question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>A particle of mass $m=0.5kg$, is attached to a spring of natural length $l=0.6m$ and modulus of elasticity $\lambda=60N$, and the setup is on a horizontal smooth table. The other end of the spring is attached to a fixed point $A$ on the table. The particle is then pulled so that the distance $AP=0.9m$, and is then r... | g8060 | [
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<p><a href="http://en.wikipedia.org/wiki/Maxwell%27s_equations" rel="nofollow">Maxwell</a>'s <a href="http://en.wikipedia.org/wiki/Mathematical_descriptions_of_the_electromagnetic_field" rel="nofollow">Equations</a> written with usual vector calculus are</p>
<p>$$\nabla \cdot E=\rho/\epsilon_0 \qquad \nabla \cdot B=0$... | g8061 | [
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<p>In the context of Cosmology models, What are examples of metrics with off-diagonal terms?</p> | g8062 | [
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<p>I've been having an unusually difficult time solving kinematics problems in comparison to all the other students in the classroom. It appears that I'm one of the unfortunate people with an anti-math mind (although I've been expecting as much for some time now). In short, I have no idea how to solve this problem:</... | g8063 | [
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<p>As in the title, I'm wondering is it possible.</p>
<p>I think it is possible, because we have powerful enough radiotechniques and gamma radiation are just EM waves, not particles. However I think is useless, because it costs too much.</p>
<p>Can anyone say something more about this? </p>
<ul>
<li>How much powe... | g8064 | [
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<p>The entropy of an isolated system always increases,</p>
<p>Considering an intelligent actor in the system who can organise different objects in the system, doesnt the measure of disorder reduce albeit for short periods?</p> | g265 | [
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<p>Does the speed of light apply to the speed of (waves?) in every known field, or does it only apply to the electromagnetic field?</p> | g8065 | [
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<p>Since quantum Gauge theory is a quantum mechanical theory, whether someone could explain how to construct and write down <strong>the Hilbert Space of quantum Gauge theory with spin-S</strong>. (Are there something more rich/subtle than just saying the Hilbert Space are composed by the state space of infinite many se... | g8066 | [
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<p>I subconsciously feel not fully comfortable about <strong>Wick rotating or analytic continuation from Euclidean to Minkowski space</strong>. I simply wonder whether there is any subtlety here, and when we need to be conscious whether <strong>(i) this continuation can be dangerous or the continuation cannot be done; ... | g8067 | [
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<p>I am a bit lost how one has deduced the formula for electric field with electric dipole because of some inconsistency between different sources. The <a href="http://en.wikipedia.org/wiki/Dipole#Field_from_an_electric_dipole" rel="nofollow">Wikipedia article</a> contains a delta function in the formula, but <a href="... | g8068 | [
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<p>I was reading up on <a href="http://en.wikipedia.org/wiki/De_Sitter_space" rel="nofollow">De Sitter space</a>s, which states that the gravitational effects from a black hole is indistinguishable from any other spherically symmetric mass distribution. This makes a lot of sense to me.</p>
<p>I'm now super curious, c... | g8069 | [
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<p>How to derive the selection rules $\Delta L= \pm 1$, $\Delta S=0$ for electron spectroscopy?</p> | g8070 | [
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<p>I will start with an example. Consider a symmetry breaking pattern like $SU(4)\rightarrow Sp(4)$. We know that in $SU(4)$ there is the Standard Model (SM) symmetry $SU(2)_L\times U(1)_Y$ but depending on which vacuum we use to break this symmetry, in a case you can totally break the SM symmetry, with the vacuum :
$$... | g8071 | [
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<p>This is a very simple question, but I can't find an answer anywhere.</p>
<p>Earth's gravity at sea level is 1 (approximately 9.8m/s^2)</p>
<p>What happens being under sea level in a cavern/chasm/ravine, how much does gravity increase normally here on Earth?</p> | g8072 | [
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<p>I ran into this while looking at measures of humongous amounts of data. How does the information (data) collected in an inverse femtobarn exposure compare to a gigabyte of data ?</p> | g8073 | [
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<p>I'm having some trouble identifying a reference Landau and Lifshitz make in volume 3 - non-relativistic quantum mechanics - of their Course of theoretical physics. This is the page from the Oxford, Pergamon, 1977 edition:</p>
<p><img src="http://i.stack.imgur.com/OqC2L.png" alt="enter image description here"></p>
... | g8074 | [
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<p>Explanations I have read of why photons are emitted from atoms mention electrons being 'excited' to another energy level, and then returning to their base level, releasing a photon. I have also seen the occasional mention of 'fields' and I vaguely expect from what I've read that interaction of the electrons with the... | g8075 | [
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<p>I'm looking for an explanation on why darker light filters let through less light than lighter filters (secondary/high school level). Although this seems to the layman like the obvious outcome, our science teacher was unable to explain why a darker blue and darker green filter let through less light than a yellow or... | g8076 | [
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<p>This question is more practical than theoretical, but I am interested in the theoretical considerations as well.</p>
<p>My wife just bought a Samsung S3 phone with a 8 MP image sensor hiding behind a tiny lens. In daylight the pictures come out fine, but it suffers horribly in low-light conditions. Is there a theor... | g8077 | [
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<p>According to Poincare's Lemma, if $U\subset \mathbb{R}^n$ is a <a href="http://en.wikipedia.org/wiki/Star_domain" rel="nofollow">star-shaped set</a> and if $\omega$ is a $k$-form defined in $U$ that is closed, then $\omega$ is exact, meaning that there's some $(k-1)$-form, say $\eta$ with $\omega = d\eta$. Now, tran... | g8078 | [
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<blockquote>
<p>A bar magnet is released from rest along the axis of a very long,
vertical copper tube. After some the the magnet :</p>
<p>(a) will stop in the tube.<br>
(b) will move with almost constant speed.<br>
(c) will move with an acceleration g.<br>
(d) will oscillate.</p>
</blockquote>
<h2>Atte... | g8079 | [
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<p>I know that in free space, the width of a Gaussian beam can be written as $W=W_0\sqrt{1+(\frac{z}{z_0})^{2}}$. However, I was wondering if it was possible to express this width as a function of refractive index instead (since I don't believe a Gaussian beam originating in say, glass, will diverge in the same manner ... | g8080 | [
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<p>From the perspective inside a black hole: Is information about everything outside a black hole - the rest of the cosmos - represented on the inside of the (event) horizon too?
NB. I realize it is the notion of a so called stretched horizon that is being used about the 2d-like sheet that information is scrambled on, ... | g8081 | [
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<p><a href="http://en.wikipedia.org/wiki/Gamma-ray_burst" rel="nofollow">Gamma-ray bursts</a>(GRBs) are flashes of gamma rays associated with extremely energetic explosions</p>
<p>why nasa interested to Gamma ray burst?</p> | g8082 | [
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<p>I've been thinking about the following problem for some time now and was wondering if anyone could shed any light on it.</p>
<blockquote>
<p>At time $t = 0$, turtle <code>A</code> sits at $(0,0)$ and turtle <code>B</code> sits at $(d,0)$. <code>B</code> begins moving straight upwards perpendicular to the $x$-axis... | g8083 | [
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<p>I have heard that the traditional resistor-based fan speed regulators are inefficient. In fact, I have noticed that such regulators tend to get hot when the fan is set to low speed. However, does that mean that they save <strong><em>no power at all</em></strong> at low speeds, or is it just that power is saved but t... | g8084 | [
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<p>The top rated answer to <a href="http://physics.stackexchange.com/questions/8850/alcubierre-drive-clarification-on-relativistic-effects">this question about the Alcubierre drive</a> asserts, "spacetime can dynamically evolve in a way which apparently violates special relativity," but according to <a href="http://en.... | g8085 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2066/why-does-adding-solutes-to-pure-water-lower-the-the-specific-heat">Why does adding solutes to pure water lower the the specific heat?</a> </p>
</blockquote>
<p>Why do higher concentration salt solut... | g266 | [
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<p>I was flicking through Zettili's book on quantum mechanics and came across a 'derivation' of the momentum operator in the position representation on page 126. The author derived that $\langle\vec{r}|\hat{\vec{P}}|\psi\rangle = -i\hbar\vec{\nabla}\langle\vec{r}|\psi\rangle$ (I've omitted the full derivation). However... | g8086 | [
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<p>I'm an undergraduate mathematics student trying to understand some quantum mechanics, but I'm having a hard time understanding what is the status of the Schrödinger equation.</p>
<p>In some places I've read that it's just a postulate. At least, that's how I interpret e.g. the following quote:</p>
<blockquote>
<p... | g8087 | [
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<p>The hypothesis of confirmational holism ( <a href="http://en.wikipedia.org/wiki/Confirmation_holism" rel="nofollow">http://en.wikipedia.org/wiki/Confirmation_holism</a> ) speaks to all sciences, but seems especially trenchant in fundamental physics, the would-be end of the road for any reductionist (or modified redu... | g8088 | [
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<p>When solving the hydrogen atom, as a 2 body problem, we have the motion of the center of mass and the motion relative to the center of mass. The well known energy spectrum, $E_n$, that goes like $1/n^2$ is the one resulting from studying the motion relative to the center of mass.</p>
<p>Now the energy of the cente... | g8089 | [
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0.03651183098554611,
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0.07381165027618408,
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-0.0184697974473238,
0.027771228924393654,
0.022181076928973198,
0.03314836323261261,
0.046... |
<p>Most of the Bodies and Objects in space are <em>likely to have</em> an <strong><a href="http://en.wikipedia.org/wiki/Atmosphere" rel="nofollow">atmosphere</a></strong>. Since the space is empty, the gases in atmosphere should have either <em>dissolved or emptied</em> into space. But, Why doesn't this happen? Still t... | g8090 | [
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0.03796953335404396,
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<p>E.g. if I know that my topology is that of a hyperboloid, how much freedom do I have left for my choice of the metric?
And the other way around: if my metric is some conformal factor times the unit hyperboloid how much freedom do I have left in my choice for the topology? Am I forced to conclude that the topology o... | g8091 | [
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<p>The Ising model is a mathematical model of ferro-magnetism in statistical mechanics. The model consists of discrete variables that represent magnetic dipole moments of atomic spins that can be in one of two states (+1 or −1). The spins are arranged in a graph, usually, a lattice, allowing each spin to interact with ... | g8092 | [
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<p>If I understand this right the Ricci flow on a compact manifold given by </p>
<p>$\partial g_{\mu \nu} = - 2R_{\mu \nu} + \frac{2}{n}\!R_{\alpha}^{\alpha} \,g_{\mu \nu}$</p>
<p>tends to expand negatively curved regions and to shrink positively curved regions.</p>
<p>Looking at the above definition I`m wondering i... | g8093 | [
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<p>How do you effectively study physics? How does one read a physics book instead or just staring at it for hours? </p>
<p>(Apologies in advance if the question is ill-posed or too subjective in its current form to meet the requirements of the FAQ; I'd certainly appreciate any suggestions for its modification if need ... | g115 | [
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<p>This year, the racetrack at Daytona has been repaved. The track was always faster than other tracks NASCAR raced at and several cars in a "train" were faster than single cars or smaller trains. This year is different, however, because two car groups are by far the faster than any other groupings. When a third car... | g8094 | [
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<p>So I have the following statement.</p>
<p>"A merry-go-round is spinning with a fixed angular speed. As a person is walking towards the edge, the force of static friction must increase in order for the person not to slide off."</p>
<p>I have no clue why is it true.
I tried to figure out the problem with the followi... | g8095 | [
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... |
<p>What is the variation of <a href="http://en.wikipedia.org/wiki/Gauss%E2%80%93Bonnet_gravity" rel="nofollow">Gauss-Bonnet</a> term total derivative of?</p>
<p>i.e. Variation of Gauss-Bonnet combination $= \nabla_{\mu} C^{\mu}$. </p>
<p>What's $C^{\mu}$ in 4-dimensions?</p> | g8096 | [
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<p>I was recently introduced to <a href="http://en.wikipedia.org/wiki/Dimensional_analysis" rel="nofollow">dimensional analysis</a> and I wanted good references for learning the ideas behind it and representation of the natural world. I'm a grad student in biology. I don't have much of a physics background.</p> | g8097 | [
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<p>Okay, so I know that the wavelength of an electron is <code>5e-7m</code> and I am asked to calculate its minimum velocity and hence minimum energy.</p>
<p>Calculating the minimum velocity via $\lambda = h/p$ gives <code>1454.67 m/s</code>. Next step is to calculate the associated energy.</p>
<p>The actual answer g... | g8098 | [
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<p>The headline question: Is it known how to construct an equivalent of the 3-D Ising Fixed point theory on an arbitrary 3-D manifold? Or any non-trivial d > 2 fixed point?</p>
<p>The answer is maybe as simple as a careful conformal mapping of the action . I don't even know whether this is a hard question not.</p>
<p... | g8099 | [
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<p><img src="http://i.stack.imgur.com/6EXpa.png" alt="enter image description here"></p>
<p>Why does the object not go inward, into the circle if the acceleration is inward? I think its because the velocity to outward? So they sort of cancel each other out? But if the speed is kept constant and the acceleration is inw... | g8100 | [
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<p>This is probably gonna be a dumb question but I don't know exactly where I am making the mistake. I have been taught in highschool that simple harmonic oscillator phase plot is the $sin(\omega t)$:
<img src="http://i.stack.imgur.com/v8EOE.png" alt="enter image description here"></p>
<p>However now that I am thinkin... | g8101 | [
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<p>Ok - fair warning - Non-physicist asking dumb-assed questions here again.
I've been reading a lot of Einstein, Feynmann, Ferris etc. I'm just loving this stuff.</p>
<p>But I suddenly found myself looking at the 4-D sphere concept of our expanding universe, as well as the distortion of spacetime caused by objects wi... | g8102 | [
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<p>The notes I'm using for QFT give an orthonormality condition for the following plane wave:
\begin{align*}
u_{r,k}(x) = \frac{1}{\sqrt{V}} \varepsilon_r(\mathbf{k})e^{ik \cdot x}
\end{align*}
(where $\varepsilon_r(\mathbf{k})$ is a linear polarisation vector satisfying $\varepsilon_r(\mathbf{k}) \cdot \varepsilon_s(\... | g8103 | [
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... |
<p>In physics, usually <a href="http://en.wikipedia.org/wiki/Taylor_series" rel="nofollow">Taylor series</a> is used to express a quantity which keep changes with coordinate. For example the potential energy of a molecule changes with coordinate, so we express the potential energy as a Taylor expansion with respect to ... | g8104 | [
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<p>My book uses the argument that the multiplicities of a few macrostates in a macroscopic object take up an extraordinarily large share of all possible microstates, such that even over the entire lifetime of the universe, if each microstate had an equal chance of being accessed, fluctuations away from equilibrium woul... | g877 | [
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<p>Temperature is the measure of movements of atoms. So if something is said to have high temperature it means that its atoms are moving fast or have high KE energy.</p>
<p>There are basically two ways heat can be travels from on object to another. 1) conduction. 2) Radiation. </p>
<p>My question is how does radiatio... | g8105 | [
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<ol>
<li><p>Using high laser intensity to produce electron-positron pair, is it still required interaction with nucleus as is the case when gamma rays are used?</p></li>
<li><p>What causes the pair creation ? </p></li>
</ol> | g8106 | [
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<p>I was recently wondering what would happen if the force sliding two surfaces against each other were somehow weaker than kinetic friction but stronger than static friction. Since the sliding force is greater than the maximum force of static friction, $F > f_s = \mu_s F_N$, it seems that the surfaces should slide. Bu... | g8107 | [
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<p>In principle, we could describe all physics without EM fields (or photons), as they are mainly a useful tool to describe "action at distance" (which does not mean instantaneous) between charged particle. In some sense, I could always integrate out photons, and describe only electrons and not have any changes in the ... | g8108 | [
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<p>Consider the scattering of a quantum particle in one dimension, caused by a step in the potential (this appears in many undergrad level QM books):</p>
<p>$$ V(x) = \begin{cases} V_1 & x<0 \\ V_2 & x>0\end{cases}. $$</p>
<p>The particle is incident from the left, so it's wavefunction is:</p>
<p>$$ \p... | g8109 | [
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<p>How is a photon emission energy balance maintained ?</p>
<p>If an electron is in motion across space at 260,000 kilometers per second, and it releases a photon in that same direction of travel, the photon will be in motion across space at the speed of 300,000 kilometers per second, thus there will be a difference o... | g8110 | [
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<p>I would like to know how this object would rotate in free space out of curiosity.</p>
<p>Below is a diagram of the object. It is of uniform density and has a center of mass in the center of the object, denoted by the green cross.</p>
<p>On each long end of the bar, on opposing sides, are thrusters. They are placed... | g8111 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/19825/torque-required-for-a-motor-to-move-an-object-on-wheels">Torque Required For a Motor to Move an Object on Wheels?</a> </p>
</blockquote>
<p>I want to build a 4 wheel robot. the maximum weight of th... | g267 | [
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0.01991736888885498,
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<p>This is a question about the properties and strength of glass. I know that glass is an amorphous solid but I am not sure if that is relevant to my question. My question is that if there's no physical cracks or blemishes, is it possible for glass to be damaged? For example, metal can be damaged by a sharp hit or forc... | g8112 | [
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<p>I'm looking at a review question I was given and it quite frankly has me stumped. </p>
<p>"Using matrix representations find $L^{3}_{x},L^{3}_{y},L^{3}_{z}$ and from these show that $L_{x}, L_{y},L_{z}$ satisfy the same algebraic equations."</p>
<p>What has me stumped is the $L^{3}_{x},L^{3}_{y},L^{3}_{z}$, I'm no... | g8113 | [
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<p>I'm trying to develop my understanding of spinors. In quantum field theory I've learned that a spinor is a 4 component complex vector field on Minkowski space which transforms under the chiral representation of the Lorentz group. </p>
<p>Now I've been reading that we can derive spinor representations by looking at ... | g8114 | [
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<p>A circular/inclined to the equator/non-polar orbit is typical for natural satellites; apparently a consequence of the energy/velocity requirements. This is applicable to natural satellites around planets, planets around Sol ... and perhaps upwards on the scale. </p>
<ul>
<li>When can a natural satellite possibly be... | g8115 | [
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<p>I'm trying to solve the driven Two-Level System (TLS or qubit) question using a Fourier transform of the Schrodinger equation (SHE), but I'm getting stuck on solving the equation. </p>
<p>Given Hamiltonian
$$H=\left(
\begin{array}{cc}
-\frac{\omega _0}{2} & \frac{1}{2} V e^{i t \omega _D} \\
\frac{1}{2} V e^... | g8116 | [
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0.006881851237267256,
0.02... |
<p>Consider two orbits $x(t),\space y(t)$ representing the origin and destination for some spaceflight of interest. These could be, for example, cycloids describing LEO and another orbit circling, say, the moon or Mars.</p>
<p>Suppose I want to leave at $x(t_i)$ and arrive at $y(t_f)$, departing and joining those orbi... | g8117 | [
0.01745004579424858,
0.005395534913986921,
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0.0503... |
<p>If one measures the projection of spin of a spin half particle along the $x$ axis one will always get $\pm\tfrac12\hbar$.</p>
<p>Measuring it along the $y$ axis one will always get $\pm\tfrac12\hbar$.</p>
<p>Measuring it along the $z$ axis one will always get $\pm\tfrac12\hbar$.</p>
<p>Measuring it along "any" ax... | g8118 | [
0.02610599994659424,
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0.025... |
<p>I read from some books of number theory that $$\sum_{n=1}^{\infty}\frac{1}{n^s} = -\frac{1}{12}\text{,when } s=-1.$$</p>
<p>Now is there such a result $$\sum_{n=1}^{\infty}\frac{1}{n^s} = \pi \text{,when } s=1,$$or $$\sum_{n=1}^{\infty}\frac{1}{n^s} = c \pi \text{,when } s=1 \text{,where } c \text{ is a rational n... | g8119 | [
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... |
<p>I've been wondering, what causes the normal force to exist?</p>
<p>In class the teacher never actually explains it, he just says "It has to be there because something has to counter gravity." While I understand this is true, it never explains <i>why</i>.
Whenever I ask anyone else they always respond in a similar... | g268 | [
0.04349758103489876,
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0.01310512... |
<p>I would like to know how much of the Big Bang theory is dependent on the constancy of the speed of light. </p>
<p><strong>P.S.</strong>: It might be guessed that I am asking this because of the recent CERN news.
Yes, of course, I am. I was having some chat over this topic and I hit a wall before I could come to an... | g8120 | [
0.027061354368925095,
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... |
<p>The <a href="http://en.wikipedia.org/wiki/Crystallography_restriction" rel="nofollow">crystallography restriction</a> states that any 2-dimensional lattice can have rotational symmetry of degree 1, 2, 3, 4 or 6 - and that's it. A simple proof of I've heard of this is: the magnitude of $rot_\theta(x)-x$ is less than ... | g8121 | [
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<p>The weight function comes from Dirac's book, PRINCIPLES OF QUANTUM MECHANICS. On page 66,he says that sometimes it is more convenient not to normalise the eigenvectors, i.e. $$\langle\xi_1'...\xi_u'|\xi_1''...\xi_u''\rangle=\rho'^{-1}\delta(\xi_1'-\xi_1'')...\delta(\xi_u'-... | g8122 | [
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0.00018... |
<p>I just read <a href="http://idealab.talkingpointsmemo.com/2011/09/mit-setting-up-industrial-scale-graphene-printing-press.php" rel="nofollow">this story</a> on MIT working on industrial scale, km^2 sheet production of graphene.</p>
<p>A quick check of <a href="http://en.wikipedia.org/wiki/Graphene#Mechanical_proper... | g8123 | [
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0.023112615570425987,
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<p>Googling yields contradictory results, so here my question:</p>
<p>When I sing, my vocal chords vibrate, but my whole body is the resonance body, right? So I would say that when I think about standing waves etc. I must think of a resonantor that's closed (i.e. hard boundary conditions) at both ends, because my bott... | g8124 | [
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0.018... |
<p>How much energy would it take to add to the earth's orbital velocity to push the earth into mars' orbit?</p>
<p>My thoughts:
So, in 1-2 billion years, the sun will gradually get brighter.</p>
<p>Suppose a future civilization wanted to gradually move the earth farther from the sun. And for, now, please ignore that... | g8125 | [
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<p>I have been doing some readings on superconductivity and have come across the <a href="http://en.wikipedia.org/wiki/London_penetration_depth" rel="nofollow">London penetration depth</a>. I somewhat understand how it comes into play with the London equation and Ampère's law.</p>
<p>Right now, I am having a hard time... | g8126 | [
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0.021716134622693062,
0.028856588527560234,
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<p>I understand that assuming light is quantized implies that if a lower energy interacts with metal, it is possible that that quanta will not have enough energy to eject the electron. What prevents two quanta from interacting with the electron at the same time, though, and summing to have enough energy to release the... | g388 | [
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0.0... |
<p>I'm trying to track down the origin of the False Vacuum paradigm. Is it Coleman and de Luccia's "Gravitational Effects on and of Vacuum Decay"
<a href="http://www.slac.stanford.edu/pubs/slacpubs/2000/slac-pub-2463.html" rel="nofollow">http://www.slac.stanford.edu/pubs/slacpubs/2000/slac-pub-2463.html</a></p> | g8127 | [
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0.0509... |
<p>I heard that Schrodinger pointed out that (classical/statistical) thermodynamics is impaired by logical inconsistencies and conceptual ambiguities.</p>
<p>I am not sure why he said this and what he is talking about. Can anyone point some direction to study what he said?</p> | g8128 | [
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<p>Higgs Boson detected at LHC is massive. It has high relativistic mass means it has non-zero rest mass.</p>
<p>Higgs Boson gives other things rest mass. But, how does it get rest mass by itself?</p> | g269 | [
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0... |
<p>I'm trying to figure out a nice way to describe to a kid the physics behind these experiments:</p>
<p>Assuming ideal conditions, we have a small boat with a sale, close to a lake's shore and a fan fixed on the shore, oriented towards the boat's sale. Once the fan is turned on, the boat will start to move slowly awa... | g8129 | [
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<ol>
<li><p>Is it <strong>always</strong> allowed to represent the <a href="http://en.wikipedia.org/wiki/Metric_tensor" rel="nofollow">metric tensor</a> $g_{\mu \nu}$ in <a href="http://en.wikipedia.org/wiki/General_Relativity" rel="nofollow">General Relativity</a> as a $4\times 4$ matrix?</p></li>
<li><p>If the last o... | g8130 | [
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0.012946069240570068,
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0.045291878283023834,
... |
<p>The <a href="http://en.wikipedia.org/wiki/Shell_theorem" rel="nofollow">shell theorem</a> states that:</p>
<blockquote>
<p><em>A uniform spherical shell of matter attracts a particle that is outside the shell as if all the shells mass were concentrated at its center.</em></p>
</blockquote>
<p>Now, I have to solv... | g8131 | [
0.042916420847177505,
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<p>Black holes have no-hair so there are uniquely specified by a mass, charge and angular momentum. Imagine a cloud of charged rotating dust. There will be a magnetic field associated with the current of charge that is rotating. As this cloud collapses to form a black hole, how is the magnetic field excluded from th... | g403 | [
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<p>I am a little stuck on the concept involved in part b) of the following problem:</p>
<p>A $5 m$ long road gate has a mass of $m = 15 kg$. The mass is evenly distributed in the gate. The gate is supported at point A by a rod attached to the ground below the gate. Point A is located $20 cm$ from the left end. The gat... | g8132 | [
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<p>I don't really understand horizontal projectile motion.
Suppose I throw a ball horizontally.
Given $\theta$ = 0 degrees, time = 0.5 seconds, horizontal range = 15.5 metres, </p>
<p>the "initial horizontal velocity of the ball" would just be the average velocity which is displacement divided by time? Or is it $V\si... | g8133 | [
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-0.0... |
<p>Suppose there is a perfect ideal conducting solid sphere. Suppose somehow a charge of $+Q$ is kept exactly at the center of the sphere and its surface is also given a $+Q$ charge uniformly distributed at the same time.</p>
<p>We know electric field inside a charged conductor is zero. But in this situation, a $+Q$ c... | g8134 | [
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<p>A week ago I <a href="http://physics.stackexchange.com/q/38963/2451">asked</a> people on this forum what mathematical background was needed for understanding Quantum Physics, and most of you mentioned Linear Algebra, so I decided to conduct a self-study of Linear Algebra. Of course, I'm just 1 week in, but I have so... | g53 | [
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0.05310942977666855,
0.006467650178819895,
... |
<p>Where does a sparkly (CO$_2$) water bottle have more pressure? At a higher altitude (7000 feet) or under sea level (-8 feet)?</p> | g8135 | [
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0.054971251636743546,
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0.001533034723252058,
0.0359930694103241,
-0.02... |
<p>I watched this Google Tech Talk recently - <a href="http://www.youtube.com/watch?v=dEaecUuEqfc" rel="nofollow">Quantum Conspiracy</a></p>
<p>Now I have done some investigating concerning these ideas and their implications, and also have dug up two relevant science papers written on this subject. You'll have to look... | g8136 | [
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0.029452193528413773,
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0.... |
<p>I am given the fact that at a certain pressure a liquid boils at a corresponding temperature, at a different pressure it boils at a different temperature, and then I am asked to find the latent heat from that information, how do I do that?</p> | g8137 | [
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<p>When you tune your radio (digital or analog) to receive say 100 MHz frequency and while in the environment there are hundreds of channels everywhere around the radio. How does it chooses to receive the frequency only at 100 MHz? How does the radio receiver works? Is it possible to explain this in simple concept?</p> | g8138 | [
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-0... |
<p>I was trying to understand the derivation of the boundary layer equations at p.145 of <a href="http://www.unimasr.net/ums/upload/files/2012/Sep/UniMasr.com_919e27ecea47b46d74dd7e268097b653.pdf" rel="nofollow">http://www.unimasr.net/ums/upload/files/2012/Sep/UniMasr.com_919e27ecea47b46d74dd7e268097b653.pdf</a>. : the... | g8139 | [
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0.013696669600903988,
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... |
<p>In simple terms, why is beta negative decay more common than beta positive? </p>
<p>I know it's something to do with occuring inside/outside the nucleus - but I can't find a simple, easy to understand explanation!</p> | g8140 | [
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<p>Back in college I remember coming across a few books in the physics library by <a href="http://en.wikipedia.org/wiki/Mendel_Sachs" rel="nofollow">Mendel Sachs</a>. Examples are:</p>
<p><em>General Relativity and Matter</em></p>
<p><em>Quantum Mechanics and Gravity</em></p>
<p><em>Quantum Mechanics from General Re... | g8141 | [
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-0.01... |
<p>This is a relativity-paradox which I can't resolve:</p>
<p>The distance between interference lines in the double-slit experiment is:</p>
<p>$$\ w = z \lambda/d$$</p>
<p>Where:</p>
<p>w: Distance between fringes</p>
<p>z: Distance from slits to screen.</p>
<p>$\lambda$: Wave length of light</p>
<p>$d$: Distanc... | g8142 | [
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<p>I have to prove the (non abelian) gauge invariance of the following lagrangian (for a certain value of $\lambda$):
$$\mathcal L= -\frac14 F^{\mu\nu}_aF_{\mu\nu}^a + \frac{k}{4\pi}\epsilon^{\mu\nu\rho}\operatorname{tr}[A_{\rho}\partial_{\mu}A_{\nu} + \lambda A_{\mu}A_{\nu}A_{\rho}]$$
Is there an easier way than exp... | g8143 | [
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<p>As photons bounce around and finally find their way into our eyes, are they continually relinquishing the information of the previous thing they "bounced off of"? Is this the reason why we receive a coherent, continuous image and not a chronologically chaotic image of the past meshed with the present? </p> | g8144 | [
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<p>A ball is launched as a projectile with initial speed $v$ at an angle $\theta$ above the horizontal. Using conservation of energy, find the maximum height $h_\text{max}$ of the ball's flight.
Express your answer in terms of $v$, $g$, and $\theta$.</p>
<p>I am doing:</p>
<p>$$\begin{align*}
\frac{1}{2}mv^2 &= ... | g8145 | [
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<p>This might be a question purely of words and the meaning of them but isn't Newtonian physics more "relative" than Einstein's Special relativity? Newtonian physics predicts that laws of momentum & inertia behave the same at whatever speed you are traveling. Einstein said things change, and do more and more the cl... | g8146 | [
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<p>I have exactly 0 clue on how to start this problem, but I would be forever grateful for a hint in the right direction.</p>
<p>Given the operators $\hat x=x$ and $\hat p=-i\hbar \frac{d}{dx}$, prove the following relation:</p>
<p>$$
[\hat x, g(\hat p)]=i\hbar\frac{dg}{d\hat p}.
$$</p> | g8147 | [
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<p>I'm working on a project and I need help generating a strong magnetic field over an air gap with the lowest material weight that could be achieved. I have tried to use permanent magnets but its not effective so I need to know the best way to generate a strong fixed electromagnetic field with the lightest material.
... | g8148 | [
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<p>Why in the general case of classical field theory canonical stress-energy tensor doesn't have symmetry of the permutation of the indices? </p>
<p>For explanation, let's have a "derivation" of an expression for tensor by using symmetry of translations.</p>
<p>For translations we have
$$
x'^{\nu} = x^{\nu} + \omega^... | g8149 | [
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