... | g356 | [
0.049727607518434525,
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0.030109260231256485,
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-0.00... |
<p>For a <a href="http://en.wikipedia.org/wiki/Ising_model#Two_dimensions" rel="nofollow">2D Ising model</a> with zero applied field, it seems logical to me that the phases above and below T_c will have different <a href="http://en.wikipedia.org/wiki/Percolation_theory" rel="nofollow">percolation</a> behaviour. I would... | g11079 | [
0.03354000672698021,
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-0.0390... |
<p>Why is the ground state assignment $0^{+}$ whenever the number of neutrons and protons are both even? </p> | g11080 | [
0.008718855679035187,
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0.0317... |
<p>Many hall sensors on the market have a datasheet that explain the proportional relationship between the analog voltage that is outputted and the relative gauss/tesla reading (for example: 2.5mV = 1Gauss). How would one go about selectively measuring AC fields in the same manner with for example this Hall effect sens... | g11081 | [
0.04335838183760643,
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<p>I'm working on a physics engine for a game and I need something clarified.</p>
<p>Let's say I have a stationary sphere, sitting atop a platform. The sphere's mass is 10kg, and gravity is $10m/s^2$, for the sake of simplicity. That means that, due to $W = mg = F$, it is exerting a force of 100N on the platform.</p>
... | g11082 | [
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0.012432556599378586,
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0.03... |
<p>I work on the Kitaev toy model for Majorana fermions. He writes that in Majorana basis the Hamiltonian becomes in general</p>
<p>$$
H = \frac{i}{4} \sum_{l,m} A_{l,m}\gamma_{l}\gamma_{m}
$$</p>
<p>where $\gamma$ is the creation operator for Majorana fermions and $A$ is a skew-symmetrix matrix. Now he say that the ... | g11083 | [
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<p>Can someone give a simple expose on <a href="http://en.wikipedia.org/wiki/Coleman%E2%80%93Mandula_theorem" rel="nofollow">Coleman Mandula theorem</a> and what <a href="http://en.wikipedia.org/wiki/Mandelstam_variables" rel="nofollow">Mandelstam variables</a> are?</p>
<p>Coleman-Mandula is often cited as being the k... | g11084 | [
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<p>Meaning, why is it the exact number that it is? Why not 2x10^8 /mps instead of 3? Does it have something to do with the mass, size or behavior of a photon? To be clear, I'm not asking "how we determined the speed of light". I know there isn't a clear answer, I'm really looking for the prevailing theories.</p> | g283 | [
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<p>My book says: </p>
<blockquote>
<ul>
<li><p>A pure semiconductor at room temperature possesses free electrons and holes but their number is so small that conductivity offered by the pure semiconductor cannot be made of any practical use. By addition of impurities to the pure semiconductor in a very small ratio... | g11085 | [
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<p>I've heard that one of the reasons that we don't have commercial supersonic flight is because of the sonic boom produced. Is this really a deal-breaker and if not, how do you get around/minimize the nuisance?</p> | g11086 | [
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<p>Today, the obliquity of the earth is about 23.4°.
6500 years ago, it was about 24.1°</p>
<p><img src="http://i.stack.imgur.com/i8p2T.png" alt="enter image description here"></p>
<p>Imagine the blue square is the constellation of Orion, and the yellow star is the sun. Viewpoint B is you, on earth, today, when the ... | g11087 | [
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<p>Given an astrophoto with a resolution between 0.5 and 5 arcseconds per pixel, which ways exist to identify the direction of view, field of view, and objects in the picture?</p>
<p>I believe most amateur astrophotographers are in this resolution range, and I believe most of us would like to confirm the captured imag... | g11088 | [
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<p>I've already posted <a href="http://www.quora.com/What-is-the-average-distance-between-stars-throughout-the-galaxy-and-does-the-mean-distance-decrease-towards-the-centre-of-the-galaxy" rel="nofollow">here on quora</a>. But, I'm not totally sure if it's the most reasonable method. </p>
<p>Would anyone care to elabor... | g11089 | [
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<p>We've all seen the telescope photographs of andromeda galaxy:
<img src="http://i.stack.imgur.com/l4EOK.jpg" alt="enter image description here"></p>
<p>I'm wondering if it were possible to travel close enough to the andromeda galaxy could you achieve a same perspective with the naked eye? What distance away from and... | g11090 | [
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<p><a href="http://lightyears.blogs.cnn.com/2011/11/03/asteroid-to-pass-closer-to-earth-than-the-moon/?hpt=hp_t2" rel="nofollow">In the news</a>, it has been stated that there will be a fairly large asteroid passing fairly close to Earth soon. I've been trying to find a good observation guide, including determining how... | g11091 | [
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<p>I always see pictures of the solar system where our sun is in the middle and the planets surround the sun. All these planets move on orbits on the same layer. Why?</p> | g231 | [
0.022835643962025642,
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<p>Well there is a problem in my book which lists this problem:</p>
<blockquote>
<p>Calculate the probability that a particle will be found at $0.49L$ and $0.51L$ in a box of length $L$ when it has (a) $n = 1$. Take the wave function to be constant in this range.</p>
</blockquote>
<p>The answer in the solutions man... | g11092 | [
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0.0231269... |
<p>A superconducting wire($SC$) is moved rapidly in a magnetic field( $1$ $Tesla$), what would happen to the wire? Are there any forces induced of attraction or repulsion? </p>
<p>In a typical conductor, we know that if it is moved around a magnetic field $-V$ is induced within the wire based on Faraday's law, however... | g11093 | [
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<p>If you were staring to the sky in a big city and electricity is turned off in a big area around you, would you be seeing the sky with little light pollution instantly?</p> | g11094 | [
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<p>I think in quantum mechanics we assign to each system a specific Hilbert space i.e. if systems are different then their Hilbert spaces are different.
Is this true? If not why?
For differernt system I mean their hamiltonians are different.</p> | g11095 | [
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0.02218550629913807,
0.021563943475484848... |
<p>Related: <a href="http://physics.stackexchange.com/questions/116452/why-did-high-quality-mirrors-use-aluminum-coatings-instead-of-silver/116547#116547">Why did high quality mirrors use aluminum coatings instead of silver?</a></p>
<p>After reading Chris White’s and LDC3’s comments in the above related link, it got m... | g11096 | [
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-0.003466... |
<p>Here at the company we've been working on a new product, and it will more than a few times a day and with a considerable force, slide on a plastic surface, being itself, another plastic body, roughly the same material, on will be injected to a mould and the other extruded, thats the main difference. </p>
<p>As we d... | g11097 | [
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0.023488277569413185,
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0.03108... |
<p>The total mass is 2300kg (weight = 5072lbs). Find the size of the force due to wind and rolling friction when the van speed is 44.86mph (1mph= 0.447m/s).</p>
<p><img src="http://i.stack.imgur.com/oXku9.gif" alt="image"></p>
<p>I am really at a loss of what to do here.</p>
<p>Part 2:</p>
<p>How much net power, in... | g11098 | [
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-0.004856412764638662,
0.017431916669011116,
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... |
<p>I have looked at <a href="http://physics.stackexchange.com/questions/54556/how-to-calculate-the-intensity-of-the-interference-of-two-waves-in-a-given-point">this</a>, but it did not help with <em>locations</em>. Really this just comes down to mathematical manipulation, which for some reason I fail to see. Here is my... | g11099 | [
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0.023724040016531944,
0.006795189809054136,
0.014219806529581547,
... |
<p>I have heard about <a href="http://en.wikipedia.org/wiki/Dark_matter" rel="nofollow">dark matter</a> that's called the Master Of The Universe. What's this and is the dark matter the reason galaxies exist?</p> | g11100 | [
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<p>What is exactly a <a href="http://en.wikipedia.org/wiki/Dobsonian_telescope" rel="nofollow">Dobsonian telescope</a>, and what are the differences between this technical choice over a <a href="http://en.wikipedia.org/wiki/Schmidt%E2%80%93Cassegrain_telescope" rel="nofollow">Schmidt-Cassegrain</a> or a <a href="http:/... | g11101 | [
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<p>Can any telescope, such as a 8" reflector, that is normally used at night to look at planets be used or adapted for solar observing?</p>
<p>What kind of adapters or filters are required or is it better to get a dedicated solar telescope?</p>
<p>I'd like to look at sunspots, flares, prominences, eclipses, etc.</p> | g11102 | [
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<p>Sorry for posting what may be an obvious question but we just learning about friction at school and my teacher couldn't explain well enough to me and I would appreciate your inputs.</p>
<p>Consider the following 3 cases:</p>
<p>1) A load of mass $m_2$ lies on a surface. The coefficient of friction between the load... | g11103 | [
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0.03253858536481857,
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<p>Is there any (interesting) HEP process whose study would take advantage from $e^-e^-$ or $e^+e^+$ collisions with respect to $e^+e^-$ collisions?</p> | g11104 | [
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0.02464... |
<p><a href="http://en.wikipedia.org/wiki/Deformation_%28mechanics%29" rel="nofollow">Strain</a> is defined as
$$\epsilon=\frac{1}{2}\left( \nabla u + \nabla u^T\right).$$</p>
<p>I found a formula for the strain tensor in 3D decomposed into volumetric and deviatoric components:</p>
<p>$$\epsilon= v + d,$$<br>
where $v... | g11105 | [
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... |
<p>$$\nabla_{j} v^{i}~=~g^{ik}\nabla_{j}v_{k}.$$</p>
<ol>
<li><p>Does this equality involve an intermediate step, where I take the metric inside the derivative, and then use the fact that covariant derivative of the metric is zero? </p></li>
<li><p>Or is this true just because the covariant derivative transforms as a ... | g11106 | [
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0.016346167773008347,
0.03037945367395878,
-0.053... |
<p>I'm a physics major so bear with me here on the math. This is related to a problem from the textbook General Relativity - Wald. In classical electromagnetism if we have a vector field say $V$ defined on all of $\mathbb{R}^{3}$ such that $V\rightarrow 0$ , dropping off as $O(1/r^{3})$, in the limit as $r\rightarrow \... | g11107 | [
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<p>In non-abelian gauge theories self interaction of gauge fields is permitted, allowing coupling such as $WWZ$ (i.e. $Z$-boson decaying to $W^+W^-$) or ggg (i.e. gluon splitting into two new gluons). </p>
<p>The aforementioned particles are spin-1 particles, thus I'd assume that the above processes are prohibited fr... | g11108 | [
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<p><img src="http://i.stack.imgur.com/tGcgA.png" alt=""> </p>
<p><strong>In the equation (1.18) they omitted the translation vector $a^\mu$, but why?</strong></p> | g11109 | [
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0.003065... |
<p>As I understand it, the explanation of the windchill factor goes like this:</p>
<blockquote>
<p>Your body is warmer than the air around it, therefore it loses a
certain amount of heat to the air. This warms up the air immediately
around you first. The heat will then gradually be transferred to the
air fur... | g11110 | [
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0.0... |
<p>I think this problem is much more difficult than what I've learned so far.</p>
<blockquote>
<p><img src="http://i.stack.imgur.com/OCh1Z.jpg" alt="Problem"></p>
</blockquote>
<p>B) is the problem I'm having a hard time with. I think it is much more difficult to consider because as the red object begins compressin... | g11111 | [
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0.0... |
<p>I have seen two form of <a href="http://en.wikipedia.org/wiki/Hubbard_model" rel="nofollow">Hubbard model</a>, one is:
$$H=-t\sum_{<ij>s}c_{is}^\dagger c_{js}+h.c.+U\sum_i(n_{i\uparrow}-1/2)(n_{i\downarrow}-1/2)-\mu\sum_{is}n_{is}$$</p>
<p>The other is a more familiar one, which writes:</p>
<p>$$H=-t\sum_{&l... | g11112 | [
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0.01306944154202938,
0.03362399339675903,
0.0256... |
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