question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I'm trying to code a simple physics simulator in C++ but I'm stuck on the air resistance issue.
Surfing the Internet I only find a drag coefficient for very basical area shapes when the air is perpendicular to the area.
However, even when simulating a falling parallelepiped, I found this not sufficient to describe ... | g16109 | [
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<p><img src="http://i.stack.imgur.com/wMTwy.png" alt="enter image description here"></p>
<p>I am trying to find the tension of the cable but I don't know what to do.</p> | g16110 | [
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<p>Here is an extract from some badly-written slides:</p>
<ul>
<li><p>A planet in an orbit with radius $R$ having a period $T$ falls through a distance of $R$ in a time $T/4$.</p></li>
<li><p>A planet has a speed of $R/T$ and an acceleration of $R/T^2$.</p></li>
<li><p>Comparing gravity on Earth $g$ with the moon $g_m... | g16111 | [
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<p>When a coil connected to an AC generator creates an EMF in another nearby coil (mutual inductance), is self inductance simultaneously occurring in both coils? </p> | g16112 | [
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<p>How do we measure a quantum particle properties? (length, mass and time)</p> | g16113 | [
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<p>I have saw this picture in wikipedia</p>
<p><img src="http://i.stack.imgur.com/ofR4p.jpg" alt="enter image description here"></p>
<p>and I begin to wonder why doesn't current space launches take consideration of avoiding space debris, as say you want to sent a robotic mission to mars, during the launching phase do... | g16114 | [
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<p>I have a fairly simple question about a normalisation factor. After normalising a wavefunction for a particle in an infinite square well on an interval $-L/2<x<L/2$ I got a quadratic equation for a normalisation factor $A_0$ which has a solution like this: </p>
<p>$$A_0 = - \frac{8\pi}{6} \pm \sqrt{\frac{8^2\... | g16115 | [
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<p>Atomic clocks use laser induced fluorescence in order to detect excited atoms, how does this work?</p>
<p>Apparently the clocks need to detect the states of nearly 100% of the atoms being examined. In an atomic fountain clock, a gas of Cesium atoms is excited and then a probe laser causes the altered atoms to fluor... | g16116 | [
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<p>I am working on a project to model heat transfer in a data center. I have basic models for a one dimensional heat transfer using conduction and convection. Such as, taking a server and modelling the temperature decrease over time and models taking distance into account based Fourier's equations. However I am now loo... | g16117 | [
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<p>I am currently trying to calculate apparent positions from raw JPL data.<br>
I've got it pretty much figured out, but there is one thing that's bugging me: Has the light time correction of the moon to be done heliocentric or geocentric?</p>
<p>Light time correction is needed because the speed of light is finite and... | g16118 | [
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<p>In an Amazon review of "Schaum's Outline of Lagrangian Dynamics" I found <a href="http://www.amazon.com/review/R1OP6ULYOYDI23/#R1OP6ULYOYDI23" rel="nofollow">this</a>:</p>
<blockquote>
<p><em>I recommend that you type <a href="http://www.google.com/search?as_q=&as_epq=lagrangian+dynamics" rel="nofollow">"Lagr... | g16119 | [
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<p>When I move an object that object should move me as well. I tried standing on a skateboard to reduce friction, and holding a heavy barbell, move myself away from it (while still holding it) but I haven't noticed any movements of a skateboard. Am I missing something here?</p> | g16120 | [
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<p>Does anyone know how AC magnetic fields behave in 'metallic' magnetic induction tomography (MIT). Do they form a magnetic circuit around a metallic specimen or penetrate through it, or both? This would be in respect of the skin effect limiting the penetration of the AC magnetic driving field (primary).</p>
<p>MIT w... | g16121 | [
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<p>I've been told to use the term <a href="http://en.wikipedia.org/wiki/Ampere">ampere</a> in exams and class (I'm in high school), instead of amp as it's not a valid unit, although I've been using the amp for years along with all of my friends who do electronics.</p>
<p>Is this technically invalid or acceptable as fa... | g16122 | [
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<p>If all the lights in a city, and the area surrounding it were shut off. How long would it take for the light pollution to clear, so the light from stars could be seen?</p> | g16123 | [
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<p>How can two clocks be synchronised with each other at some instant without being at the same place and same time $?$ considering that simultaneity is a relative concept .</p> | g16124 | [
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<p>Suppose there are two observers A & B, separated in space and one is moving towards the other. Their clocks were somehow synchronised at the beginning meaning they both started from $0$ or just started noting $\Delta t$. Now their clocks have same reading, now as soon as they both reach the same place in space-t... | g249 | [
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<p>Suppose there is a lever arm of length $L$, a mass $m$, and it is fixed at one end. The lever is parallel to the ground. So the force acting on the center of mass of the lever would be $mg$.</p>
<p>Now let's look at the moment when the lever is released. </p>
<p>Equating the equations for torque, we have $Fr=I \al... | g16125 | [
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<p>What's an atomic superstate/<a href="http://en.wikipedia.org/wiki/Quantum_superposition" rel="nofollow">superposition</a>, and how is it possible?</p>
<p>I understand the basics - being something can be moving and staying still at the same time; the observer changes the behaviour - but I'd like to know a little mor... | g16126 | [
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<p>The standard FRW metric with cosmic time is
$$ ds^2 = -dt^2 + a^2(t)(\gamma_{ij}dx^i dx^j),$$
and we can measure $t$ as the proper time for comoving observers. Thus it makes sense to talk about the age of the universe $t_0$ in terms of the coordinate $t$. </p>
<p>When using conformal time, the metric becomes
$$ds... | g16127 | [
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<p>I need to understand a step in the derivation of Lorentz Transformation.</p>
<p><img src="http://i.stack.imgur.com/9dtdK.jpg" alt="taken from thecuriousastronomer.wordpress.com"></p>
<p><img src="http://i.stack.imgur.com/uBQNm.png" alt="taken from thecuriousastronomer.wordpress.com"></p>
<p>I cannot understand ho... | g16128 | [
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<p>I'm reading <a href="http://arxiv.org/abs/0909.1038" rel="nofollow">S. Mathur's paper on the information paradox</a> and I can't seem to understand the reason why we choose spacelike slices. Is it because we want to have a global timelike vector so that we will be able to define the vacuum state "canonically"?</p>
... | g16129 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/12560/software-for-simulating-3d-newtonian-dynamics-of-simple-geometric-objects-with">Software for simulating 3D Newtonian dynamics of simple geometric objects (with force fields)</a> </p>
</blockquote>
... | g495 | [
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<p>There is quite foggy day today here, I cannot see end of the street. This made me think about how much worse can it be.</p>
<p>So here is my question: how thick a fog can be? What's the smallest visibility distance possible? </p>
<p>By visibility distance I mean how far I can see a black object against a white bac... | g16130 | [
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<p>Is supercritical CO$_2$ a <a href="http://en.wikipedia.org/wiki/Newtonian_fluid" rel="nofollow">newtonian fluid</a>?</p>
<p>I can't seem to find any articles describing the stress-strain relationship for <a href="http://en.wikipedia.org/wiki/Supercritical_carbon_dioxide" rel="nofollow">carbon-dioxide in a supercrit... | g16131 | [
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<p>We have an electron revolving in a the $n$th Bohr orbit of an atom of hydrogen. The problem is to prove that the circumference of the orbit is an integral multiple of wavelength of this electron $\lambda_e$. </p>
<p>$$2\pi r_n = k\lambda_e, \ k \in \mathbb{N}$$</p>
<p>where $r_n$ is the radius of the $n$th Bohr or... | g16132 | [
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<p>The action describing the edge theory of the Fractional Quantum Hall effect is
given by
\begin{equation}
S = \frac{1}{4\pi} \int \mathrm{d}x \ \mathrm{d}t \left[ K_{IJ} \ \partial_{t}\phi_{RI} \partial_{x}\phi_{RJ} - V_{IJ} \partial_{x}\phi_{RI}\partial_{x}\phi_{RJ} \right]
\end{equation}
for scalar fields $\phi_{... | g16133 | [
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<p>Moshe's recent questions on <a href="http://physics.stackexchange.com/questions/4068/formalizing-quantum-field-theory">formalizing quantum field theory</a> and <a href="http://physics.stackexchange.com/questions/4961/is-quantum-field-theory-defined-by-its-lattice-regularization">lattices as a definition of field the... | g16134 | [
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<p>I have only basic knowledge of physics.
Could you please explain to me if a "Quantum" laws can theoretically (perhaps in the future?) be used to explain everything in macro levels? </p>
<p>I'm having problems to understand how we can have "two physics" at the same time.
are Newton's laws only a simplification?</p> | g141 | [
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<p>I was watching the documentary Carl Sagan did about gravity (I believe it's quite old though) and wondered about space being "flat" and that mass creates dents in this plane as shown at about 3 minutes in this clip (<a href="http://www.youtube.com/watch?v=Y-db4iC0aHw" rel="nofollow">http://www.youtube.com/watch?v=Y-... | g16135 | [
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<p>As a follow up to <a href="http://physics.stackexchange.com/questions/37823/why-cant-light-pass-through-walls-but-sound-can">this question</a>, Could we <em>really</em> compute the magnitude of the stress caused by sound waves on a wall? If so, How do we do that?</p> | g16136 | [
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0.02998482808470726,
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-0.011542601510882378,
-0.045210354030132294,
0.031844645738601685,
0.012717729434370995,
0.019762... |
<p>Imagine a linear decrease in concentration from left to right. Using Fick's first law,</p>
<p>$J = -D \frac{d \psi}{d x}$</p>
<p>for all x, from left to right, we have the same flux amount because the decrease is linear. </p>
<p>So $J(x) = m$</p>
<p>According to Fick's second law,</p>
<p>$\frac{d \psi}{d t} = -... | g16137 | [
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0.06562234461307526,
0.04671... |
<p>With the form $y(x,t)=A\sin(kx-\omega t+\phi_0)$, there are two variables, How do I find the velocity? I don't know I can apply derivative with two variables.</p> | g16138 | [
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<p>If an isolated system goes from a state A to B, will it always eventually fluctuate back to state A? If not, give an simple example. Is it right to say that entropy only says that the probability for reversal is very low, but not actually 0, ie that it will take a very long time for some processes to reverse thems... | g16139 | [
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<p>I would be glad if someone can help me understand the argument in appendix B.1 and B.2 (page 76 to 80) of <a href="http://arxiv.org/abs/hep-th/0310285" rel="nofollow">this paper</a>. </p>
<p>The argument in B.1 supposedly helps understand how the authors in that paper got from equation 3.6 to 3.8 on page 18 of the ... | g16140 | [
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0.020... |
<p>A jar is filled with two types of balls, red and green. Red balls have radius $r_1$ and mass $m_1$, green balls have radius $r_2$ and mass $m_2$.</p>
<p>If initially the balls are randomly placed throughout the jar, and we are to shake this jar, generally one type of balls will tend to gather at the top. Why does t... | g16141 | [
-0.01642901450395584,
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0.0017271109391003847,
... |
<p>I have a particle at rest. At $t = 0$ a periodic force like $F_0 \sin\omega t$ starts acting on my particle. Can such a force transport my particle to infinity when $t \to \infty$? Please answer this question without solving the mechanical problem, just by intuition.</p> | g16142 | [
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... |
<p>I was reading some questions on your site about using a Trebuchet to launch a payload into space.
Would it be possible to use the same sort of principle, but to have, say a 100 mile steel cable attached to the earth, or tower, on the other end have a rocket launching straight up, and use the rotation of the earth to... | g16143 | [
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0.0070571694523096085,
0.021047351881861687,
... |
<p>Maxwell's equations on a pseudo-Riemannian manifold $(M,g_{ab})$ say,</p>
<p>$$d_a F_{bc} = \nabla_{[a}F_{bc]} = 0,$$</p>
<p>$$\nabla_a F^{ab} = J^b,$$</p>
<p>where $d_a$ is the exterior derivative, $\nabla_a$ is the covariant derivative compatible with $g_{ab}$ (i.e. $\nabla_a g_{bc}=0$), and $F_{ab}$ is antisym... | g16144 | [
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<p>We all know about the <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/invsqs.html" rel="nofollow">inverse square law of sound</a>. In short the power of the wave will get evenly spread on an ever increasing spherical expansion and this will dissipate the power of the wave at a rate of inverse squared to... | g16145 | [
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0.0215346124023... |
<p>M = black hole mass
Gravitation is about 1/r^2
Schwarzschild radius r is ~ to M</p>
<p>Greater BH -> weaker gravitation on its horizon.
Lets take black hole so enormous that the gravitation on its horizon is negligible.</p>
<p>Person A is 1 meter 'outside' the horizon, person B is inside (1 meter from the horiz... | g16146 | [
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<p>I would like to know if there are any theoretical results on the distribution of the eigenvalues of <a href="http://en.wikipedia.org/wiki/Hankel_matrix" rel="nofollow">Hankel matrices</a>. I seek a result like the <a href="http://en.wikipedia.org/wiki/Marchenko%E2%80%93Pastur_distribution" rel="nofollow">Marchenko–P... | g16147 | [
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<p>For an $N$-degree-of-freedom system to be integrable, the usual definition imposes the existence of $N$ independent conserved quantities, which must be in involution to each other, i.e., </p>
<p>$$\{ F_i, F_j \} ~=~ 0\tag{1}$$</p>
<p>Why this extra condition? Why is </p>
<p>$$\{ H, F_i \}~=~0 \tag{2} $$</p>
<p>i... | g16148 | [
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<p>as far as i know the range of an obliquely projected body which is projected with a velocity of <strong>u</strong> with some angle $\theta$ with the horizontal under the action of gravity is
R=$u^2sin2\theta$/g by which we can calculate the range of projected body when it comes to the same level of the point of proj... | g16149 | [
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<p>When a plastic bag is crushed in air it makes noise. But when immersed in water and then crushed we hear very little noise. Why is it so?</p>
<p>Even if I go inside water, I do not hear the noise the same as I hear in the air.</p> | g16150 | [
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<p>An observer is anything that can cause a wave function to collapse. That is an interpretation of wave function collapse (usually referred to as <strong>the measurement problem</strong>). Now, </p>
<ol>
<li><p>when can photons be trapped in a cavity and manipulated? </p></li>
<li><p><a href="http://easteinstein.wor... | g16151 | [
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<p>For a spin of $\frac{1}{2}$ the angular momentum operator can be written as $\vec{S} = \frac{\hbar}{2} \vec{\sigma}$ in matrix form. Find the eigenvalues and eigenvectors of $S_x$ where
$\sigma_x = \begin{pmatrix} 0 & 1 \\ 1 & 0 \\\end{pmatrix}$</p>
<p><strong>Attempt:</strong></p>
<ul>
<li><em><strong>Fin... | g16152 | [
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<p>The trace of matrix is always sum of its eigen values , which can be seen if $\hat{U}$ transforms the matrix $\alpha_i$ into it's diagonal form .
$$ \begin{pmatrix}
A_1 & 0 & \cdots & 0 \\
0 & A_2 & \cdots & 0 \\
\vdots & \vdots & \ddots & \vdots \\
0 & 0 & \cdot... | g16153 | [
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0.004622453358024359,
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0.01... |
<p>Potential gradient is the negative of the electric field. Does the <em>negative</em> (here) means that its direction is opposite to electric field.? </p>
<p>If it does mean this, How is the direction of the potential gradient <em>opposite</em> to that of electric field..? Explanations would be helpful...</p> | g16154 | [
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<p>I'm to work out the internal forces in a truss, but I can't get my head around the geometry of the truss itself. I'm starting to think there may have been information on the diagram which I missed. Could I get some directions on how to find x? </p>
<p><img src="http://i.imgur.com/aesgDl.png" alt=""></p> | g16155 | [
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<p>If some kind of source was able to supply an infinite amount of energy, does that imply that it also must have an infinite mass? Is the contrary also true?</p> | g16156 | [
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<p>Why is the value of Hall conductance directly proportional to the number of edge channels in the sample?</p> | g16157 | [
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<p>are metals shiny because of the electron sea which surrounds the atomic lattice of the metal sample.
are metals more shiny because the electron are more evenly distributed on the surface?</p> | g16158 | [
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<p>For homework I have the following question, but I am stuck on finding the torque on the cylinder.</p>
<p>An infinite cylinder of radius $R$ carries a uniform surface charge $\sigma$. We start rotating the cylinder to a final rotating speed of $\omega_{f}$. How much work will this take per unit length? Do it in the ... | g16159 | [
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<p>Suppose you have a 120 volt, 20 amp circuit which only has a light bulb connected. When measuring the voltage going to the light bulb my meter reads 120 volts. The basics taught me that a circuit is a circle, so the back and forth movement of electrons continues after the light bulb along the neutral wire back to ... | g16160 | [
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<p>Why time is considered to be a dimension? And the other 7 (except the 3 dimensions of space, and the dimension of time) dimensions that string theory suggests, why can't they be realized?</p> | g16161 | [
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<p><img src="http://i.stack.imgur.com/vsPmJ.png" alt="enter image description here"></p>
<p>What should be the value of Q?</p>
<p>I am doing the basics of coulomb's law,can anyone explain this to me?</p> | g16162 | [
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<p>Imagine I am standing on Earth, and pushing a tennis ball away from me. The ball moves. If it is very heavy, I will move back instead of the ball. Now consider the same scenario in outer space, where both the ball and I are hanging without any third body to support/assert gravity on us. What happens in this case? Wi... | g16163 | [
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<p>These are purely mathematical questions in some sense but I believe this is relevant in string theory as the title says.</p>
<p>I wonder if it is possible to perform <a href="http://en.wikipedia.org/wiki/T-duality" rel="nofollow">T-duality</a> of <a href="http://en.wikipedia.org/wiki/Taub%E2%80%93NUT_space" rel="no... | g16164 | [
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<p>I know that an electron or any other particle for that matter, has a measured spin which is either up or down. This spin is along the z-axis. But what if we do not measure it along the z-axis and do it along the x-axis instead. What will the result be?</p>
<p>Will it get deflected along the x-axis in a Stern Gerlac... | g16165 | [
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<p>What does "accessibility" mean in statistical mechanics?</p>
<p>Is it an equivalent concept to accessibility in mathematical control theory?</p>
<p>I'll provide an example:
When two systems A and B interact on a subspace of their respective spaces, i.e. where they overlap in space, does accessibility of states of... | g16166 | [
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<p>The Ising model with vanishing external field possesses the $Z_2$ symmetry:</p>
<p>$$\sigma_i \rightarrow - \sigma_i$$</p>
<p>implying that the 1 pt function vanishes:</p>
<p>$$<\sigma_i> \;= 0$$</p>
<p>In the same way, shouldn't all the n point functions vanish for n odd?</p>
<p>But at its critical point... | g16167 | [
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<p>I am trying to self-study string theory, beginning with Ibanez and Uranga (String Theory and Particle Physics). Unfortunately, the book contains no problems, so I'm not sure whether I am fully understanding the material.</p>
<p>Are there any pedagogical string theory problem sets, for a beginner, preferably with so... | g16168 | [
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<p><code>Question:</code></p>
<blockquote>
<p>Two identical, non-interacting spin-$1/2$ particles are in a 1D Harmonic Oscillator Potential. Their Hamiltonian is given by </p>
<p>$$H=\frac{p_{1x}^2}{2m}+\frac{1}{2}m\omega^2 x_1^2+\frac{p^2_{2x}}{2m}+\frac{1}{2}m\omega^2x_2^2
$$</p>
<p>What is the ground st... | g16169 | [
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<p>I've been looking into Feynman Diagram for quite some time, and the fact that anti-particles point backwards in time after an interaction has been puzzling me. I understand this to be some convention regarding charges and conservation, yet I wish to know what does this all mean. Does the fact that the pair of partic... | g16170 | [
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<p>Assuming there is a time varying magnetic field (B), how to determine the direction of the induced electric field due to B. and to which parameters does it depend?</p>
<p>P.S. determining the electric field in an arbitrary point in space such as P</p> | g16171 | [
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<p>Say I was trying to design padding to absorb impacts using polymers or similar materials, such as rubber. I have a good understanding of any relevant physics, most likely, but I wouldn't know where to start in calculating the degree of impact that can be absorbed by a material as a function of the dimensions, densit... | g16172 | [
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<p>Let me split the question in a few parts, </p>
<ul>
<li><p>Can someone give me a reference which explains the CFT properties of the critical $O(N)$ model in $2+1$? Like how are the CFT correlators (in a $1/N$ expansion?) and the central charge in that calculated? </p></li>
<li><p>I guess that by "light" operators o... | g16173 | [
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0.002825124654918909,
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<p>In string theory, it's possible to collide a number of strings only in the asymptotic past, and get a final asymptotic state which contains a D0-brane, an anti D0-brane, and a number of strings. If space is compactified, the D0-brane can be replaced by some wrapped D-brane particle, or a stable bound state of a numb... | g16174 | [
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<p>Quantum mechanics: Suppose that there is a particle with orbital angular momentum $|L|$. But the particle also has spin quantity $|S|$. The question is, how do I reflect this into Schrodinger equation? I do know how Schrodinger equation becomes for each case - when a particle has particular orbital angular momentum ... | g16175 | [
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<p>Except when a particle is spin-0, field of all particles transforms when frame of reference is changed, and this defines what spin is. The question is, specifically how does the quantum field transform in the corresponding equation, and how does this relate to the quantity of spin? I want to see how this works mathe... | g16176 | [
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<p>I'm looking at the spin representation of the orthogonal algebra $so(2m,C)$.
This representation is $2^m$ dimensional and an explicit construction with gamma matrices
is well known (see for example <a href="http://hitoshi.berkeley.edu/230A/clifford.pdf" rel="nofollow">http://hitoshi.berkeley.edu/230A/clifford.pdf</a... | g16177 | [
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<p>from hand book of optical constant of soild, i can know the different reflective of gold in different wavelength of light. but when u wanna set a drude model in CST, it also needs the eps infinity to modify the model..
the equation is shown below
ε=ε(∞)−ω2pω2+iγω.
How do I get the value of ϵ(∞) for gold? Is there an... | g16178 | [
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<p>I've seen some treatments in the scientific popular press (podcasts) that consider the possibility that dark matter can be explained by an error (or new term) in our understanding of gravitation & mechanics. I don't see anyone (in the podcasts) considering whether our understanding of "emission" or blackbody ra... | g16179 | [
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<p>How are they formed? And why are they so bright?</p> | g16180 | [
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0.... |
<p>I mean to ask why there is $4\pi$ present in force equations governing electricity? Though all objects in universe are not spherical and circular, the constant of proportionality in both equations contain $4\pi$. Why?</p> | g254 | [
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<p>For the Stern-Gerlach experiment done in 1922:</p>
<ol>
<li>Why were silver atoms used?</li>
<li>Silver atoms contain many electrons in different shells (with different angular momemtum quantum numbers. Why are those not affected by the magnetic field like the $5s$ electron?</li>
</ol> | g16181 | [
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<p>I am a chemical/biological scientist by trade and wish to understand how quantum EM phenomena translates to our more recognizable classical world.
In particular I want to get a mechanistic picture of what is going on when a tuned antenna is interacting with a photon of the desired frequency? I believe an individual... | g16182 | [
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<p>i'm not doing anything related to physics, but i'm just curious : What really happen when i short circuit an alkaline battery ? some article in the net shown that fire/explosion can be happened when short circuit the battery. How can this happen? coz i got some article said that there is an 'internal' resistance of ... | g16183 | [
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<p>I was reading Brian Greene's "Hidden Reality" and came to the part about Hawking Radiation. Quantum jitters that occur near the event horizon of a black hole, which create both positive-energy particles and negative-energy particles, produce the so-called Hawking radiation. However, I do not understand why only the ... | g570 | [
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<p>gravitational waves are strictly transversal (in the linear regime at least), also their amplitudes are tiny even for cosmic scale events like supernovas or binary black holes (at least far away, maybe we should ask some physicists located a bit closer to the center of the galaxy), but lets put all those facts aside... | g16184 | [
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... |
<p>Is it possible to transfer electricity from one place to another without the help of physical wires.</p> | g16185 | [
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<p>I was reading the Feynman lectures in physics and after thinking about it for a while it seems particularly unreasonable to talk about hidden variables. Let us say that the electron has some internal variables as yet unknown which determine its trajectory given a set of initial conditions just like in classical mech... | g947 | [
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<p>How do we calculate the effective mass of an electron in an Aluminium lattice? Is there any simple analytical way to work it out?</p> | g16186 | [
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<p>As pointed out before, it orginated inside the reactor vessel but exploded outside: how did it get there? Did it pass the shell by diffusion or was it released by the engineers?</p> | g16187 | [
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<p>Let say we have the classical hamiltonian of a harmonic oscillator: $$H=\frac{p_x^2+p_y^2+p_z^2}{2m}+\frac{k_1x^2+k_2y^2+k_3z^2}{2}$$
and we want to find the hamiltonian operator in quantum mechanics, we use the transformations $x\rightarrow x$, $y\rightarrow y$, $z\rightarrow z$, $p_x\rightarrow -i\hbar\frac{\parti... | g16188 | [
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<p>This might be stupid, but is gravity a form of energy? And, if so, couldn't we use it for power?</p> | g16189 | [
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<p>Suppose we want to calculate vacuum expectation
$$
\tag 1 D_{lm}(x - y) = \langle \Omega | \hat {T}\left( \hat {\Psi}_{l}(x)\hat {\Psi}_{m}^{\dagger}(y)\right)| \Omega\rangle = \langle \Omega| \hat {T}\left( \hat {\Psi}_{l}(x)\hat {\Psi}_{m}^{\dagger}(y)\right)| \Omega\rangle ,
$$
where $\hat {\Psi}_{a}(x)$ refers... | g16190 | [
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0.0... |
<p>If I switch on my electronic kitchen scale while it's on the table, it reads 0 grams. If I pick it up, it reads around -500 grams. Conversely if I switch it on in my hand it tares to 0g and then reads about 500 grams when I put it down.</p>
<p>What's the difference, physically, between resting on my (not moving) ha... | g16191 | [
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<p>We know that proton is positive, and electron is negative. But where does come notion of negativity and positivity? Does charge come from some specific particles, or they specific order?</p> | g189 | [
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<p>A hydrogen nucleus consists of a single proton.
A 2-hydrogen (deuterium) nucleus consists of a proton and a neutron.
A tritium nucleus consists of a proton and two neutrons.</p>
<p>This makes me wonder how an atomic nucleus made of a proton and a "minus one neutron" would look like, and the closest thing to a "minu... | g16192 | [
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<p>I'm just starting with magnetism and stuff and I was reading about different types of magnetism. Such as ferromagnetism, anti-ferromagnetism and paramagnetism. If I understand it correctly, examples of ferromagnetic elements are Iron, Cobalt and Nickel. They are permanent magnets (if the crystal structure is correct... | g16193 | [
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<p>I'm not really interested in the actual number of times, but rather an explanation of a closed Universe. How do we still measure the background radiation of the Big Bang? Those electromagnetic waves should have all passed this point in space a long time ago. Unless the Universe is closed and those Electromagnetic... | g16194 | [
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0.07670... |
<p><strong>Background:</strong> I was recently reading a book on the planets to my son and I noticed a pattern in the distributions of the planets. The planets' distances roughly follow an exponential distribution.</p>
<p>Below is a plot of scaled, log orbital distances
$$
\tilde{d_n} = \frac{\log(d_n/d_1)}{\log(d_2... | g729 | [
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<p><em>I have several questions. Perhaps it would be better to separate them into different posts. However, given their relative closeness to each other, I think putting it all in one place would be better. On suggestion, I will modify this post.</em></p>
<p>I am reading Penrose's paper on the conformal treatment of i... | g16195 | [
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<p>For example, if you were to go out into deep space, and just slow down and stop your rocket. Everything inside the rocket that's not strapped in, starts floating. Why is that if every object has mass and thus attracts everything else. If a book was accelerated to the center of mass of the whole rocket + everything i... | g16196 | [
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0.05848583... |
<p>Here's a thought experiment that I came up with a while ago. It might be hard to visualize, so I'll describe it as best I can.</p>
<p>Take a rocket in a vacuum, in outer space. Attach a large "box" to the end, so that the exhaust gases from the nozzle will shoot straight into it/ Let's make the box large. Really la... | g16197 | [
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0.... |
<p>If you haven't seen the video of the FlyBoard, please have a look: <a href="http://www.youtube.com/watch?v=Cd6C1vIyQ3w&feature=youtube_gdata_player" rel="nofollow">http://www.youtube.com/watch?v=Cd6C1vIyQ3w&feature=youtube_gdata_player</a></p>
<p>Yes, it's amazing, but do the physics make sense or is this a... | g16198 | [
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<p>Radio signals are being transmitted in a frequency of $ 8.4 \times 10^9 s^{-1} $ and being received by an antenne that is capable of receiveing power of $ 4 \times 10^{-21} watt $ ($ 1 watt = 1 J s^{-1} $ ) . </p>
<p>Estimate that number of photons per second of this electromagnetic radiation that this antenne is c... | g16199 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Partition_function_%28statistical_mechanics%29">partition function</a> plays a central role in statistical mechanics.</p>
<p>But why is it called ''partition function''?</p> | g16200 | [
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