question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>That's how it's framed in my Physics school-book.</p>
<p>The question (or rather, the explanation) is that of the thrust of rockets and how the impulse is equal (with opposite signs) on the thrust-gases and the rocket itself.</p>
<p>$( m \frac { \Delta v}{ \Delta t} ) = -(v \frac {\Delta m}{ \Delta t} ) = F_i$ </p... | g12028 | [
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<p>Consider two identical heat pumps, for example, split-system air conditioners. There're two ways to make them work - in parallel or sequential. Parallel means that "hot" radiators of the machines are put outside the room, while the "cold" radiators are put inside the room. Sequential means that the cold radiator of ... | g12029 | [
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<p>I had a special relativity course at university. Now I'm trying to extract what new insight <a href="http://en.wikipedia.org/wiki/Mass-energy_equivalence" rel="nofollow">$E=mc^2$</a> did give us. I mean that moving mass has/is energy (kinetic) not new. The energy merely changed from classical kinetic energy to some ... | g12030 | [
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<p>Suppose you have dynamics of a coherent state. The state presents a normal distribution of finding the particle. Does anyone know of any attempts to connect modern advances in the probability theory to quantum dynamics of a coherent state.</p> | g12031 | [
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<p>There are many free fermion systems that possess topological edge/boundary states. Examples include quantum Hall insulators and topological insulators. No matter chiral or non-chiral, 2D or 3D, symmetry protected or not, their microscopic origins are similar. Explicitly speaking, when placing such a system on a geom... | g12032 | [
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<p>Is double well potential related to Maxican hat potential?
I have found on Quantum Field Theory in a Nutshell
by A. Zee</p>
<p>He wrote the double well potential as : $V (φ) = (λ/4)(φ^ 2 − v^2)^2$.
Can anyone give me an argument for writing the equation like that.</p> | g12033 | [
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<p>Let's temporarily ignore spin. If 3 denotes the standard representation of SU(3), 1 the trivial rep, 8 the adjoint rep and 10 the symmetric cube then it's well-known that</p>
<p>3 x 3 x 3 = 1 + 8 + 8 + 10</p>
<p>Interpreting the 3's as the space of up/down/strange flavour states for a quark, the tensor cube is int... | g12034 | [
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<p>E.g. in exploding nuclear bomb or some other big explosions.</p>
<p>I mean if the speed of electrons as waves/particles is a constant or changes according to other "forces" involved?</p> | g12035 | [
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<p>I found this on <a href="https://en.wikipedia.org/wiki/Black_body" rel="nofollow">Wikipedia article on black bodies</a>:</p>
<blockquote>
<p>A black body in thermal equilibrium (that is, at a constant
temperature) emits electromagnetic radiation called black-body
radiation. The radiation is emitted according ... | g12036 | [
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<p>I've done basic or introductory mechanics at the level of Resnick and Halliday. I'm currently studying calculus of variations and the Lagrangian formulation of mechanics on my own. I read somewhere that an understanding of classical mechanics is necessary for appreciating quantum mechanics. Can someone please give m... | g12037 | [
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<p>By definition scalar fields are independent of coordinate system, thus I would expect a scalar field $\psi [x]$ would not change under the transformation $x^\mu \to x^\mu + \epsilon^\mu $. Correct?</p>
<p>Now when I look in the book "Introduction to QFT" by Peskin and Schroeder they state (in an example) that the... | g12038 | [
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<p>I'm trying to calculate the Integrated Water Vapor (IWV) using GPS data.</p>
<p>I'm following the equations in the following publication: </p>
<blockquote>
<p>GPS Meteorology: Remote Sensing of Atmospheric Water Vapor Using
the Global Positioning System, MICHAEL BEVIS et al. 1992. <a href="http://nldr.l... | g12039 | [
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<p>This question is because something made me confused. I always thought that the idea behind electrodynamics was to postulate some things, like <a href="http://en.wikipedia.org/wiki/Coulomb%27s_law" rel="nofollow">Coulomb's law</a> in electrostatics and so on, and then manipulate those things to derive <a href="http:/... | g12040 | [
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<p>I'm trying to figure out the density (g/cm^3) of La2CuO4. I know that the mass is 405.355 g/mol; what do I have to do to calculate the volume? Thanks!</p> | g12041 | [
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<p>Lets imagine an electromagnetic wave is vertically polarized. If you ignore the magnetic component, the electric field lines would point upwards from the ground or downwards in a cyclical way and of course vary in field strength.</p>
<p>Now lets say you attach a battery to two metal plates and you produce an electr... | g12042 | [
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<p>I have often read that the generators for $\mathrm{SU(N)}$ gauge theories must be $N \times N$ matrices; see for instance these notes at the top of page 3: <a href="http://www.staff.science.uu.nl/~wit00103/ftip/Ch12.pdf" rel="nofollow">http://www.staff.science.uu.nl/~wit00103/ftip/Ch12.pdf</a>. Why is this?</p>
<p... | g12043 | [
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<p>What's a good book (or other resource) for an advanced undergraduate/early graduate student to learn about <a href="http://en.wikipedia.org/wiki/Symmetry_%28physics%29" rel="nofollow">symmetry</a>, <a href="http://en.wikipedia.org/wiki/Conservation_law" rel="nofollow">conservation laws</a> and <a href="http://en.wik... | g12044 | [
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<p>Take for example a slide of 3m tall. </p>
<p>Would an object (starting from rest) sliding down a gentle slope have a lower speed than a steep slope? (Note: Height of slide is the same,disregard friction.)</p>
<p>Why is this so?</p>
<p>What if the slide was a spiral one?</p> | g12045 | [
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<p>I want to ask about the workings of the <a href="http://en.wikipedia.org/wiki/Hall_effect" rel="nofollow">Hall effect</a>. Why do the electrons come to rest on the edge of the wire? The magnetic field pushes them up, and the electric field pushes them forward. Shouldn't they reach the top of of the conductor and the... | g12046 | [
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<p>I was reading about second-harmonic generation (SHG) crystals (or frequency-doubling crystals) used to produce green laser light from IR. </p>
<p>What low-level process in the crystal is actually driving the combination of two photons into one? I'm thinking of a process at the QED level (or at least motivating what... | g12047 | [
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<p><a href="http://physics.stackexchange.com/q/110692/">Here</a> there is the old problem.
I know from the old problem that the work $W_v$ that I need to make a rocket fast enough to reach the escape velocity is
$$W_v= G \frac{mM}{r}$$
therefore because $$W_v=F\cdot S = G \frac{mM}{r} \rightarrow F_v=\frac{W}{S}=G \f... | g12048 | [
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<p>Like all my questions, I fear this will be very naive, because my physics background is very limited. Please bear with me. </p>
<p>I think of the electromagnetic field as a section of a vector bundle over spacetime, but I think nothing will be lost if we just treat it as a function $f:{\mathbb R}^4\rightarrow{\ma... | g12049 | [
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<p>I came across some problems related to finding the center of pressure. Please guide me how to go about them. Posting them all so that I can find out the intricacies involved when there are so many different geometrical shapes involved.</p>
<ol>
<li><p>A quadrant of the ellipse $$x^2+4y^2 = 4$$ is just immersed vert... | g12050 | [
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<p>Could someone tell me about Frobenius-Schur indicator and the associated cups and caps notation in context of anyon model. One possible reference could be Parsa Bonderson thesis which is freely accessible here: <a href="http://thesis.library.caltech.edu/2447/2/thesis.pdf" rel="nofollow">http://thesis.library.caltech... | g12051 | [
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<p>To calculate the pressure at the outlet of a pump we use pump performance characteristics i.e. charts giving pump head as a function of volumetric flow. When the fluid flows through a pump, it's temperature slightly rises.</p>
<blockquote>
<p>Is there a formula or other method to calculate the temperature rise in... | g12052 | [
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<p>I firstly apologise if this question is off the topic.</p>
<p>I am a first year undergraduate student and the required textbook for the course Advanced Physics is Fundemental of physics by Halliday. This textbook is huge and to be honest I was scared when I saw the size of the textbook. There are too much text to ... | g115 | [
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<p>Lets assume that we can produce a quark-gluon plasma and then we try to cool it down, what will happen to it ?</p> | g12053 | [
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<p>I am reading Steven Weinberg's <em>Gravitation and Cosmology</em>. On page 10 he says:</p>
<blockquote>
<p>In $D$ dimensions there will be $D(D+1)/2$ independent metric
functions $g_{ij}$, and our freedom to choose the $D$ coordinates at
will allows us to impose $D$ arbitrary functional relations on the
$g_... | g12054 | [
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<p>I've been wondering lately about a problem that comes from, among other places, an old video game "Lunar Lander". In the game there is a spaceship that has a small tank of fuel, and you're supposed to pilot the ship from an initial height down to the surface of the moon. You win if the landing is sufficiently soft. ... | g12055 | [
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<p>I know that the work capacity of the heart is</p>
<pre><code>Work capacity of the heart = pumping capacity x aortic impedance.
</code></pre>
<p>I would mark work by W and impedance by Z.
However, I am not sure how to mark the pumping capacity.</p>
<p>I think the units of W are joules and of impedance Ns / m.
So p... | g12056 | [
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<p>what actually does the spin quantum number of a particle describe about? What it means when we say photon has spin 1, Higgs boson has spin 0, etc..?? What actually does that numerical value explain? I do hope the + or - sign definitely talks about direction of spin! (kindly elaborate!)</p> | g383 | [
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<p>Since the mutual repulsion term between electrons orbiting the same nucleus does not commute with either electron's angular momentum operator (but only with their sum), I'd assume that the electrons don't really have a well-defined angular momentum (i.e., they do not occupy a pure $\left|lm\right>$ state). I woul... | g12057 | [
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... |
<p>The solution of Poisson equation is given by
$$
\mathbf E = \int \frac{\rho (\mathbf r )(\mathbf r_{0} - \mathbf r )}{|\mathbf r_{0} - \mathbf r|^{3}}d^{3}\mathbf r.
$$
I tried to use this term for a field of uniformly charged ball and got incorrect result: for the field inside the ball integration gives
$$
\int \fr... | g12058 | [
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-0.... |
<p>I have a question about the Michelson Interferometer with spherical waves: I know that the pattern produced by this kind of waves is a pattern of concentric circles. But what I'm not sure is how the pattern changes when I move one mirror. I believe that If I move the mirror away from the beam spliter, the circles in... | g12059 | [
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<p>I am hosting a dinner tonight for which I'll be serving white wine (Riesling to be more specific). Generally white wine is best served chilled (not COLD!) at around <code>50 F</code> or <code>10 C</code>. </p>
<p>Just for kicks, I thought I'd treat this as a problem of transient conduction. I assume that (forced)co... | g12060 | [
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<p>I am working through some notes of Gould and Tabochnik <a href="http://www.compadre.org/STP/document/ServeFile.cfm?ID=7271&DocID=445" rel="nofollow">here</a> and I am confused by their argument showing that entropy does not change in a quasi-static adiabatic process. First, entropy is defined to be an additive f... | g12061 | [
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<p>Exercise 12.2.2 in <a href="http://www.amazon.co.uk/Principles-Quantum-Mechanics-R-Shankar/dp/0306447908" rel="nofollow">Shankar's Principles of Quantum Mechanics</a> asks to derive the expression for the angular momentum operator $L_z$
\begin{equation}
L_z = XP_y-YP_x
\end{equation}
using its commutation relation... | g12062 | [
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<p>How do I make a ripple effect in a bowl of water. I have tried throwing small pebble sin but it just splashes and sinks. I have read that I need to make the water a thicker liquid ie add glycerine, will this work and why? </p> | g12063 | [
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<p>How should I compute the amount of energy of an EM wave absorbed by a material?
Can I just use the divergence of the Poynting vector?</p> | g12064 | [
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<p>For a fixed current load, will the voltage drop be larger in a small cell or a big cell battery? Why?</p> | g12065 | [
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<p>I considered a Ring-like one dimensional geometry. In this, if we fix an origin (at some point on the circumference), we can think of <strong>set of all displacements along the circumference</strong> to form a <strong>vector space</strong>. Now one vector can be denoted by (for some reasons that will become clear),
... | g12066 | [
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... |
<p>Dimensional analysis, and the notion that quantities with different units cannot be equal, is often used to justify very specific arguments, for example, you might use it to argue that a particular formula cannot possibly be the correct expression for a particular quantity. The usual approach to teaching this is to ... | g12067 | [
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<p>Can anyone see a reason for $$\left(1+{U_\rho U^\rho\over c^2}\right)\left(U_\nu{d^2 U^\nu\over d\tau^2}\right)=0$$?</p>
<p>Here $U^\rho$ is the 4-velocity for a particle and $\tau$ the proper time. The context is for a particle moving in an electromagnetic field.</p>
<p>I believe it may be useful to introduce the... | g12068 | [
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<p>Given: </p>
<ol>
<li>A <a href="http://en.wikipedia.org/wiki/Wave_plate" rel="nofollow">half wave plate</a> freely floating in space. </li>
<li>Circularly polarized light, falling perpendicularly to it.</li>
</ol>
<p>The plate changes polarisation of the beam to the opposite one. Therefore it receives angular mome... | g12069 | [
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<p>I'm designing a new calendar and I want the first day of the year to be the first day after the longest night of year in the northern hemisphere. Under this plan, "natural" leap years, where the first day of two adajacent years are 366 days apart, will occur every four years, but sometimes with a five year gap inste... | g12070 | [
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<p>Which sky map application for mobile devices have the best "feature satisfaction"-to-investment ratio?</p>
<p>I would like to have a comparison between "sky map" applications for mobile devices and it should be a factual comparison made by astronomy professionals, enthusiasts, and hobbyists. The result would be a u... | g12071 | [
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<p>I know of the <a href="http://en.wikipedia.org/wiki/Ariane_5#Variants" rel="nofollow">Ariane 5 ECA</a>, the <a href="http://en.wikipedia.org/wiki/Delta_IV" rel="nofollow">Delta IV</a> rocket and a few more, but which of the present day's rockets is the top heavy lifter, say, to <a href="http://en.wikipedia.org/wiki/... | g12072 | [
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0.020551148802042007,
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0.05454108491539955,
... |
<p>Reading this wiki page about the <a href="http://en.wikipedia.org/wiki/Observable_universe" rel="nofollow">observable universe</a>, (and visible universe), implies that we humans, on this rock in the milkyway are seeing a static representation of the universe that is still effectively in the past. They're also sayin... | g12073 | [
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0.056604545563459396,
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0.0185... |
<p>What would happen if instead of $F=m*d^2x/dt^2$, we had $F=m*d^3x/dt^3$ or higher? </p>
<p>Intuitively, I have always seen a justification for ~1/r^2 forces as the "forces beeing divided equally over the area of a sphere of radius r".</p>
<p>But why the 2 in $F=m*d^nx/dt^n$ ?</p> | g12074 | [
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0.03785285726189613,... |
<p>Could someone explain the correspondence between lines in twistor space and minkowski space-time points? a basic derivation would suffice</p> | g12075 | [
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<p>In Lorentzian AdS space there are both normalizable and non normalizable solutions and we also know (at least for scalar fields in bulk) what do they correspond to in the boundary. But I saw the calculation only for scalar fields. Can someone please give me a reference where people have calculated these modes for a ... | g12076 | [
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<p>As I learned, nuclear fission doesn't occur without the control of a human made nuclear reactor, by hitting a neutron to a fissile isotope. Thus, the fission reaction is considedred as a part of 'ARTIFICIAL REACTIONS' category.</p>
<p>But, I've just noticed in a wikipedia article (<a href="http://en.wikipedia.org/w... | g12077 | [
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0.0135... |
<p>In eternal inflation, how can bubble universes collide if the space between them is exponentially stretching and moving them further and further away?</p> | g12078 | [
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0.0118712168186903,
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-0.... |
<p>Chirality can be interpreted as a property of Lorentz group - Lorentz transformation of field through representation $(s, 0)$ or representation $(0, s)$. For the massless particles one says, that chirality and helicity are the same (helicity values are a chirality values multiplied by $ \hbar $). So it means, that c... | g12079 | [
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0.015487589873373508,
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0.03840695321559906,
0.018722305074334145,
... |
<p>For the observation of solar or galactic gamma rays, one should ideally be above the atmosphere. Quoting the <a href="http://en.wikipedia.org/wiki/Gamma-ray_astronomy" rel="nofollow">Wikipedia article on Gamma-ray astronomy</a>:</p>
<blockquote>
<p>Most gamma rays coming from space are absorbed by the Earth's at... | g12080 | [
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0.0593891404569149,
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-0.... |
<p><em>Is the following a possible scenario? If not, why not?</em></p>
<p>Assume there is a supermassive black hole $Z$ isolated in inter-galactic space.
Nearby and stationary relative to $Z$ is observer $A$.
A number of light years away spaceship $X$ is travelling at, say, $0.25c$ directly towards the black hole and ... | g12081 | [
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0.01... |
<p>I remember studying that air pressure and temperature are inversely proportional. Now I saw in book that "Atmospheric pressure decreases as we go higher and higher." But in height the temperature is less, and so the air pressure is high. But it is given atmospheric pressure increases with altitude. I googled and ... | g12082 | [
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0.04793152958154678,
0.0029... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/28228/why-is-matter-drawn-into-a-black-hole-not-condensed-into-a-single-point-within-t">Why is matter drawn into a black hole not condensed into a single point within the singularity?</a> </p>
</blockquote>... | g384 | [
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0.044065169990062714,
-... |
<p>I need help to settle an argument about aeronautics. Particularly model aircraft. </p>
<p>It has been observed by some that when a model airplane flying with the wind turns back into the wind , some aircraft tend to pitch up and gain altitude indicating an increase in airspeed. Alternately, when flying into the win... | g12083 | [
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0.0409... |
<p>I'll write the question but I'm not fully confident of the premises I'm making here. I'm sorry if my proposal is too silly.</p>
<p><a href="http://en.wikipedia.org/wiki/Hilbert%27s_sixth_problem">Hilbert's sixth problem</a> consisted roughly about finding axioms for physics (and it was proposed in $1900$). I guess ... | g203 | [
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0.03133928030729294,
-0.000982... |
<p>In Rivasseau's and Wang's <a href="http://arxiv.org/abs/1304.5913" rel="nofollow">How to Resum Feynman Graphs</a>, on page 11 they illustrate the intermediate field method for the $\phi^4$ interaction and represent Feynman graphs as ribbon graphs. I had to read up about ribbon graphs as I've never heard of them befo... | g12084 | [
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<p>Just a thought experiment since bats are probably not swift enough to take evasive action in the scenario described.</p>
<p>If a cloud of bats were to encounter a B-2, or F-35, or F-117 or any of the other stealth aircraft in stealth-mode, would they detect the airframe in time, or fly smack into the aircraft?</p> | g12085 | [
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<p>This is a question I got for my class.</p>
<p>We have the following situation.
We take two tuning forks, we hit them, then we take one of the tuning forks and walk away with it.
The sound changes as we walk away and it isn't consistent anymore. </p>
<p>Why?</p>
<p><strong>EDIT:</strong> I see I was a bit unclear,... | g12086 | [
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0.05624997243285179,
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0... |
<p>I have two earthed metal plates, separated by a distance $d$ with a plane of charge density $\sigma$ placed a distance $a$ from the lower plate. I want to derive expressions for the strength of the electric field in the regions between the plane and the top plate and the plane and the bottom plate.</p>
<p>I'm not s... | g12087 | [
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0.008170112036168575,
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0.012721315026283264,
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0.018689515069127083,
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-0... |
<p>The apparent size of an object decreases with increase in distance that's why we see rails get closer as they get farther. We don't see the rails parallel throughout their length but converging. But there is a contradiction:</p>
<p>Let,
the real size of the object be <strong>s</strong>, </p>
<p>the distance betwe... | g12088 | [
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0.013626118190586567,
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0.0031666159629821777,
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0.02838730625808239,
0.013876455835998058,
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0.027801766991615295,
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0.03479491174221039,
0.06721638143062592,
0.0... |
<p>In his 1970 science fiction novel <a href="http://en.wikipedia.org/wiki/Ringworld" rel="nofollow">Ringworld</a>, author Larry Niven describes the eponymous Ringworld, a gigantic structure shaped as a ring with a radius of around 1 AU, rotating around a star in the center of the ring. This system is described as phys... | g12089 | [
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-0.005628574173897505,
0.018047960475087166,
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... |
<p>What I'm really looking for is a formula for a <a href="http://en.wikipedia.org/wiki/Trebuchet" rel="nofollow">trebuchet</a> that I can input the desired initial velocity after launch and mass of the object, and from that figure out how long the long arm, short arm, sling and pivot need to be, and how much mass I ne... | g12090 | [
0.0910988450050354,
0.03762267529964447,
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0.0... |
<p>I need a book dealing in particular with the intermolecular forces and, if possible, the diffusive processes. Someone knows an appropriate one?</p> | g12091 | [
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0.029195062816143036,
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0.013580288738012314,
-0... |
<p>This question is in reference to question 13.2 in the QFT book by Peskin and Schroeder. </p>
<p>To put it in general - I would like to know how does one define "anomalous dimensions" if one is given the wave-function renormalization in the "epsilon" regularization scheme? (..without having to redo the whole calcula... | g12092 | [
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0... |
<p>My <a href="http://books.google.com/books?id=ntZwxttZF-sC&lpg=PA28&ots=LU-xi3_Vw5&dq=lunar%20dichotomy%20method&pg=PA27#v=onepage&q=lunar%20dichotomy%20method&f=false" rel="nofollow">text</a> says that Aristarchus (310 BC – ~230 BC) measured the "angle subtended by the Earth-Moon distance at ... | g12093 | [
0.03165895491838455,
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-... |
<p>I can't figure out how to find the charge density for the following problem:</p>
<blockquote>
<p>A conductor is placed in an external electrostatic field. The external
field is uniform before the conductor is placed within it. The
conductor is completely isolated from any source of current or charge.</p>
... | g12094 | [
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0.030570486560463905,
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<p>First off, I know that a <a href="http://en.wikipedia.org/wiki/Black_hole" rel="nofollow">black hole</a> can theoretically exist at any size, and I know about the Schwarzschild radius, etc. Snowflakes could also exit at just about any size, and they of course vary considerably in different environments. But there's ... | g12095 | [
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<p>In position basis, we have,</p>
<p>$$\langle x \mid \hat p \mid \Psi(t) \rangle = -\imath \hbar \frac{\partial{\langle x \mid \Psi(t) \rangle}}{\partial{x}} $$</p>
<p>Now i know $\hat{p}$ is a hermitian operator which should be self adjoint. </p>
<p>The self adjoint operators are said to satisfy :</p>
<p>$$\lan... | g12096 | [
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-0.0... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/6384/why-does-dilation-invariance-often-imply-proper-conformal-invariance">Why does dilation invariance often imply proper conformal invariance?</a> </p>
</blockquote>
<p>What exactly is the difference b... | g385 | [
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<p>In my calc-physics class we were given the following question:</p>
<blockquote>
<p>A movie stuntwoman drops from a helicopter that is $30.0 m$ above the ground and moving with a constant velocity whose components are $10.0 \frac{m}{s}$ upward and $15.0 \frac{m}{s}$ horizontal and toward the south. You can ignore ... | g12097 | [
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0.0294... |
<p>For the sake of clarity and brevity, here is the description from my textbook (Halliday & Resnick 9th):
<img src="http://i.stack.imgur.com/KMZZQ.jpg" alt="enter image description here"></p>
<p>This description states that the electric field is doubled. I am seriously confused. When the two plates are brought to... | g12098 | [
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-0.044... |
<p>In oil droplet experiment, x-ray makes the air molecules negatively charged. How does that work? X-ray carries high energy and ionizes air, doesn't that make air positively charged?</p> | g12099 | [
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<p>I would like to know if there is any analytical proof or relationship which can show that for a dynamical system in presence of chaos signal, if the phase space volume (PSV) minimization leads to the minimization of Kolmogorov Entropy (dynamical entropy). Say, I have a chaotic signal $c(t)$ from a
logistic map of di... | g12100 | [
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<p>Inspired by these two question on tex.SX</p>
<ul>
<li><a href="http://tex.stackexchange.com/questions/108818/asymmetric-uncertainties-with-siunitx-package">Asymmetrical tolerancing</a></li>
<li><a href="http://tex.stackexchange.com/questions/108818/asymmetric-uncertainties-with-siunitx-package">Asymmetric uncertain... | g12101 | [
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0.04446056857705116,
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0.002693070098757744,
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0.041544996201992035,
0.07568644732236862,
-0.003786948... |
<p>A few years ago there was a story about the Large Hadron Collider where a possible tachyon was supposedly observed. It was later shown it didn't occur yet the incident made me think. If a large experiment using extreme amounts of energy trying to duplicate some processes or events of the 'distant' past , would the ... | g83 | [
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0.002583811292424798,
0.027144065126776695,
0.0513... |
<p>Scientists succeeded in unifying EM with the weak force, then with the strong force to achieve the standard model. They then studied supersymmetry and GUTs that showed improved gauge coupling unification at high energies. The final dream was to unify all the known forces at very high energy, including gravity. In th... | g12102 | [
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0.02064054273068905,
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0.02633081004023552,
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0.05371307209134102,
-0.0... |
<p>Approaching the following problem:</p>
<blockquote>
<p>A plane monochromatic electromagnetic wave with wavelength $\lambda = 2.0 cm$,
propagates through a vacuum. Its magnetic field is described by $
> \vec{B} = ( B_x \hat{i} + B_y \hat{j} ) \cos(kz + ωt) $,
where $B_x = 1.9 \times 10^{-6} T, B_y = 4.7 \ti... | g12103 | [
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0.0036111215595155954,
0.02018752321600914,
0.0276845283806324,
0.006092803552746773,
0.03... |
<p>You know that for a potential function (conservative force/fields) that</p>
<p>$\nabla U = \pm \vec{F}$</p>
<p>In math, we don't have that minus sign, we have only the plus one. </p>
<p>What does it mean if you get rid of the plus sign? I remember the minus signs tells us that the force is always in the opposite ... | g12104 | [
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0.017024509608745575,
0.029117809608578682,
-0.0102... |
<p>I am planning to use an air compressor to inflate a rubber balloon. I need to size the compressor for inflating the balloon, but for sizing the compressor I need the pressure required to inflate the balloon. So, can anyone guide me to calculate the required pressure for inflating a rubber balloon?</p> | g12105 | [
0.019238801673054695,
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0.016877705231308937,
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0.016258826479315758,
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0.004524261225014925,
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<p>I'm currently working on maxwell equations and in order to lower the fields dimension, we perform a Fourier decomposition (according to $\theta$) due to the system symmetry. For any vector field $\mathbf{U}(r, \theta, z)$, we have,
$$ \mathbf{U}(r,\theta,z) = \sum_\alpha \tilde{\mathbf{U}}^\alpha(t,z)e^{i\alpha \th... | g12106 | [
0.07788167893886566,
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0.012431529350578785,
0.036310236901044846,
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0.0... |
<p>The question is sometimes referred to as the "psychological arrow of time" (Hawking, 1985). Here the past is understood as a moment or time when the entropy of the universe was lower, and contrarily for the future. So it is generally thought that PAOT is a consequence of the thermodynamic arrow of time of our univer... | g12107 | [
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0.015926755964756012,
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-0.00984980445355177,
0.004100962076336145,
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0.01... |
<p>In electromagnetism we say that all the electromagnetic interactions are governed by the 4 golden rules of <a href="http://en.wikipedia.org/wiki/Maxwell%27s_equations" rel="nofollow">Maxwell</a>. But I want to know: is this(to assume that there is no requirement of any other rule)only an assumption, a practical obse... | g12108 | [
0.03702881932258606,
0.08748051524162292,
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0.0... |
<p>I have a background in engineering so I have some familiarity with basic math and science. I've recently been reading about other topics such as Einstein's relativity and have become interested in learning more about this and other similar topics in science.</p>
<p>Are there any books you can recommend that explain... | g98 | [
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0.023848537355661392,
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0.0383240282535553,
0.0034231499303132296,
0.059290602803230286,
0.023052752017974854,
0.06186031177639961,
0... |
<p>If the universe is heading for a big crunch, when the universe starts to collapse will entropy decrease and the arrow of time consequently reverse or not? I'm interested in the explanations, not just the answer.</p> | g12109 | [
-0.008061934262514114,
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-... |
<blockquote>
<p>Before answering, please see <a href="http://meta.physics.stackexchange.com/a/4698">our policy</a> on
resource recommendation questions. Please try to give substantial answers that detail the
style, content, and prerequisites of the book or paper (or other resource). Explain what the
resource is... | g12110 | [
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0.07371603697538376,
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0.07179541885852814,
-0.0051121... |
<p>A half pipe of a skateboard park consists of a concrete trough with a semicircular section of radius 5m, I hold a frictionless skateboard on the side of the trough, pointing down toward the bottom and release it; how long will it take to come to back to the point of release?</p>
<p>Note: I am supposed to use Newton... | g12111 | [
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0.01505452860146761,
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0.001220... |
<p>At the LHC, researchers smash particles into each other at speeds close to speed of light. Photons, on the other hand, already move at the speed of light. Do they ever smash into each other? Or do they just go through each other? Why?</p> | g386 | [
0.028937770053744316,
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0.0021295256447046995,
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-0.011272242292761803,
-0.03523942828178406,
-0.05... |
<p>I know that $\frac{\lambda_2}{\lambda_1} = 1 + z$</p>
<p>Suppose a galaxy had redshfit $z=3$. Does this mean that the wavelength becomes $4\lambda$?</p>
<p>Then by wien's law where $\lambda \propto \frac{1}{T}$, does this mean that the temperature now observed is $\frac{1}{4} \times 2.73 K$?</p> | g12112 | [
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... |
<p>I wonder if I could use the technique for finding the tunneling rate given by $$ \Gamma=2 \Im[ F]$$ where $F$ is the free energy in case of time dependent potentials?
Relevant to the previous question, how can I find the perturbation to an instanton with a week time dependent potential?</p>
<p>I appreciate your ... | g12113 | [
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<p>The explanation of shear rate in laminar flow is straightforward: We imagine small layers of fluid that glide on each other. Now, in turbulent flow, this does not work as there are no layers. I'm not even sure that shear rate is a meaningful concept in turbulent flow.</p>
<p>If I want to know the apparent viscosity... | g830 | [
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<p>I have always wondered why salt is white, water is clear and gold is, well, gold. What determines the color of a substance? Does it have something to do with the electrons? And is it possible to predict the color of a substance by looking at the formula?</p> | g12114 | [
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<p>I'd like to know (my knowledge at physics are realy poor) what would happen if I've got a generator connected to another generator and both of them generating electricity for a house or whatever.</p>
<p>Like this:</p>
<p>G1 is connected to G2 and the plug. So it gives electricity to both of them making G2 to "load... | g12115 | [
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<p>Comparing the simples form of the forces of both phenomena: the law of Newton for gravitation $V\propto \frac{1}{r}$, and the Coulomb law for electrostatics $V\propto \frac{1}{r}$, one might think that if one can be extended relativistically to a curvature in space-time, that the other one would lend itself to a si... | g247 | [
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<p>In the recent <a href="http://cdsweb.cern.ch/record/1406042" rel="nofollow">Higgs seminar</a> at 73:38 <a href="http://cdsweb.cern.ch/record/1173837" rel="nofollow">Guido Tonelli</a> the spokesman for CMS, makes a mistake and refers to a Z-prime in a context that would imply that they see them frequently. He swiftl... | g12116 | [
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<p>I understand this is a homework problem. I don't expect anyone to do my homework for me, but help me understand what I am doing wrong.</p>
<blockquote>
<p>The problem goes: Two shuffleboard disks of equal mass, one orange and
the other green, are involved in a perfectly elastic glancing
collision. The green d... | g12117 | [
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