question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p><strong>EDITED AND SOLUTION</strong>: In fact my stupid mistake was to take the wrong value for my $P_1$ and I was getting an 1.2998 that finally is a 1,9178 within just a difference about 7%. So at the end they are not equal but it is not a $1.9\neq1.3$, but $1,9\neq1,9278$. </p>
<p>In spite of everything, <em>it ... | 5,376 |
<p>How to show that
$$
\int d\Psi d\bar {\Psi}e^{i \int d^{4}x\bar {\Psi} \hat {A} \Psi} = det (\hat {A})?
$$
$\Psi , \bar {\Psi}$ refers to Dirac spinors (the second is $\bar {\Psi} = \Psi^{\dagger}\gamma^{0}$).</p> | 5,377 |
<p>In a lecture (<a href="http://teorica.fis.ucm.es/TAE2012/CHARLAS.DIR/MEISSNER.DIR/part2.pdf" rel="nofollow">look</a> at the chapter "The fermion determinant in a constant field", p. 5) I found some strange transformation, which is given by eq. 18. How to prove it? Exactly, I don't understand the appearance of some c... | 5,378 |
<p>If I had a static thin (a few mm) film of water lying on a surface and I tried to push a squeegee across the surface in order to move the water. Would the water rise up in front of the squeegee? Would the angle be possible to calculate if the speed were to increase and or the force of gravity were to increase?</p> | 5,379 |
<p>What is the physical constraint that gauge invariance is a required condition for electromagnetic fields? What would happen if the electromagnetic fields were not gauge invariant?</p> | 5,380 |
<p>There was an announcement at a recent UCLA symposium on dark matter by the <a href="http://fermi.gsfc.nasa.gov/" rel="nofollow">FERMI collaboration</a> which hints at some evidence of dark matter. The results aren't yet published, but the <a href="http://m.ucla.edu/newsroom/item.php?name=News&path=http%3A%2F%2F... | 5,381 |
<ul>
<li>Suppose there is a habitable star with a significantly large mass, and thus a huge gravitation field. It has a clock on it that ticks each local second. And it also has a mirror. This is Star A.</li>
<li>Suppose there is another habitable star with a much smaller mass, also with a clock, called Star B. </li... | 5,382 |
<p>Does the photino in super-symmetry have a mass, Or is this different in different super symmetric models?</p> | 5,383 |
<p>Quantum entanglement bridges space and time: entangled particles show correlations independently of where and when they are measured. This is most evident in "delayed choice quantum eraser" experiments, where the outcome of single measurments <em>now</em> depends on which measurements are done <em>in the future</em>... | 5,384 |
<p>Why capacitors are used in flashlights of cameras instead of attaching the light directly to the battery? How this leads more light?</p> | 5,385 |
<p>I talked to a professor about solar panels and their efficiency. It seemed that the main reason solar panels aren't that efficient is because it can only accept a single energy input size. Anything below is ignored and anything above only gives the energy of that single limit.</p>
<p>That is, say the limit is 1W. A... | 5,386 |
<p>I know the magnetic field strength increases as the number of turns in the solenoid increases.</p>
<p>However, I've learnt the field inside the solenoid is usually nearly uniform.</p>
<p>So, does the number of turns in the solenoid effect the uniformity of the field inside the solenoid? Does the field gets closer ... | 5,387 |
<p>Anthropic principle, at least in laymen explanations that I have encountered so far, sounds something like "the physical universe suits us exceptionally well because among all the possibilities we, the observers, tautologically encounter the one that can support us."</p>
<p>I was wondering whether this principle ca... | 5,388 |
<p>while studying scattering formula for the supercurrent (<a href="http://arxiv.org/abs/cond-mat/9611162" rel="nofollow">Beenakker</a>)
I encountered that the density of states for discrete and continuous spectrum can be simultaneously described by taking $\epsilon\ ->\ \epsilon + i\delta $ in the following formula... | 5,389 |
<p>How to show with Maxwells Equations that nonaccelerating charges don't radiate?</p> | 5,390 |
<p>A wedge of mass $M$ rests on a rough horizontal surface with coefficient of static friction $\mu$. The face of the wedge is a smooth plane inclined at an angle $ \alpha$ to the horizontal. A mass $m_1$ hangs from a light string which passes over a smooth peg at the upper end of the wedge and attaches to a mass $m_2... | 5,391 |
<p>What do you mean by charge? Why should a particle have a charge?</p> | 189 |
<p>I know that the equation for it is $$v^2 = \frac{2GM}{r},$$ and with that, the rocket should be launched at that speed. But could it go much slower spending much more fuel to escape from gravity right? </p>
<p>Wouldn't it be easier to calculate it with energy? </p> | 5,392 |
<p>Is it possible to derive an uncertainty relation (Karolyhazy Uncertainty: <a href="http://dx.doi.org/10.1007/BF02717926" rel="nofollow">http://dx.doi.org/10.1007/BF02717926</a>) with photons? I brainstormed a bit to get the following:</p>
<p>$$ \Delta x_0 \Delta p_0 = \frac{\hbar}2,$$ </p>
<p>and then, </p>
<p>$... | 5,393 |
<p>It is well known that if you blow horizontally on a bottle top it creates a sound. Pouring water to the bottle changes the pitch.</p>
<p>I have been doing experiments on the relation between the sound's main frequency (or rather the corresponding wavelength) and the vertical distance between the bottle top and the ... | 5,394 |
<p>Many times in physics when we analyze a physical system mathematicly we get divergences, but when those divergences has no dependence on any actual physical quantity of interest we tend to disregard those "infinity Constants". </p>
<p>An example where such a thing happens is in the derivation of the Casimir force f... | 190 |
<p>I was looking up for how polarisers work, I understood mostly everything except the part that explains that the polariser filters everything except light that is in a certain orientation.</p>
<p>Here are my questions. How do waves have different orientation except being either vertical or horizantal? What determine... | 5,395 |
<p>Mathematician here with a speculative physical question -- feel free to boot me if the level isn't right.</p>
<p>Suppose one finds, or builds, a constellation of several black holes arranged in a circle. (To get a stable arrangement, presumably one could put a bunch of small positively charged black holes at equal ... | 5,396 |
<p>Assume a small square block $m$ is sitting on a larger wedge-shaped block of mass $M$ at an upper angle $\theta$ such that the little block will slide on the big block if both are started from rest and no other forces are present. The large block is sitting on a frictionless table. The coefficient of static friction... | 5,397 |
<p>What is the value of $g$ at the centre of the Earth? Is it zero or infinity?
My attempt: I know it's zero but applying law made me on fused.</p> | 50 |
<p>Folks, I have a naive question regarding the subject of dark energy and an accelerating universe:</p>
<p>From what I understand/read, it seems that the further we look out into deep space, the faster the objects are moving away from us - in all directions. </p>
<p>Is this basically what is meant by "accelerating u... | 336 |
<p>I'm working on a problem with celestial bodies and for my purpose days and AUs are more appropriate units than seconds and meters. So I tried to convert the constant of gravitation, $G$, like this:</p>
<p>$$
k= \frac{\frac{\text{AU}^3}{\text{kg}\times \text{D}^2}}{\frac{\text{m}^3}{\text{kg}\times \text{s}^2}}=(\fr... | 5,398 |
<p>There's some constant relating to electrons that also has the same value as the speed of light. What is it, what is the value, and how are they related?</p>
<p>EDIT: Is it the fine-structure constant?? Are there any other similar constants? If you posted that answer before, you shoulda left it (to the person who de... | 5,399 |
<p>I've been looking for a long time and I've not had a lot of luck. I've found sources that <strong>use</strong> fermions in 3d Euclidean space but I can't find any that explain the Wick rotation from Minkowski space. </p>
<p>This <a href="http://arxiv.org/abs/hep-th/9608174" rel="nofollow">source</a> provides a nice... | 5,400 |
<p>Will a CFL light bulb and an incandescent light bulb, in separate respective closed systems, produce exactly the same amount of overall temperature increase over time?</p>
<p>Assume you have two identical closed systems with gray walls, with a system input of 20 watts of power each. </p>
<p><strong>EDIT added for ... | 5,401 |
<p>This question is essentially a duplicate of <a href="http://physics.stackexchange.com/questions/67810/gibbs-paradox-why-should-the-change-in-entropy-be-zero">Gibbs Paradox - why should the change in entropy be zero?</a>. The question concerns the following situation: I have some gas of identical particles and they a... | 5,402 |
<p>I am confused about the current and voltage. My intuitive example would be that of a pipe of say water. The diameter of the pipe determines the amount of water flowing per second but the pressure is comparable to voltage. Am I right?</p>
<p>And what is the difference between voltage source and current source? In wh... | 5,403 |
<p>This question was asked to me.</p>
<p>My first thought was that electrons may ionise the air and potential difference that was applied may increase or decrease the current which should have been observed. I'd like to know whether this is the right reason or if there is any other reason which I should take into acc... | 5,404 |
<p>what is the ram-facing side of a satellite? What does it mean and why is it called "ram"-facing?
Thanks.</p> | 5,405 |
<p>Wired magazine ran an <a href="http://www.wired.com/magazine/2011/04/st_equation_sodapop/" rel="nofollow">article</a> this month on carbonation in soft drinks.</p>
<p>If all soft drinks are manufactured effectively identically, why do some types fizz more than others?</p>
<p>For example, root beer is always extrem... | 5,406 |
<p>More specifically, in quantum field theory books, we usually have this:</p>
<p>\begin{equation}
Z = \int D(\bar{\psi}, \psi) e^{-S + \int_0^\beta d\tau \sum_l [\bar{\eta}_l (\tau) \psi_l (\tau) + \bar{\psi}_l (\tau) \eta_l (\tau) ]} \hspace{10mm} (1)
\end{equation}</p>
<p>where $S = \int_0^\beta d\tau \sum_l (\ba... | 5,407 |
<p>First of all, I know there's a much alike question <a href="http://physics.stackexchange.com/questions/15762/what-is-a-wave">here</a> but this is not duplicate since I couldn't find there the answer I'm seeking. My problem is the following: I know that intuitively we have a wave when we have some quantitiy (that as ... | 5,408 |
<p>In order to derive the Lorentz transformation one can use the picture of a light clock. A Photons bounces back and forth between two mirrors. This is then observed in two different inertial systems. If the relative speed of the inertial systems is perpendicular to the propagation direction of the photon deriving, ex... | 5,409 |
<p>The formula for centripetal (radial) acceleration is well known, and there exist many proofs for it: $$||a_c|| = \frac{||v||^2}{r}$$</p>
<p>However, all the proofs I've seen rely on the fact that it is <em>uniform</em> circular motion and the magnitude of the tangential velocity vector does not change. For instance... | 5,410 |
<p>After reading <a href="http://www.nasa.gov/topics/technology/features/new-nano.html" rel="nofollow">this NASA article</a> about the "blackest material", the following stuck out to me.</p>
<blockquote>
<p>The tiny gaps between the tubes absorb 99.5 percent of the light that hits them</p>
</blockquote>
<p>Is it po... | 561 |
<p>I am reading the two concepts mentioned in the title. According to the definition of torque and moment of inertia, it would appear that if I pushed on a door, with the axis of rotation centered about its hinges, at the door-knob, it would be difficult, relative to me applying a force nearer to the hinges. However, I... | 5,411 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/7584/how-do-we-know-that-some-radioactive-materials-have-a-half-life-of-millions-or-e">How do we know that some radioactive materials have a half life of millions or even billions of years?</a> </p>
</block... | 191 |
<p>Some metal containers such as the Nissan Thermos ones, even if 100 C water is filled inside, the container is still cold to the touch on the outside. It won't be even warm:</p>
<p><img src="http://i.stack.imgur.com/E3Cbs.jpg" alt="enter image description here"></p>
<p>At the same time, some that look similar are ... | 5,412 |
<p>When I whistle, I find that I can vary the volume by pushing more or less air through my mouth at once. However, when I increase volume past a point, I start to hear a blend of rushing air and a faint whistle sound. Why? Is the air just subtly pushing my lips out of shape, or is there some other maximum (such as ... | 5,413 |
<p>Recently, I have stumbled upon a YouTube video by Veritasium describing the conductivity of fire. My question is: how exactly does fire conduct electricity? I am a high school student; therefore appropriate language is expected. </p>
<p><a href="http://youtu.be/a7_8Gc_Llr8?hd=1">http://youtu.be/a7_8Gc_Llr8?hd=1</a>... | 354 |
<p>I read according to 'Newtonian' Mechanics any set of physical activity of particles can be reversed ( I think) so a set of complicated dynamic systems of particles and matter can reverse their 'behaviour'. Yet a Star collapsing towards a 'Black Hole' will probably not 'stop' and reverse it's behaviour. So could Grav... | 5,414 |
<p><strong>EDIT</strong>: I haven't forgotten to accept answer, the question is still open.. </p>
<hr>
<p>I need a clarification about Poisson brackets. </p>
<p>I'm studying on Goldstein's Classical Mechanics (1 ed.).</p>
<p>Goldstein proves that Poisson brackets are canonical invariants for any functions F and G. ... | 5,415 |
<p>I have been searching on the Internet but have not found a derivation of the formula for the self gravitational potential energy of a sphere. Can someone show how to do this? I assume it involved 6 nested integrals (3 for each particle $dm$ and 3 for integrating the potential energy for all other particles).</p> | 5,416 |
<p>Trying to get a better understanding of the relation between a SU(N) Yang Mill theory and its number of "color" <a href="http://www.stat.physik.uni-potsdam.de/~pikovsky/teaching/stud_seminar/Classical_Yang_Mills.pdf" rel="nofollow">space</a>.</p>
<p>Most of the description I've found so far are either way to comple... | 192 |
<p>What is thermal velocity? What is it's physical significance?
<a href="http://en.wikipedia.org/wiki/Thermal_velocity" rel="nofollow">Wikipedia says</a>: </p>
<blockquote>
<p>The thermal velocity or thermal speed is a typical velocity of the thermal motion of particles which make up a gas, liquid, etc. Thus, indir... | 5,417 |
<p><a href="http://www.mazda.com/mazdaspirit/skyactiv/engine/skyactiv-g.html" rel="nofollow">Here's a description</a> of new combustion engine improvement by Mazda, called SkyActive-G. They claim that in a "generic" engine...</p>
<blockquote>
<p>when the exhaust manifold is short, the high pressure wave from the gas... | 5,418 |
<p>For a time dependent wavefunction, are the instantaneous probability densities meaningful? (The question applies for instances or more generally short lengths of time that are not multiples of the period.)</p>
<p>What experiment could demonstrate the existence of a time dependent probability density?</p>
<p>Can an... | 5,419 |
<p>First of all, I should note that I'm a programmer and have only an extremely basic understanding of physics; I only know how to explain my question in layman's terms and I apologize if I'm unclear or unnecessarily verbose.</p>
<p>If there's a rigid square object of size 1x1 and mass 1 on a two-dimensional frictionl... | 5,420 |
<p>I have asked this question before on other forums, but only got the classical answer of the impossibility of the probability interpretation for single particle in QFT. Now, there seems to be also doubt in multi particle interpretation of the Dirac "sea". while in QFT the multi particle seems to be the result of prom... | 5,421 |
<p>Is the structural similarity between atoms ( smallest) and universe (biggest) a coincidence? Or there can a reason for this beyond imaginations?</p>
<p>It seems like, if one starts travelling out from atoms... and grows bigger and bigger, one ends in a similar structure somewhere in the universe. Kind of a circular... | 5,422 |
<p>I am very puzzled by the quintet of Higgs bosons in the MSSM: two charged, two scalars and a pseudoscalar. I wonder if they could be understood better if they were considered jointly with the three "bosons" that are "eaten" by the Higgs mechanism. For instance, if they were two charged bosons and a pseudoscalar one,... | 5,423 |
<p>I read what is <a href="http://en.wikipedia.org/wiki/Computational_science" rel="nofollow">computational science</a> in Wikipedia but the explanation and understanding are not very clear. </p>
<p>So, I could you please give a simple example computational science project and what all basic skills a person should hav... | 5,424 |
<p>Do you know why in the quantization of SU(2) Yang Mills Gauge Theory, it is always chosen the Weyl (temporal) gauge to derive the Hamiltonian?</p>
<p>Is it possible to fix another gauge?</p> | 5,425 |
<p>What will be the tensor product of two doublets
$$
(x_1,x_2) ~\text{and}~ (y_1,y_2)?
$$
I am very much confused in determining this.</p> | 5,426 |
<p>I'm contemplating particle-hole symmetry, and as an example I am looking at either an electron moving along a hypothetical lattice of hydrogen ions, or a hole moving along a hypothetical lattice of helium atoms. </p>
<p>According to some lecture notes I found, the hopping integral I get when I treat this in a tight... | 5,427 |
<p>Could you please suggest the software, where I can load my 3D model and see how it behave on various conditions (speed - preferably including supersonic, temperature, pressure)?</p>
<p>Both free & commercial variants are interesting.</p> | 5,428 |
<p>A physical quantity can be represented by the following form:</p>
<p>$A = a_1\sigma_1 + a_2\sigma_2 + a_3\sigma_3$ where $\sigma$ matrices are Pauli matrices.
Also suppose that there is $B = b_1\Sigma_1 + b_2\Sigma_2 + b_3\Sigma_3$.</p>
<p>A. I read that $a_1,a_2,a_3$ are direction vectors, and when the sum of A's... | 5,429 |
<blockquote>
<p><strong>Question:</strong> The maximum range of projectile is $R$ and the maximum height attained by the particle is <em>H</em>. </p>
<p>If the area covered by the particle between its path and horizontal line is $A$, then $A$ =</p>
<ol>
<li><p>$\frac{2}{5}$</p></li>
<li><p>$\frac{2}{3... | 5,430 |
<p>My nephew is 3 and weighs around 30 pounds I am guessing. However, I would like to weigh him at home. I have kitchen scales, one flat one that goes up 1kg and one that looks like this picture that goes up to 5kg. <img src="http://i.stack.imgur.com/u3rsam.jpg" alt="enter image description here"></p>
<p>What is a sa... | 5,431 |
<p>The textbook explanation is that, at <a href="http://en.wikipedia.org/wiki/Brewster%27s_angle" rel="nofollow">Brewster's angle</a>, the electric dipoles excited by the incident light can't reradiate to the reflection direction since it's aligned with the dipole moments.</p>
<p>Is there a deeper understanding of the... | 5,432 |
<p>Antimatter and matter particles annihilate. But does <a href="http://en.wikipedia.org/wiki/Dark_energy" rel="nofollow">dark energy</a> annihilate energy?</p>
<p>We consider energy to be photons, and such, correct? So when we say energy, we're actually talking about some bosons, right? </p>
<p>So photons and anti-p... | 5,433 |
<p>Why does Mother Nature allow bound states in arbitrarily weak attractive potential in 2D but not in 3D?</p>
<p>See, for example, this article: <a href="http://scitation.aip.org/content/aip/journal/jmp/44/2/10.1063/1.1532538" rel="nofollow">http://scitation.aip.org/content/aip/journal/jmp/44/2/10.1063/1.1532538</a><... | 5,434 |
<p>There are lots of models of gravity mediated SUSY breaking with various spectra as well as various general gauge mediation models. Are there any "smoking gun" experimental singnatures that could definitely distinguish between the two scenarios? Would this be possible to do at the LHC or would we need an ILC-type mac... | 5,435 |
<p>The phenomenon of high temperature superconductivity has been known for decades, particularly layered cuprate superconductors. We know the precise lattice structure of the materials. We know the band theory of electrons and how electronic orbitals mix. But yet, theoreticians still haven't solved high Tc superconduct... | 5,436 |
<p>When computing the first order perturbative corrections to string theory over a curved background, we find the background has to be Ricci-flat if the dilaton is constant and we have no fluxes. Such is the case for Calabi-Yau compactifications. However, to fourth order in perturbation theory, we find nonzero contribu... | 5,437 |
<p>In the strong coupling limit of type IIA and heterotic E8 string theory, we get 11 dimensional M-theory in which we have no strings. Instead, we have M2 branes.</p>
<p>Are there any other backgrounds in string theory which can't be described by first quantized string theory?</p> | 5,438 |
<p>What are possible effects of electromagnetic pulse / EMP on superconductor-based devices/equimpent/transportation?</p>
<p>Are they resilient or more sensitive to EMP?</p> | 5,439 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/36131/friction-between-atoms-in-spring">Friction between atoms in spring</a> </p>
</blockquote>
<p>thanks john:when we apply a stress within elastic range of metal/spring,due to flow of atoms the particu... | 193 |
<p>I can't find any numbers about table tennis. What accelerations occur during a forehand smash for example?</p>
<p>Thanks in advance & kind regards,
Hans</p> | 5,440 |
<p><img src="http://i.stack.imgur.com/Vl3a6.jpg" alt="Picture of gravity"></p>
<p>We assume that the earth planet is a black hole.
When a light beam is fired.
The only way that even light can move is A and B which means this is impossible that light move on other ways C, D, E</p>
<p>Isn't it true?</p> | 5,441 |
<p>Let's assume that the aircraft is 1000kg and it is flying in a air density of 1.225kg/m^3 at the speed of sound in air. </p>
<p>Just how much energy does it require per second to maintain flying at this speed.(Please make other necessary assumptions.) </p>
<p>Thank you.</p> | 5,442 |
<p>Force-Weight <a href="http://en.wikipedia.org/wiki/Pinewood_derby" rel="nofollow">Pinewood Derby</a> Car.</p>
<p>I'm trying to make a fast derby car. I was wondering if I could make a car that can drop/eject weight once it comes off of the incline. Would that increase speed or would it make it slower?</p> | 5,443 |
<p>I understand mathematically how one can obtain the conservation equations in both the conservative
$${\partial\rho\over\partial t}+\nabla\cdot(\rho \textbf{u})=0$$</p>
<p>$${\partial\rho{\textbf{u}}\over\partial t}+\nabla\cdot(\rho \textbf{u})\textbf{u}+\nabla p=0$$</p>
<p>$${\partial E\over\partial t}+\nabla\cdo... | 5,444 |
<p>Similar question has been asked but did no get good answers.</p>
<p>We know that black hole can confine light, but can we create an ocean black hole -
which can confine surface water waves or sound waves in water?</p>
<p>Definition:</p>
<ul>
<li>What is a static water flow which can CONFINE water waves?</li>
<li>... | 5,445 |
<p>Non-linear waves do not superimpose to each other, but why?
What characteristics give this property?</p> | 5,446 |
<p>I am looking at a 2 Nucleon potential of the form
$$V(r)=V_0(r)[a+bI_1\cdot I_2]$$
Where a and b are constants. $I_1,I_2$ are isospins. $V_0(r)$ is of the square well form. My goal is to find an equality for a and b, given that deuteron exists, and that diproton and dineutrons do not. </p>
<p>My approach has be... | 5,447 |
<p>This question is not about phase velocity changed which causes refraction, but about the real time itself being slower by the gravity of any object (from general relativity).</p>
<p>If so, would this mean any light traveling inside a glass would be slower than in the air because it is directly affected by gravity o... | 5,448 |
<p>This problem is similar, but also different question from my previous question. They are both unfortunately long.</p>
<p><strong>Problem/Solution #1</strong></p>
<p><img src="http://img215.imageshack.us/img215/6696/problem2f.jpg" alt="">!
<img src="http://img59.imageshack.us/img59/4281/sol2pp.jpg" alt="">!</p>
<p... | 5,449 |
<p>So - a little bit of background. Obviously from Einstein's equations it's shown that energy can be converted to matter and vice versa; in essence, energy and matter are different manifestations of the same "stuff". </p>
<p>Now, I've done a bit of reading about the interplay between space and time. Some of what I've... | 11 |
<p>How is the speed of an object in space measured? Also more importantly how do you measure your own speed in space? On the road we use a speedometer which tells us the speed easily. How is it done in space?</p> | 5,450 |
<p>When did astronomers realise that the stars were similar to the Sun? I'm not asking for when this was established, but when also the hypothesis was first proposed. </p> | 5,451 |
<ol>
<li><p>We all know that wavefunction collapse when it is observed. Uncertainty principle states that $\sigma_x \sigma_p \geq \frac {\hbar}{2}$. When wavefunction collapse, doesn't $\sigma_x$ become $0$?, as we will know the location of the particle. Or does standard deviation just become smaller?</p></li>
<li><p>A... | 5,452 |
<p>If a body is under non-uniform circular motion, will it experience or will there be any impact of centrifugal force on the body upon eliminating the centripetal force?
update-sorry.the title of question was incorrect.</p> | 5,453 |
<p>How can I determine the direction of the force acting due to gyroscopic couple on a car's wheels when it is taking a turn to it's left side?</p> | 5,454 |
<p>In "String Theory and M-Theory: a modern introduction" by K.Becker, M. Becker and J.H.Schwarz, they say that BPS D-brane is stable as it preserves half of the Supersymmetry. I really want to understand more about this statement and see detail calculations. What is the mechanism of D-brane stability? Is there any der... | 5,455 |
<p>How does the temperature vary along the length of the rod if its both ends are at different temperature. As an example, consider the problem:</p>
<blockquote>
<p>20 cm long rod has rod at one end 100 ºC and another end at 0 ºC. Find the temperature at the center of the rod when it's in thermal steady state.</p>
<... | 5,456 |
<p>I was looking at rockets and stuff and thought about how they move through a vacuum using newtons 3rd law, and then I started thinking of any other ways you could move through a vacuum without using this and then I thought about the photon. I then thought how does the photon move through a vacuum? So I searched it o... | 5,457 |
<p>Galileo discovered that the distance fallen is proportional to the square of the time it has been falling.Why is it proportional to the square of the time and not just time?
i.e $d \propto t^2$ why not just $d \propto t$</p>
<p>I know this question involves some common sense which i'am not able to use for some reas... | 5,458 |
<p>I have used a new term <a href="https://drive.google.com/file/d/0B5sD2PI0YoRvMmwyeE04emptTzQ/edit?usp=sharing" rel="nofollow">spinning apparatus</a> as I was unable to name it.
I have tied a thread to a stone and was spinning it and I heard a sound something like that of a rotating propellor of a helicopter and th... | 5,459 |
<p>We know that a simple application of Gauss's law tells us that the field inside of a uniformly charged spherical shell is zero. Does this hold for all uniformly charged closed surfaces? If so, how could we prove this? Or does it hold only for certain shapes? </p> | 5,460 |
<p>I saw this in an art museum:
<img src="http://i.stack.imgur.com/LLO24.jpg" alt="Floating Rock"></p>
<p>How is this possible? The materials used to make this were foam, wood, stone dust, paint, electromagnets, and metal. I would like to know how this was make and how I could make something similar.</p>
<p>Thank You... | 5,461 |
<p>In this <a href="http://arxiv.org/abs/1108.3003v1" rel="nofollow">article</a> it is claimed that certain type of string theory called EGBd allows for traversable wormhole solutions that do not require exotic matter.</p>
<p>What is this EGBd model and how it fits in the grand scheme of things of string theory? is th... | 5,462 |
<p>The following blue-cone <a href="http://en.wikipedia.org/wiki/Metric_expansion_of_space#Understanding_the_expansion_of_Universe" rel="nofollow">Wikipedia diagram</a> confuses me.</p>
<p><img src="http://upload.wikimedia.org/wikipedia/commons/3/32/Embedded_LambdaCDM_geometry.png" alt=""></p>
<p>At any point of cosm... | 5,463 |
<p>Some authorities have stated publicly and without explanation that if the theories of Special and General Relativity were not taken into account in the design of the <a href="http://en.wikipedia.org/wiki/Global_Positioning_System#History" rel="nofollow">GPS</a> (by building the satellite clocks to run 38us/day slowe... | 5,464 |
<p>I was running the washing up water this morning, and started to think about why the cold tap isn't hot, and why the water doesn't get hotter the faster it is flowing (if anything, the cold tap gets colder the faster it flows).</p>
<p>From my understanding</p>
<p>$K.E = \frac{mv^2}{2}$</p>
<p>and temperature is di... | 5,465 |
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