question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Reading about cloud formation, I learned that to a droplet to form, the water vapour needs a <a href="http://en.wikipedia.org/wiki/Cloud_condensation_nuclei" rel="nofollow">Cloud Condensation Nuclei</a>, which is an aerosol with a size in the order of 0.0001mm. And if no CCN is found temperatures as low as -13°C are... | g10286 | [
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<p>From what I understand the expansion of the universe has no "center". If we're flying through space away from the "center of the big bang", there's basically no way to tell. Every two given points in space gets farther away from each other, and we can pick any point as center if we like.</p>
<p>I also understand th... | g10287 | [
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<p>Could someone help explain the uses of AC <a href="http://en.wikipedia.org/wiki/Electromagnet" rel="nofollow">electromagnets</a>. Wherever I look it says that DC electromagnets create stronger magnetic fields. I understand why AC electromagnets could be used in transformers but why use them in motors for example? Po... | g10288 | [
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<p>This question came to me when I realized how the linear speed varies while listening to a Vinyl LP.</p>
<p>The linear speed variation has to be compensated with a variation in the resolution of the grooves, that is, since the linear speed decreases, the groove resolution also has to decrease in some measure. What i... | g10289 | [
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<p>I <a href="http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1431&context=ecetr" rel="nofollow">read</a> a statement saying that the inner product between divergence-free current and a gradient field is zero.</p>
<p>Divergence-free surface current is $\nabla\cdot\vec{J}=0$, and $\vec{J}$ could be represent... | g10290 | [
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<p>I read in a physics today paper,</p>
<p>The electron can have nonvanishing EDM only if nature violates symmetry under time reversal (T) and under the combined operations of charge conjugation (C), which replaces particle by antiparticle (as we all know), and parity inversion (P).</p>
<p>I checked <a href="http://p... | g329 | [
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<p>Our eyes contain 3 photoreceptor cells (cones) to perceive three wavelength ranges of light. Here is a visual representation of the wavelengths by these receptors (S, M and L).</p>
<p><img src="http://i.stack.imgur.com/5olj4.png" alt="Wavelength per photoreceptor"></p>
<p>So if we have light of 440 nm, it results ... | g10291 | [
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<p>Is the construction of an etalon / <a href="http://en.wikipedia.org/wiki/Fabry%E2%80%93P%C3%A9rot_interferometer">Fabry-Pérot interferometer</a> within the reach of amateur telescope makers? Are there any resources pointing to such projects?</p> | g10292 | [
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<p>What do these units mean: the large velocity widths of emission lines (in AGN) are 2,000 - 10,000 km s^-1? I've looked for the answer but keep getting swamped in myriads of details. I want to know what the term <em>velocity</em> means in <em>large velocity widths</em> and also why <em>km s^-1</em>. Thanks</p> | g10293 | [
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<p>I would like to know if acceleration is an absolute quantity, and if so why?</p> | g10294 | [
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<p>Astronomers estimate that there are between 200 billion to 400 billion stars contained within the Milky Way and Andromeda Galaxy probably has 1 trillion stars. There may be around 500 billion galaxies in the observable universe. </p>
<p>So, my question is, statistically speaking because of the number of stars, ther... | g10295 | [
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<p>It is generally believed that $10^{-35}$ seconds after the Big Bang, the symmetry of a GUT was broken and after $10^{-12}$ seconds the electroweak force was broken:</p>
<p>\begin{equation}
\mathrm{SU(2)} \times \mathrm{U(1)} \rightarrow \mathrm{U(1)}
\end{equation}</p>
<p>This symmetry breaking is a result of the ... | g10296 | [
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<p>Diffraction theory is scalar. How you deal with beam propagation in fourier optics that is sensitive to the to the polarization?</p>
<p>If I have linearly polarized gaussian beam incident on glass surface, how is the polarization included in the propagation code/theory ?</p>
<p>What I am ultimately interested is t... | g10297 | [
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<p>I know that if some object acquires potential energy, it also gains mass- is it the same for kinetic energy?</p> | g10298 | [
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<p>I am trying to get the definition of capacitance nailed down. This is my work so far:
$$
\frac{\mathrm{d}U}{\mathrm{d}t} = \frac{\mathrm{d}}{\mathrm{d}t} \int_{\Omega_a}{ u(\mathbf{x},t)\mathrm{d}t} = \int_{\Omega_a}{ \partial_t u(\mathbf{x},t)\mathrm{d}t} = -\int_{\Omega_a}{ \mu_0^{-1}\nabla\cdot[\mathbf{E}\times\m... | g10299 | [
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<p>Suppose I place a gyroscope in a theoretically perfectly quiescent, closed room. Let its output be given as a vector ${\bf v} = (v_x, v_y, v_z)$ indicating rate of rotation around three orthogonal axes, where the $x$-axis points towards true north and the $z$-axis points vertically. Given the data, how could I calcu... | g10300 | [
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<p>Neutrinos travel straight through earth at the speed of light. Therefore, it seems that they could be great for intercontinental communication. Of course, I assume a lot still needs to be learned about detecting, producing and controlling neutrinos before they can be used for the practical purpose of communication.<... | g10301 | [
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<p><a href="http://en.wikipedia.org/wiki/AdS/CFT_correspondence">AdS/CFT</a> seems like a really hot topic and I'd like to start reading about. I am looking for the best introduction at my level, i.e. I have a background in QFT, CFT and general relativity at the level of a master student in theoretical physics. What wo... | g555 | [
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<p>In the weak interaction limit, behaviors of electrons can still be described by a 1-partitcle equation with a modified mass, where the change in mass can be understood as effects of other neighboring electrons as a single electron drags along. Since the cluster of electrons couples to gravity as usual, then the effe... | g10302 | [
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<p>I'm having real problems trying to solve the following:</p>
<p>"The particle is moving in the plane. The trajectory is given by $y=cx-bx^2$, where $c$ and $b$ are positive constants. The acceleration of the particle is always constant and given by $\underline{a}=-\underline{j}$. Find the speed of the particle at th... | g10303 | [
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<p>So here's the statement:</p>
<p>A pulley of a mass $M$ is hanged using a spring (stiffness of the string being $k_1$), as shown in the image. What is the frequency of the pulley's oscillation?</p>
<p><img src="http://oi43.tinypic.com/255lxf5.jpg" width="300" height="360"/></p>
<p>So that's as far as I could get:<... | g10304 | [
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<p>In my introductory physics class, $V$ is the symbol for electric potential (joules per coulomb) and $U$ is the symbol for electric potential energy (joules). </p>
<p>Since the Schrodinger equation is the sum of Kinetic and Potential energies in the system, $V(r)$ must represent $U$... if so, is there any particula... | g10305 | [
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<p>Every possible reaction in chemistry is to attain stability. In physics, the alignment of an electric dipole in an external electric field and in all other physical systems (at least those I study in high school) attains stability at the lowest energy state. But, why is it so? </p> | g10306 | [
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<p>I need a good and simple reference for studying about ADM mass. Can someone introduce me one?</p> | g330 | [
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<p>I know this is probably an easy question, but it's been a while since I've studied physics and I've started reading some circuit analysis textbooks.</p>
<p>I'm finding hard to understand the relationship between between the verbal definition of quantites and the mathematical definitions. For instance, in the Sadik... | g10307 | [
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<p>We have the formula for the Lorentz force $$\textbf{F} = q \space(\textbf{E} + \textbf{v} \times \textbf {B})$$</p>
<p>This is a simple formula you learn in high school, but I'm interested to self-study electromagnetism and I found out a different notation for this formula:</p>
<p>$$ \textbf{F}(\textbf{r}, \dot{\t... | g10308 | [
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<p>I'm not really sure if this is the place to ask this, but anyway here is my question:</p>
<p>Let's say I have the Kepler orbital elements of the ISS, for example, (<a href="http://www.spaceflight.nasa.gov/realdata/sightings/SSapplications/Post/JavaSSOP/orbit/ISS/SVPOST.html" rel="nofollow">NASA stuff</a>). Now I wa... | g10309 | [
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<p>I cannot seem to find any peer-reviewed (or other) reference to an integer-spin Stern-Gerlach experiment. It shouldn't be too hard to do: just find you friendly neighbourhood Deuterium ion and shoot it through a Stern-Gerlach magnet.</p>
<p>Can one devise a photonic Stern-Gerlach experiment, i.e. spatial seperation... | g10310 | [
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<p>I have four questions about black holes and universe formations.</p>
<ol>
<li><p>Do new universes form on the other side of black holes?</p></li>
<li><p>Was our own universe formed by this process?</p></li>
<li><p>Was our big bang a black hole seen from the other side?</p></li>
<li><p>Are there solid reasons why th... | g10311 | [
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<p>I am trying to show the invariance of the following Yang Mills Lagrangian:
$$L= -\frac{1}{4} F^a_{\mu \nu} F_a^{\mu\nu} + J_a^\mu A_\mu^a$$
under the following gauge transformation ($\theta$ being a rotation in color space and $g$ related to the structure constant):
$$L \rightarrow -\frac{1}{4} \left( F^a_{\mu\nu} +... | g10312 | [
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<p>If an air cylinder is pushing two platens apart with a force of $100\: \mathrm{lbs}$, do the platens need to push back at $100\: \mathrm{lbs}$ or $50\: \mathrm{lbs}$ each to keep the cylinder from moving? Assume no friction and both platens are not fixed.</p> | g10313 | [
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<p>If time is treated as a fourth dimension of spacetime, what is relation between length and time units?</p>
<p>Or in other words, how can I convert time units to length units, for instance seconds to meters?</p> | g10314 | [
0.04143262282013893,
0.007606495637446642,
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-0.0548880361020565,
0.00748436851426959,
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0.018992263823747635,
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0.... |
<p>In <a href="http://profmattstrassler.com/2012/10/15/why-the-higgs-and-gravity-are-unrelated/#comment-22975" rel="nofollow">this comment in a blog</a> kudzu computes the energy of a marshmallow with mass $M=25 grams$ by using $E=mc^2$:</p>
<p>$E=Mc^2 = 2.247\times 10^{+15} Joules$</p>
<p>I may be wrong but this see... | g10315 | [
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0.008373413234949112,
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0.026666909456253052,
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0.... |
<p>I was looking through my bathroom window this night and I was wondering if any of the photons my retina is hit with are from 13 (40) billion light years away ?!</p>
<p>I was looking through it a few seconds, was that too less of a time?</p>
<p>Do I need a Hubble for this?</p> | g331 | [
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0.0359337143599987,
0.00007424302748404443,
-0.04045739769935608,
-0.00... |
<p>Why is one-point Green's function for scalar field equal to zero? Can one prove it using path integral formalism? </p> | g10316 | [
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<p>In inelastic collisions, the kinetic energy of the system is not conserved but the momentum is. </p>
<p>Kinetic energy is: $0.5 \times \text{mass} \times \text{velocity}^2$. Momentum is: $\text{mass}\times\text{velocity}$. </p>
<p>I think that, considering that mass is constant:</p>
<ul>
<li><p>if Ke must be diff... | g10317 | [
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... |
<p>I'm an undergraduate student in Chemistry currently studying quantum mechanics and I have a problem with unitary transformations.
Here in my book, it is stated that </p>
<blockquote>
<p>Every unitary operator $\hat{\mathcal{U}}$ can be written in an exponential form as follows:
$$\mathrm{e}^{-i\alpha\hat{\math... | g10318 | [
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0.0... |
<p>I have been trying to understand the difference between the Work function of a metal and the Local Work Function. </p>
<p>I did some experiments to find the Local Work function of Graphite using an STM and found values ~0.3-0.7 eV. However, the work function of Graphite is ~4eV. Literature values indicate that my e... | g10319 | [
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<p><strong>Motivation:</strong></p>
<p>I'm working with a highly non-linear spherical wave-like equation (second order PDE). The equation can be written on the form</p>
<p>$$\ddot{u} = f(t, \dot{u},\dot{u}',u',u'')$$</p>
<p>where $'=\frac{d}{dr}$ and $\dot{} =\frac{d}{dt}$. (The expression for the function $f$ is lo... | g10320 | [
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<p>Can we have elctromagnetic waves which are characterized by parallel electric and magnetic field $\vec{E} || \vec{B}$ ? I am not talking here about free space, but maybe some kind of materials or waveguides or something else.</p> | g10321 | [
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<p>Please forgive a string theory novice asking a basic question.</p>
<p>Over at <a href="http://physics.stackexchange.com/questions/70821/the-problem-of-a-relativistic-path-integral">this question</a> Luboš Motl gave an excellent answer, but he made a side comment that I've heard before and really would want to know ... | g10322 | [
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<p>We know that universe is expanding and galaxies are moving away from each other. Does this mean the galaxies are also expanding in itself and therefore I guess growing larger in volume? Depending on the answer of that, does the solar system also expands? </p> | g56 | [
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<p>I don't know quantum mechanical model. So, I'm referring to just bohr's model of atom.</p>
<p>Any atom emits energy when it makes transition from higher excited state to lower excited state. Now, some times they say that this energy is light energy and some times heat energy. </p>
<p>I'm confused. What decides the... | g10323 | [
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<ol>
<li><p>Consider a charged particle (electron or proton) at rest. It is surrounded by its own electric field.</p></li>
<li><p>Now consider an electron moving with certain velocity (less than speed of light), Still is there electric field around it?</p>
<p>i. If it has electric field around it, why is it that when ... | g10324 | [
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0.0... |
<p>I read that:</p>
<p>If you take a rough surface and make it smooth, the coefficient of friction decreases. But if you make it <strong>super</strong> smooth, then the coefficient of friction increases. How come?</p> | g10325 | [
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<p>I am working on a project involving a simulation of the motion of a projectile (in 3D) aimed at a moving target. The way projectile motion is analyzed in most introductory physics books is not accurate enough for this project. I would like to know what other influences on the motion of a projectile, including air re... | g10326 | [
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0.03339280188083649,
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0.07420754432678223,
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<p>Is there a definition of a <a href="http://en.wikipedia.org/wiki/Black_hole" rel="nofollow">black hole</a> in a generic spacetime? In some books, for example Wald's, black holes are defined for asymptotically flat spacetime with strong asymptotic predictability, although the definition makes sense without the second... | g10327 | [
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0.0497257336974144,
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0.05816344916820526,
0.025... |
<p>I read some methods but they're not accurate. They use the Archimedes principle and they assume uniform body density which of course is far from true. Others are silly like this one:</p>
<p><em>Take a knife then remove your head.<br/>
Place it on some scale<br/>
Take the reading<br/>
re-attach your head.</em></p>
... | g10328 | [
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0.06664754450321198,
0.00689741550013423,
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0.0680680125951767,
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<p>Just what the title states.
What is the reason that a Nuclear reactor has a characteristic dome/bell shape?</p> | g10329 | [
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<blockquote>
<p>An open container is being filled with water from the top at a constant volumetric flow rate $300 \frac{cm^3}{s} $. At the same time, water is leaving the container trough a circular whole at the bottom, whose surface area is $0.6 cm^2$. What is the water level in a stationary state. </p>
</blockquot... | g10330 | [
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0.03294561430811882,
0.00915620755404234,
0... |
<p>Surface tension appears at the interface of two immiscible fluids if the cohesive force of attraction is more than adhesive force. What will be the physical effect if the <em>adhesive</em> force is more than <em>cohesive</em> force?</p> | g10331 | [
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<p>I'm working to craft a space-horror themed <a href="http://en.wikipedia.org/wiki/Role-playing_game" rel="nofollow">RPG</a> a la Dungeons & Dragons and I've run into a situation I can't resolve on my own.</p>
<p>At what rate is atmosphere lost to space through various sized apertures? I'm looking generally at th... | g10332 | [
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0.031852319836616516,
0.020661501213908195,
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<p>I'm solving an exercise about the Lagrange-Euler equations, that states the following:</p>
<blockquote>
<p><em>Let $\gamma (t) = \{ (t,q) : q = q(t), t_0 \leq t \leq t_1\}$ be a curve in $\mathbb{R} \times \mathbb{R}^2$. Further let $F(q,\dot{q},t)$ be the function from $\mathbb{R}^2 \times \mathbb{R}^2 \times \m... | g10333 | [
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0.025438427925109863,
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0.016234105452895164,
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0.058650027960538864,
0.04550444334745407,
-0.... |
<p><img src="http://i.stack.imgur.com/WcibA.png" alt="enter image description here"></p>
<p>In the answer section it is written that,The magnetic field at O due to the current in the straight segments $AA^\prime$ and $CC^\prime$ is zero because ds is parallel to along these paths. </p>
<blockquote>
<p>My querry is ... | g10334 | [
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-0.028182124719023705,
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0.03448763117194176,
-0.0003159225161653012,
-... |
<p><strong>Why don't most physics programs study the primary sources?</strong> In other words: Why don't they include Newton's <em>Principia</em>, Lagrange's <em>Analytical Mechanics</em>, etc., in the curricula?</p> | g10335 | [
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<p>What classical information is carried by $\alpha|0\rangle+\beta|1\rangle$ and $\alpha|00\rangle+\beta|11\rangle$? How to quantify it? To be specific, A GHZ state, $\frac{1}{\sqrt 2}[|000\rangle+|111\rangle]$ can deterministically teleport both the states. Both the states appears to be same from the teleportation poi... | g10336 | [
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<p>Historically, Bekenstein estimated the entropy associated with a black hole in 1973, obtaining:
$$
S_B = \frac{\ln(2)k_Bc^3}{8\pi\hbar G}A.
$$
He already acknowledges in his article that his estimates are based on classical principles and that a quantum mechanical treatment will yield a different constant, though wi... | g10337 | [
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<p>I really want to understand about the Surface Plasmon of metal nanoparticles, if anyone can explain it to me i'll be grateful.</p>
<p>I have checked Wikipedia for it but didn't get anything clear.</p> | g10338 | [
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-0.0472772... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/1775/why-is-there-no-absolute-maximum-temperature">Why is there no absolute maximum temperature?</a> </p>
</blockquote>
<p>On the Kelvin scale, absolute zero represents the temperature at which there is ... | g237 | [
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0.02... |
<p>I was wondering : </p>
<p>does the weight on the planet earth is equal over the years ?</p>
<p>meaning : </p>
<p>all the people , ground , water ,gas.</p>
<p>does the weight stays the same over the years ?</p> | g10339 | [
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... |
<p>Let me admit beforehand that this is quite possibly a very stupid question. I was also uncertain of where to post this question, as it doesn't fit cleanly into either physics or math stackexchange.</p>
<p>In dimensional analysis, it does not make sense to, for instance, add together two numbers with different units... | g820 | [
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<blockquote>
<p><strong>Q:</strong> Calculate the voltage that V1 has to provide</p>
<p><strong>Given:</strong> The following circuit. The voltage through LAMP1 is 5.0V. A (U,I) chart (not shown). LAMP1 and LAMP2 are identical, non-ohmic lightbulbs.</p>
</blockquote>
<p><img src="http://i.stack.imgur.com/3tFZy.... | g10340 | [
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0... |
<p>I just realized that anomalous dimensions in quantum/statistical field theory is not that different from fractal dimensions of objects. They both describe how quantitaive objects transform under a scale transformation (renormalization group transformation in the QFT case and dilation of the mesh/ruler when computing... | g10341 | [
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<p>I have been told always that
$F$ is directly proportional to acceleration.</p>
<p>My question is that for finding such a relationship there should be source that produces desired force and in which the force can be adjusted i.e. Twice, thrice and more.
But the problem is initially before the discovery of laws of m... | g332 | [
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<p>Or to put the question another way - what is the result of a proton-positron collision, or an up quark-charm antiquark collision, etc.? As far as I know, annihilation happens only between particles of opposite charge and same mass, but perhaps I am wrong?</p>
<p>And if the types of annihilation mentioned above cann... | g10342 | [
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<p>I'm trying to determine the electric field at a point P (located on the +Z axis) due to a square of side length [L] and centered at the x-y plane origin. The square has a constant surface density [s]. I'm thinking that I should go about splitting up the square into four smaller squares (one in each quadrant) and the... | g10343 | [
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<p><img src="http://i.stack.imgur.com/Whguh.gif" alt="double slit ray diagram"></p>
<p>This is from Young Double slit experiment. But How to prove the the two $\theta$ are equal, I meant, how $\angle EAD= \angle PEC$? I see from the both triangle have $90^0$ but what about others?</p> | g10344 | [
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<p>I am curious to see what people think of the abiotic theory of oil deposit formation versus the traditional theory.</p>
<p>I have long wondered how enough organic material became trapped underground to degrade and form oil deposits. Especially when you consider the shear amount of oil that we have found underground... | g10345 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2481/would-you-be-weightless-at-the-center-of-the-earth">Would you be weightless at the center of the Earth?</a> </p>
</blockquote>
<p>Supposing there is a cavity at the center of the Earth, what is the ... | g50 | [
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<p>Radio-telescopes (e.g. the <a href="http://en.wikipedia.org/wiki/Very_Large_Array" rel="nofollow">Very Large Array (VLA)</a>) can simulate one gigantic dish by using separate smaller dishes.</p>
<p><strong>Q:</strong> Could such an array of <em>optical</em> telescopes potentially see an exoplanet at say 20 LY away?... | g10346 | [
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<p>How can light be called <em>electromagnetic</em> if it doesn't appear to be <em>electric</em> nor <em>magnetic?</em></p>
<p>If I go out to the sunlight, magnets aren't affected (or don't seem to be). And there is no transfer of electric charge/electrons (as there is in AC/DC current in space). </p>
<p>In particul... | g485 | [
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<p>I have a very basic question on the <a href="http://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect">Aharonov-Bohm</a> effect.</p>
<p>Why is the curve integral $\oint_\Gamma {A}\cdot d{r}$ non-zero ?
$\Gamma$ is the "difference" of both paths $P_1$ and $P_2$.
If the magnetic field is limited to the interior of... | g10347 | [
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<p>Sorkin is well known for his <a href="http://arxiv.org/pdf/Gr-qc/9904062.pdf" rel="nofollow">causal growth dynamics</a>. I think it is a sensible question to ask if his growth dyanamics, which I think can be seen as a poset map (though his work is much more complicated than that), represents a galois connection.</p... | g10348 | [
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<p>It is common to find models built on a compact spacetime. In mathematics, compactness is a very nice property $-$ and lot of powerful results depend on it.
But </p>
<ul>
<li>how <em>safe</em> is assuming compactness of spacetime in physics? </li>
</ul>
<p>Minkowski space is not compact, but, for instance, the tre... | g10349 | [
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<p>What is meant with the fact that supersymmetry with $\mathcal{N}=4$ in three (2+1) dimensions is equivalent to supersymmetry with $\mathcal{N}=2$ in ordinary four (3+1) dimensions?</p>
<p>Which way does one go from one formulation to the other?</p> | g10350 | [
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<p>Consider photons and gluons have 0 mass and 0 charge. In many respects they're already understood as the absence of a particle by mathematical models. Couldn't this be interpreted to mean they operate by phenomenon similar to the charge carrying "holes" responsible for transmitting electro-magnetic waves (at the s... | g10351 | [
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<p>I'm probably missing something obvious and basic here but I can't make sense of certain usages of Observables as present in basic treatments of Quantum Mechanics that i've come across.</p>
<p>$$ \hat{A}|\Psi\rangle = a|\Psi\rangle $$</p>
<p>The above equation implies to me that a single eigenket gives a single eig... | g10352 | [
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<p>I have undertaken a project examining lattice model and trying to construct algorithm that could work on all lattice (in physical sense, or crystal structure). I notice there is a branch in mathematics called lattice theory which deals with ordering. </p>
<p>I am wondering whether the lattice theory in mathematics ... | g10353 | [
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<p>I'm working with a mass density gradient with length $L$ and I'm trying to solve the heat equation in 1-D (mass diffusion equation, $\partial_t\rho(t,x)=D\Delta\rho(t,x)$), but I'm not sure which boundary conditions should I use and what would they physically mean.</p>
<p>The starting mass density profile ($\rho(0,... | g10354 | [
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0.04... |
<p>Can one show that in quantum field theory <em>at least some example</em> massive particles propagate with speed less than speed of light, while massless travel at speed of light? Well, motion is a different thing in QM than in classical mechanics, and question might be formulated differently.</p> | g10355 | [
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<p>And if so, can we observe a difference in the electron scattering cross section with transversely polarized VS longitudinally polarized protons?</p>
<p>P.S. Let me make my question more precise. Consider the charge shape of the proton. In the rest frame of a proton with spin in +z direction, what's the spatial depe... | g10356 | [
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<p>Why commercial wind generators usually have just 2-3 blades?</p>
<p>Having more blades would allow to increase power OR decrease diameter.
Decreased diameter would also reduce stress due to different wind speed on different height...</p>
<p>But despite that commercial generators have few blades...</p> | g565 | [
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<p>I just saw a great clip on the <a href="http://espn.go.com/action/skateboarding/story/_/id/8098465/mischo-erban-breaks-world-record-fastest-skateboard-speed" rel="nofollow">fastest skateboarder</a> to date. He wants to reach 160 mph from a dropped board, but says his speed is limited by the roads currently available... | g10357 | [
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... |
<p>Must all symmetries have consequences?</p>
<p>We know that transnational invariance, for example, leads to momentum conservation, etc, cf. <a href="http://en.wikipedia.org/wiki/Noether%27s_theorem" rel="nofollow">Noether's Theorem</a>.</p>
<p>Is it possible for a theory or a model to have a symmetry of some kind w... | g10358 | [
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<p>Imagine I have an infinitely strong container of volume $v_1$, and I fill it with some monoatomic fluid like liquid hydrogen. I then proceed to compress the walls of the container to reduce its volume by some fraction to $v_2$. </p>
<p>How much force/energy is required to reduce the volume of the container to ~99... | g10359 | [
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... |
<p>Consider a simplest case of a heat exchanger - two parallel pipes of flowing liquids (say, hot and cold) that have physical contact along some part of their length. Hot water of a certain temperature goes from A to B. Cold water can go either from C to D or from D to C. Assume that heat exchange between liquids occu... | g10360 | [
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<p>Why do waves on the sea shore move towards the shore even when the tide is going out?</p> | g10361 | [
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<p>Hydrogen fusion requires two hydrogen nuclei to get close enough (typically a few fm) to fuse. Much of the problem of creating a fusion reactor is overcoming the Coulomb repulsion between a pair of nuclei - the millions of degrees for Maxwellian distributions, the Bremstrahlung losses for inertial confinement. </p>
... | g10362 | [
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-0.021099... |
<p>A particle in one dimension moves under the influence of a potential $V(x)= ax^6$, where $a$ is a real constant. For large $n$, what is the form of the dependence of the energy $E$ on $n$?</p> | g10363 | [
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<p>Following up on this answer, is the point at which waves break on the sea shore a guide to the depth of the sea at that point? Could it indicate eg hidden rocks?</p>
<p><a href="http://physics.stackexchange.com/questions/13841/explain-the-direction-of-waves-on-sea-shore/13844#13844">Explain the direction of waves o... | g10364 | [
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0.015822... |
<p>I have thought about this and looked for answers for a long time now, but I do not have any name or label for this problem, which is the reason for the long title of this question.</p>
<p>I have come across this many times, but I have never found any rationale for this, i.e. a clear interpretation or explanation, s... | g10365 | [
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<p>I want to know the other forms of <a href="http://en.wikipedia.org/wiki/Beta_function_%28physics%29" rel="nofollow">beta-function</a> that make manifest certain properties of <a href="http://en.wikipedia.org/wiki/Renormalization_group" rel="nofollow">renormalization group</a>, for instance dependence on poles/residu... | g10366 | [
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0.06336... |
<p>First of all, I would like to apologize in advance if I make stupid mistakes. I am a mathematician and I am trying to apply the Boltzmann distribution to places where I am not sure if it is applicable (albeit I have no choice). </p>
<p>The situation is: I have a system which consists in a discrete line of $M$ posit... | g10367 | [
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... |
<p>I want to learn how to code in Java and am in need of some cool computational physics projects that would provide motivation to do so. I was wondering if you guys could list some medium-level computational physics projects (from any field) that you think would provide a well-rounded insight into programming.</p> | g10368 | [
0.03142518177628517,
0.06662841886281967,
0.020751019939780235,
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0.00476120226085186,
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<p>I've seen in a few gravity simulation games (ie. bouncing balls) the equation:</p>
<pre><code>force = G * m1 * m2 / distance^2
</code></pre>
<p>shortened to this by removing the gravitational constant:</p>
<pre><code>force = m1 * m2 / distance^2
</code></pre>
<p>I accept that it works fine and saves some calcula... | g10369 | [
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0.008770599961280823,
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0.017377423122525215,
-0... |
<p>I have to do this exercise:</p>
<blockquote>
<p>9. The current $I(t)$ at time $t$ flowing in an electric circuit obeys the differential equation</p>
<p>$$I''(t) + RI'(t) + I(t) = \sin \omega t$$</p>
<p>where $R$ and $\omega$ are positive constants. The solution can be expressed in the form $I(t) = F(t) ... | g10370 | [
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0.02749301865696907,
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0.03831... |
<p>In Griffiths' <em>Introduction to Electrodynamics</em>, Problem 1.28 (the triangular prism question) is especially challenging for me. I do not know how the limits of x are <strong>0</strong> to (<strong>1-y</strong>).
My concern is the latter limit, <strong>1-y</strong>. Can you explain systemically how this is ar... | g10371 | [
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<p>I've been looking for questions about dark matter, and I've read some very interesting answers. However, I desire too look into it deeply. </p>
<p>This is not actually a question. I'm asking the community to recommend interesting references to understanding dark matter and dark energy. </p>
<p>I accept all sort of... | g438 | [
0.07375527918338776,
0.024715468287467957,
0.01382126659154892,
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<p>I have problems fully understanding the concept of work, so please forgive me if this is simple. If I take a box of mass $ m $, and lift it a distance $ d $ vertically, <strong>why is the work I have done equal to $ gmd $, where $ g $ is the force gravity exerts on the box?</strong> I understand that work is equal t... | g315 | [
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<p>Can you suggest some references for rigorous treatment of thermodynamics? I want things like reversibility, equilibrium to be clearly defined in terms of the basic assumptions of the framework.</p> | g10372 | [
0.06865724921226501,
0.029522182419896126,
-0.013440682552754879,
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-0.015081577003002167,
0.0316200777888298,
-0.0... |
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